Lake Challa Project Final Report

Coast Development Authority

THE LAKE CHALLA WATER RESOURCES

INTEGRATED DEVELOPMENT PROJECT

FINAL ENGINEERING REPORT

MAY 2012


Contents

LOCATION MAP

PROJECT SUMMARY

CHAPTER 1: INTRODUCTION

1.1 BACKGROUND .................................................................................................................................. 1-14

1.2 OBJECTIVES OF THE PROJECT ...................................................................................................... 1-14

1.3 SCOPE AND OBJECTIVES OF THE CONSULTANCY SERVICES ............................................. 1- 15

1.4 SCHEDULED OUTPUTS ................................................................................................................... 1-15

1.5 SCOPE OF THIS REPORT ................................................................................................................ 1- 16

CHAPTER 2: DESIGN OF IRRIGATION COMPONENT

2.1 INTRODUCTION ........................................................................................................................... 2-7

2.2 GENERAL ....................................................................................................................................... 2-7

2.3 EVAPOTRANSPIRATION............................................................................................................. 2-7

2.4 THE PROJECT AREA .................................................................................................................... 2-8

2.5 CURRENT AGRICULTURAL PRODUCTION .......................................................................... 2-21

2.6 PROPOSED CROPPING PATTERN FOR PROJECT AREA ..................................................... 2-22

2.7 IRRIGATION METHODS ............................................................................................................. 2.22

2.8 CHOICE OF IRRIGATION METHOD ........................................................................................ 2-28

2.9 COMPARISONS OF VARIOUS IRRIGATION METHOD(S) ................................................... 2-30

2.10 PREFERRED IRRIGATION METHOD(S) .................................................................................. 2-30

2.11 CROP AND IRRIGATION WATER REQUIREMENTS ............................................................ 2-34

2.12 PROPOSED IRRIGATION SYSTEMS COMPONENTS ............................................................ 2-59

CHAPTER 3: DESIGN OF WATER SUPPLY SYSTEMS

3.1 GENERAL .......................................................................................................................... 3-4

3.2 SOURCES OF WATER ..................................................................................................... 3-4

3.3 INTAKE .............................................................................................................................. 3-5


3.4 LAKE CHALLA TANK ..................................................................................................... 3-6

3.5 TIMBILLA TANK .............................................................................................................. 3-7

3.6 TRANSMISSION PIPELINES ............................................................................................ 3-7

3.7 DOMESTIC WATER SUPPLY .......................................................................................... 3-8

3.8 ANCILLARY WORKS ....................................................................................................... 3-9

3.9 MATERIALS SPECIFICATIONS .................................................................................... 3-10

CHAPTER 4: COST ESTIMATES AND PROJECT PHASING

4.1 GENERAL ................. ……………………………………………………………………..4-3

4.2 BASIS FOR ESTIMATION OF COSTS ............................................................................. 4-3

4.3 SUMMARY OF ESTIMATED COSTS .............................................................................. 4-3

4.4 ITEMISED WORKS COST ESTIMATES ......................................................................... 4-5

4.5 PROJECT PHASING ......................................................................................................... 4-8


PROJECT SUMMARY

Project Location:

Lake Challa Water Resources Integrated Development Project is primarily located in the Taveta District which

forms part of the bigger Taita-Taveta County. The project also covers some areas in the lower Mwatate District

(Mwaktau Division) and the western part of Kinango District.

Objective of the Project

The main objective of the Lake Challa Water Resources Integrated Development Project is to improve the living

standards of Taveta residents through Poverty Alleviation and Sustainable Development. This shall be

accomplished by;

Provision of water for domestic, irrigation and livestock uses.

Increasing food production for domestic use, export market and Income generation.

Enhancement of environment conservation and sanitation.

Promotion of eco-tourism.

Creation of employment for youth and women.

Lake Challa

Lake Challa is situated on the western side of Taveta District. It is a volcanic crater fresh water Lake on the South

Eastern slopes of the Kilimanjaro Range 45 km south of the summit and about 10 km North of Taveta town on the

Kenya – Tanzanian border. It is a volcanic crater fresh water lake.

Latitude: - 3015’ and 3

025 ‘S; Longitudes: - 37

0 40' and 37

045’E; Surface Area: - 3.44 km

2 Depth = 100 m

Volume of water in the lake is approximately 300 to 350 million cubic meters.

KEY FINDINGS, RESULTS, RECOMMENDATIONS

Mean Monthly Climatical Data for Project area

Item Description Item Description

Temp.(Max) (0C) 30.4 Daily Wind Run (km/day) 141

Temp.(Min) (0C) 16.6 Sunshine hours (h) 12

Open Water Surface Evaporation (mm/day) 5.28 Mean Rainfall (mm) 673

Relative Humidity (%) 61.2

Soil Chemical Characteristics of Project Area

Area Remarks

Kilanga The soils are well suited for irrigation on the account of their very favourable

chemical and physical characteristics.

Challa (near Market)

Soils are well suited for irrigation due to their lack of salinity, high fertility

and good physical properties.

Nakuruto

Soils not suited for irrigation due to their very shallow depth in spite of having

good chemical properties.

Timbila

Based on the available physical and chemical characteristics, the soils are

suited for irrigation.

Jipe The soils in the upper areas are well drained and are irrigable. However, the

soils close to the lake have high salinity and sodicity levels, and would not be

easy to drain.

Mwaktau Based on the available physical and chemical characteristics, the soils are

suited for irrigation.


Water Resources

Two options were identified as potential sources of water for irrigation and domestic use.

Option 1; Lake Challa and Lake Jipe

Option 2; Groundwater from boreholes

From analysis, it was found that;

Over 7,000,000 m3 of water per year can be abstracted from Lake Challa without negatively

affecting the lake levels.

3 boreholes (2 at Kilanga Scheme and one situated at Nakuruto Kasokoni producing 400 m3

per hour each and 100 m3 per hour respectively) can in combination provide over 7.0 million

m3 per year.

Quality of Irrigation Water

The water quality is satisfactory and suitable for irrigation purposes and can be used on most soils and crops. It’s

the main raw material required for the operation of the irrigation and domestic water supply system.

Electricity

The electric power will be sourced from the national power grid with a connection being done from the HT power

line running along the Taveta – Challa Road. Electricity will be supplied by the Kenya Power Company (KPC) on

a commercial basis.

RECOMMENDATIONS:

The major output of the Lake Challa Water Resources Integrated Development will be;

Development of an irrigation system that will cover 1020 ha at (five) 5 sites. These are Kilanga site,

Challa Irrigation Scheme, Timbila Scheme, Jipe Settlement Scheme and Mwaktau. Nakuruto/Kasokoni

area will also be supplied with raw water whose uses will be determined by residents.

Setting up of a domestic water supply system for households, livestock, fisheries and forestry.

Provision of water for wildlife within the park.

SALIENT FEATURES OF THE DESIGNED PROJECT

Population of Taveta District: 67,023; Land area: 4,205.63(Taveta District).

Major economic activities of Taveta District: Farming, Fishing, Quarrying and small scale trade.

Recharge/Discharge of the lake

Lake Challa is recharged by aquifers between 817m and 698m above sea level. The aquifers benefit from the

groundwater flows from the Kilimanjaro Region in the west and bounded by the fresh Basement System of rocks

in the East. Water flows in and out of the lake through these aquifers.

The groundwater basin is recharged by precipitation on Mt Kilimanjaro and local rainfall. The nearby springs also

get their recharge from the ground water basin.

Aerial Extent of the groundwater basin is approximately 10,500 Square Kilometres. Recharge in the basin

approximates 5,250 million Cubic Metres per year.


Table: Lake Challa Water Balance

No. Component Abbreviation Measurement in m3

1 Groundwater inflow Gin

8,115,279

2 Groundwater outflow Gout 122,095

3 Precipitation falling in the lake Pl 3,197,136

4 Precipitation falling in the entire Watershed Pw 15,084,162

5 Evaporation from the lake El 3,612,000

6 Change in storage ΔS 7,578,320

Pumping from the Lake at a rate of 30,000cubic metres per day will have minimal effect on the Lake water level.

Boreholes

From the Hydrogeological study of the Lake Challa Watershed Area and the simulation results of the exploratory

boreholes in the Challa Irrigation Scheme and at Nakuruto Kasokoni, sustainable discharges for each borehole

within the Challa/Kilanga area were estimated to be 400 m3/h and 100 m

3/h at Kasokoni.

Based on the above, water will be sourced and abstracted from three boreholes to be developed in the Kilanga,

Challa and Nakuruto/Kasokoni areas. The total available water from the boreholes will be 1,200 m3/h.

Hydrogeological and Geological Setting of Lake Challa Watershed

Hydro-geology of Lake Challa catchment area is defined by the Kilimanjaro aquifer. The aquifer includes the

volcanic pyroclastic and volcanic alluvium deposits found at the base of Mount Kilimanjaro and extending across

the Kenyan-Tanzanian border. These deposits form basins which extend outward from the mountain and are

limited by the surrounding Precambrian Basement rocks.

Lake Challa is part of the aquifer and its recharge and discharge is strongly linked to the volcanic pyroclastic and

volcanic alluvium deposits which allow percolation through the faults, fractures and weathered zones. The

surrounding Precambrian Basement rocks, which are impermeable zones, enhance groundwater storage and

transmission within the aquifer by preventing transmission out of the aquifer.

IRRIGABLE LAND, PLANNED AREAS

Five sites i.e. Kilanga, existing Challa Irrigation Scheme, Timbila, Jipe and Mwaktau have been identified as

being suitable for development of the irrigation schemes based on agricultural suitability, soil profile,

flooding conditions and topography of the site.

Kilanga Site

Situated next to Lake Challa and between Taveta – Loitoktok road to the east and Kenya Tanzania

border to the west.

Land presently occupied by about 120m households and used for farming and rearing of livestock.

Size of the scheme will be 140 ha. With 100 ha being used as a demonstration farm and the rest used

for construction of a reservoir, administration block and processing and value addition facilities.

Land is flat to very gently undulating with slopes ranging from 0.5% to 2% towards the west.

Soils are well suited for irrigation on the account of their favourable chemical and physical

characteristics.


Challa Scheme

Located in an alluvial plain North- west of Challa market and about 20 km north east of

Lake Challa. It is an existing irrigation scheme approximately 1680 Ha, owned by Challa Co-operative Society. It

relies on water supplied from Lumi River. The water is however not enough and more water to

compensate for the deficiency needs to be supplied.

The area is flat with slopes ranging from 0.5% to 1% towards the North.

There are no settlements within the Scheme, but people are settled within the surrounding areas.

Timbila Site

The Timbila site is located approximately 12 km south of Lake Challa and 4 km east of Taveta Town

The area has a gentle north-south slope of about 1% and there is a significant topographical height

difference of about 100 m between the site and Lake Challa.

The project area covers 2500 acres and has a population of approx. 300 households.

Jipe Settlement Scheme

The Scheme is located approximately 10 km southeast of Timbila and stretches from Voi-Taveta road

to the northern shores of Lake Jipe in the south and borders Tsavo West National Park to the east. It has

an area is about 10,000 ha.

The area was designated by the Kenyan Government as part of a new rural development area and was

subdivided into several plots to individuals ranging from 15 to 25 acres. There are about 600

households resident in the scheme but most of the plots are yet to be settled. The area is woodland

currently being used for grazing.

The topography is flat to very gently undulating with slopes ranging from 0 to 2% towards South and

South west.

Based on their physical and chemical characteristics, the soils on the upper part of the scheme are

suitable for irrigation, but are susceptible to gully erosion.

Mwaktau

The Mwaktau Site is located approximately 50 km from Timbila site (about halfway between Taveta

and Voi by road) and has a population of about 10,000 people.

The area is flat to gently undulating with slopes ranging from 0.5% to 2% towards the East and South

East.

The physical and chemical characteristics of these soils indicate that they are suitable for irrigation.

Nakuruto

This area is located on the eastern slopes of Challa crater.

The area is undulating with slopes ranging from 5 to10% towards the east.

The vegetation in the area is wooded grassland most of which is used for cultivation or grazing.

The soils are good for agricultural purposes.


Proposed Annual Irrigable Areas

Site Status Remarks Mode of irrigation Area (ha)

Kilanga Pilot Project Proposed New Development Drip (80 ha)

Sprinkler(120 ha) 200

Challa (Existing Scheme) Existing Extension Surface Irrigation 200

Nakuruto Proposed New Development Surface Irrigation 90

Timbilla(Existing Scheme) Existing Extension Surface Irrigation 200

Jipe Settlement Scheme Proposed New Development Surface Irrigation 930

Mwaktau Proposed New Development Surface Irrigation 400

Total 2,020

Proposed Cropping Pattern by Project Areas

Season Crop Area (ha) Total

Kilanga

Pilot

Scheme

Challa

Scheme

Nakuruto Timbila

Scheme

Jipe

Scheme

Mwaktau

Scheme

(ha)

Season

One

(March

to July

Maize - 20 10 20 100 40 190

Beans - - - - 45 15 60

Green grams - - - - 30 15 45

Cowpeas - 10 5 10 20 15 60

Tomatoes 20 10 10 - - 40

Kales 10 10 5 10 - - 35

Sunflower - - - - 25 15 40

Bananas 20 10 5 10 100 40 185

Melons 10 10 5 10 10 5 50

paw paws 20 10 5 10 75 25 145

Onions 10 10 5 10 50 25 110

Chillies 10 10 5 10 10 5 50

Sub-total 100 100 45 100 465 200 1,010

Season

Two

(Sept’

to Jan)

Maize - 20 10 20 100 40 190

Beans - - - - 45 15 60

Green grams - - - - 30 15 45

Cowpeas - 10 5 10 20 15 60

Tomatoes 20 10 10 - - 40

Kales 10 10 5 10 - - 35

Sunflower - - - - 25 15 40

Bananas 20 10 5 10 100 40 185

Melons 10 10 5 10 10 5 50

Paw paws 20 10 5 10 75 25 145

Onions 10 10 5 10 50 25 110

Chillies 10 10 5 10 10 5 50

Sub-total 100 100 45 100 465 200 1,010

TOTAL 200 200 90 200 930 400 2,020

DOMESTIC WATER SUPPLY

Domestic water supply has also been incorporated in the project for areas that experience acute water shortages.

These are Kasaani in Jipe, Kidongu, Nakuruto/Kasokoni, Mwaktau Trading Centre and Kwa Mnengwa.


Forestry

The forest and tree establishment will be done along the following areas;

Rehabilitation of Lake Challa escarpment - This covers the outskirt of Lake Challa crater which is steep with

high vegetation degradation and soil erosion. 255 ha and a perimeter of 10km have been identified.

Rehabilitation of Kedong Hill – This is situated within Timbila scheme, and covers an area of 130 ha and a

perimeter of 4km.

Rehabilitation of Salaita Hill – The hill has an area of 11 ha and a boundary of 1km.

Agroforestry in proposed Challa, Timbila and L. Jipe Irrigation Schemes – At each of these schemes, 10%

of the area will be put under tree cover. This will be done in different configurations including strip tree planting,

boundary tree planting, planting along canals, woodlots, pockets of forest, rehabilitation of degraded areas and

roadside tree planting.

River - line and springs – Rehabilitation of 30% of the river line with a total length of 12km shall be done.

Natural springs will be rehabilitated to ensure integrity.

Farmland - Fast growing trees species which yield required wood and non wood products will be introduced.

Fisheries

Fish ponds, dams and rehabilitation of wetlands such as rivers, Lake Jipe and springs shall be done, to increase

fish farming in the project area by 30%.

IRRIGATION WATER DEMAND, DOMESTIC WATER DEMAND & DOMESTIC & IRRIGATION

WATER SUPPLY

Water demand requirements of various project areas for irrigation, domestic needs and others;

No. Site Total Demand (m3/year)

Irrigation

Water

Demand

(m3/year)

Average

Irrigation

Water Demand

(m3/day)

Domestic

Water

Demand

(m3/year)

Domestic

Demand

(m3/day)

Total Demand

(m3/year)

1 Kilanga 810,307 2,214 0

810,307

2 Challa 881,823 2,410 0

881,823

3 Nakuruto/Kasokoni 404,834 1,107 58,552 160 463,386

4

Timbilla/

Kidong’u 881,823 2,410 44,297 121 926,120

5 Jipe 4,692,931 12,823 53,351 146 4,746,282

6 Mwaktau 1,935,868 5,290 120,400 330 2,056,268

7 Msorongo

125,369 343 125,369

8

Environment

Conservation

45,000 123 45,000

9

Wildlife (Tsavo

National Park)

91,250 250 91,250

10 Fisheries

20,000 55 20,000

Total 9,607,587

558,219 1,528 10,145,806


Water demand tabulation is based on a projection up to the ultimate year of 2035. This was derived from

population projection using population growth of 1.8%.

Water Supply

Water will be sourced from Lake Challa and two boreholes. The water abstracted will then be used for irrigation,

domestic, livestock and wildlife within the Taveta – Mwaktau corridor.

The following table shows amounts of abstractions considered from the two sources;

Recommended Abstraction Rates from Sources

Source Capacity in

m3/hr

Pumping

Hours

No. of

Boreholes

Abstraction

(m3/day)

No. of working

days

Volume

(m3/year)

Lake Challa 400 20 8,000 330 2,640,000

Boreholes 400 20 3 24,000 330 7,920,000

Total water supply for entire project 32,000 10,560,000

The system;

Intake: Will consist of two submersible pumps, one on duty and one standby, in a pump house built on girders on

a floating pontoon.

Raw water pipeline: Two main pipelines have been designed for. One will convey water from Lake Challa and

the other from the boreholes. The two pipelines merge to deliver water to 1000m3 reinforced concrete tank to be

located at the top rim of Lake Challa.

Lake Challa tank: The tank with a capacity of 1000m3 is strategically located to command flow of water via

gravity to the entire project save for Mwaktau which is at a higher ground level.

Reservoirs: The project is designed to hold three major water storage earth-fill reservoirs as follows: Kilanga -

75,000 m3; Jipe - 75,000m3; Mwaktau - 65000m3.

Timbila tank: The 1000m3 reinforced concrete tank will hold water for irrigation in the Timbila area.

Transmission pipelines: Water will be conveyed in all the pipelines by gravity except for Jipe – Mwaktau –

KwaMnegwa pipeline which is a pumping mains from Jipe to Mwaktau.

Domestic water supply: Elevated steel water tanks of capacity 200m3 have been provided for in Mwaktau and

Kasaani area, a 250m3 concrete tank provided for at Kwa Mnengwa and Kidong’u and a 1000m

3 elevated steel

tank at Nakurito. The location and design of the tanks allow the supply in the respective area by gravity.

Ancillary Works: These include administration building and laboratory, staff houses, site drainage,

workshop, pump house, access road and power supply.

Cost Estimate and financial aspects for important components;

Development and equipping of three boreholes - KSH 73.74 million

Intake Works at Lake Challa - KSH 73.80 million

Transmission Pipelines - KSH 1,076.05 million

Civil Works including reservoirs - KSH 976.24 million

Project Phasing

For speedy implementation of the Project, it proposed that the project be implemented in three phases as described

below;


1. Phase One – to cover Kilanga Pilot Irrigation Project and the existing Challa Irrigation Scheme

2. Phase Two – to include Timbila and Jipe Irrigation Schemes (including provision of domestic water within the

areas covered by the pipelines)

3. Phase Three – to include Mwaktau Irrigation Schemes (including provision of domestic water within the areas

covered by the pipelines)


CHAPTER 1- INTRODUCTION


Table of Contents

CHAPTER 1- INTRODUCTION ............................................... 1-12

1.1 BACKGROUND .............................................................................................................. 1-14

1.2 OBJECTIVES OF THE PROJECT .................................................................................. 1-14

1.3 SCOPE AND OBJECTIVES OF THE CONSULTANCY SERVICES .......................... 1-15

1.4 SCHEDULED OUTPUTS ............................................................................................... 1-15

1.5 SCOPE OF THIS REPORT ............................................................................................. 1-16


CHAPTER 1- INTRODUCTION

1.1 BACKGROUND

Coast Development Authority (CDA) is one of the six Regional Development Authorities in

Kenya under the Ministry of Regional Development Authorities (MoRDA). Its mandate is to

promote socio-economic development, within the Coastal Region and other areas of its

jurisdiction, through initiation and implementation of integrated programmes and projects

such as provision of energy, flood control, water supply for irrigation, domestic and industrial

use, as well as environmental conservation, among others.

The Authority is mandated to improve the welfare of the people in the region in particular

and the country in general, through sustainable utilization of the natural resources such as

water, minerals, wind etc. in its area of jurisdiction.

Towards this end, CDA intends to assist the communities within its area of jurisdiction

through implementation of the Lake Challa Water Resources Integrated Development

Project.

When the project is fully implemented, it would have positive benefits and improvements on

the community’s poor state of health, education, enhance food production, promotion of

ecotourism development economy and the environment in general. It would also contribute to

curbing of the rural urban migration problem, as employment opportunities will be created

with the enhanced agricultural development and related facilities.

