Investigating The Soil Erosion History of A Small Catchment Using Sediment in A Dam on The Loess Plateau, China

摘要

In the Loess hilly-gully region, as one of the most important engineering measures for controlling soil and water losses, check dams play an important role for reducing sediments and recording the historical variation of sedimentation in a small catchment. A sediment deposit profile with a vertical length of 11.325m was collected in a dam in Nianyegou small catchment in Suide County in Shaanxi Province. There were 75 flood couplets clearly evident. The peak of 137Cs content was 4.90Bq/kg in 818.5 -903.5cm couplet, which documented sediment deposited in 1963. Based on the daily precipitation from 1957 to 1990 from the local station, reservoir-capacity-curve and the thickness of flood couplets, the total sediment yield of the dam and the specific sediment yield of each flood couplet could be calculated, and the results showed that the total sediment yield of the dam was 76096.3t. The maximum specific sediment yields were 8065.9t, 6664.4t and 5487.lt, which were in 686.5-808.5cm, 903.5-1008.5cm and 818.5-903.5cm couplets. Based on the specific sediment yields, the period from 1957 to 1990 was divided into three stages. The soil erosion was strong in the initial stage of the dam construction from 1957 to 1964 because of less soil and water control measures, then the soil erosion changed smoothly from 1965 to 1983, but strong again from 1984 to 1990 because of the cultivation by the local people. Actually, there was no obvious change of annual precipitation. Totally, the sediment couplets in the study catchment documented that human activities were the most important factor on the soil erosion history in the small catchment.