Urban Water Logging and Drainage System

Introduction

Drainage network is an important element for any community. The artificial and natural drainage helps to remove sullage and storm water from surface and prevents many problems such as water logging, environmental pollution etc. So it has importance in the natural consequence as well as in our daily life. Moreover it is an important utility service for a community.

 The Delhi workshop defined drainage as “the removable of unwanted water from human settlement”. Such unwanted water can include storm runoff and flood water from seasonal rains, marsh or pond water in low lying areas, and the used domestic waste water (sullage) of the community. All these constituents have a potential impact on health and well-being (RWSG and WHO, 1991). So drainage is important in itself as utility service as well as in natural considerations.

 Drainage systems are needed in developed urban areas because of the interaction between human activity and the natural water cycle. This interaction has two main forms: the abstraction of water from the natural cycle to provide a water supply for human life and the covering of land with impermeable surfaces that divert rainwater away from the local natural system of drainage (Butler, 2002). These two types of interaction give rise to two types of water that require drainage.

 The first type, wastewater, is water that has been supplied to support life, maintain a standard of living and satisfy the needs of industry. After neither use, if not drained properly, it could cause pollution and create health risks. Wastewater contains dissolved material, fine solids and larger solids, originating from WCs, from washing of various sorts, from industry and from other water uses.

 The second type of water requiring drainage, storm water, is rainwater (or water resulting from any form of precipitation) that has fallen on a built-up area. If storm water were not drained properly, it would cause inconvenience, drainage, flooding and further health risks. It contains some pollutants, originating from rain, the air or the catchments surface.

 Bangladesh is experiencing environmental degradation due to rapid urbanization, increase in population, and industrialization. The process of urbanization is linked with the economic development, which makes an increasingly higher contribution of the national economy. However, when the growth of urban population takes place at an exceptionally rapid rate, most cities and towns are unable to cope with changing situations due to their internal resources constraints and management limitations (Bari and Hasan, 2001). Provision of infrastructure services such as, water; drainage and sanitation along with waste disposal are greatest concern to human settlements. Failure to provide these services adequately results in many of well-known costs of urbanization: threats to health, loss of urban productivity and environmental quality.

 Drainage in human settlements has assumed considerable significance due to the enormous population growth and the rapid but haphazard urbanization evident in most countries. Failure to provide adequate drainage is directly linked to the resurgence of malaria, the spread of diarrhea diseases, damage to housing and property, disrupted communications, lost income and environmental degradation. So an effective drainage network system as well as management of that system is very important.

 Background of the study 

 Dhaka is the capital city of Bangladesh and center of the socioeconomic and political activities of the country. It is one of the mega cities of the world.  Its present population is about 10 million (Islam, 2003) and it increasing day by day. The increased population has made tremendous pressure on the management of different utilities and service facilities. Drainage system is one of such facilities. The drainage congestion is now the bearing problem of the Dhaka city. Open and low land that store rain and discharge water from the residential, commercial, industrial area have been already encroached to meet housing and other demand of growing population. Elimination of local water storage areas by land filling is one of the major causes of rainfall flooding and drainage congestion in many location of the Dhaka city. The Dhaka Water and Sewerage Authority (DWASA) and the Dhaka City Corporation (DCC) are entrusted with job of keeping the city free from water logging. The city corporation has some 11,00 km. of surface drains and the water and sewerage authorities own about 3,000 km. of underground sewer lines (Ahmed, 2003).

 Water, stagnant on roads, mainly goes down the WASA sewer lines through surface drains owned by the corporation. The city corporation officials blame WASA for not maintaining the sewer lines properly and WASA officials said surface drains mostly remain clogged with solid waste and construction materials that also block the surface opening of the sewer lines (Ahmed, 2003). A proper drainage system does not mean a few sewerage lines and drains only; it means building up a network that interconnects drains and sewerage lines with the natural water-bodies such as ponds, lakes and canals. The lakes, once large and healthy, have shrunk and grown sickly by indiscriminate encroachment of the land grabbers. The consequence of such indiscriminate construction is right before our eyes. A few hours of rain inundate many of the city streets and during floods the entire low-lying areas of Dhaka go under water for days on end. If water bodies had still been around they could have easily contained the extra volume of water that might have invaded the city.

 Dhanmondi residential area is the well known place of the Dhaka city which includes many of the important and oldest residential area of the country. This area is actually affected by the drainage congestion. At present the inhabitants of Dhanmondi area suffer from severe water flooding and water logging during the monsoon from June to October. Construction of road and other infrastructure modifies the pattern of drainage flow. As a result some of the drains are fail to carry the increase discharge water. For the increased demand of land many water bodies are filled for construction of building and others uses in unplanned way that was previously play an important role in the drainage system of this area. As a result catchment loses its capacity containing excess runoff water and creates water logging. More over the surface drains in many areas remained clogged with solid waste and construction materials, contributing to drainage congestion, and thereby resulting water logging. With the footpaths going under rainwater, pedestrians had to walk with their trousers rolled up to knee.

 Renovation and repairs of city roads has ironically obstructed water outlets at some places. Manholes at some places have not been raised proportionately because of which manhole mouths remain clogged. Sustainable drainage systems can form a key part of sustainable developments by reducing the impacts that might otherwise occur to surface water runoff and water resources. If the drainage network can work properly the other utility service also can run smoothly. They are inter-related and dependent on each other to complete their recital.

