Nature-Based Solutions for Coastal Resilience
The Belcher St. Tract 5 Realignment demonstrates an Atlantic Canadian case study involving multiple nature-based adaptations.
Introduction
The Belcher St. project harnessed the forces of nature-based adaptation approaches by performing managed realignment as well as the pilot of a living shoreline. This case study represents a paradigm shift in the way we approach coastal management by moving away from traditional hard engineering towards more soft approaches. This demonstrates how habitat enrichment can be achieved over time, while also enhancing the resiliency of the Cornwallis River System and reducing the flood risk to surrounding communities.
The Belcher St. dykeland is located near Kentville, NS, on the Cornwallis River — a large, macro-tidal river that flows into the Bay of Fundy's Minas Basin.
Historical Context
Prior to restoration, the site was characterized by active and fallow agricultural land, protected by 1.34 km of dyke. The dyke was positioned close to the bank of the main river channel, eliminating the natural floodplain. As a result, the site was subject to several climate related issues, including erosion, failure of the dyke system, inadequate drainage, and potential overtopping during storms and storm surges.
Restoration Initiation
In 2017, CBWES Inc. was commissioned by Nova Scotia Department of Agriculture to develop a realignment and floodplain restoration plan for tract 5 of the Belcher St. Marsh.
Objectives
The main goals of the project were to reduce the overall amount of the dyke infrastructure; restore ~9.7 hectares of tidal wetland habitat; contribute to efforts to increase the resiliency of the Cornwallis River system; and reduce the flood risk of the towns of Kentville, New Minas, and Port Williams.
Design
Two nature-based adaptation techniques were used in this project: managed realignment and the incorporation of a living shoreline.
Managed realignment involves the reintroduction of the tidal regime to areas of previously reclaimed low-lying land, most commonly through breaching or removing the existing flood defense. This nature based technique was used to restore ~9.7 hectares of saltmarsh habitat by replacing a section of the former dyke with a shorter but stronger dyke.
Living shoreline techniques use natural, biodegradable materials, as well as plants instead of hard stone, to protect against coastal erosion while maintaining the integrity of the coastal ecosystem.
Monitoring Site Trajectory through Habitat Mapping
Habitat maps are also referred to as surface cover maps. They are a great way to depict how plant communities are changing over time which is important as vegetation is a key parameter in ensuring restoration success!
Baseline Conditions (Pre-Breach)
In 2017, the Belcher St. restoration site was largely characterized by pasture (15.4%) and wet meadow (11.5%) vegetation. At this time, there were no salt tolerant species present behind the dyke infrastructure since tidal inundation had been inhibited for decades. Despite salt marsh habitat accounting for 20.9% of the site, it was notable that the foreshore marsh was experiencing coastal squeeze in certain areas, threatening the integrity of the dyke system.
Coastal squeeze: intertidal habitat loss which arises due to the high water mark being fixed by a defence and the low water mark migrating landwards in response to sea level rise. (Pontee, 2013)
Year 1 Post-Breach
The realignment of the western component of the dyke in June 2018 resulted in drastic vegetation community change. This year represented a transitional phase in site development, shifting from agricultural land towards salt marsh habitat. Despite the high prevalence of bare ground (29.6%), dead shrubs/trees (10.6%), and dead vegetation/heavy sedimentation (10.1%), it was evident that the wet meadow and pasture vegetation that had previously dominated the site had diminished. These plant communities had slowly been replaced by salt tolerant species.
Another noteworthy change to the site from the previous year included the installation of a living shoreline (root wad) in an area that had been particularly vulnerable to erosion.
Oblique photograph of the study site in 2018.
Year 2 Post-Breach
Species richness developed considerably from the previous year as the salt marsh ecosystem began to fluorish. The areas that appeared lifeless and bare in the previous year had experienced rapid recolonization of vegetation as bare areas became largely established by mixed colonizers (30.8%) comprised of halophytic and brackish wetland plants.
Oblique photograph of the study site in 2019.
Colonization of a variety of species; notably, Epilobium ciliatum.
Adaptive management approaches were undertaken in the form of nature based strategies to reduce the amount of scouring around the living shoreline. This involved the installation of live silt fences, wattle fencing, and vegetation mats in combination with transplanting marsh vegetation to stabilize the surface.
Scouring around the living shoreline was addressed by adding materials such as brush to capture sediment.
Adaptive management approach to reduce flow velocities that were creating scour around the living shoreline.
Year 3 Post-Breach
At this time, the site had developed plant communities more similar to the reference salt marsh than its previous agricultural identity. The restored area that was previously mixed colonizers became largely colonized by Spartina pectinata (16.4%) and Spartina alterniflora (8.6%), which are target salt marsh species. It was notable that freshwater marsh vegetation such as Typha latifolia (5.5%) persisted in the back of the site.
Oblique photograph of the study site (2020).
The adaptive management approach that had been undertaken in 2019 had shown to be successful given that the living shoreline was no longer scouring, sediment had been deposited, and vegetation had begun to establish.
Sedimentation surrounding the living shoreline (root wad).
Conclusion
The Belcher St. Tract 5 Realignment showcased an Atlantic Canadian example of how multiple nature-based adaptation techniques including managed realignment schemes and a hybrid living shoreline were successful in improving coastal resilience. These positive results were attributed through monitoring multiple parameters including vegetation community structure.
By displaying a time series of change in vegetation communities using habitat maps, there was greater ease of quantifying and analyzing restoration trajectory. As a result, we were able to see the spatial and temporal scales in which the original agricultural vegetation converted into a transitional phase, then finally established into halophytic vegetation communities. The success of this site can help to guide future restoration strategies and build upon the lessons learned throughout this project.
Direct comparison of habitat maps from 2017 (left) - 2020 (right).
References
Pontee, N. (2013). Defining coastal squeeze: A discussion. Ocean & Coastal Management, 84, 204–207.
