Study On The Regulation Of Water And Sediment In Typical Watershed Of The Loess Plateau By Silt-Filled Check Dams

Check dams are widely used as an effective soil and water conservation engineering measure in the Loess Plateau region.As of 2019,nearly 70%of the check dams in the Loess Plateau region have been filled with silt.The construction of check dams will significantly change the landscape pattern of gullies and have a profound impact on the water and sediment processes in the basin.The study of the regulation of water and sediment in the basin after the silt dams are fully filled is of great significance for the high-quality development of check dams in the new era.This study takes the Wangmaogou Basin,the first sub area of the Loess Hilly and Gully Region,as the research object.Using geographic information technology and numerical simulation methods,it elucidates the regulatory role of the filled check dam system on the hydrological and runoff processes of the basin and the erosion and sediment production of the basin.The main conclusions obtained are as follows:(1)After the check dam is fully filled,it significantly weakens the lateral sediment connectivity of the channel.Under the condition of silting up the dam system,the slope length factor LS,river power index SPI,and roughness index SRI of the watershed were reduced by 7.62%,9.00%,and 3.03%compared to the non dammed watershed,respectively.The construction of check dams has changed the distribution of sediment connectivity index IC in the spatial distribution of the basin.The average sediment connectivity index of the basin under the original check dam system,the current check dam system,and the silted check dam system is2.11,-2.43,and-2.64,respectively.(2)The filled check dam system under different spatial layouts can still have a long-term impact on the hydrological process of the watershed.The simulation results show that compared to the original ditch without dam construction,the flood peak can still be reduced by 61.23%～71.09%under different layouts of the filled check dam system;After the siltation of the check dam,the flattening effect of the flood is enhanced,and the flood lag efficiency increases by 151.21%to 537.19%under different layouts of the filled check dam system.Only small dams,when fully silted,work together with key check dams and middle check dams to cause the flood peak to lag for 11 minutes;The construction of silt filled check dams has significantly changed the dynamic process of runoff in the main channel.The silt filled check dam system can reduce the average flow velocity along the channel by 45.83%～66.67%under different spatial layouts,which will greatly reduce the erosion power of runoff in the main channel.There is an inverse relationship between the sediment connectivity index IC and the efficiency of flood lag time.(3)Analyzed the regulatory effects of fully check dam systems and current check dam systems on the erosion environment of the watershed.The drainage basin is under the condition of current check dam system,and the area of 3.24km~2 with soil erosion intensity exceeding 1000t/(km~2·a)accounts for 59.89%of the total erosion area of the drainage basin;The check dam system has significantly changed the spatial distribution of watershed erosion after full siltation.The area of 3.13km~2 with soil erosion intensity exceeding 1000t/(km~2·a)accounts for 57.86%of the total erosion area of the watershed;However,the erosion intensity of the local area behind the check dam has increased,and the soil erosion intensity above 2000t/(km~2·a)has increased by 0.92%.There is a correlation between soil erosion intensity and sediment connectivity index in high value areas(R2=0.54)under the condition of fully silted check dam systems in the watershed.