ANALYSIS OF RIVER FLOW VARIABILITY FOR IRRIGATION PLANNING AND FLOOD PREDICTION – A CASE OF WHITE VOLTA RIVER

Abstract

Analysis of river flow variability under changing flow regimes is required for planning of dry season irrigation and flood prediction. River flow characteristics are changing in response to change in climate, as well as land use and land cover changes. The objective of this study was to analyze flow variability of the White Volta River for irrigation planning and flood prediction. The daily discharge data of the river was collected from Pwalugu, Nawuni and Daboya hydrological stations and trends in discharge were analysed by applying the Mann Kendall statistical test and Sen’s Slope method at significant level of 0.05. The statistic calculated value of 0.0001 was found to be lower than the alpha significance level of 0.05 which supports the hypothesis that there is flow variability in the White Volta River, with a magnitude of 0.003 as provided by the Sens Slope. Land use and land cover changes were characterized using GIS and remote sensing and, over the study period, agricultural land increased by 56.5%, whereas savannah vegetation and grassland decreased by 46.5% and 56.25%, respectively. This has affected the total dry season flows that are used for irrigation farming, hence, the need for proper planning for the same. More surface flows within the basin are lost through surface runoff into the sea in the rainy season as compared to what is stored in reservoirs and used for agricultural purposes. During the study period, the year 2020 recorded the highest discharge of 2087 m3 /s at Daboya hydrological station which has a recurrence interval of 50 years or more. Gumbel’s method was used for flood prediction and the Gumbel’s curve was plotted from which future floods with the return periods between 5 and 150 years can be worked out. The findings of this research work will be used for dry season irrigation planning as well as for storm management in the area which is critical in protecting lives and property. The findings will as well help in designing and management of dams, bridges, irrigation canals and other hydraulic structures.