Application of HEC-HMS modelling on River Storån,Model evaluation and analysis of the processes by using soil moisture accounting loss method
Abstract: River Storån, a major tributary of Lake Bolmen which is a source of fresh water to Skåne county of Sweden is found to alter the color of water in the lake due to the presence of natural organic matter. Hence it is of utmost importance to study the river to understand the dynamics of generation and flow of water from the river to the lake. This is done by application of a hydrological modelling system called HEC-HMS (version 4.3) developed by Hydrologic Engineering Centre, US Army corps. River Storån is modelled using soil moisture accounting loss method, a method chosen for simulations run for a long period of time. During the application, data collected are assembled and input into the model components of HEC-HMS. Later the model is calibrated from 2005 to 2010 followed by optimization and validation from 2011 to August 2019. The results obtained showed that the model underestimated the observed flow over the years and the reasons for underestimation was attributed to three factors, namely the climatic conditions, geological condition and topological condition. The temperature being an important climatic condition influenced processes like snowmelt and evapotranspiration, due to its inaccuracy it failed to recognize the type of precipitation specially during winter and spring. This led to the model generating low flow whenever the temperature went below 0. Further the generalization with respect to soil characteristics and depth led to quick response of the model to the precipitation which resulted in the simulated flow being more dependent on baseflow than on surface flow. Lastly, the exclusion of wetlands and small water bodies across the basin disregarded its impact on the process of evapotranspiration over the years. Through the model evaluation it was found that the RSR, NSE and Pbias value of both calibration and validation was found be same i.e., 0.9, 0.2 and -1% respectively. The PEPF was found to be 18% and 16% for calibration and validation and PEV was found to be 1% and -3% respectively. Although the model evaluation does not meet the expected value it is found to be satisfactory as the model successfully generates total volume, peak discharge and date of peak discharge very close to the expected value. This was followed by a discussion on the limitations of the model and recommendations to overcome it. The hydrological model HEC-HMS application to River Storån did not give the expected result but was found to work well for the areas which is prone to snowfall and heavy precipitation all through the year. The model is user friendly and is found compatible with Arc GIS which makes the parameterization easy. Further research and study are highly recommended to upgrade the model for better efficiency of the model.
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