DESIGN OF AN UNDERGROUND DRAINAGE SYSTEM IN A …

DESIGN OF AN UNDERGROUND DRAINAGE SYSTEM IN A WATERLOGGED

A FINAL YEAR PROJECT REPORT

SUBMITED TO KAMPALA INTERNATIONAL UNIVERSITY IN PARTIAL

FULFULMENT OF THE REQUIREMENTS FOR THE AWARD OF A BACHELOR OF

SCIENCE IN CIVIL ENGINEERING

BY

MOGA JAMES 1153-03104-01415

&

HYUHA PETER 1153-03104-02581

SCHOOL OF ENGINEERING AND APPLIED SCIENCES

DEPARTMENT OF CIVIL ENGINEERING

AUGUST 2019

i

DECLARATION

I MOGA JAMES and HYUHA PETER declare to the best of our knowledge that this work

is original compiled by us after our thorough studies on the design of an underground

drainage system for a withstanding foundation in a water logged area case study

Namanve Industrial Park and that it has not been submitted to any University or

institution for the award of certificate, diploma or degree.

Signed………………………………………………………………………

Date………………………………………………………………………...

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APPROVAL

This is to certify that MOGA JAMES and HYUHA PETER, students of Kampala

International University undertook this study in design of an underground drainage

system for a withstanding foundation in a water logged area case study Namanve

Industrial Park and consequently carried out design for the underground channel in the

same area. This report is being forwarded for examination to the board of Kampala

International University having been approved.

Mr. BUKENYA STANLEY

Signature: ………………………………… Date…………………………………

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DEDICATION

We dedicate this report to our own parents, guardians and other family members for

accepting us to unconditionally leave home for our studies and for being there for us

during our studies, aiding our education right from the very beginning of our education,

supporting us financially throughout the training period and for putting us in their

prayers tirelessly.

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ACKNOWLEDGEMENT

We hereby place on record my sincere gratitude to the following:

Mr. Bukenya Stanley our supervisor, who at every stage in our project buildup, played a

principle role by offering technical advice, relevant information, alterations, corrections,

additions and omissions to our work.

Employees of Mukono Town Council especially the works and technical services, who

provided us with more information necessary for our project success.

Our thanks also go to the Uganda National Meteorological Authority (UNMA) who

provided us with rainfall data, analyzing the data and correction where necessary.

We also acknowledge the efforts of our parents, brothers and friends, for their support

in our education, financially and morally.

Above all our sincere thanks go to the Almighty God in Heaven who has provided us

with life, knowledge and wisdom to write and accomplish this project work. Glory unto

Him Who is in heaven.

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TABLE OF CONTENTS

DECLARATION ................................................................................................... i

APPROVAL ....................................................................................................... ii

DEDICATION .................................................................................................... ii

ACKNOWLEDGEMENT ....................................................................................... iv

TABLE OF CONTENTS ....................................................................................... v

LIST OF FIGURES ............................................................................................ vii

ABSTRACT ...................................................................................................... vii

CHAPTER ONE .................................................................................................. 1

INTRODUCTION ............................................................................................... 1

1.0 Introduction................................................................................................ 1

1.1 Background of the Study ............................................................................. 1

1.2 Problem statement. ..................................................................................... 3

1.3 Project justification ...................................................................................... 4

1.4 Project Objectives ....................................................................................... 4

1.5 Scope. ........................................................................................................ 5

1.6 Significance/Importance/Contribution ........................................................... 6

CHAPTER TWO ................................................................................................. 7

LITERATURE REVIEW ....................................................................................... 7

2.0 Introduction................................................................................................ 7

2.1 Drainage .................................................................................................... 7

2.2 Bridges ..................................................................................................... 14

CHAPTER THREE : METHODOLGY .................................................................... 16

3.0 Introduction.............................................................................................. 16

3.1 Desk Study ............................................................................................... 16

3.2 Field visits ................................................................................................ 16

3.3 Design of drainage system ......................................................................... 17

3.4 Data processing and hydraulic analysis ....................................................... 18

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3.5 Hydraulic design ....................................................................................... 20

3.6 French Drain ............................................................................................. 21

CHAPTER FOUR: DATA PRESENTATION ANALYSIS AND DISCUSION ................... 23

4.2 DISCUSSION ............................................................................................ 33

CHAPTER FIVE ............................................................................................... 34

CONCLUSIONS AND RECOMMENDATIONS ........................................................ 34

5.1 CONCLUSION ........................................................................................... 34

5.2 RECOMMENDATIONS ................................................................................ 34

WORK PLAN: DURATION (MONTHS) From November 2018 - May 2019 .............. 39

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LIST OF FIGURES

Figure 1: Showing a Satellite map of Namanve Industrial Park .......................................................... 3

Figure 2: Showing water ponding next to a building ............................................................................ 4

Figure 3: Showing an Open Drain [Local Government and Municipal Knowledge Base] ................ 8

Figure 4: Showing a French Drain [Wikipedia, 2018] ........................................................................... 9

Figure 5: Showing surface drainage [NC State University] ................................................................ 10

Figure 6: Showing a Sub-surface drainage [Drainage Resources] ................................................... 11

viii

ABSTRACT

This is a final year project report for students pursuing Bachelor of science in Civil

Engineering at Kampala International University that presents the Design of an

Underground Drainage System for a withstanding foundation in a waterlogged area [

Namanve Industrial Park, Uganda] which is located in Mukono District near Kampala in

the central part of Uganda along the Kampala-Jinja highway.

