Relationship between Rainfall-Runoff on the White Volta River at Pwalugu of the Volta Basin in Ghana

Abstract

Rainfall and runoff patterns affect mans activities in so many ways and as such, designs of agricultural, storm water management, telecommunication, erosion, droughts, food security etc.  It is essential that the role of rainfall and stream flow are recognized, understood and taken into account when modelling hydrological processes within any Basin. The Pwalugu  catchment in the White Volta Basin experiences one rainy season which usually begins from April and peaks up in July, August, and September and gradually end with some showers in October and part of November. The basis of the analysis comprises of the rainfall events and runoff of the White Volta River at Pwalugu, to determine the relationship between the rainfall events and runoff and also estimates the contribution of rainfall to runoff by a certain threshold of rainfall. The analysis shows that the period is characterized by high inter-seasonal rainfall and discharge variability with a correlation coefficient of 0.78 which showed a strong positive relationship between rainfall and runoff in the catchment.

For the linear regression relationships of cumulated rainfall events and discharges for the various years considered for the study, it is realized that 2003 and 2009 recorded the highest coefficients of correlation of 0.96 and 0.92 respectively. The studies showed that the minimum rainfall that can cause runoff in the catchment is 25mm which was set as a threshold. It is also observed from the analysis that a rainfall of at least 18mm can contribute 0.2m³/s of water to river flow with a correlation coefficient of 0.90 indicating a strong relationship between rainfall and riverflow.

Keywords:Rainfall, Runoff, Volta Basin, Intensity, Threshold