Estimating stream discharge of Aboine River Basin of Southeast Nigeria using modified Thornthwaite climatic water balance model

The study attempts to estimate the stream discharge of the Aboine river basin, southeast Nigeria, using modified climatic water balance approach. Moisture deficit in the basin generally begins from January and lasts up to April while utilization begins from October up to December. The basin attains a field capacity from August to September and decreases in moisture storage from October when more water is removed from the basin to meet plant water needs. The value of the circularity ratio of 0.29 showed that the Aboine Basin will produce little surface runoff. Results of bifurcation ratio, compactness coefficient, stream length and modeling of inter-basin parameters showed that the Aboine drainage basin is basically a flat surface. This will affect both the amount of water available from the basin for any water resources projects. Such information also provides the basis for demonstrating the effects of environmental control on the fluvial system and also for predicting the basin output variables. Surface runoff contribution to discharge was computed as a residual of our modified climatic water balance equation while groundwater flow contribution to discharge was determined from the separation of water stage hydrograph available for the study area from 1984 to 1987, using the hydrograph separation technique. Comparison of calculated discharge values using modified THWB climatic water balance with stream discharge determined from water- stage showed significant difference between computed stream discharge from water stage and discharge estimated from our water balance model at 0.05 level of confidence. This suggests that our modified water balance model if further improved maybe suitable for generating information on all the aspects of the moisture relationship in the basin in the absent of measured stream flow data.Keyword: Stream discharge, basin morphometry, surface flow, groundwater flow, water resourc