Exploitation of Groundwater for Irrigation in Nganjuk District, East Java, Indonesia

Nganjuk District experienced fast growth in agricultural sector during 1991-1998. Cropping intensity was increasing from 2.31 crops/year in 1991 become to 2.93 crops/year in 1998. The increasing caused increasing water consumption, especially from groundwater with irrigation wells. Objective of this research is to analysis groundwater exploitation for irrigation by using GIS. Data was collected from a government office and other studies (i.e. irrigation wells, earth shape map and hydrogeology). All hardcopy of map was transformed to digital spatial data with digitizing process. Field data were input as spatial data. Land-use/land-cover map was developed from LANDSAT data using ERDAS 8.4. Overlay analysis was used to get actual utilization of irrigation well in dry season. The number of irrigation wells until year 2006 was more than 15,741 wells with discharge varied at 4-60 l/s. Radius influent of well in the research areas are varied at 118-348 m (Prastowo 2007 and Liyantono 2001) and these values are using as assumption for developed irrigation well density (IWD) criteria. IWD varied from 0-2.995 well/ha. Very high exploitation (IWD >1 well/ha) has conducted in 29 villages and high exploitation (IWD >0.5-1 well/ha) has conducted in 50 villages. Both areas should be integrated management of wells and pumps to reduce exploitation. Potential areas in 47 villages can be developed irrigation wells around 82-292 wells. Based on land-use/land-cover 2004 classification (Landsat ETM+, August 19, 2004), irrigated areas are distributed in central of Nganjuk with area around 43, 094.61 ha. Irrigated area with crop and IWD >0.05 well/ha has 82.68% of area. Irrigated with crop and IWD ≤0.05 well/ha has 17.32% of area. This state showed that irrigation wells were used in dry season. The further research will continue to estimate irrigation water requirement and groundwater withdraw to supplement the surface water irrigation in this area.