The report comprises of Five chapters, reflecting the order in which the design was

carried out.

Chapter One

Presents a detailed introduction of the proposed project that was considered for,

including problem statement, background, objectives, scope and significance of the

project.

Chapter Two

This chapter reviews the information about what has been done elsewhere in regard to

the area of this study in this research. This is supported by scholarly information from

various authors. It also contains the researchers view on what should be done to

improve the situation.

Chapter Three

In this chapter, the methods that will be used to execute the project are revised. The methods

include the type of data to collect tools for data collection, sources of data collection and

analysis of data.

Chapter Four

Contains the data presentation and analysis, the overall design, sizing of the

pipe for the French drain.

Chapter Five

Contains the conclusions, recommendations, references, biography and appendix.

1

CHAPTER ONE

INTRODUCTION

1.0 Introduction

This chapter presents the background to the study, Problem background, Statement of

the problem, Justification, Specific objectives, scope of the study and the significance of

the study.

1.1 Background of the Study

Drainage

This is the process of interception and removal of water from over, and under the

vicinity of a surface. Drainage can be surface (where water is conveyed on the surface

and drainage channels), or sub-surface (water flows underneath the surface)

[According to Amimoto, 2008].

Surface and sub-surface drainage of surroundings critically affects their structural

integrity of buildings within that vicinity, life and safety to users, and is thus important

during design and construction. Designs therefore have to provide efficient means for

removal of this water; hence the need for drainage designs. Drainage facilities are

required to protect the structures against damage from surface and sub-surface water.

(Darrach, 2013)

Poor drainage can also compromise the structural integrity and life of a pavement.

Drainage systems combine various natural and manmade facilities e.g. ditches, pipes,

culverts, curbs to convey this water safely (Beschta, 2011).

Surface runoff (also known as overland flow) is the flow of water that occurs when

excess storm water, melt water, or other sources flows over the Earth's surface. This

might occur because soil is saturated to full capacity, because rain arrives more quickly

than soil can absorb it, or because impervious areas (roofs and pavement) send their

2

runoff to surrounding soil that cannot absorb all of it. Surface runoff is a major

component of the water cycle and is the primary agent in soil erosion by water.

Runoff that occurs on the ground surface before reaching a channel is also called

a nonpoint source. If a nonpoint source contains man-made contaminants, or natural

forms of pollution (such as rotting leaves) the runoff is called nonpoint source pollution.

A land area which produces runoff that drains to a common point is called a drainage

basin. When runoff flows along the ground, it can pick up soil

contaminants including petroleum, pesticides, or fertilizers that become discharge or

nonpoint source pollution.(North Carolina department of environment and water

resources)

Storm water drainage is the process of draining excess water from streets, sidewalks,

roofs, buildings and other areas. The systems used to drain storm water are often

referred to as storm drains and are also called storm sewers and drainage wells

(Harshil, H. Gajjar, 2006).

3

Figure 1: Showing a Satellite map of Namanve Industrial Park

1.2 Problem statement.

Setting up a solid foundation in a waterlogged area is one of the hardest tasks because

it is risky, consumes a lot of time, energy and money. In these areas often experience

heavy soaking rains which flood yards and damage foundations due to continues water

presence which with time affects the walls and causes dampness.

Expansive clay soils increase in volume when it gets wet, when it expands this soil can

exert strong pressures against the foundation hence a need of drainage system

underground which continuously drains away the constant water. [Daily Monitor;

Wednesday 28 August 2013]

A design of French drain comes in play to remove sub-surface water, where the water

will be led into major Drainages which is in the master plan for KCCA to mitigate floods.

[PML Daily; 2018]

4

Figure 2: Showing water ponding next to a building

1.3 Project justification

With the increased need for development and industrialization, this will avail the

technique to construct in the designated location within waterlogged areas without

killing the swamp.

It increases the comfortability of staying in those houses when their foundations are

properly built i.e. the cases of wet basements will be eradicated.

Prevent standing or ponding water on the area where the house is constructed.

Prevent soil erosion.

Adversely affect the supporting foundation soil behavior.

1.4 Project Objectives

Main Objective

To design an underground drainage system (French drain) which constantly drains

away continuous water coming to the foundation.

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Specific objectives

To carry out a reconnaissance survey to determine the site conditions and

nearby drainage systems such as trenches.

To collect and analyze hydrological data in the area.

Determine the water shade area, and topography of the area

Design the underground drainage system.

Produce the drawings and graphs of the project.

1.5 Scope.

Content scope

The study focuses on how to manage sub-surface and surface run off in Namanve

Industrial Park. It involves the determination of run-off quantities of the sub-catchment

areas comprising the drainage area and then comparing them to the existing drainage

capacity. However, the study specifically looks at the ways of managing sub-surface

and surface run off, the challenges in managing and the strategies to control sub-

surface and surface run off in relatively flat areas.

