Designing an Effective Drainage System for Magura Pourashava: A GIS

based Approach

MD. Mahabubur Rahman

Student ID: 090413

Urban and Rural Planning Discipline, Khulna University,

Khulna 9208, Bangladesh

ABSTRACT

The rapid urbanisation and population growth; creates the need for better planning and

management of the urban infrastructures. Urban drainage system is one of the vital services

needed for any urban area and designing an effective drainage system is a challenge because of

the dynamic of its hydrology. Right now only 50% households are enjoying drainage coverage in

Magura pourashava without having any networked drainage system. The existing system is

based on natural drains and unplanned man-made drains. This unplanned drainage system

without having any network is causing several negative environmental impact including water

logging, flood and damage of road. This situation is worsening in rainy season. In this context

this paper attempts to design an effective drainage system for Magura pourashava using GIS

based approach. The system developed in this paper focuses on integrated drainage system

design of the municipalities using the advanced GIS (Geographic Information System) tools. Arc

hydro GIS have been used for exploring the natural drainage line and its catchment considering

spot-height and contour-map. Overlaying existing man-made drainage system on the natural

drainage line remains as the major tool for preparing the drainage network. The expected result is

a new approach for urban drainage infrastructure planning which may help municipalities to

have a dynamic planning tool to improve the effectiveness of their investments.

KEY WORDS: Arc-hydro GIS, Drainage System, Spot Height, Digital Elevation Model (DEM),

Magura Pourashava

BACKGROUND

In 1971 the urban population of Bangladesh was 5.5 million while in 2001; the population

climbed up to 29 million. The present trend shows that by 2020 around 40% of the total

population of Bangladesh will live in urban areas. In implementing various infrastructures for

development; drainage is the most important component for development. This scenario is

particularly true for Bangladesh, although among different types of infrastructures, drainage has

by far the heaviest impact on physical infrastructure network. In absence of an effective drainage

system, physical environment, health and standard of living suffer seriously. Public sectors funds

are allocated for the projects are mostly spent on structures, roads and other infrastructures and

drainage has always been less prioritised. In the urban sector development if drainage is not

given due priority, the sufferings of the inhabitants and stakeholders will continuously increase

with the passage of time. Drainage problem is the one of the main problem in Magura

pourashava. At present Magura pourashava has natural drainage system which supports 50% of

the total households. For future planned development of the pourashava, this system need to be

incorporated in the drainage plan. Magura pourashava is located on the bank of Nabogonga

River, which is the main natural drainage system for this city. The current study attempts to

explore the impact of Nabogonga River on drainage system of Magura pourashava and provides

a GIS based drainage system for ward number 9 of Magura pourashava.

STUDEY AREA

The pourashava area is located at the center of the Magura pourashava and has developed on the

bank of Muchikhali River. Another Nabaganga River is spread over the pourashava area. Magura

pourashava area is bounded on the east by Kasundi and Chaulia union, on the west by Hazrapur

union on north by Atharakhada union and on the south by Moghi and Jagdal union. It lies on 230

29’ north latitude and 890 25’ east longitudes. Ward-9 is located near the Nabaganga River and it

is the centre of Magura pourashava. Magura came into existence in 1845 as a sub-division. The

Magura town committee was established in 1965. It was replaced by the Bangladesh local

councils and municipal committees 1972. In 1984 Magura pourashava was declared as a B class

pourashava and in 1993 Magura pourashava was declared as an A class pourashava.

Figure 1: Map of Magura Pourashava

APPROACH AND METHODOLOGY

Basic information of Magura pourashava has been collected from pourashava office. Landuse,

physical feature and topographic data have been collected from pourashava. On the basis of

outfall dividing the total water-shed has been divided into number of drainage zones,

improvement of drainage network has been proposed by construction of new primary, secondary

and tertiary drains considering the existence of water-logged areas.

A representative Digital Elevation Model (DEM) has been considered as an effective tool in

different literature for drainage system planning. A DEM and shape files of existing road

networks, bridges and culverts, drain networks and land use pattern have been produced after

performing a quality survey using the modern survey equipments. Then a field visit has been

performed for understanding the existing drainage system, possible outfalls, water logged areas

and average flood level. The study area has been classified according to the average yearly flood

level. The land above the average yearly flood level is brought under gravity drainage system.

