2D FLOOD MODELING USING HEC-RAS

Abstract

Floods caused by over flowing river can have devastating effect on life and property resulting in economic loss. Modeling of floods is very important for planning, of mitigative measures and protection works. High intensity rainfall for Continous period in the catchment of the river can result in floods. Number of river basins in the Indian subcontinent regularly face floods in the monsoon seasons(80% of the annual rainfall happens in just 60 days time). To cope with such wide spread flood events affecting habitats and life of tens of crores of people flood prediction and the areas prone to flooding need to be identified for planning of damage control measures. Hydrological studies are the basic inputs for the calculation of the river flows. Protection works can be designed after consideration of the historical flows of 15, 25, 50, 100 year frequency. The spread of the flood caused by the overflowing river depends on the terrain of the flood plain this requires the contour maps/Digital Elevation Models of the area. Inundation mapping using contour maps and river flow data at the time floods/theoretical flood values can help in creating maps of terrains going to get affected by all kind of flood frequencies. Certain modern softwaresmake it very convenient to carry out inundation modeling using area DEM and differ river flow rainfall scenarios .Digital elevation models can be prepared from field survey data/contour maps on even remote sensed aerial data/satellite composite pictures of the terrain. In this study, it is aimed to construct flood inundation maps for flooding caused due to North American River (wolf) and its two tributaries .Topographic data of the study area is defined for hydraulic model by sectioning along the river on digital terrain model (DTM) which is created by ArcGIS, a geographical Information System (GIS) software. Data migration between ArcGIS and HEC RAS is provided by using an intermediate module, HEC GeoRAS After required geometrical and hydraulic structure data are constituted, flood inundation maps are obtained by inputing flow data into the model. The hydraulic simulation was performed under a subcritical steady flow regime for 100-year recurrence period for two downstream boundary conditions i.e for Normal depth and for known water surface elevation at downstream point. Flood hydrograph is made for both river and tributaries at specific location for recurrence interval of 100 year. Hydrograph is made for month of December for 3 days for hydraulic v

modeling as rainfall is more in month of December. As a result of hydraulic modeling- maximum flood depth, maximum velocity and area extent of submergence are found. This present work deploys HEC-RAS software on wolf river system on a Pre-Processed Digital terrain model (DTM) of wolf river system basin of North America which was obtained from published source at (www.hydrosheds.cr.usgs.gov.in)The objective is to find extent of flooding and water surface elevation along the river for flood protection works.