Page - 275 - in Book of Full Papers - Symposium Hydro Engineering

COMMISSION INTERNATIONALE DES GRANDS BARRAGES ------- VINGT-SIXIÈME CONGRÈS DES GRANDS BARRAGES AUTRICHE, JUILLET 2018 ------- EROSION AND SEDIMENTATION OF UPSTREAM ASAHAN AND ITS COUNTERMEASURES FOR THE SUSTAINABILITY OF SIRUAR DAM NORTH SUMATERA Muhammad L. CHAKIM1) Sugik E. SARTONO2) 1)Head of Development Area and Asset Optimization Division, JASA TIRTA I PUBLIC CORPORATION 2)Chief of Technical Planning Unit, JASA TIRTA I PUBLIC CORPORATION INDONESIA 1. INTRODUCTION Asahan River becomes the main source of water flow for Siruar, Sigura gura and Tangga Dam. The Siruar dam serves to regulate the stability of the water coming out of Lake Toba to the Asahan River and to supply water to the power station constantly to the Asahan hydroelectric power plant (Asahan I, Siguragura and Tangga power plant). This type of dam is a mass concrete with a height of 39 meters. Since the changes of land use in the most Asahan catchment area, erosion and sedimentation became problem for the Siruar Dam especially for the operation of Asahan I hydroelectric power plant. Jasa Tirta I as state own enterprise which has authority to manage water resources in Toba Asahan River Basin (given by Government with Presidential Decree No. 2/2014) conducted comprehensive study to indentify the rate and sources of sedimentation and the countermeasures as well in 2016 - 2017. 2. DATA COLLECTING METHOD The primary data taken by topographic survey, bathymetry and also sediment sampling along 14.5 km of upstream Asahan and 5 km of its tributaries which are Bolon and Mandosi River, and water sampling for quality test. In order to get deeper analysis, secondary data also collected through government institutions such as statistical agency, planning and development agency, geophysics and meteorology agency, ministry of public works and ministry of forestry. 275