Greening shorelines to enhance resilience: An evaluation of approaches for adaptation to sea level rise

摘要

This paper describes the results of a study intended to assist the advancement of policies and practices in British Columbia, Canada, to promote increased consideration of the use of "soft" shoreline armoring alternatives, within the context of expected climate change and sea level rise (SLR), to provide protection against coastal storm-related flooding, while maintaining or enhancing the marine ecological services provided by the foreshore marine environment. The study was initiated by the Stewardship Centre for British Columbia (SCBC), with the support of Natural Resources Canada (NRCan). The intent of the study was to consider specific Case Example sites, and evaluate the effectiveness of the "soft" shore armoring alternatives, compared to an equally appropriate "hard" alternative, both developed based on the following requirements: 1. Ability to accommodate 1 m of local SLR. 2. Provide a defined level of safety against flooding during an expected coastal storm. 3. Maintain, enhance, or minimize any effect on the marine ecological services provided by the adjacent inter-tidal area. 4. Develop equivalent life cycle cost estimates for both the "hard" and "soft" alternatives including initial capital cost and expected maintenance cost over the service life of each concept. For the purpose of this evaluation, three conceptual "soft" shore alternatives were selected for evaluation: 5. Use of a mainly beach nourishment or shore replenishment alternative, consisting of supply and placement of typical beach inter-tidal substrate materials at the site. 6. Use of nearshore — mainly inter-tidal — rock features, including boulder clusters and inter-tidal and sub-tidal rock habitat reefs. 7. Use of a typical headland-beach system to maintain a conventional beach inter-tidal substrate in an area exposed to incident waves from more than one primary direction. For the first two case example sites, the "soft" shore alternative is applied to the adaptation of an existing community scale hardened shoreline. For the third case example site, the "soft" shoreline alternative was already in place. In this case, the "soft" shore alternative is compared to a conventional sea dike alternative. In all cases, the "hard" and "soft" alternatives provided appropriate levels of flood protection for the specific case example land use behind the shoreline. The results of this assessment indicate that in all cases, the "soft" alternative provides a significant cost advantage over the "hard" alternative. The margin of cost saving varies, ranging from approximately 30% of the cost of the "hard" alternative for Case 2 to 70% of the cost of the "hard" alternative for Case 1. In all cases, based on the evaluation framework for ecological services developed for this study, the "soft" alternatives provided better or neutral opportunities to maintain ecological resilience of the shoreline.