Slope-gully systems on the Loess Plateau, China cause severe soil erosion. Planting vegetation and the construction of check dams are the most effective measures utilized for the mitigation of soil erosion in this region. Among them, due to the sedimentation behind the dam, the erosion basis was lifted, resulting in a decrease of the runoff path length (Runoff Path Length Decrease; RPLD) of the slope-gully system. However, the synergistic effects of vegetation and check dams to reduce the runoff and sediment yields of the slope-gully system has not been addressed often. In the present study, 10 physical models of slope-gully systems, including grass coverage on a slope (0% and 33%) and the RPLD (0, 1, 2, 3, and 4 m), were constructed to evaluate the synergistic effects of these measures. The results indicated that grass coverage reduced runoff and sediment yields by 42.63% and 25.66%, respectively. The combination of grass coverage and RPLD could control water erosion of slope-gully systems more effectively than the independent measures. With increasing RPLD, the runoff and sediment yield reduced significantly. Grass coverage and RPLD exhibited a synergistic effect on the erosion caused by water, which increased with RPLD as follows: 4 m (19.83%) > 3 m (18.68%) > 2 m (17.39%) > 1 m (16.70%). These results demonstrate that grass coverage on slopes and the RPLD synergistically influence hydrological processes. The synergistic effects not only should be incorporated to develop soil and water conservation regulations, but also should be considered in soil erosion models. 

Grass coverage and the runoff path length decreased by sedimentation have synergistic effects on runoff and sediment yields in a slope-gully system, revealed by rainfall simulation experiments

Research on flood events is one of the most important parts to study runoff and sediment transport in the typical watershed on the Loess Plateau. Based on 101 floods in Period I (PD-I, 1970 to 1990) and Period II (PD-II, 2006 to 2018), and combined with rainfall data, the study indicated the evolution of runoff and sediment transport characteristics during flood events in the Chabagou watershed, and reveal its influencing factors in both periods. Results showed: (1) Sediment yield (SY) increased linearly with runoff amount (RA), and the increasing rate of SY in PD-II was around 20% of PD-I, the relationship between peak flow (PF) and sediment concentration (SC) was the power function, and the SC in PD-II was lower than that in PD-I under the same PF. (2) SY was more sensitive to P (precipitation) of the flood event than rainfall intensity (RI), and the sensitivity of RA and SY to P in PD-II was greater than that in PD-I. The sediment delivery modulus (SDM) with rainfall erosivity (RE) was also linear, and the increasing rate of SDM in PD-II was 27% of PD-I. (3) The better improvement of the underlying surface not only raised the threshold of RA and corresponded with peak SC, but also shortened the duration of high sediment concentration and lowered the sediment transportation capacity by contrasting the flood processes.

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Evolution of the Relationship between Runoff and Sediment Transport during Flood Event in the Chabagou Watershed of the Loess Plateau

• Higher erosion intensity and smaller size of check dam resulted in greater variation in soil particles. • Soil OC and N in check dams decreased with the distance from the dam body to the gully head. • Silt content was more important than clay content in influencing the distribution of OC and N in check dam soils. Check dams are effective soil and water conservation structures worldwide that play an important role in preserving sediments containing carbon (C) and nitrogen (N). However, in terms of the depositional characteristics of C and N in check dams, research on the relative effects of erosion intensity and depositional area is limited, hindering our understanding of the fates of eroded C and N. This study compared the horizontal and vertical distributions of soil particles, organic C (OC), and total N (TN) in check dams of various sizes and erosion intensities in the Loess Plateau. The results showed greater variations in the horizontal and vertical patterns of soil particles of smaller check dams and highly serious erosion (erosion modulus = 15040 t km - 2 a -1 ) than those that of larger check dams and strong erosion regions (erosion modulus = 5151 t km - 2 a -1 ). Soil OC and TN contents decreased from the dam body to the gully head, especially in the highly serious erosion region. Notably, the effect of smaller check dam on the vertical distributions of soil OC and TN was more intense than that of the larger check dam in the strong erosion region. In contrast, a minor effect of check dam size was observed in the highly serious erosion region. Moreover, a closer relationship between the distribution of OC and TN with silt content rather than with clay content in check dams was observed, and this relationship was enhanced by an increase in erosion intensity. Overall, the synergistic effects of erosion intensity and check dam size affected the spatial patterns of OC and TN in sediments on the Loess Plateau. Careful consideration of these two factors is beneficial for accurately assessing the C and N fates in depositional areas. 

