Research On Hydrological Connectivity At Different Scales In Yanhe River Catchment

The sediment loaded into the Yellow River had been dramatically decreased since 21 century.The vegetation restoration was regarded as the main driving force for the reduction due to increasing resistance for the runoff and sediment transportation.However,how sediment and runoff was blocked by vegetation is not well understood.In this research,we selected the Yanhe river catchment,located in hilly area of Loess Plateau,as the research area.We try to use the hydrological connectivity index concept in plot scale and catmint scales,and analyze the relationship between the index and runoff/sediment to explain how vegetation controls runoff or sediment.Twelve field rainfall-simulation experiments were conducted in plot scale,and the volume of runoff and sediment collected in each plot was record.Five kinds of hydrological connectivity indices(M_Flowlength,Flowlength11,Flowlength01,Flowlengthr and Flowlengths)was calculated by the topographic layer and vegetation layer of each plot.In the catchment scale,the hydrologic data of Ganguyi hydrologic station(1990,1992,1995,2000,2005,2010)was collected.The IC(Index of connectivity)of each year was calculated,using the DEM of Yanhe river catchment and Cs,namely the Vegetation structural index,which was acquired by remote sensing inversion using Landsat5 TM data.At plot scale,the results showed that :1)the total sediment was more related to vegetation cover than total runoff;2)M_Flowlength had a negative liner relationship with vegetation cover,and the relationship was greater with the increasing vegetation cover,however the other four hydrological connectivity indices(Flowlength11,Flowlength01,Flowlengthr and Flowlengths)had a positive liner relationship with vegetation cover;3)Total runoff yielding and sediment yielding has a significant power function relationship with the Flowlengh11 and Flowlength12,respectively.In catchment scale,the result shows that: 1)three kinds of IC index in the river channel was greater than that in hillslope;2)IC index,from 1998 to 2010,had been decreased in most area;3)the mean of IC index in the research area decreased with the revegetation;4)the IC_c index had a negative liner relationship with annul runoff volume(R2=0.83)and the IC_f index had a negative liner relationship with annul sediment discharge(R2=0.78).The hydrological connectivity indices are useful tools to explain the variation of runoff and sediment yield in the arid and semi-arid areas.Combing the terrain data and vegetation data,they could intuitively indicate the hydrological response to vegetation change.The research provides approach to detecting the variation of runoff and sediments with the vegetation restoration as well as it could provide some advice to the catchment management.