Fundy Dyke Risk Assessment
WOOD
Client Name: Nova Scotia Department of Agriculture (NSDA) / New Brunswick Department of Transportation and Infrastructure (NBDTI).
Start Date: February 2017 Completion Date: June 2018.
Project Description: There are 344 kilometres (km) of coastal dykes on the Bay of Fundy - the NSDA and the NBDTI have responsibility overseeing the construction, operation, and maintenance of these dykes and associated aboiteaux structures.
Historically these dykes have protected agricultural land from the inundation of salt water, however, they are increasingly being relied upon for the protection of infrastructure, transportation corridors and municipal townships.
The Fundy Dyke Risk Assessment was funded by the National Disaster Mitigation Program. The following key components - executed via desktop review, field studies and modelling - included: examining geotechnical limitations of the dykes; determining engineering standards and required safety factors for infrastructure protected; assessing storm risk to determine what type of storm will create a flood.
Wood’s deliverables included a guidance document on the design, construction and rehabilitation of coastal dykes, hydrodynamic model, design case studies, and dyke safety reviews (DSR) including geotechnical investigations. Four (4) priority dykes were selected to represent different regions within the upper Bay of Fundy - the hydrodynamic model and DRSs focused on those priority sites.
Guidance Document: a comprehensive guidance document illustrates the parameters to be considered in the construction, rehabilitation, operation, and maintenance of coastal dykes in the Maritimes. A key element of the guidance document was the development of a classification scheme for coastal dykes based on established national and provincial classification schemes written for dam infrastructure. The classification scheme informed the design criteria established in the guidance document with inputs from established Canadian Dam Association (CDA) criteria and the hydrodynamic model being developed.
Design Cases were developed for multiple scenarios to provide examples illustrating the implementation of the guidance document in practice (i.e., new dyke construction and rehabilitation of existing dykes, both with and without available foreshore).
DSRs were completed following guidance from CDA including geotechnical programs, laboratory testing and dyke safety inspections. The focus of DSR was to:
• Identify potential failure modes and hazards for the dyke and assessing the safety of the dyke with respect to each failure mode;
• Assess the initial design basis against current guidance;
• Review the performance of the dykes; and
• Outline potential concepts to achieve the desired design elevation.
Hydrodynamic Modelling for the Bay of Fundy was implemented to provide high resolution data at each of the representative dyke sites. The model included:
• Tidal range characterization – high-resolution hydrodynamic modelling of the tide propagation.
• Wave climate characterization – wave climate transfer from regional to local scales using high-resolution spectral wave models, in conjunction with modelling locally wind-generated waves
• Storm surge elevations – based on modelling of the site-specific impacts of storm events, incorporating surge contributions observed in up-to-date tide gauge data
• Presence of a tidal river and associated effects – based on hydrodynamic modelling of the combined tidal and riverine flows and their interactions
• Sea level rise – based on the latest scientific projections of global sea level rise, with adjustments for local factors including land subsidence
Model outputs of the full range of required physical environmental parameters were visualized and reported to address engineering and design requirements, including currents, incident wave heights and runup elevations. These outputs provided accurate information to aid in establishing crest elevations for the representative dykes.
Key Achievements: Two key guidelines were developed for coastal and estuarine dykes along New Brunswick and Nova Scotia tidal areas, promoting standard application of safety and design of dykes along the Fundy tidal areas. The introduction of dyke-life-stage Factors of Safety (FOS) provides clear safety objectives at end-of-construction, during its operation and during a seismic event. Implementation of the overall process was used for the Oxbow Dyke (NB24), in Aulac, New Brunswick, for the design of an 800 m long dyke.