Objective of the Study

The ultimate goal of the study is to improve the drainage condition of the Dhanmondi residential area due to remove the water logging problem of the area. However there are some specific objectives to full fill the goals. These are,

  • To make an inventory of the existing drainage network of the Dhanmondi residential area.
  • To identify the causes of drainage congestion of the Dhanmondi residential area.
  • To investigate the problem of drainage congestion on city life.
  • To suggest some recommendation for improving the drainage condition of Dhanmondi residential area.

Scope of the Study

The study will present a rigorous picture of the drainage network of the study area and try to find out the causes of drainage congestion, problems on city life and finally give some appropriate solution for improving the drainage system of the Dhanmondi residential area through direct field investigation and gather information from different secondary sources. This study will not focus on the over all drainage network of the Dhaka city. This study will also try to propose some effective waste management solution which will obviously lead to improve the drainage condition and environmental sustainability. This study will also provide effective coordination mechanism between DCC and DWASA. Some practical solution about protecting the natural water bodies will also focus on the present study. The study will not focus in cost involvement in the development of the drainage network of the study area.    

 Study area

Geographical Location

Dhanmondi a planned residential area of dhaka city. Though Dhaka was one of the capital cities of Bengal, it had lost its glory during the colonial period and was reduced over time to being merely a mofussil district town. Dhaka was once again made a capital, this time of East Pakistan, after the Partition of Bengal in 1947. The dictates of the new capital necessitated the establishment of offices and physical infrastructure. An autonomous authority, Dhaka Improvement Trust (DIT), was established in 1956 to turn Dhaka town into a planned metropolis. With this objective in view, a Master Plan was drawn in 1959Dhanmondi (dhaka district) with an area of 7.74 sq km, is bounded by tejgaon and mohammadpur thanas on the north, lalbagh thana on the south, ramna thana on the east, hazaribagh and Mohammadpur thanas on the west. Administration Dhanmondi thana was established in 1976. It consists of thr 3 wards, 20 mouzas.

 Area and Population of the Study area

The study area is about 7.74 sq. km. The total population of the study area is 162088;  persons in 2009. The annual growth rate of the population of the study area is 5.6 percent per year ((Banglapedia, 2009). Average literacy rate 70.9%; male 54.87% and female 45.13%; % The decadal growth rate of the population is 23.79 %. Muslim 98.02%, Hindu 1.3% and others 0.68%. The decadal growth rates of population in Dhanmondi in the last 50 years are shown in Table

Table 1.1: Decadal Growth Rate of Population of Dhanmondi residential area

DecadeGrowth rate (%)
1941-195129.5
1951-196131.2
1961-1974262.1
1974-198188.8
1981-199123.8
1991-200156

         Source: BBS, 2009

Map-1.1: Location map of the study area

 Topography and land form

The elevation of Greater Dhaka is 2 to 13 meters above the mean sea level (msl) and most of the urbanized areas are at elevation of 6 to 8 meters above the msl (Tawhid, 2004). The study area ranging from 6 to 8 meters msl.

Climate

The tropical climate of study area is marked by the fairly different six seasonal variations. Rainfall in Dhaka occurs from three main sources: i) the western depression of winter, ii) the early summer thunderstorms know as Nor’westers, and iii) the summer monsoon. It is hot and humid during May to October while cool and dries during November to February. The rainy season generally prevails from June to October. Approximately 90 percent of the annual rainfall occurs during this time and the average annual rainfall is about 2000 mm (Tawhid, 2004). Heavy rainfalls, sometimes extending up to several days, are common during the monsoon. The total annual rainy days vary from 95 to 131 days. Rainfall is rather scarce during the months from November to February. The lowest temperature during this period may drop down to about 110C. On the other hand, temperature as high as 390C may occurs during the warm months of March and April.

Table-1.2: Climate Condition of the Dhanmondi residential Area

ParameterJanFebMarAprMayJunJulAugSepOctNovDec
Temperature O c
Maximum21.727.3303431.931.628.925.931.731.229.826.1
Minimum11.717.219.324.024.425.826.726.625.025.119.416.9
Average 16.722.324.729.028.228.727.826.328.428.224.621.5
Avg. Rainfall (mm)02596123140473191202264134045
Rainy days / M*12481419222216921

Source: BBS, 200,*JICA, 1991.

Land use of the study area

The study area is mostly residential area. After preparation of the Master Plan of the city in 1958, the residential center of the city was moved to different direction. Besides, Power and Water Development Board, RAJUK and many government and private offices are located here. The Dhanmondi Lake is passing through the middle of this area. At present the land use of Dhanmondi area include residential, commercial and offices 70% and15%, low marshy fallow land 15% (Banglapedia, 2004).

 Introduction

The term “methodology” means a set of principle and way by which particular activity have been done. The nature of research methodology widely varies from subject to subject as well as availability of resources. For successful completion of research adopting appropriate method and techniques are vital for any kinds of research. The present study have been done by the following three Phase-

Phase-I, involved conceptualization, develop theoretical framework and fixing goals and objectives and defining the scope of the study.

Phase-II, involved data and information collection. Data and information are collected from both primary and secondary sources.

