During a flood event or over time, dikes can fail in a number of ways:
- Seepage: The movement of water through the dike or under its foundation can undermine its stability or cause the dike to sink
- Erosion: Water and debris flow, wave action or ice can erode the surface of the dike
- Overtopping: When water levels are higher than the dike, water can flow over the top
- Earthquake: In seismically active areas, dikes risk being damaged or displaced by an earthquake.
Most dikes in BC are owned and managed by diking authorities, most of which are local governments. The Government of British Columbia provides guidelines for dike design and construction. All construction of and changes to dikes must be approved by the Province under the Dike Maintenance Act.
In the Lower Mainland, dikes are the main form of structural works for flood protection. Since the late 1800s, dikes have been built as flood protection from the Fraser River and its tributaries. Despite these efforts, protected areas have been subject to flooding on more than one occasion.
Most of the region’s dikes were constructed or upgraded in the 1960s and 1970s as part of the federal-provincial Fraser River Flood Control Program. The region currently has 600 km of coastal and river dikes and related works, such as flood boxes, pumps, ditches, culverts and erosion protection works.
The current diking system does not offer contiguous or comprehensive coverage. For example, many First Nations communities are without dikes or alternative protection.
A recent study by the Province found that the region’s dikes are overall too low, and that they are vulnerable to overtopping or other failure, or to damage from earthquake. Some areas have “non-standard” or orphan dikes that do not have a local authority to operate and maintain them.
The majority of dikes will need to be upgraded or rebuilt to meet provincial standards for flood as well as seismic hazards. Climate change is anticipated to increase many flood hazards across BC and must be considered in the future review and updating of provincial dike standards.