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Dikes and Related Works

Around the world, dikes have allowed people to settle on flood-prone lands. A dike (also called a dyke or levee) is an embankment constructed along a riverbank or coastal shoreline to prevent the flow of floodwaters onto land behind the dike. It is typically made of compacted earth and outfitted with flood boxes, gates and pumps to help regulate the water level on the landward side of the dike.

Dikes can be protected by riprap (an engineered layer of rock pieces) or vegetation to minimize erosion, for example, by surface runoff, stream flows or wave action.

Dikes are typically designed to defend against a specified level of flooding. To remain effective, they need to be inspected, maintained and upgraded.

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.

Potential Benefits	Potential Challenges
Diking may be the main infrastructure option for densely developed, low-lying coastal communities with development space constraints There may be less upfront capital cost for dikes compared to other types of large-scale barriers or large property buy-outs (depends on multiple factors) Dikes can provide publicly accessible open space for other uses such as walking, running and cycling	Over-reliance on dikes can lead to more development behind the dikes and higher losses if dikes fail Dikes and associated bank hardening can negatively affect riparian and coastal habitats Dikes can narrow a river channel, increasing water speeds and reducing room for water flow or flood storage during a flood, worsening flooding and erosion downstream Dike upgrades are expensive and may require extra land, careful siting, rights of way, consultations and regulatory approvals Regular maintenance and inspection is expensive and necessary

Potential Benefits

Potential Challenges

Diking may be the main infrastructure option for densely developed, low-lying coastal communities with development space constraints
There may be less upfront capital cost for dikes compared to other types of large-scale barriers or large property buy-outs (depends on multiple factors)
Dikes can provide publicly accessible open space for other uses such as walking, running and cycling

Over-reliance on dikes can lead to more development behind the dikes and higher losses if dikes fail
Dikes and associated bank hardening can negatively affect riparian and coastal habitats
Dikes can narrow a river channel, increasing water speeds and reducing room for water flow or flood storage during a flood, worsening flooding and erosion downstream
Dike upgrades are expensive and may require extra land, careful siting, rights of way, consultations and regulatory approvals
Regular maintenance and inspection is expensive and necessary

In BC/Lower Mainland

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.