 Phase-III, involved analysis and tabulation of field data, interpretation of maps, identify the problems, suggest some recommendation for mitigate those problems and finally preparing the report.

Literature Review

Drainage congestion is a very common problem like the others regular problem of Dhaka City. But very few studies have been conducted on drainage system of the city and there is no study been conducted to find out the causes of such problem and impacts on the human life as well as the economy. Some studies related to the drainage system of Dhaka City, which has been conducted are described below:

A study named “Flood Management and Vulnerability of Dhaka City” done by Huq and Alam, 2003 described that after implementation of the flood control project in the Dhaka West, unplanned and uncontrolled expansion of urban area stretched rapidly toward the low-lying areas adjacent to the flood protection embankment. These are deeply flooded floodplain areas close to the river. The residents of the houses in these lowlands suffer from inundation due to accumulation of rainwater after heavy rainfall. Land development through land filling processes in the low-lying areas is causing a drastic reduction in water storage areas. Construction of embankments through low-lying areas without providing adequate drainage facilities has caused internal flooding adversely affecting the residents in those areas.

Bari and Hasan, 2001 in their study “Effect of Urbanization on Storm Runoff Characteristics of Dhaka City” investigated the impact of land use changes due to urbanization on storm runoff characteristics in the eastern part of Dhaka City. They found that the volume of peak rate runoff increases with growth in urbanization. Most of the low lying lands, which once acted as retarding basin, have been filled up. Computed results show that runoff volume is increasing with increase in built-up area in Dhaka city.

 Chowdhury, J. U, 1998 in their study, “Measurement and Analysis of Rainfall Runoff in Selected Catchments of Dhaka City” shown from the analysis of rainfall data that the spatial variability is quite large. The areal reduction factor is likely to be substantially lower than that used in the storm water drainage master plan for Dhaka City. Analysis of storm rainfall and runoff data indicates that the initial loss is much higher than those expected in cities in developing countries. The runoff ratio and runoff coefficient are found substantially smaller than those used in the storm water drainage master plan for Dhaka City. There are domestic wastewater discharges in the storm sewers and the relative magnitude was highest in the unplanned high-density residential area. Deposition of solid materials and rubbish is larger in the surface drains than that in the underground sewers.

In the study “Causes and Effects of Water Logging in Dhaka City”, Tawhid, K. G., 2004, describe the causes of the water logging in Dhaka city, and effect of water logging to the city life. In the study the writer also suggest some recommendation to improve the water logging situation of the Dhaka city.

In the study “Dhaka City Storm Water Quality Assessment”, Khan S.A. and Chowdhury, J.U. (1998), described that the deterioration of storm water quality in Dhaka has become a matter of concern in the recent years. Identified as one of the most densely populated cities in the world, Dhaka is unable to provide urban quality of living to its over 6 million inhabitants. Much of this inability has resulted from failure to maintain the required water environment of the city.

Data and Information Collection

To fulfill the objective of the study both primary and secondary data and information are needed. All the necessary data and information has been collected from various sources.

Collection of Maps

For the purpose of the present study, three different types of maps have been collected. The existing land use map has been collected from Ganibangla and RAJUK. The existing drainage layout map (both storm and sewerage) was also needed and this has been collected form Dhaka Water and Sewerage Authority (DWASA). Surface drainage map collecting Dhaka City Corporation. The CS map collected from Directorate of Land Records and Survey.

Other Secondary Data

Rainfall data and the storm water and sewerage drainage system data were needed for the study. The rainfall data has been collected from Meteorological Department of Bangladesh (MDE) and the drainage data has been collected from Dhaka Water and Sewerage Authority (DWASA). The past and present data on natural drainage system has been collected from different land use maps prepared by RAJUK. Some literature related to the topic has been reviewed for better understanding of the problem and their main objectives and outputs are attached at the starting  of this chapter.

Collection of Photographs

Lot of photographs has been also needed to illustrate the situation of drainage congestion, related obstacles into the smooth drainage of urban runoff and its effects on urban life. Some of these photographs have been collected directly from field survey and some other from daily news papers as well as from internet websites.

 Questionnaire Survey and Informal Interview

To find out inherent causes of drainage congestion of the study area and its associate problem on city life, a field survey as questionnaire survey, informal interview has been conducted with the authorities of different concerned organizations, experts and people living in different parts of the study area. The sample questionnaire is given in

Appendix-1. The sample size of these survey activities was 50. Again the respondents were selected in different part of the study area. It also covered the people’s perception on conservation/sustainable development of drainage system. Informal interview of official experts of different development agencies was also done in order to know their view of causes and problem of drainage congestion in the study area and sustainable solutions.

Data Analysis and Presentation

All the data both spatial and non spatial collected from different sources has been analyzed separately. The spatial data has been analyzed by using some Geographic Information System (GIS) like Arc/view etc. and spatial data has been analyzed using some other statistical computer software like, Microsoft Excel, Microsoft Word, SPSS etc. Finally the both types of analyzed data have been integrated and presented as maps, tables, and graphs and putted in the report.

Preparation of Final Report

Finally a report has been prepared with sequential chapters where all gathered information and data have been presented in text, map, chart and graphical forms. An assigned format, instructed by the supervisor, has been maintained throughout the report and a draft report was prepared and submitted to the study supervisor for correction, modification and recommendation. After fulfillment of the required guidelines the final study report was submitted to the supervisor.

