Aplikasi Model Tangki untuk Pendugaan Neraca Air dan Laju Sedimentasi menggunakan Metode MUSLE di Sub DAS Lahar Kabupaten Blitar

Abstract

Lahar Sub-Watershed has the elongated shape of the river with a narrow width whereas the main river has 16.86 km length. Under these conditions affect the distribution of water flow to the downstream. Tank Model is one of the hydrologic models that is able to estimate the distribution of water flow either vertically or horizontally. To estimate the sedimentation rate using MUSLE method, which the erosivity parameter in this method is run off data from Tank Model. In order to know distribution of water flow at Lahar Sub-Watershed so used Tank Model. Application of this model is an attempt in a better management of Watershed. The purpose of this researches is to estimate the characteristics of water balance in Lahar Sub-Watershed and to estimate the sedimentation rate using Tank Model application and MUSLE method. This research is located in Lahar Sub-Watershed, Blitar, East Java that has an area of 1418.80 ha. Land cover in Lahar Sub-Watershed consist of 261.58 ha natural forest, 905.46 ha farm field, 54.96 ha agricultural field, 63.76 ha rice field, and 133.04 ha residential area. Soil types in Lahar Sub-Watershed is consist of grey andosol and grey regosol association, grey regosol and brown latosol association, reddish brown mediteran and brown regosol with undulated until mountainous topography and the elevation between 291 ̶ 1093 mdpl. The average temperature in this area between 23.3°C with the highes temperature is 34.7°C and the lowest is 19,2°C, it was a B3 and C3 climate type. Result of the calibration data obtained correlation between water level and water flow, y=6.238TMA1.495 with R2=0.918 and correlation between water flow and sedimentation rate y=43.56Q2.118 with R2=0.853. Total of rainfall in 2009 is 1702 mm/yr and in 2010 is 3304 mm/yr. Total of observation sedimentation rate in 2009 is 12366 ton/yr or 8.7 ton/ha/yr and in 2010 is 20180 ton/yr or 14 ton/ha/yr. Result of Tank Model optimation obtained R=0.65 and water balance, the rainfall is 2590 mm/yr, the evapotranspiration is 797 mm/yr, and the outflow calculation is 1308 mm/yr that distributed through surface 203.5 mm (15.56%), intermediate flow 324.5 mm/yr (24.82%), sub-base flow 520.8 mm/yr (39.83%), and base flow 258.7 mm/yr (19.79%), so the value of storage is 479 mm/yr. Result of the MUSLE method obtained formula R2=0.631. It is shown that MUSLE model could estimate sedimentation rate well. Total of sedimentation rate from June 1st until May 31th 2010 is 26899 ton/yr (19 ton/ha/yr or 1.6 mm/yr). This indicates that sedimentation rate in Lahar Sub-Watershed included to medium category.