Effects of runoff and sediment reduction on engineering accumulation slopes under different soil and water conservation temporary measures

An engineering accumulation slope as one of the main sources of soil erosion, has posed a serve environmental threat to the urban production and construction projects in recent years. Vegetation restoration has been also considered as one of the most efficient measures to control the erosion of the engineering accumulation slopes. However, the newly vegetation still needs a long time for the ideal cover degree. Before that, the soil and water conservation temporary measures (SWCTMs) are required to mitigate the severe soil erosion from engineering accumulation. This study aims to quantify the requirements of SWCTMs in the regulations of soil and water conservation for the production and construction projects. Based on the results of a field investigation which was performed on the SWCTMs, slope gradient of engineering accumulations, and rainfall intensity in the urban production and construction projects, an indoor rainfall simulation was carried out with three rainfall intensities (i.e. 1.45, 2.56, and 3.33 mm/min), two slope gradients (i.e. 20° and 30°), and six SWCTMs (i.e. blocking, cover, blocking + 25% cover (BC25%), blocking + 50% cover (BC50%), blocking + 75% cover (BC75%), and blocking + 100% cover (BC100%)), taking Shenzhen city, Guangdong Province, China, as the study area. A measurement was performed on the runoff and sediment yield on engineering accumulation slopes during runoff duration. The results showed that: 1) The runoff reduction of temporal blocking and cover decreased significantly, with the increase of rainfall intensity, indicating a similar performance. Specifically, the runoff reduction efficiencies were 22.46%-38.22% and −20.59%-38.34%, respectively, under the rainfall intensities of 1.45-3.33 mm/min, comparing with the bare slope. 2) The sediment reduction efficiencies under temporal blocking were 62.89%, 15.41%, and 80.83%, respectively, under the rainfall intensity of 1.45, 2.56, and 3.33 mm/min, when the slope gradient was 20°. The reason was that the eroded sediment from the upslope was deposited behind the blocking, rather than completely delivered to the outlet. Nevertheless, the sediment reduction of blocking decreased significantly, as the slope gradient increased during operation. 3) The reduction efficiencies of surface flow velocity and sediment were 29.68%-55.76%, and 70.06%-97.35%, respectively, compared with the bare slope. It infers that the temporal cover performed better than the temporal blocking on surface flow velocity and sediment reductions. Since the dust screen protected soil surface was directly depended on the raindrop splash, a large numbers of tiny sediment mounds were generated on the dust screen, thereby to enlarge the roughness of slope surface for the sediment deposit with relatively short transport distances from the original location. The average runoff velocity and erosion rate of engineering accumulation decreased, with the increase of the cover coverage, where the erosion rate decreased by 32.98%-97.79% under the temporal blocking + 25%-100% cover measures, compared with the bare condition. The threshold of temporal cover coverage is 50%~75% when the effect of runoff and sediment reduction on slope reaches the best under the temporal blocking + cover measures. Consequently, it can be strongly suggested to construct the SWCTMs of temporal blocking and cover with over 50% coverage near the production and construction projects. The findings can provide a strong reference for the decision making on the soil and water conservation in the production and construction projects.