Flood Forecasting For Litang River, Yalong Region Based On HEC-HMS

Flood has been one of the major water problems in China. Practice of flood control and drought relief has proved that hydrology information forecast played an important role in flood control and drought relief. This article selects the western Yalong River basin as the research object, according to local actual condition, using HEC-HMS hydrological model to simulate the rainfall-runoff relationship.The flood characteristic and Change within the year and inter year of hydrological elements in rainfall, runoff are analyzed in researched area. The average rainfall for years is in 500~900 mm and concentrated in May to October. Although, there is a little annual change of runoff, there is great difference in its flood and dry seasons. Runoff of wet season which is from June to November accounts for about 82% of the whole year. According to the hydrologic statistics of Liewa station, the maximum of mean annual runoffs and the minimum is the mean for many years 1.77 times and 0.62 times respectively. Historical runoff change is on the decline, the slope is-1.34.Basing on HEC-HMS hydrological model, the Litang river basin hydrological model was constructed. SCS Curve Number, SCS unit hydrograph method and Muskingum method are selected to apply to parameter sensitivity analysis, rainfall-runoff simulation, and model verification in Litang river basin.Analyzing parameter sensitivity of HEC-HMS model and studying the change of parameter sensitivity in different spatial scales of sub basin. Results indicate that CN is the most sensitive parameter of flood volume and peak discharge, and CN is relatively more sensitive in smaller sub basin, other parameters such as initial loss, percentage of impervious area and constant monthly have a certain extent effects to flood volume and peak discharge, but little impact on the time of flood emergence. The lag is the most sensitive Parameters for the time of flood emergence and it is not sensitive to the flood volume, has a certain extent effects to peak discharge.The result of flood simulation indicates that HEC-HMS has a good adaptability to short-term rainfall flood simulation in Litang river basin, and it can be used for application of practical problems.The model can be used in short-term flood forecast of Litang river basin.The paper analyses the researched area flood forecast accuracy error factors, including material data, natural factors and model.