Abstract

Many studies of global sediment yields have ignored SE Asia, probably because the land area is only 2% of the global total. However, it has been suggested that up to 70% of the sediment entering the oceans comes from SE Asia and Oceania. To test such estimates one would normally calculate total yields from many measured rivers but there are very few relevant data for the region. A possible solution is to use algorithms which estimate sediment yields based on factors such as elevation, local relief, area, climate and runoff. To assess the value of different algorithms we first compared their predictions to known yields using a global data set tabulating a range of basin variables. All were poor predictors, but using a subset of the global data, based on rivers from SE Asia, there is an improved correlation between observed and calculated yields. However, the data set is small and the rivers may not be representative of the entire region. Bearing in mind these reservations, different algorithms were used to estimate sediment yields from SE Asia. Calculations can be performed quickly with a GIS because most parameters can be extracted from published maps and digital elevation models. We used the HYDRO1K database of hydrologically consistent drainage information based on the USGS GTOPO30 DEM. ERMapper and MapInfo were used to extract the essential parameters. Sediment yields were calculated for 650 basins and for the main island groups. The total estimated sediment discharge from SE Asia is between 1500 and 5000 million t/yr, between two thirds and twice that of the Himalayas. Based on these estimates, all Cenozoic sediment in SE Asian basins could be locally derived, but this raises the question of the tectonic processes acting to cause the elevation required to maintain sediment supply for many millions of years.