CAMINHOS DE GEOGRAFIA - revista on line http://www.ig.ufu.br/revista/caminhos.html Instituto de Geografia ufu ISSN 1678-6343 Programa de Pós-graduação em Geografia ENVIRONMENTAL IMPACT OF FLOOD AND THEIR SUSTAINABLE MANAGEMENT IN DELTAIC REGION OF WEST BENGAL, INDIA1 Vibhas Chandra Jha Professor and Ex-Head Department of Geography,Visva-Bharati University Santiniketan731235, West Bengal, India, [email protected] Haraprasad Bairagya Researcher, Dept. of Geography, Visva-Bharati University, Santiniketan, Birbhum, West Bengal, India, [email protected] ABSTRACT Flood is one of the basic factors for sustainable development and environmental management in the humid, tropical and sub-tropical regions. Flood characteristics decide the status of the terrain for its capability for sustaining the increased population of that area. In this paper, an attempt has been made to analyze the flood characteristics using the Gumble‟s Method and their impact on sustainable development and environmental management in the Deltaic Region of West Bengal, India. The Murshidabad District of the West Bengal State, India has been selected as a case study to assess the environmental impact of flood and their characteristics which includes different measures like flood elevation, discharge, volume and duration. The physical and socio-economic condition of the study-area have also been analyzed. An attempt has also been made to suggest some measures for the development of the study-area. Key Words: Flood, Flood Plain, Flood Characteristics, Gumble‟s Method, Sustainable Development and Environmental Management INTRODUCTION Flood in deltaic region is a disaster which can destroy the total environmental set up of the area. It causes river bank erosion, depression of land, shifting of river course, river channel widening etc due to it‟s high discharge, elevation, volume and longer duration. It leads to create agricultural deficiency, unemployment, sexual exploitation, and even starvation death. So, proper and scientific management of the flood in this district is necessary to solve the environmental problems to give better life for the next generation population. The district of Murshidabad is in the northern part of Brahmaputra Delta. It is a low flat terrain having elevation of 10-30m above the m.s.l in Ganga Brahamputra Delta. Delta building processes are active over southern part, while northern part in which the Murshidabad district is situated, shows the characteristics of a mature deltaic landscape. This Delta is named as „khadar‟. The „khadar‟ deposits are as a resultant feature confined to the vicinity of the present channels. The clays have less „Kankar‟ and the organic remains. The „Khadar‟ imperceptibly merges into the deltaic and other accumulations of the pre-historic times. The delta of Ganga-Brahmaputra is merely the sea ward prolongation of the „Khadar‟ deposits of the respective river valleys. The present study aims to analyze the flood characteristics using the Gumble‟s Method and their impact on sustainable development and environmental management in the Deltaic Region of West Bengal, India. To assess the environmental impact of flood, the following objectives have been considered relevant for this study. Various Workers in the field of applied hydrology have attempted as basics and case studies in different parts of West Bengal. Particular mention may be made of P.K. Basu, M.C.Burke, V.T. Chow, D.R Maidment, L.W Mays, D.N Wadia, Aveek Datta, Anjan Dasgupta, S. K. Garg, „O‟ Mally, Chandan Ray, K Subramanya, K Rudra, and Islam Khan Zafarul. 1 Recebido em 20/07/2011 Aprovado para publicação em 28/08/2011 Caminhos de Geografia Uberlândia v. 12, n. 39 set/2011 p. 283 - 296 Página 283 Environmental impact of flood and their Vibhash Chandra Jha sustainable management in deltaic region of West Haraprasad Bairagya Bengal, India In fact, the deltaic parts are characterized by specific characteristics of stream rises and their impacts on flood plains which affects the sustainability of the local people with severe environmental consequences. This paper is based on the findings of the field data and the empirical results. It is concerned with: To analyse the flood characteristics such as flood elevation, discharge, volume and duration in the study-area; To apply the Gumbel’s method for analyzing the River Discharge and its Flood Frequency; To find out the Environmental Problems related to flood in the study-area, and; To suggest some measures for the sustainable development and management of the study-area. Data Base and Methodology The present study is based on the flood data of 35 years of the region. The quantitative- statistical method i.e. Gumbel‟s method has been adopted to analyse the flood frequency. The topographical sheets on 1:50,000 (SOI), and the Satellite Imageries of IRS P6, LISS