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[.]
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 PROBABLE ANALYTICAL SOLUTIONS A CASE STUDY ON WATER LOGGING PROBLEMS IN AN URBAN AREA OF BANGLADESH AND PROBABLE ANALYTICAL SOLUTIONS N.F.Anisha1* S Hossain2 1* Undergraduate student, Dept of WRE, BUET, Dhaka-1200, Bangladesh,Email: anishahossain@yahoo.co.uk Junior 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 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 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 1|Page 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 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) 2|Page Figure 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 Cr = runoff coefficient A = catchment area (hectares) 3|Page 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 About 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 zones for drainage improvement plan as shown in Figure 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 Catchment S1 Length m Area sqkm Drain Type Outfall 393.01 0.03 Sec/Rec/ RCC S2 482.32 0.06 Sec/Rec/ RCC Proposed BMD Drain S3 449.99 0.02 Sec/Rec/ RCC Kayokkhali Khal S3_1 216.36 0.02 Sec/Rec/ RCC S3 to Kayokkhali Khal S4 261.29 0.04 Sec/Rec/ RCC Kayokkhali Khal S5 733.33 0.07 Sec/Rec/ RCC Kayokkhali Khal S6 632.67 0.05 Sec/Rec/ RCC Kayokkhali Khal S7 504.25 0.04 Sec/Rec/ RCC Heccha Khal Proposed BMD Drain Table 2: Frequency Analyses for WL at the Outfall Channels of TEKNAF Urban area Return Period Water Level (mPWD) 1.1 year 0.11 year 1.16 2.33 year 1.34 year 2.12 20 year 3.37 4|Page An assessment is made by correlating the land elevation of the core area of TEKNAF Urban area to the water level at outfalls which is given in Figure 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 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 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 Disruption in Traffic Movement 76 Water pollution 68 Disruption in Normal Life 94 Water borne diseases 71 Damage of roads 82 Damage of trees and vegetation 49 Damage of houses 69 Increase of insects 38 Damage of household goods 45 Increase of construction 22 and maintenance cost Damage of underground service lines 62 Death and damage of fisheries 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|Page RECOMMENDATIONS Proposed drainage systems have priority needs secondary drains Detailed engineering survey is a prerequisite 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 cross 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 & 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 & 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 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 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 6|Page View publication stats THÔNG TIN HỎI ĐÁP: -Trong trình làm Essay, bạn muốn tìm kiếm thêm nhiều tài liệu mẫu, cách làm Essay cập nhật Trung tâm Best4Team Liên hệ dịch vụ thuê viết essay tiếng anh Hoặc qua SĐT Zalo: 091.552.1220 email: best4team.com@gmail.com để hỗ trợ nhé!