Lake Challa Water Resources Integrated Development Project is one of the flagship projects

of Vision 2030 and is slated for implementation during the first Medium Plan (2008 – 2012).

1.2 OBJECTIVES OF THE PROJECT

The main objective of the Lake Challa Water Resources Integrated Development Project is to

improve the living standards of Taveta residents through Poverty Alleviation and Sustainable

Development.

Specific objectives include;

Provision of water for irrigation, domestic and livestock uses,

Increasing food production (for domestic use and export markets) and Income,

Enhancement of environment conservation and sanitation

Promotion of eco-tourism,

Creation of employment for youth and women


1.3 SCOPE AND OBJECTIVES OF THE CONSULTANCY SERVICES

The Consulting Services are intended for the implementation of Lake Challa Water

Resources Integrated Development Project with the following as the main components:-

Review of Previous Studies /Reports

Feasibility Study, Preliminary Designs and Implementation Programme

Environmental and Social Impacts Assessments

Detailed Engineering Designs

Preparation of Tender Documents and assistance in the Tendering Process

Institutional Development / Capacity Building

1.4 SCHEDULED OUTPUTS

The Consultant was required to prepare and submit the following reports:-

1. Inception Report

2. Interim Report

3. Feasibility Study Report & Preliminary Design Report

4. Environmental Impact Assessments – Project Environmental Management

Reports

5. Resettlement Plan

6. Detailed Design Report

7. Tender Documents

8. Final Study Report

This Report forms the sixth output.


1.5 SCOPE OF THIS REPORT

Reports Nos. 1, 2, and 3 have already been submitted and accepted by CDA. Subsequently,

the Consultants carried out the field work in detail such as topographic survey, geological &

geotechnical investigations, agricultural, environmental and socio-economic surveys, etc. The

detailed desk studies such as hydrological studies, water demand studies, simulation studies,

irrigation planning, cost estimate and financial & economic analysis have also been carried

out to arrive at the feasibility of the project which has already been submitted and accepted

by the Client.

The survey, investigations, studies, project configuration, cost estimates and financial &

economic analysis are covered in the feasibility report. Design of irrigation systems and water

supply components were included in the Preliminary Design Report submitted to CDA earlier

and accepted by the client.

Report No. 4 (Environmental Impact Assessments – Project Environmental Management

Report) is submitted together with this Report (Detailed Design Report). Also submitted with

this Report is the;

A. Tender Documentation comprising of;

Tender documents for civil works.

Tender documents for pumps.

Tender documents for electrical supply & control equipment, power lines and sub-

station equipment

Tender documents for irrigation equipment/system.

B. Final Estimates & Financial requirements

As per the Terms of Reference (ToR), this is Report No. 6 i.e. Detailed Report and comprises

of the following;

1. Detailed Design Report

1.4 Chapter 1; Introduction

1.5 Chapter 2; Design of Irrigation Systems

1.6 Chapter 3; Design of Water Supply Systems

1.7 Chapter 4; Cost Estimates

2. Tender documents

2.1 Conditions of Billing/contract – Volume 1

2.2 Works Requirements – Volume 2

2.3 Book of Drawings – Volume 3


CHAPTER 2: DESIGN OF IRRIGATION COMPONENT

Table of Contents

List of Tables ........................................................................................................................................ 2-20

List of Figures ...................................................................................................................................... 2-21


List of Abbreviations and Acronyms ................................................................................................... 2-21

List of Symbols .................................................................................................................................... 2-22

CHAPTER 2 DESIGN OF IRRIGATION COMPONENT ........................................................... 2-23

2.1 INTRODUCTION ................................................................................................................... 2-23

2.2 GENERAL ............................................................................................................................... 2-23

2.3 EVAPOTRANSPIRATION..................................................................................................... 2-23

2.3.1 Evaporation .......................................................................................................................... 2-23

2.3.2 Transpiration ........................................................................................................................ 2-24

2.4 THE PROJECT AREA ............................................................................................................ 2-24

2.4.1 General Climatic Data .......................................................................................................... 2-24

2.4.2 Project Sites ......................................................................................................................... 2-26

2.4.3 Soils in the Project Area ....................................................................................................... 2-29

2.4.4 Quality of Irrigation Water .................................................................................................. 2-34

2.5 CURRENT AGRICULTURAL PRODUCTION .................................................................... 2-37

2.5.1 Agriculture and Land Use ........................................................................................................... 2-37

2.5.2 Crop Production .......................................................................................................................... 2-37

2.5.3 Conclusions ................................................................................................................................. 2-38

2.6 PROPOSED CROPPING PATTERN FOR PROJECT AREA ............................................... 2-38

2.7 IRRIGATION METHODS ...................................................................................................... 2-40

2.7.1 Surface Irrigation ................................................................................................................. 2-41

2.7.1.2 Furrow Irrigation .............................................................................................................. 2-41

2.7.1.3 Basin Irrigation ................................................................................................................ 2-41

2.7.1.4 Border Strip Irrigation ...................................................................................................... 2-41

2.7.2 Sprinkler Irrigation ............................................................................................................... 2-42

2.7.3 Drip (Or Trickle) Irrigation .................................................................................................. 2-43

2.8 CHOICE OF IRRIGATION METHOD(S) ............................................................................. 2-43

2.8.1 Natural Conditions ............................................................................................................... 2-44

2.8.2 Type(S) of Crop(S) .............................................................................................................. 2-45

2.8.3 Type and Level of Technology ............................................................................................ 2-45

2.8.4 Previous Experience with Irrigation..................................................................................... 2-45

2.8.5 Required Labour Inputs ....................................................................................................... 2-46

2.8.6 Costs and Benefits ................................................................................................................ 2-46

2.9 COMPARISONS OF VARIOUS IRRIGATION METHOD(S) ............................................. 2-46

2.10 PREFERRED IRRIGATION METHOD(S) ............................................................................ 2-48

2.11 CROP AND IRRIGATION WATER REQUIREMENTS ...................................................... 2-50

2.11.1 Crop Water Requirements (ETCROP)................................................................................. 2-50

2.11.2 Net Irrigation Water Requirements (NIR) ....................................................................... 2-55

2.11.3 Gross Irrigation Water Requirements (GWR) ........................................................................... 2-65

2.12 PROPOSED IRRIGATION SYSTEMS COMPONENTS ...................................................... 2-72

2.12.1 Introduction ...................................................................................................................... 2-72


2.12.2 Design Criteria and Data .................................................................................................. 2-72

2.12.3 Project Components ......................................................................................................... 2-75


LIST OF TABLES

Table 2.1 - Mean Monthly Climatical Data for Taveta District

Table 2.2 - Saturated Hydraulic Conductivity Classification

Table 2.3 -Basic Infiltration Rates for Various Soil Types

Table 2.4 - Physical Characteristics of Soils in Taveta District

Table 2.5 – Salinity and Sodicity of Soils

Table 2.6 - Values for Volumetric Water Content of Soils in Taveta District

Table 2.7– Soils Suitability for Irrigation

Table 2.8 - Guidelines for Interpretation of Water Quality for Irrigation

Table 2.9 - The pH and ECw of Water from the Proposed Sources

Table 2.10 - Food Crop Production Statistics, Taveta District- 2009/2010

Table 2.11 - Proposed Overall Cropping Pattern

Table 2.12- Proposed Cropping Pattern by Project Areas

Table 2.13 - Comparison of Irrigation Methods

Table 2.14 - Preferred Method(s) of Irrigation for Various Crops

Table 2.15 - Estimated Reference Evapotranspiration (ETo

Table 2.16 - Crop Coefficients

Table 2.17 - Cropping Calendar and Applicable Crop Coefficients

Table 2.18 - Estimated Crop Water Requirements (ETcrop)(mm)

Table 2.19 - Estimated Annual Crop Water Requirements (ETcrop)(mm)

Table 2.20 - Effective Soil Storages

Table 2.21 - Estimated Effective Rainfall (REFF) (mm)

Table 2.22 -Estimated Net Irrigation Water Requirements (NIR)(mm)

Table 2.23 -Net Monthly Irrigation Water Requirements per Crop

Table 2.24 -Net Monthly Irrigation Water Requirements per Site

Table 2.25- Irrigation Systems Efficiencies

Table 2.26 - Gross Irrigation Water Requirements (m3)


Table 2.27- Summary of Gross Irrigation Water Requirements (m3)

Table 2.28 - Proposed Annual Irrigable Areas

Table 2.29 - Design Parameters for Drip Irrigation System

Table 2.30 - Design Parameters for Overhead Sprinkler Irrigation System

Table 2.31 - Design Parameters of Straight Furrow Irrigation

LIST OF FIGURES

Figure 2.1- Annual Rainfall Pattern in the Project Area

Figure 2.2– Comparison of Rainfall and Evaporation

Figure 2.3 – Typical Potable Lateral Move Overhead Sprinkler System

LIST OF ABBREVIATIONS AND ACRONYMS

oC - Degree Centigrade

cm3 - cubic centimetre

dS/m - deciSemens per metre

ECw - electrical conductivity

FAO - Food and Agricultural Organization

G - gramme

GS - Galvanised Steel

ha - Hectare

HDPE - High Density Polyethylene

HP - Horsepower

km - kilometer

Ksh. - Kenya Shilling

KVA - kilo Volt Ampere

lps - litres per second

m - metre

m2

- square metre


m3

- cubic metre

me/l - milliequivalent per litre

mg/l - milligrams per litre

mm - millimeter

mm/h - millimeter per hour

m/s - metre per second

mS/cm - milliSiemems per centimetre

No. or nr - Number

PE - Polyethylene

PE 63 Class 2 - 63 mm diameter Polyethylene Class 2

SAR - Sodium Adsorption Ratio

TDS - Total Dissolved Solids

µPVC - Un-plasticized Polyvinyl Chloride

µPVC 110 A - 110 mm diameter Un-plasticized Polyvinyl Chloride Class A

List of Symbols

o - Degree

Ø - Diameter

≈ - approximately

“ - inch

% - per cent


CHAPTER 2 DESIGN OF IRRIGATION COMPONENT

2.1 INTRODUCTION

The irrigation systems design for the various sites within Lake Challa Integrated Water

Resources Development Project include the following components:

Estimation of crop and irrigation water requirement

Availability of Irrigation Water

Efficient Irrigation Water Distribution Systems

2.2 GENERAL

Irrigation is generally defined as the artificial application of water to the soil to supplement

natural rainfall in supplying the moisture essential for plant growth. Irrigation is desirable

where natural rainfall does not meet the plant water requirements for all or part of the year.

The most positive impact of irrigation compared to rain-fed agriculture is the improved food

security, followed by a rise in income, wellbeing, and empowerment.

2.3 EVAPOTRANSPIRATION

Evapotranspiration is the loss of water through the combined effort of evaporation from the

soil surface and transpiration from the crop. Weather parameters, crop characteristics,

management and environmental conditions are the major factors affecting evaporation and

transpiration.

The principal weather parameters affecting evapotranspiration are radiation, air temperature,

humidity and wind speed. The crop type, variety and development stage also affect the rate of

evapotranspiration.

Management and environmental factors such as soil salinity, poor land fertility, limited

application of fertilizers, the presence of hard or impenetrable soil horizons, the absence of

control of diseases and pests and poor soil management may limit the crop development and

reduce the evapotranspiration.

2.3.1 Evaporation

Evaporation is the process whereby liquid water is converted to water vapour and

subsequently removed from the evaporating surface. Apart from the water availability in the

topsoil, the evaporation from a cropped soil is mainly determined by the fraction of the solar

radiation reaching the soil surface. This fraction decreases over the growing period as the

crop develops and the crop canopy shades more and more of the ground area. When the crop

is small, water is predominately lost by soil evaporation, but once the crop is well developed

and completely covers the soil, transpiration becomes the main process.


2.3.2 Transpiration

Transpiration is the process by which plants remove moisture from the soil and release it to

the air as vapour. It consists of the vapourisation of liquid water contained in plant tissues and

the vapour removal to the atmosphere.

Crops predominately lose their water through stomata which are small openings on the plant

leaf.

2.4 THE PROJECT AREA

2.4.1 General Climatic Data

2.4.1.1 DATA COLLECTION

Meteorological data was mainly acquired from Taveta Water Development Station of the

Ministry of Water and Irrigation. However, data for the sunlight hours is based on the

guidelines provided by the FAO (Food and Agricultural Organization) irrigation and

Drainage Paper No. 56.

2.4.1.2 TEMPERATURES, EVAPORATION AND HUMIDITY

The mean monthly maximum and minimum temperatures vary between 27.4 to 33.1C, and

13.5 to 18.4C, respectively. The daily evaporation varies from 4.35 to 6.25 mm per day. The

coldest period is between June and September while the hottest months are October, January,

February and March (Table 2.1).

The average annual open water surface evaporation and relative humidity are estimated to be

1930 mm and 61%, respectively.

2.4.1.3 RAINFALL

The total annual rainfall is about 673 mm. In general the project area has a bi-modal rainfall

pattern as it experiences two rain seasons; the long rains between the months of March and

May and the short rains between November and December.

The rainfall pattern presented in Figure 2.1, below, distinctly shows the occurrence of long

and short rainy seasons in the project area.


Figure 2.1- Annual Rainfall Pattern in the Project Area

2.4.1.4 SUMMARY OF CLIMATIC DATA

In general, the rainfall is very erratic in terms of amount and distribution and hence is not

reliable for successful production of crops. The mean annual pan evaporation is 1930 mm is

three times higher than the annual rainfall of 673 mm. Therefore, irrigation is necessary for

the development of agricultural production.

A comparison between the average rainfall and evaporation is graphically shown in Figure

2.2 below.

Figure 2.2– Comparison of Rainfall and Evaporation


The long term mean monthly temperature, evaporation, relative humidity, wind speed,

sunshine hours and rain data for Taveta Town, which could be considered as representing the

project area climate characteristics, are given in the table below.

Table 2.1 - Mean Monthly Climatical Data for Taveta District

Month Temp.

(Max)

(0C)

Temp.

(Min)

(0C)

Open Water

Surface

Evaporation

(mm/day)

Relative

Humidity

(%)

Daily Wind

Run

(km/day)

Sunshine

hours

(h)

Mean

Rainfall

(mm)

Jan 32.4 16.2 5.65 57.5 195 12.2 57

Feb 33.0 17.0 6.25 56.5 178 12.1 42

Mar 33.1 17.9 5.65 59.5 148 12.0 95

Apr 30.6 18.4 5.00 68.0 103 11.9 143

May 28.8 17.3 4.52 67.5 106 11.8 64

Jun 27.7 15.8 4.50 62.5 126 11.8 19

Jul 27.4 15.1 4.35 61.0 123 11.8 12

Aug 27.6 15.0 4.68 61.5 105 11.9 12

Sep 29.4 13.5 5.50 58.0 118 12.0 12

Oct 31.5 16.9 5.97 52.0 134 12.1 21

Nov 31.6 18.2 5.83 60.0 160 12.2 120

Dec 31.5 18.0 5.65 70.0 195 12.2 76

Total/Average 30.4 16.6 5.28 61.2 141 12.0 673

2.4.2 Project Sites

Six sites were identified as being suitable for development of irrigation projects based on the

following aspects:-

Agricultural suitability

Soil profile

Flooding conditions

Topography of the site

2.4.2.1 KILANGA

The Kilanga area is situated next to Lake Challa and falls between Taveta- Loitoktok road to

the east and Kenya-Tanzania international border to the west and is currently occupied by

about 120 households. Much of the land is used for farming and rearing of animals.

However, most of the parcels near the international boundary are vacant. A demonstration

plot measuring 140 ha has been identified out of which 100 ha would be used to set up a

demonstration farm, leaving the rest for other uses – reservoir, adminstration block,

processing and value addition facilities etc. About 115 land owners will be affected by the

acquisition of the demonstration plot.


This proposed irrigation scheme is located in an alluvial plain west of Challa market. The

area is flat to very gently undulating with slopes ranging from 0.5 to 2% towards the west.

The area is low lying without an obvious drainage system but ultimately excess water drains

into Lumi River.

The soils are well drained, extremely deep, very dark reddish brown clays with weak

prismatic structure breaking into moderate to weak fine sub-angular blocky structure. The

topsoil is dark brown clay. These soils are slightly acid to medium alkaline and are non-

saline. Available physical and chemical characteristics indicate that the soils are well suited

for irrigation on the account of their very favourable chemical and physical characteristics.

2.4.2.2 CHALLA IRRIGATION SCHEME

The Challa site is located in an alluvial plain North- west of Challa market and about 20 km

north east of Lake Challa.

This is an existing irrigation scheme of approximately 1,680 Ha and is owned by the Challa

Co-operative Society whose members own plots in the range of 4 and 6 acres. It relies on

water supplied from the Lumi River to supplement rainfed irrigation. The farmers are,

however, demanding more water to compensate for a critical decrease in the volume of water

flowing in the Lumi.

The area is flat with slopes ranging from 0.5 to 1% towards the North. The area is low lying

with slow surface drainage into Lumi River. Soils of the area are extremely deep, brownish

black clays.

There are no settlements within the scheme but people are settled within the surrounding

areas. Though the area is secured by means of fencing, it is prone to human/wildlife conflict.

2.4.2.3 NAKRUTO

This area is located on the eastern slopes of Challa crater. The area is undulating with slopes

ranging from 5 to10% towards the east. The area is drained by Lumi River and its seasonal

tributary, Kirimeri River. The vegetation in the area is wooded grassland most of which is

used for cultivation or grazing.

Soils of the area are developed on volcanic ash and are well drained, very shallow to

moderately deep, dark reddish brown clays and are chemically good for agricultural purposes.

2.4.2.4 TIMBILA

The Timbila site is located approximately 12 km south of Lake Challa and 4 km east of

Taveta Town. The area is demarcated by Taveta – Voi Road to the south, the railway line to

the north,Lumi River to the west and the Road to Ziwani Sisal Estate to the east

The area has a gentle north-south slope of about 1% and there is a significant topographical

height difference of about 100 m between the site and Lake Challa.

The area covered is about 2,500 acres, with a population of approx. 300 households and the

average land size ranges between a quarter (¼) and five (5) acres, although there are some

larger plots of 18 acres. Some of the households are involved in farming and livestock


keeping. The land sizes held by the people are generally small, thus the area is densely

populated.

The area is flat to very gently undulating with slopes ranging from 0.5 to 2% towards South

east. The area is drained by the perennial Lumi River. The original vegetation in the area is

riverline forest which has been cleared for human settlement and cultivation. Farmers

produce rain fed food crops and horticultural crops under irrigation.

Soils of the area are well drained, extremely deep, dark reddish brown silt loam to clay. The

topsoil is dark brown clay and is moderately saline. High salinity occurs only in the topsoil

leading to the suspicion that the soils are being salinized through irrigation with water from

River Lumi. Based on physical and chemical characteristics, the soils are well suited for

irrigated agriculture and are currently under furrow irrigation. However they have high

porosity and low bulk density leading to high infiltration rates and internal permeability.

2.4.2.5 JIPE

The Jipe Settlement Scheme is located approximately 10 km southeast of Timbila and

stretches from Voi-Taveta road to the northern shores of Lake Jipe in the south and borders

Tsavo West National Park to the east and has an area is about 10,000 ha.

The area was designated by the Kenyan Government as part of a new rural development area

and was subdivided into several plots to individuals ranging from 15 to 25 acres. There are

about 600 households resident in the scheme but most of the plots are yet to be settled.

The area is woodland currently being used for grazing. Wildlife-human conflicts were

common here in the past but have now reduced significantly since an electric fence was

erected by the Kenya Wildlife Services.

The topography is flat to very gently undulating with slopes ranging from 0 to 2% towards

South and South west. The area is drained by the Lumi River.

Based on their physical and chemical characteristics, the soils on the upper part of the scheme

are suitable for irrigation, but are susceptible to gully erosion. As noted in Section 2.4.2.5 of

this report, the soils in the scheme are susceptible to gully erosion. There are two major

gullies draining the waters from Salaita Hills and Tsavo West National Park to Lake Jipe.

2.4.2.6 MWAKTAU

Mwaktau is located approximately 50 km from Timbila site (about halfway between Taveta

and Voi by road) and has a population of about 10,000 people.

This proposed irrigation area will be located about 400 m east of Mwaktau Secondary School

along Mwaktau-Msorongo road on the Tsavo Plain. The area is flat to very gently undulating

with slopes ranging from 0.5 to 2% towards East and South east. The area is drained by a

seasonal stream on the eastern border.

Soils of the area are well drained to excessively drained, extremely deep, red to dark reddish

brown sandy clay loam to clay with ‘murrum’ starting at depths of 80-110cm. The topsoil is

reddish brown to dark reddish brown sandy clay loam to sandy clay. The physical and

chemical characteristics of these soils indicate that they are suitable for irrigation.


2.4.3 Soils in the Project Area

2.4.3.1 INTRODUCTION

Soils play an important role in plant growth because they are a source of nutrients and water.

Soils determine the suitability of the land for irrigation by influencing rooting depth for

crops, aeration status, nutrients availability, salinity and sodicity.

The soil physical and chemical characteristics are important in the determination of the

suitability of land for irrigation. The findings of the studies carried out during the Feasibility

Study stage are summarised below.

