Distribution Of Initial Soil Moisture In Xin’anjiang Model

Xin’anjiang model has been widely used in rainfall runoff simulation and prediction of small and medium-sized watersheds in humid and semi-humid areas.In the model,the model of runoff formation in excess of storage is used to calculate runoff generation,and the uneven distribution of soil moisture deficiency is considered by the watershed storage capacity-area distribution curve.On this basis,the total runoff is calculated for flood process simulation and prediction.It is believed that the distribution ofinitial soil moisture also conforms to the variation of watersheed storage capacity curve.In the application,in the application,the simulation results sometimes will appear that the initial stage of simulated flood does not coincide with the observed flood hydrograph.Initial soil moisture has different distribution according to different conditions,and different variation ofdistribution will also affect the fitting of flood hydrograph and the accuracy of the model.It proposes a new distribution form of initial soil moisture,It is considered that the initial soil moisture in some areas of the basin tends to be 0 with the effect of evapotranspiration after a rainfall.and the characteristics of runoff generation are compared with the original method.It is found that under the same rainfall conditions,the new method calculates lessrunoff generation before full storage than the original method,but the whole basin is full storage ahead of schedule.The runoff generation calculated by the two methods after full storage is the same.When the initial soil moisture is 0 and WM,the results of the two methods are the same.Pre and post improvement of Xin’anjiang model is applied to flood simulation in Shanxiying Basin and Yandu River Basin respectively,and the simulation results were analyzed and compared.The simulation results of the original initial soil moisture distribution of 16 floods in the Shanxiying basin from 1981 to 1986 were selected: the mean value of deterministic coefficient is 0.89,and the percent of pass is 87.5%;the mean value of deterministic coefficient of the new method is 0.94 and the percent of pass is 87.5%.The simulation results of the original methed of 20 floods in the Yandu River basin from 1981 to 1986 were selected:the mean value of deterministic coefficient is 0.88,and the percent of pass is 90.0%;the mean value of deterministic coefficient of the new method is 0.91 and the percent of pass is 95.0%.The accuracy of the simulation results in both basins is improved.In the simulation of flood process,the new method is more suitable for the actual flood processes than the original method in the initial flood section,which accords with the theoretical analysis.Although the errors of peak discharge will be increased in part,the overall fitting degree will be improved,which indicates that the new improved method has certain applicability.There are 29 figures,24 tables,and 112 references in this thesis.