The Town of Mahone Bay Living Shoreline

In 2022, Coastal Action implemented a 60-meter living shoreline in the Town of Mahone Bay to mitigate current and future climate change impacts such as sea level rise, storm surge, and increased precipitation, which result in flooding, coastal erosion, and an increase in contaminated stormwater runoff. To help protect the town and shoreline from coastal hazards, Coastal Action proposed the “Flood Protection and Shoreline Stabilization Project,” better known as Mahone Bay’s Living Shoreline, to the Town of Mahone Bay. The project was built on conceptual designs within the Flood Prevention and Shoreline Enhancement Plan produced in 2016 by CBCL Limited for the Town. The plan includes in-depth modelling and conceptual shoreline protection options and designs developed from a detailed study of current and future local shoreline, wave, and water level conditions. Contrary to previous flood prevention strategies that focused on hard infrastructure, this project used a nature-based approach that provided many co-benefits such as shoreline protection, habitat creation, carbon sequestration, and an increase in biodiversity. The living shoreline was constructed in June 2022 with the help of volunteers and community members to serve as a scalable proof of concept. It comprises rock sills, a tidal wetland, and a vegetated bank. The project is being monitored and research is being conducted at the demonstration site by research partner, TransCoastal Adaptations, to test the applicability and success of natural infrastructure techniques in buffering climate change impacts under variable winter conditions. The next steps for the project include continuing to seek funding to expand the living shoreline along an additional 700 meters of coastline.

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Understanding and Assessing Impacts

The Town of Mahone Bay’s 2013 Municipal Climate Change Action Plan identified the climate hazards that were expected to occur more frequently in the future, including coastal and inland flooding, and extreme weather events, such as hurricanes, winter storms, heat waves, and drought. These hazards will likely result in increased flooding, coastal erosion, and contaminated stormwater runoff entering the harbour.

A 2016 study examined how future sea level rise would impact coastal flooding and storm surges in Mahone Bay. Sea level rise projections were obtained from Fisheries and Oceans Canada and were based on regional projections from the IPCC Fifth Assessment under the business-as-usual RCP 8.5 scenario. According to projections, Mahone Bay could experience 0.53 m of sea level rise by 2065 and 1.08 m by 2100. Sea level rise projections were then applied to stormwater and storm surge levels to determine maximum water levels in 2045, 2065, 2100, and 2115. In 2015, Mahone Bay’s higher water high tide was 1.52 m and the stormwater/storm surge levels ranged from 1.86 – 2.67 m, with Hurricane Juan representing the maximum upper bound of 3.02 m. Based on calculations incorporating sea level rise, by 2065, Mahone Bay could face higher water high tide at 2.05 m and stormwater/storm surge levels ranging from 2.39 – 3.20 m. A hurricane like Hurricane Juan could result in up to a 3.55 m storm surge. The project website includes an interactive flood map of the immediate area that can be used to visualize the effects of tide and storm surges both with and without installing a living shoreline.

Identifying Actions

In 2016, a Flood Prevention and Shoreline Enhancement Study was initiated, which assessed future water levels in Mahone Bay under climate change and also proposed different adaptation options that incorporated future water level projections. Traditionally, the community has used hard infrastructure like rock walls or stone armouring to mitigate flooding and storm surges. However, many of these protection mechanisms are deteriorating, being overtopped, or are at risk of being washed out. Recommended adaptation options ranged from coastal flood mitigation such as raising roads, floodproofing buildings, and adding armoured stone walls, to coastal erosion mitigation, such as living shorelines. It wasn’t until 2020 when Coastal Action proposed a collaborative project that the living shoreline planning began to move forward. By having a non-profit organization as the lead on this project, the living shoreline project was eligible for more diverse funding streams than a municipality alone would be eligible for. Coastal Action reached out to industry and academia and fostered successful partnerships to increase the expertise and community involvement of this project.

Implementation

Construction of the living shoreline began in June 2022 with the help of local volunteers and community members. The 60-meter living shoreline in Mahone Bay Harbour on Edgewater Street was constructed of rock sills, a tidal wetland, and a vegetated bank. Rock sills were introduced parallel to the shoreline, to reduce wave energy and storm surge impacts. The tidal wetland, situated between the rock sills and vegetated bank, was planted with native species to filter stormwater runoff and reduce wave energy. The vegetated bank was planted behind the tidal wetland and was populated with native shrubs and herbaceous perennials to help stabilize the soil. Both the wetland and vegetated bank provide valuable habitat for local terrestrial species, while the tidal wetland and rock sills provide valuable habitat for local marine species. A trail along the living shoreline was also expanded to provide public access and interaction with the project.

Outcomes and Monitoring Progress

The Mahone Bay Living Shoreline project had three main goals: minimize erosion, minimize coastal flooding risks and hazards, and improve the water quality of contaminated stormwater runoff entering the harbour. An additional long-term goal of the living shoreline was to create infrastructure that could naturally adapt to climate change. Since construction, the living shoreline has been monitored to ensure the plants remain undisturbed and can establish roots. Fortunately, the living shoreline remained undamaged by the recent hurricane Fiona that devastated other areas of Atlantic Canada. Research will be conducted to measure the effectiveness of the natural infrastructure including progress toward the three main living shoreline goals. The results of the monitoring and research will be compiled in a 2023 report. Finally, to support community education and engagement, a project website and interactive 3D map of Mahone Bay and the living shoreline were launched by Coastal Action.

Next Steps

The 2016 project recommendations originally designed a living shoreline that would extend 700 meters in length from the Mushamush River mouth to the Ernst Brook Bridge along Edgewater Street. Further funding will be required to finish the entire length of the living shoreline. The next steps include seeking provincial, federal, or private sector funding opportunities to expand the living shoreline either in phases or as a whole.

The Mahone Bay Living Shoreline project was selected as one of six case studies to help inform TransCoastal Adaptation’s Making Room for Movement: A Framework for Implementing Nature-based Coastal Adaptation in Nova Scotia. Projects such as Mahone Bay’s Living Shoreline have been recognized for demonstrating positive community engagement, strong political leadership, and a willingness to implement unique nature-based techniques to adapt to climate change.

Resources

Link to Full Case Study

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