KALMUNAI MUNICIPAL COUNCIL

FEASIBILITY STUDY ON DRAINAGE

ON SELECTED SUB-PROJECT PROPOSALS

UNDER NELSIP

(NORTH EAST LOCAL SERVICES IMPROVEMENT PROJECT

Gama Neguma Inter Divisional Rural and Small Township Development Initiative

For the North and East Province)

Prepared By: Eng.A.J.A.H.Jowsi Municipal Engineer

CONTENTS

Executive Summary 1.0 Introduction

1.1 General 1.2 Objective of the Project 1.3 Project Location 1.4 Data collection 1.5 Maps Used

2.0 DESCRIPTION OF THE STUDY AREA

2.1. Location 2.2. Topography 2.3. Climatic Features

3.0 SOCIO-ECONOMIC ASPECTS 3.1. General aspects 3.2. Socio- Economic Background 3.3. Infrastructure

4.0 DEMOGRAPHIC ASPECTS 4.1. Population of the Study Area 4.2. Population Projection 4.3. Population to be benefitted 4.4. Special Consideration

5.0 EVALUATION OF EXISTING DRAINAGE FACILITIES

5.1. Inundation Problem 5.2. Existing Drainage 5.3. Solid Waste Management 5.4. Environmental Health

6.0 Analysis and Computations

6.1 Design approach 6.2 Rainfall data 6.3 Design criteria for drainage 6.4 Rainfall intensity 6.5 Land use pattern in watersheds 6.6 Catchment areas 6.7 Estimation of peak storm water flow 6.8 Runoff coefficient

6.9 Return Period 6.10 Checking Adequacy of drainage system 6.11 Drain and culvert design 6.12 Filling levels and reservation for roads

7.0 Environmental impacts 8.0 Project Cost Estimates

9.0 Project Evaluation

10.0 Recommendations and conclusions

Annexes A.1- Design Calculation and Tables A.2 –Drawings A.3-Bill of Quantities

Executive Summery

Kalmunai Munical council was selected to get financial assistance from the

Ministry of Economic Development under the world bank funded project

NELSIP ( North East Service Improvement Project). Improvement of the storm

water drainage system has been identified as the most significant issue in

Kalmunai Municiapl Council during problem identification meetings with the

local residents .

This report is intended to provide information about the technical feasibility of

the selected Sub-Project Proposals to be implemented under the block grants in

2011 and 2012 .

The study is focused on adapting the existing drainage network capable of

handling monsoonal flood in the project area of concern. There was a master plan

prepared by the SriLanka Land Reclamation and Development Corporation

(SLLRDC) in 1999. This master plan has wider sections passing through premises

as it has larger catchment areas. During 2008-2009 United Nations Office for

Project Services (UNOPS) has implemented a drainage project worth of 130

Million. Under this project , existing drainage network was adapted by diverting

flows through bypassing pipes to existing outfalls or new outfalls . That

experience was incorporated in designing the drains under this project.

1. INTRODUCTION

1.1 General

Kalmunai Municipality is a low lying coastal town located at the eastern coastal

belt in Ampara District. The area is a strip of land along the coast line having an

average of 1km width and 10km length, average ground elevation is +2.5m MSL.

The municipality area is locked with Indian Ocean along its east edge, lagoons

and swamps along the west edge. North and South boundaries are Periya

Neelavanai of Baticaloa District and Karaithivu Pradeshiya Sabha, respectively.

Kalmunai is a densely populated town and the most urbanized areas of the town

are lying on the sand dunes.

Kalmunai town is situated approximately 250 Km East of Colombo City that is

one of the highly tsunami effected town in the East of Sri Lanka.

Due to the conflict prevailed for almost three decades, various infrastructures

have been damaged. That has been seriously affected the economic activity in

this region. The mean house hold income per month in the Eastern Province is

estimated to be 60 percent of national average. This figure indicates rather

deteriorated economic situation of the region in comparison with other provinces

in Sri Lanka.

The residents living in this area have been suffered from inundation caused by

the storm water in rainy season.

1.2 Objective of the Project

The main objective of this project is to reduce the flooding risk in

Kalimunaikudy and Islamabad.

The study is focusing on followings:

• Evaluate the condition of existing drainage facilities within the study

area and recommend the future use.

• Propose a technically feasible, economically viable and socially

acceptable solution for drainage system for the study area with the

consideration of proper implementation methods for the most viable

solution.

The drainage design is targeted to two major aspects.

1. Remove the storm water as soon as possible to prevent flood

damages.

2. Bring down the ground water table to a reasonable level to prevent

over flow of house hold septic tanks.

The outcomes of this study will be the conceptual design after carrying

out a detailed investigation and shall provide the following information.

i. Existing and proposed drainage paths.

ii. Existing and proposed sea outfall details.

iii. Average drain sizes and shape.

iv. Tentative cost Estimation

1.3 Project Locations

The study is mainly focus on decreasing the risk of flood and volume of

stagnant water in three areas; part of Kalmunaikudi, Kalmunai town and

and Islamabath area. ( See Fig.1.1 Project Locations )

Year Name of the Roads Estimated

amont (Millons)

2011 1. Mosque Road ,Thaika Road Kalmunaikdy

2. Islamabad Mosque road and Ameer Road

,Kalmunai Town

6

3.7

2012 Sahibu Road (New Outfall ) and Mosque lane 7

Fig 1.1- Drainage Project Locations in 2011 and 2012 under NELSIP

1.4 Data Collection

Detail Survey was carried out for all individual three sites providing

layout of proposed area, existing drains and culverts, spot levels of the

area etc.

Plans available with the Survey Department, the newly surveyed plans

and recent Satellite Images have been examined along with the

Meteorological data collected from Department of Meteorology.

Social survey was carried out in the project area to collect information

including flood level of the area, flooding segments, frequency of flooding,

reasons for flooding and other opinion related to flooding were collected

from following sources.

� Interviews with community members experiencing floods and

drainage related problems.

