Eden Coastal Setback Lines – South Magazine

eden-dmSouth Africa, George – With climate change and the dynamic nature of coastal zones in mind, the prediction of sea level changes and calculation of the related risk to coastal communities have become a necessity in the face of the potentially extensive impact of sea level rise-related storms and storm surges on the coastal zone. The Western Cape Department of Environmental Affairs & Development Planning proposes to delineate coastal set-back lines for the EDEN DISTRICT as one strategy through which responsible coastal management can be ensured.

According to Mr Vernon Gibbs-Halls, Eden’s Environmental Control Coordinator:

“Delineation of coastal set-back lines must be undertaken in accordance with the National Environmental Management: Integrated Coastal Management Act (Act No. 24 of 2008) (ICM Act), the National Environmental Management Act (Act No. 107 of 1998) (NEMA), Environmental Impact Assessment (EIA) Regulations, 2010, as well as the Western Cape Provincial Spatial Development Framework (PSDF). Coastal set-backs are proposed as a means to facilitate improved planning and management of sensitive and often vulnerable coastal areas.”

It is envisaged that the project will consist of two main components – modelling of coastal processes on the one hand, and the determination of management guidelines on the other. The technical modelling includes the determination of a refined high water mark (HWM), and various lines describing natural coastal processes and risks. Management guidelines are then derived by means of a robust stakeholder engagement process which is based on the technical information.

It is envisaged that at the end of the project, the following would be available:

  1. An accurate delineation of the high water mark;
  2. A line demarcating physical processes or hazards;
  3. One or more management lines, or coastal set-back lines, that can be used to manage development along the coast; and
  4. A line demarcating the Coastal Protection Zone (CPZ) as required by the

Integrated Coast Management (ICM) Act.

It is envisaged that the project will consist of 4 phases

  1. Natural coastal regression or accretion;
  2. Areas of littoral active zones (mobile sand);
  3. Sea level rise (SLR); and projections of storm-driven coastal erosion.
  4. Public consultation (phase 4) is imperative, as public input is required to determine how the information should be used to inform the management of development along the coast, and ultimately one or more coastal set-back lines.

Coastal Set-back Lines in terms of the ICM Act

Coastal set-back lines, as detailed in the ICM Act, are prescribed boundaries that indicate the limit of development along ecologically sensitive or vulnerable areas, or an area that poses a hazard or risk to humans. The coastal set-back line may even be situated outside the coastal zone. The coastal set-back line prohibits or restricts the construction, extension or repair of structures that are either wholly or partly seaward of the line. The intention of the coastal set-back line is to protect or preserve coastal public property; coastal private property; public safety; the coastal protection zone; and the aesthetics of the coastal zone (Celliers, et al. 2009).

The establishment of coastal set-back lines is a provincial responsibility but a relevant Member of the Executive Council (MEC) can only declare such a set-back line(s) after consultation with municipalities and interested and affected parties (I&APs). The MEC must communicate this by publishing regulations in the Gazette.

Once determined this line must be delineated on the map or maps that form part of the municipal zoning scheme. This is done so that the public may determine the position of the set-back line in relation to existing cadastral boundaries (Celliers, et 2009).

The coastal set-back is proposed to give specific direction in respect to locating the future development footprint and coastal planning schemes will zone the coastline in respect to proposed activities and land use. Effective coastal governance structures should ensure that future decision making is in line with the National Coastal Management Programme (CMP) and its proposed norms and standards to assist decision makers in respect to best practice.

Coastal set-back lines may be established for various reasons and there may be more than one set-back line in any given area. For example, one set-back line may be an anticipated erosion set-back line, while another may relate to aesthetics and control the height of buildings to protect a specific scenic landscape. Set-back lines will assist in controlling development along an ecologically sensitive or vulnerable area, or any area that poses a hazard or risk to humans.

Mr Vernon Gibbs-Halls spelt out the ultimate intention of the coastal set-back line is to “protect or preserve the following:

  • Coastal public property such as beach amenities and other infrastructure such as parking;
  • Coastal private property such as private residences and business properties;
  • Public safety in the face of extreme climate and other natural events;
  • The coastal protection zone; and
  • The aesthetics or “sense-of-place” of the coastal zone.”

A holistic and comprehensive engagement process is proposed to ensure that interested or affected members of the public have the opportunity to contribute meaningfully to the delineation of the proposed coastal set-back lines and the associated development management proposals.

The consultation process will be undertaken in two stages.

