See discussions, stats, and author profiles for this publication at https //www researchgate net/publication/265848376 A CASE STUDY ON WATER LOGGING PROBLEMS IN AN URBAN AREA OF BANGLADESH AND PROBABL[.]
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A CASE STUDY ON WATER LOGGING PROBLEMS IN AN URBAN AREA OF BANGLADESH AND PROBABLE ANALYTICAL SOLUTIONS
A CASE STUDY ON WATER LOGGING PROBLEMS IN AN URBAN AREA OF
BANGLADESH AND PROBABLE ANALYTICAL SOLUTIONS
N.F.Anisha 1 * S Hossain 2
1* Undergraduate student, Dept of WRE, BUET, Dhaka-1200, Bangladesh,Email: anishahossain@yahoo.co.uk
2Junior Engineer, Institute of Water Modelling(IWM),House # 496, Road # 32, New DOHS, Mohakhali, Dhaka-1206,
Bangladesh Email: shlitonbuet@gmail.com
ABSTRACT
In Bangladesh, located on the extensive flood plains of the Ganges and Brahmaputra Rivers flooding is
a natural part of life Thus water logging in the urban area is not a new problem It's a part of life but the frequency of this problem is increasing The urban area has been experiencing water logging for the last few years even a little rain causes a serious problem for certain areas Increased urban development’s not providing sufficient drainage results in water logging leaving parts of urban area inundated for several days This causes naturally large infrastructural problems for the city Most of the time during the monsoon, the water level of the river remains higher than the terrain inside the urban area Hence, standard draining by gravity may not always be possible It has been identified that improvement of the drainage system is one of the highest priority needs of the urban authority for living environment of its urban population The urban area suffers from drainage congestions and water logging especially during rainy season It creates an unhealthy environmental situation and causes inconvenience to the residents of the urban including damages to the infrastructure, loss of business and spreading of diseases It is observed that there is a lack of planned and adequate drainage network system in the Teknaf, a small urban area of southern part of Bangladesh beside the Bay of Bengal The developed technology can easily be transferred and applied to catchment areas experiencing similar problems
Keywords: Waterlogging, Urban Area, Drainage Study, Teknaf
1 INTRODUCTION
Bangladesh is a country of heavy rainfall and regular floods The mean annual rainfall is about 2320mm Being the most densely populated country of world, the cities here face some regular problems like traffic congestion, water logging, water pollution, improper waste management etc Water logging is one of the major problems of the urban areas With uncontrollable growth of population and unplanned urbanization, the drainage and sewer facility are not developing accordingly This study aims to do a case study of the current urban water logging in Bangladesh, trying to highlight the main causes behind it, the influence of undertaken projects and people’s perspective about the effects of water logging in their urban areas
The improvement of drainage system of Teknaf urban area has the following specific objectives:
▪ On the basis of outfall, dividing the total water shed into number of drainage zones to check the discharging capacity of the outfalls and analyzing the existing conditions related to drainage facility in urban area
▪ Improvement of drainage network by construction of new primary and secondary drains
▪ Improvement of outfalls to accommodate runoff from present and future urbanized area
▪ Cleaning and removal of blockage from existing drains and repair and rehabilitation of
existing primary, secondary and tertiary drains and protection of the water quality at outfall (Kabir,2013)
* anishahossain@yahoo.co.uk
Trang 22 METHODOLOGY
Drainage system of an urban area is assessed through a sequence of analytical processes and it finally results in a proposed drainage system The study includes data collection from secondary sources, analyzing and checking of data, development of hydrological model, reviewing and correlating urban area drainage system with existing regional models, identification of design year and simulation of the model for the design year, determination of design flows from model simulation, calculation of design parameters from design flows etc and proposes design plan for gravity drainage
2.1 Location and Topography
TEKNAF Urban area is located in TEKNAF Upazila, COX’S BAZAR District under Chittagong Division The land elevation of the urban area effectively ranges between 0.88 mPWD and 10.33 mPWD and is gradual in most of the urban area Insignificant fractional percent of land lies outside the above range.It is assessed that only 20% land of the urban area is below 0.88 mPWD while 41%, 66%, 87%, 97%, 99% and 100% of the land are below 2.46 mPWD, 4.03 mPWD, 5.61 mPWD, 7.18 mPWD, 8.75 mPWD and 10.33 mPWD respectively The use of present urban area’s area can be broadly divided into lands for agricultural (10%) and non-agricultural (90%)
2.2 Rainfall
Design rainfall storm intensity for the urban area is assessed from that of known design storm intensity
of Dhaka applying a conversion factor which relates the rainfall events between Dhaka and reference station for the urban area.Kutubdia is a rainfall gauging station (R316) with reasonable length of records and is located nearest to the Teknaf It is selected as the reference station for assessment of storm intensity for TEKNAF Urban area The station is about 115 km distant from the urban area
