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Floods in Ghana have become a perennial challenge in the major cities and communities located in low-lying areas. Therefore, cities and communities located in these areas have been classified as potential or natural flood-prone zones. In this study, the Digital Elevation Model (DEM) of the Accra Metropolis was used to assess the drainage density and elevation patterns of the area. The annual population estimation data and flood damages were assessed to understand the damages and population trend. This research focused primarily on the elevation patterns, slope patterns, and drainage density of the Accra Metropolis. Very high drainage density values, which range between 149 and 1117 m/m2, showed very high runoff converging areas. High drainage density was also found to be in the range of 1117–1702 m/m2, which defined the area as a high runoff converging point. The medium and low converging points of runoff were also found to be ranging between 1702–2563 m/m2 and 2563–4070 m/m2, respectively. About 32% of the study area is covered by natural flood-prone zones, whereas flood-prone zones also covered 33% and frequent flood zones represent 25%. Areas in the Accra Metropolis that fall in the Accraian and Togo series rock types experience high floods. However, the lineament networks (geological structures) that dominate the Dahomeyan series imply that the geological structures in the Dahomeyan series also channel the runoffs into the low-lying areas, thereby contributing to the perennial flooding in the Accra Metropolis.

Groundwater is the main water resource which supplies more than half of the residents of Afram Plains. Recent studies show that the aquifer is subject to deteriorating quality from several anthropogenic activities. The aquifer vulnerability to contamination was assessed using the widely known DRASTIC model. This paper aimed to determine the depth-to-water table, identification of the various soil types, topography, recharge rate, and major lithological units in the area. The degree of vulnerability was identified by an index which is computed by superimposition of all the parameters considered for the model. Based on the vulnerability assessment, it was found that, 20.72% (1044.28 km2), 49.78% (2508.91 km2) and 29.50% (1486.80 km2) of the total area was classified as low, moderate and high, respectively. The final vulnerability index was largely influenced by the depth-to-water table, impact of the vadose zone, net recharge and aquifer media parameters. The model was validated with on-ground nitrate concentrations in groundwater in the study area. The DRASTIC model exhibits highly correlated areas in mapping vulnerable regions. The maps produced in this study could be used as a general guide to vulnerability by planners, groundwater managers and decision-makers on the implementation of measures aimed at the protection of this vulnerable resource.

The State Point Analysis (SPA) tool implemented in BioWin software was used to study the impact of Solids Retention Time (SRT) on the secondary clarifier as it relate to effluent quality in a full-scale treatment plant. SRT is the operating parameter which replaces loading factor as the key design parameter in the activated sludge design. It influences a number of factors, such as; growth rate of microorganisms, nitrification, biomass stabilization, degradation of slowly biodegradable organics, selection of microbial composition of the mixed liquor and its settling and treatment characteristics. SRT is the most difficult parameter to manipulate, its control is paramount to ensure effective waste water treatment. Studies have shown best operating SRT’s, nevertheless, the clarifier working conditions in those studies were not considered. SPA is a practical tool developed for the purposes of assessing clarifier performance under different operating scenarios. This study shows the usefulness of SPA in determining optimum operating SRT while maintaining clarification and thickening without compromising clarifier operation. The SPA results revealed that the clarifier is overloaded at the present operating SRT (16 days). However, it was found that the treatment plant performs better at 12 days SRT without violating effluent concentrations and without being critically loaded.