JESC SEMINA

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APROJECT SEMINAR

ON

DRAINAGE DESIGN AT CRUTECH STAFF QUARTERS

BY

IFERE, JESAMEDET

06/CEN/057CIVIL ENGINEERING DEPARTMENT

DEPARTMENT OF CIVIL ENGINEERINGFACULTY OF ENGINEERING

CROSS RIVER UNIVERSITY OF TECHNOLOGY CALABAR.

IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THEAWARD OF THE DEGREE OF BACHELOR OF ENGINEERING

(B.ENG.) IN CIVIL ENGINEERINGOF THE CROSS RIVER UNIVERSITY OF TECHNOLOGY

CALABAR

AUGUEST, 2011


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CHAPTER ONE

1.0 INTRODUCTION

1.1 DRAINAGE

.

There are several concerns about the sustainability of irrigation

and drainage project, and there are water quality project

related to the disposal of drainage water. There are also

problems with land degradation due to irrigation induced

salinity and water logging. There have been instances where

saline or high nutrient drainage water has damaged aquatic

ecosystems. Drainage had continued to be a vital and

necessary component of agricultural land and other areas

thereby excesses water is dispose from the surface. Drainage is

the process by which water or liquid is drained from an area of

land. It is also termed as the provision of adequate drainage

facilities to convey excess surface and sub-surface water

across, along or away from the ground, from the roofs of

buildings, from pavements etc. Inadequate drainage facilities or

slow drainage of water can lead to a lot of aesthetical,

environmental and physical health hazards and the

deterioration of the ground surface.

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Surface drainage involves the removal of water mostly from

rain or melting snow that falls directly on the road and

interception and removal of waters coming to the road on the

adjacent terrain. Sub-surface drainage is concerned with the

removal of water from the sub-grade and with interception of

underground water coming to the sub-grade.

Various types of facilities are used for drainage of surface and

sub-surface water. The design of such facilities involves the

following:

i. Hydrological analysis estimating the peak rate of run-

off to be handled;

ii. Hydraulic design selecting the types and sizes of

drainage facilities to most economically accommodate

the estimate flow from the hydrological studies; and

iii. Making sure that the design does not create erosion

and our environmental problems.

1.2 STATEMENT OF PROBLEM

Surface run-off constitutes a lot of problem to any environment

if not properly checked. It damages among other things include

destruction of the natural environment. Weakening of

structures foundation, destruction of access way and even

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promoting health hazard such as the proliferation of

mosquitoes which in turn causes malaria. Despite the fact that

the Universitys town campus is situated on a nearly flat

terrain, erosion has been one of the natural problems faced by

the institution. This has led to the rapid expansion of ravines

nearer the Administrative block of the school and recently the

structural defeat in the boys hostel. From the prelim nary

survey, (through physical inspection and one on one interview),

it was discovered that this problem was either caused by the

inadequate provision of drain and the wrong drain size. There

was a deliberate attempt to discharge the run-off against the

natural slope which consequently introduced waterlog problem

in the affected catchment area, most sections of the existing

drains were exaggerated because there was no appropriate

design work carried out before the actual construction of the

drain, which could have possibly led to the cost of construction

being higher than normal. There is also the problem of

inadequate provision of drainage facility around the catchment

where the female hostel is situated. Aside from being

aesthetically displeasing, the waterlog portions of the drains

also breeds a lot of mosquitoes around the vicinity. This and

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many more inspired the writer to research into the possible

cause of these problems and consequently arrived at an

optimized and most economical design of the drainage systems

at CRUTECH town campus.

1.3 OBJECTIVE OF THE PROJECT DESIGN

This design project among other things is aimed at:

i. Determining the cause of waterlog in some parts of the

campus

ii. Determining where a new drainage structure or system

can be cited

iii. Designing the best economical section for the design in

order to ease these problems and economize the

materials.

