Browsing by Author "Wemegah, David Dotse"

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    Hydro-Climatic Modelling of an Ungauged Basin in Kumasi, Ghana
    (Hydrol. Earth Syst. Sci. Discuss., 2018) Osei, Marian Amoakowaah; Amekudzi, Leonard Kofitse; Wemegah, David Dotse; Preko, Kwasi; Gyawu, Emmanuella Serwaa; Obiri-Danso, Kwasi
    The Owabi catchment which is about 69 km2 provides about 20 % of water needs of the Kumasi metropolis has been in recent times prone to high anthropogenic activities that threaten water resource management. The Soil-Water-AssessmentTool (SWAT) was used to assess the extent of these activities on the hydrology on the catchment from 1986 to 2015. Specifically, the model simulated historic and projected stream-flow and water balance. Initial results revealed the forest and topography 5 played major role in water loss at the catchment as evapotranspiration and surface runoff were the dominant modulating processes. Monthly calibration/validation of the model yielded satisfactory results with NSE (0.66/0.67), R2 (0.67/0.67), PBIAS (8.2%/8.0%) and RSR (0.59/0.58). Nine sensitive parameters of which the catchment slope (CN2) ranked principal were found to control runoff amounts into the river. The model uncertainty was also quite low as the 95PPU enveloped about 50% of the observed streamflow within a width of 0.45 - 0.55. Furthermore, future streamflow predictions were modelled under RCP2.6, 10 RCP4.5 and RCP8.5 climatic scenarios, and two landuse scenarios, landuse category 1 and 2 (LU1 and LU2). An increasing trend of the downscaled rainfall totals between 2021 to 2050 for all RCPs were observed. This will positively impact streamflow generation at the catchment under LU1. There is an expected deficit of streamflow amounts under LU2 relative to LU1, and a marginal reduction as compared to the baseline. In general, the model proved efficient in determining the hydrology parameters in the catchment and therefore has potential to be used for further modelling of water quality and pollution to aid 15 effective water resource decisions at the catchment. 1 Introducti
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    The impact of climate and land-use changes on the hydrological processes of Owabi catchment from SWAT analysis
    (Journal of Hydrology: Regional Studies, 2019-07-24) Amekudzi, L.K.; Osei, Marian Amoakowaah; Wemegah, David Dotse; Preko, Kwasi; Gyawu, Emmanuella Serwaa; Obiri-Danso, Kwasi
    Study region: The 69 km2 Owabi catchment in Ghana. Study focus: The Soil-Water-Assessment-Tool (SWAT) was used to assess the hydro-climatic variability resulting from anthropogenic activities from 1986 to 2015. Specifically, the model simulated historic and projected stream-flow and water balance. Future stream-flow projections were modelled for three climate ensembles under three different representative concentration pathways (RCPs) for two land-use categories. New hydrological insights for the region: Initial results revealed that forest and topography played major role in water loss, whereas evapotranspiration and surface runoff were the dominant modulating processes. Monthly calibration/validation of the model yielded acceptable results with NSE, R2, PBIAS and RSR values of 0.66/0.67, 0.67/0.67, 8.2%/8.0% and 0.59/0.58 respectively. Uncertainty was fairly low and the model enveloped about 50% of the observed stream-flow. The RCP projections for all land use categories showed decreasing rainfall and streamflow trends. The model proved efficient in determining the catchment hydrology parameters and has potential to be used for further modelling of water quality and pollution to aid in effective water management.
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    The impact of climate and land-use changes on the hydrological processes of Owabi catchment from SWAT analysis
    (Journal of Hydrology, 2019-09) Osei, Marian Amoakowaah; Amekudzi, Leonard Kofitse; Wemegah, David Dotse; Preko, Kwasi; Gyawu, mmanuella Serwaa; Obiri-Danso, Kwasi
    Study region: The 69 km2 Owabi catchment in Ghana. Study focus: The Soil-Water-Assessment-Tool (SWAT) was used to assess the hydro-climatic variability resulting from anthropogenic activities from 1986 to 2015. Specifically, the model simulated historic and projected stream-flow and water balance. Future stream-flow projections were modelled for three climate ensembles under three different representative concentration pathways (RCPs) for two land-use categories. New hydrological insights for the region: Initial results revealed that forest and topography played major role in water loss, whereas evapotranspiration and surface runoff were the dominant modulating processes. Monthly calibration/validation of the model yielded acceptable results with NSE, R2, PBIAS and RSR values of 0.66/0.67, 0.67/0.67, 8.2%/8.0% and 0.59/0.58 respectively. Uncertainty was fairly low and the model enveloped about 50% of the observed stream-flow. The RCP projections for all land use categories showed decreasing rainfall and streamflow trends. The model proved efficient in determining the catchment hydrology parameters and has potential to be used for further modelling of water quality and pollution to aid in effective water management.
