SEDIMENTATION STUDY ON GAJAH MUNGKUR RESERVOIR IN WONOGIRI REGENCY, CENTRAL JAVA PROVINCE

• Main Author: ROMULUS HUTAGAOL - NIM: 95015311 , COKI
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/26317
• Institution: Institut Teknologi Bandung

<p align="justify">Gajah Mungkur Reservoir is located in Wonogiri Regency, Central Java Province. This reservoir was built in 1981 which functions as flood control, irrigation and power plant. Changes in land use around the watershed and high agricultural activity using annual crops on steep slopes led to erosion or erosion entering the reservoir area, and the density of the surrounding population became the main cause of high sedimentation in the Gajah Mungkur Reservoir. Sedimentation have also affected the water supply to the powerhouse and downstream irrigation systems around the intake, among the six sub-watersheds in the upper reservoirs, Keduang sub-watershed which contributes most to the reservoirs. The purpose of this study is to examine the characterics of streams and sedimentation pattern that occur in the reservoir by simulating the flow and sedimentation with MIKE 21 software and looking for erosion of existing land in the catchment area of Gajah Mungkur Reservoir. The discharge into the reservoir was calculated from the rainfall data by the NRECA method while for sediment concentration is calculated by using the approach of the correlation between the water discharge of NRECA method calculation with sediment discharge calculation result of MUSLE method. Sedimentation simulation using MIKE 21 Flow Model FM with combination of two modules: Hydrodynamic Module (HD) to simulate flow pattern and Mud Transport Module (MT) to simulate sedimentation that occurs relationship between the water discharge of NRECA method calculation with the sediment discharge method result. Sedimentation simulation using MIKE 21 Flow Model FM with combination of two modules are: Hydrodynamic module (HD) to simulate flow pattern in reservoir. Sediment simulations were performed for 4 (four) conditions for wet year discharge, normal year, dry year and for discharge in 2004. The result of the MUSLE method analysis, the rate of land erosion in 2004 to 2005 is smaller than land erosion year 1993-2004. The simulation results with MIKE 21 software on the condition of wet year discharge, normal year, year of dry sediment the biggest deposition during the year in wet year discharge condition followed by the condition of normal year and dry year, while from the simulation result of year 2004 close to value for simulation of MIKE 21 normal year discharge, so it can be concluded sedimentation of reservoir that occurred in year 2004 according to condition of sedimentation condition of normal year discharge. From the simulation and analysis result, it can be concluded that the factors affecting the deposition and sedimentation process include grain size analysis of bed load and suspended load, sediment concentration, flow pattern and current speed which will affecting base shear stress, critical shear stress for erosion and deposition. <p align="justify">