Application of Topkapi model for runoff estimation and landuse management at Pungu near Navrongo
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Date
2009-08-23
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Abstract
The Hydrological Services Department of the Ministry of Water Resources Works and Housing in Ghana is the body mandated to collect, analyse, store and disseminate runoff data on all river networks through the development of hydrological monitoring networks in the country. However, the number of hydrological monitoring networks established in the Volta Basin in Ghana has declined by 48% over the years due to lack of adequate resources to operate and maintain them. Furthermore, only 38% of the networks which are currently still in operation have stage-discharge measurements which are necessary for the generation of runoff data. Significantly, none of the monitoring stations in the basin has thirty years of continuous runoff data which is generally considered to be the basic requirement in most hydrological analysis. Again, to minimize the effects of prolonged dry season on the socio-economic activities, subsistence agriculture, of the people in the Kassena-Nankana District of the Upper East Region, several dams and dug-outs have been constructed to address the problem of water scarcity without a detailed study of the dynamics of rainfall-runoff processes in the area. This study therefore presents the results from field observations and subsequent application of the TOPKAPI model as a tool for filling-in missing runoff data and studying the effects of land use changes on runoff generation in the sub- catchments of the Volta Basin in Ghana. In this study, the distributed TOPKAPI model was calibrated in a small experimental site in the Volta Basin at Pungu near Navrongo in the Kasena-Nakana District of the Upper East Region. The model was calibrated using field observations as input data. The calibrated model was used as a tool to fill-in missing runoff data in the Nabogo catchment, a sub-catchment of the Volta Basin. The model was also used to test different scenarios of land-use changes. With a model efficiency of 0.877, the TOPKAPI model provided reasonable estimates of missing runoff data in the Nabogo catchment in the Volta Basin. Results from the quantitative assessment of the land-use scenarios also show that tillage conservation increases water movement into the soil leading to high percentage of saturation volumes and subsequently declining mean annual runoff. Finally, the model was found to be more sensitive to the channel Manning's roughness coefficient than that of the surface Manning's roughness coefficient.
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A Thesis submitted to the Board of Graduate Studies, Kwame Nkrumah University of Science and Technology, in fulfilment of the requirement for the Award of the Degree of Master of Philosophy in Water Resources Engineering and Management.