Drains, catchments and zones was delineated with the help of GIS considering existing roads,

infrastructure, homestead, contour maps, outfalls, natural canals and rivers in and around the

pourashava. The drain line, drainage point, flow direction, flow accumulation, stream definition,

stream segmentation and catchment areas have been calculated by the GIS software. Discharges

have been calculated by modified rational method. Finally, detailed profiles of the drains have

been drawn with drain sections.

Figure 2: Methodology Diagram of Drainage Plan

Collection of

topographic data

Prepare DEM map

from topo to ruster

Collected necessary

shape file

Prepare Fill sink

map of study area

Calculation of Flow

Direction

Calculation of Flow

accumulation

Stream Definition

map of study area

Drawing a Drain

profile

Design of primary,

seconder and tertiary

drain

Overlay between

Land uses, physical

feature and

calculated drainage

line

Rational Method for

calculation of

drainage run-off

Hydro Network

Generation of

selected area

Calculation of

drainage line and

drainage point

Find out the

catchment area and

catchment Polygon

Stream segmentation

map of study area

MAIN PROBLEM OF THE EXISTING DRAINAGE SYSTEM

A wider scope for construction of a drainage system may be provisioned in the pourashava. At

least central areas are open for such development immediately and other areas may be followed

for projected period as designed in the plan. The pourashava has an advantage to introduce a new

drainage system as it has not any drainage system right now. In this context rationalistic

approach is very much suitable for Magura pourashava. The principles required for drainage plan

are also available in the study area. Land slope, nearness of the natural drainage, sparse

population density and soil condition are in favour of drainage construction.

Existing drains in the pourashava have not formed any network; only household centered

construction to drain out waste water is in presence. Existing canal is trying to manage the

drainage requirements. The canal is not well linked with man-made drain and river. No pond /

ditch have been found connected with existing drains / canals. Lack of drainage network is

causing water-logging for 4 months in the Ppourashava area in the rainy season. In this context,

the entire drainage network is required to be developed with primary, secondary and tertiary

drains to mitigate the current water-logging problem.

Drainage congestion may increase further with urban sprawl development. Faulty design; solid

waste and rubbish dumping; encroachment and un-authorised structures; siltation; and lack of

renovation and re-excavation are the main causes of drainage congestion. Drainage system that

exists in the study area is not capable to carry the surface run-off properly. The outlets of these

drainage networks are mostly connected with the natural channels or khals. These khals are

losing effectiveness due to siltation; as a result, drainage congestion has been generated.

Therefore many areas are subjected to water-logging during the heavy rainfall causing

inconvenience to the people of the area.

Man Made Drains

During the drainage survey, 216 numbers with two types, pucca and katcha man-made drains

were identified covering different parts in different wards. Total length of those drains is 26.31

km. Total length of pucca drain is 23.94 km with two types – secondary and tertiary. Secondary

pucca drain is 5.21 km and tertiary drain 18.73 km. Average width of secondary pucca drain is

1.24 metre and average depth 1.39 metre. Average width of tertiary pucca drain is 0.71 metre and

average depth 0.72 metre. Total length of katcha drain is 2.38 km with two types – secondary

and tertiary. Secondary katcha drain is 0.43 km and tertiary drain 1.95 km. Average width of

secondary katcha drain is 1.10 metre and average depth 1.15 metre. Average width of tertiary

katcha drain is 0.95 metre and average depth 0.60 metre.

Drainage Strom Water Outfalls

Magura pourashava lies in the tropical monsoon climatic region and more specially, represents

the climate of Jessore district. It has a normal rainfall of 325.4 mm in the month of June which is

highest among all other months. In September, it falls to 232.5 mm; again falling to 145.8 mm in

October. The rainy season begins with April/May and usually ends in the end of October.The

highest number of normal rainy day is in July, which is the highest rainfall month. About 14

rainy days at an average in July, followed by 15 rainy days in August, 14 in June, 11 in May and

September has been the characteristics of rainy day as the data reveals.

No peak hour run-off storm water discharge is found. During rainy season, rain water is being

drained through the man-made drains. All pucca drains are linked with the natural water bodies

like canal and Naboganga river as an outfall. As a result, waters of the river and canals are

polluting through those discharging elements. The adjacent Naboganga river is the outfall of all

natural and man-made drained water.