The design was limited to the reconnaissance survey, hydrological data collection and

analysis and the design of the underground drainage.

Geographical scope

The study was carried out in Namanve Industrial Park which is an industrial center

located in Mukono district near Kampala in the central part of Uganda located along the

Kampala – Jinja highway. The district boarders with Kampala, Wakiso, Jinja, Kayunga,

Namayingo and Luweero. Mukono lies in a relatively flat land which makes the flow of

water quite hard from the roadside drainages to the intended drainages designed by

the local authority.

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Time scope

The study was carried out within a period of seven months that’s from November 2018

to May 2019.

1.6 Significance/Importance/Contribution

a) The study was carried out on the management of sub-surface and surface run-

off in relatively flat areas were intended to broaden the knowledge in areas of

management of water for application in the field when such challenges emerge.

b) This intended to solve a problem of water stagnating in surrounding of the

selected area.

c) It also aimed at protecting the structures against damages that are caused by

water both surface and sub-surface which may arise to the alteration of the

foundation.

d) The study leads to identifying failures in the drainage system and its causes with

a view of making recommendations on how to improve it and obtain a higher

efficiency. Thus the study involved the collection and analysis of rainfall data for

the area under study.

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CHAPTER TWO

LITERATURE REVIEW

2.0 Introduction

This chapter reviews the information about what has been done elsewhere in regard to

the area of this study in this research. This is supported by scholarly information from

various authors. It also contains the researchers view on what should be done to

improve the situation.

2.1 Drainage

Drainage is the practice of removing unwanted water so as to facilitate other activities

like construction, reducing crop stress, reducing soil salinity and avoid flooding. The

factors that determines necessity of a drainage system in a waterlogged area are soil

type, topography, method and type of foundation, precipitation and level of the water

table.

The principle types of drainage systems are: open drain, piped (positive) Drain, French

Drain.

Open drains

Are used to carry away surface water and can also pick up some subsoil water

(depending on depth). Open drains facilitate the early visual detection of blockages but

their use may be restricted by the lack of space and safety considerations around

homes

8

Figure 3: Showing an Open Drain [Local Government and Municipal Knowledge Base]

Piped Positive Drain

Is normally associated with an urban situation and is used in conjunction with gullies

and kerbs. It may also be used in some rural embankment situations where it is

deemed important that water from the road and hard shoulder should not be allowed

drain onto the embankment.

This system consists of perforated pipes placed at the bottom of a narrow trench and

backfilled with a filter material such as coarse sand. It is generally used along the toes

of cut or fills slopes. The trench should be below the groundwater surface and dug into

a lower, more impervious soil layer to intercept groundwater. The drains may be made

of metal, concrete, clay, asbestos-cement, or bituminous fiber and should be 15

centimeters (6 inches) in diameter or larger.

This system requires regular maintenance.

9

French Drain

Generally French Drains include a permeable drainage pipe surrounded by a filter cloth

and buried with gravel. However, some sources show only a trench filled with gravel

without a drainage pipe. The filling material does not have to be gravel specifically, but

can be any sort of rock, stone, or coarse aggregate. French Drains are applicable right

outside of external walls of buildings to prevent water from accessing the foundation. It

is important to note French drains will eventually clog and require some ongoing

maintenance to drain properly 20 (Nusite Waterproofing, 2012). Typically, French drains

are 1.5 feet deep and 10-12 inches wide (Fairfax County, Virginia, 2013).

Figure 4: Showing a French Drain [Wikipedia, 2018]

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Drainage features

Surface drainage

Surface drainage encompasses all means by which surface water is removed from the

ground.

Figure 5: Showing surface drainage [NC State University]

Subsurface drainage system

The need for subsurface drains as alternatives to open drains depends on site

conditions; however, they require careful consideration owing to their cost. These types

of drains are required in urban areas, places with subsoil wells and in some types of

cuttings. Subsurface drains include under drains (French drains) and trench drains.

They serve the following purposes; intercept water before it gets to the foundation

lower the water table and remove excess free moisture from the foundation.

Subsurface drainage consists of three basic elements. A permeable base which is

required to provide for rapid removal of water which enters the ground, a method of

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conveying the removed water away and this may consist of a base sloped towards a

drainage ditch. At the most, this may consist of a pipe collector system and a filter layer

to prevent the migration of fines into the underground pipes.

All sub drains should be able to maintain the flow lines and the design slopes. The

outlet water flow should be clear and uniform, indicating that erosion is not occurring

and the system is not clogged.

Figure 6: Showing a Sub-surface drainage [Drainage Resources]

Elements of a good subsurface drainage

Granular drainage layer

A well maintained granular drainage layer is uniform in thickness, the width detailed in

the plans and specifications, and of the proper material gradation.

Under drains

A well maintained system of transverse and longitudinal drainage pipes effectively

intercepts and carries water out of the granular layer. Perforated pipes installed in a

trench parallel to the foundation, which is then backfilled with an open graded

aggregate. Caps of impervious soils are placed on top of edge drains to prevent surface

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water from draining into them. Filters may be used to prevent fine grained soils from

clogging the open graded aggregate or the pipe itself. Water from the under drains is

collected in a non-perforated edge drain pipe that discharges into a nearby ditch or a

storm water system.