� Group discussions with community leaders, MC officials and other

representatives from UDA Office, RDA, Agrarian Development

Department, Irrigation Departments, Samurdhi Centers etc.,

1.5 Maps Used

The following maps were used for this study from various sources given

below.

Type of Map Scale Source

1. Topo Sheet 1:50,000 Survey Dept.

2. ArcView GIS - KMC

3. Survey Profile Vertical 1:100

Horizontal 1:1,000

Survey by KMC

4. Survey LS/Cross Sections 1:50 Survey by KMC

02 DESCRIPTION OF THE STUDY AREA

2.1 Location

Kalmunai is situated in the coastal area of Ampara district of Eastern

Province along Baticallo – Ampara (A4) road. It is at nearly 250 km East of

Colombo city and lies between 81°-28’ to 81°-52’ E longitude and 7°-05’ to

7°-30’ N latitude.

Figure 2.1:-Location Map of Study Area

Topography

The study area is a flat terrain along the costal of 2.5 m elevation from the Mean

Sea Level in average, on a permeable sandy soil surrounded by the India Sea and

swamps on the west. It has approximately 67 square kilometers of land area and

it is stretching near 10 kilometer along the coast.

The town is in the Indian Ocean and the lagoon drainage basin. About 90% of the

town area is drained by these two basins, and the distance between these two

drainage areas is about 700m. There is no stream to interconnect these two, as

shown in Figure 2.2.

Because of the characteristics of flat low lying terrain where the town is located,

an elevation with only +2.5m MSL on an average, the discharge of storm water is

considerably difficult. Further more, as it is surrounded by lagoons and swamps,

and also due to comparatively higher ground elevation at the beach, the situation

is more critical. According to a questionnaire survey carried out by a JAICA

study team in September 2005 and it was revealed that the inundation depth

exceeds 1m in some locations and flood water remains for 10 – 15 days during

heavy rainy season.

Figure 2.2:- KALMUNAI Town- Topo Map

2.2 Climatic Features

There are two major rainy seasons in a year in Sri Lanka, normally

Southwest Monsoon in May to September and Northeast Monsoon in

December to February. Due to the topological feature of Ampara and

Baticallo area, it is dry during Southwest Monsoon period having an

average rainfall less than 250 mm. the Northeast Monsoon brings more

rainfall about 500-1000 mm. The average annual rainfall during 1961-2005

is about 1000-2000 mm.

The average temperature is about 28.70°C, and during dry period in April

to August temperature is 30.4°C. The temperature variation in this area

from year to year is less than 10%. The Table 2.1 shows the monthly

average rainfall and monthly average temperature in Ampara district.

Table 2.1:- The monthly average rainfall and temperature in Ampara district.

Month Rain fall (mm) Temperature (0C)

January 200 – 400 25.0 – 27.5

February 100 – 200 22.5 – 25.0

March 50 – 200 25.0 – 27.5

April 50 – 100 25.0 – 27.5

May 25 – 100 27.5

June 25 - 50 27.5

July 25 – 100 27.5

August 25 – 100 27.5

September 25 – 100 27.5

October 100 – 200 25.0 – 27.5

November 300 – 400 25.0 – 27.5

December 200 – 400 25.0 – 27.5

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03 SOCIO-ECONOMIC ASPECTS

3.1 General Aspects

Kalmunai is situated in the coastal area of Ampara district of Eastern

province with the total area of 23 km2, adjoining Batticaloa and

Sammanthurai electorates. The district has developed along the Gal Oya

Scheme, Nation’s first irrigation scheme after independence, and known at

present as a rice-producing district.

According to the 1981 census, population of Kalmunai Municipal Council

is about 78,000 and 2001 census population is 94,500. In the past ten years,

population in Kalmunai Municipal Council is increased by 16,500.

Estimates suggest the Muslim population currently stands at some 75 per

cent, the Tamil population around 24 per cent, with the remaining one per

cent comprising Sinhalese and others. For the most part ethnic

communities tend to be segregated and internally homogeneous, with

urban clusters predominantly comprising a series of Tamil and Muslim

communities, often abutting. Building density in Muslim communities

tends to be higher, and household numbers tend to be larger, resulting in

higher population density.

3.2 Socio- Economic Background

The main source of income is derived from employment, business, and

agricultural activities. The agriculture particularly paddy cultivation is

predominant in most of these areas, besides fishery as secondary activity.

The area is characterized ethnically to be the Muslims and Tamil society

forming their own different culture and it is reported that the society of

the area will never intermingle each other. This fact must be taken into

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account for the future water and sanitation and other development

activities.

Economy of the area is assumed to predominantly rely on agriculture. As

previously, stated 60 percent of the total population is estimated to be

engaged in agriculture, 20 percent in business, 10 percent in fishery 10

percent in various types of occupations. Only a handful number of people

earn their living from business and office work.

3.3 Infrastructures

The neatest railway station is Baticalloa which is 38 km away from

Kalmunai town. A major trunk road namely Baticallo – Ampara road A4

traverses the coastal segment of the project area.

Electricity is available for full day operation supplying to Municipal and

limited number of rural areas from the national grit. Electricity is available

for coastal towns including the project area.

Pipe borne water supply is available for most of the areas such as

Sainthamaruthu, Kalmunai and Natpitimunai cities in Kalmunai

Municipal Council whereas Maruthamunai is getting pipe borne water

supply from the second phase of the ECTAD Water Supply Scheme. The

balance gets water from well and browser supply.

There are two hospitals in Kalmunai. Ashroff Memorial hospital is located

at Sainthamaruthu, and Kalmunai Base hospital is located in the North of

Kalmunai. Both hospitals which are the main hospitals in this area tottaly

have 230 beds. National Medical Statistical data indicate that diarrhoea

and gastro-enteritis diseases are common.

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04 DEMOGRAPHIC ASPECTS

4.1 Population of the Study Area

The population of Kalmunai Municipal Council is presented in Table 4.1

below extracted from 2001 census report. This illustrates the population

based on male and female and ages below 18 and over 18.

