westcoast district coastal set-back lines. presentation overview west coast district project...

Westcoast District Coastal set-back lines

Presentation Overview

• West Coast District project overview• ICM Background• Default coastal zone• Purpose of coastal set-back determination• Determination of risk – open coasts• Determination of risk – estuaries• Next steps• Questions asked of participants

Westcoast Set-back Lines Project - overview

• Royal HaskoningDHV core project team:– Tandi Breetzke, Gerard van Weele, Dr Andrew Mather & Petrie

Swart

• 8 steps1. Inception, preliminary work & stakeholder notification 2. Modelling to determine Coastal Processes / Hazard line 3. Stakeholder engagement now

4. Draft Set-back line(s) & coastal protection zone determination

5. Stakeholder engagement

6. Draft Final report

7. Stakeholder review

8. Final report

Background

• Vulnerability of Coastal Ecosystems / coastal zone• Impacts associated with dynamic processes (Both

erosion and accretion)• Global climate change – no longer debated & the coast

is bearing the brunt• In response - Integrated Coastal Management – Green

Paper – White Paper – ICM Act – specific management tools:– Coastal Committees– Coastal Management Programmes– Estuary Management Plans– Set-back/management lines

• Proactive rather than reactive response to issues

Default coastal zone

ICM Act Parameters

CPZ includes:• Littoral active zone• Protected area• Wetlands / lagoon etc.• Land below HWM• Land flooded during 1:50 flood or storm• 100m / 1km from HWM

FOR NOTING: Existing requirement for EIA:• 100m from HWM• Specified areas e.g. sea, estuary or littoral

zone

Default coastal zone

Set-back Lines – ICM Act, No 24 of 2008

“An MEC must… (a) establish or change coastal set-back lines—

(i) to protect coastal public property, private property & public safety;(ii) to protect the coastal protection zone;(iii) to preserve the aesthetic values of the coastal zone; or(iv) for any other reason consistent with the objectives of this Act; &

(b) prohibit or restrict the building, erection, alteration or extension of structures that are wholly or partially seaward of that coastal set-back line.”

Set-back Lines – for noting

• ICM Act Coastal set-back lines are proposed to be re-named as Coastal Management Lines to avoid confusion with the EIA Regulations Development Setback Lines

• Western Cape set-back methodology developed and extensively presented, tested and reviewed:– Initially at Milnerton and Langebaan– Then in the Overberg District

• Different methodology applied by the City of Cape Town• Lessons learnt / direction provided by the implementation

all of these studies will be applied in determining the West Coast coastal set-back / management lines

Set-back lines - For noting

• Lidar imagery used – excellent topographic data and aerial photos

• KMZ files prepared for viewing via Google Earth (access via websites)

• Technical report detailing process also available on website

• GIS viewer developed to allow easy access to data / images / draft lines

• Relevant environmental information was abstracted from the WCD CMP, IDPs and websites and reflected spatially

• Risk is depicted in the short, medium and long term

OBTAIN OFF SHORE WAVE HEIGHT DATAWAVE WATCH III

Deep water wave statistics

EXTREME STORM ANALYSISDetermine and rank largest storms on record

EXTREME VALUE ANALYSISPerform Extreme Value Analysis and determine 1:10, 1:20, 1:50 and

1:100 year wave statistics

• Scientific• Process based• No scope for

subjective assessments

Determination of the Physical Processes / Hazard Line(s)(Open coasts)

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Off-shore Wave Statistics

• Technical modeling process using: – Wave Direction– Wind Speed– Significant Wave Height– Peak wave Direction and period

• Interesting points to note:– When determining Significant Wave Height 36 individual

storm events were identified– 50% of these storms have occurred in the last five years

(less than a third of the total record period) – The largest storm on record occurred in Aug 2012

TRANSFORM OFF SHORE WAVE TO NEARSHORE WAVE STATISTICS (SWAN)

Wave direction & height

WAVE RUN UPCurrent wave run up (HWM), short, medium & long term wave run

up

SLR (BRUUN’S RULE)The amount of shoreline retreat for short, medium & long term sea

level rise

STORM BEACH RETREATA fixed distance - 20m

LONG TERM BEACH RETREATAnalysis of old aerial photography

• Scientific• Process based• No scope for

subjective assessments

Determination of the Physical Processes / Hazard Line(s)(Open coasts)

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TRANSFORM OFF SHORE WAVE TO NEARSHORE WAVE STATISTICS (SWAN)