2.4.3.2 SOIL PHYSICAL CHARACTERISTICS

Texture

Soil texture refers to its composition in terms of the sizes of soil particles. The texture of a

soil has an influence on several important soil characteristics including infiltration rate and

available water capacity and may be broadly classified as below;

a. Coarse textured soils - sand predominant - "sandy soils

b. Medium textured soils - silt predominant - "loamy soils"

c. Fine textured soils - clay predominant - "clayey soils"

The depth of soil is particularly important where water harvesting systems are proposed.

Deep soils have the capacity to store the harvested runoff as well as providing a greater

amount of total nutrients for plant growth.

Bulk Density

Soil bulk density is an indicator of the packing of soil particles and it influences the amount

of water retention and transmission. Soil bulk density changes in response to management. It

is influenced by land use, especially in the surface horizons.

Hydraulic Conductivity

Hydraulic conductivity is a measure of the ease with which water moves through a soil. It is

determined by size and continuity of water filled pores. Saturated hydraulic conductivity,

Ksat, is an indication of the ability of pores to conduct water maximally when water is not

limiting and describes water movement through saturated soil.

Saturated soil hydraulic conductivity plays an important role in soil drainage i.e. removal of

excess water and salts. Table 2.2 gives the classification of soils in relation to the saturated

soil hydraulic conductivity.


Table 2.2 - Saturated Hydraulic Conductivity Classification

Classification Saturated Hydraulic Conductivity (mm/h)

Extremely slow 4.167E-05

Very slow 0.0041667

Slow 0.42

Moderate 41.67

Fast 416.67

Very fast 4166.67

Soil Water Infiltration Rate

The infiltration rate is the velocity or speed at which water enters into the soil. It is usually

measured by the depth (in mm) of the water layer that can enter the soil in one hour. In dry

soil, water infiltrates rapidly. This is called the initial infiltration rate. As more water replaces

the air in the pores, the water from the soil surface infiltrates more slowly and eventually

reaches a steady rate. This is called the basic infiltration rate.

The infiltration rate depends on soil texture (the size of the soil particles) and soil structure

(the arrangement of the soil particles) and is a useful way of categorizing soils from an

irrigation point of view. A very low infiltration rate can be detrimental because of the

possibility of waterlogging in the cultivated area. The soils of the cropped area should,

however, be sufficiently permeable to allow adequate moisture to the crop root zone without

causing waterlogging problems.

The infiltration rate of a soil depends primarily on its texture. Typical comparative figures of

infiltration rates are as given below;

Table 2.3 -Basic Infiltration Rates for Various Soil Types1

Soil Type Basic infiltration Rate (mm/h)

Sand more than 30

Sandy Loam 20- 30

Loam 10- 20

Clay Loam 5 - 10

Clay 1 -5

A summary of the physical characteristics of soils in various sites is given in Table 2.4.

Table 2.4 - Physical Characteristics of Soils in Taveta District2

1 Ministry of Water and Irrigation, 2005 .Practice Manual for Water Supply Services in Kenya: Part B. Irrigation

2 Feasibility Study and Preliminary Design -Lake Challa Water Resources Integrated Development

Project- August 2011


2.4.3.3 SOIL CHEMICAL CHARACTERISTICS

Salinity/Sodicity

A salinity problem exists if salt accumulates in the crop root zone to a concentration that

causes a loss in yield. In irrigated areas, these salts often originate from a saline, high water

table or from salts in the applied water. Yield reductions occur when the salts accumulate in

the root zone to such an extent that the crop is no longer able to extract sufficient water from

the salty soil solution, resulting in a water stress for a significant period of time. If water

uptake is appreciably reduced, the plant rate of growth is slowed down.

Salts that contribute to a salinity problem are water soluble and readily transported by water.

Salt content of the root zone varies with depth. It varies from approximately that of the

irrigation water near the soil surface to many times that of the applied water at the bottom of

the rooting depth. Salt concentration increases with depth due to plants extracting water but

leaving salts behind in a greatly reduced volume of soil water.

Sodic soils, which have a high exchangeable sodium percentage and saline soil which have

excess soluble salts, should be avoided for irrigation systems. These soils can reduce

moisture availability directly, or indirectly, as well as exerting direct harmful influence on

plant growth.

Classification

Salinity in a soil influences different plants differently and classification for suitability needs

to be plant specific. However, a general indication of salinity and sodicity for some sites is

shown in Table 2.5.

Area

Depth

(mm)

Preliminary

Classification

Bulk

Density

(g/cm3)

Saturated

Hydraulic

conductivity

(mm/ h)

Conductivity

Class

Infiltration

Rate

(mm/ h)

Infiltration

Class

Kilanga

0-300

Chromic

CAMBISOLS

1.23

6.1

Very slow 72.6 Moderately

rapid

300-900 1.39 6.1 Very slow

Challa

0-300

Chromic

LUVISOLS

1.18

6.0

Very slow 56.1 Moderately

rapid

300-900 1.40 2.4 Very slow

Timbila 0-300 Chromic

CAMBISOLS 0.94 18.0 Slow 31.6 Moderate

300-900 1.41 0.6 Very slow

Jipe 0-300 Rhodic/ orthic 1.60 16.7 Slow 22.5 Moderate

300-900 FERRALSOLS 1.46 6.0 Very slow

Mwaktau 0-300 Rhodic/ orthic

FERRALSOLS 1.48 13.4 Slow 19.1 moderate

300-900 1.73 4.0

Very slow


Table 2.5 – Salinity and Sodicity of Soils3

Area Salinity Sodicity

Kilanga Non-saline Non- sodic

Challa Severely saline Medium-sodic

Timbilla moderate Medium-sodic

Jipe Non-saline Non-sodic

2.4.3.4 SOIL WATER

Available Water Capacity (AWC)

Soil water influences plant growth and crop production. The water in the soil is from

precipitation, irrigation or groundwater. It is either taken up by plants, lost through direct soil

evaporation or deep drainage beyond the rooting zone.

The capacity of soils to hold, and to release adequate levels of moisture to plants are vital to

irrigation. AWC is a measure of this parameter, and is expressed as the depth of water in mm

readily available to plants after a soil has been thoroughly wetted to "field capacity".

Field capacity refers to the water content in a field soil after the drainage rate has become

small and it is an estimate of the amount of water that may be temporarily stored in the soil

profile for plant use. On the other hand, the permanent wilting point or percentage is the soil

water content below which plants growing in that soil remain wilted even when transpiration

is nearly eliminated.

The amount of water released by the soil between field capacity and permanent wilting is

called the available water.

Generally, the available water for various types of soils is given as4;

Heavy textured soil : 200 mm/m

Medium textured soil : 140 mm/m

Coarse textured soil : 60 mm/m

The relationship between soil water potential and the amount of water in the soil (on the basis

of volumetric water) was determined during the Feasibility Study Stage. The values for the

volumetric water content of soils in potential irrigation sites are summarised in Table 2.6.



4 Practice Manual for Water Services in Kenya– Ministry of Water and Irrigation (October 2005)


Table 2.6 - Values for Volumetric Water Content of Soils in Taveta District

Site

Volumetric water content (cm3/cm

3) Available water

Soil layer

(mm)

Available

water

content

at field

capacity

Water

content at

permanent

wilting

point

Available

water

capacity

In layer

(mm)

In profile

(total mm/m)

Kilanga 0-300 0.25 0.017 0.24 7.2 117

300-900 0.16 0.014 0.15 4.5

Challa 0-300 0.28 0.012 0.27 8.1 177

300-900 0.33 0.012 0.32 9.6

Kilanga 0-300 0.25 0.017 0.24 7.2 117

300-900 0.16 0.014 0.15 4.5

Timbila 0-300 0.4 0.017 0.39 11.7 204

300-900 0.3 0.011 0.29 8.7

Jipe 0-300 0.19 0.011 0.18 5.4 126

300-900 0.25 0.007 0.24 7.2

Mwaktau 0-300 0.36 0.006 0.35 10.5 189

300-900 0.29 0.006 0.28 8.4

The soils with highest and lowest available soil water were at Timbila and Kilanga,

respectively.

2.4.3.5 SUMMARY OF SOILS SUITABILITY FOR IRRIGATION

The suitability of the various soils for irrigation purposes is summarised and tabulated below;

Table 2.7– Soils Suitability for Irrigation

Area Remarks

Kilanga The soils are well suited for irrigation on the account of their very

favourable chemical and physical characteristics.

Challa

Soils are well suited for irrigation due to their lack of salinity, high

fertility and good physical properties.

Nakuruto

Soils not suited for irrigation due to their very shallow depth in spite of

having good chemical properties.

Timbila

Based on the available physical and chemical characteristics, the soils

are suited for irrigation.

Jipe The soils in the upper areas are well drained and are irrigable. However,

the soils close to the lake have high salinity and sodicity levels, and

would not be easy to drain.

Mwaktau Based on the available physical and chemical characteristics, the soils

are suited for irrigation.


2.4.4 Quality of Irrigation Water

2.4.4.1 GENERAL

The suitability of water, from quality point of view, is determined by its potential to cause

problems and its relation to the special management practices needed.

The quality of irrigation water influences various aspects of irrigation; including infiltration

rates, salinity and sodicity of soil which affects crop yields and land productivity. It is

therefore imperative to assess water quality to ascertain its quality for irrigation. The criteria

mostly used for rapid assessment includes electrical conductivity (ECw) and sodium

adsorption ratio (SAR) of the water intended for irrigation.

2.4.4.2 INFILTRATION

Infiltration problem related to water quality occurs when the rate of water infiltration into and

through the soil is reduced (because of water quality) to such an extent that the crop is not

adequately supplied with water and yield is reduced. A low infiltration rate makes it more

difficult to supply the crop with adequate water and may greatly add to cropping difficulties

through crusting of seed beds, waterlogging of surface soil and accompanying diseases,

salinity, weed, oxygen and nutritional problems.

Infiltration problems are evaluated through the following parameters;

Total salts in the water (ECw):

Total salts in water are indicated by the electrical conductivity of the water (ECw).

Low salt content in water causes low soil infiltration due to the tremendous

capacity of pure water to dissolve and remove calcium and other solubles in the

soil.

Sodium Adsorption Ratio (SAR) is the relative content of sodium to calcium and

magnesium in the water.

Where: Na, Ca and Mg represent the concentration in milli-equivalents per litre

(Me/l).

The SAR determines the exchangeable sodium (ESP) of a soil. A high ESP defines a soil

which has a high degree of saturation with exchangeable sodium – or an alkali soil.

Carbonates and bicarbonates can also affect infiltration and must be evaluated.

Bicarbonates and carbonates in irrigation water increase the potential for problem by reacting

with soil calcium and magnesium to form insoluble compounds. Removing calcium and

magnesium from soil creates room for sodium to accumulate on the soil colloids.


The above three factors interact in determining the long-term influence of water on the soil

infiltration rate.

2.4.4.3 SALINITY

Salinity problem occurs in soils when the total quantity of salts in the irrigation water is high

enough for the salts to accumulate in the crop root zone to the extent that yields are affected.

Excessive soluble salts in the root zone inhibit water uptake by plants. The plants suffer from

salt-induced drought. Plants respond more critically to salinity in the upper part of the soil

profile than to the salinity levels at depth.

2.4.4.4 TOXICITY

Toxicity problem occurs when harmful ions in the water are taken up by the crop and

accumulate in amounts that reduce crop yield. In arid and semi-arid areas the toxic specific

ions in water include boron, chloride and sodium.

2.4.4.5 MISCELLANEOUS

Various other problems may occur including excessive nitrogen in the water supply, white

deposits on fruit due to high bicarbonate in sprinkler applied water, and suspected

abnormalities indicated by water with unusual pH.

2.4.4.6 GUIDELINES ON CLASSIFICATIONS SUITABILITY OF IRRIGATION WATER

The criteria for assessing the suitability of irrigation water as recommended by FAO and

shown in Table 2.8 was used to classify suitability of the three main sources of irrigation

water in the Taveta area.

Table 2.8 - Guidelines for Interpretation of Water Quality for Irrigation5

Potential Irrigation Problem Restriction on Use

Units None Slight to

Moderate

Severe

Salinity (affects crop water availability)

ECw dS/m <0.7 0.7 - 3.0 >3.0

TDS mg/l <450 450 - 2 >2 000

Infiltration (affects infiltration rate of water into

the soil. Evaluate using ECw and SAR together)

SAR =0-3 and ECw

= 3 - 6 = >1.2 1.2 - 0.3 <0.3

= 6 - 12 = >1.9 1.9 - 0.5 <0.5

= 12 - 20 = >2.9 2.9 - 1.3 <1.3

= 20 - 40 = >5.0 5.0 - 2.9 <2.9

Specific Ion Toxicity (affects sensitive crops)

Sodium (Na)

Surface irrigation SAR <3 3 - 9 >9

Sprinkler irrigation me/l <3 >3

5 Adapted from University of California Committee of Consultants, 1974


Chloride (Cl) V

Surface irrigation me/l <4 4 - 10 >10

Sprinkler irrigation me/l <3 >3

Boron (B) mg/l <0.7 0.7 - 3.0 >3.0

Miscellaneous Effects (affects susceptible crops)

Nitrogen (NO3-N) mg/l <5 5 - 30 >30

Bicarbonate (HCO3) (overhead sprinkling only) me/l <1.5 1.5 - 8.5 >8.5

pH (Normal Range 6.5 - 8.4)

Notes:

1. ECw means electrical conductivity, a measure of the water salinity, reported in

deciSemens per metre at 25°C (dS/m).

2. TDS means total dissolved solids, reported in milligrams per litre (mg/l).

3. 1SAR means sodium adsorption ratio. SAR is sometimes reported by the symbol Tte. At

a given SAR, infiltration rate increases as water salinity increases. Evaluate the potential

infiltration problem by SAR as modified by EC. Adapted from Rhoades 1977; and Oster

and Schroer 1979

4. NO3-N means nitrate nitrogen reported in terms of elemental nitrogen. (NH4-N and

Organic-N should be included when wastewater is being tested).

Chemical and physical characteristics of water from the proposed water sources are shown

Table 2.9.

Table 2.9 - The pH and ECw of Water from the Proposed Sources

Parameter

Water Source

Lake Challa

Challa Irrigation

Scheme Borehole

Nakuruto

Borehole

pH 8.19 8.13 7.62

Electrical Conductivity

mS/cm 0.26 0.27 0.26

Sodium (me/l) 0.56 0.56 0.46

Potassium (me/l) 0.06 0.06 0.03

Calcium (me/l) 2.06 1.93 3.50

Magnesium (me/l) 1.58 1.21 1.27

Carbonates (me/l) Not Detected Not Detected Not Detected

Bicarbonates (me/l) 4.34 4.35 4.05

Chlorides (me/l) 3.50 3.75 3.38

Sulphates (me/l) 0.42 0.35 2.19

Sodium Adsorption Ratio 0.42 0.45 0.30

2.4.4.7 SUMMARY OF WATER QUALITY

The water quality is satisfactory and suitable for irrigation purposes and can be used on most

soils and crops.


2.5 CURRENT AGRICULTURAL PRODUCTION

2.5.1 AGRICULTURE AND LAND USE

Agriculture is the mainstay of majority of rural communities in Kenya and as such, people in

Taveta derive their livelihoods directly or indirectly from agriculture.

The agricultural potential of the arable land in the district is estimated to be 33,550 ha. The

area under cultivation is estimated to be 9,721 ha out of which 3,943 ha is under irrigation.

About 356,160.7 ha of land is covered by the National Park and forests.

The major land uses in the Lake Challa project area are subsistence rain-fed agriculture and

livestock keeping. Due to the harsh climatic conditions livestock production systems are

more extensively practiced than crop production. This is also aggregated by crop invasion by

wildlife particularly elephants. Other land uses include forest cover, bush land.

2.5.2 CROP PRODUCTION

Crop production in Taveta and Mwatate Districts is dominated by:

Food crops, which comprise cereals, pulses and root crops;

Horticultural crops, which include vegetables, fruits and fruit trees; and

Industrial crops, which include the factory processed crops such as sunflower, sisal

and tobacco.

Crop production is largely dependent on rainfall with a few acreages of horticultural crops

under irrigation. The major cropping season is the long rains and farming systems are

characterized by low levels of input use and are labour intensive.

Table 2.10 gives the statistics food crop production in Taveta District during the- 2009/2010

financial year.

Table 2.10 - Food Crop Production Statistics, Taveta District- 2009/2010

Crop

LONG RAINS

(2009 crop)

SHORT RAINS

(2009/10 crop)

Total

(ha) Yield/ha Total

Production

Area

(ha)

Target

Yield /ha

Total

Production

Maize 1,071 18 20, 992 3,115 18 25,330 46,322

Sorghum 40 10 400 16 0 0 400

Rice 178 8 1,680 107 8 886 2,566

Millet 22 10 160 0 0 0 160

Beans 337 8 3,200 335 8 2,037 5,237

Pigeon

peas

22 8 176 1 8 2 178


Green

Grams

101 8 812 55 8 162 974

Cowpeas 117 8 1,448 39 8 154 1,601

Sweet

Potatoes

21 12 253 5 12 59 312

Cassava 39 12 451 21 12 181 632

Arrow

roots

11 12 128 4 12 20 147

Source: Farm Management Guidelines, Taveta District, 2009/2010

From the table above, it is evident that the yields of most crops are low compared to the

potential/ recommended yields. The low crop yields could be attributed to among others lack

of water and harsh climatic conditions.

2.5.3 CONCLUSIONS

The present agricultural production is largely under rain-fed conditions. The rainfall is not

sufficient to meet the water requirement of crops and this result in extremely low crop yields.

Irrigation farming is, therefore, the most reliable source of livelihood in the District.

2.6 PROPOSED CROPPING PATTERN FOR PROJECT AREA

Water availability, climate and type of crops grown at present are considered as key factors in

determining the proposed cropping pattern for the project area. Other factors such as farmers’

preference, labour availability during peak season, cash requirement, market conditions and

the likes were also considered in the determination of cropping pattern.

The following selection criteria were taken into consideration for determining the cropping

pattern for the project area.

Adaptability of the crops to the general conditions of soil and climate of the

area.

Intended objectives of the project which among others include :

- To bring about a state of sustainable food security in the target area in

particular and the whole region in general.

- Promote the production of high value and market oriented crops.

- Promote increased production of industrial and export crops

Availability of improved production technologies.

Existing market demand around the project area and in the neighbouring areas

in general.

Based on the results of an agro-economic baseline survey undertaken by the Consultants,

during which various agronomic and socio-economic issues were considered, major and

minor existing and proposed irrigated food security and commercial crops were accordingly


ranked. In addition, recommendations were sought from various stake holders. The list of

crops and acreages to be considered under irrigated agriculture is presented in the Table 2.11

below.

Table 2.11 - Proposed Overall Cropping Pattern

Season Type of

Crop

Area

(ha)

%

Area

Individual

Crops

Irrigated Area

per Season

(ha)

% Area

Season One

(March to

July

Cereal 190 19 Maize 190 19

Legumes

165

17

Beans 60 6

Green Grams 45 4

Cowpeas 60 6

Vegetables

285

28

Tomatoes 40 4

Kales 35 3

Water Melons 50 5

Onions 110 11

Chillies 50 5

Fruits

330 32

Bananas 185 18

Pawpaws 145 14

Oil Crop 40 4 Sunflower 40 4

Sub-total 1,010 100 1,010 100

Season Two

(September

to January)

Cereal 190 19 Maize 190 19

Legumes

165

17

Beans 60 6

Green Grams 45 4

Cowpeas 60 6

Vegetables

285

28

Tomatoes 40 4

Kales 35 3

Water Melons 50 5

Onions 110 11

Chillies 50 5

Fruits

330 32

Bananas 185 18

Pawpaws 145 14

Oil Crop 40 4 Sunflower 40 4

Sub-total 1,010 100 1,010 100

TOTAL 2,020 100 2,020 100


Table 2.12- Proposed Cropping Pattern by Project Areas

Season Crop Area (ha) Total

Kilanga

Pilot

Scheme

Challa

Scheme

Nakuruto Timbila

Scheme

Jipe

Scheme

Mwaktau

Scheme

(ha)

Season

One

(March

to July

Maize - 20 10 20 100 40 190

Beans - - - - 45 15 60

Green

grams - -

- - 30 15 45

Cowpeas - 10 5 10 20 15 60

Tomatoes 20 10 10 - - 40

Kales 10 10 5 10 - - 35

Sunflower - - - - 25 15 40

Bananas 20 10 5 10 100 40 185

Melons 10 10 5 10 10 5 50

Pawpaws 20 10 5 10 75 25 145

Onions 10 10 5 10 50 25 110

Chillies 10 10 5 10 10 5 50

Sub-total 100 100 45 100 465 200 1,010

Season

Two

(Sept’

to Jan)

Maize - 20 10 20 100 40 190

Beans - - - - 45 15 60

Green

grams - -

- - 30 15 45

Cowpeas - 10 5 10 20 15 60

Tomatoes 20 10 10 - - 40

Kales 10 10 5 10 - - 35

Sunflower - - - - 25 15 40

Bananas 20 10 5 10 100 40 185

Melons 10 10 5 10 10 5 50

Pawpaws 20 10 5 10 75 25 145

Onions 10 10 5 10 50 25 110

Chillies 10 10 5 10 10 5 50

Sub-total 100 100 45 100 465 200 1,010

TOTAL 200 200 90 200 930 400 2,020

2.7 IRRIGATION METHODS

There are three methods of irrigation commonly practiced in the country;

Surface Irrigation

Sprinkler Irrigation

Drip (Trickle Irrigation)


2.7.1 Surface Irrigation

Surface irrigation refers to a broad class of irrigation methods in which water is distributed

over the field by overland flow. A flow is introduced at one edge of the field and covers the

field gradually. The rate of coverage (advance) is dependent almost entirely on the

differences between the discharge onto the field and the accumulating infiltration into the

soil.

