Executive Summary - Coastal Sea Level Rise Risk Assessment
Attachment 2 to the Sea Level Rise report, providing an executive summary of the CRD's first phase coastal risk assessment project.
Executive Summary
Project Context. With global sea levels projected to continue rising, public and private assets and shoreline land uses across the Capital Regional District (CRD) have the potential to experience an increase in frequency and magnitude of periodic inundation events as well as permanent inundation. The Coastal Sea Level Rise Risk Assessment project has been developed as a first phase in CRD’s multi-year project to gather information to support future analysis and policy response for sea level rise (SLR) within the CRD. CRD is the first BC regional district to have completed mapping based on the draft provincial guidelines for floodplain mapping and intends to use the mapping and findings from this project to consult and provide feedback to the Province on the proposed guidelines, and planning for the impacts that SLR will have in the CRD region. Mapping based on provincial guidelines shows that any significant impacts from sea level rise will not be felt until 2050 or beyond, and advanced planning can be applied to help avoid or manage such impacts before they are realised.
Uses and Limitation. This project is the very first step to assess how the region’s shoreline may look 35, 85 and 185 years in the future. The mapping from this study considers static sea level rise, coupled with relatively extreme 1 in 500 year storm surge conditions, so while areas may be depicted within an inundation zone, this does not mean these areas will necessarily experience flooding due to sea level rise and storm surge in the future. Significant further analysis is necessary to fully understand what the effects of future sea level rise may be in these coastal areas. Establishing flood hazard boundaries is a responsibility of local government, and each municipality within the region will determine how they will respond to future sea level rise. Once future flood hazard area boundaries are established by municipalities, there are many tools that can be used to address sea level rise within these areas. These include planning and regulatory tools, land use change or restriction, structural tools including flood protection works, and non-structural tools such as soft armouring by wetland construction. Future work for specific locations should be used to confirm the data used and produced in this report.
Project Objectives. The primary purpose of this project was to identify and map areas that are vulnerable to SLR within the CRD. The secondary purpose was to understand the potential economic consequences of SLR, thereby providing information to support development of future policy and land use regulations. The technical scope of work to deliver these objectives was designed to align with the available project funding, and the mapping (Appendix A) and other data reporting (Appendix B) was focused on 24 key areas (“Sea Level Rise Focus Areas”) that were selected because of the relatively high levels of expected future inundation and / or the key community assets that are present in those areas. Three high-level case studies were developed to help identify the potential service disruption effects that could occur under sea level rise and storm surge conditions. These case studies were for transportation disruption (based on disruption to Highway 14 south of Shirley), local community disruption (in the Oak Bay Windsor Park residential area), and business disruption (in the Victoria Inner Harbour).
Approach to Mapping. The maps developed for the project show the anticipated future shoreline at high tide, and during storm surge conditions in 2050, 2100 and 2200. The mapping is based on the 2011 Province of BC Coastal Floodplain Mapping Guidelines and Specifications Report, and uses the recommended SLR levels for those time periods and 1 in 500 year storm surge conditions. A digital elevation model was developed for across the region, and then factors that will influence future sea levels were layered onto the model to give an estimation of the future shoreline. These factors include projections for static SLR, highest high water large tide (HHWLT) values collected from hydrological monitoring at over 30 sites across the region, vertical land elevation figures which address seismic activity, and the 1 in 500 year storm surge conditions.
SLR Focus Areas. Once maps were developed for the entire CRD coastline a workshop was run with the CRD Project Team to identify the key assets (e.g. key municipal infrastructure) that exist within the coastal areas that could be subject to flooding for the scenarios considered. This was used to help define SLR Focus Areas for a selection of areas with key assets and relatively high levels of expected future inundation. A set of 24 SLR Focus Areas were then defined and for each area maps were produced to show inundation levels for the different sea level rise scenarios (for 2050, 2100 and 2200, and with and without 1 in 500 year storm surge conditions).
Description of land and assets within each SLR Focus Area. Data were compiled to define land use, shoreline sensitivity to sea level rise, valuation of land and improvements, roads and presence of key public assets within the areas that would be flooded within the selected scenario of SLR in year 2100 plus the 1 in 500 year storm surge conditions. These data were provided by CRD and included: municipal zoning data, BC Assessment data for actual use of land and market valuation of land and improvements, location of roads, and replacement cost estimates for key public assets. These data are reported in Appendix B and help describe the assets that would theoretically be at risk for the selected scenario if the 1 in 500 storm surge scenario occurs and assuming no management measures were put in place.
- Key Findings and Recommendations. a. As a result of varying topography there are different levels of inundation that may occur across the CRD coastline for the SLR and storm surge scenarios that were considered as part of this project. Many of the lower lying areas that may have higher levels of inundation coincide with developed and populated areas, leading to the potential for infrastructure damage, safety risk and service disruption. As well as the key areas represented in the 24 SLR Focus Areas, there are other parts of the CRD outside of these selected areas that could have inundation effects under these scenarios and these areas should also be considered during future mapping and planning work. b. For the 24 Focus Areas used for this project the total valuation of land and improvements (as defined by BC Assessment) within the year 2100 + 500-year storm surge inundation line ranges from $330 million (for the Oak Bay Windsor Park SLR Focus Area) to $3.4 million (Albert Head SLR Focus Area). These are total asset values based on market valuation and do not infer expected losses that would occur from periodic inundation. Across the 24 SLR Focus Areas, BC Assessment data show that residential property has the highest total assessed value followed by commercial and then civic, institutional and recreational land uses. c. The key assets that would be at least partially inundated for this selected scenario (and assuming no future management measures are put in place) within the 24 SLR Focus Areas are principally network structures for water and wastewater, and some road bridges could be affected. There is the potential for some large businesses to be at least partially inundated, with some of their operations (e.g. ferry, float plane) being regionally important for the tourism sector. There are also a large number of marine docks that are within the inundation line for this scenario, though it has not been assumed that infrastructure damage would necessarily occur to the dock structures themselves. d. One of the main areas of Highway inundation for the year 2100 plus 1 in 500-year storm surge scenario is at Highway 14 between Sooke and Port Renfrew, and this area was used as a case study for transport service disruption. In other SLR Focus Areas there are a range of local and connector roads that would be subject to inundation for this scenario. e. The key recommendation is that CRD use the analysis and mapping conducted for the 24 SLR Focus Areas as an evidence base for the identification and appraisal of options for a future model bylaw that deals with SLR management for the CRD. In particular, the data reported in this project demonstrates the types of land use, key assets, services and indicative economic values that exist in areas at inundation risk, and this evidence will help to develop the objectives for and assess the impacts of different management options.