The 1988 Orange River flood, Upington Region, Northwestern Cape Province, RSA

Abstract

ABSTRACTThis paper describes aspects of the 1988 Orange River flood. The Orange River is a perennial, bedrock‐controlled river which experienced severe flooding (flood peak: 8300 m3 s‐1) during February‐April of 1988. This flood resulted in the loss of life and damage in excess of $126 million. Negligible bank erosion took place in the main channel margins due to the stabilizing effect of tree‐lined banks. In contrast, areas removed from the channel margin were characterized by erosion and deposition.Within the confines of the natural flood channels, macroturbulence gave rise to scour holes which sometimes amalgamated into large erosion fields acres in extent. In many cases scour holes were present but macroturbulence‐originating obstacles were not, and it is suggested that these were removed by flood‐erosion processes. In some instances amalgamation of scour‐hole trails (orientated down‐current) led to the formation of steep‐sided flood channels. Deposition took the form of large sandsheets constructed from fluvial‐dune fields and braid‐bar accumulations. Post‐flood winds reworked some of the deposited sand into aeolian dunes.