In surface irrigation systems, water moves over and across the land by simple gravity flow in

order to wet it and to infiltrate into the soil. Surface irrigation can be used for all types of

crops and may be commonly classified into furrow, border-strip or basin irrigation.

2.7.1.2 Furrow Irrigation

Furrows are small, parallel channels, made to carry water in order to irrigate the crop. The

crops are usually grown on the ridges between the furrows which must be carefully dug to

ensure an even distribution of water. Water is applied to the upper end of each furrow and

flows down the furrow with water infiltrating into the beds or ridges between the furrows on

which the crop is grown.

The flow of water into a furrow should be large enough to reach the end, but small enough

not to cause erosion, flooding or excessive tail losses. The size of the flow must be adjusted

to the infiltration rate of the soil, land slope, furrow length, erosion hazard and depth to be

applied. Depending on available water, and skill of irrigator, several furrows are irrigated at

the same time.

2.7.1.3 Basin Irrigation

Water is applied from a small canal by gravity to fill a level basin surrounded by earth buds.

The design is based on rapid application of water over the entire basin at a rate of least 2 to 4

times the infiltration rate of the soil6. The method is suitable for very flat and level land and

soils with low infiltration rates.

The cultivation of paddy rice is normally done using basin irrigation.

2.7.1.4 Border Strip Irrigation

Borders are usually long, uniformly graded strips of land, separated by earth bunds. In

Contrast to basin irrigation these bunds are not to contain the water for ponding but to guide

it as it flows down the field.

The field to be irrigated is divided into a number of level strips between ridges. Water is

applied from one end and, in flowing downslope, progressively covers the entire strip with a

thin sheet of water. Length and width of the strip depend on soil and land characteristics.

6 Civil Engineer’s Reference Book – Fourth Edition (Blake, L. S.)


2.7.2 Sprinkler Irrigation

In the sprinkler method of irrigation, water is sprayed into the air and allowed to fall on the

ground surface, somewhat resembling rainfall. Water is distributed through a system of pipes

and then sprayed into the air through sprinklers so that it breaks up into small water drops

(between 0.5 and 4.0 mm in size) which fall to the ground. The spray is developed by the

flow of water under pressure through small orifices or nozzles.

The small drops fall close to the sprinkler whereas the larger ones fall close to the edge of the

wetted circle. Large drops can damage delicate crops and soils and so in such conditions it is

best to use the smaller sprinklers. Drop size is also controlled by pressure and nozzle sizes.

When the pressures are low, drops tend to be much larger as the water jet does not break up

easily.

Sprinkler irrigation can be used for almost all crops (except rice and jute) and on most soils. It

is, however, not usually suitable in very fine textured soil (heavy clay soils), where the

infiltration rates are very low, less than about 4 mm/h, and is particularly suited to sandy soils

that have a high infiltration rate.

Sprinkler irrigation is suited for most row, field and tree crops and water can be sprayed over

or under the crop canopy. Sprinkler irrigation is adaptable to any farmable slope, whether

uniform or undulating.

The application of water by overhead sprinklers takes many forms which include the

following.

1. Permanent and Solid Set

This consists of a network of pipes and sprinklers which covers the whole area to be

irrigated. This is the most expensive form of sprinkler irrigation.

2. Lateral Move Sprinklers

This consists of sprinklers on a lateral line that is moved by hand after each irrigation

application to the next area of irrigation to be irrigated. This is the most widely used system.

3. Traveller Systems

These are motorized methods of moving sprinklers and include:

Side roll - lateral pipe and sprinklers on wheels pushed by hand or small motor

from one position to the next irrigation position;

Mobile rain gun – single gun winched across field whilst irrigating and fed

from a hose reel;

Centre pivot – overhead lateral with sprinklers which rotates about centre

whilst irrigating;

Linear move – similar to centre pivot but moves laterally across the field.

The most common system in developing countries is the lateral move sprinkler system.


Figure 2.3 – Typical Portable Lateral Move Overhead Sprinkler System

2.7.3 Drip (Or Trickle) Irrigation

Drip irrigation works by applying water slowly, directly to the soil. Water is delivered at or

near the root zone of plants, drop by drop to individual trees, groups of plants or plant rows

through a system of small diameter plastic pipes fitted with outlets called drippers or emitters,

placed on laterals delivering a flow of between 2 to 20 1/h each.

Water is applied close to plants so that only part of the soil in which the roots grow is wetted,

unlike surface and sprinkler irrigation, which involves wetting the whole soil profile.

Drip Irrigation is the most expensive, but most water-efficient, method.

2.8 CHOICE OF IRRIGATION METHOD(S)

The choice of an appropriate irrigation method is determined by the following factors;

a. Natural conditions

b. Type(s) of crop(s)

c. Type and level of technology

d. Previous experience with irrigation

e. Required labour inputs


f. Costs and benefits.

2.8.1 Natural Conditions

The natural conditions such as soil type, slope, climate, water quality and availability, have

the following impact on the choice of an irrigation method.

Soil Type

On loam or clay soils all three irrigation methods can be used, but surface irrigation is more

commonly used.

Sprinklers are best suited to sandy soils with high infiltration rates although they are

adaptable to most soils. Sprinklers are not suitable for soils which easily form a crust. If

sprinkler irrigation is the only method available, then light fine sprays should be used. The

larger sprinklers producing larger water droplets are to be avoided.

Furrows can be used on most soil types. However, as with all surface irrigation methods, very

coarse sands are not recommended as percolation losses can be high. Soils that crust easily

are especially suited to furrow irrigation because the water does not flow over the ridge, and

so the soil in which the plants grow remains friable. Clay soils with low infiltration rates are

ideally suited to surface irrigation.

When a variety of different soil types is found within one irrigation scheme, sprinkler or drip

irrigation are recommended as they will ensure a more even water distribution.

Slope

Sprinkler or drip irrigation are preferred over furrow irrigation on steeper or unevenly sloping

lands as they require little or no land levelling. Sprinkler irrigation is adaptable to any

farmable slope, whether uniform or undulating. The lateral pipes supplying water to the

sprinklers should always be laid out along the land contour whenever possible. This will

minimize the pressure changes at the sprinklers and provide a uniform irrigation.

Uniform flat or gentle slopes are preferred for furrow irrigation. These should not exceed

0.5%. Usually a gentle furrow slope is provided up to 0.05% to assist drainage following

irrigation or excessive rainfall with high intensity.

On steeper sloping land, contour furrows can be used up to a maximum land slope of 3%. On

undulating land furrows should follow the land contours

Climate

Strong wind can disturb the spraying of water from sprinklers. Under very windy conditions,

drip or surface irrigation methods are preferred. In areas of supplementary irrigation,

sprinkler or drip irrigation may be more suitable than surface irrigation because of their

flexibility and adaptability to varying irrigation demands on the farm.


Water Availability and Quality

Water application efficiency is generally higher with sprinkler and drip irrigation than surface

irrigation

Surface irrigation is preferred if the irrigation water contains much sediment. The sediments

may clog the drip or sprinkler irrigation systems.

A good clean supply of water, free of suspended sediments, is required to avoid problems of

sprinkler nozzle blockage and spoiling the crop by coating it with sediment

Low-quality water (high in salts) should not be used, unless filtered, due to potentially

devastating effects of clogged emitters. Also, the use of water high in soluble salts will result

in localized soil salinity buildup around plants, since drip irrigation is an ineffective leaching

method.

2.8.2 Type(s) of Crop(s)

Sprinkler and drip irrigation, because of their high capital investment per hectare, are mostly

used for high value cash crops, such as vegetables and fruit trees. They are seldom used for

the lower value staple crops.

Sprinkler irrigation is suited for most row, field and tree crops and water can be sprayed over

or under the crop canopy. However, large sprinklers are not recommended for irrigation of

delicate crops because the large water drops produced by the sprinklers may damage the crop.

Furrow irrigation is best used for irrigating the following crops:

Row crops such as maize and vegetables;

Crops that would be damaged by inundation, such as tomatoes, vegetables, potatoes,

beans;

Fruit trees such as citrus, mangoes, bananas

2.8.3 Type and Level of Technology

The type of technology affects the choice of irrigation method. In general, drip and sprinkler

irrigation are technically more complicated methods. The purchase of equipment requires

high capital investment per hectare. To maintain the equipment a high level of 'know-how'

has to be available.

Surface irrigation systems, in particular small-scale schemes, usually require less

sophisticated equipment for both construction and maintenance (unless pumps are used). The

equipment needed is often easier to maintain.

2.8.4 Previous Experience with Irrigation

The choice of an irrigation method also depends on the irrigation tradition within the region

or country. Introducing a previously unknown method may lead to unexpected complications.

It is not certain that the farmers will accept the new method. The servicing of the equipment

may be problematic and the costs may be high compared to the benefits.


2.8.5 Required Labour Inputs

Furrow irrigation requires, regular maintenance and a high level of farmers' organization to

operate the system than sprinkler or drip irrigation systems

Sprinkler and drip irrigation require little land leveling and the systems operations and

maintenance are less labour-intensive.

2.8.6 Costs and Benefits

Sprinkler irrigation methods are more expensive than furrow irrigation, but are more efficient

at using water.

The drip irrigation method is the most water-efficient but the most expensive.

Construction/installation, operation and maintenance costs are compared with the expected

benefits (yields) to determine the most profitable method.

2.9 COMPARISONS OF VARIOUS IRRIGATION METHOD(S)

In order to choose an appropriate irrigation method(s), some of the advantages and

disadvantages of the various methods should be considered to determine the one which suits

the local conditions best. A comparison of the various irrigation methods, based on ten

important parameters, is presented in the table below.

Table 2.13 - Parameters Affecting the Choice of Irrigation Methods

No Parameter Surface Irrigation Sprinkler Irrigation Drip Irrigation

1 Initial

Investment

Cost

Relatively inexpensive

(where water costs are low)

method per given area.

These systems can be

developed at the farm level

with minimal capital

investment. The control and

regulation structures are

simple, durable and easily

constructed with

inexpensive and readily-

available materials like

wood, concrete, brick and

mortar, etc.

Initial cost per given

area is higher than

surface irrigation.

High water pressure

required (>25 m

head)

More expensive than

a more traditional

sprinkler system per

given area

2 Operations Surface systems tend to be

labour-intensive. Labour

engaged per irrigation is

higher than sprinkler and

drip.

Labour engaged per

irrigation is higher

than drip.

A drip irrigation

system can be

automated.

Labour required only

for starting and

stopping the system.


3 Ground

Topograph

y

Not suitable for undulating

ground and slopes of more

than 3%.

Suitable for

undulating ground

and slopes of up to

16%

Suitable for steep/

undulating land.

Pressure

compensating emitters

are available, so the

field does not have to

be level.

Table 2.13 - Parameters Affecting the Choice of Irrigation Methods (continued)


4 Land

Preparation

Perfect land smoothening

and levelling required.

(May be difficult to use on

irregular slopes as

considerable land levelling

may be required to achieve

the required land gradients).

Only land

smoothening is

required

Only land

smoothening is

required

5 Depth and

Porosity of

soil

Not suitable for shallow

and porous soils- Deep

percolation is more in light

soils while Runoff loss is

more in heavy soils.

Not suitable for coarse sand

(with an infiltration rate of

more than 30 mm/h)

Suitable for shallow/

deep and all types of

soils except fine

textured soils (heavy

clay soils), where the

infiltration rates are

less than about 4

mm/h.

Adaptable to nearly

all irrigable soils

since sprinklers are

available in a wide

range of discharge

capacity.

Suitable for shallow/

deep and all types of

soils as flow rates can

be controlled.



6 Water Use

and

Application

efficiency

Losses occur due to

percolation, runoff,

and evaporation.

Application efficiency

of

50-60%

Higher water

application efficiency

(75-85%)

No channels for

conveyance, therefore

no conveyance loss.

Uneven water

distribution due to

high winds -difficulty

in irrigation during

wind in sprinkler

Evaporation loss when

operating under high

Runoff and deep

percolation losses are

minimal with an

application efficiency of

90-95%


temperatures.

7 Weeds

Infestation

Weeds infestation is

very high.

Weeds infestation is

high.

Enhance weed control

by keeping much of the

soil surface dry.

8 Diseases

and Pests

Infestation

High Problems due to foliar

moisture-some

diseases can arise if

over watering occurs.

Relatively less because

of less atmospheric

humidity and reduced

contact of water with

crop leaves, stems, and

fruit.


No Parameter Surface Irrigation Sprinkler

Irrigation

Drip Irrigation

9 Quality of

water

Saline water cannot be

used for irrigation.

Saline water cannot

be used for

irrigation.

Frequent irrigation

avoids the built up of

salt concentration

within root zone by

pushing salts away

from root zone.

10 Application

of

Chemicals

(Fertilisers,

Herbicides,

Insecticides,

and

Fungicides

Not suitable for

application of agricultural

chemicals

Not suitable for

application of

agricultural

chemicals

Agricultural

chemicals(herbicides,

insecticides, and

fungicides can be

applied more

efficiently with drip

irrigation

(Fertigation)

2.10 PREFERRED IRRIGATION METHOD(S)

Based on the factors enumerated in sections 2.8 and 2.9 of this report, above, the following

observations and recommendations were made in the project areas;

1. Water application efficiency is generally higher with sprinkler and drip irrigation than

surface irrigation methods. The drip irrigation method is the most water-efficient but

the most expensive.

2. Sprinkler and drip irrigation, because of their high capital investment per hectare, are

mostly used for high value cash crops, such as vegetables and fruit trees. They are

seldom used for the lower value staple crops.

3. Sprinkler or drip irrigation methods are preferred over furrow irrigation on whether

uniform or undulating loping lands as they require little or no land levelling. On the

other hand while surface irrigation methods can be used for all types of crops, they

may be difficult to use on irregular slopes as considerable land levelling may be

required to achieve the required land gradients.


4. The type of technology affects the choice of irrigation method. In general, drip and

sprinkler irrigation are technically more complicated methods. The purchase of

equipment requires high capital investment per hectare. To maintain the equipment a

high level of 'know-how' has to be available. The choice of an irrigation method also

depends on the irrigation tradition within the region. Introducing a previously

unknown method may lead to unexpected complications. It is not certain that the

farmers will accept the new method. Servicing of the required equipment may be

problematic and the costs may be high compared to the benefits. Surface irrigation

systems, in particular small-scale schemes, usually require less sophisticated

equipment for both construction and maintenance

5. The use of water high in soluble salts will result in localized soil salinity buildup

around plants, since drip irrigation is an ineffective leaching method. This method is

not recommended on any of the sites.

6. A combination of the drip and overhead sprinkler system is recommended for the

Kilanga Scheme. The fact that the farm is expected to be a pilot scheme which will be

managed by CDA who in a position to engage qualified personnel to operate and

maintain the required equipment.

7. For Nakuruto, Jipe and Mwaktau Schemes, the preferred method of irrigation would

be the furrow irrigation. The people in the region are already practicing it in the

nearby Challa and Timbila Schemes. Furthermore, the use of the overhead sprinkler

systems would incur additional capital, operational and maintenance costs. The initial

cost per given area is higher for sprinkler than surface irrigation as high water

pressure of at least 25 m head is required.

The preferred methods of irrigation for different proposed crops are given in Table 2.14

below;

Table 2.14 - Preferred Method(s) of Irrigation for Various Crops

Area Crop Mode of irrigation

Kilanga Pilot Project

Tomatoes Drip

Kales Sprinkler

Bananas Drip

Melons Sprinkler

Pawpaws Sprinkler

Onions Sprinkler

Chillies Sprinkler

Challa (Existing Scheme) All crops Surface (Furrow) Irrigation

Timbila(Existing Scheme) All crops Surface (Furrow) Irrigation

Jipe All crops Surface (Furrow) Irrigation

Mwaktau All crops Surface (Furrow) Irrigation


2.11 CROP AND IRRIGATION WATER REQUIREMENTS

2.11.1 Crop Water Requirements (ETCROP)

2.11.1.2 DEFINITION

Crop water requirement, ETcrop, is defined as the depth of water required by the crop to meet

the water loss through evapotranspiration. The modified Penman Method (FAO paper No.56,

1998) is a globally accepted empirical method for estimating the crop water requirement

utilizing the available climatological data for a particular location. The Modified Penman

equation is given by;

ETcrop = ETO x KC…………………………………………………………………….. (1)

Where

ETcrop is the Crop water requirement (mm)

ETo is the Reference Evapotranspiration (mm) and

KC is the Crop Coefficient (dimensionless).

2.11.1.3 REFERENCE EVAPOTRANSPIRATION (ETo)

The evapotranspiration rate from a reference surface, not short of water, is called the

reference crop evapotranspiration or reference evapotranspiration. A large uniform grass field

with specific characteristics is considered worldwide as the reference surface. ETo expresses

the evaporating power of the atmosphere at a specific location and time of the year and does

not consider the crop characteristics and soil factors.

The only factors affecting ETo are climatic parameters. Consequently, ETo is a climatic

parameter and can be computed from weather data.

For Kenya7, ETo can be found by multiplying the evaporation from a free water surface (Eo)

by an adjustment factor, this one being;

· For highlands (above 1,100m) = 0.75

· For hot and dry low areas (below 1,100m) = 0.80

Hence for Taveta Area,

ETo = 0.8 x

Eo……………………………………………………………………………………(2)

Values for Eo (open water surface evaporation) found in “Studies of Potential Evaporation in

Kenya” by T. Woodhead8, alongside the computed values of ETo, are shown in the Table 2.15

below.




Table 15 - Estimated Reference Evapotranspiration (ETo)

Month

Eo -Open Water

Surface evaporation

(mm/month)9

Eo -Open Water

Surface evaporation

(mm/day)

ETo Estimated

Reference

Evapotranspiration

(mm/day)

January 175 5.65 4.52

February 175 6.25 5.00

March 175 5.65 4.52

April 150 5.00 4.00

May 140 4.52 3.61

June 135 4.50 3.60

July 135 4.35 3.48

August 145 4.68 3.74

September 165 5.50 4.40

October 185 5.97 4.77

November 175 5.83 4.67

December 175 5.65 4.52

2.11.1.4 CROP COEFFICIENT (Kc)

Factors affecting the value of KC are mainly crop characteristics, crop planting data, crop

development, length of growing season and climate considerations. Crop transpiration

increases over the growing season with the growth of the canopy surface while the soil

evaporation decreases proportionally over the growing season as the ground surface is

increasingly shaded by the crop canopy. There are four distinguishable crop growth stages

1. The initial stage: when the crop uses little water;

2. The crop development stage, when the water consumption increases;

3. The mid-season stage, when water consumption reaches a peak;

4. The late-season stage, when the maturing crop once again requires less water

The effect of both crop transpiration and soil evaporation are integrated into a single crop

coefficient KC incorporating crop characteristics and average effects of evaporation from the

soil.

The table below shows the crop coefficients of the selected crops at various stages of

development while the next table superimposes the applicable crop coefficients with the

proposed cropping calendar.



Table 2.16 - Crop Coefficients10

(Kc)

No.

