Impact of changes in biophysical factors on streamflow and suspended sediment in the Chi river basin [Thailand]
1991
Nipon Tangtham (Kasetsart Univ., Bangkok (Thailand). Faculty of Forestry. Dept. of Conservation) | Supat Paksachan
Impact of changes in biophysical factors including deforestation on streamflow and water quality have long been controversial in Thailand. This investigation aimed to find out of what extent deforestation or forest conversion in the northeastern region could affect such phenomena. Biophysical factors in terms of drainage area, average basin slope, relief ratio, forest cover area, annual rainfall and proportion of watershed classes in 11 subwatersheds of Chi River Basin were employed to determine their effects on annual flow and suspended sediment. Historical recorded data on runoff discharge and suspended sediment observed by the RID and NEA during 1962 to 1984 were compiled corresponding to land use changes mapped as forest map by RFD. Watershed class distribution prepared by ONEB was also linked to those information and statistically analysed by step-wise regression. Results indicated that of all parameters employed for detecting the mentioned impacts, forest conversion showed insignificant influence on changing annual runoff. The relational equations, however, indicated increasing annual runoff discharge at about 37 MCM/yr for every 10 percent of decreasing forest cover in the basin. This increasing runoff caused to add more 5,671 tons of annual suspended sediment yield. Results also imply that upstream reservoirs can help increase both summer and wet flow of this basin.
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