 Introduction

Drainage in human settlements has assumed considerable significance due to the enormous population growth and the rapid but haphazard urbanization evident in most countries. Failure to provide adequate drainage is directly linked to the resurgence of malaria, the spread of diarrhea diseases, damage to housing and property, disrupted communications, lost income and environmental degradation. Drainage is a cross-sectional issue, involving such fields as housing, roads, solid waste management, water supply and excreta disposal. The chapter focuses on the theoretical framework of the study. This chapter tried to clarify the terminologies and others important matter which will give a clear idea regarding the subject matter of the study.

Some Operational Definition

Drainage

The Delhi workshop defined drainage as “the removable of unwanted water from human settlement.” Such unwanted water can include storm runoff and flood water from seasonal rains, marsh or pond water in low lying areas, and the used domestic water (sullage) of the community. All these constituents have a potential impact on health and well-being (WHO, 1991). A comprehensive drainage study requires topographic, hydro-meteorological (rainfall and evaporation) and hydrometric (discharge and water level) data. The topographic data is also important to develop layouts and estimation of earthwork for the proposed road and drainage channel.

Waste water

Waste water is the liquid waste conveyed by a sewer and may include domestic and industrial discharges as well as storm sewage, infiltration and inflow.

 Domestic sewage

Domestic (sanitary) sewage is the liquid waste which originates in the sanitary conveys water closets (WC), urinals, baths, sinks etc. of dwellings, commercial or industrial facilities and institution. This is some time also referred to as black water.

Sullage

Sullage is the liquid discharge from kitchen, wash basins etc and exclude discharge from WCs and urinals. Sullage also known as grave water is less foul then domestic sewage and can be discharged through open surface drain in unsewared areas.

Strom water and storm water runoff

Strom water is the surface runoff obtains during and immediately after the rainfall, which enters sewage through inlets. Strom water is not as foul as sanitary or industrial sewage and hence can be carried through open drains or cannels and disposed of in natural rivers or streams without any treatment.

 Infiltration

Infiltration is the water which enters the sewers from the ground through leaks or faulty joints.

Need of Drainage

Drainage systems are needed in developed urban areas because of the interaction between human activity and the natural water cycle. This interaction has two main forms: the abstraction of water from the natural cycle to provide a water supply for human life and the covering of land with impermeable surfaces that divert rainwater away from the local natural system of drainage.

 The first type, wastewater, is water that has been supplied to support life, maintain a standard of living and satisfy the needs of industry. After neither use, if not drained properly, it could cause pollution and create health risks. Wastewater contains dissolved material, fine solids and larger solids, originating from WCs, from washing of various sorts, from industry and from other water uses.

 The second type of water requiring drainage, storm water, is rainwater (or water resulting from any form of precipitation) that has fallen on a built-up area. If storm water were not drained properly, it would cause inconvenience, drainage, flooding and further health risks. It contains some pollutants, originating from rain, the air or the catchments surface.

Need of Drainage in Urban area

 When rainfalls on to undeveloped land, most of the water will soak into the topsoil and slowly migrate through the soil to the nearest watercourses or groundwater. A small proportion of the rainfall – usually 15 to 20 percent – becomes direct surface runoff that usually drains into watercourses slowly because the ground surface is rough (because of vegetation). This means that the effects of rainfall are spread out over a period of several hours. Even short, heavy storms may have little on flow rates in the receiving waters because much of rainwater may be absorbed into the ground. When catchments are developed, the proportion of the land covered by impervious surface (roads, parking areas, roofs, driveways) will increase, preventing the natural infiltration of rainfall into the ground. In developed catchments, direct runoff can increase to more than 80 percent of the rainfall volume. At the same time, because paved surfaces may be less rough than natural surfaces, water may travel over them faster and as a result runoff will reach the receiving watercourses more quickly. The flow rates in the receiving waters are therefore much more sensitive to rainfall intensity and volume than those in undeveloped catchments.

Volume and rates of runoff both increase significantly after development. Peak flow rates can increase by a factor of up to ten, which means that streams and rivers have to cope with larger and often sudden runoff flows. It also means that drainage is needed to reduce flood risk within the developed areas.

Considerations for storm, sullage and wastewater drainage

During rain the fields become wet. The water infiltrates into the soil and is stored in its pores. When all the pores are filled with water, the soil is said to be saturated and no more water can be absorbed. The remaining water flow overland (overland flow) towards the main stream channel and is called the surface run-off. The storm drainage designed primarily concerns this surface runoff. The primary objective of this drainage system designed is to drain out this storm water either through open surface drains or through underground sewers. An important parameter for the design of storm water system is the rate and volume of runoff to be conveyed through the system as a consequence of storms. Runoff estimates are carried out based on knowledge of the occurrences of heavy rain storms and a relation between rainfall and the corresponding runoff. The quantity of runoff depends on the geometry and physical properties of the catchments. Rainfall occurs at irregular intervals and intensities and frequencies and duration vary within catchments. Due to this random nature of occurrence of rain events, the storm drainage system is designed considering estimated runoff based on the analysis of past rainfall records.