Table 4.1:- Population of Kalmunai Municipal Council

DS Division and Sector

Total No. of persons

Sex Age

Male Female Under 18 Yrs

18 Yrs & Over

Kalmunai -Muslim & Kalmunai –Tamil

70,439 34,231 36,208 27,041 43,398

Sainthamaruthu 24,018 11,936 12,082 9,716 14,302

Total (KMC) 94,457 46,167 48,290 36,757 57,700

Source: - Census of Population and Housing, 2001

4.2 Population Projection

The population of Kalmunai Municipal Council is estimated for the year

2005 is 102,000 as shown below. Future population of the township is

estimated to be 114,000 in the year 2010 and 150,000 in 2020 and 176,000 in

2030 according to the estimation of Municipal Development Authority’s

(UDA’s) Eastern Province Physical Plan.

Table 4.2:- Population Projection Kalmunai Municipal Council

DS Division and Sector

Population

2001 2005 2010 2020 2030

Kalmunai –Muslim Kalmunai –Tamil

70,439 76,000 85,000 112,000 131,000

Sainthamaruthu 24,018 26,000 29,000 38,000 45,000

Total (KMC) 94,457 102,000 114,000 150,000 176,000

Increase from 2005 - - 12,000 48,000 74,000

Annual Increase Rate - 2.1 2.2 2.7 1.6

Source: - Census of Population and Housing, Population Estimates (Eastern Province Physical Plan)

4-2

According to the collected data in the Kalmunai Municipal Council area,

population in the year 2001 is 94,457. Population forecast for the year of

2030 is 1765,000.

4.3 Population to be benefited

The project will cover the following Grama Niladhari Division (GND) and

the population of each division is given below. The total population of

beneficiaries will be about 12835 in year 2012.

No. GND Division Population

1. Islamabath 1061 2. Kalmunaikudi 4 1125 3. Kalmunaikudi 5 1675 4. Kalmunaikudi 6 1210 5. Kalmunaikudi 7 1592 6. Kalmunaikudi 8 1193 7. Kalmunaikudi 9 2276 8. Kalmunaikudi 10 994 9. Kalmunaikudi 11 1259

Total 12835

4.4 Special Consideration

Most part ethnic communities tend to be segregated and internally

homogeneous, with urban clusters predominantly comprising a series of

Tamil and Muslim communities, often abutting. Building density in

Muslim communities tends to be higher, and household numbers tend to

be larger, resulting in higher population density. This can be clearly seen

on Figure 4.1 shown below.

4-3

Figure 4.1 Arc View Map of the Project Area

5-1

05 CHARECTERISTICS OF EXISTING DRAINAGE FACILITIES

5.1. Inundation Problem

Certain areas of Kalmunai town including roads and residential,

commercial areas are subjected to flooding during heavy rains due to

following reasons:

Flat terrain, low-lying area, proximity to the sea and high water

table.

Inadequate drainage network or absence of drains.

Rapid developments makes increment in built up area resulting

higher runoff.

Unauthorized fillings and urbanization depleting the flood

retention areas.

Closure of drains due to building operations.

Poor maintenances of existing drainage channels.

Solid waste disposal in to drainage system.

Problems prevailing in existing drainage outfall system.

Municipal Council of Kalmunai has been suffered from inundation

problem, particularly during not only in the rainy but also in dry season

because of the above reasons. The depth of inundation frequently exceed

more than 1.0 meter, and brings about social-economic problems al well as

environmental pollution.

In order to solve this inundation problem or flood hazards and to lower

the shallow ground water table, the storm water should be discharged

efficiently by providing adequate size of drain, culverts, retention ponds

etc.

5-2

5.2. Existing Drainage

There is no pipe borne drainage in the project area like in the other

Municipal areas whereas few roads have road side gutters and the storm

water mixed with grey water discharged in to canals and finally to the sea.

Household’s wastewater from kitchen and bathrooms, and wastewater

from commercial and government institutions in the town are drains

through the town, which leads to some common discharge points. The

greywater (domestic wastewater from baths, showers, washbasin, kitchen

etc. other than blackwater) is discharged into the ground around their

buildings and most of the times to road a side drain especially in town

area that is a common practice in many Municipal areas of South East

Asia.

Roadside gutters in the municipality area are frequently clogging and this

requires frequent cleaning activities by the relevant authorities. The local

authority maintains the drains and arrangements are to be made to clean

them in most of the places.

Outsides the town area households use their wastewater on home

gardens. Most householders see this as a valuable resource during the

long dry spell. Storm water flows along natural drainage paths to the

major river and to the sea.

The followings recommendations are proposed to minimize the flooding in

the above certain areas.

- Improvements of drains and culverts.

- Proper maintenance of the drain channels.

- Water retention ponds to be kept.

- People awareness programs.

5-3

5.3. Solid Waste Management

Based on the unit waste rate of 0.4 kg/person/day and population data,

the present municipal waste generation from household in Kalmunai

Municipality is estimated at approximately 40 tons/day.

The tractor-trailers of Kalmunai Municipal Council collects rubbish

dumped by the side of the road and carts it to a dumping site located in

the central part of the Municipality. The frequency of collection is

generally irregular from once a day to once a week depending on the area.

Currently the Municipality has seven tractors of which capacity is

approximately 2 tons.

Municipal Council of Kalmunai has not been carrying out recycling

activities up to date. There are some private recycling shops in Kalmunai

Municipality. They collected materials such as plastic, glass bottle and

metal such as scrap iron, brass and aluminum, and generally transport to

Colombo and exported to other countries such as India.

Since the dumping areas are far from residential areas, householders

throw their waste in to drains or on road side, they do not see pollution as

a problem. However it may create an environmental problem in the future

and therefore the local authority should take remedial action to prevent

this. Households outside the town area either waste if they have space or

burn it.

It is recommended to have a proper strategic plan to collect the solid

waste in time and dispose, which will prevent blocking of the drainages.

5-4

5.4. Environmental Health

The health risk arising from side drains containing greywater depend

upon the pathogen content of the drain and the possibility of either direct

contact between persons, particularly children, and the drain or

contamination of water supplies by ingress of polluted drain water,

particularly for shallow well supplies and leaking distribution on

networks where interrupted supplies are frequent.

