Inverse analysis for transmissivity and the Red river bed's leakage factor for Pleistocene aquifer in Sen Chieu, Hanoi by pumping test under the river water level fluctuation

Abstract

Aquifer parameters and riverbed hydraulic resistance to an aquifer have an important role in the quantitative assessment of groundwater sources, especially the aquifer recharge from river. The analytical determination of aquifer parameters and riverbed hydraulic resistance to the aquifer is rather complicated in case if the water level in the river fluctuates before and during the pumping test time. This is especially true for Pleistocene aquifer along the Red River in Hanoi city, where the riverbed has been changed very much during the recent decades. A trial-error inverse analysis in the parameters' determination by a group pumping test data obtained with a test located close to the Red river bank in Sen Chieu area, Phuc Tho district, Hanoi city was carried out. Before and during the pumping test time the water level in the river changed five times. The results have shown that the Pleistocene aquifer has a relatively high hydraulic conductivity of 55.5 m/day, which provides a good role in the transport of a large volume of water recharged by the river to the abstraction wells located near the river. The aquifer storage coefficient had lightly decreased with the pumping time, which is corresponding to the physical nature of that the aquifer stativity is a function of the aquifer pressure. A special point is worthwhile to be noted that the Red river bed resistance to the Pleistocene is very low, about 0.537 days, which is corresponding to the increase of the distance from the river bank further from the well in 28.4 m to have the river as a specified water level boundary of the aquifer. In contrast, the 1990's investigations had found that the Red river bed resistance to the Pleistocene aquifer to be about 130 days (Tran Minh, 1984), which is corresponding to the increase of the distance from the river bank further from the well in a thousand of meters to have the river as a specified water level boundary for the aquifer.

Improvement of Credal Decision Trees Using Ensemble Frameworks for Groundwater Potential Modeling

“…The average yearly rainfall value in the study area ranges from 4.80 to 7.23 mm (Figure 2h). River density is the inverse proportionality with infiltration [48,[83][84][85]. The study area has a high river density (7.565km/km 2 ) thus less probability of recharge (Figure 2i).…”

Classification of hydrogeological structure along the Red River in the Hanoi area

“…The groundwater in the distant sites from the Red river and the urban regions is much lowered because the wells' location in some wells fields and the inner city generally has been designed and installed irrationally as their close distances, or the impropriety for the local hydrogeological condition. Besides, the wells located along the riverside, such as Nam Du, Luong Yen, Yen Phu, Cao Dinh, Thuong Cat, etc., are still operated and developed usually thanks to the direct supply from the Red river [3,4,6]. Therefore, the Red river has an essential role in recharging the groundwater.…”