Abstract:
Conceptual mathematical models are useful tools for rainfall runoff modeling of river
basin. Thus, this study attempts to identify relationships between suitable conceptual
rainfall-runoff model structures and catchment types, and demonstrates an objective
procedure for selection of model structures for Gilgel Abbay, Dedessa and Neshe
catchments. In this study four conceptual model structures have been tested on three
catchments in Abbay River Basin. All the model structures are combinations of the water
balance and routing components since they are conceptual models. Three catchments were
selected to cover a range of hydrological types based on known average catchment
characteristics. The important points in objectively selecting model structures for discharge
simulation are proposed as: performance in calibration and validation, trade-off between
high, mean and low flow performance and FDC, and model complexity (here represented
as the number of parameters).
Although, the results in this study provide no detail evidence of relationships between
catchment type and preferred model structure with greater certainty, the study indicates that
out of the four model structures, the ARNO model has greater performance in Gilgel
Abbay catchment, SMAR has fairly good performance value in Dedessa catchment and
HBV has good performance index in Neshe catchment. Eventhough, all model structures
have poor performance index in low flow simulation, all models relatively suitable for
runoff simulation under mean and high flow for selected catchments. The biased occurred
between simulated and observed runoff may be due to in adequacy of model structure,
human activities done, incorrect estimation of parameters especially in case of manual
optimization , if there is an interflow between catchments, the quality of data and the
absence of any substantial, consistent , or coherent relationship in the data used to calibrate
the models.
