Model of sedimentation control of reservoir due to land erosion and landslide in Bili-Bili Dam South Sulawesi

Abstract

The main objective of this research is to design the model of sedimentation control of reservoir that has sustainability oriented to improve miner and farmer incomes without dismissing environmental interests. In particular, the general objective is achieved through several phases with their aims as follows; (1) determine the level of soil erosion in the sub watershed Jeneberang, as well as the impact of land management and information to determine the direction of land management in the watershed, (2) determine the impact of caldera landslide at Jeneberang sub watershed to sedimentation rates in the Bili-Bili dam, and (3) formulate the model of sedimentation control of reservoir due to land erosion and landslide. Research is conducted in Bili-Bili dam, South Sulawesi, from Juli 2009 until Pebruari 2010. First, research has conducted to determine land erosion using MWAGNPS as a model of cell-based rainfall events with the main components were topographic maps, land use and soil type. This model able to determine the source of erosion and the erosion that occurs. Second, research was conducted based on field survey of caldera landslide at upstream and sedimentation rate in the Bili-Bili dam. And the last, design the dynamical model of sedimentation control of reservoir using Stella 9.0.2 program analysis. The Result Showed that Jeneberang sub watershed dominated by steep areas topography is 10.080 ha (26.22%) and the closure of forested land is 12.250 ha (31.87%). Simulation MWAGNPS model showed when watershed Jeneberang has 31.66 mm of rain events with 30-minute rainfall intensity (EI30) can caused erosion 44.81 tons/ha and the sedimentation rate is 2,22 tons/ha. The source of erosion in the sub watershed Jeneberang from farm/moor caused erosion is 29,552.14 tons/ha/year and a total of 4,562,625.84 tons of sediment. Caldera landslide in 2004 caused sediment flow from upstream of Jeneberang watershed was 45,027,954 m3. Sabo dam as a sediment control along the Jeneberang upstream has function effectively. It was seen from the volume flow of sediment that can be controlled up to the year 2008 is 1,915,671 m3. Sedimentation rate before the event of landslide caldera, sediment deposited in Bili-Bili dam cumulatively is 8.376 million m3 (April 2001). Five years after the landslide sediment volume has reached 75.055 million m3 in 2009. Based on Trap efficiency showed that efficiency of Bili-Bili dam was decrease from 90.81% in 1997 to 73.34% in 2005, and then increased in 2007 (92.57%) and in 2008 decrease become 89.79%. Dynamical model simulation of reservoir sedimentation control showed sedimentation in dead storage capacity increase to completed in year of 2022. Moderate and optimistic scenario more effective in decreasing sedimentation in reservoir and increasing community income especially for the miner. Finally, moderate scenario can use of sedimentation control of reservoir in Bili-Bili dam, South Sulawesi.