Flood pulse alterations of some river basins in Ghana

2014

English

Flood analysis is crucial for designing drainage, managing water quality, assessing the impact on lives and properties among others. The objective of the study was to determine the trends, occurrences and magnitude of floods in Ghana using hydrological data. The study looked at flood phenomenon in Ghana, because flooding has been observed recently as the most common natural hazard in the country. Specifically, the rainfall amounts from selected gauging stations in Ghana and river discharges from the three main river systems namely, Volta (at Bamboi), south western (at Twifu Praso) and the coastal (at Okyereko) river systems in Ghana were considered. Peak streamflows from the selected river systems were also analysed. Flood frequencies were derived using the flow duration curve (FDC), and the high flow frequency (return period) determined to support the analysis. The threshold values above which streamflows are peak flow were estimated from the FDC at 90 per cent probability of non-exceedance for the selected rivers. The results of the analysis showed that increases in the number of occurrence of high streamflows with declining trends of monthly rainfall in the last decade (2000-2010) have been prevalent. This means that rainfall amount is not necessarily the major cause of recent high streamflows (or flood), though there are evidences of direct runoff during rainy season in Ghana. It is, therefore, recommended that as a country, there is the need to improve the drainage systems in the cities, and also provide adequate storage for floods during the rainy seasons. It is further recommended that flood pulse analysis be carried out on a continuous basis as and when new meteorological and hydrological data is available.

Logah, F. Y.; Kankam-Yeboah, K.; Ofori, D.; Gyau-Boakye, P.