R. J. Oosterbaan



Rainfall-Runoff Relations of a Small Valley Assessed with a Non-Linear Reservoir Model

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A non-linear reservoir model is used to analyze the rainfall-runoff relations in a small valley (watershed, hydrological catchment), in Sierra Leone. The concept of a linear reservoir, which uses a constant reaction factor, for use in hydrological modeling is well known but often not effective. Non-linear reservoirs, having reaction factors that increase with increasing water storage, are less frequently applied but they have more promise. One may use reaction factors that are a linear function of the storage, which implies that the reservoir reacts quicker to rainfall under wet than under dry conditions. The reaction factor could also be a quadratic function of the storage so that the discharge increases progressively with increasing water storage. The characteristic functions of the reaction factors of the catchments are first found by calibrating part of the data, and thereafter they are verified with the remaining data. In the case study, the calibrations were done with a high precision. The verification (validation), however, was complicated by the fact that the valley bottom was used for rice cultivation and that the farmers interfered in the natural runoff process so that the reservoir characteristics changed in time. Yet, the non-linear reservoir model could be verified reasonably well finding the reservoir function by calibration over a 10-day period and applying that function to a two-day period of peak discharges within the selected 10 days. Hence, the non-linear reservoir model has proved to be effective. Free software for non-linear reservoir models is available.


rainfall-runoff relations, small valley, rice cropping, non-linear reservoir model


Cite this paper

R. J. Oosterbaan. (2019) Rainfall-Runoff Relations of a Small Valley Assessed with a Non-Linear Reservoir Model. International Journal of Environmental Science, 4, 20-27


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