An infectious is one that can be transmitted from one person to another

directly or indirectly. All infectious diseases are caused by pathogens.

These are living organism such as bacteria, viruses or parasitic worms. A

disease is transmitted by the passing of these organisms from one person’s

body to another. Excreta related diseases are caused by pathogens

transmitted in human excreta, normally in the faeces. Inadequate facilities

for excreta disposal reduce the benefits of even a safe water supply by

transmitting pathogens from infected to healthy people by various routes

involving excreta.

Water level varies with the seasons. During the wet season groundwater

levels are high, close to ground level. And most of the septic tank and

soak-away pits contaminate the ground water which leads to the potential

for pathogens to migrate through the ground from the soakage pit to the

drains. Pathogens are not removed during the passage of effluent through

this process. Moreover, those household without their own latrines share

their neighbors’ latrine or excrete in the open areas.

The followings recommendations are proposed to minimize the

contamination in the above certain areas.

� Proper latrine facilities to those who excrete in the open area,

� People awareness programs.

5-5

� Legal action to be imposed against the people or factory owners

who do not take proper action to dispose their affluent

according to the approved standard set by the CEA.

6-1

6.0 ANALYSIS AND COMPUTATIONS

6.1 Design Approach

The data were collected by various methods and verified as far as possible

with the help of Kalmunai Municipal Council. According to the discussion

held with the officials from KMC, Agrarian Development Department, and

studying of the hydrological aspects of the area and an appropriate design

was adopted to avoid any hydrological problems arising from the project by

attending to the following tasks.

� Identified the topography that consists of flood plains and, wetlands.

� Familiarized with the climate and catchment characteristics inherent with

the change over from wet zone to dry zone.

� Analyzed the intensity, duration and frequency of rainfall.

� Ascertained the permeability of soil, slope of ground, land use pattern

with a view to drive a realistic discharge across the road trace.

� Obtained stream flow data and corresponding water levels.

6.2 Rainfall Data

Sri Lanka has a tropical monsoon climate. In the study area the mean annual

precipitation is around 1,650 mm. there are two main monsoon seasons called

Northeast monsoon and Southwest monsoon as given below.

Table 6.1 Annual Rainfall and Highest day Rainfall at Baticallo

Season Months

Second Inter- Monsoon October - November

Northeast Monsoon December - February

First Inter- Monsoon March – April

Southwest Monsoon May – September

Rainfall has not been gauged in Kalmunai, but in Baticalloa and Ampara.

Therefore, the data of Baticallo station have been considered for hydrological

analysis as it is the closet area with the same conditions. With regard to the

6-2

topography there are similarities and being coastal areas Kalmunai and

Baticallo are similar in elevation, tidal action, catchments characteristics etc.

Data was collected from the department of Metrology.

Average monthly rainfalls for 1996-2000 and 2001-2005 have been plotted

separately in Figure 6.1 below. There is no significant deviation in rainfall

pattern from 1996 to 2005.

0

100

200

300

400

500

600

700

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

Reinfall (mm/day)

Average 19961-2000 Average 2001-2005

Figure 6.1 Monthly Rainfall Pattern in Baticallo

It shows that the study area is getting much rain during the northeast

monsoon season starting from December to February.

0

20

40

60

80

100

120

0 50 100 150 200 250 300 350 400

Time (Days)

Reinfall (mm/day)

Figure 6.2 Daily Rainfall Pattern in Baticallo

6-3

The following Table and Graph shows annual rainfall, daily rainfall for the

last 10 years.

Table 6.2 Annual Rainfall and Highest day Rainfall at Baticallo

Year Annual Rainfall (mm/Y) Highest Daily Rainfall (mm/day)

1996 1,681 101.2

1997 1,631 123.4

1998 1,010 65.3

1999 1,990 134.7

2000 2,022 97.0

2001 1,636 110.8

2002 1,873 134.7

2003 1,853 102.9

2004 2,595 236.7

2005 1,223 75.6

1,752 (Average) 236.7 (maximum)

0

500

1,000

1,500

2,000

2,500

3,000

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Rainfall (mm)

Annual Rainfall (mm/Y) Highest Daily Rainfall (mm/day)

Figure 6.3 Rainfall Data in Baticallo (1996-2005)

6-4

6.3 Design Criteria for Drainage

The flowchart below describes the criteria used for the drainage design in this

study.

Identification of Drainage Network

Identification of Catchment and Subcatchment

Site Maps & Survey Plans

Improvements to existing drainage structures

Checking the adequacy of the

existing Drainage

Land use pattern

Runoff coefficient

Design of Sizes & Invert levels of new drains &

related structures

Project Return Period

Rainfall Data

Rainfall Intensity Estimation

of peak runoff

Checking of Flow Profile

6-5

6.4 Rainfall Intensity

Rainfall intensity (I) normally given in millimeter per hour is a function of

time of concentration (Tc), can be estimated using several methods.

Time of concentration is directly depending on length of main stream in the

catchment area and the average slope of the catchment. The empirical

measurable catchment physiographic characteristics are as follows.

Tc = L + 15 V x 60

Where,

Tc - Time of concentration in minutes.

L - Length of maximum stream length in meters

V - Average velocity in meters per seconds

15 - Time for over land flow (till it connects to a proper path)

The magnitude of Average Velocity can be adopted from the table given

below in Table – 6.2 for the appropriate catchment slope.

Table– 6.3 Average Velocity for stream slope

Average Gradient of the Stream in Percentage

Average Velocity / (m/Sec)

0 to < 1 1 to < 2 2 to < 4 4 to < 6

≥ 6

0.45 0.60 0.90 1.20 1.50

Source: Design of Irrigation Head works for small catchments- A.J.P. Ponrajah.

The relationship between Time of Concentration (Tc) and rainfall intensity (I)

is given in Table – 6.2, and also schematically presented in Fig. 6.2. For an

appropriate recurrence period to be project Rainfall Intensity (I) could be

found using this relationship.