 Sullage is all household waste water except human excreta. The volume of sullage produced depends on type of water supply. When water supplies are hand carried small amount of sullage are usually disposed of simply by throwing them on the ground around the house without much concern. But when the volume of sullage is large with yard tap or in-house water supplies, inadequate disposal can cause considerable nuisance and health risk

 Waste water is the liquid waste conveyed by a sewer and may include domestic and industrial discharges. Planning for waste water collection and disposal requires to consideration of the following:

  • Waste water volume and strength.
  • Location, type and sizing of collection system.
  • Location and type of treatment facilities.
  • Disposal of liquid effluent and solid waste.

(American Society of Civil Engineers, 1986)

Different types of drainage 

Drainage can be either natural or artificial. Many areas have some natural drainage which means the excess water flow to the lakes and rivers. Natural drainage, however, is often inadequate and artificial or man-made drainage is required.

There are two types of artificial drainage: surface drainage and subsurface drainage.

 Surface drainage

Surface drainage is the removal of excess water from the surface of the land. This is normally accomplished by shallow ditches, also called open drains. The shallow ditches discharge into larger and deeper collector drains. In order to facilitate the flow of excess water toward the drains an artificial slope is maintained throughout the planned area.

 Subsurface drainage

Subsurface drainage is the removal of water from the root zone. It is accomplished by deep open drains or buried pipe drains.

 Various drainage layout used in planning

There are several types of drainage layout used in planning. They are discussed in following:

Dendritic drainage systems

Dendritic drainage systems are the most common form of drainage system in the world and looks like the branching pattern of tree roots. They consist of a main river with tributaries with their own tributaries. From above, it looks like a tree or a river delta in reverse.

Parallel drainage system

Parallel drainage system form where there is a pronounced slope to the surface. A parallel system also develops in regions of parallel, elongate landforms like outcropping resistant rock bands. Tributary streams tend to stretch out in a parallel-like fashion following the slope of the surface. A parallel pattern sometimes indicates the presence of a major fault that cuts across an area of steeply folded bedrock.

 Trellis drainage systems

Trellis drainage system look similar to their namesake, the common garden trellis. Trellis drainage develops in folded topography like that found in the Appalachian Mountains of North America. Down-turned folds called synclines form valleys in which resides the main channel of the stream. Short tributary streams enter the main channel at sharp angles as they run down sides of parallel ridges called anticlines. Tributaries join the main stream at nearly right angles.

 Radial drainage system

A radial drainage system features a pattern of waterways which flow away from a central high point in all directions. This may be visualized as appearing like the spokes of a wheel. Most small islands and especially volcanic ones have this pattern.

 Centripetal drainage systems

As opposed to the formation of a radial drainage system, centripetal water movements are results of geological depressions and water flowing across them. Due to the gravitational pull, water from the surrounding elevated relief flows towards a central pool of water in the depression, usually resulting in the formation of a lake over time. This pattern is typical in the western and southwestern portions of the United States where basins exhibit interior drainage. During wetter portions of the year, these streams feed ephemeral lakes, which evaporate away during dry periods. Salt flats are created in these dry lake beds as salt dissolved in the lake water precipitates out of solution and is left behind when the water evaporates away

Rectangular drainage system

The rectangular drainage system is found in regions that have undergone faulting. Streams follow the path of least resistance and thus are concentrated in places were exposed rock is the weakest. Movement of the surface due to faulting off-sets the direction of the stream. As a result, the tributary streams make shape bends and enter the main stream at high angles.

 Deranged drainage system

A deranged drainage system is a drainage system in watersheds where there is no coherent pattern to the rivers and lakes. It happens in areas where there has been much geological disruption. The tributary streams appear significantly more contorted than they were prior to glaciations.

 Review of Dhaka Integrated Flood Protection Project

After the devastating flood of 1988, a comprehensive study in the name of Flood Action Plan (FAP) was launched. In support of the Government’s flood action programmers, both the Government of Japan and the Asian Development Bank (ADB) agreed to provide assistance for the Dhaka Town Protection component, FAP-8. This was a two part coordinated action plan.

  • FAP 8A – Master Plan Study for Greater Dhaka, Tongi, Savar, Keraniganj and Narayanganj (carried out by JICA), and
  • FAP 8B – Dhaka Integrated Flood Protection Project (DIFPP), which has the objective of identifying drainage, flood protection and complementary environmental improvement projects, and preparing feasibility studies for the immediate investment needs in the Greater Dhaka.

 FAP 8A

The Greater Dhaka protection Project (FAP-8A), funded by JICA, formulated a framework for comprehensive flood control and storm water drainage in the Dhaka metropolitan area, covering an area of 850 km2. The Master Plan, prepared by JICA, proposes structural measures to protect existing and (JICA’s) predicted future urban areas to 2010 from a flood of 100 year frequency (of the scale of the 1988 flood). It is proposed that an area of 453 km2 would be protected.

 FAP 8B

The Dhaka Integrated Flood Protection project (FAP- 8B) for the western part of Greater Dhaka is under execution and funded by the ADB. It addresses the integration of flood protection works for Dhaka Metropolitan Area, covering an area of 260 km2, with other infrastructure and environmental improvement measures in order to maximize its impact. Priority is given to investment proposals that have emerged from previous studies. Components include embankment strengthening, pumping stations, drains, slum/squatter area improvement, sanitation/ sewers, and solid waste management, as well as institutional and implementation recommendations. The Study was undertaken in 1991, and execution is ongoing.

