Simulation And Evaluation Of The Hydrologic Process Based On AnnAGNPS Model In Luoli-Cun Watershed Of China

With the development of urbanization,the water supply crisis is becoming more and more serious all over the world,and the water environment of the river has been paid more and more attention.Distributed hydrological model can take the spatial heterogeneity of climate and underlying surface into account to realize the discretization of the watershed according to the characteristics of topography and hydrology.The hydrological physical process revealed by the model is more in line with the actual situation.The scientific and reasonable simulation of watershed hydrological processes can provide scientific basis for water environment sustainable management.Bahe River is the primary tributary of Weihe(the Yellow River tributary),a typical urban river in Xi'an.The Bahe River Watershed is located in the Northwest Semiarid area and rainfall is the main way of runoff supply.The application of AnnAGNPS(Annualized Agricultural Non-point Source Pollution model)has not been reported in Bahe River Watershed.The Luoli-Cun Watershed is located in the upstream of Bahe River,which was selected as the study area in this study.Based on the optimal division of Cell,daily runoff and sediment database base was constructed for AnnAGNPS.The watershed baseflow was segmented.The yearly-monthly-daily runoff and sediment load were simulated and analyzed.The simulation results confirmed the applicability of AnnAGNPS model in the Luoli-Cun Watershed,which provided a theoretical reference for understanding the hydrological characteristics of the watershed and achieving the rational management.The main results of this study showed as follows:(1)When the Critical Source Area(CSA)and the Minimum Source Channel Length(MSCL)were 100hm2 and 70 m respectively,the watershed was divided into 1030 Cells and 420 Reaches,and the model could well describe the characteristics of the underlying surface such as terrain,landuse and so on.(2)The Kalinin algorithm was used to segment the watershed baseflow,and the baseflow index was 47.48%.(3)Based on the sensitivity analysis of model parameters by Differential Sensitivity Analysis(DSA).The sensitivity parameters ranking of runoff from high to low were runoff Curve Number(CN),Field Capacity(FC),Saturated Conductivity(SC)and Mannings_n(Mn).The sensitivity parameters ranking of sediment from high to low were Residue Cover Remaining(RCR),Cover-management Factor(C),Support Practice Factor(P),Soil Erodibility Factor(K),Initial Random Roughness(IRR),Field Capacity(FC),Annual Root Mass(ARM),Area Disturbed(AD)and Surface Cover Residue(SCR).In addition,Mannings_n(Mn)had no effect on sediment output.(4)Through calibration and verification,the efficiency coefficient(Ens)of the yearly-monthly-daily runoff,during the calibration period(2001-2005)and the validation period(2006-2010),was greater than 0.51,and the decisive coefficient(R2)was greater than 0.55.The relative error(Re)were controlled within 10%.The results at monthly scale were best,which Ens and R2 were greater than 0.78.The simulated results of medium rainfall events were better than those of storm events.The simulated deviation of rainfall events increased with the increase of rainfall intensity.The results of the runoff spatial distribution showed,the contribution of farmland flow was the strongest,and the arbor forest flow was the weakest.AnnAGNPS model was reliable for simulating the runoff process of Luoli-Cun Watershed.The watershed water environmental capacity calculation showed that the water environmental capacity of COD and NH3-N were 3814t/a,223t/a respectively in the mainstream river segment.The mainstream had a moderating effect on the non-point source pollution of the watershed.(5)Due to the complexity of sediment transport process,the simulated precision of that was lower than that of runoff.Re was about-30%.Ens and R2 of monthly scale during the calibration period were 0.35 and 0.36 respectively,and were 0.27 and 0.35 respectively during the verification period.On the whole,AnnAGNPS could better reflect the change process of sediment discharge.There was little or no soil erosion question in the watershed.