Wave direction & height

WAVE RUN UPCurrent wave run up (HWM), short, medium & long term wave run

up

SLR (BRUUN’S RULE)The amount of shoreline retreat for short, medium & long

term sea level rise

STORM BEACH RETREATA fixed distance - 20m

LONG TERM BEACH RETREATAnalysis of old aerial photography

• Scientific• Process based• No scope for

subjective assessments

Determination of the Physical Processes / Hazard Line(s)(Open coasts)

Transform Off-shore to In-shore Wave Statistics

• Technical modeling process• Use the Delft SWAN (Simulating WAves Nearshore) model

(http://www.swan.tudelft.nl) to transform offshore waves• Take account of bathymetric (sea bottom) changes• Determine the in-shore wave statistics

TRANSFORM OFF SHORE WAVE TO NEARSHORE WAVE STATISTICS (SWAN)

Wave direction & height

WAVE RUN UPCurrent wave run up (HWM), short, medium & long term wave run

up

SLR (BRUUN’S RULE)The amount of shoreline retreat for short, medium & long term sea

level rise

STORM BEACH RETREATA fixed distance - 20m

LONG TERM BEACH RETREATAnalysis of old aerial photography

• Scientific• Process based• No scope for

subjective assessments

Determination of the Physical Processes / Hazard Line(s)(Open coasts)

Wave run up modeling

• Near-shore waves modeled as run up the beach

TRANSFORM OFF SHORE WAVE TO NEARSHORE WAVE STATISTICS (SWAN)

Wave direction & height

WAVE RUN UPCurrent wave run up (HWM), short, medium & long term wave run

up

SLR (BRUUN’S RULE)The amount of shoreline retreat for short, medium & long

term sea level rise

STORM BEACH RETREATA fixed distance - 20m

LONG TERM BEACH RETREATAnalysis of old aerial photography

• Scientific• Process based• No scope for

subjective assessments

Determination of the Physical Processes / Hazard Line(s)(Open coasts)

Sea Level Rise (Bruuns Rule) & Storm Beach Retreat• Using Bruun’s Rule predicted sea level rise reflected as low

(200mm), medium (500mm) & high risk (1000mm)• Storm beach retreat - determined by measuring shoreline

before and after storm events, however this was not possible so a conservative allowance of 20m has been provided for.

TRANSFORM OFF SHORE WAVE TO NEARSHORE WAVE STATISTICS (SWAN)

Wave direction & height

WAVE RUN UPCurrent wave run up (HWM), short, medium & long term wave run

up

SLR (BRUUN’S RULE)The amount of shoreline retreat for short, medium & long

term sea level rise

STORM BEACH RETREATA fixed distance - 20m

LONG TERM BEACH RETREATAnalysis of old aerial photography

• Scientific• Process based• No scope for

subjective assessments

Determination of the Physical Processes / Hazard Line(s)(Open coasts)

Long term beach retreat

• Determine the long term erosion based on a detailed analysis of historical shoreline positions from available aerial photography for sandy shorelines only.

• Stable coastlines and accreting coastlines will be assumed to require no retreat.

Examples - Strandfontein

Examples –Elandsbaai (Railway Line)

[graphic to be added by Andrew all lines for railway line]

Examples – Yzerfontein (Sandy shoreline)

Examples – Yzerfontein (Rocky shoreline)

1:50 or 1:100 YR FLOODLINESIdeal but no floodlines available

5m and 10m contour lines

Vegetation assessment - use in part of set-back / management line determination

• Scientific if floodlines used

• Vegetation assessment to inform process

Determination of the Physical Processes / hazard Line(s)(ESTUARIES)

Hazard line determination for estuaries

• Use the existing 1:50 or 1:100 floodlines to determine hazard edge

• In the event of no suitable 1:50 and 1:100 yr floodlines then map the +5m and +10m above mean sea level contours.

• +5m is typically the height floodwater will rise to in a closed estuarine system.

• +10m allows a buffer for future SLR as well as estuarine vegetation regeneration areas.

Examples - Langebaan

Examples – Paradise Beach

Example –Berg River

Way forward

1. Assess the environmental, heritage & access layers to determine any additional set back allowances.

2. Assess the economic issues to determine any additional or reduction in set-back allowances to accommodate economic nodes/activities

3. Determine the extent of set-back / management line in the study area.

4. Add authority perspective to determine the CPZ boundary

Questions asked

• Are you happy with the anticipated storm erosion estimate?

• What are the environmental issues that should be considered?

• Where are the environmentally sensitive areas?• Where are the wind-blown sand corridors?• How should authorities respond to this determination of

risk?• What controls could be included for urban areas

seaward of the physical processes / hazard line?

www.rhdhv.com/pages/services/environmental/current-projects.php

Or

www.eadp.westerncape.gov.za/calendar/month

(click on calendar, click on these w/s to find documents)