Sediment yield variability in the Upper Yangtze, China

The development and increasing availability of global environmental data sets provides an opportunity to examine systematically the relationship between sediment yields and controlling catchment variables, employing Geographical Information Systems. Few studies have attempted to harness such information to analyse variations in sediment yields within large catchments. Sediment yields from 62 long-term gauging stations within the catchment of the Upper Yangtze River, China, have been analysed in relation to variables describing hydrology, climate, topography and population density. This analysis is particularly significant as the 106 km2 catchment area of the Upper Yangtze will shortly be impacted by the world's largest dam scheme (the Three Gorges Project). There is a high degree of scatter in sediment yields because of natural diversity in the catchment, but this scatter is reduced when the data are grouped according to tributary location, catchment size and maximum elevation. Sediment yields generally increase with precipitation, runoff and population density and decrease with elevation, but there is evidence of scale dependency and of variation between geographic regions within the basin. The small number of variables used are capable of explaining the majority of variance in the comparatively ‘natural’ western tributaries but are less adequate in areas affected by large-scale agricultural activity. In future, improvements in the resolution and accessibility of environmental data sets will allow more detailed analysis of regional variability in sediment yield.