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
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.
3. METHODOLOGY Location of the study
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.