Human Impact and Channel Hydrological Modification: A Study on Dwarka River of Eastern India Surajit Let and Dr. Swades Pal along river to draw immediate profit from river the intensity of Abstract — With course of time the physical landscape of flood has increased many times and it carries huge sand the river is getting changed and at the same time human instead of fertile silt and flood is considered as human fears. interference also has massively topsy-turvied the normalcy of As a result problem of flood today become great challenge to the river. Dwarka River is one of the Tributary of Bhagirathi our society, to our economy as well as sustain the status of River in eastern India. This river basin covers densely development. populated tracts of Jharkhand and West Bengal state. Now due In this present study author would like to show how flood to the desperate intervention of human being through characters have been proliferating over time and what the main construction of barrage across river, embankment along river causes of such extreme hydrological modification are. banks, lodge construction along river banks etc. to draw immediate profit from river and river command area, river has II. ABOUT THE STUDY AREA changed its hydrological character in diversified ways. One of the most important modified hydrological phenomena in The Dwarka River - a tributary of Mayurakshi is a well Dwarka river basin is flood. If morphodynamics of the flood is known name in the river atlas of Rarh Bengal including parts possible to manage with very cooperative way the execution of of West Bengal and Jharkhand states of India. Originating at wise resource use of the basin will be made possible. Kushpahari of SanthalParganas of Jharkhand it has been flowing through Mayureswar and Rampurhat police station Keywords — Spatial flood dynamics, Flood frequency, Flood areas of Birbhum district and ultimately joins the Mayurakshi water stagnation period, human interference, Hydrological near Hizole wetland in Kandi Police station of Murshidabad modification. district, West Bengal. Its basin area can be delimited by 23°58' to 24°29' North I. INTRODUCTION latitudes and 87 °18' to 88°12' East longitudes covering an IVER basin is one of the most important and lucrative area of 3569.76 km2. Total length of the river is 156.54 km. Rhabitat of human living. Within a basin a large set of Administratively, the study region includes Pakur and hydrological phenomena has been working on in its own way. Dumka districts of Jharkhand and Birbhum and Murshidabad Over pressure of population and their behavioral change has districts of West Bengal and 12 CD blocks of the same been altering the normal pattern of hydrological phenomena. districts. As per normal law people again has been getting back its negative result. One of the most important modified hydrological phenomena in Dwarka river basin is flood. Flood is simply defined as a state of high water level along the river channel or on coast that leads to inundation of land which is normally submerged. Once a time flood was seemed to be beneficial for human civilization when fertile silt carried out by the rivers enriched the production ability of an agriculture land and flood phenomena was fruitfully rhythmic in manner. But now a day due to desperate invention of human being through construction of dam, across river, embankment Surajit Let is a Research Scholar with Department of Geography, Visva Bharati, Santiniketan, India. (E-mail: [email protected]). Dr. Swades Pal is working as a lecturer in Deptt. Of Geography Fig. 1 Reference map of the study area Rampurhat College, Rampurhat, W.B. India. (E-mail: [email protected]) III. PHYSICAL BACKDROP The secondary data has also been collected from Survey Geologically the upper part of the basin dates back to the of India toposheetand Google image. deposition of Dharwanian sedimentary followed by Hercinian The flood intensity character of individual year(1978, 2000 orogeny from Cambrian to Silurian period. The extreme and 2007) for Dwarka River basin have been estimated using eastern part of upper basin is characterized by unclassified two parameters namely flood heightand flood stagnation Ggranitic Gneiss with enclaves of metamorphic geomaterials. period. In this study weighted score method has used for The two major deposition is divided by a narrow stretch (N.E integrated flood intensity map. to S.W) of Silt stone, Sand stone and Shales with coal Integrated flood map is prepared using three parameters deposition. There are some small patches of Hornblende, flood level high, flood frequency and flood stagnation period. Schist and Amphibolites, Charnockite/acid granulite and Augen gneiss and Migmatite, Sandstones and Shales etc. The middle catchment is mostly characterized by the (1) deposition of Lateritic soil and hard clays impregnated with Caliche nodules. The platform of this region was set through Where M = Maximum value of column, the tectonic