2.3 Flood
The Urban area lies in the Naf River basin The water level gauging in close vicinity of the urban area
is available at Saflapur (200) on the Matamuhuri River From field visit, local people’s opinion and Satellite base flood map analysis the water level of Matamuhuri River is adjusted for TEKNAF Urban area Thus average year flood level at the Urban area is estimated to 1.36 mPWD.It is assessed that 70% of land of the Urban area is above the average flood level The rest of the land ranges from moderate to very deep flooding It is assessed that 6%, 18% and 6% of land is subjected to moderate (30-90 cm flood depth), deep and very deep (90-180 cm flood depth) flooding in reference to average year flood
2.4 River and Khal System
Regional river system adjacent to the urban area is shown in Figure: 1.The Teknaf urban area lies on
the right bank of Naf River The Naf River flows north to south beside the Teknaf urban area The khal
system of this area is shown in Figure 1 There are two khals named Heccha Khal and Kayokkhali
Khal branch Heccha Khal flows through the urban area and the downstream route to Naf River and finally falls into Bay of Bengal Kayokkhali Khal carries storm water from major parts of the Urban area and drains into Naf River and finally to Bay of Bengal There are some low lying lands on the eastern part of the urban area which serves as runoff destination of storm water from some parts of the urban area and finally route to Naf river system
2.5 Existing Drainage System
There exist few lined and unlined drains within the urban area These can drain some local areas of the urban area The capacity and outfalls of existing drainage system is not planned with well defined consideration of drainage areas/zones for the whole urban area The lengths of existing lined and unlined drains are about 8.79 km.In absence of planned and adequate drainage system, the Urban area
in places suffer from drainage congestion and water logging after heavy rainfall The main concerns for drainage issues of the Urban area can be summarised as: i) undersized drains, ii) obstructions in the drainage system to outfall, iii) damages of drains, iv) inappropriate / temporary location of outfalls, and v) absence of planned and systematic drainage network system (Khalequzzaman, 2001)
Trang 3Figure 1:
Regional River system adjacent to the Teknaf
2.6 Water Logged Area
Inundation occurs in some localized places of the urban area after heavy rainfall in absence of appropriate drains and routes Presently mentionable water logging is observed following moderate to heavy rainfall in and in the vicinity of ward -3, 4, 5& 6.The depth and duration of inundation vary from place to place Such areas are freed from inundation by the process of evaporation and infiltration The reasons for inundation/water logging are technical, social and institutional These water logged areas have been considered and brought under proposed drainage network
2.7 Design Criteria
The drains are designed to collect excess rainfall that is generated as surface runoff from urban area, convey the runoff and finally discharge them to outfalls The design of drains involves hydrological computations of runoff from the drainage basin and also hydraulic computation of section of drain from result of hydrologic computations
Modified Rational Method is one of the simplest methods of calculation of runoff It gives reasonably accurate result and widely used method for calculation of runoff for last few decades In designing primary and secondary drains of TEKNAF Urban area the Modified Rational Method is practiced The runoff by Modified Rational Method is:
Peak runoff, QP = CsCrIA/360
Where; Q = Peak runoff flow rate (m3/s)
I = rainfall intensity (mm/hr)
Cs = storage coefficient
A = catchment area (hectares)
2.8 Identification of Outfalls
The outfalls for the present and
expanding core area of the urban area are
in the Heccha Khal and Kayokkhali Khal
branch The outfalls of the proposed
drains and drainage zones have been
identified and exhibited in the following
section
2.9 Proposed Drainage System
Trang 4About 70% of land of the urban area is above the
average flood level Proposed drainage system
(Table 1) has been planned for the core area of the
urban area as well as for the extended area in near
future in consideration of priority needs.The area of
the urban area has been planned for improvement
under gravity drainage system The whole urban
area has been divided into 9 zones for drainage
improvement plan as shown in Figure 2 The
proposed drainage system for the Urban area
focusing the drainage basins/zones, sub basins/ sub
zones, dependency of zones/sub zones, drainage
network, outfalls
(khals/rivers/beels/destination).Zones 4-7, Zone 10,
Zone 14 and Zone 16 are planned with proposed
storm drains as they are in the core area of Urban
area or will be characterized as core area in near
future
Figure 2: Proposed Drainage system for Teknaf Table 1: List of proposed drainage system in TEKNAF Urban area
Sl No ID of Drain and
Table 2: Frequency Analyses for WL at the Outfall Channels of TEKNAF Urban area
Return Period Water Level (mPWD)
An assessment is made by
correlating the land
elevation of the
core area of TEKNAF
Trang 5Urban area to
the water level at outfalls which is
given in Figure 3 It is observed that
average land level of core area in the
urban area is higher than the average
water level (Table 2)
Figure 3: The land elevation of the core area of TEKNAF urban area
3 EFFECTS OF WATER LOGGING IN URBAN AREA