Under Phase-I of the DIFPP, construction of the Dhaka Western embankment was completed in 1997. That is why the western part of the Dhaka City was flood-free during the 1998 flood. After the flood, the Government of Bangladesh decided to construct the Dhaka Eastern embankment presently. Bangladesh Water Development Board (BWDB) prepared a TOR for construction of the Eastern embankment and a Bypass. The preferred option combined construction of the embankment by the right side of the Balu River, and a low-level Bypass through the Dhaka eastern floodplain.

In 1999, the Japan International Cooperation Agency (JICA) intended to acquire baseline information on the status of propositions made under FAP 8 studies and the implementation made during the period 1991-2000. SWMC was entrusted to conduct a study for the baseline information survey for Dhaka City and its adjoining areas, with special reference to the Dhaka East areas. The main objective of this study was for a baseline assessment of the hydrological, morphological and demographic changes that have taken place in the project area after the assessment made in 1991 by JICA during the FAP 8A study.

Review of DMDP Master Plan (1995-2015)

The Master Plan of the Metropolitan Dhaka City, known as the Dhaka Metropolitan Development Plan (DMDP), prepared by the RAJUK, is divided the Dhaka city into sub-areas which are characterized by a particular set of urban development policies.

 The project planning component is presented as a package of plan outputs which collectively address Dhaka’s urban planning issues at three geographic levels; sub-regional, urban and sub-urban. The Dhaka Metropolitan Development plan is comprised of the three following components.

  • Structure Plan
  • Urban Area Plan
  • Detail Area Plan

 Urban Area Plan (1995-2005)

This plan provides an interim mid term strategy for the 10 years to 2005 and covers for the development of urban areas within metro Dhaka management area. The important features are discussed in the following:

Drainage and Flood Protection

Substantial drainage and flood protection proposals have been initiated in the past decade, though plans do not always extend into peripheral pourashavas and thanas, where natural khals and roadside drains take away storm water. Drainage responsibility rests with a profusion of agencies; porashava and thanas, DWASA, RAJUK, DCC, and DPHE. Major projects currently under way are:

  • Dhaka City Storm Water Drainage Improvements, funded by JICA, include Khal improvement, main drains, culverting and dredging. These are substantially completed (DWASA).
  • Badda urgent project to remove water logging (DWASA).
  • Dholai Khal Rehabilitation and area development (DCC/World Bank)
  • FAP 8B, funded by ADB. Detailed design is currently underway. Completion of construction is scheduled for mid-1997 and will ensure protection of most of the existing urban core. The Western Embankment will be strengthened and completed with pumps and sluice gates, and drainage improvements within the protected area are proposed.

 To manage the internal drainage and storm water, storm water management boards will have to be established for each of the drainage areas that are part of the flood protection and management system.

These storm water management boards also will have to oversee the protection of the required retention pond area (12%) within their management area. The retention pond area either should be:

a) A lake situated adjacent to the embankment/pumping station at the lowest, (technically and financially most feasible) location,

(b) A network of connected widened khals that meet the retention requirement or

(c) A combination of the above alternatives.

 Sewerage, Sanitation and Solid Waste

Only part of the DCC area is severed by sewers and not all properties are connected within this served area. Peripheral areas are not linked to the system. DWASA estimates that only 30% of the urban population is served.  The system is designed for sludge and storm water. The flow is from north to the south to Pagla Treatment Works which is currently running at full capacity.

 The DMDP has studied the solid waste management issue of Dhaka has recommended that in addition to new Matuail site, sanitary landfill site should be developed in the East and West to meet the growing need for adequate disposal. However, there are as yet no firm new proposals by the respective agencies.

Strategic Planning Zones (SPZs)

The DMDP Master Plan has categorized the various areas of the City into 19 (nineteen) Spatial Planning Zones (SPZs). Some of these have been further subdivided into sub-zones, so that the actual total becomes 26. Master Plan particularly identified specific features of the each SPZ, and demarcated few rivers, Khals, small water bodies/retention ponds, lake and open spaces and obliged legally to protect them from illegal developments. Specifically fourteen SPZs are identified mentioning its mouzas as flood flow zones, and clearly prohibited earth filling without due permission from the concerned authority.

Flood protection

The major structural components of the FAP flood protection strategy (and as included in the Structure Plan) are the embankments, their associated works and the

flood retention pond. Flood protection requires land to be reserved for construction of those major components.

The location of these protection related features where land reservation is required the extent of flood flow zones where different kind of development control are recommended are shown in the Map-3.2. It might also be desirable to restrict development in areas which could be required in the long term. However, some degree of certainty regarding a proposal is needed before action can be taken to reserved land. Land reservation for long period would also have a detrimental effect by restricting development and consequently difficult to sustain.

The flood flow zone

These zones were determined by FAP-8A studies, and lie largely outside the present urban area. The land study recommended that development in low lying flood plain areas be restricted since it could obstruct natural flood flow. Such restriction would cause a rise in water level and changes flood direction affecting the entire metropolitan area.

