2009 Volume 22 Issue 3 Pages 188-197
This study estimated soil erosion rates on the hillslopes of forest and cultivated land using Pb-210ex naturally occurring radionuclide in order to comprehend the increase of sedimentation rate in Sengguruh reservoir in upper Brantas river basin, Indonesia. In addition to this, sediment contribution rates from two potential sediment sources (surface erosion on cultivated land, sediments originated from gully and shallow landslide scar) were estimated by analysis of Pb-210ex activities in the deposited sediment collected from upper Brantas river basin, Lesti and Amprong river basin and in the lake sediment of Sengguruh reservoir. The estimates of soil erosion rate for the forest hillslope and the cultivated land were 0.4 t ha-1 y-1and 11.1 t ha-1 y-1, respectively, suggesting that sediment production from the cultivated land was greater than that from the forest hillslope. The sediment contribution rate from the cultivated land over upper Brantas river basin was estimated as approximately 30 %. The results of this study indicated that the surface erosion on the cultivated land was one of the primary sediment sources in upper Brantas river basin. Also, the total sediment production from both the forest hillslope and the cultivated land in upper Brantas river basin was calculated as approximately 800,000 t y-1. This estimation explains almost 30 % of average annual sedimentation rate in Sengguruh reservoir calculated by existing study, and matches well with the contribution ratio of cultivated land in upper Brantas river basin.