6-6

The Intensity Duration Frequency Curve for Baticallo, developed by

Department of irrigation, is used in this hydrological analysis.

Table 6.4 Rainfall Intensity Duration Frequency Curve for Baticallo

Time (hrs)

Rainfall Intensity (mm/hr)

Return Period in Years

2 5 10 25 50

0.25 92 110 121 135 146

0.50 70 84 94 106 115

1 50 60 67 76 83

2 30 39 46 54 60

6 13 18 21 25 28

Source: Rainfall Intensity Studies for Sri Lanka- G.T.Dharmasena and S.M. Premasiri

0

20

40

60

80

100

120

140

160

0 20 40 60 80 100 120

Reinfall Duration (min)

Rainfall Intensity (mm/hr)

2 5 10 25 50

Figure 6.4:- Rainfall intensity-Duration Curve (Baticallo)

6.5 Land-use Pattern in Watersheds

The general land-use pattern of watershed is urban, with business and

contiguous residential premises. The major land-use in watersheds is

identified from maps and site investigation. After confirmation on the main

watershed, sub basins, drainage network and outlets, the following

parameters were selected for the use of run off calculations.

6-7

� watershed are

� length of the longest drainage

� slope of the different segment of longest river

� land-use pattern

� extent of the localized flood detention areas

6.6 Catchment Areas

From the Contour maps and the topographical elements such as main roads,

natural streams, ponds etc., the catchment boundary of the project area was

identified and hence areas of the catchments were determined. These

catchments were divided into sub-catchments to design internal elements

such as drains, culverts, retention ponds etc. Figure 6.3 shows the main

catchments of the project areas.

6.7 Estimation of Peak Storm Water Flow

Estimation of peak flow is vital for the design of the drainage system. The

peak flow estimates would enable to identify the environmental concern such

as overflows and inundation depth in more scientific manner.

The peak flow estimates are made either by analyzing the available flow

records, extrapolating representative flow records or applying rainfall-run off

relationship.

The flow estimation for the watersheds draining into the canal system, need

to be based on rainfall-runoff relationship. Such relationship either

incorporates empirical parameters or use parameters that are based on

watershed characteristics. The accuracy of the estimates depends on the

accuracy of the parameters and hence a verification process is often carried

out using measured data. In the presents of measured value, flow can be

made using reliable watershed models and with observed data of recent past.

6-8

This work is an application of commonly used peak flow hydrological models

on each watershed concern. The values obtained with each model were

compared and judgment were made giving due considerations to the model

structure, model parameters and the reliability of these inputs and observed

flood records during the last one year.

With the availability of data, the estimation of expected peak storm water

flows were ascertained using rational formula, which is widely used in

engineering practice for small catchments.

Rational Formula

Rational formula is stated as a reliable method to estimate peak flow in small

watersheds. However, due to the importance of these watersheds, being

located in the main city and adjacent to the city it was decided that only the

very small watersheds would be modeled using rational formula.

Rational formula Q = CIA/360

Where

Q - Flow in cubic meters per second

C - Run off co efficient expressing the fraction of the rainfall that is

considered as effective direct runoff.

I - Rainfall intensity in mm/hr for a duration corresponding to the time

of concentration for the catchments area and having a recurrence

period appropriate to the project.

A

-

Catchments area in hectares.

6.8 Run off coefficient

Run-off coefficient (C) expressed as factor of imperviousness or coefficient of

discharge depending on catchment characteristics which is widely used to

estimate the stream flow rates. For large catchment areas, compound run-off

6-9

coefficients have been calculated based on terrain and soil features. Table 6.3

shows the typical values of Run-Off coefficient for various types of ground

features.

Table – 6.5 Typical Values for Runoff Coefficient – C for Urban Areas

Description of Area Runoff Coefficient [C]

Business

Downtown Areas

Neighbourhood

0.70 – 0.95

0.50 – 0.70

Residential

Single Family Areas

Multiunits, Detached

Multiunits, Attached

0.30 – 0.50

0.40 – 0.60

0.60 - 0.75

Residential (Suburban) 0.25 – 0.40

Apartment Dwelling

Areas

0.50 – 0.40

Industrial

Light Areas

Heavy Areas

0.50 – 0.80

0.60 – 0.90

Parks, Cemeteries 0.25 – 0.35

Play Grounds 0.25 – 0.35

Railroad Yard Areas 0.30 – 0.40

Unimproved Areas 0.20 – 0.40

Streets

Asphalt

Concrete

Brick

0.70 – 0.95

0.80 – 0.95

0.70 – 0.85

Drives and Walks 0.75 – 0.85

Roofs 0.75 – 0.95

Lawns; sandy Soil

Flat, 2%

Average, 2 – 7%

Steep, 7%

0.05 – 0.10

0.10 – 0.15

0.15 – 0.20

Lawns; Heavy Soil

Flat2%

Average2 – 7%

Steep, 7%

0.13 – 0.17

0.18 – 0.22

0.25 – 0.35

6.9 Return Period

The planning scale or the recurrence interval (Return period) for the design,

depends on the degree of importance of importance of the drainage. In a river

basin, a balance of planning scale should be maintained between upper and

lower reaches as well as between main streams and tributaries in a view of

6-10

consistency in planning scale for the entire basin. When a planning scale is

applied for a main stream in lower reaches, an equivalent or lower planning

scale is given for that main stream in its upper reaches. Planning scales for

tributaries are lower than that for min stream.

Drainage Return Period

A Importance stretches in large scale rivers 100 - 200 years

B Middle scale rivers 50 - 100 years

C Small scale rivers/ Streams/ Tributaries 10 - 50 years

D Urban Drainage 5 - 10 years or less

When area is very congested the design return period is restricted to 2 years.

In this study 5 years return period is adapted for the design of urban drainage

Computation of Retention Period

Most of the cases the governing factor for the determination of retention area

depend on the downstream boundary conditions such as culverts, drains

those can not be improved or flood level in the mainstream. Considering

these factors maximum discharge passes through the down stream structures

has been calculated. Hence the minimum volume that has to be kept as

retention is calculated. By having the longitudinal sections of the ground and

considering other factors as land value, existing ground features etc., the

retention ponds are kept in appropriate places.

