Gauff Design Report - 05-2012 · b) To design pipeline route from Luzira borehole to elevated water tanks including hydraulic design, plan and profile drawings, technical specification

REPUBLIC OF SOUTH SUDAN MINISTRY OF WATER RESOURCES AND IRRIGATION YEI RIVER COUNTY

In Cooperation with

CONSULTANCY SERVICES FOR DETAILED DESIGN AND TENDER DOCUMENTATION FOR WATER AND SANITATION FACILITIES FOR YEI TOWN

PROJECT REPORT

MAY 2012

Water and Sanitation Project, Yei, Southern Sudan May 2012 Consultancy – Design and Tender Documentation Detailed Design Report

Gauff Ingenieure ii

Consulting Services for the Design and Tender Documentation for Water and

Sanitation Facilities in Yei Town, South Sudan

DETAILED DESIGN REPORT

Table of Contents

1 INTRODUCTION .............................................................................................................. 1-1 1.1 Background and Context ........................ ....................................................................... 1-1 1.2 Objectives of the Project ..................... ........................................................................... 1-1 1.3 Scope of Services ............................. .............................................................................. 1-2 1.4 Project Area .................................. .................................................................................. 1-2 1.5 Topography .................................... ................................................................................. 1-3 1.6 Geology ....................................... .................................................................................... 1-3 1.7 Climate ....................................... ..................................................................................... 1-4 1.8 Vegetation .................................... ................................................................................... 1-4 2 DESIGN CRITERIA .......................................................................................................... 2-1 2.1 Hydraulic Design Criteria ..................... .......................................................................... 2-1 2.1.1 Hydraulic Calculation ........................................................................................................ 2-1 2.1.2 Pressures ......................................................................................................................... 2-4 2.2 Materials and Fittings ........................ ............................................................................. 2-4 2.2.1 Pipe Materials ................................................................................................................... 2-4 2.2.2 Air Valves ......................................................................................................................... 2-4 2.2.3 Washouts ......................................................................................................................... 2-4 2.2.4 Isolation and Section Valves ............................................................................................. 2-5 2.3 Structural Design Standards ................... ...................................................................... 2-5 2.3.1 General ............................................................................................................................ 2-5 2.3.2 Design Codes and Data .................................................................................................... 2-5 2.3.3 Loading Conditions ........................................................................................................... 2-6 2.3.4 Exposure Conditions ........................................................................................................ 2-6 2.3.5 Foundations ...................................................................................................................... 2-6 2.4 Structural Criteria ........................... ................................................................................ 2-6 2.4.1 Limit States ....................................................................................................................... 2-6 2.4.2 Design Factors ................................................................................................................. 2-7 2.4.3 Characteristic and Design Loads and Strength ................................................................. 2-7 3 TRANSMISSION AND DISTRIBUTION PIPELINES ......... ............................................... 3-1 3.1 Overview ...................................... ................................................................................... 3-1 3.2 Present and Future Water Production ........... ................................................................ 3-1 3.2.1 Existing Hai Gabat Borehole GAB-BH-10 ......................................................................... 3-1 3.2.2 Future Luzira Borehole LUZ-BH-1 .................................................................................... 3-1 3.3 Water Consumption.............................. .......................................................................... 3-1 3.4 Proposed Water Transmission System ............ ............................................................. 3-2 3.4.1 Reconnecting the Existing Hai Gabat Borehole Pipeline ................................................... 3-2 3.4.2 Construct New Pipeline for Luzira Borehole ...................................................................... 3-2 3.5 Proposed Water Distribution System ............ ................................................................ 3-2


Gauff Ingenieure iii

3.5.1 Demand Assumptions....................................................................................................... 3-2 3.5.2 Pipeline Design................................................................................................................. 3-3 4 WATER KIOSKS AND PIPELINES ...................... ............................................................ 4-3 5 WATER TANKER FILLING STATION .................... ......................................................... 5-1 6 ABLUTION BLOCK WITH BIOGAS UNIT ................. ...................................................... 6-1 7 SEPTIC TANKER DISCHARGE BAY ..................... ......................................................... 7-1 8 SEPTIC TANK FOR SLAUGHTER HOUSE ................. .................................................... 8-1 8.1 Soakaways and Drainfields ..................... ....................................................................... 8-3 9 CONSTRUCTION PLANS .............................. .................................................................. 9-1 10 ENGINEER’S COST ESTIMATES FOR THE WORKS ........ .......................................... 10-1 FIGURES

Figure 1-1: Location map ............................................................................................................ 1-3

Figure 1-2: Geological map ......................................................................................................... 1-4

Figure 6-1: Fixed Dome Biogas Units ........................................................................................... 6-2

TABLES

Table 1-1: Coordinates of the Boundary Points ............................................................................ 1-2

Table 6-1: Characteristics of waste produced and corresponding viable gas yield ....................... 6-1

Table 8-1: Minimum distance of septic tanks and soakaways ...................................................... 8-2

Table 8-2: Percolation rating ........................................................................................................ 8-3

Table 10-1: Cost Estimate .......................................................................................................... 10-1

ANNEXES

Annex 1 – Design Calculations Annex 2 – Drawings Annex 3 – Engineer’s Estimate


Gauff Ingenieure iv

LIST OF ABBREVIATIONS AfD Agence Française de Développement BoQ Bills of Quantities BS British Standard DN Diameter Nominal GFA GFA Consulting Group GITEC GITEC Consult GmbH GIZ Deutsche Gesellschaft für Internationale Zusammenarbeit GOSS Government of Southern Sudan GPS Global Positioning System KfW Kreditanstalt für Wiederaufbau mamsl metres above mean sea level m3 Cubic meters m3/day Cubic meters per day m3/h Cubic meters per hour m3/s Cubic meters per second MWRI Ministry of Water Resources and Irrigation NGO Non Governmental Organisation OD Outside Diameter (for PVC and PE pipes) O&M Operation and Maintenance PE Polyethylene (HD = High Density) ROSS Republic of South Sudan SDG Sudanese Pounds SSP South Sudanese Pounds SSUWC South Sudan Urban Water Corporation TOR Terms of Reference YRC Yei River County YTP Yei Town Payam UNHCR United Nations High Commissioner for Refugees UNMIS United Nations Mission in Sudan VIP Ventilated Improved latrine


Gauff Ingenieure 1-1

1 INTRODUCTION

1.1 BACKGROUND AND CONTEXT

Signing of the Comprehensive Peace Agreement (CPA) in 2005 and independence in 2011 brought a period of peace which had been unknown to South Sudan for decades. The immediate post-conflict priority has been the establishment of government administrative structures, rehabilitation of primary infrastructure and delivery of basic services. The Government of the Republic of South Sudan (RoSS) recognises the central role of the water sector. A key priority is the sustainable management and effective delivery of water and sanitation services and thus the improvement of health and welfare of the people of South Sudan.

