Study On The Regulating Effect Of Check Dams On The Topography And Processes Of Runoff And Sediment In Basin

As one of the most important soil and water conservation measures,check dams play an important role in the ecological management process of the Loess Plateau.In-depth research on the impact of check dams on watershed topography and water sediment processes is of great significance for the construction and development of check dams in the Loess Plateau region.In this study,the Xiliugou Basin,a primary tributary of the Yellow River in Inner Mongolia,was selected as the study area.Field remote sensing monitoring,digital terrain analysis,and numerical simulation methods were used to analyze the differences in watershed topography before and after the construction of the check dams.By comparing the differences in channel terrain in typical small watersheds,the impact of check dams on the development of channel erosion was explored.The study revealed the regulatory effect of newly constructed check dam systems on runoff and erosion dynamics during minor flood events and clarified the impact of dam systems on sediment transport processes in the watershed.The main research findings are summarized below:(1)Based on the digital elevation model,the impact of check dam construction on the topographic features of the watershed was analyzed.After the construction of check dam system,the topography of Xiliugou watershed is more gentle compared with that before the construction,the change of slope and surface relief of the watershed is more obvious,the distribution of gentle slope in the watershed is increased,the area is increased by 4.20%,the area of surface relief in the range of 0-10 m is increased by 0.16%,and the surface roughness and cutting depth are reduced in different degrees.By comparing the topographic features of typical small watershed gullies with high hydrological similarity,we found that the gully ratio and gully evolution index in the dammed watershed were smaller than those in the undammed watershed,and the width-todepth ratio of gully cross-section in the dammed watershed was larger than that in the undammed watershed,indicating that the erosion of gullies in the undammed watershed was more intense than that in the dammed watershed,and the construction of check dams could slow down the process of gully erosion.(2)The regulating effect of the check dam system on the runoff process of the watershed is clarified.Compared with the undammed case,the check dam system with parallel distribution of branch channels can play a significant role in reducing flood peak and flood volume.Under the three typical precipitation conditions,the dam system can reduce the flood flow at the outlet of the basin by 21.81%～30.69%and the total flood volume by 33.39%～33.95%respectively;and the average flood flow along the main ditch can be reduced by 37.07%～39.41%.(3)The influence of the check dam system on the erosion dynamics of the watershed channel is revealed.The construction of check dam system can significantly change the distribution of erosion dynamics of gully runoff in the watershed.Under three typical precipitation conditions,the dam system can reduce the average maximum flow velocity along the main channel by 13.84%～16.72%,the average maximum runoff shear force by 18.52%～21.44%,and the average maximum runoff power by 29.54%～33.10%;the maximum peak flow velocity along the main channel is reduced by 6.86%～13.28%;and the maximum runoff power is reduced by 13.28%.13.28%;12.22%～17.96%reduction of maximum runoff shear and 17.68%～29.30%reduction of maximum runoff power.Moreover,the regulation effect of the check dam system on erosion dynamics is stronger in the middle reaches of the basin,but gradually weakens in the downstream.(4)The effect of check dams on sand production and transport in the watershed was analyzed.Under single dam conditions,the time and intensity of hydraulic scour erosion in the gully downstream of the dam site are reduced.The construction of the check dam system leads to different degrees of reduction in runoff erosion power and sand transport modulus along the watershed.The average reduction of runoff erosion power in the basin is 52.52%～55.77%,and the average reduction of sand transport modulus is 51.60%～54.89%,which is regulated by the dam system.The control ability of the branch gully dam system is stronger in the upper and middle reaches of the basin,and the effect of the dam system on sand transport modulus in the lower reaches of the basin gradually decreases as the mileage increases.(5)Quantifying and elucidating the role of check dam systems in regulating the sand transport process in the watershed.The dam system causes the peak reduction rate of sand transport rate at the basin outlet to reach 40.55%～53.93%,and the total amount of sand transport is reduced by 55.34%～56.92%,respectively.The time to stabilization of sand transport in the basin under the sub-flood condition is advanced with increasing flood volume,and the time difference between the sand transport stabilization in the un-dammed and dammed conditions gradually decreases,and the sand transport stabilization time in the dammed condition is earlier than that in the undammed condition.The reduction rates of sediment transport modulus(RMs),peak sediment transport rate(RStr),and sediment reduction rate(RSf)vary similarly along the watercourse with the ratio of controlled area by the interval dam system,and in scenarios with high rainfall intensity,there is a certain linear correlation between the cumulative dam control area ratio and the three sand reduction indicators,which can be used to predict and study the sand reduction effect of the dam system.