Design of drainage structures

Hydrological analysis

This deals mainly with precipitation and runoff in the area of interest. When rainfall,

which is the main source of water, falls onto an area some of the water infiltrates into

the soil while the remaining portion either evaporates or runs off. The portion that

remains as runoff is the one of major concern in the design of surface drainage

facilities.

Determination of runoff

Runoff at a particular point is determined with respect to a given catchment area and

depends on a number of factors such as; type and condition of the soil in the

catchment, kind and extent of vegetation or cultivation, length and steepness of the

slopes of the area among others.

The following formula known as the rational formula is used for calculation of runoff

water for highway drainage. Applicable for small catchment areas less than 25km2

[Gichaga, 1998].

Q= 0.28CIA

Where:

Q = Flood peak at catchments exit in m3/s

C = Rational run off coefficient

I = Average rainfall intensity over the whole catchment in mm/hr.

A = Catchment Area in km2

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Hydraulic Design

Once the design runoff Q is determined, the next step is the hydraulic design of drains.

The side drainage and other structures are designed based on the principles of flow

through open channels.

If Q is the quantity of surface water (m3/sec) to be removed by a side drainage and V is

allowable velocity of flow (m/s) on the side drainage, the area of cross section A of the

channel (m2) is found from the relation below:

Q=A.V

The velocity of unlined channel must be high enough to prevent silting and it should not

be too high as to cause erosion. The allowable velocity should be greater than one

(1m/sec) for lined channel. The slope S of the longitudinal drain of known or assumed

cross section and depth of flow determined by using Manning’s formula for the design

value of velocity of flow V, roughness coefficient n and hydraulic radius R.

V=1/n (R2/3S1/2) [Edwards, 2006]

Where;

V = Flow velocity (m/s);

n = Manning’s roughness coefficient;

R = Hydraulic radius (m);

S = Stream bed slope (m);

A = Flow cross section area (m2);

Q = Flow Discharge (m3).

14

Table showing run off coefficient for the rational method

Structure Return Period (in Years)

Major Bridges 25

Minor Bridges 20

Slab and Box Culverts 15

Pipe Culverts 10

Ditches 5

2.2 Bridges

Bridges often represent the preferred channel crossing alternative in areas where

aquatic resources are extremely sensitive to disturbance. However, poor location of

footings, foundations, or abutments can cause channel scour and contribute to debris

blockage.

Bridges have been designed using a variety of structural materials for substructure and

superstructure. Selection of a bridge type for a specific site should take into

consideration the functional requirements of the site, economics of construction at that

site, live load requirements, foundation conditions, maintenance evaluations, and

expertise of project engineer.

Some arbitrary rules for judging the minimum desirable horizontal and vertical stream

clearances in streams not subject to navigation may be established for a specific area

based on judgment and experience. In general, vertical clearances should be greater

than or equal to 1.5 meters (5 feet) above the 50-year flood level plus 0.02 times the

horizontal distance between piers. Horizontal clearance between piers or supports in

forested lands or crossings below forested lands should not be less than 85 percent of

15

the anticipated tree height in the forested lands or the lateral width of the 50-year

flood. (US Environmental Protection Agency, 1975)

Of course, longer bridge spans will require careful economic evaluations since higher

superstructure costs are often involved. Subaqueous foundations are expensive and

involve a high degree of skill in the construction of protective cofferdams, seal

placement and cofferdam dewatering. In addition to threats to water quality that can

occur from a lost cofferdam, time and money losses will be significant. Subaqueous

foundations often limit the season of construction relative to water level and relative to

fish spawning activity. Thus, construction timing must be rigidly controlled.

It is suggested that the maximum use be made of precast or prefabricated

superstructure units since the remoteness of many mountain roads economically

precludes bridge construction with unassembled materials that must be transported

over great distances. However, the use of such materials may be limited by the

capability to transport the units over narrow, high curvature roads to the site, or by the

horizontal geometry of the bridge itself.

Another alternative is the use of locally available timber for log stringer bridges. An

excellent reference for the design and construction of single lane log bridges is Log

Bridge Construction (Handbook, by M. M. Nagy, et al., and is published by the

Forest Engineering Research Institute of Canada.) The reader is referred to this

publication for more detailed discussions of these topics.

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CHAPTER THREE : METHODOLGY

3.0 Introduction

Methodology is a set of methods and principles for data collection and analysis. This

chapter covers the approach from desk study to the final design for the project.

Specifically, it deals with the, various studies, the experimental design involving soil

observation and hydrological data employed in the project for the purposes of analysis.

It attempts to show the procedures adopted in each stage of the project.

Its recommend that a complete study is carried out and a drainage plan prepared

for the waterlogged area before installing subsurface drainage pipes. The survey, used

in conjunction with soils and groundwater information, enables the contractor or

designer to layout the drain system in the most effective and cost-efficient way.

This enables the landowner to install the system with consideration of time, labor or

finances and a plan record for future modification or maintenance which should be

passed on to subsequent landowners.