The approval of the Water Policy (2007) represented a significant milestone for water sector development in South Sudan. RoSS has embarked on the development of implementation strategies for the four sub-sectors (Urban Water Supply, Rural Water Supply, Water Resource Management and Sanitation/ Hygiene).

The German Government has been asked to provide technical assistance to the Ministry of Water Resources and Irrigation (MWRI) and to the South Sudan Urban Water Corporation (SSUWC). GIZ has been commissioned to provide the requested support. Since mid-2009, a comprehensive program co-financed by AfD has been set-up. At present, it can be divided into four main lines of action:

a) Technical assistance (TA) to MWRI for implementation of policies

b) TA to SSUWC for operations support and training of staff

c) TA for the implementation of pilot measures for Yei Water Station

d) Capacity development

1.2 OBJECTIVES OF THE PROJECT

The overall objective of this consultancy is to prepare documentation for the construction of water and sanitation facilities for Yei Town.

The specific objectives are:

a) To elaborate detailed design and bills of quantities (BoQ) of the planned system in the centre of Yei: designs, structural drawings, technical specifications and BoQs for water kiosks (different designs to pilot different approaches) in the locations specified by GIZ (Hai Gabat scheme) including design, technical specifications and BoQs for pipelines.

b) To design pipeline route from Luzira borehole to elevated water tanks including hydraulic design, plan and profile drawings, technical specification and BoQ.

c) To elaborate detailed design, structural drawings, technical specification and BoQ for water tanker filling station.

d) To elaborate detailed design, structural drawings, technical specifications and BoQ of public latrine including ablution block and biogas.

e) To elaborate detailed design, structural drawings, technical specifications and BoQ of septic tanker discharge bay – a preliminary disposal site for faecal sludge.



f) To elaborate detailed design, structural drawings, technical specifications and BoQ of septic tank at the slaughter house.

1.3 SCOPE OF SERVICES

The services that the Consultant has to perform under this assignment are as follows:

• Detailed design

• Drawings – plan & profile, structural

• Bills of quantities

• Technical specifications

• Construction plan

• Cost estimates

This report covers the detailed design of the various components and is presented together with detailed drawings, bills of quantities and technical specifications.

1.4 PROJECT AREA

The Project covers the urban centre of Yei Town Payam with an estimated population of approximately 75,000 people in the central urban area and about 170,000 in the enlarged area which is considered to make up Yei Town in 2010. Yei is some 150 km south-west of Juba (about 3 hrs drive) and is situated at the confluence of the Yei and Kembe Rivers.

The roads within, to and from the town are gravel and are in fairly good condition. The boundary points for the project area along the four main roads leading from the town have been demarcated and their coordinates are given in the table below.

Table 1-1 : Coordinates of the Boundary Points

Location Easting Northing Location Easting Northing

Maridi Road 30.618275o 4.125268o Juba Road 30.804072o 4.161167o

Lasu Road 30.625220o 4.058500o Kaya Road 30.736890o 4.018630o

The location of the project town is shown in the figure overleaf.



Figure 1-1: Location map

1.5 TOPOGRAPHY

The town has a slightly undulating topography with the centre of town being the highest point at 830 mamsl. The town is built along the Yei River and the Kembe River that have an approximate elevation of 790 mamsl resulting in an approximate height difference of 40 m between the town centre and the river valleys.

1.6 GEOLOGY

According to the 1:2,000,000 geological map of Sudan (overleaf) the catchment areas of the Yei and Kembe Rivers (schematically represented by the green line) are underlain in the north, west and south by undifferentiated gneisses (Pg) and in the central western part by intrusive batholic granites, grey granites and pegmatites (γ1). There are no clearly distinguishing tectonic features, but regional fault zone orientations are visible.

The general thickness of the overburden, which consists of weathered bedrock (rhyolites), laterites, vertisols (black cotton soil) and alluvial deposits, increases upstream in the river basins, according to local drillers. The dominant soil types in the town area include sandy loam soils, gravel soils and sandy soils.



Figure 1-2: Geological map

1.7 CLIMATE

The area experiences a hot tropical climate with higher temperatures during the dry season – November to February (average of 24 0C to maximum of 34 0C) and cooler temperatures during the wet season – March to October (average of 21 0C to minimum of 2 0C).

The rainfall distribution increases southwards, with a distinct uni-modal rainy season distribution pattern from June to September. It ranges from humid to hyper humid, receiving an average of 1,421 mm of rainfall per year.

1.8 VEGETATION

The project area is within an equatorial vegetation zone, which comprises equatorial forest patches in the south and savannah woodlands and grasslands in the north that extend from DRC to Southern Sudan. The forest patches are comprised of teak trees (Tectona Grandis) with a few widely scattered mahogany trees (Khaya Grandifoliola) along the rivers.



2 DESIGN CRITERIA

2.1 HYDRAULIC DESIGN CRITERIA

2.1.1 Hydraulic Calculation

Head losses are calculated by using the Darcy-Weisbach-Equation:

2gv

DLf

Η2∗∗=

H = headloss (m)

f = resistance coefficient

L = length of pipe (m)

D = diameter of pipe (m)

v = velocity of flow (m/s)

g = gravity of acceleration = 9.81 (m/s²)

The resistance coefficient “f” is determined according to the formula of Prandtl and Colebrook (a variant of the Colebrook-White formula).

Following the DVGW paper W302 of 1981 (amended in 1985), for the calculation of head losses, a roughness factor of k=1 mm is applied for distribution pipes (this takes into account the junctions and fittings), k=0.4 mm for transmission lines which have few fittings and k=0.1 mm for the mainly long distance and nearly straight transmission pipelines and rising mains.

