EFFECT OF LAND USE CHANGE ON LAM PHRA PLOENG RESERVOIR SEDIMENTATION IN NORTHEASTERN THAILAND

摘要

In order to classify the effect of land use change on reservoir sedimentation, the method for calibrating the siltation and sediment deposition in the reservoir to build up rates is needed. Effect of Land Use Change on Lam Phra Ploeng dam was predicted by comparision of 1970 original data and reservoir survey data from 1983 to 1991 with the catchment forest cover area ratios in each year (until to 2000). This shows the capacity was reduced by sedimentation stored in the reservoir. The annual sediment volume in the reservoir for the original from the year 1970 to 1983 was totally 2.230 mcm and the calculated erosion rate is about 2.72mm·km~(-2)·yr~(-1) due to the forest area has been reduced 76.87 % . The annual sediment volume in the reservoir by the first reservoir survey from the year 1983 to 1991 has a total amount of 1.625 mcm and the calculation of erosion rate is about 1.98mm·km~(-2)·yr~(-1) due to the forest area has been reduced 1.30 % . And since 1991 to 2000, the forest area was maintained at the same rate. This maintaining of the forest area can be used to assess the decreasing of the sedimentation rate and the annual sediment inflow was totally reduced to 0.365,53 mcm and the calculated erosion rate is about 0.445 mm·km~(-2)·yr~(-1). Most of eroded sediment was trapped by the meandering riverbed in both upstream and downstream of Lam Phra Ploeng Catchment, which reduced the water storage capacity of the reservoir. Distribution of the sediment deposition in the reservoir was estimated by using the Empirical Area Reduction method. In the period of 21 years the reservoir sedimentation has reduced 28% of reservoir's utility. This result suggests that the lifespan of the reservoir was predicted as 32 years since its completion.