Yuequn Dong

Impacts of Gravel Mulch on Sediment Yield Process under Simulated Rainfall Conditions

Abstract: In agricultural practice of arid and semiarid regions, gravel mulch on soil surface is used to increase rainwater infiltration, reduces surface runoff and soil erosion, and protects natural environment while increase agricultural productivity. Gravel mulch has great impacts on soil surface conditions to affect rainwater infiltration and surface runoff processes, as well as sediment yield process. A series of laboratory experiments were conducted to investigate the impacts of gravel mulch of different sizes on soil infiltration-runoff processes under different rainfall intensities and slope gradients with a laboratory rain simulator and portable runoff flumes. The experiments involved 3 rainfall intensities (60, 90, 120 mm/h), 2 slope gradients (0°and 10°), and 4 surface mulches (gravel size of 0.5, 2.5, and 5.0 cm, and control). Runoff samples were collected at 5-minute intervals after runoff generation for runoff and sediment determination. The sediment in runoff samples were weighed with laboratory electronic balance after ovendried in drying oven at 105 centigrade. The results indicated that gravel mulch affected significantly the sediment yield process, in terms of sediment content, detachment rate and cumulative sediment. Gravel size was the most influencing factor. Gravel mulch of smaller size produced less sediment yield. Rainfall intensity and slope gradient were secondary influencing factors on sediment yield as compared with gravel size. The results help to understand the mechanism of gravel mulch for reducing sediment yield and preventing soil erosion so as to benefit dry-land farming practice and protect the environments.

Design and installation of runoff-sediment cascade monitoring stations at parallel Qiaozi-East and Qiaozi-West watersheds

Abstract: Monitoring of soil loss at small watershed has significant effect on understanding of soil loss trend, prediction of soil loss damage and selection of directional management measures. Monitoring with control station has been commonly used at parallel small watershed and cascade small watershed, but there is no cascade monitoring at parallel small watershed or no parallel monitoring at cascade small watershed. In this study, the three-class cascade monitoring stations were established at Qiaozi-East and Qiaozi-West watershed on loess plateau, with control areas of 1.0, 0.1, 0.01 km2 grades. The stream network and sub-watersheds were generated from the digital elevation model by GIS, and the location of monitoring stations was made with surveying. According the measured maximum flow rate of Qiaozi-East and Qiaozi-West watershed, the maximum flow rates of second and third cascade monitoring stations were determined. Considering of terrian conditions and the weir-flume property and application, rectangle thin-wall weir and triangle thin-wall weir were selected for second and third cascade monitoring stations respectively. After design and installation, the three-class cascade monitoring stations were completed combined with previous first-level monitoring stations, to measure water level, flow rate and sediment content automatically. The establishment of runoff-sediment cascade monitoring stations will support the study on effect of soil and water control measures, conduct the soil and water control practice at small watersheds, and provide data validation for soil erosion model. It has significant theoretical and practical meaning.