Sea Level Rise and Coastal Planning: A Call for Stricter Control in River Mouths

Abstract

Drift-aligned type deltas are common to the South African coastline across the whole range of river sizes. They are dynamic environments and by virtue of their potential for rapid morphological change, they are inherently unsuitable for development. South Africa has a relatively short history of intense coastal development. As a result, these estuaries appear to have some margin of stability and are rapidly becoming developed.

Sea level rise will increase the occurrence of extreme flood and erosional events in these estuaries and poorly planned development contained within them will come under exaggerated risk. Two case studies of potential impacts of sea level rise are considered: the Diep river near Cape Town and the Umgeni river at Durban. Increased coastal erosion resulting from a small rise in sea level is shown to shorten the channel of the Diep, seriously affecting housing on the spit barrier and exposing previously sheltered development to direct wave attack. The combination of sea level rise with river floods and/or sea storms is shown to induce a switch in the Umgeni from a modern short channel, to a longer, abandoned channel. Durban city centre is located in the middle of this palaeochannel. The potential for flood damage is extreme. Increased coastal erosion will also significantly reduce the available tourist beaches.

Drift-aligned deltas occur in many locations worldwide and any development contained within them is highly vulnerable to changes in mean sea level. The increased vulnerability of these environments is therefore of international significance. Their development needs to be strictly controlled with new town planning ordinances, capable of addressing the sea level rise issue.