The logged water becomes polluted with solid waste, silt and contaminants that are washed off from roads The increase in volume and rate of logged water causes erosion and siltation It becomes a burden for the inhabitants of that urban area, leading to unhygienic environment and creating adviser social, physical, economical as well as environmental impacts (Towhid, 2004) A survey done through
a common questionnaire in four major urban areas of Bangladesh, Dhaka, Mymensingh, Chittagong and Sylhet, in various parts of those urban areas shows a brief perspective of them inhabitants about
the problems caused by water logging The Table 3 below is made with a sample of 50 samples in
each city
Table 3: Different Types of Problems Faced due to Water Logging in Urban Areas (Sylhet, Dhaka, Mymensingh and
Chittagong) of Bangladesh (Source: Field survey)
Problem Percentage Problem Percentage
Damage of household goods 45 Increase of construction
and maintenance cost
22 Damage of underground service lines 62 Death and damage of fisheries 9
4 CONCLUSIONS
The highlight features of the urban area system in connection with the issues of its storm drainage are that Teknaf lies on the right bank of Naf River The relatively low lying area of the urban area is flood affected from internal rain feed The part on the north and south of urban area is affected by the internal rain fed flood It is assessed that 70% of land of the urban area is above the average flood level The rest of the land ranges from moderate to very deep flooding It is assessed that 6%, 18% and 6% of land is subjected to moderate (30-90 cm flood depth), deep and very deep (90-180 cm flood depth) flooding in reference to average year flood There exist few lined drains within the urban area They are much unplanned and lack in systematic drainage network Some localized places of the urban area suffer from inundation due to internal storm water drainage congestion, and water logging in few places in absence of adequate gravity drainage provision and routes and also for choked up with solid wastes Lack in social awareness is a huge concern for smooth functioning of the drains
5 RECOMMENDATIONS
Proposed drainage systems have priority needs secondary drains Detailed engineering survey is a pre-requisite for planning of tertiary drains About 12 nos of cross drainage works (e.g.; box culverts/ pipe culverts) will be required in connection with the whole proposed drainage network About 08 nos of
Trang 6cross drainage works will be required for the priority drainage systems and the rest will be required for
the future drainage systems.Raising low land with earth fill above the flood level is a pre-requisite for
the land be brought under gravity drainage It is recommended that such land is raised to the similar
level of high land (not less than 1.34 mPWD) of the urban area Protection works at outfalls will have
to be provided in consideration of design energy dissipation.The existing drains and also those will be
constructed shall have to cleaned at regular interval Maintenance and cleaning of drains shall have to
done at least once in every year specially before starting of monsoon season Zone 7 & 9 of the urban
area will drain overland across the urban area boundary to the lying beels and finally route and drain to
Naf River The Urban area authority will have institutional linkages with all relevant line agencies for
the continuation of drainage provision of Zones 7 & 9 in view of long term consideration.The Urban
area authority will monitor the water level of Outfall Khals & Rivers, record the drainage congestion
area of each significant storm, and maintain the existing river and khal and also will have institutional
linkages with all relevant line agencies such as BWDB, LGED and in particular with DPHE in
connection with operational bottlenecks of the planned system and for maintenance of appropriate
section all through its natural drainage routes
6 ACKNOWLEDGEMENT
The authors would like to acknowledge the contribution of all team members of this study
Particularly, Mr.Robin Raihan, Project Direcor, Ground Water Management Project, DPHE is
appreciated for his kind consent to the authors for this publication the invaluable support of Mr
Emaduddin Ahmad, Team Leader, Comp-I,Mathematical Modelling for safe Drinking Water Source
Identification, DPHE and Mr S M Mahbubur Rahman,Director, Water Resources Planning Division,
IWM
7 REFERENCES
Journal Article
Kabir, S., Khan, N.M.E.A, Water sensitive urban design: Dhaka city, Second International Workshop
on Design in Civil and Environmental Engineering, June 28-29, 2013, WPI
Khalequzzaman, M 2001 Flood Control in Bangladesh through Best Management Practices.
Department of Geology & Physics, Georgia Southwestern State University Americus, GA 31709
USA
Electronic Online Articles
Water Logging in Satkhira District An Analysis of Gaps between Needs and Response,Early Recovery
Facility, UNDP Bangladesh,2011
Flooding & Prolonged Water-logging in South West Bangladesh,Coordinated Assessment in 10
Uppazillas of Satkhira, Jessore and, Khulna,September 2011
Thesis
Towhid, K.G., Causes and Effects of Water Logging in Dhaka City, Bangladesh,TRITA-LWR Master
Thesis, Department of Land and Water Resource Engineering,Royal Institute of Technology,2004
Mathematical modelling for safe drinking water source identification under the project called
Groundwater management and feasibility study for 148 pourashava having no piped water supply
under DPHE
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