Assessment of groundwater dynamics in Quaternary aquifers of the Phrae Basin, northern Thailand, using isotope techniques

The Quaternary sequences in the Phrae Basin, northern Thailand, can be classified into three aquifers based on depth. The groundwater dynamics and recharge of these aquifers were assessed using isotope techniques, and flow directions were acquired using groundwater level of selected wells. Groundwater flows from northwest and west to the centre of the basin on the western side of the Yom River, while flow is from northeast and east to centre on the eastern side. The groundwater mean residence time (MRT) within the shallow aquifer is 1-30 years using H-3 time series, estimated by the exponential piston-flow model (EPM), which is one option of the selected lumped-parameter model (TracerLPM). Groundwater in the shallow aquifer mainly originated from local rainfall and surface water. Recharge rates were estimated using MRT and chloride mass balance, with results of 305 mm year(-1) and 301-309 mm year(-1), respectively. The groundwater age range (1,087-22,920 years BP) was determined by C-14 dating and corrected using C-14-DIC models. The horizontal velocities of the deep aquifer were between 3 and 5 m year(-1), and vertical velocity was similar to 0.0235 m year(-1) based on C-14 ages and depth. Groundwater in the intermediate and deep aquifers was recharged mainly from local rainfall at 220-300 m above mean sea level. Interactions between groundwater and river water were detected close to the Yom River when it was in full flow. These fmdings on groundwater dynamics and quantity could aid water resource management within the Phrae Basin.

Automated summary

The Quaternary sequences in the Phrae Basin, northern Thailand, were classified into three aquifers based on depth. The groundwater dynamics and recharge were assessed using isotope techniques, revealing flow directions and sources. The study found that groundwater in the basin mainly originated from local rainfall and surface water. Additionally, parameters such as recharge rates and groundwater age were estimated.