Adapting Metro Van Dyke Flood Control Systems to Future SLR
Dyke protection of properties in Delta, Richmond and other areas along the Fraser River began in the 19th century by the early Pioneers who sought to farm the rich soils of the deltas with simple side-casting of ditch spoils adjacent to their farms. After a number of damaging floods over many decades, caused by the breaching of these simple structures, the science of sound Engineered Flood Control systems was finally implemented by the Canada-British Columbia Fraser River Flood Control 1968 Agreement. The program resulted in an extensive construction of very effective flood control dykes (compacted granular materials) and pump stations using 200 year return flood level criteria.
overview of the idea
Over the last century or more, these communities along the Fraser River have gone from Agricultural to Institutional to Commercial to Residential and Industrial Communities. Now with physical, environmental and economical constraints along the existing dykes, it seems very difficult to address the problem of sea level rise to continue to protect communities from costly damages caused by flooding. As an example, the Municipality of Delta has at risk, $5.85 billion of Land & Building Value (2008 $’s not including business losses) within 61 km of existing flood control dyking systems (Delta RAC Sea Level Rise Adaptation Visionary Study 2012).
There are also a number of properties located outside the dyke, unprotected from high tides even today. As well, there are properties which could not be continuously protected by the 1968 dyking system and in some cases were designated as ‘Special Areas’ requiring sandbag and other means of protection during a high tide event.
With the expected Sea Level Rises (1.2-1.5m) over the next century and beyond, it is imperative that we find ways to mitigate the problems now with as little impact to our communities and as economically as possible with systems that are and will be adaptable to even the unforeseen levels in the future.
The existing dykes in Delta constructed in the mid-late1970’s were designed and constructed to sound, professional Engineering specifications as set out under the Canada-British Columbia Fraser River Flood Control 1968 Agreement Program. In general, these dykes were built with impervious core materials and compacted to prescribed specifications (eg. Proctor Densities) including erosion control where needed, for flood protection, recreational and maintenance equipment purposes under the Program.
Based on the above, this team is confident that these structures can be retrofitted with higher elevation levels of flood protection systems adapting to the Sea Level Rises expected by 2100 and beyond, continuing to protect our communities as they do now.
how it works
To meet or exceed the challenge of the expected 1 metre rise in sea level, we propose a combination of professionally Engineered, readily available large and small non-mortar masonry block seawall & retaining wall systems (see Page 9) and the construction of a higher elevated dyke core within these walls, built to design specifications similar to those constructed under the 1968 Program.
The blocks will be placed along the outside of the existing 3.66 m (12 ft.) dyke crests to an elevation of at least 1.2 metres above the current 200 year elevation. The core dyke material will then be placed between the blocks compacted to the required Engineering specifications (see Sketch Page 8).
Other main features of this project will include items such as handrails along the top of the blocks and shoreline erosion protection such as rock rip rap along the water side of the blocks where needed.
A Class D estimate (+/- 30-50%) for the main block and dyke material supply and place is $500/lineal metre or $30,500,000 for 61 km’s of Delta dykes. In comparison to the affected Land and Building Values this is only about ½ of 1% of these values (2008 $’s).
Addressing Critical Issues
This proposal will only have positive improvements on the current level of flood protection of Delta’s properties and businesses. As well, the environmental impact is very minimal due to a footprint slightly larger than the current 12 ft. (3.7 m) width of the existing dyke crests and the cost-efficienct benefits are tremendous.
A Proposal for Metro Vancouver Communities to Adapt and Thrive in the Context of a 1 metre or More Rise In Sea Levels by 2100 and Beyond
Full details of the proposal including Background, Technical Review, How Communities Will Adapt and Thrive, Examples, References. Download.
How communities will adapt and thrive
Our Communities will uninterruptedly continue to grow and prosper with these applications. As noted previously, there are some ‘special challenges’ to adapt to such as access to those properties unprotected outside of the dykes and the protecting of current views from other existing structures. Some suggested solutions to the problems this project may incur are construction of common driveway/dyke accesses for these properties and maintenance vehicles. As well, raising of some of the existing buildings’ habitable floor spaces may be required, which with the pending SLR would need to be achieved anyhow. We suggest that maybe some kind of funding for those owners requiring these adjustments be made available (e.g. Low interest loans, Grant program etc.) and included in the budget.
This proposal reinforces the significance of the Metro Vancouver Communities’ existing Flood Control Systems designed and constructed under the Canada-British Columbia Fraser River Flood Control 1968 Agreement Program and other government programs along the MVC shorelines, and with its’ improvements the future is very encouraging. The Economic Benefits, Minimal Environmental Impact, Sound Engineering Feasibility and Social Benefits should allow the public and the governments to embrace this kind of proposal with high enthusiasm. The ‘icing on the cake’ so to speak, is the paradigm shift we must take, away from how we look at the issues and instead we need to look forward to enjoying our beautiful shoreline environment from the new sea walls, as we take control and enjoy our destiny with the pending Sea Level Rises.
More precisely, we must be confident that our high-level Flood Control Dyke Systems will continue to prevent damages to the beautiful, rich lands and communities we love.