Effects Of Dam Construction On Watershed Underlying Surface Characteristics And Water-Sediment Effects

The middle reaches of the Yellow River,with its unique soil texture,makes the geomorphology and water pattern of the watershed more complex,and the structural characteristics and development stages of the water system geomorphology vary greatly in different areas.The extensive construction of soil and water conservation projects,especially the construction of silt dams,both reduces soil erosion and changes the original geomorphology of the watershed,resulting in a more complex water-sand relationship in the watershed.In this study,the geomorphological and hydrological characteristics of the Kuye River basin,a first-order tributary of the Yellow River,were calculated and their spatial distribution patterns were analyzed.A SWAT model of the study basin is constructed,and based on this model,the spatial distribution and convergence characteristics of runoff,sediment,and runoff erosion power in the Kuye River basin with and without dams from 2010 to 2018 are analyzed.Finally,the main geomorphic water system factors affecting runoff,erosion energy and sand production in the basin are studied,and the influence of geomorphic water system characteristics on the regulation of runoff,erosion energy and sand production in the check dam system is analyzed.The main research results of this paper are as follows:(1)The geomorphological and hydrological characteristics of the Cwino River basin were calculated and its spatial distribution was analyzed.The largest area is occupied by the 0-15° slope of the Kuye River basin,which has a relatively gentle topography,and the landforms are mostly plains and low hills.The watershed is in the juvenile stage of development,with low erosion,and the landscape tends to be a flat plain.From the northwest to the southeast of the basin,the average slope of the basin becomes steeper and more undulating,the density of the river network becomes sparse,the fractal dimension of the water system becomes smaller,and the fractal dimension of the geomorphology becomes larger;the average branch ratio of the basin and the information entropy of the basin geomorphology show the characteristics of large upstream and small downstream,large main stream and small tributaries.(2)SWAT model for the Kuye River basin was constructed and the applicability of the model in this basin was evaluated.Based on the basic data,meteorological data,and hydrological data of the Kuye River basin,the SWAT model of the basin was constructed.The decision coefficient R2 and Nash efficiency coefficient NS were used to quantitatively evaluate the results of water-sediment simulation in the Kuye River basin.The results show that the SWAT model is suitable for water-sediment simulation in the Kuye River basin and can simulate the real hydrological conditions of the basin well.(3)The spatial distribution pattern and convergence process of in the Kuye River basin were clarified.The spatial distribution pattern of runoff,erosion energy and sand production in the Kuye River basin is small in the upstream,large in the downstream,large in the east and small in the west.The convergence pattern of runoff,erosion energy and sand production is that the convergence of runoff shows a pattern of small upstream and large downstream,with each sub-basin converging toward the main ditch along the direction of water flow,the convergence of sand transport shows a characteristic of small upstream and large downstream,and the convergence of erosion energy of runoff shows a characteristic of small upstream and large downstream,with large tributaries and small main streams.The main runoff-producing areas in the basin are mainly distributed in the locations with steeper slopes and sparser river networks,and the main sand-producing areas are concentrated in the locations with steeper slopes and less water systems,which have higher erosion potential.(4)The influence of geomorphic water system characteristics on the regulation of runoff,erosion energy and sand production in the check dam system was elucidated.The runoff reduction rate in the Kuye River basin shows a pattern of large upstream and small downstream,large west and small east,the sand production reduction rate shows a pattern of large upstream and small downstream;the runoff erosion power reduction rate decreases gradually from upstream to downstream.The main factors affecting the watershed water and sand reduction are the average slope of the watershed,the fractal dimension of the landform and the density of the river network.