FLASH FLOOD HAZARD MAPPING IN FOOT HILLS AREA USING GEOINFORMATICS

Abstract

Flash flood is a type of natural hazard which occurs as a result of heavy rainfall in short duration. The basic difference between a normal flood and flash flood lies in the fact that a flood can be a result of continuous rainfall occurring for days, whereas a flash flood is an event that will occur within 6 hours of the happening of the cause behind it, the cause may be a heavy rainfall, outburst of any hydraulic structure, ice jams etc. this type of natural hazards are becoming one of the most dangerous and unpredictable event occurring frequently and posing a threat to the life of number of people living in the foothills area. Therefore it is the call of the hour to come up with some technique which can minimize the harm caused by these hazards to the livings and hence the development of flash flood hazard map came into picture. The flood hazard maps will facilitate authorities in making decision regarding illegal encroachment near river beds and also near areas vulnerable to flash floods. The work has been carried out using geomatic tools along with hydraulic models. The flood inundation maps are developed after doing the steady and unsteady flow analysis using HEC-RAS for discharge occurring at 100 year return period; thereby, calculating the inundated area under the two conditions and mapping the result using ARC-GIS .The second method involves six parameters, affecting the vulnerability of the flash floods, they are- land cover classification, slope, drainage density, surface runoff, type of soil. Ratings and weights have been assigned to the different parameter using Analytical Hierarchical Process (A.H.P) to determine the final hazard index. The hazard index value varies from 50-121 and it is being classified into four categories- very high, high, moderate, low. Finally all the outputs obtained prior in the work are processed in the GIS environment using the overlay index method to get the final Flood Hazard Map