Analysis of the Control Processes Upon Storm Water Dynamics Using ECCRARO Model in Eyong Creek and River Catchments in South-Western Nigeria

Abstract

ECCRARO model, which registers flood-stage response to rainfall impulse in Enyong/Ikpa rivers' catchments, was applied in conjunction with the analysis of the physical properties of the catchment system to establish how surface runoff/subsurface drainage to the floodplains/rivers and the flood routing through the catchment rivers control flood stages, hence flooding of the catchments. The control of the rising and falling flood stages under rainfall impulse was dominated by the combined processes of runoff production/drainage and flood routing. However, drainage through the floodplain was slower in Enyong Creek catchment than the routing of floodwater through its river system, hence, drainage problem was a priority in upstream Enyong Creek. In Ikpa river catchment, the sluggish flood routing in its river system dominated flooding problem more than the runoff production process, making flood routing a priority problem. The runoff coefficients, generating surface runoff from excess effective rainfall into runoff were twice higher in Enyong Creek than in Ikpa river catchments, while the groundwater flows in Ikpa sub-catchments exceeded those from corresponding sub-catchments in Enyong basin. On the other hand, the Lag between stage accretion and recession rates was wider in Ikpa than Enyong rivers, while the time of concentration of 3.5 to 4.5 hours in Enyong was far greater than the Lag time of 0.5 hour in Ikpa catchments. The lower surface gradient in Ikpa river at its confluence with Cross river retarded its entrance flow rates, causing a higher upstream backwater that exacerbates flooding in Ikpa tributary swamps, while the entrance in the Enyong Creek was smoother at its confluence due to its positive surface gradient at its confluence with Cross river. Drainage of runoff is priority flood control problem in Enyong Creek catchment while flood routing is priority in Ikpa river catchment. Keywords : Control processes, storm water dynamics, drainage, flood routing, ECCRARO Journal of Applied Science, Engineering and Technology Vol. 6 (1) 2006 pp. 39-47