In the Main flood flow zone, now mostly agricultural land, urban development should be prohibited. Only development having no adverse hydraulic effect should be permitted. Such development includes:

  • Agriculture
  • Open space for recreation
  • Ferry terminals
  • Brick yard

The sub-flood flow zone is less affected by flood flow. It includes village and homestead areas. Development in this zone should only be allowed provided that:

  • The developed land is raised more than the design flood water level.
  • The slope of such land is sufficiently gentle to prevent slope failure and is protected from erosion.
  • Structure orientation is designed to minimize flood flow obstruction.
  • Floor elevation of structures housing any toxic material is higher than the design flood water level and the structures themselves are sufficiently strong to withstand flood damage.

For both types of flood one, it is important that laws preventing land fill soon come into forces, otherwise controlling development in these zones will be very difficult and the effectiveness of flood protection measures will be seriously compromised.

Retention Ponds

The proposed retention ponds are intended to hold internal storm water within the protected areas until it is pumped out or until river levels outside are low enough to the sluice gate to be opened. If in investment already made and already assured for flood protection is to bring maximum benefits it is essential that areas for retention ponds are protected.

Structure Plan (1995-2015)

This plan provides a long term strategy to the year 2015 for the development of Dhaka metropolitan region. It identifies the magnitude and direction of growth and recommends spatial and sect oral policies over the long term for the DMDP area of control of about 590 square miles.

 Features of the Spatial Development Strategy

The following key features have influenced the proposed development strategy outlined in the DMDP Structure Plan.

  • The DMDP research and past planning studies have recognized the constraints imposed on Dhaka’s urban land resources by flood risk. The DMDP further acknowledges the associated serious problem of water logging resulting from urban encroachment on natural depressions and khals /lakes.
  • The options to reduce and minimize these major constraints rests with utilizing and optimizing naturally flood-free land and carrying out major flood protection works and protecting existing natural depressions and khals /lakes.
  • In order to optimize the full potential of existing and potential new development land areas, the areas designated as retention ponds in natural depressions and the city’s existing natural drainage system and khals /lakes must be protected at all costs.

Flood Plains, Rivers and Water Bodies

The rivers and flood plains within the DMDP Structure Plan area play an important role in both the ecology and the economy of the capital region. As well as being the source of flood risk to urban development, they are the provider of water both for agricultural irrigation and for urban uses.

Flood Plain Treatment

The wedge-shaped island of Dhaka is contained to the east by the Lakhya/Balu River system and to the west by the Buriganga/Dhaleshwari River system, the two river systems converging and exiting the DMDP Structure Plan area in its south east corner, immediately south of Narayanganj.

Flood Retention Ponds

Flood retention ponds are a key and critically important component of the proposed FAP 8A and FAP 8B flood protection Schemes. The proposed retention ponds will be designed to reduce the intensity of local flooding within the protected areas and also reduce pumping requirements at times of maximum surface water run-off.

Policy RS/5- Flood Retention Ponds

Control will be maintained over the areas designated in the DMDP Structure Plan for flood retention ponds in order to ensure that they remain capable of fulfilling their primary function of water storage at times of flooding.

Reason

The flood retention ponds will be designed to reduce the intensity of local flooding within the protected areas and to reduce pumping requirements and as such, are an integral part of the proposed flood protection schemes. Their location should be the subject of detailed geological survey to ensure that the city’s natural drainage system is not compromised and that the effects of water logging are minimized.

Means of Implementation

With wholesale acquisition by the Government of the proposed designated retention pond areas unfeasible (most of the areas are in private ownership), the primary means of policy implementation will be via land-use controls

Controls

The use of the land within designated retention pond areas to be restricted to the following activities:

  • Agriculture;
  • Fish cultivation; and
  • Recreation.

 Detailed area Plan (DAP)

These plans provide more detailed planning proposals for specific sub-areas of Dhaka. However they do not initially cover the entire Dhaka structure Plan Area (590 Sq miles). While all sub-areas will eventually require a DAP, only priority areas will be dealt with initially.

 Introduction

The total area of the study area of 7.74 sq km. In the past the present Dhanmondi was full of ponds and lakes (BBS, 2002). But for urbanization the pond are filled up to meet the demand of land for excess population. The lakes is the main channel for natural drainage of the study area. Though the report is confined with the artificial drainage system of the study area but with the relative importance on the natural drainage system is also mentioned. And that is why the overall drainage of the study area is segregated into following two types.

 Natural Drainage System

Natural water bodies play an important role in the drainage system of any area. The water body performs together with the functions of water reservoir and the discharge sites of artificial drains. The natural drainage system can be divided into two types-

  • Storage area
  • Channel

 Storage area

In the past the present Dhanmondi area was full of pond, lake, low land etc. This storage was play important role of the drainage system of the Dhanmondi area.  Now a days Dhanmondi area is the residential center of the Dhaka city. Most of the low land, pond etc. are filed up and developed to meet the increasing demand for land. At present in the study area have no low land, pond. But at the middle of the area have some low land and water body (Map-4.1). These lands are also going to fill up.

 Cannels

One of the major drainage channels of the study area is the Dhanmondi Lake, which is  a prominent depression within Dhaka metropolitan area. It is situated in the middle of dhaka City (about 23°43’N latitude and 90°26’E longitude). It lies within the vicinity of Dhanmondi residential area. Originally Dhanmondi Lake was an abandoned channel of the ‘Karwan Bazar Nadi’ (‘Karwan Bazar’ is commonly spelled and pronounced as ‘Kawran Bazar’), previously known as the ‘Carevan River’, whose alignment was possibly along Begunbari Khal-Green Road-Kalabagan-Dhanmondi Lake to the turag river. Part of this lake still functions as a storm water drain and falls into the Begunbari Khal. Expansion of urbanisation in this area during Pakistan period has changed the natural water system in this place. Dhanmondi residential area was developed in 1956 with 240.74 ha of land including the lake.

