Application of geoinformatics for flood study at Tarapur union of Gaibandha

Abstract

Tills study has been taken 10develop vulnerability maps for agriculture using Remote Sensing (R:'.) and Geographic Information System (GIS) regarding different return period for flood hazard vulnerability asse."rnenl in a flood prone area, farapur llnio~ ()f Sundargal1i thana under Gaibandha district of Ba~gladesh, The study mainly focuses on the development (If a vulnerabilily function for preparing vulnerability maps for agriculture. For tlte development of vulnerability function depth-damage relation has been followed. For establishing relationship between flood depth and agricultural damage, an extensive field _,urvcyhas been carried (lut in the study area. Satellite images and other relaled data are also widely analyzed for establishing the relation more fruitfully. A Landsat and a Radarsat image of the sllldy area nave been u,ed 10 identify agrieullllral land and for identification of flooded and non-flooded area. Although the study area is located in a flO<ldplainlocality but the terrain is not so much flat. Due to lhis, depth of flood level varies in different location corresponding to a fixed level rise of water leveL In this regard for the development of a depthdamage function, the ,tudy area has bocn divided into four categories based on lhe elevation. In monsoon (July to September), one meter rise of water level leads 100 % damage of all the crops in the very low lying river associated land. Wherea, about 2 meter rise of water level causes 100% damages of ali the crop" in low iand aml 2.5 meter and 3 meter ri,c of water level; eauses 100% damages in all medium and high land crops of the study area respectively. For the deveiopment of flood inundation and floo<! depth map, Digital Elevation Model (DEM) and water level data of the study area have been collected form Bangiadesh Waler Development Board (AWDB). Water levels are used based on flood frequency analysis for 2-, 5-, 10-, 20-and 50-year return periods, The agricuitural land of the study area has been found in between the clevation>22,9 to <25.9i meter, Vuinerability fun~tion was ba..ed upon these land areas. The magnitude of vulnerability for agriculture of Tarapur union is found to increase linearly up to three meter dcpth of water and then it becomes horizontal. From the vulnerability maps it has been observed that for ali the return periods, the study area is very much vllinerable, And area cio~e to river bank is relalively more vulnerable compared to the area tur away from the river bank. Flood levei dlle to 20- and 50-year return periods damages 100% damages of crops.