URBAN FLOOD MODELLING: A CASE STUDY OF ROORKEE CITY

Abstract

Urban development may lead to changes in local hydrology and water environment. Increasing levels of impervious surfaces in urban areas result in a higher volume of runoff with higher peak discharge, shorter travel time and more severe pollutant loadings. In this study, Storm Water Management Model (SWMM) developed by the Environmental Protection_ Agency (of the United States) was used to simulate the runoff and transport storm water through drainage networks by performing hydrologic and hydraulic analyses of storm water. SWMM is a dynamic rainfall-runoff simulation model used for single event or long-term (continuous) simulation of runoff quantity and quality primarily in urban areas. The City of Rookee was chosen as the study area. Rainfall data (SRRG) was available for the period (1977-2007) from the hydrometeorological observatory of the Department of Hydrology, IIT Roorkee. The rainfall data was analysed to calculate design storm for different durations and return periods. Annual maximum 24 hours rainfall was also used in simulation. Gumbel's Extreme Value distribution was used to find out 5 yrs, 10 yrs, 15yrs and 25 yrs return period rainfall. Hourly distribution factors provided by Indian Meteorological Department (IMD) and Central Water Commission (CWC) were used for the distribution of rainfall within 24 hours. The design return period was taken as 5 years. For I-D-F the design intensity for 30 minutes duration was taken as 101.1 mm/hr and for 24 hr maximum rainfall was 173.11 nun/day. GIS was used to prepare study area maps and to delineate the sub-catchments. Digital Elevation Model (DEM) and Digital Surface Model (DSM) were generated using spot elevations. According to the natural drainage pattern, the study area was divided into three sub-catchments having different flow directions, 1) IIT, Roorkee_ campus and surroundings area up to Solani River, 2) from BSM College up to the railway station southwards and 3) from BSM College north wards up to Solani River. The selected design .storm was used for storm water simulation using SWMM. Because of no flooding observed in sub-catchments 1 & 2, only sub-catchment 3 was analysed further. Simulation shows that the part of the sub-catchment 3 (in Ambertalab area) remains flooded (95 cm at node J3 and 80 cm at node J4) for about 1.5 hours.