Crop

Type

Crop

Growing Period

(Days)

Initial

Stage

Crop

Development

Mid

Season

Late

Season

At

Harvest

1 Cereals Maize 120 - 140 0.40 0.80 1.15 0.90 0.60

2

Legumes

Beans 90-110 0.35 0.75 1.15 0.70 0.30

Green Grams 90-110 0.35 0.75 1.15 0.70 0.30

Cowpeas 90-110 0.35 0.75 1.15 0.70 0.30

3

Vegetables

Tomatoes 90-110 0.45 0.75 1.15 0.90 0.60

Kales 75-100 0.45 0.75 1.05 0.95 0.90

Water Melons 125-145 0.45 0.75 1.0 0.85 0.70

Onions 90-110 0.50 0.80 1.1 0.90 0.80

Chillies 90-110 0.35 0.70 1.1 1.0 0.85

4

Fruits

Bananas >365 0.60 0.85 1.1 1.1 0.1

Pawpaw >365 0.60 0.85 1.1 1.1 1.1

5 Oil crops Sunflower 120-140 0.305 0.75 1.15 0.75 0.40

Table 2.17 - Cropping Calendar and Applicable Crop Coefficients

Crop Mar Apr May Jun Jul Aug

Maize 0.4 0.8 0.8 0.8 1.15 1.15 1.15 0.9 0.6

Beans 0.35 0.75 0.75 1.15 1.15 0.7 0.3

Green Grams 0.35 0.75 0.75 1.15 1.15 0.7 0.3

Cowpeas 0.35 0.75 0.75 1.15 1.15 0.7 0.3

Tomatoes 0.45 0.75 0.75 1.15 1.15 0.9 0.6

Kales 0.45 0.75 1.05 1.05 0.95 0.9

Water Melons 0.45 0.75 0.75 0.75 1.0 1.0 0.85 0.85 0.7

Onions 0.5 0.8 0.8 1.1 1.1 0.9 0.8

Chillies 0.35 0.7 0.7 1.1 1.1 1.0 0.85

Bananas 0.6 0.6 0.6 0.6 0.85 0.85 0.85 0.85 1.1 1.1 1.1 1.1

10

Practice Manual for Water Services in Kenya– Ministry of Water and Irrigation (October 2005)


Crop Mar Apr May Jun Jul Aug

Pawpaw 0.6 0.6 0.6 0.6 0.85 0.85 0.85 0.85 1.1 1.1 1.1 1.1

Sunflower 0.35 0.75 0.75 1.15 1.15 1.15 0.75 0.75 0.4

Crop Sep Oct Nov Dec Jan Feb

Maize 0.4 0.8 0.8 0.8 1.15 1.15 1.15 0.9 0.6

Beans 0.35 0.75 0.75 1.15 1.15 0.7 0.3

Green Grams 0.35 0.75 0.75 1.15 1.15 0.7 0.3

Cowpeas 0.35 0.75 0.75 1.15 1.15 0.7 0.3

Tomatoes 0.45 0.75 0.75 1.15 1.15 0.9 0.6

Kales 0.45 0.75 1.05 1.05 0.95 0.9 0.6

Water Melons 0.45 0.75 0.75 0.75 1 1 0.85 0.85 0.7

Onions 0.5 0.8 0.8 1.1 1.1 0.9 0.8

Chillies 0.35 0.7 0.7 1.1 1.1 1 0.85

Bananas 0.6 0.6 0.6 0.6 0.85 0.85 0.85 0.85 1.1 1.1 1.1 1.1

Pawpaw 0.6 0.6 0.6 0.6 0.85 0.85 0.85 0.85 1.1 1.1 1.1 1.1

Sunflower 0.35 0.75 0.75 1.15 1.15 1.15 0.75 0.75 0.4

Key to Table 2.17

Season

One

Annual crops Season

Two


2.11.1.5 ESTIMATION OF CROP WATER REQUIREMENTS (ETcrop)

The applicable CROP WATER REQUIREMENTS (ETcrop) have been computed by applying

equation (1) and using the values of ETo and applicable crop coefficients (KC) as determined

in Sections 6.1.2 and 6.1.3 and tabulated in the Table below.

Table 2.18 - Estimated Crop Water Requirements (ETcrop)(mm)

Crop Mar Apr May June July Aug Total

Season

One

Maize 83.1 96.0 128.8 110.7 33.4 - 452.0

Beans 76.1 114.0 104.4 16.2 - - 310.7

Green

Grams 76.1 114.0 104.4 16.2 - - 310.7

Cowpeas 76.1 114.0 104.4 16.2 - - 310.7

Tomatoes 83.3 114.0 115.3 32.4 - - 345.0

Kales 83.3 126.0 103.7 - - - 313.0

Water

Melons 83.3 90.0 112.0 91.8 - - 416.1

Onions 90.3 114.0 112.4 43.2 - - 359.9

Chillies 72.7 108.0 117.8 45.9 - - 344.4

Bananas 119 102 123.2 118.8 64.8 69.6 597.4

Pawpaw 119 102 123.2 118.8 64.8 69.6 597.4

Sunflower 76.1 114.0 128.8 81.0 22.3 - 422.2

Crop Sept Oct Nov Dec Jan Feb Total

Season

Two

Maize 79.2 118.4 161.0 144.1 43.4 - 546.0

Beans 72.6 139.6 129.5 21.7 - - 363.4

Green

Grams 72.6 139.6 129.5 21.7 - - 363.4

Cowpeas 72.6 139.6 129.5 21.7 - - 363.4

Tomatoes 79.2 139.6 143.5 43.4 - - 405.7

Kales 79.2 155.4 129.5 0 - - 364.1

Water

Melons 79.2 111.0 140.0 119.0 50.6 - 499.8

Onions 85.8 139.9 140.0 57.8 - - 423.5

Chillies 69.3 132.2 147.0 61.4 - - 410.0

Bananas 112.2 125.8 154.0 154.0 84.0 87.0 717.0

Pawpaw 112.2 125.8 154.0 154.0 84.0 87.0 717.0

Sunflower 72.6 139.6 161.0 105.0 28.9 - 507.1

Worked Example 1

Estimation of Crop Water Requirements

ETcrop = ETO x KC as per equation (1)

For Maize in the month of March,

ETo = 4.52 mm/day and KC= 0.4 (16 days) and KC = 0.8 (15 days)


Therefore; ETcrop = 4.52 x [(0.4 x 16) + (0.8 x 15)] = 83.097 mm…………(3)

Other detailed calculations are tabulated in Table 2.18.

Table 2.19 - Estimated Annual Crop Water Requirements (ETcrop) (mm)

Long Rains Short Rains Total

Maize 452.0 546.0 998.0

Beans 310.7 363.4 674.1

Green Grams 310.7 363.4 674.1

Cowpeas 310.7 363.4 674.1

Tomato 345.0 405.7 750.7

Kales 313.0 364.1 677.1

Water Melons 416.1 499.8 915.9

Onions 359.9 423.5 783.4

Chilies 344.4 410.0 754.4

Bananas 597.4 717.0 1314.4

Pawpaw 597.4 717.0 1314.4

Sunflower 422.2 507.1 929.3

2.11.2 Net Irrigation Water Requirements (NIR)

2.11.2.2 DEFINITION

The Net Irrigation Water Requirement (NIR) is defined as the amount of water needed to

meet the Crop Water Requirement (ETCROP) less portion of rainfall stored in soil and

effectively utilised by the crop. Basically, the irrigation water requirement basically

represents the difference between the crop water requirement and effective precipitation.

Hence NIR = ETCROP - REFF ………………………………………………….…… (4)

Where, NIR = Net Irrigation Requirement (mm)

ETCROP = Crop Water Requirement (mm)

REFF = Effective Rainfall (mm)

2.11.2.3 EFFECTIVE RAINFALL

Crop water needs can be fully or partly met by rainfall. Not all rainfall that falls is effective

(for the crops), as part of it may be lost by run-off, deep percolation or evaporation, hence the

term effective rainfall. The amount of effective rainfall mainly depends upon intensity of

rainfall, crop water requirements, soil type, and root depth of plant.

The average monthly effective rainfall is obtained based on its empirical relationship with the

mean monthly rainfall (Table 2.1) for different values of average monthly ETCROP (Crop


water requirements) (Table 2.18). A storage factor is applied when effective storage in the

root in the root zone differs from 75mm.11

The average available water in soil profile for all the project sites, as per the Soils Report in

the Feasibility Study, is 162.6 mm/m.12

Table 2.20 gives the effective soil storages and the applicable factors for the various crops as

extracted from the Practice Manual for Water Services in Kenya– Ministry of Water and

Irrigation (October 2005). An adjustment factor of 1.06 is applicable where the effective

storage is greater or less than 75 mm.

Table 2.20 - Effective Soil Storages

Crop

Average Root

Zone13

(m)

Effective Storage

(mm)

Adjustment Factor14

Maize 1 162.6 1.06

Beans 0.6 97.6 1.02

Green grams 0.6 97.6 1.02

Cowpeas 0.6 97.6 1.02

Tomatoes 0.7 113.8 1.03

Kales 0.3 48.8 0.93

Water Melons 0.8 130.1 1.04

Onions 0.3 48.8 0.93

Chillies 0.5 81.3 1

Bananas 0.5 81.3 1

Pawpaws 0.5 81.3 1

Sunflower 0.8 130.1 1.04

The result of effective rainfall estimation for various crops, as extrapolated from the Practice

Manual for Water Services in Kenya– Ministry of Water and Irrigation (October 2005) is

given in Table 2.21.

11




13 Irrigation and Drainage Paper No 56 - Food and Agricultural Organisation (FAO) 1998



Worked Example 2

Estimation of Effective Rainfall (REFF)

Average available water in soil profile = 162.6 mm/m (See Section 2.11.2.3 of this Report)

For Maize, Average Root Zone = 1 m, (Table 2.20)

Therefore;

Effective Storage =162.6 mm/m x 1 m =162.6 mm (An adjustment factor of 1.06 is

applicable as per Table 2.20)

For ETcrop = 83.097 mm (equation (3)) and mean monthly rainfall of 95 mm (Figure 2.1) and

through extrapolation from Table 7 of the Practice Manual for Water Services in Kenya–

Ministry of Water and Irrigation (October 2005) and applying a Storage Factor of 1.06 then

Estimated Effective Rainfall (REFF) = 58 x 1.06 = 61.480 mm ………………….…… (5)

Table 2.21 - Estimated Effective Rainfall (REFF) (mm)

Season Crop Mar Apr May June July Aug Total

Season

One

Maize 61.5 95.4 48.8 15.9 4.2 225.8

Beans 59.2 91.8 45.9 6.1 - - 203.0

Green Grams 59.2 91.8 45.9 6.1 - - 203.0

Cowpeas 59.2 91.8 45.9 6.1 - - 203.0

Tomatoes 57.7 92.7 46.4 6.2 - - 202.9

Kales 52.1 85.6 42.8 - - - 180.4

Water

Melons 64.5 87.4 44.7 14.6 8.3 - 219.4

Onions 57.7 83.7 44.6 7.4 - - 193.4

Chilies 62.0 90.0 46.0 8.0 - - 206.0

Bananas 66.0 90.0 43.0 13.0 7.0 8.0 233.0

Pawpaw 66.0 90.0 43.0 13.0 7.0 8.0 227.0

Sunflower 58.2 95.7 48.9 15.6 8.3 - 226.7

Season

Two


Maize 8.5 15.9 91.2 60.4 21.2 - 197.2

Beans 8.2 15.3 81.6 20.4 - - 125.5

Green Grams 8.2 15.3 81.6 20.4 - - 125.5

Cowpeas 8.2 15.3 81.6 20.4 - - 125.5

Tomato 7.2 15.5 82.4 20.6 - - 125.7

Kales 6.5 13.0 70.7 - - - 90.2

Water

Melons 9.4 13.5 90.5 56.2 20.8 - 190.3

Onions 8.4 14.9 76.3 25.1 - - 124.6

Chilies 9.0 13.0 85.0 25.0 - - 132.0



Bananas 9.0 15.0 85.0 53.0 36.0 26.0 224.0

Pawpaw 9.0 15.0 85.0 53.0 36.0 26.0 224.0

Sunflower 8.3 16.6 91.5 58.2 20.8 - 195.5

2.11.2.4 ESTIMATED NET IRRIGATION WATER REQUIREMENTS (NIR)

Based on equation 3, the estimated monthly and yearly net irrigation water requirement (NIR)

for the proposed project cropping scheme is given in Table 2.22.

Table 2.22 -Estimated Net Irrigation Water Requirements (NIR)(mm)


Season

One

Maize 21.7 0.6 80.0 94.8 29.2 - 225.7

Beans 16.9 22.2 58.5 10.1 - - 107.7

Green Grams 16.9 22.2 58.5 10.1 - - 107.7

Cowpeas 16.9 22.2 58.5 10.1 - - 107.7

Tomato 25.6 21.3 68.9 26.2 - - 142.1

Kales 31.2 40.4 60.9 0 - - 132.6

Water Melons 18.8 2.64 67.3 77.2 30.7 - 194.1

Onions 32.7 30.3 67.7 35.8 - - 166.5

Chilies 10.7 18.0 71.8 37.9 - - 138.4

Bananas 53.0 12.0 80.2 105.8 57.8 61.6 370.4

Pawpaw 53.0 12.0 80.2 105.8 57.8 61.6 370.4

Sunflower 17.9 18.3 79.9 65.4 14.0 - 195.5

Season

Two


Maize 70.7 102.5 69.8 83.6 22.2 - 348.9

Beans 64.4 124.3 47.9 - - - 236.7

Green Grams 64.4 124.3 47.9 - - - 236.7

Cowpeas 64.4 124.3 47.9 - - - 236.7

Tomato 72.0 124.2 61.1 22.8 - - 280.0

Kales 72.7 142.4 58.8 - - - 273. 9

Water Melons 69.8 97.5 49.5 62.8 - - 309.5

Onions 77.4 125.0 63.7 32.7 - - 298.9

Chilies 60.3 119.2 62.0 36.4 - - 278.0

Bananas 103.2 110.8 69.0 101.0 48.0 61.0 493.0

Pawpaw 103.2 110.8 69.0 101.0 48.0 61.0 493.0

Sunflower 64.3 123.0 69.5 46.8 8.1 - 311.6

Worked Example 3

Estimation of Net Irrigation Water Requirements (NIR)

Through extrapolation from Table 7 of the Practice Manual for Water Services in From

Equation 4 and applying the figures in equations (3) and (5)

NIR = ETCROP - REFF =83.097 – 61.480 = 21.617m

For the existing Challa Irrigation it is proposed that water for an additional 20 ha will


Be provided

Hence, the volumetric Net Irrigation Water Requirements (NIR) for the month of March is

estimated to be

NIR = 21.617 mm x 20 ha x 104 m2/ha x 10

-3 m/mm

=4,323.4 m3……………………………………………………………(6)

Based on the above and the areas to be irrigated as proposed in Chapter 2.6 of this report, the

estimated Net Irrigation Water Requirements, by crops and specific sites, are shown in Tables

2.23 and 2.24, respectively.


Table 2.23 -Net Monthly Irrigation Water Requirements (by Crops)

Crop/

Site

Area

(ha)

Net Irrigation Water Requirements (NIR)(m3)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual

MAIZE

Kilanga 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Challa 20 4,431.0 0 4,323.4 120.0 16,008.0 18,960.0 5,841.0 0 14,144.0 20,500.0 13,968.0 16,728.9 115,024.3

Nakuruto 10 2,215.5 0 2,161.7 60.0 8,004.0 9,480.0 2,920.5 0 7,072.0 10,250.0 6,984.0 8,364.5 57,512.1

Timbilla 20 4,431.0 0 4,323.4 120.0 16,008.0 18,960.0 5,841.0 0 14,144.0 20,500.0 13,968.0 16,728.9 115,024.3

Jipe 100 22,154.8 0 21,617.0 600.0 80,040.0 94.800.0 29,205.0 0 70,720.0 102,500.0 69,840.0 83,644.5 575,121.3

Mwaktau 40 8,861.9 0 8,646.7 240.0 32,016.0 37,920.0 11,682.0 0 28,288.0 41,000.0 27,936.0 33,457.8 230,048.5

Total 190 42,094.2 0 41,072.0 1,140.0 152,076.0 180,120.0 55,490.0 0 134,368.0 194,750.0 132,696.0 158,925.0 1,092,730.0

BEANS

Kilanga 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Challa 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Nakuruto 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Timbilla 0 0 0 0 0 0 0 0 0 0 0 0 0

Jipe 45 0 0 7,621.5 9,990.0 26,330.8 4,536.0 0 0 28,998.0 55,955.3 21,555.0 574.8 155,561.5

Mwaktau 15 0 0 2,540.5 3,330.0 8,776.9 1,512.0 0 0 9,666.0 18,651.8 7,185.0 191.6 51,853.8

Total 60 0 0 10,162.0 13,320.0 35,107.7 6,048.0 0 0 38,664.0 74,607.1 28,740.0 766.42 207,415.4

GREEN GRAMS

Kilanga 0 0 0 0 0 0 0 0 0 0 0 0 0

Challa 0 0 0 0 0 0 0 0 0 0 0 0 0

Nakuruto 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Timbilla 0 0 0 0 0 0 0 0 0 0 0 0 0

Jipe 30 0 0 5,081.0 6,660.0 17,553.9 3,024.0 0 0 19,332.0 37,303.5 14,370.0 383.2 103,707.7

Mwaktau 15 0 0 2,540.5 3,330.0 8,776.9 1,512.0 0 0 9,666.0 18,651.8 7,185.0 191.6 51,853.8

Total 45 0 0 7,621.5 9,990.0 26,330.8 4,536.0 0 0 28,998.0 55,955.3 21,555.0 574.8 155,561.5

COWPEAS


Crop/

Site

Area

(ha)



Kilanga 0 0 0 0 0 0 0 0 0 0 0 0 0

Challa 10 0 0 1,693.7 2,220.0 5,851.3 1,008.0 0 0 6,444.0 12,434.5 4,790.0 127.7 34,569.2

Nakuruto 5 0 0 846.8 1,110.0 2,925.6 504.0 0 0 3.222.0 6,217.3 2,395.0 63.9 17,284.6

Timbilla 10 0 0 1,693.7 2,220.0 5,851.3 1,008.0 0 0 6,444.0 12,434.5 4,790.0 127.7 34,569.2

Jipe 20 0 0 3,387.4 4,440.0 11,702.6 2,016.0 0 0 12,888.0 24,869.0 9,580.0 255.5 69,138.5

Mwaktau 15 0 0 2,540.5 3,330.0 8,776.9 1,512.0 0 0 9,666.0 18,651.8 7,185.0 191.6 51,853.8

Total 60 0 0 10,162.1 13,320.0 35,107.7 6,048.0 0 0 38,664.0 74,607.1 28,740.0 766.4 207,415.4

TOMATOES

Kilanga 20 0 0 5,128.5 4,260.0 13,780.3 5,244.0 0 0 14,398.0 24,839.0 12,220.0 4,551.0 84,420.8

Challa 10 0 0 2,564.3 2,130.0 6,890.2 2,622.0 0 0 7,199.0 12,419.5 6,110.0 2,275.5 42,210.4

Nakuruto 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Timbilla 10 0 0 2,564.3 2,130.0 6,890.2 2,622.0 0 0 7,199.0 12,419.5 6,110.0 2,275.5 42,210.4

Jipe 0 0 0 0 0 0 0 0 0 0 0 0

Mwaktau 0 0 0 0 0 0 0 0 0 0 0 0

Total 40 10,257.1 8,520.0 27,560.7 10,488.0 0 0 28,796.0 49,678.1 24,440.0 9102.0 168,841.7

KALES

Kilanga 10 0 0 3,124.3 4,044.0 6,091.0

0 0 0 7,269.0 14,238.0 5,882.0 0 40,648.3

Challa 10 0 0 3,124.3 4,044.0 6,091.0

0 0 0 7,269.0 14,238.0- 5,882.0 0 40,648.3

Nakuruto 5 1,562.1 2,022.0 3,045.5

3,634.5 7,119.0 2,941.0 0 20,324.2

Timbilla 10 0 0 3,124.3 4,044.0 6,091.0

0 0 0 7,269.0 1,4238.0 5,882.0 0 40,648.3

Jipe 0 0 0 0 0 0

0 0 0 0 0 0 0 0

Mwaktau 0 0 0 0 0 0

0 0 0 0 0 0 0 0

Total 35 0 0 10,935.0 14,154.0 21,318.6

0 0 0 25,441.5 49,833.0 20,587.0 0 142,269.0

SUNFLOWER

Kilanga 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Challa 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Nakuruto 0 0 0 0 0 0 0 0 0 0 0 0 0 0


Crop/

Site

Area

(ha)



Timbilla 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Jipe 25 2,025.8 0 4,464.2 4,580.0 19,980.0 16,350.0 3,494.2 0 16,070.0 30,751.3 17,370.0 11,690.0 126,775.5

Mwaktau 15 1,215.5 0 2,678.5 2,748.0 11,988.0 9,810.0 2,096.5 0 9,642.0 18,450.8 10,422.0 7,014.0 76,065.3

Total 40 3,241.3 0 7,142.7 7,328.0 31,968.0 26,160.0 5,590.7 0 25,712.0 49,202.1 27,792.0 18,704.0 202,840.8

BANANAS

Kilanga 20 9,600.0 12,200.0 10,600.0 2,400.0 16,040.0 21,160.0 11,560.0 12,320.0 20,640.0 22,160.0 13,800.0 20,200.0 172,680.0

Challa 10 4,800.0 6,100.0 5,300.0 1,200.0 8,020.0 10,580.0 5,780.0 6,160.0 10,320.0 11,080.0 6,900.0 10,100.0 86,340.0

Nakuruto 5 2,400.0 3,050.0 2,650.0 600.0 4,010.0 5,290.0 2,890.0 3,080.0 5,160.0 5,540.0 3,450.0 5,050.0 43,170.0

Timbilla 10 4,800.0 6,100.0 5,300.0 1,200.0 8,020.0 10,580.0 5,780.0 6,160.0 10,320.0 11,080.0 6,900.0 10,100.0 86,340.0

Jipe 100 48,000.0 61,000.0 53,000.0 12,000.0 80,200.0 105,800.0 57,800.0 61,600.0 103,200.0 110,800.0 69,000.0 101,000.0 863,400.0