3.1 Desk Study

Information or written works obtained from several sources regarding the rainfall data

was critically analyzed at and comprehended. Class Notes and textbooks were

consulted in order to provide fundamental foundation to the study. Internet use for

example google as another source of information for a better view of modern

technology and several current developments of the underground drainage system.

3.2 Field visits

Consultations/ Interviews

Consultations and discussions with various individuals like: supervisors, lecturers, fellow

students and then relevant district officials was held where data was gathered by tests,

experiments, interviews and captured by like questionnaire, audio and video recording

and then by observation.

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3.3 Design of drainage system

Determination of the catchment area.

This was obtained by use of Google Earth Pro software and contours were got using

TCX converter. The area was used in the determination of the discharge in the design

of the drainage structure and the contours to determine height difference.

Collection of Hydrological data.

Data on the mean annual rainfall for the catchment area under consideration was

gathered in order to tell how rainfall is distributed in the design area a factor that was

used to estimate the size and type of drainage to be used in the catchment area. This

rainfall data about the area was obtained from the Uganda National Metrological

Authority (Entebbe).

The coefficient of discharge

The runoff coefficient used was the weighted runoff coefficient. The approximate area

of land use in the watershed were determined using ArcGIS software.

Determining Peak Runoff

The Rational Method was used to determine surface runoff. The relationship for peak

runoff rates is given by: Qp = 𝐶𝐼𝐴 Where:

Qp: Peak runoff in m3/s

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C: Run off Coefficient (dimensionless)

I: Rainfall Intensity (m/s)

A: Area of the catchment in m2

3.4 Data processing and hydraulic analysis

The analysis involved the following detailed process.

Developing Intensity Duration and Frequency curves and determining rainfall

intensities for different return periods

Intensity Duration and Frequency (IDF) curves have been found to be very helpful in

the estimation of design flow for the design of hydraulic structures like culverts and

sewers. Intensity Duration and Frequency curves show the intensity of rainfall for a

given duration and expected frequency. From the curves intensities of a given duration

at required return periods are obtained and used in estimating peak flows.

Various methods are used to develop intensity Duration and Frequency Curves which

include some of the following.

Watkins and Fiddes.

Bells method.

Of the above two methods we adopted the Watkins and Fiddes method for our study in

developing the Intensity Duration and Frequency curves and goes as follows:

Rainfall data for the study area was obtained from Uganda National Metrological

Authority (Entebbe).

Data collected involved rainfall depth together with duration of occupancy. The

maximum daily rainfall for every month was considered from which maximum annual

rainfall was selected for the selected years of study that is from 2003-2014.

The daily maximum rainfall values were then ranked from 1-N (the number of years) in

the descending order

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The corresponding return periods for each year were estimated using Welbull’s plotting

position formula. T= (𝑁+1)/𝑟 Where N=Number of years under study, r=is the event

rank number (1,2,3…….N)

The maximum rainfall depths were then plotted against return periods on a semi-log

paper and a line of best fit plotted through the points.

The correlation coefficient between the maximum daily rainfall and log of return period

was determined.

From the graphs maximum rainfall depths at desired return periods were read off from

the graphs.

The desired sequence of duration for example (10, 15, 30 minutes) was chosen for

each data set and used to calculate the rainfall intensity using the basic mathematical

form of the Intensity-Duration-Frequency curve represented by rectangular hyperbola:

Where;

I = is the intensity (mm/hr.),

t = is the duration (hours),

a, b, and n = coefficients/constants developed for each IDF curve.

The intensities were plotted against duration for each desired return period to give the

Intensity Duration and Frequency curves.

The following procedure was adopted for the determination of coefficients a, b, and n in

the formulae used.

A value of b from other studies in the region (East Africa b=1/3) was adopted. The

effective duration of storms in the area teff was estimated. This is the length of time

over which 60% of the day’s rainfall occurs. This can be done by either judgment,

20

discussion with local experts or review of the local storm data. The latter option was

used in this study.

The value of n from the original Watkins and Fiddes equation was calculated as follows:

From the graphs, the maximum daily rainfall for return period RT24 can be determined.

This is divided by 24 to determine the daily rainfall intensity for a particular return

period IT24= RT

24/24

The value of aT for each return period was calculated using the formula below:

aT= IT24X(b+24)n

The value of aT and other constants b and n were applied in the equation to determine

the intensities in mm/hour for a particular duration and return period i.e.

3.5 Hydraulic design

Depending on the design runoff value Q calculated a suitable hydraulic structure that

suites the discharge was determined.

If Q is the quantity of surface water (m3/sec) to be removed by a drainage and V is

allowable velocity of flow (m/s) on the side drainage, the area of cross section A of the

channel (m2) is found from the relation below:

Q=A.V

The velocity of unlined channel must be high enough to prevent silting and it should not

be too high as to cause erosion. The allowable velocity should be greater than one

(1m/sec) for lined channel. The slope S of the longitudinal drain of known or assumed

21

cross section and depth of flow, determined by using Manning’s formula for the design

value of velocity of flow V, roughness coefficient n and hydraulic radius R.

