Jc Smithers

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

Abstract 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 (TC), lag time (TL) and time to peak (TP). 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 TC is recognized as the most frequently used time parameter, followed by TL. In acknowledging this, as well as the basic assumptions of the approximations TL = 0.6TC and TC ≈ TP, along with the similarity between the definitions of the TP and the conceptual TC, 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. Editor Z.W. Kundzewicz; Associate editor Qiang Zhang

The development and assessment of a daily rainfall disaggregation model for South Africa

Abstract In this study a daily to hourly rainfall disaggregation model developed in Australia has been modified and applied in South Africa. The structure of the model allows for the generation of 480 different temporal rainfall distributions varying from uniform to very peaked. The model was independently tested at 15 locations in differing climatic regions in South Africa. At each location, observed hourly data were aggregated to yield daily values and were then disaggregated using the methodology. Results show that the model is able to retain the statistical characteristics of the hourly rainfall.