Rainfall, rational formula and regional maximum flood - some scaling links

Abstract

In South Africa, the properties of rainfall can be expressed as a simple scaling formula: P_d,T = αP_1day,2[1 + βy_T] d^1-η, a product of three factors: the median one-day rainfall, a function of location; a function of the return period; a power function only of duration. It is shown that the area reduction factor in South Africa is constant for storm duration equal to the time of concentration. These facts extend the usefulness of the Rational Formula to larger areas than commonly accepted. Corroboration is made against Regional Maximum Flood data.

Keywords:

• IFD
• ARF
• Time of concentration
• rational formula
• scaling

Additional information

Notes on contributors

Geoffrey G S Pegram

Geoff Pegram is professor of Hydraulic Engineering at University of Natal, Durban, South Africa. He obtained his PhD from Lancaster UK on Stochastic Reservoir Theory. A South African professional engineer, he is the author of 32 journal publications, coauthor of a book on Water Resources, 52 papers given at conferences and symposia and 13 technical reports. His fields of interests are stochastic and deterministic hydrology and physical and computational hydraulics. A collaborating researcher in the CRC for Catchment Hydrology, he was at the University of Melbourne in 2001 as the recipient of the prestigious Miegunyah Fellowship Award and returned again to the University of Melbourne to work with the CRCCH for 2 months in 2002 and 2003. His current research interests include space-time modelling of rainfall from radar and satellite images, real-time flood forecasting using radar and linear meta-models, modelling of rainfall measured by large networks of gauges and large water resources system analysis and reliability, extensions of his love of stochastic hydrology.