V=1/n (R2/3S1/2) [Edwards, 2006]

Where;

V = Flow velocity (m/s);

n = Manning’s roughness coefficient;

R = Hydraulic radius (m);

S = Stream bed slope (m);

A = Flow cross section area (m2);

Q = Flow Discharge (m3).

3.6 French Drain

A French drain was implemented around the buildings. Typically, a French drain of

about 10-12 inches wide and has a depth of about 1.5 feet (Fairfax County, Virginia,

2013). Manning’s equation used to calculate the slope of the trench, size of the trench,

and size of the perforated PVC pipe.

This approach allowed for a design with a circular pipe and varying flow.

The depth chosen to allowed for plumbers to effectively use their equipment to clean

the debris that may accumulate in the French drain. The clean outs consist of PVC

sweep T’s that are 4 inches in diameter with a 4-inch diameter cap at the top to avoid

infiltration from the above surface. Pea gravel (3/8-inch diameter) with an infiltration of

0.16 ft/s was applied on top of the sand and perforated pipe in order to promote

infiltration to the pipe. It is assumed that the infiltration through the gravel was a unit

gradient gravity of 25 flow, and allowed for the designed infiltration of 0.005 ft/s to

effectively reach the permeable pipe. To reduce clogging of the gravel and perforated

pipe, filter fabric was applied around the perimeter of the trench and perforated pipe.

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Manholes.

Manholes were constructed in intervals along the pipes to check blockages and for

routine maintenance work.

Choice of Materials

Most commonly used drainage materials includes; perforated PVC pipes (PPVC), clay

pipes, porous concrete drains (PCD), rock filled French drains (RFFD) and bagasse filled

drains (BFD).

Advantages of PPVC over concrete drains and clay pipes.

They are easy to wrap with an envelope material

They are flexible and easily folded therefore facilitating transportation, handling

and installation.

They are light in weight hence easier in handling even in great length

installation.

They are inert to most chemicals.

Disadvantages of PPVC over concrete drains and clay pipes

Can easily collapse under sudden loads

Affected by long exposure to sunlight

Becomes brittle and therefore can easily break when exposed to low

temperatures

Easily burns when in contact with fire.

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CHAPTER FOUR: DATA PRESENTATION ANALYSIS AND DISCUSION

Table showing maximum annual rainfall for each of the study years rank and

computed return periods for the study years

Year maximum daily rainfall (mm) rank r Return period

2009 96.683 1 13.0

2007 93.537 2 6.5

2011 93.258 3 4.3

2012 87.904 4 3.3

2014 78.434 5 2.6

2005 78.212 6 2.2

2008 66.543 7 1.9

2013 63.302 8 1.6

2006 62.138 9 1.4

2010 59.357 10 1.3

2004 57.373 11 1.2

2003 35.209 12 1.1

( +1)/

A graph of maximum annual rainfall for various years against computed

return periods

0.000

20.000

40.000

60.000

80.000

100.000

120.000

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

M

A

X

I

M

U

M

R

A

I

N

F

A

L

L

RETURN PERIODS

24

Table 2; used to compute aT for each return period, maximum hour intensity

maximum hour rainfall.

Maximum 24hr rainfall (mm) Return period (T) Max. Hour intensity(i T24) at = T/(b+t)n

63.6 1 2.6 42.6

67.4 2 2.8 45.1

79.0 5 3.3 52.9

98.2 10 4.1 65.8

156.0 25 6.5 104.4

252.2 50 10.5 168.9

444.7 100 18.5 297.7

teff = 60% of 2.5 hours

teff = 0.6 * 2.5

teff = 1.5 hrs

𝑛 =𝑖𝑛

14.4𝑡𝑒𝑓𝑓

𝑖𝑛𝑏 + 24

𝑏 + 𝑡𝑒𝑓𝑓

𝑛 =𝑖𝑛

14.41.5

𝑖𝑛1/3 + 241/3 + 1.5

n =0.87

25

26

Table 3; showing computations of rainfall intensities for various return

periods years for different channel structures.

1 2 5 10 25 50 100

Duration (min) Duration (hrs)

10 0.17 5.58 5.91 6.94 8.63 13.69 22.14 39.03

20 0.33 3.10 3.28 3.85 4.79 7.60 12.29 21.66

30 0.50 2.19 2.32 2.72 3.38 5.36 8.68 15.29

40 0.67 1.71 1.81 2.12 2.64 4.19 6.77 11.94

50 0.83 1.41 1.49 1.75 2.18 3.45 5.58 9.84

60 1.00 1.20 1.27 1.49 1.86 2.95 4.77 8.41

70 1.17 1.05 1.11 1.31 1.63 2.58 4.17 7.36

80 1.33 0.94 0.99 1.16 1.45 2.30 3.72 6.55

90 1.50 0.85 0.90 1.05 1.31 2.08 3.36 5.92

100 1.67 0.77 0.82 0.96 1.19 1.89 3.06 5.40

110 1.83 0.71 0.75 0.88 1.10 1.74 2.82 4.97

120 2.00 0.66 0.70 0.82 1.02 1.62 2.62 4.61

Return period T (yr)

0.00

5.00

10.00

15.00

20.00

25.00

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Rai

nfa

ll in

ten

sity

(m

m/h

r)

Duration (minutes)

IDF CURVE FOR MUKONO TOWN COUNCIL FOR RAINFALL DURATION (2003-2004)

1 year 2 year 5 year 10 year 25 year 50 year 100 year

27

Time of Concentration

Kirpich’s formula was used to calculate the time of concentration.

tc = 0.06628L0.77S−0.385

Where;

tc – Time of concentration in (minutes)

L - Maximum length of travel of water (meters)

H- Difference in elevation between the most remote place in the basin and the outlet.

