TOWARDS A DELIMITATION OF SOUTHWESTERN NIGERIA INTO HYDROLOGICAL REGIONS

Fifteen third-order drainage basins (1:50,000) on the Basement Complex rocks of southwestern Nigeria are classified into hydrological regions using hydrologic response parameters of average daily mean specific discharge (Q//A); daily mean specific discharges equalled or exceeded 90% (Q//9//0), 50% (Q//5//0) and 10% (Q//1//0) of the study period; variability index of flow (VI); recession constant (K) of flow from peak discharge at the end of the rainy season to minimum discharge in the dry season; total annual runoff (RO); total runoff within the dry season (DSRO); dry season runoff as a percentage of total annual runoff (%DSRO); runoff coefficient (ROC); and, number of days during the study period when there was no flow (NFD). An ordination technique and a classification algorithm derived from cluster analysis technique and incorporating the analysis of variance (ANOVA) tests to determine the level of significance of the homogeneity of derived classes, were used to classify the fifteen basins into five hydrologically homogeneous regions.