INNOVATION September-October 2012

Climate Change Adaptation Guidelines for sea Dikes and Coastal Flood Hazard Land Use In BC, the Province ’s role in flood hazard management includes providing technical guidance and advice for flood management authorities (mainly local governments) on design of flood protection structures (eg, dikes) and flood hazard area land use. In 2011 the Flood Safety Section of the Ministry of Forests, Lands and Natural Resource Operations published draft Climate Change Adaptation Guidelines for Sea Dikes and Coastal Flood Hazard Land Use (www. env.gov.bc.ca/wsd/public_safety/flood/fhm-2012/draw_report. html#1). The purpose of the project was to determine reasonable sea level rise planning benchmarks for coastal development and methods for incorporating sea level rise into coastal dike design and defining shoreline setbacks and flood construction levels. The draft guidelines discussed below are presented in three volumes: Policy Discussion Paper, Sea Dike Guidelines and Coastal Flood Hazard Land Use Guidelines.

How Much sea Level rise should We Plan For? The Policy Discussion Paper recommends planning for 0.5 m of global sea level rise by the year 2050, 1.0 m by the year 2100 and 2.0 m by the year 2200 (figure 1). This recommendation is based on a number of factors including a review of sea level rise projections published in 2007 or later, practices adopted in other jurisdictions and relative sea level rise projections available in BC. Because the scientific understanding of global and local sea level rise is continuing to advance, the recommended sea level rise planning curve will be reviewed and updated every five years. sea Dike Guidelines The Sea Dike Guidelines provide a methodology for incorporating tides, sea level rise, storm surge, wind set-up and wave effects into calculations of dike crest elevation and other dike design factors. Because deeper water results in larger waves, sea level rise has a compounding effect on near-shore extreme water levels. For some exposed areas, such as the example depicted in figure 2, maintaining dikes in their current locations will require raising them by several meters to provide an adequate level of flood protection. Coastal Flood Hazard Land Use Guidelines The Guidelines for Management of Coastal Flood Hazard Land Use provide a method for estimating the future location of the natural boundary, including the effects of tides, sea level rise, storm surges and wind/wave action. To ensure new buildings and infrastructure are protected from future coastal flooding throughout their lifetimes, today’s construction needs to plan for future conditions. These guidelines also suggest the use of “sea level rise planning areas” to gradually change land use zoning and construction requirements over time to accommodate sea level rise. mapping-2011.pdf ). Floodplain maps are an essential tool for identifying areas that may be impacted by flooding, and planning flood response. They can provide a visual representation of the Guidelines for Coastal Flood Hazard Land Use and key information for land use planners to determine what lands are safe for development and where development should be avoided or adjusted to minimize damages from occasional flooding. The town of Campbell River was used as a case study to demonstrate application of the guidelines. Costs of Adaptation to sea Level rise Coastal Floodplain Mapping Guidelines To accompany the guidelines discussed above, the Flood Safety Section also commissioned development of Coastal Flood Plain Mapping – Guidelines and Specifications that include consideration of sea level rise. (www.env.gov.bc.ca/wsd/ public_safety/flood/pdfs_word/coastal_floodplain_ The introduction of sea level rise considerations into flood hazard management will result in costs for increasing the standard of flood protection and providing flood protection in newly-exposed areas.

FIGURE 1

Figure 1. The red line is the recommended sea level rise planning curve for BC of 0.5 m by 2050, 1.0 m by 2100 and 2.0 m by 2200. The shaded gray area represents the ranges of global sea level rise published in the scientific literature. Source Ausenco Sandwell.

FIGURE 2

Figure 2. Conceptual drawing of increased coastal dike elevation and width required to accommodate increased extreme water height resulting from year 2100 sea level rise. Source: Ausenco Sandwell.

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