In comparison, A.C. Twort’s Water Supply handbook recommends friction factors of 0.05 mm for bitumen lined iron and plastic pipes and 0.5 mm for new distribution networks and 1.25 mm for 30 year old networks.

The Advanced Water Distribution Modelling handbook by Haestad recommends C-values of 137-148 for coated steel and 147-153 for plastic pipes. C-value of 140 equals about 0.1 mm and 150 equals 0.05 mm.

International publications do not differentiate much between the friction factors of coated/lined steel pipes and PVC/PE pipes, but they do indicate that friction factors for networks should be higher than for straight transmission mains. Therefore, based on international literature and our own hydraulic design experience we recommend the use of the friction factors indicated in the DVWG paper (included overleaf).







2.1.2 Pressures

In order to provide an acceptable level of services to consumers, water must be supplied at adequate pressure. The minimum pressure proposed should be 7 metres (0.7 bars) at the consumer point, whilst 12 metres (1.2 bars) should be attained in the main supplying pipes. Therefore, the minimum pressure proposed for design is 12 metres (1.2 bars) in tertiary feeding mains, provided that this can be achieved where existing storage reservoirs will be reused in the project. The absolute minimum pressure to be considered will be 7 (0.7 bars) metres at peak hour demand.

In order to provide this minimum pressure it will be necessary to have higher pressures in the upstream parts of the system and in low lying areas. In view of the relationship between pressure and leakage it is recommended that the maximum pressures in the distribution networks should not exceed 60 metres (6 bars).

2.2 MATERIALS AND FITTINGS

2.2.1 Pipe Materials

Polyethylene (PE) pipes are proposed to be used with either mechanical, butt-welded or electro-fusion couplings, whilst fittings (bends, tees) are proposed to be epoxy coated and lined steel fittings for easy installation of adjacent valves and easier future detection of junctions and change in direction points.

It is further suggested to lay tracer tape on top of the pipelines to facilitate easier future pipe location and leak detection.

2.2.2 Air Valves

Air valves serve mainly three purposes, namely:

• To release air from the pipeline during the filling process

• To release air from the pipeline during the normal operation of the water supply

• To allow air to enter into the pipeline in order to prevent vacuum to occur

Anti-shock and anti-surge (triple action) air valves are proposed to be installed at all high points with respect to the pipeline profile and hydraulic gradient. Furthermore, it shall be ensured that there is at least a minimum of one air valve for every 1,000 metres of pipeline to prevent air accumulation.

All air valves shall be equipped with isolating valves for easy removal and repair of the air valves.

2.2.3 Washouts

Washouts should be placed only at accentuate low points on pipelines of inside diameter DN 80 or larger (although in some instances washouts will be placed on smaller diameter line in order to ensure proper flushing of lines). In this context it may be considered that a low point is accentuate if the succeeding major high point is situated 10 m higher.

Assuming a shear stress of 10 N/m2 on the walls of the main pipe and an available pressure of 0.1-.0.2 MPa the diameter, d, of the washout should be:

d = 0.6 D if the upstream and the downstream sides of the main are washed simultaneously.



d = 0.4 D if only one side is washed at a time

Where:

d is the diameter at the washout in mm

D is the diameter of the main pipe in mm

There shall be a valve only on the washout pipe and not on the main pipeline unless the valve can be combined with a section valve. There shall be an open drain leading the water from the washout to a suitable steam or discharge point nearby.

2.2.4 Isolation and Section Valves

Isolating valves will be located at junctions and will be installed underground with an extension spindle and surface box.

Section valves should be located every 2 or 3 km along main pipelines. Whenever possible the section valves should be placed in a joint valve chamber with air valves or washouts and upstream of these valves.

2.3 STRUCTURAL DESIGN STANDARDS

2.3.1 General

The basic premise upon which all structural elements will be designed is that they will each be capable of resisting applied loads without any appreciable deformation; and that they will be generally robust and durable. Therefore the design will include calculations of, or other means of assessing and providing resistance against, the moments, forces, and other effects on the structural members. The purpose which the design will achieve is that all structures will fulfil their intended function, that they will be economical and that they will be safe to use.

To achieve these objectives and to ensure that the design is sound, trusted and tested standards codes of practice will be used. British standards have been used extensively especially in structural design. We propose to take this approach in our design process.

2.3.2 Design Codes and Data

The following design codes will be used:

• BS 8110 (1985) British Standard – Structural Use of Concrete – Part 1. Code of practice for design and construction.

• BS 5337 (1976) British Standard – Code of Practice for the Design of Water Retaining Structures

• BS 5950 : (1988) British Standard – Structural Steel Design

• CP 3 : (1972) British Standard – Code of Basic Data for the Design of Buildings

In addition other design data to be utilised will be:

• Handbook to BS 5337 : 1976

• Handbook to BS 8110 : 1986



2.3.3 Loading Conditions

The following loading conditions will be applied for the structural design elements:

• Water density equivalent to 9.81 kN/m3.

• Reinforced concrete density equivalent to 25 kN/m3.

• Wind speed 4 m/sec

• (Water temperature as ambient).

2.3.4 Exposure Conditions

The following exposure conditions will be applied for the structural designs:

• Moderate (external)

• Mild (internal)

In relation to the above exposure conditions, the following factors will be taken into account

a) Although the top internal surfaces are subject to alternate wetting and drying, the flexural stresses at this level are very low.

b) The limit state designs which will be followed use concrete thicknesses less than 225 mm, and exposure therefore applies both internally and externally.

2.3.5 Foundations The following will be considered in the design of foundations:

• The loads of the structure must be transferred to soil layers capable of supporting them without failing.

• The deformations of the soil layers underlying the foundation should be compatible with the deformations which the foundation itself and its super structure, as well as adjoining structures, can safely undergo.

• Construction operations must not affect safety and stability of adjoining structures.

2.4 STRUCTURAL CRITERIA

2.4.1 Limit States

Each structural member will be appropriately analysed. Thereafter it will be necessary to determine the internal forces caused by the external loads it will carry, to select the cross-sectional area required to withstand these forces, to choose the cross-sectional area of junction elements (if several members are assembled to form a single entity), and to determine the necessary volume of reinforcement (if the member is made of reinforced concrete). This will be done to ensure adequate behaviour of the structural members during the entire service life at a minimum cost and minimum material consumption.

