Pustaka Ilmiah Universitas Padjadjaran

Abstrak

An Assessment Of The Erosion Intensity Of Quaternary Volcanic Rocks In The Upper Stream Of Citarum River Southern Part Of Bandung Basin

The erodibility of the area in the drainage basin of Citarum river tributaries in southern part of Bandung basin influences the intensive deposition in Citarum river bed. It presumably generates the acute flooding in the southern part of Bandung. To estimate the amount of the eroded materials (A), the Universal Soil Lass Equation (USLE) formula A= RKLSCP (EI-Swaify et al., 1982) is commonly used. It involves the erosivity index of the ground surface (R), soil erodibility (K), topography (L, length and S, slope), the vegetation covers (C) and land management (P). The formula was derived from the generalization of predominant geological elements. Prior to the application in Citarum upper stream basin, the validity of the formula has been evaluated. The upper stream of Citarum river is located on the formation of volcanic products of Quaternary age (Alrear, et al., 1992; Silitonga, 2003). The evaluation consists of 1,184 grid boxes each of about 25 ha covering the entire investigated area. The results show that the erosion intensity strongly and positively correlates (r = 0.93) with the silt grain size of the weathered volcanic rocks. The ratio between very fine fraction of clay (C), fine silty clay (M., mud) and fine to coarse sands (S) determines the erodibility index. Those fractions relate closely with the geological processes consisting of weathering, alteration, and tectonics. A further calculation yields the corrected USLE formula for the erosion intensity of volcanic terrain (Ev) with a constant of [E.(S+C)-1], the formula thus becomes EV = K`[M.(S+C)-1]. RKLSCP, where K` is C-M-S ratio constant of weathered volcanic rocks product in the investigated area The high plasticity clay and high plasticity silt of volcanic rocks weathered product attain the erosion coefficient of 0.51 and 0.77 respectively. Based on the results of the investigation, it is recommended to delineate the physical characteristic of volcanic rocks weathered product, then the land management controlling the erosion. The remote sensing method might be beneficial to identify those types of rocks and their weathered product with a manipulation process of various channels.