1.4 SIGNIFICANCE OF THE PROJECT DESIGN

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This design shall when implemented solve the drainage

problem in the Campus, because of its most economic design.

1.5 LIMITATION OF THE PROJECT

Stress and inadequate finances may be the major challenges

faced by the designer during the design process which involved

data collection, analysis and design. This however did not in

any way affect the design procedures.

1.6 DELIMITATION OF THE PROJECT

The designer decided to use the available 1: 250000

topographic map of Calabar south local government area to

obtain from the physical planning unit of the institution to

delimit the catchments area for the drainage design. With the

aid of the pre-defined survey boundary dimensions and a 50m

measuring tape, the catchments area was delimited having

estimated catchments of approximately 0.11km2, 0.21km2 and

0.31km2 and the length of the longest watershed being

229.47m, 816m and 410m.

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CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 BRIEF HISTORY

Drainage is believed to have started in Rome during the 3rd

century AD. This was when the Roman needed a way of

discharging waste water from their bath away from home. This

problem eventually led to the development of drainage

systems in Rome. Wikipeida, (2009).

According to Aguambah, (2001), drainage is the disposal of

excess water on land before they enter the stream. He went

further to classify drainage into Municipal, Land and Highway

drainage.

Professor Temiloye M. Aguala, Department of Civil engineering,

Rivers State University of Science and Technology also noted

that there are both surface and sub-surface drainage and the

design of such facilities involves the following:

i. Hydrological analysis, ii. Hydraulic analysis and design,

and iii. Economic of design. See figure 1 in the

Appendix.

2.2 HYDROLOGICAL ANALYSIS

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A hydrological analysis of the area to be drained is an essential

element in the design of drainage. Hydrological study supplies

the information on runoff and stream flow characteristics which

is used as a basis of hydraulic design.

The design flow is established by selecting the proper

combinations of rainfall and runoff characteristics that can be

reasonably expected to occur. This is usually further restricted

by establishing an interval of time or frequency period as a

basis of the design Temiloye M. Oguara, (2006). The design

criteria would then be the maximum flow carried by the

drainage structure with no

flooding or limited amount of flooding to be exceeded on the

average of once during a design period. The hydrological data

for estimating flood discharge for the drain design is yet to be

shared

2.3 METEOROLOGICAL STATION CONSTANTS, a, b, A and

B

The values of the constants have been determined by the

meteorological department of Nigeria for Lagos, Kano and Ikeja.

These established constants are used as reference for other

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regime of similar rainfall characteristics. The values are shown

in the Table 5 of the Appendix.

The Ikeja constant will be adopted for this analysis because of

its characteristics extreme thunderstorm and the monsoonal

influence.

The annual rainfall for Ikeja regime (1308mm) is used as the

reference since it is situated on the same regime as the project

site, while that of project site is taken as 2482mm. see Table

2 in appendix.

2.4 RUNOFF ESTIMATES BY RATIONAL METHOD

The runoff estimate or design discharge depends on many

variables. Some of the more important variables are duration

and intensity of rainfall; size, slope, shapes and imperviousness

of the drainage area; and probable development of drainage

are Burke etal (1994).

In the rational method, the peak rate of surface flow from a

given watershed is assumed to be proportional to the

watershed area and the average rainfall intensity over a period

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of time just sufficient for all parts of the watershed to

contribute to the outflow.

Various empirical formulas for obtaining runoff are available,

but this should be used with discretion. One of the more

reliable is the rational method relating runoff to the rainfall

intensity, given by:

Q = 0.287CIA- - - - - - - - - -1

Where Q = Quantity of runoff in m3

C = Runoff coefficient, expressed as percentage of

imperviousness of the watershed or arte of runoff to rate of

rainfall.

I = Intensity of rainfall expressed in metres per hour for a

certain time of concentration

A = area of watershed in hectares

The basic assumptions used in rational formula are as follows:

(1) The rainfall is uniform over the watershed.

