Comparative Study of Flood Calculation Approaches, a Case Study of East Rapti River Basin, Nepal

Abstract

Various approaches to high flood calculation have been used to inform the design of hydraulic structures and flood protection works in Nepal. To assess potential flood volumes, a variety of methods and calculations are employed and the highest figure is adopted as correct so as to err on the side of safety. This approach, while safe, can result in excessively uneconomic design. As well, this approach erodes the designer’s confidence in the process to determine the potential flood volume and perpetuates such sub-optimal approaches. Through the case study of East Rapti River, this paper tries to shed light on various ungauged basin approaches of flood prediction currently in practice. It also compares the relative performance of those approaches using statistical methods and observed data. From the study, Jha PCJ method (1996) yielded a comparable result with the gauged basin methods. A remarkably notable fact obtained is that all the ungauged basin methods except rational method underestimated the flood discharge as compared to that obtained from the frequency analysis based on measured data sets. Overall, our study concludes that flood forecasting on ungauged basins cannot be recommended because a number of assumptions and personal judgments influence each of the prediction methods. Therefore, a more radical shift to basin specific intensive research is desirable DOI: http://dx.doi.org/10.3126/hn.v15i0.11296 HYDRO Nepal Journal Journal of Water, Energy and Environment Volume: 15, 2014, July Page: 60-64