Making room for wetlands: Implementation of managed dyke realignment for salt marsh restoration and climate change adaptation in Nova Scotia

Making Room for Wetlands is an ongoing initiative (as of 2020) spearheaded by St. Mary’s University and the Nova Scotia Department of Agriculture along with others to address flood risks in multiple communities along the Bay of Fundy by realigning existing hard infrastructure. Existing hard infrastructure including dykes and aboiteaux have proven costly to maintain and ineffective in providing protection from intensifying flood events and storm surges. In order to ensure future adaptive capacity that is economically viable, dykes may be shortened and/or repositioned along with the removal and/or repositioning of aboiteaux. These actions will work to deliberately flood portions of previously drained lands in order to restore naturally occurring salt marshes. These marshes work as a natural defense to flooding by retaining rainwater and buffering storm surges. The goal of the Making Room for Wetlands initiative is to provide a road map in order to guide future projects of a similar nature around the province. Until now, efforts to address coastal flood risks around the Province have been mired by jurisdictional confusion creating grey areas and exposing policy gaps.

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Understanding and Assessing Impacts

Much of the work being done in Truro, Nova Scotia is in response to a fall 2012 major flood event which breached local dykes and forced the evacuation of a nearby high school. Those organizations affiliated with the Making Room for Wetlands – spearheaded by St. Mary’s University (SMU) and CB Wetlands and Environmental Specialists (CBWES) – partially relied on flood risk assessment data previously modeled by a local engineering and consulting company. These organizations also considered aspects such as site history, hydrology, and various draft dyke designs. Further, project leads went about extensive community consultation as well as forming a Marsh Body through the Nova Scotia Department of Agriculture. These steps aided in encouraging public participation and increasing agency. While a formal cost/benefit analysis was not conducted, decisions were made with an eye towards cost effectiveness and financial sustainability. The study notes that while the extent to which alterations to existing dykes positively affect adaptive capacity has yet to be determined, business as usual would have seen an increase in flood events and necessity for ever-larger engineering interventions. This case faced a variety of challenges including a lack of historical flood data, jurisdictional ambiguity, and barriers related to funding access. Despite the above complications, Truro ultimately prevailed in creating a dyke management plan thanks in large part to strong communication and extensive public consultation.

Identifying Actions

As noted above, some of the information used to identify actions was gathered through a somewhat distinct program. This information set out a number of hypothetical scenarios based on changes to flood prevention infrastructure along with the fiscal costs and effectiveness associated with each action. These flood risk scenarios along with additional modelling, LiDAR DEM, topographic surveys context research and the creation of an NSDA sanctioned Marsh Body (among a host of other strategies) were used to determine the best course of action. It has also been made clear that the focus of any new actions will be to: reduce dyke maintenance costs, enhance the protection of lands and reduce flood risk. Consultation was necessary not only with the Marsh Body and local citizens but also with CN Rail and Nova Scotia Power as both have assets intersecting the land. A historic cemetery is also within the area and so demanded consideration. Finally, major concerns revolving around the promotion of mosquito breeding with the introduction of new marsh land and thus standing water needed to be addressed before a plan could be agreed upon. Ultimately, the project leads along with the aforementioned stakeholders agreed to a plan which will see the creation of two new dykes to protect CN assets as well as the cemetery. Further, standing water will be reduced through strategic channel creation paired with deliberate dyke breaching in various locations.

Outcomes and Monitoring Progress

While implementation has not yet occurred there have certainly been a multitude of co-benefits associated with the planning phase of the Truro dyke realignment project. This project may not only increase resilience through the restoration of floodplains but also helps to reduce dyke maintenance costs. Further, reintegration of natural systems will allow for increased protection of infrastructure and property. The project also provides key takeaways which will likely be valuable to future dyke realignment endeavours in Nova Scotia. Firstly, the case of Truro has shown that communication and public engagement must be at the forefront of planning efforts should the project gain widespread support. Second, the success of this project thus far provides a positive precedent which could be pointed to when engaging with future communities in need of substantial dyke realignment. Monitoring of the project will take a few forms over a 5-year period post-implementation. Firstly, it will monitor the many uncertainties that lay ahead for this project such as the extent of flood protection (attributed to marsh development lag time), changes in sediment and ice levels as well as overall effects on the hydraulic system. Monitoring will also include the quantification of carbon sequestration and flood mitigation as infrastructure is built and altered.

Next Steps

Aside from implementation itself, the project has identified two major areas which may require further attention. The first is the extent to which realignment will aid in increasing resilience to extreme weather brought about by climate change. This factor is still unknown partly due to incomplete historical data but may also be attributed to the fact that there is inherent uncertainty when introducing natural systems (i.e., as related to the lag times mentioned in the Outcomes and Monitoring Progress section). Next, the study has also expressed concerns that interventions made at the North Onslow dyke site (Truro, Nova Scotia) may have adverse sediment deposition and ice related effects. The study also points out that some modelled scenarios suggest that planned interventions could simply geographically shift high flood risk areas. Monitoring of the hydrologic system looks to be cognizant of this possibility in the 5-year post-implementation monitoring period. Ultimately this project will be used as a potential guide for other provincial projects through the Making Room for Wetlands initiative.

Resources

Link to Full Case Study

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