Continuous simulation modelling for design flood estimation in South Africa: Preliminary investigations in the Thukela catchment

Abstract

Several recent literature reviews highlight the need for improvements in procedures for design flood estimation [Cordery, I., Pilgrim, D.H., 2000. The state of the art of flood prediction. In: Parker, D.J. (Ed.), Floods. vol. II. Routledge, London, UK, pp. 185–197; Smithers, J.C., Schulze, R.E., 2001. Design runoff estimation: a review with references to practices in South Africa. In: Tenth South African National Hydrological Symposium. SANCIAHS, Pietermaritzburg, RSA]. In general, these reviews indicate that internationally the trend is to adopt a continuous simulation modeling approach for design flood estimation. The continuous simulation modelling (CSM) approach to design flood estimation has many advantages and has the potential to overcome many of the limitations of the often used design event approach. A pilot study into the development of a continuous simulation modelling system for design flood estimation is being undertaken in the Thukela catchment in South Africa. Preliminary studies using the ACRU agrohydrological modelling system are detailed in this paper and include investigations into the appropriate scale and levels of soil and land cover information required for use in a CSM approach for design flood estimation. Results indicate that CSM with the ACRU model requires quaternary catchments to be further divided into sub-quaternary catchments, and that using area weighted soils and land cover information gives better results than using modal soils information or single dominant soil or land cover information.