Erosion intensity and check dam size affect the horizontal and vertical distribution of soil particles, carbon and nitrogen: Evidence from China’s Loess Plateau

The check dam is the most important engineering measure in place for controlling water and preventing soil loss in the gully on the Loess Plateau. This study assesses Jiuyuangou, a typical governance watershed of the Loess Plateau, and studies the influence that the check dam system has on the dynamics of sub-storm floods over different return periods by coupling the one-dimensional hydrodynamic MIKE 11 model with the distributed hydrological MIKE SHE model. This research demonstrates the following: The check dam system significantly reduces a flood’s peak flow and total volume in the basin and also increases the flood duration. The former effects are greater than the latter effect. The flood peak’s rate of reduction, the flood volume’s rate of reduction and the flood duration’s rate of increase all increase linearly as the number of check dams increase. Of all dam systems, the check dam has the best linear response to a flood peak’s rate of reduction. The check dam system reduces the flow rate of flood runoff in the basin. After the dam is built, the average flow rate in the basin decreases by 54%. The runoff velocity of the flood is reduced by different degrees over different return periods and the average peak value decreases compared with a scenario lacking any kind of dam. The check dams have a greater impact on the runoff velocity over a shorter return period, with the velocity being 58.56% slower. Finally, the check dam system significantly reduces the intensity of erosion in the middle and lower reaches of the watershed, and it changes the distribution of the intensity compared to the original channel runoff. These findings are expected to provide a scientific basis for guiding the construction and high-quality development of check dams on the Loess Plateau. In addition, check dam construction in basins can trap water, sediment and nutrients, and it can also contribute to ecosystem diversity and maintaining ecosystem imbalances around the world.

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Regulation of Flood Dynamics by a Check Dam System in a Typical Ecological Construction Watershed on the Loess Plateau, China

Abstract Erosion and sedimentation in streams, lakes, reservoirs, and watersheds are a global issue. Runoff and flood waves erode soil and streambank material, destroying agricultural land. Erosion and sedimentation in water bodies induce soil loss in the watershed and diminish channel flow depth and conveyance. Agricultural runoff can pollute aquatic ecosystems by carrying sediment. As per IPCC 2019 report, in tropical and subtropical regions, the impacts of soil erosion can be observed from the high rates of soil loss, in some cases exceeding 100 t/ha/yr. Therefore, it becomes necessary to address the problem of erosion and sedimentation with serious concern. This paper focuses on highlighting the research advancements in the field of erosion and sedimentation phenomenon, estimation of erosion and sedimentation rate in watersheds, streams and reservoirs and resulting impact assessment from reach scale to watershed scale in last five decades and assessing further research scope in this regard. A bibliometric analysis considering 1000 research articles database extracted from the Web of science has been conducted in the Biblioshiny platform using the R-programming tool. The Bibliometric analysis shows an annual scientific production growth of 2.27% in the field of erosion and sedimentation. Most of the articles have been published in the USA, followed by China, UK, and Belgium. This is the first such bibliometric analysis of erosion and sedimentation together considering one thousand articles associated with it. The study can help in observing the publication trend and identifying the recent emerging topics for research in the field of erosion and sedimentation. 

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A Bibliometric Analysis and Review of Trends in Erosion and Sedimentation studies

Check dams are applied worldwide as an effective approach for soil conservation. Its effect on hydrology, however, has not been fully understood. As a critical step towards revealing the lumped effect of check dams at the regional scale, this study explored the modified flood hydrology induced by check dams in a representative highly erodible catchment in the Loess Plateau, China. A coupled hydrological and hydraulic modeling approach was applied to simulate the flooding process in different stages of deposition and topographic changes in a check dam reservoir. The results suggest a paradigm shift of the dam effect on flood attributes, which transits from a total interception in the early stage of the dam to peak reduction and flood detention, rather than a complete loss of flood control functions, when it approaches the maximum capacity of sedimentation. Under the same level of deposition, the reduction of a minor flood by a check dam was higher than that of a major flood. The topographic changes contributed to the reduction of flood peak appreciably by reducing the flow velocity and retarding the flood propagation. Noticeably, this reduction was augmented with the advancement of siltation and topographic changes, indicating the persistence of the hydrologic effects of check dams in the long run. As a result of these hydrological changes, the reduction in the flood flow velocity induced by check dams suggests substantial reductions in sediment transport and channel erosion during floods. In addition, a dam system containing multiple, cascading check dams exhibits much more significant effect in modifying both hydrologic and hydraulic properties of flood than individual dams. The current research provides a mechanistic understanding of the effects of check dams on catchment hydrology under heavy rainstorm conditions in small catchments.

Peng Li

Papers

Influence of check dams on flood hydrology across varying stages of their lifespan in a highly erodible Catchment, Loess Plateau of China

Effects of a check dam system on the runoff generation and concentration processes of a catchment on the Loess Plateau