Abstract

GERICKE, O J  and  SMITHERS, J C. Are estimates of catchment response time inconsistent as used in current flood hydrology practice in South Africa?. J. S. Afr. Inst. Civ. Eng. [online]. 2016, vol.58, n.1, pp.02-15. ISSN 2309-8775.  http://dx.doi.org/10.17159/2309-8775/2016/v58n1a1.

Catchment response time parameters are one of the primary inputs required when design floods, especially in ungauged catchments, need to be estimated. The time of concentration (T_C) is the most frequently used time parameter in flood hydrology practice, and continues to find application in both event-based methods and continuous hydrological models. Despite the widespread use of the T_C, a unique working definition and equation(s) are currently lacking in South Africa. This paper presents the results of the direct and indirect T_Cestimation for three sets of catchments, which highlight their inherent variability and inconsistencies. These case studies demonstrate that estimates of T_C, using different equations, may differ from one another by up to 800%. As a consequence of this high variability and uncertainty, we recommend that, for design hydrology and calibration purposes, observed T_Cvalues should be estimated using both the average catchment T_Cvalue, which is based on the event means, and a linear catchment response function. This approach is not only practical, but also proved to be objective and consistent in the study areas investigated in this paper.

Keywords : catchment response time; lag time; peak discharge; time of concentration; time to peak.

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