Study On Ningxia Hydrological Regionalization And The Saturation-infiltration Excess Dominant Runoff Generation Mechanism

The small and medium-sized basins in arid and semi-arid regions in China have problems at present,such as sparse distribution of hydrological stations,discontinuous observation data and short time series,which bring certain difficulties to hydrological forecasting and limit understanding of hydrological regulars.Hydrological regionalization is a commonly used quantitative evaluation method to solve hydrological simulations in scarce or unavailable areas.It divides hydrological geographic regions by analyzing the hydrological characteristics of the watershed,topographic and geomorphic conditions,soil vegetation,and land use types,which could reflect the spatial distribution of the hydrological characteristics of the watershed.Ensure the characteristic factors of the same district have the smallest differences and the largest similarities,the largest differences and the smallest similarities between different districts.Grasping the types of watershed hydrological regionalization and watershed runoff generation mechanisms fully can reveal the similarities and differences of hydrological characteristics in different regions better,which is important for the planning and adjustment of local representative hydrological stations.Therefore,it is of great significance and practical value to carry out hydrological regionalization research in arid or semi-arid small-middle watersheds.This paper takes the Ningxia Hui Autonomous Region as the research object,which has more complicated climate and topography and geomorphology.Based on the hydrological similarity the hydrological regionalization of Ningxia is carried out.At the same time,the topographic index distribution curve and topographic curve number methods determine the saturation-infiltration excess dominant runoff generation mechanism of each regionalization respectively and conduct typical flood simulations to verify the accuracy of the runoff generation mechanism,in order to provide necessary references for the hydrological simulation of scarce or no data areas and the future development and utilization of water resources in various regions of Ningxia.The main results are as follows:(1)According to the actual watershed characteristics and hydrometeorological data in Ningxia,11 watershed characteristic factors were selected as hydrological similarity indicators.Based on the natural sub-catchment method,the geographic information system and hierarchical clustering method,fast clustering method,and fast-tracking method based on principal component analysis are adopted which Combine Ningxia's original digital elevation mode image,soil texture,land use type,and hydrometeorological original data.The clustering method integrated 493 natural sub-watersheds in Ningxia Hui Autonomous Region into 4 first-level regions,11 second-level regions and 32 third-level regions,and obtained the layout map of Ningxia third-level hydrological area finally.(2)Based on the Ningxia hydrological regionalization,the topographic index distribution curve method and topographic curve number method were used to determine the dominant runoff generation mechanism of each three-level hydrological regionalization in Ningxia.The analysis result of the topographic index distribution curve method determines the boundary between the saturation excess runoff region and the infiltration excess runoff region in Ningxia;the results of topographic curve number method show that the dominant runoff generation mechanism in the central and northern part of Ningxia is mainly infiltration excess runoff,the southern region is dominated by saturation excess runoff.(3)Taking two typical watersheds of Sanguankou and Rujigou typical watershed in Ningxia as examples,the Xin'anjiang model and the Xin'anjiang model with increased infiltration runoff generation were used to verify the accuracy of the runoff generation mechanism of the basin.From the results of flood simulations only part of the simulated rainfall-runoff process line in the Rujigou watershed is not ideal,and the certainty coefficients of the simulation results of the remaining sessions are all greater than 0.7,which is basically in line with the actual flood process in the basin.(4)Based on the Ningxia hydrological regionalization and the dominant runoff generation mechanism of each sub-basin,a comprehensive analysis of the actual topography and geomorphology,land use,vegetation type,hydrological and climatic conditions and other typical natural geographic characteristics of each basin in Ningxia were determined.What's more,the first and second levels of Ningxia were determined.The results show that from north to south,Ningxia is divided into extremely arid,arid,semi-arid,and semi-humid regions,including 11 sub-regions.Naming and qualitative descriptions are given according to the characteristics of the basins of the sub-regions finally.