Department of Civil Engineering, University of Stellenbosch, P/Bag X1, Matieland 7602, South Africa
Gericke, O.J., Department of Civil Engineering, University of Stellenbosch, P/Bag X1, Matieland 7602, South Africa; du Plessis, J.A., Department of Civil Engineering, University of Stellenbosch, P/Bag X1, Matieland 7602, South Africa
Design rainfall comprises of a depth and duration associated with a given probability of exceedance or return period. The purpose of the study was to evaluate and compare the methods used in flood hydrology to estimate depth-duration-frequency (DDF) relationships of design rainfall in South Africa based on the critical storm duration or time of concentration (T c) of a catchment. The influence of the type of rainfall, areal and temporal distribution of rainfall were also investigated to establish if a relationship exists between the catchment area, T c and areal reduction factors (ARFs). The DDF relationships based on the least-square regression analyses of Log-Extreme Value Type 1 distributions, the modified Hershfield equation, the regionalised South African Weather Service (SAWS) n-day design rainfall data and the Regional Linear Moment Algorithm and Scale Invariance (RLMA&SI) approach were compared in 3 distinctive T c -ranges. The results showed that the RMLA&SI approach can be considered as the preferred DDF relationship in future design flood estimations. The results also showed that a direct relationship exists between the catchment area and T c, thus ARFs can be explicitly expressed in terms of only the catchment area.
Areal reduction factors; Catchment area; Depth-duration-frequency; Design flood; Flood hydrology; Future designs; Least square regression; Linear moments; Probability of exceedance; Rainfall data; Rainfall estimates; Return periods; Scale invariance; South Africa; Temporal distribution; Time of concentration; Weather services; Acoustic surface wave devices; Catchments; Design; Estimation; Regression analysis; Runoff; Storms; Rain; algorithm; catchment; depth determination; flood; precipitation assessment; precipitation intensity; storm; South Africa