Determination Of Hydrologic Response Unit

Spatial discretization is a method of dividing the water-eroded slope surface into regional units of the input hydrological model,and it is the basis and only way to realize the simulation of distributed hydrological parameter model.In the research on the development process and mechanism of water erosion under micro-topography,the determination of the appropriate grid size has an important impact on the operation of the hydrological model and the simulation results.However,there are few studies on the spatial discretization of micro-topography,which limits people’s understanding of micro-topography.Construction of water erosion model under topographic conditions and in-depth understanding of water erosion development mechanism.In this paper,on the basis of scanning point cloud to build a micro-topographic digital elevation model(M-DEM),using cellular automata(CA)as the water erosion simulation platform,the two rainfall intensities of 60mm/h and 90mm/h,and five slopes(5°,10°,15°,20°,25°),artificial digging(AD)and contour tillage(CT),based on the grid data of 1～10mm side length,the erosion During the development process,staged water erosion simulation and research were carried out,and the contributions of splash erosion,sheet erosion and rill erosion to slope erosion and sediment production were systematically considered;The optimal hydrological response unit suitable for the model simulation is obtained by calculating the relative error and Nash efficiency coefficient;the local sensitivity analysis is carried out on the parameters involved in the CA-confluence sediment production model,and the quantitative parameter rate and value are used to simulate the model.The degree of influence of the results.The main research conclusions are as follows:(1)The constructed CA-confluence sediment production model can more accurately simulate water erosion under micro-topographic conditions.The sediment yield per unit time(every 30s)simulated by the model has a high degree of fit with the data collected from the artificial rainfall test.Therefore,the CA-confluence sediment production model has certain feasibility in the hydrological study of micro-topographic slopes.(2)Using the Morris local sensitivity analysis method,the cell/grid edge length,rain intensity,and average slope were respectively subjected to parameter sensitivity analysis,and the previous research results were used as the judgment basis.Length is a moderately sensitive parameter,while rainfall intensity and average slope are both highly sensitive parameters.(3)Using the CA-confluence sediment production model as a platform,the sediment production simulation was carried out on the slope surface of various farming measures,rainfall intensity,slope and erosion stage,and the relative error between the sediment production per unit time(every 30s)and the rainfall experimental value was calculated.and Nash efficiency coefficient calculation,the grid/cell edge length corresponding to the best simulation results under different conditions is determined.The results show that the hydrological response units under different conditions are mostly square grid units with side lengths of 4 mm,5 mm,6 mm and 7 mm,the corresponding Nash efficiency coefficients are all greater than 0.7,and the relative errors are all less than 20%,indicating that the CA-sink The simulation results of the aborted sand model are true and reliable.Through comprehensive calculation,it is concluded that the basic grid/cell unit side length,which is generally suitable for water erosion research under micro-topographic conditions,is 6 mm,the corresponding Nash efficiency coefficient E_f is 0.9204,and the relative errorδis 13.71%,which is the optimal hydrological response.The cell is a square grid cell with a side length of 6mm.(4)Under different tillage measures,slopes and rainfall intensity,the sediment yield gradually reached a stable state with the development of water erosion.The cumulative sediment yield,cumulative runoff and cumulative erosion all showed a linear growth trend with the rainfall duration,and had a high correlation(the correlation coefficient R~2 was mostly above 0.90).Based on the above research,the CA-confluence sediment production model constructed in this paper can be used for the simulation of micro-topographic slope confluence and sediment production.At the same time,the paper also determines a method of micro-topographic space discretization based on M-DEM and grid method,which is successful.The spatial discretization of the micro-topography is realized,and the quadrilateral grid unit with a side length of 6 mm can be used as the optimal hydrological response unit for micro-topographic water erosion model and mechanism research.