Flood Protection in Richmond
Overview
Richmond’s unique characteristics make it a great community to live, work and play. The fact that Richmond’s geod
etic location is approximately one metre above mean (average) sea level and on a floodplain, however, often raises questions about the potential for flooding.
The following sections address the risk factors for Richmond, provides information on measures the City takes to guard against the possibility of flooding, and what residents should do to prepare themselves:
- The Facts
- What are the Risk Factors?
- History of Flooding
- Flood Protection Measures
- What Can Residents Do?
The Facts
Although not officially designated as such, Richmond is located on a floodplain. A ‘floodplain’ is: “land adjacent to a watercourse that is susceptible to flooding”, such as from periods of high tide. In addition, isolated instances of flooding can occur in any community as a result of unanticipated weather events.
To protect Richmond from the possibility of flooding due to high tides or river floods, the City has constructed a comprehensive system of dykes on Lulu Island. These dykes are over 49 km in length and protect an area of 12,805 ha. Mitchell Island is protected by dykes which are privately owned and maintained. Sea Island dykes have been maintained and improved primarily by the Vancouver International Airport Authority.
The City has an extensive system to remove drainage water caused by adverse weather conditions. This system comprises 320 km of ditches and canals and 600 km of box culverts and storm sewers.
What are the Risk Factors?
There are primarily two types of events that could trigger flooding:
1. River Event
Freshet – higher than normal snow packs within the Fraser River Basin, combined with consistent, warmer than normal Spring weather patterns, can cause a rise in river discharge.
Dyke breach due to natural disaster – if the dyke were to breach at high tide, water could flow in over areas that are lower than the height of the tide until such time as the tide recedes.
2. Weather Events
Heavy rainfall – sudden, heavy rainfall events could exceed the processing capacity of drainage systems.
So, what are the chances that any of these ‘risks’ will materialize? Let’s take a look at Richmond’s ‘History of Flooding’.
History of Flooding
Freshet – The highest freshets occurred in 1894, 1948, and 1972. In each of these instances, no flooding occurred on Lulu or Sea Islands. In 1948, there was minimal flooding on Mitchell Island (where dykes had not yet been constructed).
It is also important to note that Richmond is located far to the south of the peak snow pack runoff points. This means that the water level is considerably lower in Richmond due to the widening of the river. This gives the water a larger distribution area, thus reducing its vertical influence on the river. The water then releases to the Gulf of Georgia.
Weather Events – Richmond’s drainage system is designed to accommodate a 1:10 year storm event. There have been some minor instances of property damage to low-lying properties caused by flooding during heavy rainstorms that exceeded a 1 in 10 year storm event.
Dyke Breach – There is no record of a breach which has resulted in flooding since the major dyking network was constructed by the first settlers of our community. The dykes were further upgraded in the 70’s and 80’s to accommodate a 1 in 200 year event.
The City takes a number of steps to safeguard against these unlikely events, as additional precautions. See “Flood Protection Measures”.
Flood Protection Measures
Protection from High Tides or River Floods
Richmond’s dykes are constructed to a level which is two feet above the highest ever-recorded water level at this location on the Fraser Basin,
which occurred in 1894. This meets the Provincial standard, which provides protection for a 1 in 200 year flood event.
Richmond also has a number of programs in place to ensure the integrity of our dykes. These include:
- A weekly inspection and maintenance program to ensure the dykes remain stable at all times.
- A vegetation control program, to remove any brush and tree growth that could compromise the integrity of the dykes.
- An annual dyke survey program, based on a 5-year cycle, to monitor settlement and carry out required upgrades to ensure the dyke elevations are maintained at or above the 1:200 year standard.
- 24-hour electronic river level monitoring systems at 4 key locations.
- A Floodplain Management Policy, which establishes minimum flood construction levels and outlines future initiatives to enhance flood protection.
- A dyke seismic study to determine the potential impacts of an earthquake on key areas of Richmond’s dyke network. Where required, the dykes will be strengthened.
Richmond’s programs are all carried out in accordance with the dyke maintenance guidelines established by the Ministry of Environment, Lands & Parks.
Protection from Flooding Due to Weather Events
Richmond has an extensive drainage system comprised of pump stations, flood boxes, irrigation structures, and storm sewers.
Pump Stations & Flood Boxes
There are 38 stations located throughout the island which house a total of 110 pumps. At high tide, these pump drainage water into the river. At low tide, drainage water discharges through the flood boxes into the river via gravity outflow gates.
These stations are powered by electricity and have the capacity to pump up over one million US gallons per minute, if required. All of the stations are monitored remotely, 24 hours per day, to ensure the pumps are operating effectively.
These pump stations are designed for a 1 in 10 year rainstorm. To help prevent isolated flooding, the City monitors weather forecasts and pumps down the level of drainage water in the canals prior to any anticipated rainstorms. This provides extra capacity to hold the surplus drainage water caused by the storm.
Irrigation structures
In addition to removing excess water for drainage purposes, the City supports the local farming industry by pumping water back into our system. The city has installed irrigation structures, which allow water to be drawn in from the river for our local farming operations, i.e. cranberry and vegetable farms, etc.
What Can Residents Do?
Sometimes, residents can experience localized flooding due to drainage problems on their property. This is generally caused by obstructions to their internal drainage network. To avoid this problem, the City recommends that residents:
- Keep storm grates clear of leaves or other build up which can block the storm drain,
- Ensure that drain tiles are not blocked.
- Residents with ditches should ensure that their culverts are clear so that drainage water can run freely through the system.
See How to Prepare During an Emergency for additional information on flooding.
