Abstract. Keywords: Cikeruh, Jatinangor, Bandung-Soreang Groundwater Basin, supply, demand, aquifer, groundwater strategy conservation, technopark.

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1 The Strategy of Groundwater Conservation in Cikeruh Jatinangor Indonesia Based on the Supply-Demand Assessment Analysis Greisella Kencana Kartika', M. Sapari Dwi Hadian, 2 1 Geological Engineering, University of Padjadjaran, Jatinangor, Sumedang 2 Lab. Geological Evironmental and Hydrogeology, University of Padjadjaran, Jatinangor, Sumedang Abstract Groundwater has an important role for maintaining the balance and the availability of water for daily life. As the increase of the human population in Indonesia, the utilization of groundwater is also increase. The amount of groundwater is not completed the need of human daily life. The area of research, Jatinangor, is a complex area. The supply-demand assessment obtained the supply results from the rainfall (precipitation) that seeps into the ground minus the vapor (evapotranspiration), and the demand results from the people s use of groundwater. The average rainfall calculation was computed using the Thiessen Polygon method, which connect lines in such way that shapes a polygon in the rain station in the area of research. Meanwhile, the evapotranspiration was computed using the Penman method, which uses temperature, humidity, time length of sun radiation, and the velocity of wind. The results from the supply-demand assessment prove that flood prone areas are caused by an overconsumption of groundwater, a poor lithological condition, as well as a poor aquifer condition. To overcome this problem, the strategy of groundwater conservation in Bandung and the surrounding areas is made for the effort of minimize the negative impacts of the excessive of groundwater extraction and to conserve the groundwater resource. Keywords: Cikeruh, Jatinangor, Bandung-Soreang Groundwater Basin, supply, demand, aquifer, groundwater strategy conservation, technopark. INTRODUCTION Groundwater is one of the water resources beside the water from rivers and rain, but with the increasing number of people in the world, especially in Indonesia, the number of water requirement and consumption are also increase, while the surface water quality is decreasing as the impact of industrial pollution, so that the groundwater use is increasing. The water supply is decreasing, especially when dry season, it is not balance to the human needs that always increase, and make a negative impact such as a conflict potential of the groundwater use that also increase. The fall of groundwater level, as one of the negative impact, can determine the groundwater subsidence that usually happens in Bandung. Jatinangor is a complex area, because this area is an area of education, industry, protected forest, dense human settlement, and the establishment of increasing number of apartments, give a negative impact to groundwater conditions in this area. Therefore, to ensure the number of groundwater resources interferences in Bandung- Soreang groundwater basin, that needs the comprehensive information about the status of the groundwater reservation and supply, and

2 also the number of groundwater use in Bandung- Soreang groundwater basin. The strategy of groundwater conservation in Bandung-Soreang groundwater basin has been calculated with the consideration by the condition of groundwater supply and requirement by each district through the spatial analysis. The result is the vulnerability of groundwater in Bandung-Soreang groundwater basin that will continue to be calculated as the right groundwater conservation strategy. DATA AND METHODS In this study, spatial analysis has been used, such as demography, the rate of rainfall data, climate data, land use data, and groundwater use data. The information of groundwater use is done by the groundwater potential identification (reservation) in Bandung-Soreang Groundwater Basin and the number of groundwater catchment. While the determination of the groundwater demand is based on the number of groundwater retrieval for many requirements (industry, commercial, and domestic) that has been registered in local government instance. The rainfall rate measurement of each area is done by the Polygon Thiessen methods. This methods is done by connecting a site that has a rainfall rate data to the other site with some line that form some polygon. The site that has a rainfall rate data will be calculated to get an average of rainfall rate data. with: : average of rainfall rate : rainfall rate at site 1, 2,..., n : large area of site 1, 2,... n The climate data measurement is done by Penman methods because of this methods is more accurate than other methods. This methods is a combination of mass transfer methods and balance of the energy methods for calculating the value of evaporation, then it will be multiply by some empiric constant to get an evapotranspiration. with: E n : depth of evaporation (mm/day) based on netto radiation E : evaporation ß : constant empiric (temperature) RESULTS Precipitation is a rate of a rainfall that falls from the atmosphere to surface or deep marine in different type, such as the rainfall in tropical area, and the rain and snow fall in the area with moderate climate. Because of Indonesia is a tropical area, so the precipitation means only for the rate of rainfall. Polygon Thiessen methods is done by connecting a site that has a rainfall rate data to the other site with some line that form some

3 polygon. The site that has a rainfall rate data will be calculated to get an average of rainfall rate data. Sites that used to get an average data of rainfall rate are in Cibeureum, Cicalengka, Cipaku Paseh, Kayu Ambon, Cisondari, and Cipanas Pangalengan. For the climate measurement, it is done by the Penman methods that resulting an evapotranspiration value in the research area, which is mm/year. The mount of evapotranspiration value is used to calculate the mount of recharge potential, which is the average of rainfall rate per year minus evapotranspiration value, and the result is mm/year. The coefficient of runoff is a number from the comparison between water runoff and rate of rainfall. For example, the number of runoff coefficient in the park is 0.2, it means 20% from mount of rainfall became a water runoff, and the rest will infiltrated. The higher coefficient value of runoff means the higher of water runoffs value and infiltrated water is low. Otherwise, the lower coefficient value of runoff means the lower of water runoffs value and infiltrated water is high. The measurement of water balance in research area is done by calculating the water availability, then compared to water use (industry, commercial, and domestic). DISCUSSION Based of water balance measurement, it can be conclude that Bandung-Soreang groundwater basin is in the save zone, because it still have more water availability than water retrieval by the people. But there are some districts are in the unsafe zone, such as North Cimahi, Dayeuhkolot, Ngamprah, and Cikeruh. The biggest water use is in North Cimahi by the amount m 3 /year and Cikeruh by the amount m 3 /year. No Table 1. Land Use in Cikeruh Land Use Large Area (km2) Percent (%) 1 Fresh water Grove Building Garden Human Settlement Grass Irrigated field Rain fed Rocky soil Farm lands Total Source: The calculation based on RBI Maps Based on the calculation of Qrunoff in Cikeruh shows that the water use in agriculture sector is approximately ,99 m 3 /year, while the total of water use is m 3 /year, although the ability to absorb the water in this area can make it to ,59 m 3 /year. To optimize the water infiltration, there are some ways that can be used, such as groundwater recharge area and make a recharge well.

