JESC SEMINA
Transcript of 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
A = area of watershed in hectares
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
A = area of watershed in hectares
Where Kn = A + Biog10n .3.2
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