6.10 Checking the Adequacy of Drainage System

Survey work of existing drainage scheme has been carried out along the

canals including flood prone areas with the view to determine the adequacy

of existing drainage scheme. Mathematical modeling has been carried out to

check the existing situation and improvements has been proposed by

considering the future scenarios.

6-11

6.11 Drain and Culvert Design

The proposed drainage scheme has been arrived at after ascertaining the

catchment areas and the discharges resulting from such catchment areas. The

objective is to remove surface water and ground water to some extent from

developed residential areas, paved roads and their immediate surrounding

areas. This is achieved by providing a system of drains and culverts all

connected together in one network and ultimately discharging into a main

stream and then to the sea outfalls and to the lagoon drainage.

The size and type of the drain and the culverts are then chosen for the design

discharge by considering headwater and tail water elevations and allowable

outlet velocity.

Velocity of Flow

The velocity of that has been adapted is such that is neither erosion nor

siltation. Minimum velocity of 0.6 m/s and maximum velocity of 3m/s has

been adapted for proposed lined drains and culverts.

Manning’s formula is widely used to compute the canal cross sections and the

openings of culverts where the flow is approximated to be normal flow under

gravity. Flow discharge is calculated using the Manning’s formula as given

below for the appropriate return period.

Q = (1/n).A.R 2/3 S ½

Where Q - flow in cubic meters per second.

n - Manning’s roughness coefficient (see Table 04)

A - Cross Sectional area of Flow

R - Hydraulic gradient of drain

S - Slope of the canal bed.

6-12

The following factors have been considered in the hydraulic design of drain

channels and their stability.

� Design frequency

� Channel gradient, which effects both the channel size and velocity

� Channel shape and alignment

� Flow discharge and velocity of flow

� Free board (average 20% of water depth)

� Local soil condition

Table 6.6 given below shows the values of roughness coefficient ‘n’ used for

the design of drains and culverts.

Table– 6.6 Values of Roughness Coefficient “n”

Type of Channel Description

Minimum Normal Maximum

Lined or Built – up Channels 1. Metal

a. Smooth steel surface

i. Unpainted

ii. Painted

b. Corrugated

0.011

0.012

0.021

0.012

0.013

0.025

0.014

0.017

0.030

2. Nonmetal

a. Cement

i. Neat, surface

ii. Mortar

b. Wood

i. Planed, untreated

ii. Planed, creosoted

iii. Unplanned

iv. Plank with battens

v. Lined with roofing paper

c. Concrete

i. Trowel finish

ii. Float finish

iii. Finished, with gravel on bottom

iv. Unfinished

v. Gunite, good section

vi. Gunite, wavey section

vii. On good excavated rock

viii. On irregular excavated rock d. Concrete bottom float finished with

sides of

i. Dressed stone in mortar

ii. Random stone in mortar

iii. Cement rubble masonry,

plastered

iv. Cement rubble masonry

v. Dry rubble or riprap

e. Gravel bottom with sides of

0.010

0.011

0.010

0.011

0.011

0.012

0.010

0.011

0.013

0.015

0.014

0.016

0.018

0.017

0.022

0.015

0.017

0.016

0.020

0.020

0.017

0.011

0.013

0.012

0.012

0.013

0.015

0.014

0.013

0.015

0.017

0.017

0.019

0.022

0.020

0.027

0.017

0.020

0.020

0.025

0.030

0.020

0.013

0.015

0.014

0.015

0.015

0.018

0.017

0.015

0.016

0.020

0.020

0.023

0.025

0.020

0.024

0.024

0.030

0.035

0.025

6-13

i. Formed concrete

ii. Random stone in mortar

iii. Dry rubble riprap

f. Brick

i. Glazed

ii. In cement mortar

g. Masonry

i. Cemented rubble

ii. Dry rubble

h. Dressed ashlars

i. Asphalt

i. Smooth

ii. Rough

j. Vegetal lining

k. Concrete pipes and box culverts

0.020

0.023

0.011

0.012

0.017

0.023

0.013

0.013

0.016

0.030

0.012

0.023

0.033

0.013

0.015

0.025

0.032

0.015

0.013

0.016

0.015

0.026

0.036

0.015

0.018

0.030

0.035

0.017

0.500

0.018

6.12 Filling levels and Reservation for roads

Filling levels of the project areas are based on the flood levels considered,

water logging problem, sewerage, structural requirements and to have

minimum depth in the canal sections. The adjoining permanent properties

and filled land in the vicinity also considered before proposing the fill level of

the area.

Prior to commencement of proposed work, it is necessary to ensure that

sufficient reservation is available along the canal to construct maintenance

road for a required width. The municipal council is expected to give high

priority for this task, for the removal of obstructions and debris along the

canal, and to maintain well.

6-14

7.0 Environmental impacts

The proposed project will

� Minimize damages to houses, business establishments, public offices,

infrastructure facilities etc., due to ineffective storm water drainage

system which prevails in the project area.

� Reduce cost of maintenance and repair of roads and public

infrastructure.

� Improve the water quality of the existing canals.

� Reduce health hazards caused by stagnant storm water, specially water

borne diseases like diarrhea, Diesentry and also reduce breeding of

mosquitoes thereby reducing the spread of vector diseases such as

Malaria, Dengue etc.,

� Increase land values due to reduction in water logging and inundation.

9-1

8.0 Project Cost Estimates

The following shows the project cost estimated for improvements of flood

protection and drainage improvements

No Description Amount (Rs)

1.

Construction of Drain along Mosque Road , Thaika Road and Thaika –Mosque Roads Connection. To be implemented in the 2011 Project

6,000,000.00

2.

Construrction of Drain along Sahibu Road , Laying of Precast Concrete pipes , Construction of sea outfall , Construction of drain at Mosque lane , Mosque road - Mosque lane connection. To be implemented in the 2012 Project

7,000,000.00

3.

