By Dadang Nurdin – (Thesis M.Si Sriwijaya University, 2013). Supervised by Prof. Charlotte de Fraiture Ph.D., M.Sc. (UNESCO-IHE), Prof. Ir. Robiyanto H. Susanto, M.Agr.Sc., Ph.D (Sriwijaya University), Laszlo Hyde, PhD, MSc (UNESCO-IHE).
Upper Cikapundung Sub watershed is the upstream part of Citarum watershed which is the largest watershed in West Java Province. Citarum river has 237 km length with the area of 181.027 ha. The water availability from the watershed has been continually supplying the water consumption for several sectors such as industries, agriculture or irrigation, household, and drinking water at eight agencies in West Java and Jakarta.
The vegetation coverage in the upstream part of the watershed has significantly contributed the river water availability all years. Especially the forest that generates almost two third of the stream flow through the surface runoff, base flow and lateral flow. Since the last two decades, the area of forest coverage along the upstream of the Citarum watershed has been decreasing. In 1994 the forests area were 42,517 ha while in 1997 36,815 ha, in 2001 they decreased to 20,604 ha. During the period of 1983 to 2002 the forests coverage in Cikapundung Watershed decreased about 4,869 Ha (-13%).
Along with these deforestations and land use changes, flood, drought, and water scarcity were frequently occurred in the watershed especially at the downstream. Flood fallen about 35,713 ha in 2005 and 139,677 ha in 2006, drought in paddy field about 14,031 ha in 2005 and 172,186 ha in 2006. On the other hand, and about 669 springs have been threatened by scarcity due to the river discharge declining.
Evaluating the existing forest coverage (2011) upper Cikapundung sub watershed as well as the scenarios of forest coverage changes and their relationship to river discharge is necessary to be carried out to prevent further adverse effect of deforestation. The core of this study is investigating the river discharge generated by the forest coverage within the watershed. With the designed scenarios, the research analyzes the river discharge resulted in by the forest coverage changes/deforestation in 2014, 2020 and 2025. Furthermore, the result of the study will evaluate the river discharge in relation to flood and drought. Flood is indicated by the increasing of surface runoff/direct flow while drought is revealed by the depleted base flow/ground water.
The resulted monthly river discharge in 42% of forest area upper Cikapundung sub watershed indicates 1.36 m3/s, the forest coverage change scenarios result in the average monthly discharge of 1.36 m3/s in base line scenario, 1.54 m3/s in scenario 2014, 1.54 m3/s in scenario 2020 and 1.55 m3/s in scenario 2025. The scenario 2025 with no forest area generated higher discharge compared to three scenarios; base line scenario with 41% forest, scenario 2014 with 35% forest, and scenario 2020 with 15% forest area in the watershed. Nevertheless, the forest coverage generate the highest lateral flow among those scenarios.
Keywords : Forest Coverage changes, Discharge, SWAT Model.