HR: 0800h
AN: H11A-1251    [Abstracts]
TI: Large Scale Groundwater Flow Model for Ho Chi Minh City and its Catchment Area, Southern Vietnam
AU: * Sigrist, M
EM: micha@geosys.t.u-tokyo.ac.jp
AF: Department of Urban Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan
AU: Tokunaga, T
EM: tokunaga@k.u-tokyo.ac.jp
AF: Institute of Environmental Studies, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan
AU: Takizawa, S
EM: takizawa@env.t.u-tokyo.ac.jp
AF: Department of Urban Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan
AB: Ho Chi Minh City (HCMC) has become a fast growing city in recent decades and is still growing at a high pace. The water demand for more than 7 million people has increased tremendously, too. Beside surface water, groundwater is used in big amounts to satisfy the need of water. By now, more than 200,000 wells have been developed with very little control. To investigate the sustainability of the water abstraction, a model had been built for the HCMC area and its surrounding. On the catchment scale (around 24,000km2); however, many questions have remained unsolved. In this study, we first gathered and complied geological and hydrogeological information as well as data on groundwater quality to get an idea on regional groundwater flow pattern and problems related to the temporal change of the groundwater situation. Two problems have been depicted by this study. One is the construction of a water reservoir upstream of the Saigon River. This construction has probably changed the water table of the unconfined aquifer, and hence, has significantly changed the properties of soils in some areas. The other problem is the distribution of salty groundwater. Despite the distance of more than 40km from the seashore, groundwater from some wells in and around HCMC shows high concentrations of chloride. Several wells started to produce non-potable water. The chloride concentrations show a complicated and patchy distribution below HCMC, suggesting the possibility of the remnant saltwater at the time of sediment deposition. On the other hand, seawater invades along the streams far beyond HCMC during the dry season and this might be one of the possible sources of salty groundwater by vertical infiltration. A large-scale geological model was constructed and transformed into a hydrogeological model to better understand and quantify the groundwater flow system and the origin of saltwater. Based on the constructed model and numerical calculation, we discuss the influence of reservoir construction on the groundwater situation at the upstream Saigon River, and possible factors for the existence of salty groundwater underneath HCMC.
DE: 1804 Catchment
DE: 1829 Groundwater hydrology
DE: 1847 Modeling
DE: 1857 Reservoirs (surface)
SC: Hydrology [H]
MN: Fall Meeting 2005