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16) THERMAL ANALYSES FOR GROUNDWATER FLOW ASESMENT IN JAKARTA GROUNDWATER BASIN Rachmat Fajar Lubis, Research Student for Graduate School of Science and Technology, Chiba University Japan,. Yasuo Sakura, Department of Earth Science, Chiba University Japan, Robert Delinom, Research Centre for Geotechnology, Indonesia Institute of Sciences, Indonesia. 1. INTRODUCTION measurements (Fig.1) were carried out in 51 observation wells We generally know that the distribution of subsurface (40 – 200 m deep). temperature is affected by not only thermal conduction but also Generally the normal geothermal gradient of the subsurface advection owing to groundwater flow. In this study, analyses of thermal regime is affected by groundwater flow and changes in groundwater flow suggested by borehole temperature surface temperature. A theoritical analysis of temperature field measurement in Jakarta Groundwater Basin are presented.. distortion by topographically driven groundwater flow was The main objective of this work were to identify the show that groundwater temperature increases with the depth component and direction of water flow inferred from the under the influences of both heat conduction and advection. At thermal properties. the same altitude, subsurface temperature in the recharge area is lower when groundwater flow is included than under no 2. GEOLOGICALAND HYDROGEOLOGIC flow conditions. In the discharge area temperature is higher SETTING OF THE STUDY AREA with groundwater flow than under no flow conditions. To Jakarta which is the capital of the Republic of Indonesia, it is estimate groundwater flow system in the subsurface thermal o o o located between 106 33’ - 107 ’E Longitude and 5 48’ 30” - field in Jakarta Groundwater Basin, the temperature o 6 10’ 30” ’S Latitude with an area around 652 km2 (Fig.1).. distribution in cross section were constructed (Fig.1) Greater Jakarta has a humid tropical climate; annual rainfall is high between 1500 - 2500 mm due to influence of monsoon. 4. CONCLUSION Greater Jakarta is located in the groundwater basin known as Based on a 2-D vertical distribution of subsurface temperature the Jakarta groundwater basin. The base of the aquifer system along a cross section, showed a good relationship with is formed by impermeable Miocene sediments, which also geological condition of the area and reflects a good sign of crop out at the southern boundary of the basin. The basin fill, groundwater flow condition. which consists of marine pliocene and quaternary sand and This tendency will be used to indicate recharge and discharge delta sediments, is up to 300 m thick. Individual sand horizons area, compiled by other hydrogeological data such as are typically 1 - 5 m thick and comprise only 20% of the total hydraulic heads, hydrochemistry and stable isotope tracers. fill deposits. Silts and clays separate these horizons. Fine sand and silt is very frequent component of these aquifers. N Figure 1. 3. METHODOLOGY Location of the study 0 2 Subsurface thermal measurements were generally made in Km site, Monitoring well observation wells, which are assumed to be in thermal and Isotherm Cross equilibrium with the surounding aquifer. Temperature section.
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