III Precision geocoded on 1:50000 of December2006, field photographs as well as daily, monthly and annual rainfall data for the period of 10 years have been used to draw the results of the present investigation. Study-Area The Murshidabad District covers an area of 5324 km2 out of 1,30,00km2 area of total delta composed of repeated alternations of clays, sands and marls with recurring layers of pit, lignite and some forest beds (Wadia 1975, pp370). The Murshidabad District is prone to flood almost in every year due to it‟s geographical location. It is situated almost in the middle part of the West Bengal flood plain. The northern boundary of the district is confined by Ganga River. This district is almost equally divided into east and west to the south flowing Bhagirathi River, which is an important tributary of River Ganga. The district Murshidabad centrally located in West Bengal lies between the Latitude of 23043'30"N to 24050'20"N and longitude of 87049'17"E to 88044'00"E (Fig.1). River Ganga forms the north and eastern boundary and separates it from Bangladesh. Extending over an area of 5,324 sq. km, the district has 58, 63,717 persons (30, 04,385 are males and 28, 59,332 females census 2001). Fig.1 Location of Study-Area Caminhos de Geografia Uberlândia v. 12, n. 38 jun/2011 p. 283 - 296 Página 284 Environmental impact of flood and their Vibhash Chandra Jha sustainable management in deltaic region of West Haraprasad Bairagya Bengal, India Flood Characteristics Man must acquaint himself with the characteristics of floods if he is to control them. Floods vary as the weather-from month to month and year to year. The first step in becoming better acquainted with flood is to measure them. The important measures are: Flood elevation, Flood discharge, Flood volume and Flood duration Flood Elevation The elevation of a peak is the most often used fact of all flood data. The recording of the peak elevation should be done carefully. The maximum flood height at a staff gauge may be noted by an observer at the time of flood peak or may be indicated on the gauge. Table-1 shows the maximum flood level seen in different rivers of Murshidabaddistrict. Table 1: Maximum Flood Elevation S.N. Rivers Sites Danger Level Extreme Danger Maximum Flood Date (m) Level (m) Elevation (m) 1 Ganga Nurpur 21.03 21.64 22.24 28-8-69 2 Ganga Chakghat 20.88 21.49 24.24 31-8-69 3 Bhagirathi Geria 20.57 21.18 24.29 21-8-1800 4 Bhagirathi Jangipur 20.27 20.88 23.50 26-8-70 5 Bhagirathi Berhampore 17.22 17.83 19.26 14-8-1890 6 Dwarka Ranagram 17.36 17.86 18.67 1-9-71 7 Dwarka Sankoghat 20.42 21.00 23.03 1-9-71 8 Bhairab Akherigang 18.44 19.05 20.87 20-8-90 9 Mayurakhi Panchthupi 23.99 24.57 24.31 25-9-73 . Flood Discharge Flood discharge is an important characteristic of flood. It can be measured. In fact it indicates the quantum of flood and it‟s capability of destruction. The principal river Bhagirathi and its tributaries are responsible for Murshidabad flood condition. Thus, the Bhagirathi river discharge and its flood frequency analysis can be analysed using Gumbel‟s method. Flood Frequency Analysis by Gumble’s Method Chow (1951) has shown that most frequency – distribution functions applicable in hydrologic studies can be expressed by the following equation known as the general equation of hydrologic flood frequency analysis: XT =X+KSd Where, XT = value of the variate X of a random hydraulogic series with a return period T, X = mean of the variate ,Sd= standered deviation of the variate , k= frequency factor which depends upon the return period,T and the assumed frequency distribution. The commonly used frequency distribution function for the prediction of extreme flood values is the Gumble‟s method. This extreme flood value distribution was introduced by Gumble(1941)and is commonly known as Gumble‟s distribution .It is the most widely used probability distribution function for extreme values in hydrologicstudies and meteorological studies for the prediction of flood peaks,max. rainfall, maximum wind speed etc. According to Gumble, a flood as the largest of the 365 daily flows and the peak annual series of flood flows.The general formula for the prediction of extreme flood values and it‟s probability of occurance , is given by Gumble as below: Qp = Q¯ +K.Sd n-1 Caminhos de Geografia Uberlândia v. 12, n. 38 jun/2011 p. 283 - 296 Página 285 Environmental impact of flood and their Vibhash Chandra Jha sustainable management in deltaic region of West Haraprasad Bairagya Bengal, India Where, Sd n-1 = standerd deviation of the sample size, N = √∑ (Q¯-Q) ²/√N-1,Q = Flood discharge, K = Frequency factor expressed as K =Yt-Y¯n/Sn in which Yt = reduced variate, a function of T and is given by Yt = - [In.In T/T-1] Or, Yt = -(0.834+2.303LogLogT/T-1), Yn = reduced mean , a function of sample size N table.