The impact of improved landuse cover on the range of modelled sediment yield from two sub-catchments of the Mae Chaem, Thailand

Abstract

A sediment source, transport, and deposition model known as SedNet has been applied to two sub-catchments of the Mae Chaem River in Thailand, the Mae Suk (95 km 2) and the Mae Kong Kha (91 km 2). The applied models were analysed to determine the dominant sources and sinks of suspended sediment in these catchments, and to examine the impact of an improved landuse coverage on the range of modelled sediment loads. SedNet model scenarios were run using landuse grids from 1995 to 2003. The 1995 landuse classification was derived from satellite imagery and contained a relatively undifferentiated landuse classification (lumping all forest types into one category); the other in 2003 was derived from a mix of satellite imagery, ground truthing, and mapping, and better differentiated between landuse types (dividing forest types into evergreen, deciduous, and pine plantations). Results indicate significant differences in predicted sediment export in 2003 compared to 1995. It is difficult to say whether these changes were due to actual changes in landuse between 1995 and 2003, or due to the improved landuse classification in 2003. The source areas of suspended sediment also changed significantly between 1995 and 2003, and these changes in source area can clearly be linked to the improved mapping of landuse in 2003. The improved landuse classification in 2003 also led to significant reductions in the range of possible suspended sediment exports from both catchments. Despite these improvements in landuse classification, significant uncertainty in predicted suspended sediment yield still exists for both sub-catchments. Further improvements in identifying the total volume and source areas of suspended sediment will best be achieved through an improved landuse coverage which identifies the type of crop being grown.