Using check dam deposits to investigate recent changes in sediment yield in the Loess Plateau, China

Abstract

Check dams are one of the most important engineering measures for controlling soil and water loss from watersheds and can play a key role in reducing sediment loads in rivers. In addition, the associated sediment deposits can in some circumstances provide a valuable source of information on changing rates of sediment production from the upstream watershed through time. A sediment profile with a depth of 11.325m was examined within the deposits associated with a check dam at the outlet of the Nianyangou catchment, in the northern Loess Plateau, China, with a drainage area of 0.181km2. The profile contained evidence of a total of 75 clearly identifiable flood event couplets, which corresponded to storm events occurring during the period 1960–1990. The variability of the grain size composition (clay content) of the sediment and its 137Cs activity and organic matter (SOM) content down the profile was used to identify individual flood event couplets and the record of event rainfall (particularly extreme storm events) was used to establish a chronology for the individual flood event couplets. Based on the reservoir capacity curve and information on couplet thickness and sediment bulk density, the sediment yield associated with each flood couplet has been calculated. Using these data, annual sediment yields were estimated to range between zero in 1965 to 9750t in 1984. The period from 1960 to 1990 was divided into three distinct phases based on evidence for changing rates of sediment production within the watershed above the check dam provided by a double mass plot of cumulative sediment yield versus cumulative precipitation. These phases represent the periods: 1960 to 1964, 1965 to 1983 and 1984 to 1990, which were characterized by mean annual specific sediment yields of 26,220tkm−2year−1, 5590tkm−2year−1 and 19,130tkm−2year−1, respectively. This study is seen as demonstrating the potential for using the sediment deposits associated with check dams to obtain retrospective assessments of changes in sediment yield in repose to land use change and the implementation of soil conservation and sediment control measures.