Design Flood Estimation based on Synthetic Unit Hydrograph Method for an Indian catchment

Design flood estimation is necessary for the effective planning and management of various hydrologic
structures such as dams. Mostly these structures are located in remote locations where observed
streamflow data is seldom available. There is a need to develop effective strategies to predict reliable
estimates of design flood at ungauged locations. The concept of Synthetic Unit Hydrograph (e.g.,
Snyder’s method, Soil Conservation Service method, Taylor and Schwarz method, Mitchell’s method,
etc.) that considers the use of catchment descriptors related to stream network and topography in
predicting the design flood estimates at ungauged locations is being widely used. The Central Water
Commission (CWC) method was specifically developed for predicting reliable estimates of design
floods at the ungauged locations in India. In the present study, we have estimated the design flood
estimate for Swan river which is a tributary of Satluj River in India located in upper Indo-Ganga
plains. Design flood estimates are obtained corresponding to a rainfall input having return periods of
100 years. In addition, physical upper bound of precipitation i.e. probable maximum precipitation is
also considered for estimating the probable maximum flood (PMF) for the catchment. The design
flood corresponding to 100-year return period rainfall is found to be 2537 cumecs while the PMF is
observed to be about 7863 cumecs. Further, a comparative study between the CWC method-based
design flood estimate and design flood estimates based on Snyder’s method, Soil Conservation
Service method, Taylor and Schwarz method, and Mitchell’s method are performed. These estimates of
design flood can be used to plan river training works on Swan river.