Streamflow Variability in Ossiomo River Catchment and Implications for Basin-wide Water Resources Management

Time series analysis of streamflow data from gauges installed in the main rivers of the Ossiomo River catchment has been undertaken using the Australian Cooperative Research Centre for Catchment Hydrology’s Time Series Analysis computer code. The results show that all the rivers are perennial, receive groundwater contribution all the year round throughout their entire lengths and that this groundwater contribution is on the average, responsible for more than 70 per cent of total flow.  This large percentage contribution also modulates the response of the rivers to the higher flows in the wet  season, and as such, mitigates flood risks. The results also show that there are tremendous groundwater reserves available for development in the Benin Formation that releases the groundwater to the rivers from only its upper layers. The Flow Duration Curve for the Ikhowan River, the smallest river with a gauge, shows that Q50 is on the average about 5.5 m 3 s -1 , and thus, has good potential for small hydropower development.  Finally, while flow characteristics have been determined from the very short and patchy records that are available, they give an insight into the water resources potential of  Ossiomo River catchment  and could have application, in some respects, for other rivers that flow on the Benin Formation but are ungauged.