Abstract
Monitoring of the coastal zone is necessary to assess its vulnerability and help formulate coastal management plans. A predetermined stretch of beach along the northern rim of False Bay known locally as Monwabisi Beach was chosen to compare different monitoring techniques and from the data acquired, see if accurate comment could be made regarding sediment dynamics and its implications regarding any coastal encroachment on anthropogenic infrastructure. Digital elevation models of the study area were created from data acquired with a mobile laser scanner in April 2013, April 2014 and August 2014, chosen to cover a yearly and a seasonal cycle. Conventional beach profile data were acquired using a differential global positioning system (DGPS) in April 2014 and LiDAR data were acquired in November 2014. From the laser scanning datasets it has been calculated that a nett erosional trend exists for the study area with sediment moving towards the north. In the western portion of the study area, where a coastal road has been undercut and complete failure has occurred, the progress of cliff retreat has been accurately measured to reveal an average rate of retreat of 2.2m/yr. Although accurate figures were determined for sediment erosion and accretion, the rate of change of each could not be determined with any degree of confidence as the survey intervals were not regular enough to consider nett amounts; rather the gross amounts have been presented.
Highlights
40% of South Africa’s population live within 100km of the coast (Unterner et al, 2011) and coastal resources are relied on for commercial opportunities as well as for food, recreation and transport, thereby facilitating job creation and general economic upliftment
Quantification of erosion and accretion rates of sediment dynamics in the coastal zone is invaluable for the formulation of coastal management plans
Regular monitoring is necessary to formulate these management plans which rely upon the acquisition of high precision digital elevation models (DEM) to characterise the geomorphology of the coastline
Summary
40% of South Africa’s population live within 100km of the coast (Unterner et al, 2011) and coastal resources are relied on for commercial opportunities as well as for food, recreation and transport, thereby facilitating job creation and general economic upliftment. Quantification of erosion and accretion rates of sediment dynamics in the coastal zone is invaluable for the formulation of coastal management plans. Regular monitoring is necessary to formulate these management plans which rely upon the acquisition of high precision digital elevation models (DEM) to characterise the geomorphology of the coastline. Multiple and regular acquisitions of DEM data can be used to monitor erosion or sedimentation rates. Several techniques for the extraction of elevation data have been developed. This research aims to assess some of the more affordable techniques to extract high resolution and high precision digital elevation data. Multiple data acquisitions were used to quantify the sediment dynamics in the area of interest with the focus on the development of tools for the long term monitoring and quantification of sediment dynamics
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