Application of Hydrologic Modelling System (HEC-HMS) for Flood Assessment; Case Study of Kelani River Basin, Sri Lanka

Abstract

Kelani River Basin in Sri Lanka experiences frequent flooding resulting in loss of lives and properties in this basin. Keeping this in view, a study is taken up for Flood Assessment in Kelani River Basin, Sri Lanka up to Hanwella gauging site using HEC-Hydrologic Modelling System (HEC-HMS) tool. In the study, various available options of HEC-HMS have been considered for evaluation using various goodness of fit criteria, such as NashSutcliffe model efficiency (NSE), Percent Error in Peak, and Percent Error in Time to Peak and Percent error in Discharge Volume (Volume Deviation (D_v)). The Basin model has been selected considering the Kelani river basin up to Hanwella gauging site as a single basin for simulation of flood hydrographs and, in eteorological model, the Gaged weight option, of HEC-HMS, is considered for rainfall analysis. For the transform model or direct runoff model, Clark UH, SCS UH and Snyder UH models are considered. The calibration (manual and automatic) and validation of model parameters are carried out using hourly rainfall-runoff data of the five storm events observed during the monsoon seasons of the years 2017, 2016, 2014 and 2012. The Arc Map-ArcGIS and HEC-GeoHMS have also been used to process the different types of spatial data required as input for the HEC-HMS model application. It is found that the Clark model is the best-suited model for flood assessment of Kelani River Basin. The calibrated and validated Clark model can be very much useful for water managers and decision-makers to adopt structural and non-structural measures to minimize the losses due to frequent occurrence of floods in Kelani River Basin.