The lake is about 16% of the total area of Dhanmondi and has been playing a vital role in maintaining the only drainage system of Dhanmondi and adjacent areas. It also shows some trellis pattern together with the dendritic pattern of drainage system.
Dhanmondi Lake, Dhaka

Beginning from Jigatola (Dhanmondi Road # 2) the lake extends up to Road # 27 (new l6A), and bounded by the Mohammadpur-Lalmatia area in the north, Satmasjid Road in the west, BDR (bangladesh rifles) Gate (Dhanmondi Road # 2) in the south and in the east by Kalabagan residential area. It is 3 km in length, 35-100m in width, with a maximum depth of 4.77m and the total area of the water body is 37.37 ha. There is one box culvert in the lake near Sukrabad area, which is the only outlet of the lake. Excess floodwater due to heavy rainfall passes through this outlet. So water level in the lake remains almost the same in all seasons.

 The lake is under the management of several authorities looking after its various aspects. The Ministry of Works has its ownership; the Fisheries Department looks after fishery development; the dhaka city corporation, being the principal civic body, exercises some responsibility in its improvement. The Department of Environment (DOE) looks after the aspects of proper environment and protection of aquatic resources of the lake. In and around Dhanmondi Lake some renovation works were carried out from 1998 to 2001 with a view to making the lake a pollution free recreation zone.

 Artificial Drainage System

Artificial drainage system of the study area can be divided into two groups. These are,

  • Waste water drainage
  • Sewerage drainage

These are discussing in bellow:

Waste Water Drainage

Waste water drainage is the liquid waste conveyed by a sewer and may include domestic and industrial discharges as well as storm sewage, infiltration and inflow of the study area. These drainage systems are further divided in to two categories. They

  • Strom water drainage system
  • Surface drainage system

 Storm Water Drainage

All the Sullage and storm water are carried by the storm drain. Dhaka WASA is responsible for the storm water drainage of Dhaka city. The operation and maintenance of the storm water drainage system is organized by the Drainage Circle of Dhaka Water Supply and Sewerage Authority (DWASA). For the better management of the city drainage system DWASA divided the whole storm water drainage in to six zones (Map-4.3). The present storm water drainage network under Dhaka WASA covers an area of approximately 140 sq. km (Rabbi, 2001). Important components of storm drainage network are briefly summarized below

i) 22 open canals having width of 10 to 30 m and total length of approximately 65 km (Rabbi, 2001).

ii) 225 km. of underground pipes having diameter ranging between 450 to 3000 mm. (Rahman, 2004).

iii) 8 km. of box culvert of sizes between 2.5 m * 3.4 m to 6 m * 4.1 m. (Rahman, 2004).

iv)  2 storm water-pumping stations, of capacity of 9.6 m3/s and 10 m3/s at Narinda and Kallyanpur respectively (Rahman, 2004).

v) Recently DCC has constructed one storm-water pumping station, having capacity of 22 m3/s at the confluence of river Buriganga and Dholai khal. Dhaka WASA has taken over the operation and maintenance of the pumping station (Rabbi, 2001).

Bangladesh Water Development Board (BWDB) has also constructed one pumping station (capacity 22 m3/s) at the northwestern part (Goran Chadbari at the outfall of the Degun khal into the Turag River) of the city. There are also 65 small pumps with individual capacities of 0.142 cumec, installed temporarily by DWASA to drain out storm water from various locations (Rabbi, 2001).

Moreover, DCC have constructed and maintains at least 130 km small diameter underground drains which carry storm water to the main sewer lines (Rabbi, 2001). RAJUK also constructs roadside underground drainage lines during the construction of new roads. The responsibility of development, operation and maintenance of drainage system in Dhaka City lies with the DWASA. But several agencies are working for development of the city drainage system, with little or no coordination among them.

Surface Drainage

Dhaka City Corporation is responsible authority for the surface water drainage of the Dhaka city. Surface drainage is the removal of excess water from the surface of the road. This is normally at the side of the road accomplished by shallow ditches, also called open drains. The roads are sloped toward the surface drain and the surface drain is connected with the storm drainage network. The storm water and other water that fall on roads are run off to the surface drain and descent to the storm drain. The connection between the surface drain and the storm drainage system can be seen in Figure -4.3.

The city corporation has some 1100 km. of surface drains (Rahman, 2004). The responsibility of development, operation and maintenance of surface drainage system in Dhaka City lies with the Dhaka city corporation.

 Sewerage Drainage

DWASA is responsible for the Sewerage drainage of Dhaka city. The operation and maintenance of the sewerage drainage system is organized by DWASA. For the better management of the city drainage system DWASA divided the whole sewerage drainage system into in to six different zones. Important components of sewerage drainage network are briefly summarized below:

  • 631 km of underground Sewerage Line
  • Sewer Connection (number) 45,325
  • Sewage Lift Station (number) 23
  • 1 Sewage Treatment Plant at pagla.

Drainage System