Structural Connectivity of Sediment Affected by Check Dams in Loess Hilly-Gully Region, China

Leichao Bai,Juying Jiao,Nan Wang,Yulan Chen

doi:10.3390/w13192644

Abstract

Check dams play an irreplaceable role in soil and water conservation in the Chinese Loess Plateau region. However, there are few analyses on the connection between check dams and the downstream channel and the impact on structural connectivity and sediment interception efficiency. Based on a field survey, this study classified the connection mode between check dams and the downstream channel, and the actual control area percentage by discharge canal in dam land was used to quantitatively evaluate the degree of the structural connectivity of sediment between the check dam and the downstream channel. The analysis results show that the connection mode can be divided into eleven categories with different structural connectivity. The different connection modes and its combination mode of check dams and downstream channels in dam systems have a large difference, and the structural connectivity of the dam system is less than or equal to that of the sum of single check dams in a watershed. The degree of structural connectivity of a dam system will be greatly reduced if there is a main control check dam with no discharge canal in the lower reaches of the watershed. Compared with a single check dam, the structural connectivity of a dam system is reduced by 0–42.38%, with an average of 11.18%. According to the difference in connection mode and structural connectivity of check dams and dam systems in the four typical small watersheds, the optimization methods for connection mode in series, parallel and hybrid dam systems were proposed. The research results can provide a reference for the impact of a check dam on the sediment connectivity and the sediment interception efficiency in a watershed and can also guide the layout of a dam system and the arrangement of drainage facilities.

Highlights

The Loess Plateau is the area most seriously affected by soil and water loss in the world, and its soil and water loss control has been the focus of attention and research by scholars
According to the survey results, the connection modes between check dams and downstream channels can be classified into eleven categories: (1) Disconnected (Figure 2a); (2) Connected through spillway (Figure 2b); (3) Connected through shaft (Figure 2c) or horizontal pipe (Figure 2d); (4) Connected through shaft and spillway (Figure 2e), or horizontal pipe and spillway (Figure 2f); (5) Connected through shaft, horizontal pipe and spillway (Figure 2g); (6) Connected through dam body damaged gap (Figure 2h); (7) Connected through discharge canal (DC) (Figure 2i); (8) Connected through discharge canal to shaft (DS1 ) (Figure 2j); (9) Connected through discharge canal to spillway (DS2 )
From the perspective of different connection modes, check dams without drainage canals are disconnected, while check dams with discharge canals have different combinations of drainage buildings and spillways (DBS) and dam body damaged gap, resulting in a difference of the sediment of check dams to downstream channels (SCCD)

Summary

Introduction

The Loess Plateau is the area most seriously affected by soil and water loss in the world, and its soil and water loss control has been the focus of attention and research by scholars. The average annual sediment discharge at the Tongguan hydrological station has decreased from 1.6 billion tons before the 1970s to 179 million tons in 2010–2020 [1], which shows that the water and soil control and management of the Loess Plateau have achieved remarkable results. The reduction of the sediment put into the Yellow River does not fully explain that the soil erosion of the Loess Plateau has been effectively controlled because the whole watershed has been treated as a “black box” when the sediment discharge was monitored at the outlet, and it is difficult to explain the degree and process of soil erosion on multiple scales in the watershed [2,3]. Among the many soil and water conservation measures in the Chinese Loess Plateau region, check dams are one of the most effective ways to intercept sediment and control erosion in both the short-term and the long-term [6]. There were 56,422 check dams in the area controlled by Tongguan hydrological station on the Loess Plateau, of which

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Conclusion