A structure or element will be deemed unfit for service, if:

• the internal forces in it exceed its ultimate strength, so that the material fails at the most heavily loaded sections, or some of the component members or the entire structure loses stability;



• the loads imposed on it lead to excessive deformations (such as sag, vibrations, or settlement) or cracks which may open which are wider than allowable.

In the course of structural design, it will be advisable to employ the load values and stress-strain relations recommended by element codes. The structures will be designed using limit-state approach - it clearly establishes the limit states of structures and sets up a system of design coefficients which guarantee that a structure will not attain such states under the worst load combinations and at the minimum strength of the materials. The principal limit states to be considered are those of:

• ultimate strength, and

• serviceability.

Design in terms of ultimate strength will be carried out for all types of structures, whereas design in terms of serviceability (also called design in terms of the second category of limit states) will be done only for structures whose deformation may cause failure before the internal forces exceed the load-carrying capacity. Design in terms of serviceability for reinforced concrete structures will provide for a cross section that will not only prevent a structure from exceeding the limit of sag, but will also help to keep the width of cracks within the specified limits or even to avoid cracking altogether.

2.4.2 Design Factors These will be employed to allow for the variability in load and the mechanical characteristics of materials. They include:

• overload factors (partial safety factors in terms of load);

• safety factors (partial safety factors in terms of materials);

• service factors which will take into account some aspects of the material behaviour that cannot be allowed for explicitly in the course of design.

2.4.3 Characteristic and Design Loads and Strength

The loads that may be imposed on a structure in service are specified in the relevant codes. Such loads are known as characteristic loads. Design loads will be obtained by multiplying the characteristic values by appropriate overload (partial safety) factors. The relevant codes specify that the main parameter defining the strength of a material shall be its characteristic strength. This is established with allowance for the statistical variability of strength and will be taken as the least observable ultimate strength. The minimal level of confidence (confidence coefficient), as set by appropriate specifications for the characteristic strength, is 0.95. The design strength of a material will be obtained by dividing the respective characteristic strength by an appropriate safety factor.

The values of the characteristic strength, safety factors, service factors, and design strength of the materials used in reinforced concrete, steelwork and masonry structures can be found in appropriate codes and specifications as listed above.



3 TRANSMISSION AND DISTRIBUTION PIPELINES

3.1 OVERVIEW

In the town centre, GIZ had previously implemented an initial distribution system consisting of the Hai Gabat borehole, feeding a closed-type water kiosk and a public tap directly.

This network consists of HDPE OD 110 pipes exclusively, laid in recent past. There is no distinct separation between water transmission and water distribution.

The proposed water supply system will separate water transmission lines (from boreholes to the tank) and the water distribution system (from the tank site to the consumers).

For all new water lines, it is recommended to use High Density Polyethylene pipes for diameters up to OD 315. Pipelines are designed to be covered by 0.9 m of soil. At locations where the route is subjected to vehicular traffic, the minimum cover should be increased to 1.2 m. If shallower depths are encountered due to natural ground profiles, concrete protection for pipes shall be provided.

To minimise social and environmental impacts and construction costs, all proposed pipelines will follow existing roads.

All new transmission and transmission pipelines will be equipped with air valves of the anti-shock anti-surge type (e.g. Vent-o-mat RBX double acting 25 mm or equivalent) and washouts will be placed at the most advantageous locations. For flow measurement, strainers are inserted with bulk meters at the boreholes and tank outlets.

Chlorination is not considered, as the only available contact tank is the elevated steel tank. If needed, due to the network design of separating distribution and transmission system, this can be considered when extension of Hai Gabat tank site is scheduled.

3.2 PRESENT AND FUTURE WATER PRODUCTION

3.2.1 Existing Hai Gabat Borehole GAB-BH-10

This borehole was drilled in May 2010 down to 143 m and has an inner diameter of 200 mm (8’’). It is currently the only water source for the two kiosk water supply system mentioned above.

It is reported that this borehole was mounted with a new pump in February 2012. The latest information indicates a pump rate of 19.0 m³/h.

3.2.2 Future Luzira Borehole LUZ-BH-1

The Luzira borehole was also drilled in the middle of 2010, featuring the same diameter as the Hai Gabat borehole. It is reported to be 89 m deep and yielded about 60 m³/hour during test pumping.

This borehole is currently awaiting pump installation to contribute water to the expanded water distribution system. The proposed pump is estimated to discharge 19.0 m³/h.

3.3 WATER CONSUMPTION The proposed design aims to extend the existing distribution system by:

• four additional kiosk to a total number of 6

• a tanker filling station at Hai Gabat tank site



Another water consumer will be the upcoming public ablution block at the market place.

3.4 PROPOSED WATER TRANSMISSION SYSTEM

The proposed transmission system consists of two separate pipelines, one for each borehole and both discharging to the Hai Gabat tank site.

Annex 2 contains the full set of drawings of the proposed water transmission. The profiles have been derived from elevations captured on-site by geodetic GPS system, benchmarked to officially known elevation points.

3.4.1 Reconnecting the Existing Hai Gabat Borehole Pipeline

The existing HDPE OD 110 line south of Hai Gabat borehole, about 220 m and currently part of the distribution system, is proposed to be turned into a rising main for the Hai Gabat borehole. Apart from diameter, pipe material and approximate location, not many more details are known. But as this pipeline was laid in the recent past and transmitted the borehole water to the kiosks, it is assumed that the existing pipes are in good condition, of an appropriate pressure class and have the necessary fittings to be converted to a dedicated line to the elevated water tank.

3.4.2 Construct New Pipeline for Luzira Borehole

Construction of a new pipeline, about 2.3 km from Luzira borehole to the tank site is proposed. For a steady flow of 19 m³/h, according to the estimated Luzira borehole pump discharge rate, a HDPE (PN 16, SDR 11) pipe of OD 110 is sufficient to keep the velocity and therefore the head losses (calculated at about 0.80 m at 19 m³/hour) at an appropriate level.

The borehole outlet will feature air valve, wash out and bulk meter installation. Tank inlet should be equipped with a float valve, signalizing the borehole pump to stop when the tank is full. A pressure sensor/switch will be needed at the borehole pump.