Construrction of Drain along Islamabad Mosque Road and Ameer Road , To be implemented in the 2011 Project

3,700,000.00

Total 16,700,000.00

9-2

9.0 Project Evaluation

9.1 Benefit

The benefits by implementation of the project are expected in terms of savings

on preventing inundation damages, savings on social welfare and health

expenditure, savings on income losses, savings on maintenance of roads,

increased land values.

No social economic survey was carried out this time, considering the

preliminary stage of the study. Therefore, some of the benefits were

calculated from previous studies in the past in the same area, which were

focused on the similar issues (flooding & Drainages)

1. Saving on Preventing Damages

2. Saving on Social Welfare & Health

3. Saving on Road Maintenance

4. Saving on Income losses

5. Benefit due to Land Price Increase

6. Prevention of damages by inundation

7. Prevention of communal problem

8. Saving on compensation payment due to flooding

10-1

10.0 Recommendations and Conclusions

By implementing this drainage proposal in this project area, the people living

in the vicinity will be greatly benefited. Economic feasibility of the project can

be considered to be positive taking into account both tangible and intangible

benefits. Economic benefits of the project are

� Preventing flood damages to houses, business premises, roads, canals,

gardens and cultivation.

� Saving on social welfare expenditure on flood victims.

� Saving on health expenditure relief.

� Prevent income losses of the people.

� Increase in land value.

� Reduction in adhoc development.

� Prevention of communal problem

� Saving on compensation payment due to flooding

In addition to that many intangible benefits are expected as follows:

� Promotion of economic development

� Improvement of people’s living conditions

� Reduction of inconvenience in people life.

� Improvement of the hygienic environment

� Improvement of the water environment

� Contribution to poverty reduction.

Based on above consideration, it is concluded that the proposed storm water

drainage improvement project is economically and technically viable. Hence it can

be recommended as environmental improvement project.

A-1

Annexure

-1 . D

esign C

alcula

tion and T

able

s

Sch

em

atic Layout of th

e C

atc

hm

ents

A

. C

atch

men

t -6

Haniffa Road

Thaika Road

Mosque Road

Moaque lane

Madarasa Road

Cassim Road

QH1

QH2

QMo1

QTh2

QTh1

QMo2

QMl2

QMl1

QMa2

QMa1

QMa3

QC2

QC3

QC1

Q2

Q1

QM

Q4

Q3

A-2

B

.Cat

chm

ent

-5

P.P Road

Sahibu Road

Haniffa Road

QS1

QP3

QP2

QS2

QS

QP1

QH

A-3

Speci

men C

alcula

tion

Consider M

osq

ue R

oad D

rain

leadin

g to o

utfall ( Q

M)

Len

gth

of

lon

ges

t st

rea

m p

ath

, L

=

8

00m

A

rea

of

the

catc

hm

ent,

A

=

2

5.4

Hec

. S

ay,

Cat

chm

ent

slo

pe,

S

=

0.0

4

<

1 F

rom

Tab

le 0

1, A

ver

ag

e V

elo

city

, V

=

1.

5 ft

/se

c

=

0.

457

m/

s T

ime

of

Co

nce

ntr

atio

n, T

c

=

L

+

15

V x

60

=

8

00/

(0.

457

x60

) +

15

=

44

min

ute

s

Co

nsi

der

25

Yea

rs R

etu

rn P

erio

d a

s th

e d

rain

ser

ves

lar

ger

are

a

Fo

r 25

Yea

r R

etu

rn P

erio

d,

Fro

m T

able

02

or

Fig

ure

05,

Catchments Area

Longest stream

path

Stream

Considered Discharging Point

Q

A-4

Rai

nfa

ll I

nte

nsi

ty,

I

=

95

mm

/H

r F

rom

Tab

le 0

3,

Ru

n-O

ff C

oef

fici

ent,

C

= 0

.35

R

atio

nal

Fo

rmu

la,

Dis

char

ge

at C

on

sid

ered

po

int,

Q M

=

CIA

/3

60

=

0.

35 x

95

x25

.4

360

= 2

.346

m

3/

Sec

Sect

ion D

esi

gn

C

on

sid

er s

ecti

on

wit

h 1

.2 m

Wid

th

, Av

erag

e D

epth

=1

m ,

Slo

pe

of

Dra

in (

Fro

m t

he

LS

) =

(2.

09

6-.7

63)/

(783

-29

0) =

.00

27

Fro

m T

able

5.4

n

= 0

.013

A

pp

ly M

ann

ing

eq

n,

Q =

(1/

n).

A.R

2/

3 S

½

A=

1

.2*.

1=

1.2

m2

, W

ette

d P

erim

eter

= 1

.2 +

2*1

=3

.2 m

R=

1.2

/3.

2 =

0.37

5

So

th

e F

low

Ca

pa

city

of

the

Dra

in Q

= 2

.49

4 m

3/

s >

2.3

46 m

3/

s ..

Des

ign

Sat

isfi

es

Vel

oci

ty =

Q/

A=

2.4

94/

1.2

=

2.0

8 m

/s

Fru

de

No

=

= 2

.08

/ =

0.6

64

<1

( F

low

is

sub

-cri

tica

l )

Cri

tica

l D

epth

=

=

= 0

.86

m

Cri

tica

l S

lop

e S

c=

=

0.0

153

7

A-5

TA

BLE

- 1

C

ALC

ULA

TIO

N O

F D

ES

IGN

RA

INW

AT

ER

DIS

CH

AR

GE

Ca

tch

me

nt

Ro

ad

Flo

w I

D (

Re

fer

the

Sce

ma

tic

lay

ou

t )

Ex

ten

t o

f

catc

hm

en

t (h

a)

Lon

ge

st

pa

th o

f

Dra

in (

m)

Dra

in S

lop

e

Tim

e o

f

Co

nce

ntr

ati

on

(Min

)

Re

turn

Pe

rio

d

(Ye

ar)

Ra

infa

ll

Inte

nsi

ty

Ru

no

ff

Co

eff

icie

nt

De

sin

g D

isch

arg

e

(m3

/se

c)

