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- Grundwasserüberwachung (2) (remove)
In the Garu-Tempane area and Tamne River basin of north-eastern Ghana, granitic aquifers supply nearly 80% of annually abstracted groundwater. Rapid and diffuse recharge enters the fractured and weathered Tamnean Plutonic Suite aquifers mainly granitoid, which are the dominant rock types in the study area. However, a greater challenge to the water supply in the area is posed by global climatic changes and overexploitation due to population growth. The semi-arid nature of the area together with the factors mentioned earlier has caused water scarcity, particularly in the dry season and these have affected the livelihoods of the farmers who depend mostly on the groundwater for irrigation and domestic purposes. A promising way to balance water resources in the region is using engineering technology such as managed aquifer recharge (MAR). MAR augments water levels in water-scarce areas and represents a key tool in water supply management.
For this reason, a comprehensive hydrogeological characterization involving the hydrochemistry of the groundwater, groundwater recharge process and residence time using multi-environmental tracers, and a numerical groundwater flow model was developed.
Based on the hydrochemistry results, the water quality index showed that the groundwater is very suitable for drinking. However, about 10.5 % out of the 38 groundwater samples had elevated nitrate concentrations exceeding the permissible WHO drinking water limit. These are mainly agricultural areas, which might have influenced the elevated nitrate concentrations.
Groundwater age dating using sulphur hexafluoride (SF6) and chlorofluorocarbons (CFCs) was used to date shallow groundwater in Ghana for the first time. The results proved that the mean residence time of groundwater was around 30 years, an indication of young groundwater and rapid groundwater renewability. The findings also showed different groundwater ages implying diffused flow systems occurring in the fractured granitic aquifer.
Investigation of the groundwater recharge using stable isotopes of deuterium and oxygen-18 revealed that the main source of groundwater recharge is of meteoric origin. There were little or no contributions from the stream and ponds as they were subjected to evaporative fractionation during the dry season. The White Volta River samples and samples from two big rivers were depleted in heavy isotopes, which suggested a hydraulic connection between them and the groundwater.
The numerical groundwater flow model was used to assess the feasibility of MAR and determine the maximum recharge and abstraction rates. The results showed that the aquifer had enough storage to accommodate enough volumes of floodwater without causing groundwater mounding. This shows that MAR is feasible in augmenting the water levels in the area when irrigation and domestic withdrawals are regulated.
The impact of urbanization on the quality of drinking water sources is a challenge in many developing countries. In this research, the main source of drinking water was quantified, quality baseline defined, and a thematic decision support management tool developed to protect the quality using Aba, Nigeria. Data from primary and secondary sources were obtained from desktop search, empirical instruments, satellite data, hydrogeological investigations and water quality assessment. Geoscientific and statistical tools were used to analyse the landform, characterize the land use, and create management tools to protect the water source.
The results revealed that groundwater is the main source of water for both domestic and industrial uses. An average water consumption per capita rate of 35.9 l/day was estimated, which is low compared to the WHO recommendation. The landform and land-use analyses revealed that the area is low-lying, poorly drained, and the urban land-use is the fastest-growing class growing averagely at 0.6% /annum between 1986 to 2017. Some of the urban land-use practices that harm the quality of the groundwater were identified and mapped in a contamination hotspot map.
The results of the twenty-one quality indicators in the groundwater showed that the pH was acidic (3.7-5.6), total dissolved solids (TDS) ranged between 6.5 mg/l-364 mg/l. The mean concentrations of the remaining indicators were within the WHO limits for drinking water quality. But, the EC, TDS, chloride and nitrate revealed significant differences when tube-wells between densely and sparse built-up areas are compared. Again, four dominant water types were identified in groundwater. The Na-HCO3 water type was dominant mostly in the sparse built-up area and it is assumed as the background groundwater facies in the area. Whereas Mg, Ca-Cl, Na-Cl and Ca-HCO3 water types were predominant in the densely built-up area. The bacteriological assessments of drinking water from natural and alternative (i.e. beverages and packaged water) sources revealed the presence of E. Coli and Coliform bacteria in some samples of the natural water.
The groundwater quality distribution and vulnerability assessment maps were developed based on water quality index, and DRASTIC methodologies, respectively. The quality distribution map showed that > 98% of the area has a “suitable“ rating. While the vulnerability assessment map found that the groundwater has a “medium” baseline vulnerability covering about 80%. The differences in the results were due to some observed poor urban land-use practices in the area. Finally, a thematic decision support tool that delineates priority monitoring zones and suggests possible source protected areas tailored for the area was developed. This tool is cost-effective in protecting the groundwater quality and can be applied to other developing urban areas with similar physiological conditions.