3.5 PROPOSED WATER DISTRIBUTION SYSTEM

3.5.1 Demand Assumptions

For each kiosk, 1,200 separate customer visits are estimated daily, drawing 20 l/customer/day1 each. A constant discharge pattern (factor 1) is set during the opening times (12 hours the day) for the kiosks. Hourly or daily/seasonal peak factors are not considered.

These settings result in about 2 m³/hour output per kiosk, serving 100 customers per hour, every day. A transient inflow of 0.55 l/s will be necessary to each of the kiosks. Taking some buffer capacities into account, a demand of 1 l/s per kiosk is considered for the design of the distribution system pipe diameters.

The public latrines water consumption is limited to flushing, taking a shower and washing hands. An OD 110 pipeline will provide sufficient water supply.

The tanker filling station will be supplied directly from the elevated tank using an OD110 pipe.

1 Feasibility Study for Yei, Gauff, 2011



3.5.2 Pipeline Design

The proposed distribution system design considers future connections of additional kiosks along the pipeline to kiosks 4, 5 and 6. Hence a universally applied diameter of OD 110 was determined for distribution and transmission mains. The distribution system has been modelled using Bentley’s WaterGEMs software. This model also includes scenarios for the future additional kiosks. Simulation results are available in a separate document, generated by the Software.

The reported maximum velocities for the maximum demand scenario range from 0.15 to 1.0 m/s. Due to the transmission-main-like character of the pipelines (no off-takes along the pipeline but at their ends) it was deemed necessary to include washouts along the lines for flushing (although the diameters are relatively small).

4 WATER KIOSKS AND PIPELINES

Eight different types of water kiosks and public stand posts were proposed and eventually the following types were selected:

• Closed In-Situ Water Kiosk

• Roofed Public Stand post (3 taps) with tank

• Roofed Public Stand post (6taps)

These water kiosks and stand posts will be supplied from the Hai Gabat tanks through distribution lines which are aligned to follow existing or planned roads as much as possible to minimise compensation costs and facilitate easy access to the lines and fittings. The minimum cover to the pipes will be 0.9 m, but where the pipe is subjected to vehicular traffic the minimum cover shall be 1.2 m. If shallower depths are encountered due to natural ground profiles, concrete protection for pipes shall be provided. Maximum cover to PE pipes shall not exceed 3 m.

Whenever a pipeline changes direction horizontally or vertically or changes size, concrete thrust blocks shall be provided to resist the force in the piping system.

In order to manage water consumption and prevent wastage, all water kiosk connections will be metered. Large volume consumers (e.g. schools, clinics, kiosks) require large sized DN 20 meters. It is proposed that pipe saddles (which can clamp over the HDPE pipes) and limited lengths of DN 20 HDPE pipes (about 20 m per connection) be allowed for.

With regard to the location of the kiosks initial proposals have been made based on findings in the field and technical considerations. However, before any kiosks are constructed it will be necessary to reconfirm these locations in conjunction with the potential consumers and the local authority, and preferably these will be on public land to avoid any land compensation costs.

All the kiosks are to be provided with concrete drains to allow for efficient drainage of water into a drain/ soak pit.

Details of the Water Kiosks are shown in Annex 3 Drawings No. YEI/WAT/WK/1.0-4.0



5 WATER TANKER FILLING STATION

Water from the storage tanks will be used to supply a tanker filling station. The tanker filling station will be located next to the tank site and will utilize an overhead truck fill arm for filling the tankers. This design will provide for no cross contamination during or after filling the truck.

Adequate provision for drainage must be considered since a lot of water may spill to the ground during the filling process. This will be addressed by the side drain on the side of the road.

The access road should consider that the water tankers are wide and heavy vehicles and can quickly damage poorly constructed roads. The geometric design will therefore consider the size of the trucks and most efficient traffic flow, while the structural design will consider the corresponding load at the station.

The water tanker filling station has been designed as a single DN 100 steel pipe serving as an overhead truck filling arm supported on a 203x133x25 universal beam. A flexible hose is then connected to the end of this pipe using a hose adaptor and delivers water to the truck that is parked beneath the filling arm. The water supplied to the tankers is verified using a DN 100 bulk water meter located in a chamber.

The filling station will be in a bay next to the road and has been provided with a reinforced concrete slab base due to the heavy loads exerted by the loaded water bowsers and also due to the water exposure that the ground would be subjected to. The slab will be sloped at 2.5% to the side to drain off any water that is spilled on the ground.

The layout of the Water Tanker Filling Station is shown in Annex 3 Drawing No. YEI/WAT/TFS/1.0



6 ABLUTION BLOCK WITH BIOGAS UNIT

The ablution block aims at improving the quality of life of the community by improving their sanitary conditions. It includes 5 Asian type toilets for each gender, each of which has a single toilet for the disabled. A shower place is also provided for each gender.

The ablution block as per the TOR will incorporate a bio-digester unit which will facilitate the use of biogas as an alternate energy source as well as the production and utilization of pathogen-free stabilized manure (bio-fertilizer) from faecal sludge to improve soil fertility.

The biogas unit utilises anaerobic digestion technology which is one of the appropriate methods for treating human waste wherein more than 95% of the pathogens found in human faeces get killed in the process. Fixed dome type of bio-digester have the advantage of relatively low construction costs, absence of moving or rusting steel parts, long life span if well-constructed, space economy, protection from temperature changes since it is constructed underground and it provides job opportunities for skilled locals.

Two compost pits will also need to be constructed close to the bio-digester for collection, treatment and utilization of slurry as fertilizer. The construction of two compost pits permits the filling and emptying each pit by turn. Thus, in case the first pit is filled in completely, it is left to dry for couple of weeks during which time the second one is in use.

The biogas units utilises anaerobic digestion technology which is one of the appropriate methods for treating human waste wherein more than 95% of the pathogens found in human faeces get killed in the process. When sizing the Biogas Unit, the characteristics of the waste produced and viable gas yield has to be assessed as shown in the table below.

