Page - 303 - in Book of Full Papers - Symposium Hydro Engineering

development of methods to improve its effectiveness are (a) with the combination of 2 dredging types using available dredgers and additional heavy equipment (amphibious excavators) to take out sediment which located at positions could not be done by dredgers (dry-wet excavation), (b) installation of booster pump and floating pipe as support of the dredgers, (c) modification of dredger ladder, (d) management of spoilbank by re-arrange of hauling and reloading cycles, and accelerate sediment material drying by installing vertical-horizontal drainage. By these methods the dredging of sediment can be implemented more effectively and efficiently to ensure high hydropower production, maintain effective storage capacity and prolong age of reservoir with of course considering environmental aspect around the area. Keywords : dredging, sedimentation, hydropower productivity, Sengguruh Dam 1. INTRODUCTION Sustainability of the function and lifetime of reservoirs in the world is increasingly threatened today due to the high rate of sedimentation. The conditions of the upstream area which are deteriorating due to devastated watershed and improper land management and ignoring the good aspects of soil and water conservation, has led to increased soil erosion and the rate of sedimentation in the reservoir, thus diminishing the volume of the storage reservoir. The sedimentation of reservoirs in Indonesia today is one of the issues to be a priority in efforts to handle by the government era of President Joko Widodo towards water, food and energy securities. Management of reservoir sedimentation have a variety of alternative efforts such as: a) an effort to minimize the rate of sediment entering the reservoir through watershed management (conservation, regulation of land use, etc.), and control of sediment into the reservoir with the technical construction in the river (check dams, gully plug, etc.), b) minimize the deposition of sediments in the reservoir by sluicing sediment and venting turbidity density current, and c) remove sediments from reservoirs through flushing and dredging. Reservoir dredging work is done in many countries like the USA, France, Austria, Switzerland, South Africa, Japan, China, and others. In China, the reservoir dredging routinely performed in many reservoirs such as in the Guanting Reservoir (Yang et al, 2003). In general, the dredging of reservoirs is an expensive effort in order to maintain and restore the reservoir storage capacity, and only considered if the implementation of other alternative measures are not possible or difficult to implement. Dredging the reservoir is limited to removal of sediment that accumulates in front of the intake or for the recovery of the small storage reservoirs (Basson & Rooseboom, 1999). Morris and Fan (1998) give consideration to dredging the reservoir includes four (4) basic components: 1) the sediment that will be dredged (location dredging), 2) dredging equipment, 3) equipment for deliver the dredging materials (eg. pipe for dredging 303