S - Slope of the drainage basin = (H/L)

Height difference = (Highest point – Lowest point)/L

From the contours; got using TCX converter software

Figure 7: Showing the contours in the area using TCX converter software

Highest point = 1185m

28

Lowest point =1160m

Height difference = (1185 – 1160)/L

H = 25m

The length;

Figure 8: Showing the length of the longest distance from Google Earth Pro Software

L = 1874m

So therefore, S = 0.013

Time of concentration, tc = (0.06628x1.8740.77x0.013−0.385) x 60

Therefore; Time of concentration tc =34.3 minutes.

From the IDF curve considering the 10-year curve, for duration = 34.3 minutes, I =

3.06mm/hr

29

The coefficient of discharge

The runoff coefficient used was the weighted runoff coefficient. The approximate area

of land use in the watershed were determined using ArcGIS software and are

summarized below:

Figure 9: Shows the land use types/Land cover in the catchment Table: Land use areas in watershed

Land use Counts Area (km2) Runoff

coefficient

Commercial 50 1.502 0.70

Paved Surfaces 10 3.004 0.88

Bare Surfaces 15 0.375 0.15

Vegetation 12 1.128 0.05

Streets 11 1.502 0.80

Total 98 7.51

30

Weighted Runoff Coefficient C

C = [(C1*A1) + (C2*A2) + (C3*A3) + (C4*A5) + (C5*A5)]/ [A1 + A2 + A3 + A4 + A5]

C = [(0.70*1.502) + (0.88*3.OO4) + (0.15*0.375) + (0.05*1.128) + (0.80*1.502)]/

[1.502 + 3.004 + 0.375 + 1.128 + 1.502]

C = 0.667

The area of the water shade

Using Google earth the area was found to be;

Figure 10: Showing the area of the water shade

A = 7.51km2

31

Determining Peak Runoff

The Rational Method was used to determine surface runoff. The relationship for peak

runoff rates is given by: Qp = 𝐶𝐼𝐴 Where:

Qp: Peak runoff in m3/s

C: Run off Coefficient (dimensionless)

I: Rainfall Intensity (m/s)

A: Area of the catchment in m2

Q = (0.667 * 3.06 * 7.51)/ 3.6

Q = 4.26 m3/s

Therefore, the peak discharge Qp = 4.26m3/s

But Q = VA

V = Q/A

V = 4.26 / 7.51

V = 1 m/s

From manning’s coefficient equation;

V = 𝑆

1

2𝑅ℎ

2

3

𝑛

1 = 0.013

1

2Rh

2

3

0.02

But Rh = A/P = d/4

Rh2

3 = (V * n )/ 𝑆

1

2

Rh2

3 = ( 1 * 0.02) / 0.013

1

2

Rh = 0.07m

But for a pipe Rh = D/4

32

So therefore diameter of the pipe = 0.07 * 4 = 0.28m = 28 cm

Figure 11: Showing standard sizes of PVC

So from the standard charts the recommended size of the pipe is 300mmx 6m

Figure 12: Showing the depth recommendation and spacing

33

From the chart of depth the recommended depth in clay loan soil is 0.5 – 1 m, so we

recommend 0.8 m with a spacing of 12 m.

Figure 13: Showing the gradient recommendation

From the chart above the recommended gradient of drawdown curve is 1:5 – 1: 2.5 for

silt/clay soil; so we recommend 1:5

4.2 DISCUSSION

The dimensions of the pipes were designed on the basis of the quantity of run-off

computed from the rational formula.

The proposed channels computed, a return period for 10-years was used which gives

cross-sections for the drainage systems hence larger capacity to accommodate the sub-

surface drainage

34

CHAPTER FIVE

CONCLUSIONS AND RECOMMENDATIONS

5.1 CONCLUSION

1. This French drains reduced ponding of water at the Namanve Industrial park by

continuous underground water runoff releasing it into major drainages. Hence

stabilizing the soil and achieving firm foundations.

2. This continues ground activity since the water runoff is below the surface which

increased comfortability in the structures of Namanve Industrial area without affecting

the neighbors especially people living in Kolo.

3. The Surface flow of water was reduced since there is an underground flow of water.

Setting up new structures in the area will be made easy due to constant draining of the

underground water hence reducing dampness and making the soil firm.

5.2 RECOMMENDATIONS

1. Redesign and replacement of the entire Namanve area drainage system with French

drains so as to pass the runoff as quickly as possible especially to the main drainage

channel in the collection basins to which the main Drainages discharge in Kolo.