Table 6-1: Characteristics of waste produced and co rresponding viable gas yield 2

Manure Urine

(% lw)

Dry Mass (DM)

(% of Manure)

Organic Dry

Mass (ODM) (%

of Manure)

Liveweight

(lw)C/N Gas Yield

(kg/day) (litres) (kg) (kg) (kg) (l/kg ODM)

Cattle Manure 8 5 16 13 135-800 10-25 250

Pig Manure 2 2 16 12 30-75 9-13 450

Sheep/Goat Droppings 1 3 30 20 30-100 30 200

Chicken Manure 0.08 4.5 25 17 1.5-2 5-8 460

Human Excreta 0.5 1 20 15 50-80 8 450

Animal Species

Using the above considerations, the volume of the Biogas unit can be determined. While calculating the net volume (VBP) of fixed-dome biogas plant, three distinct volumes are considered:

• the dead storage capacity (VDSC),

• the volume for gas storage (VG) and

• the volume for recommended hydraulic detention time (VD)

2 Small Scale Biogas Sanitation Systems, NETSSAF, 2006



Figure 6-1: Fixed Dome Biogas Units

For ease of calculation dead storage capacity (VDSC) is not considered, but it is assumed that the conically shaped bottom to the digester compensates for dead storage capacity.

The volume of a half round biogas plant can be determined by the equation for calculation of the volume of a hemisphere (VHSP):

VBP = (VG + VD) = VHSP = (2R3 π) / 3

Hence, on rearranging the equation you can calculate the halfmeter/ radius (RBP) of the fixed dome plant as:

RBP=((3(VG + VD) / (2 π))1/3

In fully mixed continuous digesters the retention time should be at least between 80 to 100 days to allow safe re-use of the effluent).

The net volume of the compensation tank (VCT) equals the gas storage capacity (VG) and is calculated by subtracting the volume of the free space above the overflow (RCT – H) from the volume of the hemisphere.

VCT = VG = 2RCT 3 π3 − [(RCT − H)2π �RCT − RCT − H

3 �]

The radius (RCT) of the compensation tank can be calculated from the equation above.

Maximum gas pressure occurs at a level P below the overflow level of the compensation tank, which is also the lowest slurry level. For calculation of level P the equation of the spherical calotte volume is applied to the total volume of the free space above maximum slurry level and the net volume of the compensation tank (VCT).

P

H



P2π �RBP − P3� = H2π �RBP − H

3� + VCT

Considering an approximate 100 people visit the ablution block, and the faecal excreta per person per day being 0.5kg, the bio-digester unit has been sized at 50m3. It is a fixed dome bio-digester that has been provided together with an expansion chamber.

Two compost pits sized at 7m long by 3m wide by 1.2m deep each have also been provided close to the bio-digester for collection, treatment and utilization of slurry as fertilizer. To make potent and easy-to-use fertiliser, the compost pits should be filled with agricultural residues together with slurry from the plant. It is recommended to construct a shade above the pits to avoid direct sun light. This shade could be used for growing vegetables with vines

Details of the volume and unit sizing calculations are shown in Annex 1 while the details of the ablution block and bio-digester are shown in Annex 3 Drawing No. YEI/SAN/AB/1.0



7 SEPTIC TANKER DISCHARGE BAY

Used for the emptying of vacuum tankers, “honey suckers”, septic tanker discharge bays consist of sludge drying beds. Digested sludge from septic tanks contains a lot of water and should therefore be dewatered or dried before further disposal in a landfill or used as soil conditioners/manure for planting of trees (not vegetables).

In favourably hot environments, sludge drying beds provide a suitable method for drying sludge. They are open beds of land having some filter media on which the digested sludge is spread on top. Most of the moisture drains through the filter media and is collected by under drains, whilst a portion of it is evaporated to the atmosphere. It usually takes about two weeks to two months for drying of the sludge, depending on the weather and condition of the bed.

The sludge drying bed area is usually based on the following:

a) Volume of sewage produced by existing and proposed people having septic tanks

b) Thickness of wet sludge spread on the drying bed

c) Times in a year the Sludge drying bed is utilised (loading and resting cycles)

d) Adopted size of a single sludge drying bed

A combination of the above will result in drying bed areas in the range 0.1 to 0.2 m2 per capita.

Open sludge drying beds should be located at least 100 m from dwellings to avoid odour nuisance.3

Unit Components

a) Piping: Piping to the sludge beds should be design for a velocity of at least 0.75m/s. Cast iron or uPVC pipes are normally used and should be provided together with distribution boxes with penstocks to divert sludge flow into the drying bed in use. Splash plates should also be placed in front of the sludge outlets to spread the sludge over the bed and to prevent erosion of the sand.

b) Filter Media: The sand layer should be from 200 to 300mm deep with and allowance for loss due to cleaning operations. The sand should also have a uniformity coefficient of not over 4 and an effective size of 0.3 to 0.75mm. An adequate layer of coarse gravel or crushed stone should be provided beneath the sand layer to support and cover the drainage lines beneath. A layer of geotextile material is provided between the sand and gravel. The effective size of gravel should be between 3-6.25mm. A thicker sand layer secures a good filtrate and reduces the frequency of sand replacement caused by losses from cleaning operations but generally retards the draining process.

c) Outlet Facilities: Since most of the water leaves the sludge by drainage, lateral under drains of either perforated uPVC pipes or vitrified clay pipes laid with open joints sloped at a minimum 1% and spaced 2.5 to 6m apart should be provided.

3 Wastewater Engineering Treatment and Reuse, Metcalf and Eddy.



d) Walling: A 200mm thick reinforced concrete wall can be been provided. This wall is water tight and has to be sealed at its joint with the base slab using bituminous seal.

e) Sludge removal facilities: A vehicle or wheelbarrow ramp can be been provided on the outlet side of the drying bed to be used to access the sludge drying beds. Provision should be made for driving a truck onto or alongside of the bed to facilitate loading of the dried sludge. In order to prevent unauthorised access to the sludge beds the area will be fenced. A gate house can be provided for at the entrance of the site.

The design of the sludge drying beds has been based on the volume of wet sludge as being 75% of the water demand, while the percentage of people with septic tanks has been approximated at 0.2% of the population4. The thickness of the wet sludge layer is 225 mm and the time required for wet sludge to dry has been averaged at 14 days.

The size of a single sludge drying bed is 17.5m by 9.3m and is fitted with OD 110 perforated uPVC drain pipes spaced at 750 mm c/c.

The advantages of sludge drying beds are; low cost of construction and operation, infrequent attention required and high solids content in dried product. Its disadvantages are: effect of climate changes on drying characteristics, labour intensive sludge removal (although this can double as an advantage also), insects and odours.