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    Integrated geophysical characterization of municipal solid waste disposal sites in the Kumasi Metropolis
    (2015-11-16) Wemegah, David Dotse
    Full wave spectral time-domain induced polarization, magnetic susceptibility and ground base magnetic datasets were acquired to map and characterize both engineered (Dompoase Landfill) and unengineered (Ohwim and Kwame Nkrumah University of Science and Technology municipal solid waste disposal sites) located in the Kumasi Metropolis. These geophysical datasets were selectively applied and integrated to help in full characterization of the waste disposal sites in terms of waste thickness, pollution plume mapping and the geological model development of the sites. In addition, a total of six boreholes were drilled around the sites to help in correlating the observed geophysical signatures with the waste thickness and the lithostratigraphic sequence in order to help in interpretation and characterization of the sites. The study was carried out with the aim of determining the risk posed by the waste deposit to the quality of soil and the groundwater system which is now becoming the main means of potable water supply in the metropolis due to the erratic supply supply and the inability of the Ghana Water Company (GWC) to supply water especially to new developing settlements in the metropolis. The intrinsic Cole-Cole IP parameters such as chargeability, resistivity and relaxation time as well as the normalized chargeability distributions, together with the magnetic results, aided in a full characterization of the wastes (vertical and lateral distribution), associated pollution plumes and for developing the geological model of the sites. The KNUST site was characterized using Cole-Cole parameters namely resistivity and chargeability as well as normalised chargeability and magnetic datasets. In particular, a clear contrast in resistivity and polarization effect between the saprolite layer and the granite bedrock, the main lithological units of the area aided in the development of a geological model of the site. Furthermore, it was found that the KNUST waste deposit is characterized by a low-chargeability and low-resistivity signature, and that the low-resistivity area spreads out from the waste deposit into the permeable saprolite layer, indicating the presence of a leachate plume which was mapped to be in the range of 5 to 30 m thick. A mapped fracture zone within the granitic bedrock linked to the pollution plume with the potential of aiding in leachate percolation of groundwater by serving as a conduit for infiltration of the leachate was also mapped. Similarly, the Ohwim Waste Disposal Site was mapped with the magnetic, magnetic susceptibility and full wave spectral time-domain induced polarization. These methods helped in determining the waste thickness and the extent of the pollution plume as well as the geological model of the site. The waste recorded high v magnetic anomaly, low resistivity and high normalized chargeability. The geological model of the site was developed by using the strong chargeability signature it produced. Furthermore, the Dompoase Landfill survey which was planned mainly to determine and monitor possible pollution plume around the waste, produced some intriguing result. The magnetic and the magnetic susceptibility results aided in the full mapping of the lateral extent of the waste as well as the channel of the released effluent from the treatment sewage pond, showing the high ferromagnetic iron content of the leachate. The strong IP effect in terms of chargeability and normalized chargeability as well as the low resistivity signature associated with the plume helped in mapping the plume around the catchment area of the waste. The controlled nature of the waste disposal at the Dompoase landfill makes it a possible resource for the production of natural gas. The research provides a cost effective means of monitoring and characterizing municipal solid waste site in the Kumasi Metropolis. It provides a full outline of the solid waste disposal sites investigated and also provides the information needed for assessing the future impact of the waste on the water quality in the area, and the need for designing risk-mitigation actions in these sites. The impact of waste disposal sites on the quality of the environment as shown by this work calls for a review of national policy in the waste site management with focus on reduction of the impact of the waste on the ecosystem.