Perpustakaan Digital ITB

Condition of groundwater in the Bandung Basin, in several studies, is mentioned that there has been a decline in the groundwater level in recent decades. In early 1980s, groundwater level is about 2.5 to 10 meters below the ground surface, but being 10-25 meters below surface in 1985-1990. One of the causes of declining groundwater level is the lack of groundwater due to the changing affixes land use, thereby reducing infiltration capacity. One source of recharge area of Bandung Basin is supplied from Upper Citarum Watershed, as the outlet at Nanjung (779931 meters East, 9231078 meters North). In this paper, Gridded Subsurface Surface Hydrologic Analysis (GSSHA) is used to calculate surface water from the Upper Citarum Watershed to Bandung Basin. It is a computer program based on finite difference. Some of the methods involved in GSSHA are Thiesen Polygons for rainfall distribution, Green-Ampt method for infiltration, Penman-Monteith method for evapo-transpiration, Manning's method for surface flow, and Richard's equation for soil moisture in unsaturated media. Furthermore, Hydrological components on Upper Citarum Watershed show precipitation are 1695 mm/year, actual evapo-transpiration are 816 mm/year (48.2% of precipitation), infiltration are 118 mm/year (7% of precipitation ), discharge are 602 mm/year (35.5% of precipitation), and the volume of surface water are 12.6% of precipitation. Groundwater recharge from the Upper Citarum Watershed are around 86 mm/year (149,038,594 m3 a year or 5% of the precipitation). Comparing with discharge (35.5% of precipitation) it is lower. This shows infiltration on the Upper Citarum Watershed is very small, and one reason is that land use is constantly changing to residential or industrial areas.