Details of the volume and unit sizing calculations are shown in Annex 1 and the details of the septic tank discharge bay are shown in Annex 2 Drawing No. YEI/SAN/DB/1.0

In operation, the wet sludge should be applied to the beds to depths of 200-300 mm and allowed to dry by drainage through the sludge mass and supporting sand and by evaporation from the surface exposed to air. The beds should not be filled to the brim.

The wet sludge should also be applied to partitioned individual beds of convenient size so that one or two beds will be filled in a normal loading cycle.

Drained and dried sludge which is characteristically black or dark brown with a coarse, cracked surface should be removed from the bed using rakes or forks and shovels or scrapers into wheelbarrows or trucks. The sand layer should be examined for clogging by organic matter and if found so, the entire sand should be removed and the bed re-sanded to the original depth. The water collected by the under drains is then directed to the percolation trench from which it percolates to the ground.

Records of operation of sludge drying beds should show the time and quantity of sludge drawn to each bed, the depth of loading, depth of sludge after drying time and the quantity of sludge removed.

The operation of the sludge drying beds requires the operators to always check that the flow from the under-drainage is present and clear. Maintenance steps should be undertaken when there is no flow or when the flow is not clear.

4 GITEC/GFA Feasibility Report page 27&28



8 SEPTIC TANK FOR SLAUGHTER HOUSE

Slaughterhouse wastewater flows and characteristics is dependent on the number and type of animals processed, and housekeeping practices such as flushing of the work surfaces and floors with water to clear off waste materials from the slaughtered animals. As much as is possible, blood should be carefully collected and disposed of separately from the wastewater. This is because blood itself can have BOD values of about 100,000mgL−1.

It is estimated that for every cow and pig processed, 700 and 330 litres of wastewater are generated, respectively, with an increase of 25% if further processing is carried out to produce edible products. It is also estimated that an average of 50 animals are slaughtered daily.

Screens will need to be located at the beginning of the treatment train to ensure gross particles like hair, feathers, and discarded parts of the slaughtered animals do not enter the septic system

Slaughterhouse wastewater quality depends on a number of factors, namely:

1. Blood capture: the efficiency in blood retention during animal bleeding is considered to be the most important measure for reducing biological oxygen demand (BOD)5

2. Water usage: water economy usually translates into increased pollutant concentration, although total BOD mass will remain constant;

3. Type of animal slaughtered: BOD is higher in wastewater from beef than hog slaughterhouses 6

4. Amount of rendering or meat processing activities: plants that only slaughter animals produce a stronger wastewater than those also involve in rendering or meat processing activities7

Septic tanks are most commonly used to treat sewage from individual households. In this project the septic tank is to treat wastewater from the slaughter house. The septic tank will have two compartments so that solids re-suspended from the sludge layer in the first compartment by peak flows settle again in the more quiescent second compartment. The overall effective tank volume (V, m3) will be divided into approximately two-thirds for the first compartment and one-third for the second.

Design of septic tanks considers four main active zones:

• scum storage zone,

• sedimentation zone,

• sludge digestion zone, and

• digested sludge storage zone.

5 Materials flow and possibilities of treating liquid and solid wastes from slaughterhouses in Germany. Bioresource Technology. Tritt

and Schuchardt 1992 6 Materials flow and possibilities of treating liquid and solid wastes from slaughterhouses in Germany. Bioresource Technology. Tritt

and Schuchardt 1992 7 Developments in wastewater treatment in the meat processing industry: A review. Bioresource Technology. Johns, 1995.



Scum accumulates at approximately 30 – 40 percent of the rate at which sludge accumulates, so the tank volume for scum storage (Vsc, m

3) can be taken as 0.4Vsl (sludge volume). V = P (Q + 0.1 x S1/2) Where;

P = Contributing Population Q = Flow per capita per day in m3 S = Years between desludging (approx. 0.1m3 sludge is accumulated in one year

per person and only a maximum of 10 years should be provided)

Sludge and scum accumulation is a function of the desludging interval and could vary between 0.09 to 0.15m3/hd.yr. (Refer to the 0.1m3 in the above formula). However, the volume of accumulated sludge and scum reduces with time due to progressive digestion and compaction. It is thus roughly proportional to the square root of the years of operation as indicated in the above formula8

A rectangular shape is preferred, with a length-to-breadth ratio in the range of 2:1 to 3:1. Liquid depth of the tank should be at least 0.9m, but not more than 2m, except in cases where the tank is a communal septic tank serving several households. The inlet to the tank should be the same size as the incoming connection. Sanitary tees are often used as baffles both at the inlet and outlet. The tees are extended at least 150mm above the liquid level in order to avoid the scum layer and down to around 30 – 40 percent of the liquid depth. The outlet is usually at a lower level to provide some surge storage and prevent standing of solids. Normally a drop of 75mm is recommended. A freeboard of 300mm should be provided for scum storage and ventilation.

Manholes (600 – 900mm) must be provided for removal of accumulated sludge and scum while an inspection port is provided above the inlet and outlet to facilitate cleaning of the baffle if blocked. To attain structural integrity, soil and hydrostatic loading should be taken into consideration. The World Bank recommends the following minimum distances of Septic Tanks and Soakaways in common well developed soils from the features listed:

Table 8-1: Minimum distance of septic tanks and soa kaway

Item Septic Tank (m) Soakaway (m) Buildings 1.5 3.0 Property boundaries 1.5 1.5 Wells 10.0 10.0 Streams 7.5 30.0 Cuts or Embankments 7.5 30.0 Water pipes 3.0 3.0 Paths 1.5 15.0 Large trees 3.0 3.0

It is also recommended that the tank be located near to a driveway to allow for emptying by means of a vacuum tanker and also from a health point of view to have a soil cover of 150 to 200mm over the system.

8 Process Design Manual for Small Wastewater Works.



8.1 SOAKAWAYS AND DRAINFIELDS

Effluent from septic tanks is highly contaminated and, unless piped to a sewer, should be discharged via soakaways or drainfields, pits or trenches with permeable walls and bases. A soakaway pit may be filled with rubble or other large granular material. Drainfields consist of a series of drains that act similar to soakaways. The soakaway or drainfield should provide the required area of contact surface with soil to permit the percolation of liquid into the soil. The size and dimensions of a soakaway pit or drainfield depends on the soil type. Based on Central African Standard (CAS 1959) the following table has been compiled.