2. Addition of other major drainage system all around the Industrial Park so as not to

over load the proposed drainage systems in the area.

3. Maintenance practices should be given priority; this includes removal and cleaning up

of the drains. This can be achieved by increasing budgetary allocation for

maintenances.

35

4. Given that Namanve lies in a relatively flat area, efforts should be made to reduce

runoff from the structures, this can be done by increasing vegetation cover through tree

plantation in around the structures and discouraging creation of impervious layers that

lead to high values of water accumulation in these area. This will increase rain water

infiltration into the ground.

6. Encouraging rain water harvesting technologies by building water collection tanks for

water storage within the industrial area thus reducing on the amount of water that goes

as surface runoff in the area hence reducing peak flows drastically.

7. Discourage encroachment of reserve areas for flood prone lands thus leaving enough

room for plant and machinery for maintenance and repair.

36

References

Fairfax County, Virginia. 2013. Grass-lined Channel. Available at:

http://www.fairfaxcounty.gov.

Nusite Waterproofing, what is a French Drain System? Available at:

http://nusitegroup.com/what-is-french-drain-system/.

Wikipedia. http://en.wikipedia.org/wiki/French_drain.

Local Government and municipal knowledge base: http://lgam.wikidot.com/open-drain

NC State University: https://www.researchgate.net/figure/Surface-drainage-system-

Source-NC-state-university_fig3_276834305

Drainage Resources – Subsurface drainage: http://www.wplawinc.com/drainage-

resources

Chow, Ven Te, David R. Maidment, and Larry W. Mays. 1988. Applied Hydrology

McGrwa-Hill.

Corbit, Robert A. 1999. Standard Handbook of Environmental Engineering. McGraw-Hill.

2ed.

Lindsley, Ray K., Joseph B. Franzini, Davd L. Freyberg and George Tchobanoglous.1992. Water-Resources Engineering. McGraw-Hill. 4ed.

McCuen, Richard H. 1998. Hydrology Analysis and Design. Prentice-Hall. 2ed.

Singh, Vijay p. 1992. Elementary Hydrology. Prentice-Hall.

Amimoto, P. Y. 2008. Erosion and sediment control handbook. California Division of Mines and Geology, Department of Conservation. 197 p.

Beschta, R. L. 2011. Streamflow estimates in culverts. Oregon State University, Forest Researph Laboratory, Res. Note. 67. 4 p.

Darrach, A. G., W. J. Sauerwein, and C. E. Halley. 1981. Building water pollution control into small private forest and ranchland roads. U. S. Department of Agriculture, Forest Service and Soil Conservation Service.

Forest Soils Committee of the Douglas Fir Region. 2007. An introduction to the forest soils of the Douglasfir Region of the Pacific Northwest. University of Washington.

37

Highway Task Force. 2011. Handbook of steel drainage and highway construction products (2nd Ed). American Iron and Steel Institute, 150 E 2nd Street; New York. 368 p.

Megahan, W.F. 2007. Reducing erosional impacts of roads. In: Guidelines for Watershed Management. Food and Agriculture Organization, United Nations, Rome. p 237-261.

Minematsu, H. and Y. Minamikata, 2013. Optimum spacing for open - top culverts on forest roads. University of Agriculture and Technique, Tokyo. Jour. of J.F.S. 65(12):465-470.

Packer, P. 2007. Criteria for designing and locating logging roads to control sediments. Vol.1, No. 13.

Pearce, J. K. 2012. Forest engineering handbook. U. S. Department of Interior, Bureau of Land Management. 220 p.

Reid, L.M. 2011. Sediment production from gravel-surfaced forest roads, Clearwater basin, Washington. Publ. FRI-UW--8108, Univ. of Washington, Seattle. 247 p.

Searcy, J. K. 2007. Use of riprap for bank protection. Federal Highway Administration, Washington D. C. 43 p.

USDA, Forest Service. 2011. Transportation engineering handbook. Handbook No. 7709.11.1979. Technical guide, erosion prevention and control on timber sales areas. Intermountain Region.

Yee, C. S. and T. D. Roelofs. 2008. Planning forest roads to protect salmonid habitat. U. S. Department of Agriculture, Forest Service. General Technical Report PNW-109. 26 p.

U.S. Dept. of Commerce, Bureau of Public Roads. 2013. Hydraulic Charts for the Selection of Highway Culverts, Hydraulic Engineering Circular No. 5.

38

APPENDICES

Estimated budget

ITEM COST

Typing and printing 300,000/=

Research fees: Including downloading 200,000/=

Transport costs 200,000/=

Accommodation 150,000

Miscellaneous expenses 300,000/=

Reams of papers 60,000/=

TOTAL 1,210,000/=

39

WORK PLAN: DURATION (MONTHS) From November 2018 - May 2019

ACTIVITY Sept 2018

Oct 2018

Nov 2018

Dec 2018

Jan 2019

Feb 2019

Mar 2019

Apr 2019

May 2019

Introduction

to project

proposal

Topic

selection

Problem

statement

and

justification

Literature

gathering

Methodology

Proposal

compiling

and

Presentation

Data

collection

Compilation and analysis

of information

Document

preparation

Presentation

& submission