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Flooding

What is a freshet?

A freshet is the occurrence of a high water flow resulting from heavy rain or a heavy snowpack follwed by the onset of warm weather. Freshet flooding can occur when the Fraser River begins to rise in the late spring/early summer.

Causes of Flooding

Delta's location on the Fraser River floodplain puts the community at risk of flooding. The main flood threat for Delta occurs from winter storms and then along the Fraser River in the late spring and early summer, particularly when there's a heavy snowpack and a sudden spell of hot weather following a cool spring. The area's two major floods, in 1894 and 1948, were both a result of this spring freshet. Both began on May 26th.

Several factors could cause flooding along the lower Fraser River:

See Floodplain Map of the Lower Fraser River { pdf 448KB }

View Annacis Island and Gunderson Slough Ground Elevation Map { pdf 4.7MB }

Delta's Dike System

Delta's dikes surround the entire lowland area, protecting the community from high water levels along the Fraser River, the Strait of Georgia and Boundary Bay. The dike system consists of more than 61 kilometres of river bank dikes and sea dikes. The river dikes protect areas adjacent to the Fraser River from flooding that may occur from high tides, storm surge or flood flows. Sea dikes and seawalls provide protection from high tides, storm surge, waves and debris.

There are partial secondary dikes on the Tsawwassen First Nation lands, and the Cuthburt Dike in the Brunswick Point area. Elevated roads / highways, such as Deltaport Way, Highway 17 and Highway 99, would also provide some secondary flood protection if the primary dike was breached.

Delta's dikes were built prior to the 1894 flood, rebuilt following the 1948 flood and upgraded in the 1970s and 1980s. Today, Delta's dike system is constructed to the 200-year flood level, which means the risk of flooding is estimated to be 0.5% in a given year. There is a 99.5% chance that flooding from high water will not occur. The Corporation of Delta inspects, maintains and upgrades the dikes regularly to ensure they continue to function as designed.

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Delta's Drainage System

More than 30 pump stations and floodboxes, as well as ditches regulate water levels and protect the community from flooding. This system ensures drainage of the floodplain lands by conveying storm flows to the Fraser River or the sea. When the risk of flooding is lower in the summer months, the drainage system is also used as an irrigation storage system to help local farmers with crop production.

Delta staff maintain the pipes and ditches so that water flows uninterrupted. If a spill is reported staff respond to the incident quickly in order to minimize the environmental impact.

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Flood History

The greatest flood on record occurred in 1894, affecting the southern half of British Columbia. Because development was sparse, the flood caused little damage. During a second major flood in 1948, the dikes failed. Ten people died, 2,000 homes were destroyed and 16,000 residents were evacuated. It's estimated that if this flood occurred today, it would cause $1.8 billion in damage throughout the Fraser Valley.

Delta's extensive dike system protects the area from flooding. The flood risks associated with the dike system in Delta relate to overtopping or a dike breach. If the dike system was breached an area several kilometers inland from the breach could flood.

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