Table 8-2: Percolation rating

Percolation Rating

Minutes

Types of Soil Probable Classification

Soil Suitability Soak-away Wetted Area m 2/m3/day

0.25 Coarse sand or gravel Excellent 12.5 1 Well graded sand Very good 22.2 2 Fine sand and silt Good 33.3 5 Silty sands, sandy loams Good 66.7

10 Clay with considerable sand or gravel Fair 77.0 15 Clay with some sand or gravel, clay

gravel, clay loams Fair 100

30 Clay with some silt and sand fractions Fair to Poor 125 60 Clay, heavy clay Bad -

The soakage rate refers to wetted area. For drain field design in this project, only vertical faces will be considered effective in contributing to the infiltration surface area.

Trenches adjacent to each other should be constructed with a minimum distance of twice the depth and the sides roughened to restore the natural surface. The filling material should be clean and free from silt or dust and can be from 6mm to 75mm. The trench should be filled with gravel to about 100 – 150mm from the top with a layer of finer gravel placed on top to prevent entry of soil. On average the trench should be approximately 4 meters for every cubic meter of water.

Details of the volume and unit sizing calculations are shown in Annex 1 and the details of the septic tank are shown in Annex 2 Drawing No. YEI/SAN/ST/1.0



9 CONSTRUCTION PLANS

The proposed split of the works presented below is based on considerations such as scheduling, local construction capabilities, availability of materials, and possibility of contractor achieving cost savings by consolidating the purchase of similar materials to be used for similar works in different locations.

• Contract 1 – Water Kiosks

• Contract 2 – Transmission and Distribution Pipelines

• Contract 3 – Water Tanker Filling Station

• Contract 4 – Public Ablution Block, and Bio-digester

• Contract 5 – Septic Tanker Discharge Bay

• Contract 6 – Slaughter House Septic Tank

The work plan for construction works is divided into three main time frames:

1. Tendering Evaluation and Contracting – 3 Months

2. Construction and Supervision of Works – 12 Months

3. Defects Liability Period – 12 Months

Following the successful evaluation of bids and award of contract to respective contractors, the works will commence as indicated in the schedule for implementation of works shown overleaf.



Wat

er a

nd S

anita

tion

Pro

ject

, Yei

, Sou

ther

n S

udan

Wor

k P

lan

star

t

12

31

23

45

67

89

1011

121

23

45

67

89

1011

12

A.1

Ten

derin

g &

Eva

luat

ion

& C

ontr

actin

g3.

00

1.1

tend

er p

erio

d1.

50

1.2

eval

uatio

n &

rec

omm

enda

tion

0.50

APP

RO

VAL

by G

IZ a

nd a

war

d/ s

igna

ture

1.00

A.2

Con

stru

ctio

n an

d S

upe

rvis

ion

of W

orks

12.0

0

2.1

pre-

cons

truc

tion

serv

ices

/ pro

cure

men

t1.

00

2.2

wat

er k

iosk

s4.

00

2.3

tran

smis

sion

mai

n5.

00

2.4

dist

ribut

ion

pip

elin

es7.

00

2.5

wat

er ta

nker

filli

ng s

tatio

n 4.

00

2.6

publ

ic a

blut

ion

bloc

k an

d bi

o-di

gest

er8.

00

2.7

sept

ic ta

nker

dis

char

ge b

ay10

.00

2.8

slau

ghte

r ho

use

sept

ic ta

nk9.

00

2.9

trai

ning

of o

pera

ting

staf

f3.

00

2.10

com

mis

sion

ing

of c

ompl

eted

wor

ks4.

00

A.3

Def

ect

s Li

abili

ty P

erio

d12

.00

3.1

mon

itor

mai

nten

ance

per

iod

12.0

0

3.2

final

insp

ectio

n &

han

ding

-ove

r0.

50

CO

MP

LET

ION

AN

D S

UB

MIS

SIO

N O

F R

EP

OR

TS

No.

Rep

ort

Dat

e1

23

12

34

56

78

910

1112

12

34

56

78

910

1112

1P

rogr

ess

Rep

orts

mon

thly

& q

uart

erly

dur

ing

impl

emen

tatio

n

2D

raft

Fin

al R

epor

t/ O

&M

/ dw

gs1

mon

th a

fter

com

plet

ion

cert

ifica

te

3F

inal

Rep

ort

1 m

onth

afte

r co

mpl

etio

n

Lege

nd:

Sum

mar

yF

ull T

ime

Mile

ston

es

App

rova

l Tim

eIn

term

itten

t Act

ivity

Rep

orts

Implementation Supervision and Maintenance Period

PH

AS

E 3

ACT

IVIT

IES

AN

D T

ASK

SA

.1A

.2A

.3D

urat

ion

(mon

ths)



10 ENGINEER’S COST ESTIMATES FOR THE WORKS

Estimated costs are presented in Euros and are based on:

• General price level in East Africa known from other projects

• Quotations received from suppliers and contractors in Kenya

• Rate of exchange 1 Euro = 110 KES

• Costs exclude taxes and duties

The estimated project costs are given in the table below.

Contract Description EUR

Contract 1 Water Kiosks 16,949.29

Contract 2 Transmission and Distribution Pipelines 212,693.18

Contract 3 Water Tanker Filling Station 12,030.14

Contract 4 Public Ablution Block, and Bio-digester 33,441.75

Contract 5 Septic Tanker Discharge Bay 176,782.65

Contract 6 Slaughter House Septic Tank 26,945.59

Sub-Total 478,842.60

Add 10% Contingencies 47,884.26

Total 526,726.86

Table 10-1: Cost Estimate

The detailed engineer’s estimates for the works being designed are provided in Annex 3.


Gauff Ingenieure 3

Annex 1 – Design Calculations


Gauff Ingenieure 4

Annex 2 – Drawings


Gauff Ingenieure 5

Annex 3 – Engineer’s Estimate

Documents

Gauff Design Report - 05-2012 · b) To design pipeline route from Luzira borehole to elevated water tanks including hydraulic design, plan and profile drawings, technical specification