activities associated with tertiary epoch followed N = variable by lying down of the recent (late Pleistocene) and successive Weighted values are added together to show the integrated data. On the basis of composite weighted score the entire basin southward march of the delta plain. area has been divided into four broad flood zone namely The lower catchment nearer to the confluence is mostly • Intensive flood zone (>240) characterized by recent alluvial deposition of alternative layers • Moderate flood zone (80-240) of sand silt and clay attributed by alleviation river diversion, • Low flood zone (<80) (iv) no flood zone (0). flooding and consequent shaping by twin action of Bramhani and Dwarka. The deposition of hard clays impregnated with V. RESULT AND DISCUSSION Cliché nodules of the middle continued in the lower catchment also up to the meeting place of Bramhani and Dwarka as well Table I clearly shows that flood affected areas have been as at a distance from the river course in the confluence zone. increasing over time. In last century 1978 flood year was the Physiographically, the upper Dwarka consisting of greatest in the sense of flood extension and damages. But flood SanthalPargana highland of Chotonagpur plateau fringe is year 2000 has broken down all the previous record and characterized by numerous rounded flat topped isolated account the most extensive flood character. Figure 2 and 3 hillocks with an average elevation about 271 m. The surface is respectively show the status of most intensive flood extension rugged and stony due to the effect of continuous action of and maximum flood affected areas. It is noticed that flood various agents of denudation. 2000 not only submerged the lower basin but also extensive The Lower Dwarka is consisting of Birbhum Rarh and part of upper basin area. Murshidabad Rarh Plain specifically relatively low lying region. The Birbhum Rarh is actually the eastward extension TABLE I DISTRIBUTION OF FLOOD AFFECTED AREA of Chotonagpur plateau fringe. It is slightly elevated lateritic 1978 region with exposures of Gondwana and high ravine land. The Flood zone 2000 2007 Murshidabad Rarh plain is the marginal land between delta proper in the east and lateritic Rarh in the west. Murshidabad Intensive 766.78 1023.81 613.64 2 2 2 plain is characterized by low lying topography with numerous flood zone km km km rivers and gully segments, wetlands, swamps, chars etc. Moderate 546.89 614.71 661.12 Annual rainfall in this region is about 145cm. Out of total flood zone km 2 km 2 km 2 80% rainfall happens during monsoon period (June to October). Low flood 350.91 610.43 376.97 zone km 2 km 2 km 2 IV. MATERIAL AND METHODS The present study is based on primary and secondary data. No flood 1911.32 1320.81 1917.68 2 2 2 A detail field survey has been conducted in different parts of zone km km km Dwarka River basin. The primary data are collected through questionnaires among local people and using dumpy level survey (for cross profile of river). The secondary data like flood level height, flood frequency, flood stagnation period etc. have collected from irrigation departments, block offices and statistic Hand Book of Murshidabad, Birbhum. Pakur and Dumka districts published by Government of west Bengal and Government of Jharkhand. Fig. 4 Integrated Flood Map Fig. 2 Intensive flood affected areas within basin area TABLE II DISTRIBUTION OF FLOOD AFFECTED AREA % of area Flood zone Area to total Intensive flood 207.40km 2 5.81 zone Moderate flood 898.51 km 2 25.17 zone Low flood zone 909.57 km 2 25.48 No flood zone 1554.28 km 2 43.54 Fig. 3 Maximum flood affected areas A. Flood Zoning B. Causes of Hydrological Modification On the basis of said methodology, integration of flood 1. Barrage Construction parameters has done and resulted score has been classified into Man-made barriers like dams and storage reservoirs, leads three zones like: to excessive deposition both in upstream and downstream 1. Intensive flood zone below the structure, and consequent increase of flood levels Basically the confluence catchment area of Dwarka River and extent [2]. Deucha barrage across barrage Dwarka have basin counts under intensive flood zone. Almost all the mouzas irrefutable effect onmainly lower part of Dwarka river basin. of Kandi block are experienced by intensive flood. About 32 These projects bear some boon for the upstream habitants mouzas of lower catchment isghastly lashed by flood damage. because it supplies irrigation water but it is really devastating Total area of intense flood zone is about 207.40 km2. for downstream residents. During monsoon period due to 2. Moderate flood zone heavy rain these barrages release huge water volume at a time Upper part of Dwarka River basin specially the eastern part beyond the retaining capacity of the rivers cause massive flood of Murshidabad district, eastern part of Birbhum district come in the western portion of Birbhum and entire Murshidabad under this category.