RATIONAL METHODE FOR CALCULATION OF DRAINAGE RUN-OFF

It is relatively simple, internationally used technique for designing storm drainage system in

urban areas and accordingly has been selected for use in estimating the design for discharge

proposed storm. Accordingly, the peak-flows at any given point in a drainage system can be

calculated by using the following formula:

Q = CIA/360

Where,Q = peak flow in m3/ sec

C = run-off coefficient

I = design rainfall intensity in mm/hr

A = catchments area in hectares

RESULT AND DISCUSSION

Using the nabogonga river basin area as a study area. Using Spot hight data ,contur map and

basin area boundery calculate the DEM.According to GIS analysis of DEM map of Magura

pourashava show the lower and higher elevated area of the study area. Lowest area is -0.290925

m and highest area is 9.33131 m. Violet shade shows the lowest area and gradually green shade

shows the highest area (Figure 3). Therefore sinks should be filled to ensure proper delineation

of basins and streams. If the sinks are not filled, a derived drainage network may be

discontinuous (Figure 4). Filling the lower area (lowest area is 1.14117) flow directions have

been calculated for the flow slope of the study area (Figure 5). Flow accumulation shows the

flow direction of drain in different colour drainage network (Figure 6). Stream definition shows

the flow direction of water in surface (Figure 7). Segmentation of stream map explores different

level of flow direction with different drainage caring capacity. Catchment area has been

calculated from the flow accumulation and stream segmentation catchment areas have been

divided by various size polygons (Figure 10). Drainage line map shows the drain line that

collects storm water from its catchment area (Figure 11). It travels to an outlet which could be

referred as a drainage system. The flow of water through a drainage system is only a subset of

what is commonly referred to as the hydrologic cycle, which also includes precipitation,

evapotranspiration, and groundwater flow. Drain point focus on the movement of water across a

surface. A drainage basin is an area that drains water and other substances to a common outlet.

Other common terms for a drainage basin are watershed, basin, catchment, or contributing area.

This area is normally defined as the total area flowing to a given outlet, or pour point (Figure

12).water flow network map show the trace of upstream and trace of downstream water flow

direction (Figure 13).

Figure-3: DEM map of Magura Pourashava

Figure 4: Fill Sink Map of Magura Pourashava

Figure 5: Flow Direction map

Figure 7: Stream Definition Map

Figure 8: Stream Segmentation Map

Figure 6: Flow Accumulation Map

Figure 9: Catchment Grid Delineation

Figure 10: Catchment Polygon Map

Figure 11: Drainage Line Map

Figure 12: Drainage Point Map

Typical tertiary drainage

DESIGN AND STANDARDS

Tertiary drain carry run-off or storm water received from the above mentioned plot drains and

block or Mohallah drains. Tertiary drains deliver its discharge usually to secondary drains. A

typical tertiary drain is shown as follows:

.

Secondary drains collect discharge from tertiary drains. The typical cross-section, size and

shape, and its construction material are shown as follows:

Figure 13: water flow network

Primary drains are also called main drains. Primary drains cover larger storm drainage area

than tertiary and secondary drains. . Contributing drainage water comes from tertiary and

secondary drains. Primary drains discharge its drainage water to outfall, natural khal, and river.

RECOMMENDATION

Water logging problems of Magura pourashava can be manageable if the following

recommendations can be followed:

1. Making proper drainage network in new area considering the slope and local

topographical condition.

2. Removing all unauthorised structures which have been constructed on drainage

structures.

3. Prohibiting people from dumping of rubbish and solid waste in drain.

4. Regular cleaning and maintenance by the concerned authorities.

5. Demarcating water bodies which can act as retention pond to avoid water logging from

heavy rainfall.

6. Demarcating Right of Way to preserve the natural channels.

7. n-off of rainwater. Unplanned and haphazard development of low lands has to be

stopped to preserve the natural drainages system.

8. Primary drains should be prepared and the secondary and tertiary drains will be

connected with the outlet of the domestic wastewater.

Typical secondary drainage

Typical primary drainage

9. The future drainage system should be designed to be westwards. The solid waste

collection and management capacity should be improved by the Pourashava

authority, so that the generated domestic and other waste will be not a threat for drainage

congestion.

CONCLUSION

Developing an effective drainage system is very important for an urban area. Drainage planning

is a very complicated issue of physical planning. This paper presents the application of GIS for

designing an effective drainage system which develops a network between natural and man-

made drainage system. This type of exercise provides a benchmark idea to deal with cellular

automata models for future service design. However, this paper presents the rationalistic solution

of the problem without considering the institutional aspect of the problem. Thus the institutional

issues related to service design could be a future area of research.

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