Study On The Impact Of Terraced Field And Check Dam Construction On Hydrological And Sediment Connectivity In The Watershed

Dynamic assessment of sediment connectivity is an important step towards a comprehensive understanding of sediment transport between source and sink areas,elucidating the processes between erosion and corresponding sediment production,and describing sediment transport from different parts of the landscape at different spatial and temporal scales.In recent years,the change of regional ecological environment caused by large-scale ecological construction measures is considered to be one of the main factors influencing the change of Yellow River water and sediment,but the internal mechanism is still unclear.Therefore,this study takes Gecha small watershed in the loess hilly and gully erosion area as the research object.By reconstructing the topography of the watershed before ecological construction,four ecological construction scenarios are set,namely,scenario S0:no terraces and no check dam,scenario S1:no terraces and no check dam,scenario S2:no terraces and check dam,scenario S3:terraces and check dam.Analyzing the characteristics of terrain change under different ecological construction scenarios,discussing the measurement methods of hydrology and runoff sediments,studying the characteristics of water-sediment connectivity under different ecological construction scenarios and revealing the influence of different ecological measures on water-sediment connectivity in watersheds,the main conclusions are as follows:(1)Based on object-oriented methods,identify and extract the range of terraces and check dams,use contour lines to reconstruct the terrain under different ecological construction scenarios,and analyze the terrain change characteristics under different ecological construction scenarios.Ecological construction has led to an increase in small slopes and a decrease in large slopes area within the watershed.Scenarios S0 and S2 have slopes mainly concentrated at 10-15°,while Scenarios S1 and S3 have slopes mainly concentrated at 5-15°;The combined effect of terraces and check dams changed the slope length,and the average slope length in scenario S3 decreased by 69.41%,47.26%,and 69.51%compared to scenario S0,S1,and S2,respectively;The average slope length LS factor of scenario S3 decreased by 44.72%,26.17%,and 42.86%compared to scenarios S0,S1,and S2,respectively.For the impact of ecological construction on terrain at different resolutions,the maximum slope value decreases with the decrease of resolution,the mean slope length increases with the decrease of resolution,and the mean LS factor increases with the decrease of resolution.(2)The hydrological connectivity index of watershed is calculated based on the flow direction and weight.Under different scenarios,the spatial distribution of runoff length index FL decreases gradually from mountaintop to ditch.The runoff length index in S1,S2 and S3 decreased by 9.14%,5.38%and 76.08%respectively compared with S0.When the resolution is 1m and 2m,the FL indices of scenarios S0,S1 and S2 decrease with the resolution,and vice versa.In different ecological construction scenarios,when the resolution is less than 10m,the runoff length factor under each ecological construction scenario is overestimated by about 1/3.In addition,the analysis of FL cold and hot spots shows that the cold and hot spots correspond to areas with high and low hydrological connectivity.Compared with S0,the cold and hot spots in scenarios S1,S2 and S3 decrease by 14.62%,0.63%and 58.03%respectively.(3)The connectivity index IC was calculated by the potential index of incoming sediment and the potential index of sediment transport,and the relationship between IC and ecological construction was analyzed.The sediment potential index of S1,S2 and S3 decreased by 72.93%,1.12%and 78.45%,respectively,compared with that of S0;the sediment transport potential index of S2 and S3 was less than that of S0 and S1,indicating that the construction of check dams reduced the sediment transport potential in the gully.Ecological construction reduced the connectivity index of runoff and sediment in the watershed,and the IC index in scenario S3 was 22.02%,7.26%and 18.39%lower than that in scenarios S0,S1 and S2,respectively.The effect of slope and gully measures on connectivity was greater than that of single measure.The LE-LC model in scenarios S1 and S3 increased by 39.34%,60.61%and 29.65%,49.45%respectively compared with scenarios S0 and S2,indicating that the ecological construction reduced the erosion area and the sediment connectivity of the basin.