Credit 1.2: Setback and Impact Avoidance
This credit encourages setting back existing or proposed buildings and other major improvements far enough from the shoreline or bluff crest to avoid the need for shore protection structures over the life of the improvements.
How to proceed
A) Regulatory Setback:
Many coastal jurisdictions have regulations defining the minimum setback from the OHWM/NB, or a similar baseline. Some regulations may exceed the setbacks determined according to the methods described in this section. In all cases, to meet this credit, the setback in your project must equal or exceed the setback required by regulation in your jurisdiction.
If you can demonstrate that the existing regulatory setback meets or exceeds the 75-year setback, the 75-year setback + SLR or the total impact setback (see below), then you are eligible for the points awarded for these setbacks.
B1) 75-year Setback
The first step is to estimate the erosion rate or range of likely erosion rates for your site. Erosion rates may be available for some areas through:
• Geological/Geotechnical reports
• USGS/Environment Canada published maps
• Beach Watchers and other credible citizen science organizations
However, these sources are quite limited spatially, and erosion rates can vary significantly over short distances, so applying a rate from a different location must be done with caution. Also, erosion rates cannot be determined with only short term data.
A qualified professional geologist or coastal engineer can help you determine a site-specific erosion rate, using aerial photos. Estimate the erosion rate from the best available air photos at 1:12,000 scale or better over the longest time period possible. Ideally, this would be 50 years or more, but due to limited air photo and survey records, 30-40 years is more realistic. Alternatively, small scale (less than 1:10,000) topographic or other survey maps of the site over similar time periods can be used. These maps should show bluff crest or similar identifiable shoreline features, and include documented methods so that others can assess the level of accuracy.
Once the erosion rate is estimated, the setback for the life of a building (minimum 75 years) can be calculated. For example:
If estimated average erosion rate = 4 in (10 cm)/year
Then 75-yr setback = 300 in or 25 ft (8 m) from OHWM.
In the absence of any data to support an estimate of erosion rates as described above, use a minimum setback of 75 ft (25 m).
C) 75-year Setback + SLR
To assess the impact of sea level rise, the following steps are recommended:
1. Identify the predicted sea level rise (SLR) for your area; for example, SLR levels of 0.5 m to the year 2050, 1.0 m to 2100 and 2.0 m to 2200 are predicted for most of the BC coast (Ausenco Sandwell, 2011 – see “For more information”). Several other coastal jurisdictions also assume a sea level rise of about 1 meter by the year 2100.
2. Determine how this will change the location of the OHWM on your property over the next 75 years or the life of the project, whichever is greater. This may require the assistance of a land surveyor to show this new location on the ground and on a site map. Apply the Basic Setback measured from this future OHWM/NB.
(Bonus) Total Impact Setback
For bluff and steep bank sites, the risk of large slope failures/landslides due to shoreline erosion and typical bluff failures must also be factored in to determine an adequate setback. This can be done in a general sense by applying an additional buffer of 25 ft (7.5 m) over and above the projected erosion rate-based setback. A more precise approach is to determine the largest slope failure or bluff recession in the local area over recent decades and measure the distance that the shoreline receded in that event—either on the ground or in comparing before and after aerial photos. In areas with a history of larger landslides, a minimum of twice this additional setback distance would be required.
(Bonus) Feeder Bluff
As noted above, this bonus point is to help maintain sediment input to shorelines by feeder bluffs and with it, the habitats of a bluff-beach system, particularly forage fish and other habitats reliant on sediments. Feeder bluff mapping throughout Puget Sound may be found at the Washington Dept. of Ecology website http://www.ecy.wa.gov/programs/sea/shorelines/FeederBluffs/mapping/index.html.
Where this credit applies
This credit applies to all sites with an existing or proposed home or other major building. This credit is particularly important for bluffs that provide sediment to the natural shoreline system, known as feeder bluffs, and sites exposed to high wave-energy (Johannessen and MacLennan, 2007). The use of an adequate setback to avoid damage over the life of the building or improvement is an important design consideration. Determining an adequate setback must take sea level rise and climate changes into consideration, which generally will require larger setbacks.
This credit offers up to 10 base points and 4 bonus points.
|Setback/Impact Avoidance (base points: choose A, B, or C)||
|A. Regulatory Setback: Meet the basic setback from the OHWM/NB required in your local jurisdiction, with no variance or relaxation of that local code requirement. This setback may be specified in a zoning regulation, shoreline development or habitat protection regulation, or be determined on a site-basis by local regulators. OR||
|B-1. 75-year Setback: Provide the distance from OHWM/NB needed for natural beach or bluff processes, without armoring or other major protective action, over 75 years or the life of the building, whichever is greater.B-2. Alternatively, if there are no data available to estimate an erosion rate, allow a setback of minimum 75 feet (25 m). OR||
|C. 75-year Setback + SLR: Provide the distance from OHWM/NB needed for natural beach/bluff processes, without armoring or other major protective action, over 75 years or the life of the building, whichever is greater – plus take account of changes in the level or location OHWM/NB and changes in erosion processes that which will occur due to projected sea level rise (SLR).||
|Bonus (available once 1 or more base conditions have been met)||
|Total Impact Setback: If option B, B-2 or C is achieved, provide an additional buffer to allow for a larger erosional or landslide event beyond the 75-year setback requirements. General rule of thumb is 25 ft (7.5 m) for this additional setback unless more detailed geologic/ geotechnical work is completed and indicates otherwise.||
|Bluff site: Apply any of the above setbacks at a bluff site. This bonus point is to encourage the maintenance of a “feeder bluff” (sediment input) function as well as to maintain the diverse habitats of a bluff-beach system.||
For more information
Arlington Group Planning and Architecture Inc. et al. 2013. Sea Level Rise Primer: A Toolkit to build adaptive capacity on Canada’s south coasts. Go to http://www2.gov.bc.ca/ and enter “sea level rise adaptation primer” in the search box.
Ausenco Sandwell. January 2011. Climate Change Adaptation Guidelines for Sea Dikes and Coastal Flood Hazard Land Use. For BC Ministry of Environment. Go to http://www2.gov.bc.ca/ and enter “coastal flood hazard” in the search box.
Bornhold, B. 2008. Projected Sea Level Changes for British Columbia in the 21st Century. 12 pg. Go to http://www2.gov.bc.ca/ and enter “Bornhold sea level changes” in the search box.
Coastal Geologic Services. 2010. Current and Historic Coastal Geomorphic (Feeder Bluff) Mapping of San Juan County, Washington. Friends of the San Juans. 76p. www.sanjuans.org/maps.htm
Johannessen, J.W. and A.M. MacLennan, 2007. Beaches and bluffs of Puget Sound and the Northern Straits: A valued ecosystem component. Published by WA Sea Grant, Seattle WA. Go to http://pugetsoundnearshore.org/technical_reports.html and scroll down to report 2007-04.
Lamont, G., J. Readshaw, C. Robinson and P. St-Germain. 2014. Greening Shorelines to Enhance Resilience; an Evaluation of Approaches for Adaptation to Sea Level Rise. Prepared for the Stewardship Centre of BC. 46 p. http://stewardshipcentrebc.ca/Green_shores/resources/
University of Washington Climate Impacts Group and Washington Department of Ecology. 2008. Sea level Rise in the Coastal Waters of Washington State. 11 pg. http://www.cses.washington.edu/db/pdf/moteetalslr579.pdf
Washington Dept. of Ecology, Feeder Bluff Mapping of Puget Sound http://www.ecy.wa.gov/programs/sea/shorelines/FeederBluffs/mapping/index.html