Ca

ssim

Qc1

2.1

36

00

.00

22

85

85

0.3

50

.17

35

41

66

7

Qc2

1.2

18

50

.00

22

25

86

0.3

50

.10

03

33

33

3

Qc3

11

65

0.0

02

21

58

60

.35

0.0

83

61

11

11

Ma

da

rsa

Q

Ma

12

.14

00

0.0

02

30

58

40

.35

0.1

71

5

QM

a2

1.2

18

50

.00

22

25

86

0.3

50

.10

03

33

33

3

QM

a3

11

65

0.0

02

21

58

60

.35

0.0

83

61

11

11

Mo

squ

e l

an

eQ

Ml1

4.3

58

00

.00

33

65

78

0.3

50

.32

60

83

33

3

QM

l21

13

50

.00

32

05

86

0.3

50

.08

36

11

11

1

Q3

8.5

61

00

.00

33

71

08

30

.35

0.6

85

90

27

78

Q1

13

.97

00

0.0

03

41

10

81

0.3

51

.09

46

25

Mo

squ

eQ

Mo

14

.15

90

0.0

03

37

57

70

.35

0.3

06

93

05

56

QM

o2

11

00

0.0

03

19

58

60

.35

0.0

83

61

11

11

QM

25

.48

00

0.0

03

44

25

95

0.3

52

.34

59

72

22

2

Th

aik

a

QT

h1

3.7

50

00

.00

43

35

80

0.3

50

.28

77

77

77

8

QT

h2

0.9

11

00

.00

41

95

86

0.3

50

.07

52

5

Q2

6.4

50

00

.00

43

35

80

0.3

50

.49

77

77

77

8

Ha

nif

faQ

H1

0.9

11

00

.00

41

95

86

0.3

50

.07

52

5

QH

20

.91

10

0.0

04

19

58

60

.35

0.0

75

25

P.P

Q

P1

3.6

39

00

.00

32

95

83

0.3

50

.29

05

QP

22

.12

00

0.0

03

22

58

60

.35

0.1

75

58

33

33

QP

31

.51

20

0.0

03

19

58

60

.35

0.1

25

41

66

67

Sa

hib

uQ

S1

45

35

0.0

02

35

57

80

.35

0.3

03

33

33

33

QS

21

.51

45

0.0

02

20

58

60

.35

0.1

25

41

66

67

QS

15

.25

60

0.0

02

35

10

81

0.3

51

.19

7

Ha

nif

faQ

H3

47

50

.00

53

25

80

0.3

50

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33

33

33

3

Ca

tch

me

nt-

1Is

lam

ab

ad

ro

ad

1

.64

20

0.0

05

30

58

40

.35

0.1

30

66

66

67

KA

LMU

NA

I M

UN

ICIP

AL

CO

UN

CIL

CATCHMENT-6 CATCHMENT -5

A-6

TA

BLE

- 2

De

sig

n o

f D

rain

Se

ctio

n

Ca

tch

me

nt

Ro

ad

De

sig

n

Dis

cha

rge

(m3

/se

c)

slo

pe

of

dra

in

Ma

nn

in

g

coe

ffic

e

nt

'n'

De

pth

(m) W

idth

(m

)Flo

w

are

a(m

2

)

we

tte

d

pe

rme

ter

(m)

Hy

dra

uli

c Ra

diu

s

(m)

Flo

w

Ca

pa

city

(m3

/s)

Ve

loci

ty

(m

/s)

Fru

de

No

Cri

tica

l

De

pth

Cri

tica

l

Slo

pe

Th

aik

a R

oa

d

0.2

87

78

0.0

03

80

.01

30

.60

.40

.24

1.6

0.1

50

.32

29

71

.34

60

.55

50

.21

99

0.0

46

12

Mo

squ

e R

oa

d0

.30

69

30

.00

30

.01

30

.70

.40

.28

1.8

0.1

55

60

.34

12

21

.21

90

.46

50

.22

81

0.0

46

75

Th

aik

a -

Mo

squ

e

Co

nn

ect

ion

0

.49

77

80

.00

20

.01

30

.80

.75

0.6

2.3

50

.25

53

0.8

30

71

.38

50

.49

40

.41

28

0.0

10

65

Mo

squ

e la

ne

0

.68

59

0.0

03

0.0

13

0.7

50

.65

0.4

87

52

.15

0.2

26

70

.76

37

51

.56

70

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80

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03

0.0

15

37

Mo

squ

e R

oa

d-

Mo

squ

e la

ne

con

ne

ctio

n

1.0

94

63

0.0

03

0.0

13

0.8

0.9

0.7

22

.50

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81

.32

29

51

.83

70

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60

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30

.00

73

1

Ma

in D

rain

of

ou

tfa

ll

2.3

45

97

0.0

02

70

.01

31

1.2

1.2

3.2

0.3

75

2.4

94

25

2.0

79

0.6

64

0.8

59

20

.00

39

6

Sa

hib

- H

ain

ffa

Ro

ad

co

nn

ect

ion

0.2

33

33

0.0

03

0.0

13

0.7

0.3

50

.24

51

.75

0.1

40

.27

83

11

.13

60

.43

30

.19

92

0.0

63

78

Sa

hib

Ro

ad

Ou

t

fall

- R

ect

an

gu

lar

1.1

97

0.0

03

0.0

13

0.8

0.9

0.7

22

.50

.28

81

.32

29

51

.83

70

.65

60

.56

30

.00

73

1

Sa

hib

Ro

ad

Ou

t

fall

-Pip

e1

.19

70

.00

40

.01

20

.90

.60

31

2.2

48

0.2

68

21

.32

20

92

.19

2

Isla

ma

ba

d r

oa

d

0.1

30

67

0.0

04

0.0

13

0.6

0.3

50

.21

1.5

50

.13

55

0.2

69

51

.28

30

.52

90

.19

49

0.0

63

27

KA

LMU

NA

I M

UN

ICIP

AL

CO

UN

CIL

CATCHMENT-6 CATCHMENT-5 CATCHMENT-1

A-7

An

nex

-2 D

raw

ing

s

Mas

ter

Lay

ou

t

A-8