VARIABILITY OF FLOW REGIMES OF OGBESE AND OWENA RIVERS IN SOUTH WESTERN NIGERIA

Abstract

The scarce water resources of Southwestern Nigeria could be better managed, if reliable forecast of river discharge through rainfall variability data over a long period are available. The study was aimed at carrying out analysis of rainfall data, river data of Ogbese and Owena rivers measured at Ago Aduloju and Owena respectively, on short and long term modeling forecast; using river discharge and stage of those two rivers. The data were analysed to obtain a general river discharge pattern that can be adapted for effective agricultural production planning as an index to increase food production in the study area. The data was modelled using the Box-Jenkins forecasting procedure for short and long term forecasting which was analysed using Microsoft Excel version 5.0 software package. The result obtained for short term modeling forecast for river Owena shows a correlation coefficient of 0.65 at 0 ≤ r2 ≤ 1.0 for the month of January to July and 0.8 to 1.0 for the month of August to December. The long-term model forecast for the same river gave a correlation coefficient of 0.8. The second river, Ogbese on short-term model had a correlation coefficient of 0.9 and 0.75 for long-term model forecast, for the same period of the year. The average value of river discharge obtained from modeled value compared with forecasted value for river Owena shows 91.62 m3/s against 126.10 m3/s, while for river Ogbese, 324.36 m3/s against 3.07.44 m3/s, respectively. This conservative estimate means that at any time in the forecasted year ahead, above 126.10 m3/s and 307.44 m3/s in water volume will be available for Rivers Owena and Ogbese, at their respective gauging stations. The crop grown in the study area was analysed, it was seen that the forecasted values for the two rivers (Ogbese and Owena) could be channelled or used in irrigation planningfor increased agricultural production through dry-season farming in the catchment area