Historic sediment yields in a small ungauged catchment controlled by a warping dam, using sediment deposition information and 137Cs dating

In the hilly and gully region of the Loess Plateau, China, warping (check) darns are one of the most important engineering measures for controlling soil and water loss, and reducing downstream sediment yields. Based on detailed field observations, the sediment profile upstream of the third warping dam, located in a small ungauged watershed (Guandigou) of the Wangmaogou catchment, was divided into 31 sedimentary layers, and the sediment thickness and Cs-137 activity of each layer were measured. Peaks in Cs-137 activity in the sediment layers were equated to 1963 (peak in fallout) and 1986 (Chernobyl incident). These dated layers, in combination with historical information on erosive rainstorm events, were used to date the timing of sediment deposition for each layer. Based on the information on sediment thickness for the 31 layers, and field measurements of the surface area of each layer, the specific sediment yields from 1959 to 1987 were estimated. The results indicated that the approach, i.e. the combination of Cs-137 dating and the sediment record deposited upstream of a warping dam, could be used to study soil erosion and deposition in small ungauged watersheds in the Loess Plateau region of China.