(2) The storm duration associated with the peak discharge is

equal to the time of concentration for the drainage area.

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(3) The runoff coefficient C depends on the rainfall return

period, and is independent of storm duration and reflects

infiltration rate, soil type and antecedent moisture condition.

The coefficient C, the rainfall intensity I and the area of the

watershed, A, are estimated in order to use the rational

method.

The runoff coefficient reflects the watershed characteristics.

Values of the runoff coefficient are found in drainage design n

annuals.

The assumptions inherent in rational formula are:

i. The maximum rate of runoff for particular rainfall intensity

occurs if the rainfall duration is equal or greater than the

time of concentration. The time of concentration is defined

as required for water to flow from the most distant point of

a drainage basin to the point of flow measurement.

ii. The maximum rate of runoff a specific rainfall intensity,

whgse duration is equal to or greater than the time of

concentration, is directly proportional to the rainfall

intensity.

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iii. The frequency of occurrence of the peak discharge is the

same as that of the rainfall intensity from which it was

calculated.

iv. The peak discharge per unit area decreases as the

drainage area increases, and the intensity of rainfall

decreases as its duration increases.

v. The coefficient of runoff remains constant for all storms on

a given watershed.

Although the basic principles of rational formula are mostly

applicable to urban areas with large drainage facilities of fixed

dimension and hydraulic characteristics, it simplicity and ease

of application have resulted in its being used in rural areas.

Suggested runoff coefficients C, for the rational method, given

in the Nigerian Highway Manual are as given in Table 3 of the

appendix. Where group cover is dissimilar or if different surface

types are used, it is often reliable to develop composite runoff

coefficient.

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2.5 CORRECTION FACTOR

The rational method of the quantity of flood estimation, ass

stated in equation 1 is true for catchment area exceeds. The

factor was derived by the work done by the Balasha-Jalons

consiltants (1977) on the Benin city Master Plan for drainage

scheme and can be applied for catchment area in sub-Sahara

region in Africa.

Correction factor = 1/e (1-12/Am)

Where, Am = require catchment area

Therefore, e = 0.38

2.6 DESIGN STORM FREQUENCY

The design storm frequency adopted for this analysis purpose

is 25-years. A 25-year return period of flood is used to check

the minimum required dimension to avoid any possibility of

erosion menace.

2.7 GUIDES ON HYDROLOGICAL ANALYSIS OF DRAINAGE

In simple terms, the sum of the daily rainfall minus

consumptive use rate plus one minus the soil storage change is

the drainage need. In humid regions, the amount of

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precipitation will have a direct relationship to be quantity of

water to be drained. In arid and semi-arid regions, the annual

surface run-off from rain may range from about 0 to 200 mm

while the seepage, percolation and leaching in irrigation

schemes may range from 200 to 2000 mm. loses from irrigation

systems may be of great significance. Precipitation is of little

consequence and can most often be ignored in computing

drainage discharges.

Drainage practices then can be based on crop tolerance to high

groundwater tables taking into account soil and topography

and the natural drainage characteristics of the area.

Several semi-empirical methods for estimating run-off for

drainage design have been developed; they are given in most

standard handbooks on hydrology. A simple method is

described below; the method is rather empirical and only

provides first estimates on surface run-off for general planning

purposes.

Apart from rainfall characteristics, important factors influencing

rainfall run-off are the run-off potentiality of the area; the

antecedent moisture condition; the degree of vegetal cover;

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conservation practices followed. The peak flow rates are also

strongly dependent on slope of the land and area of the

watershed. The method includes the following steps:

Processing of rainfall data: by processing records of the daily

values of total rainfall probability values at any frequency, for

any given period, are obtained for the project concerned;

Run-off potentiality: the soils are to be grouped into one of the

four hydrological classes on the basis of their run-off

potentiality which is closely schedule to their infiltration rates.

2.8 FACTORSA THAT AFFECT SURFACE RUNOFF

i. WATERSHED

An area that drains into a stream at a given location via a

network of streams is called a watershed.

