Simulation of groundwater flow in a crystalline rock aquifer system in Southern Ghana - An evaluation of the effects of increased groundwater abstraction on the aquifers using a transient groundwater flow model

Abstract

Abstract:Monitored groundwater level data, well logs, and aquifer data as well as the relevant surface hydrological data were used to conceptualise the hydrogeological system of the Densu Basin in Southern Ghana. The objective was to numerically derive the hydraulic conductivity field for better characterization of the aquifer system and for simulating the effects of increasing groundwater abstraction on the aquifer system in the basin. The hydraulic conductivity field has been generated in this study through model calibration. This study finds that hydraulic conductivity ranges between a low of 2 m/d in the middle sections of the basin and about 40 m/d in the south. Clear differences in the underlying geology have been indicated in the distribution of aquifer hydraulic conductivities. This is in consonance with the general assertion that the hydrogeological properties of the aquifers in the crystalline basement terrains are controlled by the degree of fracturing and/or weathering of the country rock. The results suggest that the system will not be able to sustain this level of abstraction as it would lead to a basin wide drawdown in the hydraulic head by 4 m by the end of the prediction period. It further suggests a safe annual increment in groundwater abstraction by 5% under business as usual recharge conditions. Identification and protection of groundwater recharge areas in the basin are recommended in order to safeguard the integrity of the resource under the scenario of increased abstraction for commercial activities in the basin.

Incipient devitrification of impact melt particles at Bosumtwi crater, Ghana: Implications for suevite cooling history and melt dispersion

“…; Yidana et al. ). The porosity and water‐bearing capacity of the unweathered basement rocks below the regolith is typically low; however, the mean porosity of unweathered Birimian phyllite–greywacke and granite lithologies found at Bosumtwi is about 8% (Plado et al.…”

“…Most of the groundwater is hosted by fractures in the bedrock, and most importantly in the weathered zone. The present-day thickness of the weathering zone varies depending upon basement lithology but reaches in average only to about 30-50 m in the Birimian metasediments (Banoeng-Yakubo et al 2009;Yidana et al 2014). The porosity and waterbearing capacity of the unweathered basement rocks below the regolith is typically low; however, the mean porosity of unweathered Birimian phyllite-greywacke and granite lithologies found at Bosumtwi is about 8% (Plado et al 2000).…”

Numerical analysis of groundwater flow and potential in parts of a crystalline aquifer system in Northern Ghana

“…This has been supported by numerical groundwater flow models (e.g. Yidana 2011a, b;Yidana et al 2011;2012;Attandoh et al 2013). The Lawra belt is about the only one oriented NNW-SSE.…”

“…A hydraulic conductivity field containing values in the range of 0.99 and 19.4 m/day was obtained, and the heterogeneity in the hydraulic conductivity field was amply suggested in the detail of the flow system. A similar approach in the Densu Basin in Southern Ghana resulted in a range of 2-40 m/day (Yidana et al 2012), suggesting a significantly heterogeneous aquifer system. The observed aquifer transmissivity data from limited pump tests carried out in sections of the crystalline basement aquifer system (Dapaah-Siakwan and Gyau-Boakye 2000; BanoengYakubo et al 2010) appear to be consistent with the range of hydraulic conductivities obtained from the current and previous studies.…”

“…For instance, Ophori (1999) constrained the spatial and vertical variations in the permeability of a regional aquifer system through model calibration. A similar approach was applied by Yidana (2011a, b), Yidana et al (2012) and Attandoh et al (2013) in parts of Ghana. Characterization of the spatial pattern of behaviour of key aquifer hydraulic parameters is an important aspect of detailed regional hydrogeological investigations.…”