The groundwater recharge regime of some slightly metamorphosed neoproterozoic sedimentary rocks: an application of natural environmental tracers

Abstract

Isotope data of precipitation and groundwater in parts of the Voltaian Basin in Northern Ghana were used to explain the groundwater recharge regime in the area. Groundwater recharge is an important parameter in the development of a decision support system for the management and efficient utilization of groundwater resources in the area. It is therefore important to establish the processes and sources of groundwater recharge. δ18O and δ2H data for local precipitation suggest enrichment relative to the Global Meteoric Water Line (GMWL) and indicate that precipitation takes place at a relative humidity less than 100%. The groundwater data plot on an evaporation line with a slope of 5, suggesting a high degree of evaporative enrichment of the precipitation in the process of vertical infiltration and percolation through the unsaturated zone into the saturated zone. This finding is consistent with the observation of high evapotranspiration rates in the area and ties in with the fact that significant clay fraction in the unsaturated zone limits vertical percolation and thus exposes the percolating rainwater to the effects of high temperatures and low humidities resulting in high evapotranspiration rates. Groundwater recharge estimates from the chloride mass balance, CMB, method suggest recharge in the range of 1.8–32% of the annual average precipitation in the form of rainfall. The highest rates are associated with areas where open wells encourage significant amount of groundwater recharge from precipitation in the area. In the northern parts of the study area, groundwater recharge is lower than 12%. The recharge so computed through the application of the CMB methodology takes on a spatial distribution akin to the converse of the spatial pattern of both δ18O and δ2H in the area. As such, the locations of the highest recharge are associated with the most depleted values of the two isotopes. This observation is consistent with the assertion that low vertical hydraulic conductivities slow down vertical percolation of precipitation down to the groundwater water. The percolating precipitation water thus gets enriched in the heavier isotopes through high evapotranspiration rates. At the same time, the amount of water that finally reaches the water table is considerably reduced. Copyright © 2013 John Wiley & Sons, Ltd.

Groundwater recharge processes in the Nasia sub-catchment of the White Volta Basin: Analysis of porewater characteristics in the unsaturated zone

“…Only two samples display d-excess values of 10.80‰ and 10.88‰; the rest of the samples have values lower than 10‰. Yidana and Koffie (2014) suggest that low infiltrating rates due to high percentage of clay sized material in the unsaturated zone may be responsible for observed lo groundwater recharge rates in some parts of the Voltaian in the north of Ghana. Infiltrating rainwater in the study area is still amenable to high dry season temperatures and low humidities which penetrate several depths below the surface.…”

A preliminary analysis of the hydrogeological conditions and groundwater flow in some parts of a crystalline aquifer system: Afigya Sekyere South District, Ghana

“…Throughout the year, high evapotranspiration attending high temperatures and low relative humidities significantly reduce the fraction of precipitation that begins transit into the aquifer system. Yidana and Koffie (2014) attributed reduced groundwater recharge in the Voltaian Basin to high levels of evaporation of infiltrating precipitation whose downward trajectory is limited due to significant clay content. This range of recharge is significant compared to the current groundwater demands in the area.…”

Hydrochemistry and Isotope Hydrology for Groundwater Sustainability of the Coastal Multilayered Aquifer System (Zhanjiang, China)

“…analysis results of 18 O and 2 H are shown in Table 2 and Figure 5. According to the monthly rainwater data obtained from the GNIP (Global Network of Isotopes in Precipitation) of the IAEA (International Atomic Energy Agency), the local meteoric water lines (LMWLs) of Hong Kong and Haikou weather stations were calculated as 2 H = 8.28 18 O + 12.78 and 2 H = 7.50 18 O + 6.18, respectively. Then, these two LMWLs were used as the LMWL of Zhanjiang.…”

“…In hydrogeological studies about the coastal groundwater management, analysis of the hydrochemistry and hydrogenoxygen isotopes data has been used widely to determine the hydrogeological conditions, such as groundwater recharge sources, recharge rates, and flow patterns [15][16][17][18][19][20]. The application of chemistry and hydrogen-oxygen isotopes can be used also to identify processes of groundwater salinization induced by seawater intrusion [21][22][23][24][25].…”