ARCHIVED - Keeping The Taps Flowing In Vancouver

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April 03, 2003— Ottawa, Ontario

Stormy weather means increased vigilance for those who guard Vancouver's water supplies. Water authorities shut down the Capilano Reservoir-the source of 40 per cent of the region's water supplies-an average of 55 days per year, when heavy rains cause landslides that carry sediments into the reservoir, via swollen rivers and creeks.

CHC modeling shows sediment plume entering the Capilano Reservoir. Sediments and organic matter make water more turbid or cloudy, hindering the ability of water treatment methods such as chlorination or ultra-violet light to kill bacteria, says Norm Crookshank of the NRC Canadian Hydraulics Centre (CHC). The higher the turbidity, the greater the health risk, so water authorities have no choice but to turn off the taps until levels decrease.

To help manage and prevent future water quality problems, Crookshank and his colleagues have developed a new watershed management system for the Greater Vancouver Regional District (GVRD). The system is based on ongoing modeling work conducted by NRC-CHC and researchers at Environment Canada. The NRC-CHC contribution involves modeling the movement of water and sediment in the Capilano and two other reservoirs, while Environment Canada focuses on modeling the hydrology of the surrounding watersheds, and the supply of water, sediment and nutrients into the reservoirs.

In 1999, the NRC-CHC researchers developed a two-dimensional hydrodynamic model of the Capilano Reservoir, and later turned their attention to the Seymour and Coquitlam reservoirs, which supply about 40 and 20 per cent of Vancouver's drinking water respectively. "The Coquitlam Reservoir has the potential to meet all of Vancouver's additional needs for safe drinking water for the next 50 years," says Crookshank. "We're developing a three-dimensional model there because the reservoir is so deep-about 250 metres. The flow of water through the reservoir is influenced by stratification due to vertical temperature variations, which in turn can affect turbidity."

The GVRD watershed management system builds on the NRC-CHC and Environment Canada models. Using the system, water managers can assess the potential turbidity problems of events such as landslides, forest fires, or insect infestations occurring in different watershed locations. "If needed, they can turn off one reservoir and get water delivered from another reservoir," says Crookshank.

The system can also help managers decide whether any mitigation measures-such as reinforcing riverbanks-are needed to prevent erosion within a watershed. Finally, it can help them make future decisions over whether to upgrade water supplies and put in new treatment facilities.

Crookshank and his colleague, Sébastien Bourban, hope to complete the Coquitlam Reservoir modeling this year, and then start upgrading their Capilano and Seymour models from two to three dimensions. "We're also planning to look at the potential effects of climate change 50, 75 and 100 years into the future," says Crookshank. "The GVRD is very concerned with how its water supplies may be affected by changes in 'snowpack' amounts in the surrounding mountains, the ultimate source of much of its drinking water."

Enquiries: Media relations
National Research Council of Canada

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