Flood Hydrograph with Synthetic Unit Hydrograph Routing

Abstract

Synthetic unit hydrographs (SUH) based on geomorphology are used as a tool to produce flood hydrographs from rainfall records, especially in ungauged and partially gauged catchments. This study presents a flood hydrograph model formulated on SUH based approach using geomorphologic parameters derived from Survey of India maps and geographical information system (GIS) techniques to simulate basin runoff. It uses linear Muskingum routing model in which the routing parameters are determined from the kinematic approach rather than from runoff data. The model employs the unit hydrograph suggested by Central Water Commission (CWC) India, as the discharge data from the sub-catchments and routes the concurrent discharges generated from them to the watershed outlet, and compared with the unit hydrograph of the lumped catchment. Application of the model is demonstrated by using data of a small watershed in the Mahanadi basin, India. The study indicates the limitations of the CWC unit hydrograph approach both in the small hilly and large plane catchments. It is observed that the CWC unit hydrograph (UH) underestimates the peak discharges both for catchments smaller than 200 km2 with steeper slope and larger than 600 km2 with flatter slope. The study further emphasizes on using two parameter Gamma distribution for preparation of UH curve instead of adopting standard practice of drawing synthetic unit hydrograph using seven known points with approximate curve fitting.