Review of methods used to estimate catchment response time for the purpose of peak discharge estimation

Large errors in peak discharge estimates at catchment scales can be ascribed to errors in the estimation of catchment response time. The time parameters most frequently used to express catchment response time are the time of concentration (T-C), lag time (T-L) and time to peak (T-P). This paper presents a review of the time parameter estimation methods used internationally, with selected comparisons in medium and large catchments in the C5 secondary drainage region in South Africa. The comparison of different time parameter estimation methods with recommended methods used in South Africa confirmed that the application of empirical methods, with no local correction factors, beyond their original developmental regions, must be avoided. The T-C is recognized as the most frequently used time parameter, followed by T-L. In acknowledging this, as well as the basic assumptions of the approximations T-L = 0.6T(C) and T-C approximate to T-P, along with the similarity between the definitions of the T-P and the conceptual T-C, it was evident that the latter two time parameters should be further investigated to develop an alternative approach to estimate representative response times that result in improved estimates of peak discharge at these catchment scales. [GRAPHICS] Editor Z.W. Kundzewicz; Associate editor Qiang Zhang