Return Periods Analysis In The Bayi Reservoir Watershed Of Fuzhou City Based On HEC-HMS Model

Flood, which is one of the most critical disasters, is famous for itshigh frequency, wide impact scope and violent oncoming force. Becauseof the typhoon storm flood during rainy season, Fuzhou, located on thesoutheast coast of China, is bearing huge calamities and economic lossannually. According to statistics, the number of heavy rain was risingannually since the1990s. At the same time urbanization processchanged urban land use status and the impervious surface ratios. Both ofthese had influences on the change of return periods. It is vitalimportant to conduct a series of studies on the change of return periods,aiming to provide guidance for flood control under the circumstance ofurban expansion.This study focuses mainly the change in return periods. The BayiReservoir watershed, situated in Jin’an district of Fuzhou city, was takenas an example in this paper. In virtue of remote sensing technology, thelanduse information can be extracted from the TM/ETM+image of studyin1989,1994,1999,2001,2002,2003,2007. Additionally, digitalelevation model (DEM) data, soil type data, meteorological andhydrological data were collected to provide model information in thestudy. The Bayi Reservoir watershed HEC-HMS hydrological modelwas well established after the pretreatment of partial data by means ofWMS software. Furthermore, the process of single rainfall-runoff in theBayi Reservoir watershed was simulated. The simulation results broadlyconsistent with the actual data, and the results are credible.The result indicated that single rainfall and runoff within24hoursboth are normal distribution. The peak time and peak flows of singlerainfall both were ahead of their designed time. Based on the theory ofrainfall-runoff and the HEC-HMS model, this paper used model to carryout two scene simulations, and got some results. The results showed thatin the same landuse, the relationship between runoff and peak flows was quadratic parabola, and in the same rainfall conditions, the relationshipbetween runoff and CN was quadratic parabola.Rainfall conditions and land use both impacted rainfall–runoff andthe return periods. This study found that the relationships between theimpervious surface ratios (Im) and CN was CN=61.842Im0.0924. And itstructured the relationship between the impervious surface ratios and thereturn periods. The study designed to combine the rainfall conditionswith landuse case to calculate the discharge, and used impervious surfaceratios and return periods as the variables, drew the graph of return periodchange. Finally according to the graph, in A sub-basin the returnperiods of100,50,25years were ahead of designed time by20,8,3yearswith the growth of impervious surface ratios. In B sub-basin the returnperiods of100,50,25years were ahead of designed time by25,10,4years.This study provided precious experiences for return periods research.The research results were beneficial to urban flood control planning andscientific establishment of emergency program for urban flood controland drainage, furthermore, the results supplied theoretical basis torational planning for land use in urban watershed and scientificprevention and treatment of non-point pollution.