The City of Delta is keeping a close eye on the ongoing flood risk.
Engineering Director Steven Lan on Monday provided council with an update on the spring freshet and how things are currently shaping up, noting it’s been a colder spring, which has delayed the snow melt.
Usually, the peak freshet flows in the Fraser basin are seen in early June, but that won’t be the case this year.
Lan noted that, as of June 1, the province advised that only 19 per cent of the snow pack has melted and runoff, but in a normal year that would be around 50 per cent.
He said Delta staff are following the conditions as well as Delta’s flood plan, which has the city currently at the first stage.
“We have completed our annual dike inspection and have a stockpile of sand and sandbags and riprap as well as making sure our equipment is available. Staff are continuing to monitor conditions daily and are attending weekly provincial updates. We are also providing a weekly email update to council,” he said.
“As of today (Monday, June 13) the river conditions are currently sitting at about 5.5 metres at the Mission Gauge and the flows at Hope around about 9,700 cubic meters a second.”
Lan’s recent report to council notes that two of the most significant recorded floods occurred in 1894 and 1948. The 1894 flood had an estimated discharge of 17,000 cubic metres per second, while the 1948 flood had an estimated discharge of 15,200 cubic metres per second.
The City of Delta has its five-stage flood plan to address the planning and response to the flood risk posed by the annual spring freshet would progress to additional stages based on the Fraser River level at the Mission Gauge, with Stage 2 being triggered when the reading reaches six metres.
Stage 2 involves pre-flooding operational activities, while Stage 3 involves, among other things, evacuating high-risk areas. The fourth stage would involve road closures and rescue services while the final stage would involve recovery efforts.
A large amount of woody debris is carried downstream during high flows, but the province operates a debris trap which is located near Agassiz to collect and remove that material.
“Weather conditions over the next two months will play a critical role in determining the rate at which the snow melts. A gradual warming with no rain would be ideal in reducing the flood risk. A prolonged heat wave followed by heavy rain can result in substantially increased flood risk. Continuing cooler than average temperatures across the province can also result in an elevated flood risk,” the Delta staff report explains.
If flooding occurs, Delta has more than 100,000 sandbags available and more than 100 tonnes of sand. There’s also more than 100 concrete lock-blocks and more than 200 tonnes of riprap.
