Study On The Construction Of Comprehensive Discriminant Indexes For The Change Of Runoff Mechanism In The Middle Yellow River

Since the 1970 s,the water volume of the Yellow River has decreased drastically,and the ecological environment and runoff situation have changed greatly.Especially since the 21 st century,a large number of soil and water conservation measures have been carried out,and the policy of “returning fields to forests and closing mountains and greening” has been implemented.The vegetation coverage in the middle reaches of the Yellow River has changed significantly,and the runoff into the Yellow River has been significantly reduced.The human activities in the basin have caused changes in the underlying surface of the basin,which in turn changed the flow pattern in the basin,resulting in a shortage of inner diameter flow in the basin,which aggravated the contradiction between water resources and social economic development.Therefore,the analysis of the change law of the runoff mechanism in the middle reaches of the Yellow River and the exploration of the indicators of the changes in the influence of the runoff mechanism in the middle reaches of the Yellow River are the contents of the current study on the changes of water and sediment in the Yellow River Basin.Under the support of the “13th Five-Year” National Science and Technology Support Program “Water and Sediment Variation Mechanism and Trend Prediction in the Yellow River Basin”(2016YFC040240203),this paper investigates the underlying surface change process in the middle reaches of the Yellow River.Based on the data acquisition situation,this paper selects the basin above the Jinghe Jingle and the Jialu River Basin as the research area with the obvious changes in the underlying surface and the relatively complete data,and analyzes the underlying surface indicators that affect the changes of the flow-producing mechanism.The main contents of the study are as follows:(1)Analysis of changes in typical river basin production flow mechanismThe typical watershed chooses the representative Jingle station control basin and the Jialu River basin.Based on the analysis of rainfall and runoff characteristics,the flow pattern of the flood occurred was analyzed.The results show that the flood generation pattern of the flood control station is changed in the control basin of the Jingle station,and the flood generation ratio of the super-seepage runoff is reduced.The runoff mode is the flood of the mixed runoff and the full runoff.The ratio of the main runoff pattern of the floods in the Jialu River Basin is super-osmotic flow,but the proportion of floods in the runoff mode is mixed with the runoff and the full runoff.(2)Analysis of variation characteristics of underlying surface indicators in typical watershedsTaking the Jingle station control basin as a typical watershed,collecting satellite remote sensing images of floods from different years,interpreting NDVI,vegetation coverage,leaf area index,soil index and pre-soil moisture content,and discovering NDVI,vegetation coverage and The leaf area index decreased first and then increased,and the soil index increased first and then decreased.The soil water content increased in the early stage of the flood.(3)Construction of comprehensive discriminant index system for change of production flow mechanism and threshold value testConstructing a comprehensive discriminative index system for the change of flowproducing mechanism,using the analytic hierarchy process to estimate the weight of the index,the soil moisture content is the largest in the early stage,and the soil index is the smallest.Then the threshold model theory is used to estimate the change of the flowproducing mechanism.The threshold values of the thresholds for super-osmotic flow,mixed production,and full-flow are 0.4182 and 0.5187,respectively.The distribution maps of each index are synthesized by weights and divided by thresholds to generate distribution patterns of watershed production patterns,and the flow generation mechanism of typical floods is analyzed,which is consistent with the results of the theory of runoff theory.For the floods in the Jialu River Basin,the comprehensive discriminating index and threshold value of the flow-producing mechanism change were used to determine the runoff pattern.The results were basically consistent with the results of the runoff theory.