Spatial Variabilityand Temporal Change of Water Discharge and Sediment Flux in the Lower Jinsha Tributary: Impact of Environmental Changes

Analysis of water discharge and sediment flux data as measured in the Longchuanjiang Basin in the Lower Jinsha tributary over the past few decades has been undertaken. The results of this study indicate that the lower reaches of the Longchuanjiang River produce relatively less runoff but higher sediment loads than the upper reaches. This can be attributed to the differences in climate, the dissected terrain and the sparse vegetation cover of the downstream river. Temporal series analysis suggests a significant increase in sediment flux, notably in the lower reaches of the river. The available data suggest the increasing sediment flux is a result of climate variations and a series of human activities such as land-use changes, mainly through deforestation and agricultural expansion. Other activities, such as road construction, urban expansion, building-material excavation and largescale terrace construction and afforestation, have also contributed to the significant increase in the sediment flux. However, the Longchuanjiang Basin as a whole has a low sediment yield (<1000 t km 2 a ), despite severe soil erosion in the catchment. This is a result of sediment deposition in the numerous reservoirs, constructed since the 1950s. Runoff in the dry season has also significantly declined due to increasing water consumption. These profound changes in the hydrological regime will have significant implications for effective soil erosion and water management. Further studies in the region are necessary to address the impact of these human activities on hydro-geomorphological processes and, particularly, water discharge and sediment flux. Copyright # 2005 John Wiley & Sons, Ltd. key words: water discharge; sediment flux; reservoir; irrigation; climate changes; Upper Yangtze