Rainfall that falls on a watershed fills the depression storage,

which consists of storage provided by natural depressions in

the landscape, it is temporarily stored on vegetation as

interception and it infiltrates into the soil. After these demand

are satisfied, water starts flowing over the land and this

process is called overland flow. Water that is stored in the

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upper soil ayer may emerge from the soil and join the overland

flow. The overland flow lasts only for short distances after

which it is collected in small channels called rills. Flows from

these rills reach channels. Flow in channels reaches the

mainstream.

When rainfall is of low intensity, the overland-rill-channel flow

sequence may not occur. In such cases, only the land near the

streams contributes to the flow. These areas are called variable

source or partial areas. Only a small area of watersheds

contributes to stream flow in humid region.

The transformation of rainfall to runoff is affected by the stream

network, by precipitation, by soil, and land use. A watershed

consists of a network of streams as shown in the figure above.

Channels that start from upland areas are called the first order

channels. Horton (1945) developed a stream order system, in

which when two streams of order (i) join together, the resulting

stream is of order (i + 1). There are several laws of stream

orders developed by Horton (1945).

If a watershed has Ni streams of order i and Ni+1 of order i + 1,

the ratio Ni/Ni+1 is called the bifurcation ratio RB, the ratio of

stream lengths Li+1 and Li belonging to orders i+1 and i the

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ratio of stream lengths RL, and the ratio of areas RA and RA+1

the area ratio. These ratios vary over a small for each

watershed. The drainage density D of a watershed is the ratio

of total stream length to the area of the watershed. Higher

values of D represent a highly developed stream network and

vice versa.

ii. RAINFALL

The second factor that significantly affects runoff is rainfall. The

spatial and temporal rainfall distribution and the history of

rainfall preceding a storm affect runoff from watersheds.

Rainfall is usually treated as a lumped variable because spatial

rainfall data are not commonly available.

iii. LAND USE

The third factor that affects runoff characteristics is the land

use. As watersheds are changed from rural to urban or from

forested to clear cut condition, runoff from these watersheds

charges drastically.

For example, when a rural watershed is urbanized, the peak

discharges from the urban watershed may be more than 100%

higher than runoff from the rural watershed for the same

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rainfall. The time to reach the peak discharge would also be

considerably shorter and the runoff volume much larger in

urban watersheds compared to rural watersheds.

A plot of variation of discharge with time is called a hydrograph.

A hydrograph may have different time scales such ass hourly,

daily, etc. hydrographs that result from storms are called storm

hydrographs.

A typical storm hydrograph may have a small flow before the

discharge increases on the rising limb, reaches a peak and

decreses along the recession limb.

2.9 FLOOD ROUTING THROUGH CHANNELS &

RESERVOIRS

As runoff land, enters into channels, the volume of water

temporarily stored in the channel increases. After the end of

precipitation water moves down the channel and the discharge

decreases at the end of a storm is analogous to the passage of

a wave and hence these are called flood waves.

Whether a flood wave moves down a channel or through a

reservoir and is naturally drained out or released. Flood routing

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is the name given to a set of techniques that are developed to

analyze the passage of a flood wave through the system.

2.10

2.11POTENTIAL HYDROLOGIC EFFECTS OF

URBANIZATION

Urbanization drastically alters the hydrologic and

meteorological characteristics of watersheds. Because of the

changes in surface and heat retention characteristics brought

about by buildings and roads, heat islands develop in urban

areas. Increase in nucleation and photoelectric gases due to

urbanization result in higher smog, precipitation and related

activities, and lower radiation in urban areas compared to the

surrounding rural areas. Some of these meteorological effects

of urbanization are discussed by Lowry (1967) and

Landsberg (1981).

When an area is urbanized, trees and vegetation are moved,

the drainage pattern is altered, conveyance is accelerated and

the imperviousness of the area is increased because of the

construction of residential or commercial structures and roads.