Mwaktau 40 19,200 24,400.0 21,200.0 4,800.0 32,080.0 42,320.0 23,120.0 24,640.0 41,280.0 44,320.0 27,600.0 40,400.0 345,360.0

Total 185 88,800.0 112,850.0 98,050.0 22,200.0 148,370.0 195,730.0 106,930.0 113,960.0 190,920.0 204,980.0 127,650.0 186,850.0 1,597,290.0

WATER MELONS

Kilanga 10 2,978.1 0 1,884.3 264.0 6,728.0 7,724.0 3,069.9 0 6,984.0 9,748.0 4,952.0 6,284.0 50,616.3

Challa 10 2,978.1 0 1,884.3 264.0 6,728.0 7,724.0 3,069.9 0 6,984.0 9,748.0 4,952.0 6,284.0 50,616.3

Nakuruto 5 1,489.0 0 942.1 132.0 3,364.0 3,862.0 1,535.0 0 3,492.0 4,874.0 2,476.0 3,142 25,308.1

Timbilla 10 2,978.1 0 1,884.3 264.0 6,728.0 7,724.0 3,069.9 0 6,984.0 9,748.0 4,952.0 6,284.0 50,616.3

Jipe 10 2,978.1 0 1,884.3 264.0 6,728.0 7,724.0 3,069.9 0 6,984.0 9,748.0 4,952.0 6,284.0 50,616.3

Mwaktau 5 1,489.0 0 942.1 132.0 3,364.0 3,862.0 1,535.0 0 3,492.0 4,874.0 2,476.0 3,142 25,308.1

Total 50 14,890.3 0 9,421.3 1,320.0 33,640.0 38,620.0 15,350.0 0 34,920.0 48,740.0 24,760.0 31,420.0 253,081.3

PAWPAWS

Kilanga 20 9,600.0 12,200.0 10,600.0 2,400.0 16,040.0 21,160.0 11,560.0 12,320.0 20,640.0 22,160.0 13,800.0 20,200.0 172,680.0

Challa 10 4,800.0 6,100.0 5,300.0 1,200.0 8,020.0 10,580.0 5,780.0 6,160.0 10,320.0 11,080.0 6,900.0 10,100.0 86,340.0

Nakuruto 5 2,400.0 3,050.0 2,650.0 600.0 4,010.0 5,290.0 2,890.0 3,080.0 5,160.0 5,540.0 3,450.0 5,050.0 43,170.0

Timbilla 10 4,800.0 6,100.0 5,300.0 1,200.0 8,020.0 10,580.0 5,780.0 6,160.0 10,320.0 11,080.0 6,900.0 10,100.0 86,340.0

Jipe 75 36,000.0 45,750.0 39,750.0 9,000.0 60,150.0 79,350.0 43,350.0 46,200.0 77,400.0 83,100.0 51,750.0 75,750.0 647,550.0

Mwaktau 25 12,000.0 15,250.0 13,250.0 3,000.0 20,050.0 26,450.0 14,450.0 15,400.0 25,800.0 27,700.0 17,250.0 25,250.0 215,850.0


Crop/

Site

Area

(ha)



Total 145 69,600.0 88,450.0 76,850.0 17,400.0 116,290.0 153,410.0 83,810 89,320.0 149,640.0 160,660.0 100,050.0 146,450.0 1,251,930.0

ONIONS

Kilanga 10 0 0 3,266.3 3,030.0 6,772.1 3,576.0 0 0 7,743.0 12,500.4 6,374.0 3,269.7 46,531.4

Challa 10 0 0 3,266.3 3,030.0 6,772.1 3,576.0 0 0 7,743.0 12,500.4 6,374.0 3,269.7 46,531.4

Nakuruto 5 0 0 1,633.1 1,515.0 3,386.1 1,788.0 0 0 3,871.5 6,250.2 3,187.0 1,634.8 23,265.7

Timbilla 10 0 0 3,266.3 3,030.0 6,772.1 3,576.0 0 0 7,743.0 12,500.4 6,374.0 3,269.7 46,531.4

Jipe 50 0 0 16,331.0 15,150.0 33,860.7 17,880.0 0 0 38,715.0 62,501.9 31,870.0 16,348.2 232,657.1

Mwaktau 25 0 0 8,165.6 7,575.0 16,930.3 8,940.0 0 0 19,357.5 31,251.0 15,935.0 8,174.1 116.328.5

Total

110 0 0 35,929.0 33330 74493.42 39,336.0 0 0 85,173.0 137,504.0 70,114.0 35,966.1 511,845.6

CHILLIES

Kilanga 10 0 0 1,071.0 1,800.0 7,178.1 3,790.0 0 0 6,030.0 11,924.5 6,200.0 3,641.9 41,635.5

Challa 10 0 0 1,071.0 1,800.0 7,178.1 3,790.0 0 0 6,030.0 11,924.5 6,200.0 3,641.9 41,635.5

Nakuruto 5 0 0 535.5 900.0 3,589.0 1,895.0 0 0 3,015.0 5,962.3 3,100.0 1,821.0 20,817.7

Timbilla 10 0 0 1,071.0 1,800.0 7,178.1 3,790.0 0 0 6,030.0 11,924.5 6,200.0 3,641.9 41,635.5

Jipe 10 0 0 1,071.0 1,800.0 7,178.1 3,790.0 0 0 6,030.0 11,924.5 6,200.0 3,641.9 41,635.5

Mwaktau 5 0 0 535.5 900.0 3,589.0 1,895.0 0 0 3,015.0 5,962.3 3,100.0 1,821.0 20,817.7

Total 50 0 0 5,354.8 9,000.0 35,890.3 18,950.0 0 0 30,150.0 59,622.6 31,000.0 18,209.7 208,177.4

GRAND

TOTAL 1,020 361,342.3 334,399.0 534,606.0 251,361.0 1,220,902.0 1,121,436.0 441531 337,688.5 1,343,322.0 1,921,792.0 1,055,165.0 1,002,444.0 9,925,989.0


Table 2.24 -Net Monthly Irrigation Water Requirements per Site

Site

Area

(ha) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total

Kilanga 100 29,321.4 32,006.2 47,220.0 24,414.0 96,937.1 83,295.7 34,591.0 32,321.0 111,407.0 157,143.0 84,375.3 77,276.7 810,307.3

Challa 100 29,075.3 20,854.7 48,764.0 27,364.0 122,322.5 100,581.0 34,993.0 21,059.8 130,689.0 198,162.0 106,113.0 89,791.0 929,769.8

Nakuruto 45 14,537.6 10,427.4 22,190.0 11,862.0 55,272.2 48,049.6 17,497.0 10,529.9 59,191.5 88,466.2 47,834.2 42,950.6 428,807.6

Timbilla 100 29,075.3 20,854.7 48,764.0 27,364.0 122,322.5 100,581.0 34,993.0 21,059.8 130,689.0 198,162.0 106,113.0 89,791.0 929,769.8

Jipe 465 190,014.9 182,479.0 263,602.0 110,229.0 587,562.3 573,111.0 234050 184,273.5 650,149.0 905,049.0 506,815.0 512,089.0 4,899,424.0

Mwaktau 200 73,105.1 67,777.8 107,761.0 50,231.0 250,167.8 232,022.0 90,399.0 68,444.4 273,286.0 392,330.0 215,853.0 204,844.0 2,026,222.0

Total 1,010 361,342.3 334,399.0 534,606.0 251,361.0 1,220,902.0 1,121,436.0 441,531.0 337,688.5 1,343,322.0 1,921,792.0 1,055,165.0 1,002,444.0 9,925,989.0


2.11.3 GROSS IRRIGATION WATER REQUIREMENTS (GWR)

The annual Gross irrigation water requirement (GWR) is summation of annual net irrigation

water requirement (NIR) and extra amount needed to compensate for possible water losses and is

given by;

GWR = NIR/ƞ and ƞ = ƞa x ƞc ……………………………..………………….(7)

Where ƞ is the efficiency of Field Application and Conveyance

ƞa = Field Application Efficiency (Ratio of Water Available to Crop versus Water at Field Inlet)

ƞc = Conveyance Efficiency (Ratio of Water at Field Inlet versus water at source including an

allowance due to water evaporation from the open reservoirs)

The irrigation efficiencies for different irrigation methods considered in the project are tabulated

in Table 2.25.

Table 2.25- Irrigation Systems Efficiencies

Irrigation

System

Field Application

Efficiency (ƞa) 15

(%)

Conveyance

Efficiency (ƞc) *

(%)

Overall Efficiency (ƞ)

(%)

Drip 90 90 81

Sprinkler 80 90 72

Surface 65 90 58.5 * Assumed

The project estimated crop-wise, monthly and yearly gross requirement in accordance with the

mode of irrigation recommended earlier and equation (7) is given in Tables 2.26 -2.29.

Worked Example 4

Estimation of Gross Irrigation Water Requirements (GWR)

From equation (7)

GWR = NIR/ƞ

For 20 ha of maize in the Challa project as per equation (6)

NIR = 4,323.4 m3

ƞ = 58.5 % (Table 2.25)

15



Therefore;

GWR = 4,323.4 m3 /58.5/100 = 7,390.4 m

3………………………..………….(8)

The Gross Irrigation Requirement is approximately 9,925,989.0 m3 for the proposed irrigation

area of 2,020 ha on annual basis as shown in Table 2.26.


Table 2.26 - Gross Irrigation Water Requirements (m3)

Crop/

Site

Area

(ha)

Gross Irrigation Water Requirements (m3)


MAIZE

Kilanga 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Challa 20 7,574.3 0 7,390.4 205.1 27,364.1 32,410.3 9,984.7 0 24,177.8 35,042.7 23,876.9 28,596.4 196,622.7

Nakuruto 10 3,787.2 0 3,695.2 102.6 13,682.1 16,205.1 4,992.3 0 12,088.9 17,521.4 11,938.5 14,298.2 98,311.3

Timbilla 20 7,574.3 0 7,390.4 205.1 27,364.1 32,410.3 9,984.7 0 24,177.8 35,042.7 23,876.9 28,596.4 196,622.7

Jipe 100 37,871.5 0 36,952.0 1,025.6 136,820.5 162,051.0 49,923.0 0 120,889.0 175,214.0 119,385.0 142,982.0 983,113.3

Mwaktau 40 15,148.6 0 14,781.0 410.3 54,728.2 64,820.5 19,969.0 0 48,355.6 70,085.5 47,753.8 57,192.8 393,245.3

Total 190 68,168.7 0 66,513.0 1,846.2 246,276.9 291,692.0 89,862.0 0 217,600.0 315,385.0 214,892.0 257,368.0 1,769.604.0

BEANS

Kilanga 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Challa 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Nakuruto 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Timbilla 0 0 0 0 0 0 0 0 0 0 0 0 0

Jipe 45 0 0 13,028.0 17,077.0 45,009.9 7,753.9 0 0 49,569.2 95,650.1 36,846.2 982.6 265,917.1

Mwaktau 15 0 0 4,342.8 5,692.3 15,003.3 2,584.6 0 0 16,523.1 31,883.4 12,282.1 327.5 88,639.0

Total 60 0 0 17,371.0 22,769.0 60,013. 10338.5 0 0 66,092.3 127,533.0 49,128.2 1,310.2 354,556.2

GREEN GRAM

Kilanga 0 0 0 0 0 0 0 0 0 0 0 0 0

Challa 0 0 0 0 0 0 0 0 0 0 0 0 0

Nakuruto 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Timbilla 0 0 0 0 0 0 0 0 0 0 0 0 0

Jipe 30 0 0 8,685.5 11,385.0 30,006.6 5,169.2 0 0 33,046.2 63,766.7 24,564.1 655.1 177,278.1

Mwaktau 15 0 0 4,342.8 5,692.3 15,003.3 2,584.6 0 0 16,523.1 31,883.4 12,282.1 327.5 886,39.0

Total 45 0 0 13,028.0 17,077.0 45,009.9 7,753.8 0 0 49,569.2 95,650.1 36,846.2 982.6 265,917.1

COWPEA


Crop/

Site

Area

(ha)



Kilanga 0 0 0 0 0 0 0 0 0 0 0 0 0

Challa 10 0 0 2,895.2 3,794.9 10,002.2 1723.1 0 0 11015.4 21,255.6 8,188.0 218.4 59,092.7

Nakuruto 5 0 0 1,447.6 1,897.4 5,001.1 861.5 0 0 5507.7 10627.8 4094.02 109.2 29,546.3

Timbilla 10 0 0 2,895.2 3,794.9 10,002.2 1723.1 0 0 11015.4 21,255.6 8,188.0 218.4 59,092.7

Jipe 20 0 0 5,790.4 7,589.7 20,004.4 3446.15 0 0 22,030.8 42,511.2 16,376.1 436.7 118,185.4

Mwaktau 15 0 0 4,342.8 5,692.3 15,003.3 2,584.6 0 0 16,523.1 31,883.4 12,282.1 327.5 88,639.0

Total 60 0 0 17,371.0 22,769.0 60,013.2 10,338.5 0 0 66,092.3 127,533.0 49,128.2 1,310.2 354,556.2

TOMATO

Kilanga 20 0 0 6,703.9 5,568.6 18,013.5 6,854.9 0 0 18,820.9 32,469.3 15,973.9 5,949.0 110,354.0

Challa 10 0 0 4,383.3 3,641.0 11,778.1 4,482.1 0 0 12,306.0 21,229.9 10,444.4 3,889.7 72,154.6

Nakuruto 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Timbilla 10 0 0 4,383.3 3,641.0 11,778.1 4,482.1 0 0 12,306.0 21,229.9 10,444.4 3,889.7 72,154.6

Jipe 0 0 0 0 0 0 0 0 0 0 0 0

Mwaktau 0 0 0 0 0 0 0 0 0 0 0 0

Total 40 15,471.0 12,851.0 41569.6 15819 0 0 43,432.9 74,929.2 36,862.7 13,728.4 254,663.2

KALE

Kilanga 10 0 0 4,339.2 5,616.7 8,459.8 0 0 0 10,095.8 19,775.0 8,169.4 0 56,456.0

Challa 10 0 0 5,340.6 6,912.8 10,412.0 0 0 0 12,425.6 24,338.5 10,054.7 0 69,484.3

Nakuruto 5 2,670.3 3,456.4 5,206.0 0 0 0 6,212.8 12,169.2 5,027.4 0 34,742.1

Timbilla 10 0 0 5,340.6 6,912.8 10,412.0 0 0 0 12,425.6 24,338.5 10,054.7 0 69,484.3

Jipe 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Mwaktau 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Total 35 0 0 17,691.0 22,899.0 34,489.8 0 0 0 41,160.0 80,621.2 33,306.2 0 230,166.6

SUNFLOWER

Kilanga 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Challa 0 0 0 0 0 0 0 0 0 0 0 0 0 0


Crop/

Site

Area

(ha)



Nakuruto 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Timbilla 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Jipe 25 3,462.9 0 7,631.1 7,829.1 34,153.8 27,948.7 5,973.0 0 27,470.1 52,566.3 29,692.3 19,982.9 216,710.2

Mwaktau 15 2,077.8 0 4,578.7 4,697.4 20,492.3 16,769.2 3,583.8 0 16,482.1 31,539.8 17,815.4 11,989.7 130,026.1

Total 40 5,540.7 0 12,210.0 12,526.0 54,646.1 44,717.9 9,556.8 0 43,952.1 84,106.1 47,507.7 31,972.6 346,736.4

BANANA

Kilanga 20 11,851.9 15,061.7 13,086.0 2,963.0 19,802.5 26,123.5 14,272.0 15,209.9 25,481.5 27,358.0 17,037.0 24,938.3 213,185.2

Challa 10 8,205.1 10,427.4 9,059.8 2,051.3 13,709.4 18,085.5 9,880.3 10,529.9 17,641.0 18,940.2 11,794.9 17,265.0 147,589.7

Nakuruto 5 4,102.6 5,213.7 4,529.9 1,025.6 6,854.7 9,042.7 4,940.2 5265.0 8,820.5 9,470.1 5,897.4 8,632.5 73,794.9

Timbilla 10 8,205.1 10,427.4 9,059.8 2,051.3 13,709.4 18,085.5 9,880.3 10,529.9 17,641.0 18,940.2 11,794.9 17,265.0 147,589.7

Jipe 100 82,051.3 104,274.0 90,598.0 20,513.0 137,094.0 180,855.0 98,803.0 105,299.1 176,410.0 189,402.0 117,949.0 172,650.0 1,475.897.0

Mwaktau 40 32,820.5 41,709.4 36,239.0 8,205.1 54,837.6 72,341.9 39,521.0 42,119.7 70,564.1 75,760.7 47,179.5 69,059.8 590,359.0

Total 185 147,236.5 187,113.0 162,574.0 36,809.0 246,007.6 324,534.0 177,297.0 188,953.5 316,558.0 339,871.0 211,652.0 309,810.0 2,648,416.0

WATER MELON

Kilanga 10 4,136.2 0 2,617.0 366.7 9,344.4 10,727.8 4,263.8 0 9,700.0 13,538.9 6,877.8 8,727.8 70,300.4

Challa 10 5,090.7 0 3,221.0 451.3 11,500.9 13,203.4 5,247.8 0 11,938.5 16,663.2 8,465.0 10,741.9 86,523.5

Nakuruto 5 2,545.3 0 1,610.5 225.6 5,750.4 6,601.7 2,623.9 0 5,969.2 8,331.6 4,232.5 5,370.9 43,261.8

Timbilla 10 5,090.7 0 3,221.0 451.3 11,500.9 13,203.4 5,247.8 0 11,938.5 16,663.2 8,465.0 10,741.9 86,523.5

Jipe 10 5,090.7 0 3,221.0 451.3 11,500.9 13,203.4 5,247.8 0 11,938.5 16,663.2 8,465.0 10,741.9 86,523.5

Mwaktau 5 2,545.3 0 1,610.5 225.6 5,750.4 6,601.7 2,623.9 0 5,969.2 8,331.6 4,232.5 5,370.9 43,261.8

Total 50 24,499.0 0 15,501.0 2,171.8 55,347.9 63,541.5 25,255.0 0 57,453.8 80,191.9 40,737.6 51,695.3 416,394.4

PAWPAW

Kilanga 20 13,333.3 16,944.4 14,722.0 3,333.3 22,277.8 29,388.9 16.056.0 17,111.1 28,666.7 30,777.8 19,166.7 28,055.6 239,833.3

Challa 10 8,205.1 10,427.4 9,059.8 2,051.3 13,709.4 18,085.5 9,880.3 10,529.9 17,641.0 18,940.2 11,794.9 17,265.0 147,589.7

Nakuruto 5 4,102.6 5,213.7 4,529.9 1,025.6 6,854.7 9,042.7 4,940.2 5265.0 8,820.5 9,470.1 5,897.4 8,632.5 73,794.9

Timbilla 10 8,205.1 10,427.4 9,059.8 2,051.3 13,709.4 18,085.5 9,880.3 10,529.9 17,641.0 18,940.2 11,794.9 17,265.0 147,589.7

Jipe 75 61,538.5 78,205.1 67,949.0 15,385.0 102,820.5 135,641.0 74,103.0 78,974.4 132,308.0 142,051.0 88,461.5 129,487.0 1,106,923.0


Crop/

Site

Area

(ha)



Mwaktau 25 20,512.8 26,068.4 22,650.0 5,128.2 34,273.5 45,213.7 24,701.0 26,324.8 44,102.6 47,350.4 29,487.2 43,162.4 368,974.4

Total 145 115,897.4 147,286.0 127,970.0 28,974.0 193,645.3 255,457.0 139,560.0 148,735.0 249,179.0 267,530.0 166,603.0 243,868.0 2,084,705.0

ONION

Kilanga 10 0 0 4,536.5 4,208.3 9,405.7 4,966.7 0 0 10,754.2 17,361.6 8,852.8 4,541.2 64,627.0

Challa 10 0 0 5,583.3 5,179.5 11,576.3 6,112.8 0 0 13,235.9 21,368.2 10,895.7 5,589.1 79,540.9

Nakuruto 5 0 0 2,791.7 2,589.7 5,788.1 3,056.4 0 0 6,618.0 10,684.1 5,447.9 2,794.6 39,770.4

Timbilla 10 0 0 5,583.3 5,179.5 11,576.3 6,112.8 0 0 13,235.9 21,368.2 10,895.7 5,589.1 79,540.9

Jipe 50 0 0 27,917.0 25,897.0 57,881.4 30,564.1 0 0 66,179.5 106,841.0 54,478.6 27,945.7 397,704.4

Mwaktau 25 0 0 13,958.0 12,949.0 28,940.72 15,282.1 0 0 33,089.7 53,420.5 27.0239.3 13,972.8 198,852.2

Total

110 0 0 60,370.0 56,003.0 125,168.6 66,094.9 0 0 143,113.0 231,043.0 117,810.0 60,432.5 860,035.8

CHILLIES

Kilanga 10 0 0 1,586.6 2,666.7 10,634.2 5,614.8 0 0 8,933.3 17,665.9 9,185.2 5,395.5 61,682.2

