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Thesis/Dissertation: BibTeX citation key:  Adeaga2005a
Adéaga, O. (2005) Modelling Rainfall-Runoff Relationship in Ungauged Basins: A Case Study of Yewa Basin. Thesis. University of Lagos.
Added by: Fanny Lefebvre 2010-09-16 15:59:49    Last Edited by: Fanny Lefebvre 2010-11-16 18:02:17
Categories: General
Keywords: Water resources
Creators: Adéaga
Publisher: University of Lagos

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This study modelled rainfall - runoff relationships and probable flood magnitudes in the River Yewa drainage basin within Nigeria, with a view to simulating the basin systems response and ascertaining its effect on water resources regimes in the basin.
The Yewa River is a transboundary (International) river between the Republic of Benin and Nigeria with a catchment area of about 5000km2. The Nigeria side of the basin falls within Nigeria’s hydrological Area 6 which is under the jurisdiction of the Ogun-Osun River Basin Development Authority.
The study employed the drainage morphometric analysis technique in examining and describing the basin topographic form and in explaining the strength and direction of fluvial and geomorphological processes in the Yewa drainage basin. In addition, a flow simulation exercise was carried out in order to examine the response of three of the Yewa sub-basins to rainfall input using a terrain based technique. The technique entailed automated analysis of the relationship between the geomorphological and hydrological indices within the drainage system of the sub-basins. The result of the simulation exercise was the generation of triangular hydrograph and Geomophological Instantaneous Unit Hydrograph with their basic hydrodynamic parameters for all the sub-basins.
The major data used are monthly hydro-climatological data (rainfall and discharge data) and the topographical maps of the basin that were sourced from Ogun-Oshun River Basin Authority (OORBA), Abeokuta and Federal Surveys Department, Lagos respectively. It should be mentioned that the hydro-climatological datasets are not of the greatest accuracy due to the manual method of their measurements and recording.
The result of the study shows that Yewa basin has double rainfall and discharge maxima and a mean annual runoff coefficient of 0.27. The linear relationship between annual rainfall and annual runoff as well as monthly rainfall and monthly runoff are described by the regression equations:
Q = 0.02 P + 12.94) …………………………………… (i)
Q = 0.02P + 1.17 ……………………………………… (ii)
The basin experiences a lot of flow irregularities and relatively lower peaks due to the non-synchronized flow in the elongated basin. The derived Geomorhological Instantaneous Unit Hydrograph using the morphological transfer function technique displays a multi-peak hydrograph in all the three sub-basins, an evidence of non-synchronized flow with probability of experiencing intermittent floods. The degree of relationship between the observed and the average simulated flow (1971) is 0.69 with coefficient of determination (R2) of 0.48.
Finally, the study makes a point for the need to increase hydrological networks in the country and while it particularly points up the need for a multidisciplinary approach to river basin studies, it equally emphasizes the use of complimentary/alternative hydrological predicting method especially the Prediction of Ungauged Basin (PUB) methods, for water resources studies in poorly gauged and ungauged basin, in order to resolve one of the 21st century challenges, which is to sustainable develop available water resources to the benefit of all.
Added by: Fanny Lefebvre    Last Edited by: Fanny Lefebvre