Increased imperviousness decreases infiltration with a

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consequent increase in the volume of runoff. Improvements in

a drainage system cause runoff to leave the urbanized area

faster than from a similar undeveloped area. Consequently, the

time for runoff to reach its peak is shorter for an urban

watershed than for an undeveloped watershed.

The peak runoff from urbanized, on the other hand, is larger

than from similar undeveloped watersheds.

Urban stormwater drainage collection and conveyance systems

are designed to remove runoff from urbanized areas so that

flooding is avoided and transportation is not adversely affected.

The cost of this and similar systems is directly dependent on

the recurrence interval of rainfall used in the design. Rainfall

with 5 to 10 years recurrence intervals is most often used in

the sizing and design of the urban storm water drainage

collection and conveyances systems.

To accommodate areas that encounter frequent floods or high

losses due to flooding and to reduce the potential for

downstream flooding, stormwater storage facilities are

developed to temporarily store the stormwater and to release it

after a storm has passed over the area.

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2.12URBANIZING INFLUENCE ON POTENTIAL

HYDROLOGIC RESPONSE

Removal of trees and vegetation increase evapo-transpiration

and interception; increase instream sedimentation.

Initial construction of houses, streets, and culverts, local relief

from flooding and concentration of floodwaters may aggravate

flood problems downstream. Complete development of

residential, commercial, and industrial areas increase

imperviousness reduces time of runoff concentration thereby

increasing peak discharges and compressing the time

distribution of flow; volume of runoff and flood damage

potential greatly increased.

Construction of storm drains and channel improvements

decrease infiltration and lowered groundwater table; increased

storm flows and decreased base flows during dry periods.

2.13TIME OF CONCENTRATION AND TRAVEL TIME

The time of concentration, t, is the time taken by runoff to

travel from the hydraulically most distant point on the

watershed to the point of interest. The time of travel T is the

time taken by water to travel from one point to another in a

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watershed. The time of concentration may be visualized as the

sum of the travel times in components of a drainage system.

The different components include overland flow, shallow

concentrated flow and channel flow. As an area is urbanized,

the quality of flow surface and conveyance facilities is

improved, and the times of travel and concentration generally

decrease. On the other hand ponding and reduction of land

slopes which may accompany urbanization increase times of

travel and concentration.

Overland flows are assumed to have maximum flow lengths of

about 300 ft. from about 300 ft. to the point where the flow

reaches well-defined channels, the flow is assumed to be of the

shallow concentrated type. After the flow reaches open

channels it is characterized by Mannings formula.

the hydraulic considerations,

the provision of space above a drain for other services,

ground conditions,

underground obstructions,

the size and depth of existing drain,

Sufficient cover for future road grading and pavement

depth.

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The main aim is to keep the drain as high as possible to keep

construction costs at a minimum.

2.15HYDRAULIC ANALYSIS

1. FLOW IN OPEN CHANNEL

Definition of an open channel: an open channel may be defined

as passage in which liquid flows with its upper surface exposed

to the atmosphere. In an open channels flow is due to gravity;

thus the flow conditions are greatly influenced by the slope of

the channel. S. Chand (2007)

2. TYPES OF FLOW IN CHANNELS

The flow in channels is classified into the following types,

depending upon the change in the depth of flow with respect to

space and time.

Steady flow and unsteady flow: when the flow

characteristics (such as depth of flow, flow velocity and

the flow rate at any cross-section) do not change with

respect to time, the flow in the channel is said to be

steady.

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Uniform flow and non-uniform flow (varied) flow: flow in a

channel is said to be uniform if the depth, slope, cross-

section and velocity remain constant over a given length

of channel.

