Shoreline recovery from storms on the east coast of Southern Africa

S Corbella,D D Stretch

doi:10.5194/nhess-12-11-2012

Abstract

Abstract. Episodic extreme waves due to sea storms can cause severe coastal erosion. The recovery times of such events are important for the analysis of risk and coastal vulnerability. The recovery period of a storm damaged coastline represents a time when the coastline is most vulnerable and nearby infrastructure is at the greatest risk. We propose that identification of the beach recovery period can be used as a coastal management tool when determining beach usage. As a case study, we analyse 37 yr of beach profile data on the east coast of South Africa. Considering beach length and cross-sectional area, we establish a global recovery period and rate and identify the physical characteristics of the coastlines that either accelerate or retard recovery. The beaches in the case study were found to take an average of two years to recover at a rate of approximately 90 m3 m−1 yr−1. Beach profiles with vegetated dunes recovered faster than urbanized beaches. Perpendicular beach structures have both positive and negative effects on beach recovery. Coastlines with rock outcrops in the surf zone tend to recover slowly and long-term sediment loss was identified in cases where storm damaged beaches have not recovered to pre-erosion levels.

Highlights

Erosion of coastlines is an age old problem faced by coastal communities. Durgappa (2008) claimed that sandy shores make up approximately 20 % of the world’s coastline and of this more than 60 % has experienced severe erosion over the past few decades
This paper reports observations of recovery times and recovery rates for beach erosion from storm events on the east coast of South Africa
The 2 m chart datum (CD) contour profile length recovery period is shorter than the 4 m CD contour length which in turn is shorter than the volume recovery

Summary

Introduction

Erosion of coastlines is an age old problem faced by coastal communities. Durgappa (2008) claimed that sandy shores make up approximately 20 % of the world’s coastline and of this more than 60 % has experienced severe erosion over the past few decades. The inter-arrival time of storm events does not necessarily influence the quantity of sediment removed during a given event. This is because a new equilibrium profile is established during the initial storm and a subsequent storm of less or equal wave power will not erode the profile any more. A storm event erodes a beach and reduces the natural buffer between the ocean and the hinterland It is at this stage that an urbanized coastline is at risk of sustaining severe damage from a subsequent, possibly less extreme, storm event before it has fully recovered to its pre-storm level (Forbes et al, 2004)

Methods

Discussion

Conclusion