4 Figure 1. Land Use Maps in Cikeruh Groundwater Recharge Area Freeze & Cherry (1979) (in Salama et al., 1993) state that to determine the recharge area and water release, some points are have to get an attention, which are: 1. The flow of surface water and groundwater 2. Climate, especially the rate of rainfall 3. Topography of recharge area, that usually high topography with relative high slope because of the groundwater level is relatively deep as the impact of drainage, otherwise the lower groundwater level become shallow and the groundwater release become dominant.

5 Because the groundwater is flowing from the area with high groundwater level to the low groundwater level, so that the subsidence of groundwater level will make an impact of the change of recharge area, which is the larger of groundwater subsidence, the larger recharge will happen. Based on the criteria above, the area that can be suitable to become the recharge area in Cikeruh, Jatinangor is in Mount. Manglayang (in the mountainside). In other hand, technopark should be built in Jatinangor, because the building reconstruction is increasing and this area needs some recharge areas to prevent the subsidence. The installation of recharge well makes some effect to the aquifer that the groundwater potential was shrink. The recharge well will make an impact for the reduced of water runoff to the surface. Rain water that falls to the roof before is not directly flowing to the ditch or to the yard, but first flowing through zinc to the well recharge. The water of rain will never spread to the yard or ditch so it will reduce the water runoff to the surface. Recharge Well The basic concept of recharge well is a drainage system that the rainfall in some roof or waterproof area will be catch in some water recharge. Recharge well is also an empty well that has an enough space to contain the water before it seep to the ground, so that the ground filling become optimal (Sunjoto, 1998), and it seen in the critical and damage area. Figure 2. Water cycle and recharge well use (source: In North Cimahi, the area that can be suitable for recharge well installation is in Cimindi. Cimindi has a flat topography characteristic, and consist of tuff that has a capacity to passed the water about 2 m 2 /day that means the area is hard to release the water, but with the elevation about 714 m so that the depth of groundwater level is about 9.1 m. With the installation of recharge well in Cimindi, it makes an impact to the water supply and seep to the groundwater. Figure 2. The installation of Vertical Recharge Well (source:

6 CONCLUSION The study of groundwater conservation in Bandung-Soreang groundwater basin is based on the water balance methods with the comparison of supply-demand assessment that resulting the condition in Bandung-Soreang groundwater basin is in the safe zone, but for some districts such as North Cimahi and Cikeruh, there are classified as unsafe zone. This is the impact of the water use (such as the industrial activity) and the hydrogeological condition (aquifer condition). Therefore, in those areas need to do the conservation of groundwater and the recharge well installation. The most important thing to prevent the groundwater condition to gets worse is that to stop the construction of the high building and industry that use the groundwater excessively that will make an impact such as the subsidence and damage the groundwater condition, and it needs the water management Purnama, Setyawan., dkk Analisis Neraca Air di DAS Kupang dan Sengkarang. Yogyakarta: Universitas Gadjah Mada. Salahudin, Arief., dkk Pemantauan Kuantitas dan Kualitas Air Tanah di Cekungan Air Tanah Bandung-Soreang, Provinsi Jawa Barat. Bandung: Badan Geologi Pusat Sumber Daya Air Tanah dan Geologi Lingkungan. Sosrodarsono, Suyono Hidrologi Pengairan. Jakarta: PT. Dainippon Gitakarya Printing. Suryatmojo, H Konsep Dasar Hidrologi Hutan. Yogyakarta: Jurusan Konservasi Sumber Daya Hutan, Fakultas Kehutanan UGM. Sudarto, Lanjar Analisis Jumlah Cadangan Air Tanah Kota Soreang Jawa Barat. Yogyakarta: UPN Veteran Yogyakarta. Sunjoto Sistem Drainase Air Hujan yang Berwawasan Lingkungan. Majalah Konstruksi No Agustus Triatmodjo, Bambang Hidrologi Terapan. Yogyakarta: Beta Offset. REFERENCES Asdak, Chay Hidrologi dan Pengelolaan Daerah Aliran Sungai. Yogyakarta: Gadjah Mada University Press. Br., Sri Harto Analisis Hidrologi. Jakarta: PT Gramedia Pustaka Utama. Fildebrandt, et al., Recharge Enhancement Using Single or Dual Well Systems for Improved Groundwater Management in the Bandung Basin, Indonesia. Adelaide: CSIRO Land and Water. Freeze, R.A. and J.A. Cherry Groundwater. Prenticec-Hall, Inc. Englewood Cliffs, NJ 604 p.