Challa 10 0 0 1,830.7 3,076.9 12,270.2 6,478.6 0 0 10,307.7 20,383.8 10,598.3 6,225.5 71,171.8

Nakuruto 5 0 0 915.4 1,538.5 6,135.1 3,239.3 0 0 5,153.9 10,191.9 5,299.2 3,112.77 35,585.9

Timbilla 10 0 0 1,830.7 3,076.9 12,270.2 6,478.6 0 0 10,307.7 20,383.8 10,598.3 6,225.5 71,171.8

Jipe 10 0 0 1,830.7 3,076.9 12,270.2 6,478.6 0 0 10,307.7 20,383.8 10,598.3 6,225.5 71,171.8

Mwaktau 5 0 0 915.4 1,538.5 6,135.1 3,239.3 0 0 5,153.9 10,191.9 5,299.2 3,112.77 35,585.9

Total 50 0 0 8,909.5 14,974.0 59,715.0 31,529.3 0 0 50,164.1 99,201.1 51,578.3 30,297.6 346,369.3

GRAND

TOTAL 1,020 351,637.8 334,399.3 521,880.0 246,828.8 1,174,589.7 1,077,971.7 428,737.8 337,688.5 1,299,952.0 1,852,981.0 1,015,361.0 965,559.0 9,607,587.0


Table 2.27- Summary of Gross Irrigation Water Requirements

Area


Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec Annual

Kilanga 29,321.4 32,006.2 47,220.0 24,414.0 96,937.1 83,295.7 34,591.0 32,321.0 111,407.0 157,143.0 84,375.3 77,276.7 810,307.3

Challa 27,655.1 20,854.7 46,836.0 26,614.1 115,316.3 94,181.2 33,121.0 21,059.8 124,090.0 83,188.2 44,828.1 40,249.2 404,834.3

Nakuruto 13,827.5 10,427.4 21,226.0 11,486.5 51,769.1 44,849.6 16,560.5 10,529.9 55,892.1 88,466.2 47,834.2 42,950.6 428,807.6

Timbilla 27,655.1 20,854.7 46,836.0 26,614.1 115,316.3 94,181.2 33,121.0 21,059.8 124,090.0 187,606.0 100,101.0 84,388.2 881,823.2

Jipe 182,914.0 182,478.6 255,588.0 108,613.7 558,157.7 542,080.3 224,689.4 184,273.5 623,351.0 864,226.0 481,360.0 485,198.0 4,692,931.0

Mwaktau 70,264.7 67,777.8 104,175.0 49,086.5 237,093.1 219,383.8 86,655.0 68,444.4 261,122.0 373,211.0 204,596.0 194,059.0 1,935,868.0

Total 351,637.8 334,399.3 521,880.0 246,828.8 1,174,589.7 1,077,971.7 428,737.8 337,688.5 1,299,952.0 1,852,981.0 1,015,361.0 965,559.0 9,607,587.0

Total Season One 3,787,697.0

Total Season Two 5,819,890.0

GRAND TOTAL 9,607,587.0


2.12 PROPOSED IRRIGATION SYSTEMS COMPONENTS

2.12.1 Introduction

One of the major objectives of the Lake Challa Water Resources Integrated Development Project

is to develop an Irrigation System that will cover 1,120 ha of various crops as detailed in

Sections 2.6 and 2.8 of this report, and as summarized below;

Table 2.28 - Proposed Annual Irrigable Areas

Site Status Remarks Mode of irrigation Area (ha)

Kilanga Pilot

Project

Proposed New

Development

Drip (80 ha) 200

Sprinkler (120 ha)

Challa (Existing

Scheme)

Existing Extension Surface Irrigation 200

Nakuruto Proposed New

Development

Surface Irrigation 90

Timbilla(Existing

Scheme)

Existing Extension Surface Irrigation 200

Jipe Settlement

Scheme

Proposed New

Development


Mwaktau Proposed New

Development


Total 2,020

2.12.2 Design Criteria and Data

12.2.2.1 DRIP IRRIGATION SYSTEM

Area of Coverage

This will be designed for the 40 ha (per season) in the Kilanga Pilot Irrigation Project. This will

consist of 20 ha each of tomatoes and bananas.

Various parameters used for the design are described below in Table 2.29.


Table 2.29 - Design Parameters for Drip Irrigation System16

Parameter Abbrev. Unit Quantity

Agro-Technical Parameters

Available Water (Amount of Water released

between Field Capacity and Wilting Point)

AWC mm/m 117

Management Allowable Deficit MAD % 50

Design (effective) Root Zone –Tomatoes (Table

2.20)

DRZ m 0.7

Design (effective) Root Zone –Bananas (Table 2.20) DRZ m 0.5

Maximum Soil Infiltration Rate IM mm/h 72.6

Gross Water Requirements (the peak is experienced

in October)- for Tomatoes(Table 2.27)

GWRT m3/month 32,469.3

Gross Water Requirements (the peak is experienced

in October)- for Bananas (Table 2.27)

GWRB m3/month 27,358.0

Total Design Gross Water Requirements GWR m3/month 59,827.3

Average CROP WATER REQUIREMENTS (TABLE 2.18)*

ETCROP mm/day 4.4

Technical Parameters

Total Area to be under Irrigation (per season) AT ha 40

Irrigation Period per week Ip day 6

Operational hours per day Td h/day 15

Spacing between drip line laterals (Tomatoes) S1 m 1.2

Spacing between drip line laterals (Bananas) S1 m 5.0 *Worked on the average value of tomatoes and bananas

12.2.2.1.1 IRRIGATION SUPPLY REQUIREMENTS

Total Design Gross Water Requirements (GWR) per month = 59,827.3 m3/month

Therefore;

GWR per day = 59,827.3 m3/month/31 days per month

=1,929.91 m3 /day…………………………………………………………(9)

The net Required Discharge is given by;

Q = GWR per day x 7 / (Id x Ip)

Where;

Q = Required Discharge in m3/h

16



GWR = Gross Irrigation Requirement (mm/day) = 1,929.91 m3 /day

Id = Operational hours per day = 15 h

Ip = working days per week = 6 days

Therefore;

Q = 1,929.91 x 7 / (15 x 6) = 150.1 m3/h ……………..................…(10)

12.2.2.1.1 IRRIGATION INTERVAL

The time interval (frequency) between successive irrigations, I, is given by;

I = MAD x AWC x DRZ days = 0.5 x 117 x 0.6/4.4 = 7.98 say 8 days…...(11)

ETCROP

12.2.2.2 OVERHEAD SPRINKLER IRRIGATION SYSTEM

Area of Coverage

This will be designed for the 60 ha (per season) in the Kilanga Pilot Irrigation Project. The crops

composition is shown in Table 2.12.

The various parameters used for the design are described below in Table 2.30.

Table 2.30 - Design Parameters for Overhead Sprinkler Irrigation System17



Available Water (Amount of Water released between

Field Capacity and Wilting Point)

AWC mm/m 117

Management Allowable Deficit MAD % 50

Design (effective) Root Zone (Average) DRZ m 0.5

Maximum Soil Infiltration Rate IM mm/h 72.6

Gross Water Requirements (the peak is experienced in

October (Table 2.27)

GWRT m3/month 98,315.7

Average CROP WATER REQUIREMENTS (TABLE 2.18)* Average CROP WATER REQUIREMENTS

ETCROP mm/day 4.3

Technical Parameters

Total Area to be under Irrigation (per season) AT ha 60

Irrigation Period per week Ip day 6

17





Operational hours per day Td h/day 15

Spacing between overhead sprinklers on lateral S1 m 12

Spacing between overhead sprinkler Laterals S2 m 18

Discharge per overhead sprinkler Qs m3/h 1.9

Overhead sprinklers designed operating head P m 30

12.2.2.2.1 IRRIGATION SUPPLY REQUIREMENTS

Total Design Gross Water Requirements (GWR) per month = 98,315.7 m3/month

Therefore;

GWR per day = 98,315.7 3 m3/month/31 days per month

= 3,174.47 m3 /day………………………………………………………(12)

The net Required Discharge is given by;

Q = GWR per day x 7 / (Id x Ip)

Where;

Q = Required Discharge in m3/h

GWR = Gross Irrigation Requirement (mm/day) = 3,174.47 m3 /day

Id = Operational hours per day = 15 h

Ip = working days per week = 6 days

Therefore;

Q = 1,929.91 x 7 / (15 x 6) = 246.67 m3/h ……………................…(13)

12.2.2.2.2 IRRIGATION INTERVAL

The time interval (frequency) between successive irrigations, I, is given by;

I = MAD x AWC x DRZ days = 0.5 x 117 x 0.5/4.3 = 6.80 say 7 days…………(14)

ETCROP

2.12.3 Project Components

2.12.3.1 SOURCE OF ENERGY

Electrical power will be acquired from the national power grid line running south-east along the

Taveta – Challa Road through the Kenya Power and Lighting Company.


2.12.3.2 PUMP STATION

There will be a booster Pumping Station next to the reservoir site to pump water to the overhead

sprinkler irrigation system. The pump house will house pump motors, control valves, pressure

gauges and gantry crane, and delivery manifold connected to the main piping.

2.12.3.3 DRIP IRRIGATION SYSTEM

The drip irrigation system will consist of;

1 All suitable connections to the sub-main piping.

2 Secondary piping and fittings.

3 Suitable Control heads.

Each control head shall comprise of a filtration unit with gravel (for removal of algae and

any other organic materials) and 120 mesh screen filters (for the removal of fine sand),

air-release valve, control valves, and other ancillary fittings. The unit will be fitted with

an automatic back flushing unit powered by a rechargeable battery and will be installed

on a paved, easily drainable and lockable enclosure. Manual gate valves shall be used to

control the flow of water through the laterals.

The gravel/sand media filters, providing filtration up to 200 mesh, will be self cleaning

through a “back-flush” mechanism. This mechanism will detect the drop in pressure due

to the accumulation of filtered particles and then flushes water back through the media to

dispose of clay, silt, and organic particles.

The screen filters shall be located in a manner that allows both easy access to and

removal of the filter elements from the housing and shall be cleaned manually by

removing the screen and washing it with clean water.

Each control head will be fitted with suitable fertiliser injectors and tanks.

4 Tertiary piping and fittings.

5 Driplines.

Driplines with pressure compensating and self- cleaning integral emitters (at 1.0 m

spacing) with associated fittings shall be installed. Pressure Compensation ensures that

all of the emitters inside the drip-line emit the same amount of water. Each row shall be

served by a drip-line with a spacing of 5 m between the rows for bananas, and 1.2 m for

tomatoes.

Each control head shall comprise of a filtration unit with gravel (for removal of algae and

any other organic materials) and 120 mesh screen filters (for the removal of fine sand),

air-release valve, control valves, and other ancillary fittings. The unit will be fitted with

an automatic back flushing unit powered by a rechargeable battery and will be installed

on a paved, easily drainable and lockable enclosure. Manual gate valves shall be used to

control the flow of water through the laterals.


The gravel/sand media filters, providing filtration up to 200 mesh, will be self cleaning

through a “back-flush” mechanism. This mechanism will detect the drop in pressure due

to the accumulation of filtered particles and then flushes water back through the media to

dispose of clay, silt, and organic particles.

The screen filters shall be located in a manner that allows both easy access to and

removal of the filter elements from the housing and shall be cleaned manually by

removing the screen and washing it with clean water.

2.12.3.4 OVERHEAD SPRINKLER IRRIGATION SYSTEM

This will consist of a fixed 315 mm Ø UPVC main piping, and 160 mm Ø UPVC sub-main

piping. The sub-main piping shall be fitted with hydrants at 54 m spacing. The spacing of 18 m

between the hydrants has been adopted in order to minimize the number of hydrants to be

installed.

There shall be portable aluminium pipes fitted with full circle twin nozzle sprinklers with a

capacity of about 1.9 m3/h at 30 m head to be spaced at 12 m in a lateral and 18 m between the

laterals. This is designed to give an equivalent “rainfall precipitation” of about 8.8 mm/h.

2.12.3.5 SURFACE IRRIGATION SYSTEMS

Area of Coverage

This will be mainly designed to cover the 465 ha and 200 ha, per annum, in the Jipe Settlement

and Mwaktau Schemes, respectively. Water for irrigation will be sold in bulk to the farmers in

Challa, Nakuruto and Timbilla Schemes in order to boost their current efforts.

Design Criteria and Data

Various parameters used for the design of furrow irrigation are described below in Table 2.31,

below.

Table 2.31 - Design Parameters of Straight Furrow Irrigation

Soil

Texture

Furrow

Slope,

(%)

Furrow

Width

(m)

Furrow

Length

( m)

Flow rate

(l.p.s)

Cut off

length

(%)

Depth applied

(mm )

Coarse 0.05 –0.1 0.6 – 0.75 60 – 90 3-4.5 100 75-100

0.1 – 0.2 0.6 – 0.75 60 – 90 3 – 4.5 95 75-100

02 – 0.3 0.6 – 0.75 60 – 75 1.5 – 3 90 50-75

Medium 0.05 – .1 0.75 – 0.90 100-150 3-4 100 75-90

0.1 – 0.2 0.75 – 0.90 60-100 1.5-3 95 60-75

0.2 – 0.3 0.75 – 0.90 50-75 1.5 –2.5 90 50-75

Fine 0.05 –0.1 0.9 – 1.0 100-200 2.5 – 3.5 95 75-100

0.1 – 0.2 0.9 – 1.0 50 – 100 1.5 – 2.5 90 60-75


Conveyance Systems

From the ground reservoir, water will be conveyed to the field through a closed pipe system for

the main distribution and secondary network leading to unlined tertiary canals. Hazen’s Williams

and Manning’s Equation are used in determining the most economical sections.

Some of the advantages of pipe line conveyance are listed below;

a) It can follow the most direct route from source to outlet points rather than following

land contours

b) Loss of land can be eliminated

c) Seepage/ evaporation losses are eliminated

Jipe Scheme

The conveyance system shall consist of UPVC 400 A (2,200 m long) main piping and UPVC 315

A (10,800 m long) secondary piping.

All the necessary tees, crosses, valves and other fittings shall be provided Farmers will be assisted

to lay strategies for the installation of the tertiary canals.

As noted in Section 2.4.2.5 of this report, the soils in the scheme are susceptible to gully erosion.

Therefore, two check dams will be constructed on each of the major gullies in the area.

Mwaktau Scheme

Like in the case of the Jipe Scheme, the conveyance system shall consist of UPVC 315 A (2,600

m long) main piping and UPVC 160 A (6,000 m long) secondary piping.

All the necessary fittings e.g. tees, crosses, valves shall be provided. Farmers will also be

expected to lay strategies for the installation of the tertiary canals.


CHAPTER 3: DESIGN OF WATER SUPPLY SYSTEMS


Table of Contents

CHAPTER 3: DESIGN OF WATER SUPPLY SYSTEMS ......................... 3-79

Table of Contents ............................................................... 3-17

List of Tables .................................................................. 3-81

3.1 GENERAL ........................................................................................................................ 3-82

3.2 SOURCES OF WATER ................................................................................................... 3-82

3.3 RAW WATER PIPELINE ................................................................................................ 3-83

3.4 LAKE CHALLA TANK ................................................................................................... 3-83

3.5 RESERVOIRS .................................................................................................................. 3-84

3.5.1 Reservoir Characteristics ........................................................................................... 3-84

3.5.2 Timbila Tank .............................................................................................................. 3-85

3.6 TRANSMISSION PIPELINES ......................................................................................... 3-86

3.7 DOMESTIC WATER SUPPLY ....................................................................................... 3-87

3.8 ANCILLARY WORKS .................................................................................................... 3-87

3.8.1 Administration Building and Laboratory ................................................................... 3-88

3.8.2 Staff Houses ............................................................................................................... 3-88

3.8.3 Site Drainage .............................................................................................................. 3-88

3.8.4 Workshop ................................................................................................................... 3-88

3.8.5 Pump House ............................................................................................................... 3-88

3.8.6 Access Roads ............................................................................................................. 3-88

3.8.7 Power Supply ............................................................................................................. 3-88

3.9 MATERIALS SPECIFICATIONS ................................................................................... 3-89

3.9.1 Transmission and Distribution Pipelines ................................................................... 3-89


3.9.2 Flow Regulating Valves ............................................................................................. 3-89

List of Tables

Table 3.1 - Recommended Abstraction Rates

Table 3.2 – Capacities of Water Reservoirs

Table 3.3- Reservoirs Technical Details

Table 3.4 – Transmission Pipelines Technical Details

Table 3.5 – Water Demands


CHAPTER 3 - DESIGN OF WATER SUPPLY SYSTEMS

3.1 GENERAL

Water will be sourced from Lake Challa and three boreholes to be sited in the Kilanga area.

Abstracted water will then be used for irrigation, domestic, livestock, environmental

conservation and wildlife within the Taveta – Mwaktau corridor.

Conveyance of this water will be by both steel and uPVC pipelines of various pressure ratings

based on the pressure requirements. There are three major areas of water supply i.e. Kilanga, Jipe

and Mwaktau, which are also the main focus for irrigation.

Irrigation system has been designed to operate by gravity save for Kilanga area where it is

pressurized.

It must also be noted that domestic water has only been supplied to areas which suffer acute

water shortages and which have otherwise not benefited from the existing TAVEVO Water and

Sanitation Company schemes. These areas include Kasokoni in Chala, Kasaani at Jipe, Kidong’u

and Mwaktau.

Between Jipe and Mwaktau the water supply system cuts through the Tsavo West National Park

managed by Kenya Wildlife Service. Between Taveta and Mwaktau a shallow water pan has

been provided for to supply wildlife with water, a phenomenon that will improve tourism in the

area as the pan will be strategically located along the Voi – Taveta Road.

3.2 SOURCES OF WATER

A combination of Lake Challa and boreholes has been identified as the sources of water for the

project.

Although Lake Challa has the capacity of supply the required demand for the entire project, to

include both irrigation and domestic water supply, trans-boundary issues had to be considered

due to the fact that Kenya shares the Lake water with Tanzania equally.

The following table shows amounts of abstractions considered from the two sources;

Table 3.1 - Recommended Abstraction Rates

Source

Volume (m3)

Annual per day per hour

1 Lake Challa 2,640,000 8,000 400

2 Boreholes 7,920,000 24,000 1,200

Total 10,560,000 32,000 1,600

The intake works will consists of two submersible pumps; one duty and the other standby; in a

pump house built on girders on a floating pontoon.


The structural components for the intake works include the reinforced concrete retaining walls,

structural steel buttress supports, reinforced concrete shaft, floating girder platforms and floating

pontoons

Retaining walls have been designed to provide a route for the transmission line and provide

access to the intake works. Due to the steep topography, the walls have been designed with a

maximum height of 5.8 m. For stability and strength considerations both the toe and heel have

been provided to safeguard against sliding and overturning.

To further support the high walls, a steel buttress structure has been designed supporting the

walls at various intervals along the height. This in effect reduced the cantilever effect of the wall

due to the active earth pressure acting behind it. Consequently, the walls have been designed as

simply supported slabs spanning between the supporting steel structures with the maximum earth

pressure at the bottom being considered for design.

The member sizing for the buttress is such as to effectively resist the horizontal forces without

overturning, excessive deflection or failure. The foundations have similarly been designed for the

resultant forces and moments.

The girder platform has been designed to accommodate the pumps and to float on the lake. This

has been achieved by designing pontoons such that the total weight of water displaced by the

pontoons is greater than the total weight of the structure. Additionally the possibilities of

fluctuations in water levels have been addressed by providing hinges on the girder thus allowing

vertical movement.

The entire steel girder is firmly secured by anchor bolts and high tensile galvanized gay cables

fixed on the buttress structure.

The pump house is a steel framed structure with sheet cladding on the external walls and the

roof. The interior is finished using a galvanized plate welded on the steel frame to form a

watertight surface. Additional surface treatment may be specified to enhance water tightness.

3.3 RAW WATER PIPELINE

There will be two main raw water pipelines for the project. One will convey water from Lake

Challa through pumping designed to deliver 8,000 m3/day via DN 300mm steel pipeline and the

other from two boreholes to deliver 16,000m3/day via a DN 400mm pipelines.

Pipelines have been designed with a Hazen-Williams ‘C’ value of 140 for new pipes.

The three raw water pipelines merge and deliver water to a 1,000 m3 reinforced concrete tank to

be located at the top rim of Lake Challa.

3.4 LAKE CHALLA TANK

The Capacity of Lake Challa reinforced concrete as mentioned above is 1000m3. The tank is

strategically located to command flow of water via gravity to the entire project save for Mwaktau

which is at higher ground level than the tank location.


3.5 RESERVOIRS

The project is designed to hold three major water storage earth-fill reservoirs as indicated in the

following table.

Table 3.2 – Capacities of Water Reservoirs

Site Capacity (m3)

Kilanga 75,000

Jipe 75,000

Mwaktau 65,000

The sizing of the required earth-fill reservoirs depends on the volume of water stored based on

the amount of water required to irrigate the projected areas. They will be rectangular in shape. It

is assumed that the earth removed from the reservoir bases during excavations will be

utilised in building the reservoir walls.