Initial public engagement is sought on the basis of the completed coastal hazard modelling. This offers the public an opportunity to engage on the scientifically defendable “risk‟ projection, and offer comments and suggestions on how the information can be used to manage development around the risk zone.

A second engagement round will follow once draft set-back lines have been determined. This will grant the public a chance to confirm that the proposed management lines are practical, appropriate, and responsive to the public comments raised during the first round of engagement.

The determination of risk zones or areas where coastal processes are active along the Garden Route is based on the application of a consistent delineation methodology applied along the study area. The process, as it unfolded, is described below and will be modelled using the following:

Data Sources – The data used for the various modelling processes in this study were sourced as:

  1. Aerial photography

A number of sets of aerial photographs covering the study area or portion thereof will be obtained from the National Geo-spatial Information (NGI), a component of the Department of Rural Development and Land Reform (DRDLR) (previously the Chief Directorate: Surveys and Mapping). All photography of the coastline will be georeferenced where necessary with particular emphasis placed on sections of sandy shoreline, where trends in long-term beach retreat or accretion will be identified.

  1. LIDAR

Existing ground topography information recently undertaken for the entire Eden coastline is accurate enough to determine the beach and rocky shore slopes. This will be used to determine the wave run up element of the analysis as well as to create the accurate digital elevation model upon which the simulation results were modelled upon.

  1. Wind and Wave data for the region

Wind and wave data will be sourced for the study area. Wave data will be obtained from actual and virtual wave buoys in the area, and analysed to determine wave heights, wave period, extreme (storm) values and wave direction. The results will then be used in a SWAN model to determine inshore (15m depth) wave characteristics.

  1. Determining the physical processes line (risk zone)

Determine the 1:10 and 1:100 year storm wave height. The 1:10 and 1:100 year storm wave height and period will be determined using available wave statistics.

  1. Determine the short term storm erosion risk along the coastline

During storm events the shoreline moves back temporarily, as the sand is lost but soon recovers to its pre storm position. This short-term loss is important to determine the risk lines. Usually this is done from measurements taken from shoreline surveys but as there is no such data available for the study area an average of 20m of short term shoreline retreat was applied along sandy sections.

  1. Determine the predicted future shoreline regression

The completed climate change related sea level rise study for the Eden District will result in the shoreline moving inland due to inundation as well as increased sediment losses from increased wave energy at the shoreline. To model this change, the most commonly applied model used is the Bruun‟s Rule (Bruun, 1962).

The amount of shoreline regression will depend on the amount of sea level rise expected. As sea level rise will vary into the future, it was decided to determine an appropriate sea level rise amount for each wave return heights. This is an attempt to match scenarios of similar risk of occurrence. Mr Vernon Gibbs-Halls pointed out, that the wave height and sea level rise are completely independent of each other, i.e. a 100 year wave event can occur with no sea level rise. To do this the maximum expected sea level rise of 1 000 mm will be equated to the 1:100 year horizon and a straight linear distribution needs to be applied to the lesser return periods.

  1. Estuaries

Estuaries are particularly dynamic ecological systems that display characteristics of both terrestrial and marine systems. This makes estuaries extremely complex and sensitive, and consequently also challenging to manage. Nevertheless, degradation of estuaries often results from increasing coastal development and the impact of human activities, and in order to preserve the remaining ecological functioning, biodiversity, and sustainable use of these sensitive coastal resources, effective cooperative management is essential.

Generally speaking, there remains a shortage of information regarding spatial, ecological and process dynamics of estuaries in the study area. To generate the necessary information within the scope of a regional coastal set-backs demarcation project will be prohibitively expensive. Consequently, an approach will be adopted that will use a simple contour height line to inform set-backs for estuaries, but with the option to defer to existing fine-scale management plans where such have been prepared.

It is recommended that the 5m amsl (Height above mean sea level) contour be used as a reference line to determine or inform development set-back lines in estuaries until such time as an adopted Estuary Management Plan and zonation plan delineate an appropriate coastal development set-back for individual estuaries.

Very important to the entire process is close co-operation and collaboration with all B municipalities, SANParks, CapeNature, and civil society to ensure that all experience and expertise is pooled for a successful venture.

For more information, please contact:

Mr Vernon Gibbs-Halls – Environmental Control Coordinator

Tel: (w) 044 803 1529 (c) 072 670 5108 / E-mail: vernon@edendm.co.za 

Ms Celeste Domingo – Acting Manager: Communications and IDP

Tel: (w) 044-803 1431 (c) 076 460 7306 / E-mail: domingo@edendm.co.za

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