COMPARATIVE PERFORMANCE EVALUATION OF HEC-HMS AND SWAT MODELS AND UNCERTAINTY ANALYSIS IN STREAM FLOW SIMULATION (IN CASE BILATE AND GIDABO WATERSHEDS)

Abstract

A number of semi-distributed hydrological models have been developed to model the hydrology of watersheds. However, it becomes difficult to potential model users to identify the most economic and efficient hydrological models for specific watershed. This study aimed to compare stream flow prediction efficiency of HEC-HMS and SWAT models and their associated uncertainty in Bilate and Gidabo watersheds. The model approach started with input data preparation, sensitivity analysis, calibration, validation and uncertainty assessment to test the capability in predicting stream flow at the outlet of Bilate and Gidabo watersheds. The parameter uncertainty is taken in to account and MCMC (HEC-HMS) and SUF-2 (SWAT) analysis are employed to analyze the parameter uncertainties. During sensitivity analysis, the results show that constant loss rate (CR) is most sensitive followed by lag time (LT) in case of HEC-HMS for both watersheds. Whereas, the most sensitive parameter detected by SWAT is ALPHA_BF in Bilate watershed and CN_2 in Gidabo watershed. The models were calibrated and validated from 2001 to 2010 and 2011 to 2015 of Bilate and from 1998 to 2003 and 2004 to 2006 Gidabo watershed respectively. The model efficiency on daily time step during calibration HEC-HMS (NSE=0.55 and0.65) and SWAT (NSE=0.53 and 0.58) were obtained for Bilate and Gidabo watersheds respectively. Similarly for validation period HEC-HMS (NSE=0.55 and 0.63) and SWAT (NSE=0.52 and 0.56) were also obtained for Bilate and Gidabo watersheds respectively. Both models are able to simulate the hydrology of both watersheds in acceptable way. Statistical indicators reveal that in both watersheds, the models performances in monthly time step are higher than in daily time step. Despite their similar modeling abilities, a comparison analysis revealed that the HEC-HMS model was performed slightly better at simulating streamflow in both watersheds based on common performance measures. Based on both plot of uncertainty and results obtained for P factor and R factor indicates that the parameter uncertainty estimated for both watersheds were found to be good. Because HEC-HMS model (with DCL method), with less input data is easy to calibrate and therefore gives better statistical result with goodcertainty values compared to SWAT model.