Laminar flow and turbulent flow: the flow in the open

channel may be characterized as laminar or turbulent

depending upon the value of Reynolds number, defined

as:

Re = pVR/u

Where, V = average velocity of flow in the channel, and

R = hydraulic radius (defined as the ratio of area of flow

to the wetted Perimeter)

When Re < 500 .flow is laminar

Re > 2000 ..flow is turbulent

500 < Re < 2000 ..flow is

transitional

Sub-critical flow, critical flow and supercritical flow: since

gravitational force is a predominant force in the case of

channel flow, therefore Froude number is an important

parameter for analyzing open channel flows. Depending

upon Froude number the channel flow may characterized

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as: uniform flow, gradual varied flow, rapid varied flow

uniform flow and non-uniform flow.

2.16MOST ECONOMIC SECTION OF A CHANNEL

The most economic section (also called the best section or

most efficient section) is one in which gives the maximum

discharge for a given amount of excavation. from continuity

equation it is evident that discharge is maximum when velocity

is maximum, the area of cross-section of the channel remains

constant. from Chezys formula and Mannings formula it can

be seen that for a given value of slope and surface roughness

the velocity of flow will be maximum if hydraulic radius R =

(A/P) is maximum. Further the area being constant hydraulic

is maximum if the wetted perimeter is minimum; this condition

is used to determine the dimensions of economical sections of

different forms of channels.

2.17ECONOMICS OF DRAINAGE DESIGN

Economic analysis of drainage design implies findings a

solution for a particular drainage problem that is cheapest on

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the long run. For any economic analysis of drainage systems,

the factors to be considered should include.

i. The cost of construction

ii. The cost of possible flood damage, based on flood

frequency in the area.

iii.Repair, clean-up and other pertinent maintenance

charges.

iv.Economic studies based on estimates of costs and

possible future damage should be made, where there are

alternative solutions to drainage problem, before the best

or optimum alternative is selected.

CHAPTER THREE

3.0 MATERIAL AND METHODOLOGY

3.1 MATERIALS USED FOR PROJECT DESIGN

Though the project was nearly analytical in nature, material used were

Mere Rule: This was used in delimiting the catchment,

Topographic Map of the Town campus: This was used to locate the contours

and the direction of run-off and

Rainfall Data: was also used in calculating the rainfall intensity.

3.2 METHODS TOBE EMPLOYED IN THE CALCULATIONS

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For the purpose of analysis, I shall adopt the Rational Method to compute the

quantity of run-off. I shall also make use of the best hydraulic section formula

which is a combination of the Continuity Equation and the Mannings equation.

This would be done as follows.

3.2.1 RATIONAL FORMULAR

We shall make use of rational formula as illustrated below to calculate our run-

off:

Q = 0.287CIA from eqn. 1

Where Q = Quantityt of runoff in m3

C = Runoff coefficient, expresses as percentage of imperviousness of the

watershed or rate of runoff to rate of rainfall. See Table 3 of the Appendix.

I = Intensity of rainfall expressed in metres per hour for a certain time of

concentration


3.2.3 MOST ECONOMIC RECTANGULAR CAHNNEL SECTION

Though we have various drainage best economic sections like, the circular,

triangular, and rectangular sections etc. we shall resolve to use the best

rectangular section for this design for case of construction arising from the

complexits of the shapes, and the less spaces for construction required. The

figure below shows the cross section of a rectangular channel. Let b and y be

the base width and depth of flow respectively See figure 1.

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Area of flow, A = b x y, - - - - - - - - -3.6

Wetted perimeter, P = b = 2y - - - - - - -- -3.7

Substituting the value of b =a

/y from eqn. (i) in eqn. (ii), we get

P = a/y = 2y- - - - - - - - - - -3.8

For the section to be most economical/ efficient, the wetted perimeter P must be

minimum.

i.e.

dp/dy = 0 or d/dy(b/y + 2y) = 0 - - - - - - -3.9

Or,

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I = Intensity of rainfall expressed in metres per hour for a certain time of

concentration


Where Kn = A + Biog10n .3.2

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JESC SEMINA