Investigation of groundwater recharge mechanism for sustainable urban water system planning and management in Hanoi city

Abstract

Seasonal variation of water levels and water quality of groundwaters and ponds was investigated to illustrate the recharge mechanism and seasonal effects of groundwater in Hanoi suburbs. Water level monitoring data showed that the upper aquifer had a fluctuating water level (variation: 2.0 m) corresponding to heavy rains, representing a substantial impact by infiltration of rainwater from the surface and perhaps pond water. In the area with less permeable surface, there was small response to rainy events, suggesting that the ground water levels were governed by a regional scale groundwater flow. The stable isotope ratios in pond waters had a clear seasonal change, in which isotopes were enriched throughout the dry season. In groundwater, isotope signatures indicated that the dominant sources had evaporation process. In studied areas, the isotope ratios in groundwaters and pore waters in the shallow soil (<25 m depth) were clearly heavier than that in the deep soil. Isotope results suggested that groundwaters close to the Red River are largely recharged by the river itself. In areas far from the river, surface waters having evaporation process (e.g., ponds and paddy fields) and the rainwater directly infiltrating from the surface mainly recharges the upper aquifer. The lower aquifer in inland locations would be recharged by lateral inflow, either from the Red River or surrounding mountains. The results revealed the recharge mechanism for groundwater budget which could contribute for the planning and sustainable development of urban water system in Hanoi City.