2015 Provincial Report: Almost All Dikes Substandard in Lower Mainland

The Lower Mainland is a floodplain. Before we began diking works around the Lower Mainland, flooding was part of the natural cycle. The great flood of 1894 kicked the construction of dikes into high gear.

In the Lower Mainland, dikes are the responsibility of municipalities or special purpose diking districts. The provincial government is responsible for regulating dikes, including inspecting dikes.

The provincial government commissioned a report called “Lower Mainland Dike Assessment” which was completed in 2015. The report’s authors found that “almost all of the dikes are substandard and most will not withstand the provincially adopted design flood events.”

They also found that “in considering dike crest elevations relative to design flood levels, only 4% of the dike segments are high enough to contain the present design event.” Dike crest elevation determines how much water level rise a dike can handle before failure occurs.

Altogether, this means that our diking system is not meeting its original flood protection design.

Getting the dike network up to modern standards, which includes accounting for climate change impacts, is cost-prohibitive for municipalities and diking authorities.

The report authors made 11 recommendations of which the following stand out:

• In connection with the Lower Mainland flood vulnerability assessment currently underway, identify which dikes most urgently need upgrading in terms of assets at risk and the substandard quality of particular dikes. Prioritize the necessary upgrades.
• Develop comprehensive flood management plans that consider a range of structural and non‐structural flood management strategies in addition to dikes. These plans must recognize that dikes are not fail‐safe and that in some cases, upgrading dikes to withstand the design events may not be feasible, especially when climate change is considered.
• Consider establishing an over‐arching agency to lead flood management and develop appropriate funding mechanisms to support comprehensive planning and dike upgrading by diking authorities.

One of the long-standing concerns of municipalities has been the lack of stable, significant funding from the provincial government to upgrade dikes.

With the events of last week, I hope that all orders of government renew their efforts to comprehensively and holistically manage and fund dikes in the Lower Mainland.

The following map shows the state-of-repair for dikes in the Lower Mainland.

Lower Mainland Dike Average Rating. Select map to view.

You can download the full report at: https://www2.gov.bc.ca/assets/gov/environment/air-land-water/water/integrated-flood-hazard-mgmt/nhc_final_lower_mainland_dike_assessment.pdf