3.5.1 RESERVOIR CHARACTERISTICS

The reservoirs will be designed with the following characteristics;

Walls will be sloping with a ratio of 1:2 on the external side and 1:4 on the internal side.

A free board of 0.7m above the maximum water level.

The reservoirs will be lined with HDPE plastic linings in order to prevent seepage.

Width of the reservoir wall’s crown will be at least 5m wide to allow vehicles to drive

round the reservoir for maintenance and fishing purposes.

The reservoirs will be surrounded by an electrified perimeter fence in order to prevent

wild animal access.

Based on the water quality analysis, it is envisaged that there be will minimal deposits at the

bottom of the reservoirs in form of sedimentation. However, sludge/silt accumulated in the

reservoir over time will be carefully scrapped manually to ensure that the HDPE lining is not

damaged.

The following table gives the technical details of each reservoir in the proposed project areas.


Table 3.3- Reservoirs Technical Details

Description Unit Kilanga

Reservoir

Jipe

Reservoir

Mwaktau

Reservoir

Reservoir Volume m3 75,000 75,000 65,000

Total Area m2 36,000 36,000 20,250

Length m 225 225 150

Width m 160 160 135

Water Surface Area m2 18,780 18,780 16,505

Reservoir Area Base m2 9,750 9,750 8,125

Water Depth m 5.3 5.3 5.3

Free Board m 0.7 0.7 0.7

Total Embankment Height m 6.0 6.0 6.0

Embankment slopes

(internal/external) 1:4 & 1:2 1:4 & 1:2 1:4 & 1:2

Plastic Lining Area

Total Embankment Area m

2

20,915

20,915

18,475

Total Embankment Length m 622 622 592

3.5.2 TIMBILA TANK

The reinforced concrete tank is designed to have a capacity of 1000 m3

to be supplied through a

DN 220mm PVC pipe. The water is intended for irrigation in the Timbila area.

However, during the design stage, no land for irrigation was identified due to settlements and

many permanent houses developed in the area. However, a provision has been made at the outlet

end of the tank.


3.6 TRANSMISSION PIPELINES

The details of the transmission pipelines are as shown in the table below.

Table 3.4 – Transmission Pipelines Technical Details

Pipeline Description

PIPELINE

Diameter

(mm)

Length (m) and Pressure Ratings uPVC

Class D PN25 PN16 PN10

Lake Challa- Challa Tank

Rising main 300

232

Challa - Jipe Pipeline 500 14000

Jipe - Mwaktau – Kwa

Mnengwa Pipeline

450 2400 7200 7200

400

22300

300

3,440

100

1,560

75

1,560

50

1,556

Kilanga - Challa Pipeline

450 2,000

400

3,500

Kidongu Pipeline 75 1,444

Jipe Reservoir Pipeline 500 225

Mwaktau Reservoir

Pipeline 300 301 301

Timbila Tank Pipeline 200

615

KWS pipeline to water pan 75

1,000

Kilanga – Existing Challa

Irrigation scheme 300

3,000

Mwaktau Tank Inlet pipe 150

250

Nakuruto Tank Inlet pipe 150

1,000

Jipe Tank Inlet pipe 50

675

Water is conveyed in all the above pipelines by gravity except for Jipe – Mwaktau – Kwa

Mnengwa pipeline which is a pumping mains from Jipe at an altitude of 865 masl to Mwaktau at

1120 masl i.e. an elevation difference of 255m. The rest of the pipelines are served by Lake

Challa which stands at a height of 914 masl.

To minimise costs, the pipeline has been designed for various pressure ratings ranging from PN

30 to PN 25 according to the pressure requirements at those specific areas.


3.7 DOMESTIC WATER SUPPLY

Domestic water supply has also been incorporated in the project for only areas that experience

acute water shortages. Areas of concern that have been considered include Kasokoni, Kasaani in

Jipe, Kidongu, Mwaktau Trading Center and Kwa Mnengwa.

In all these identified locations, a water tank has been provided, strategically located and

designed to allow the supply in the respective area by gravity.

It is important to note that an elevated steel water tank with a capacity of 200m3 has been

provided for in Kasokoni, Mwaktau and Kasaani area and a 250m3 concrete tank provided for at

Kwa Mnengwa and Kidong’u, located at the trading center and Kidong’u Hill respectively.

Water demand projections for the ultimate year of 2035 were calculated focussing on the areas of

concern. This was derived from population projection using a population growth of 1.8%.

During computation of the demand requirements; irrigation demand and domestic water were

both considered simultaneously based on the total available water from the two sources.

Table 3.5 shows the water irrigation and domestic demands for the various sites.

Table 3.5 – Water Demands

Area

Water Demands (m3/year)

Irrigation Domestic Others Total

1 Kilanga Pilot Project 810,307 - - 810,307

2 Challa Irrigation Project 881,823 - - 881,823

3 Nakuruto/Kasokoni 404,834 58,552 - 463,386

4 Timbilla/Kidong’u 881,823 44,297 - 926,120

5 Jipe 4,692,931 53,351 - 4,746,282

6 Mwaktau 1,935,868 120,400 - 2,056,268

7 Msorongo - 125,369 - 125,369

8 Environment Conservation 45,000 45,000

9 Wildlife (Tsavo National Park) 91,250 91,250

10 Fisheries 20,000 20,000

Total 9,607,587 401,969 136,250 10,145,806

3.8 ANCILLARY WORKS

The typical civil and ancillary works proposed include the following:-


3.8.1 ADMINISTRATION BUILDING AND LABORATORY

The administration building is designed to house an office, laboratory and a toilet with separate a

shower compartment. This has been provided for in Kilanga, Jipe and Mwaktau.

3.8.2 STAFF HOUSES

2 No. twin housing will be provided for the staff operating the works at Kilanga, Jipe and

Mwaktau.

3.8.3 SITE DRAINAGE

Foul water from the administration building and staff houses will be channelled into a separate

system discharging into a septic tank and soak away pit.

3.8.4 WORKSHOP

A workshop has also been provided for to help in operation and maintenance purposes of various

items within the facility in Kilanga, Jipe and Mwaktau.

3.8.5 PUMP HOUSE

A pump house has been provided for the in the Jipe site. In addition, a 1,000 m3 concrete tank to

facilitate pumping water to Mwaktau has also been included.

3.8.6 ACCESS ROADS

New site access from the road adjacent to the site will be constructed. Service roads within the

treatment works will be constructed to single seal bitumen standards.

Access to Kilanga will however involve rehabilitation of an existing 3 km long gravel road to

motorable status.

3.8.7 POWER SUPPLY

An 11KV/415V electrical power line exists in the vicinity of Kilanga, Jipe and Mwaktau sites

and this will be utilized for power supplies to the works. Arrangements will be made with Kenya

Power Company for power supply to the respective sites.


3.9 MATERIALS SPECIFICATIONS

3.9.1 TRANSMISSION AND DISTRIBUTION PIPELINES

The pipelines shall be Steel Pipes suitable for working pressures ranging from 10 to 25 bar with

their respective flanges and other fittings of equivalent pressure ratings.

Pipes shall be manufactured to BS EN 1561 250 cast iron, suitable for on or off seat installations

as shown on the drawings.

3.9.2 FLOW REGULATING VALVES

Flow Regulating Valves will be mechanically operated incorporating a cylindrical sleeve or

needle valve. They will be suitable for operating at any flow for long periods of time without

vibration or cavitation. They shall be designed for minimal maintenance, safe energy dissipation

and low operating effort. Operation shall be manual via a removable hand wheel. Valve bodies

shall be cast iron or ductile iron with stainless steel operating trim.


CHAPTER 4: COST ESTIMATES AND PROJECT PHASING


Table of Contents

CHAPTER 4 – COST ESTIMATES AND PROJECT PHASING

4.1 GENERAL ....................................................................................................................................... 4-92

4.2 BASIS FOR ESTIMATION OF COSTS ......................................................................................... 4-92

4.3 SUMMARY OF ESTIMATED COSTS .......................................................................................... 4-92

4.3.1 Intake Works .................................................................................... 4-93

4.3.2 Developing and equipping Boreholes ............................................................... 4-93

4.3.3 Transmission Pipelines ......................................................................................... 4-93

4.3.4 Civil Works ............................................................................................................... 4-93

4.3.5 Irrigation Works ..................................................................................................... 4-93

4.3.6 Trans-boundary Issues and Environment and Resettlement ...................... 4-93

4.3.7 Forestry and Fisheries .......................................................................................... 4-94

4.4 ITEMISED WORKS COST ESTIMATES ...................................................................................... 4-94

4.5 PROJECT PHASING....................................................................................................................... 4-98

4.5.1 INTRODUCTION ....................................................................................................... 4-98

4.5.2 COST BY PHASES ..................................................................................................... 4-98


CHAPTER 4 – COST ESTIMATES AND PROJECT PHASING

4.1 GENERAL

The project development will consist of irrigation works in Kilanga, Jipe and Mwaktau with a

pressurised system in Kilanga while the other two will be operated through gravity. Improvement

of the existing Challa Irrigation scheme has also been included as part of this project.

There will be three sites in total constructed for the operation and coordination of the project at

Kilanga, Jipe and Mwaktau, respectively. These sites will be fully equipped with administration

and laboratory buildings, staff houses, workshops and stores.

Domestic water supply has also been provided for areas which currently experience acute water

shortages within the project area such as Kasaani near Jipe, Kidong’u and Mwaktau areas.

Water for wild animals at Tsavo West National Park has also been provided for through a shallow

water pan to be located near Murka area along the Taveta – Voi Road.

The project also encompasses forestry and fishing activities in Taveta and Mwaktau areas.

4.2 BASIS FOR ESTIMATION OF COSTS

For the preparation of Cost Estimate, quantities for the various items in Bills Nos. 2 - 13 have been

calculated from drawings while for Bill No.1 the quantities have been estimated using the

Consultant’s experience on similar work in the past. The rates used in estimation have been derived

from unit rates and works of similar kind carried out by the Consultant in the recent past.

The rates for various items of works have been adopted after taking into account the current rates

of materials, labour and equipment prevalent in the project. A lump sum provision for some items

which cannot be quantified at this stage of project preparation are based on the experience of

consultants and also takes into consideration the current rates.

4.3 SUMMARY OF ESTIMATED COSTS

Intake Works at Lake Challa - Ksh 73.80 million

Development and equipping three Boreholes - Ksh 73.74 million

Transmission Pipelines - Ksh 1,076.05 million

Civil Works including reservoirs - Ksh 976.24 million

All the above costs are without any escalations.


4.3.1 INTAKE WORKS

Lake Challa Intake Works include submersible pumps in a pump house fully equipped with a

control panel at the surface of Lake Challa designed on a floating pontoon and a series of

reinforced concrete retaining walls cascading from the top of the rim to the to the lakeshores

reinforced by steel buttresses and girders. This adds up the cost by a further Kshs. 87.86 million

which includes for the required electromechanical installation.

4.3.2 DEVELOPING AND EQUIPPING BOREHOLES

Three boreholes will be developed in the Kilanga and Challa areas. They will be equipped with

all necessary pumping units, piping, associated accessories and other ancillary equipment all at

an estimated cost of Ksh 73.74 million.

4.3.3 TRANSMISSION PIPELINES

Transmission pipelines will be composed of steel pipes of various pressure ratings that is PN 30,

PN 25, PN 10 and uPVC Class D pipelines. The total cost of pipelines is therefore Ksh. 1,076.05

million.

4.3.4 CIVIL WORKS

Under civil works, the costs encompass the cost of reservoirs at Kilanga and Jipe, both of 75,000

m3

capacity and at Mwaktau with a capacity of 65,000 m3. It also includes for roadworks, onsite

water supply, foul water drainage, septic tanks and fencing (where fencing is mostly electric

fencing especially to areas prone to wild animals attack) at Jipe and Mwaktau areas. The total cost

of this work is estimated to be Kshs 976.24 million.

4.3.5 IRRIGATION WORKS

Irrigation works will involve the cost of infrastructure for irrigation. It also includes three

boreholes, one to supply the irrigation waters into Kilanga reservoir, and the other for Jipe and

Mwaktau. A pumping system for irrigation at Kilanga and an extension pipeline 3 km long for

expansion of the existing Challa Irrigation scheme.

Main pipelines and laterals including the necessary valves and fitting for both Jipe and Mwaktau

irrigation schemes have also been included. The total cost of Irrigation is therefore Ksh 205.59

million.

4.3.6 TRANS-BOUNDARY ISSUES AND ENVIRONMENT AND

RESETTLEMENT

A provision has been allowed as detailed in the Environmental Impact Assessment report on

Implementation of Trans boundary Action Plan due to the shared water of Lake Challa with

Tanzania and also in the implementation of the Environmental Mitigation Measures, all valued at

Ksh. 22.6 Million. A further Ksh. 10 Million has been allowed for the construction of a check dam

of a check dam on River Karimeri to be located about 200 m upstream of the bridge on the Challa

Taveta Road. The dam will mitigate the flooding effects and also serve as a water reservoir.


A provisional sum of Kshs 410 Million has been added for the resettlement of the affected

population.

4.3.7 FORESTRY AND FISHERIES

Cost of re-afforestation in identified areas and the setting up of a fisheries industry in the area has

also been factored in the works costs estimates. A provision of Kshs. 75 Million has been factored

in the project costs for this purpose.

4.4 ITEMISED WORKS COST ESTIMATES

Intake Works

Sl No Item of Works Amount (Ksh)

1 Retaining walls, steel buttress and box girder, pump

house, pumps and raw water mains.

73,808,498.00

2 Electromechanical Installations 14,057,500.00

Total 87,865,998.00

Boreholes


1 Development of three boreholes @ Kshs 6,262,000 18,786,000.00

2 Equipping three boreholes @ Kshs 18,319,680 54,959,040.00

Total 73,745,040.00

Irrigation Works


1 Kilanga Irrigation Scheme 59,111,100.00

2 Expansion of Existing Challa Irrigation Scheme 10,890,000.00

3 Jipe Irrigation Scheme 118,580,000.00

4 Mwaktau Irrigation Scheme 17,013,000.00

Total 205,594,100.00


Transmission Pipelines


1 Kilanga - Challa Pipeline 67,611,336.00

2 Challa - Jipe Pipeline 329,337,106.00

3 Kidong'u Tank Pipeline 11,753,939.00

4 Timbila Reservoir Pipeline 13,303,642.00

5 Jipe Reservoir Pipeline 6,087,396.00

6 Jipe - Mwaktau - Kwa Mnengwa Pipeline 627,310,466.00

7 Mwaktau Reservoir Pipeline 4,831,104.00

Total 1,076,051,327.00

Kilanga Works


1 Kilanga Reservoir – 75,000m3 271,796,760.00

2 Administration and Laboratory Building 2,761,060.00

3 Workshop and Store 4,524,290.00

4 Gate House 1,978,430.00

5 Civil Works 31,388,351.00


Total 312,448,891.00

Jipe Works


1 Jipe Reservoir – 75,000m3 338,300,620.00


3 Workshop and Store 4,499,050.00

4 Gate House 1,978,430.00

5 Civil Works 9,893,351.00

6 1,000m3 Reinforced Concrete Tank 15,086,240.00

7 Pump House 7,898,875.00

8 Pumps 29,299,600


Total 409,649,336.00


Mwaktau Works


1 Mwaktau Reservoir – 65,000m3 315,195,170.00


3 WorKshop and Store 4,183,090.00

4 Gate House 1,978,430.00

5 Civil Works 9,668,351.00


Total 333,798,101.00

Reinforced Concrete Tanks


1 Challa Tank - 1000m3 23,272,115.50

2 Nakuruto Tank - 1000m3 15,285,739.50

3 Timbilla Tank - 1000m3 15,527,740.00

4 Kidong’u Tank – 250m3 6,003,992.00

5 Kwa Mnegwa – 250m3 5,709,114.00

Total 74,344,286.00

Elevated Steel Tanks


1 Kasaani – 250m3 3,780,055.00

2 Mwaktau – 250m3 3,472,512.00

Total 7,252,567.00


LAKE CHALLA WATER RESOURCES INTEGRATED DEVELOPMENT PROJECT COST


1 Bill No. 1 - Preliminary and

General Items

347,066,450.00

2 Bill No. 2 - Intake Works 73,808,498.00

3 Bill No. 2B - Electromechanical

Works - Intake Works

14,057,500.00

4 Bill No. 3 - Challa Tank 23,272,115.50

5 Bill No. 4 - Transmission Pipelines 1,076,051,327.00

6 Bill No. 5 - Kilanga Works 312,448,891.00


Works - Kilanga Works

22,261,700.00

8 Bill No. 6 - Timbila Tank 15,285,739.50

9 Bill No. 7 - Kasaani Tank 3,780,055.00

10 Bill No. 8 - Kidong'u Tank 6,003,992.00

11 Bill No. 9 - Jipe Works 409,649,336.00

12 Bill No. 9B -Electromechanical

Works -

Jipe Works

26,358,400.00

13 Bill No. 10 - Mwaktau Tank 3,472,512.00

14 Bill No. 11 - Mwaktau Works 333,798,101.00


Works -

Mwaktau Works

18,812,300.00

16 Bill No. 12 - Kwa Mnengwa Tank 5,709,114.00

17 Bill No. 13 – Irrigation and

boreholes

279,339,140.00

18 Bill No. 14 - Kasokoni Tank 3,780,055.00

19 Bill No. 15 - Nakuruto Tank 15,285,739.50

Sub-Total 1 2,960,540,966.00

Add 10% Contingency 296,054,096.60

Total Cost Estimate of The

Project

3,289,265,062.60


4.5 PROJECT PHASING

4.5.1 INTRODUCTION

The major objective of the Lake Challa Water Resources Integrated Development Project is to

develop an Irrigation System that will cover 1,010 ha of various crops as detailed in the irrigation

component sections of this report,

For speedy implementation of the Project, it is proposed that the project be implemented in three

phases as described below;

4. Phase One – to cover Kilanga Pilot Irrigation Project and the existing Challa Irrigation

Scheme

5. Phase Two – to cover Timbila and Jipe Irrigation Schemes (including provision of

irrigation and domestic water within the areas covered by the pipelines)

6. Phase Three – to cover Mwaktau Irrigation Schemes (including provision of domestic

water within the areas covered by the pipelines)

4.5.2 COST BY PHASES

The project components and respective costs as itemized by phases are tabulated below.

Sl

No Item of Works

Phase I Phase II Phase III

Kilanga and

Challa

Jipe &Timbila

Mwaktau

1 Bill No. 1 -

Preliminary and

General Items

115,688,816.83 115,688,816.83 115,688,816.83

2 Bill No. 2 - Intake

Works

73,808,498.00

3 Bill No. 2B -

Electromechanical

Works - Intake

Works

14,057,500.00

4 Bill No. 3 - Challa

Tank

23,272,115.50

5 Bill No. 4 -

Transmission

Pipelines

67,611,336.00

376,298,421.00

632,141,570.00

6 Bill No. 5 - Kilanga

Works

312,448,891.00

7 Bill No. 5B -

Electromechanical

Works - Kilanga

22,261,700.00


Sl

No Item of Works

Phase I Phase II Phase III

Kilanga and

Challa

Jipe &Timbila

Mwaktau

Works

8 Bill No. 6 - Timbila

Tank

15,285,739.50

9 Bill No. 7 - Kasaani

Tank

3,780,055.00

10 Bill No. 8 -

Kidong'u Tank

6,003,992.00

11 Bill No. 9 - Jipe

Works

409,649,336.00

12 Bill No. 9B -

Electromechanical

Works - Jipe Works

26,358,400.00

13 Bill No. 10 -

Mwaktau Tank

3,472,512.00

14 Bill No. 11 -

Mwaktau Works

333,798,101.00

15 Bill No. 11B -

Electromechanical

Works - Mwaktau

Works

18,812,300.00

16 Bill No. 12 - Kwa

Mnengwa Tank

5,709,114.00

17 Bill No. 13 –

Irrigation and

Boreholes

94,582,780.00 167,743,360.00 17,013,000.00

18 Bill No. 14 -

Kasokoni Tank 3,780,055.00

19 Bill No. 15 -

Nakuruto Tank 15,285,739.50

Sub-Total 1 612,593,524.00 1,251,012,028.00 1,126,635,413.83

Add 10%

Contingency

61,259,352.00 125,101,202.00 112,663,541.38

Total Cost 673,852,876.00 1,376,113,231.00 1,239,298,955.22


Components of Phases

Phasing Main Components Cost Kshs.

Phase 1

Kilanga Irrigation Scheme

673,852,876.00

Improvement of existing Challa Irrigation

Scheme

Fishing and Forestry

Phase 2

Jipe Irrigation Scheme

1,376,113,231.00

Timbila Irrigation Scheme

Nakuruto Irrigation and Domestic Water

Kidong'u Domestic Water

Jipe Domestic Water


Phase 3

Mwaktau Irrigation Scheme

1,239,298,955.22

Mwaktau Domestic Water

Kwa Mnengwa Domestic Water

KWS Drinking Water for Animals


Total 3,289,265,062.00