As the highest water levels in decades are expected to hit the Fraser River this weekend, Langley Township has issued an evacuation alert for Glen Valley.

The June 20 alert was for those living in the floodplain in Glen Valley, and in unprotected areas of Northwest Langley, Brae Island and McMillan Island.

"This is not an evacuation order," said Township director of public works Roeland Zwaag. "The alert is being issued so that people in at-risk areas have time to make preparations, should conditions change and they need to leave their homes on short notice."

The alerts were delivered by members of the RCMP on Wednesday.

Zwaag said the Township is also supplying sand and sandbags to people outside the dike system, available at the operations centre at 4700 224 St.

The Township and province are working with the Kwantlen and Katzie First Nations, both of which have reserves located directly on the shore of the Fraser.

Township engineering staff are now patrolling the dikes at least daily, and Zwaag said the water is at the "toe" of the dikes at present. Groups working together include the Langley Emergency Program, Environment Canada, and staff from Abbotsford, as the Glen Valley floodplain crosses into both communities, and the diking system is interconnected.

Regular updates can be found online at langleyemergency.ca, on the Township's site at tol.ca, and via the Township's Twitter and Facebook pages.

Should the river overflow, the Township will activate its call centre at 604-533-6191, and recorded messages will be updated on a regular basis.

The unlikely worst-case scenario would be a replay of the events of 1948, when

Fort Langley was encircled by water, farmers had to drive stock through water to get them to higher ground, and high school students at Langley Secondary were called out of their graduation exercises to fill sandbags.

Heavy rains on the weekend have already led to flood and evacuation warnings in the Interior near Prince George.

The Forecast Centre has officially issued a High Streamflow Advisory for this week for the Lower Fraser River.

Levels at the Mission gauge peaked at 5.9 metres on the weekend before dipping again slightly. David Campbell of the River Forecast Centre said the forecasts on Wednesday suggested a high point of 6.5 metres for Friday or Saturday.

That would be higher than the 6.015 that was the peak in 2007, the last year a serious flood threat was forecast. It would mean 24hour patrols of Langley's dikes by local emergency officials.

That year, just as water levels began rising, a week of cool air settled over the province and the rate of snowmelt slowed. There was no serious flooding in the

Lower Mainland, although local fields, especially outside the dikes, were waterlogged.

In 1972, river levels hit 7.17 metres, and the major flood of 1948 was 7.6 metres.

The forecast may be wrong if weather in southern B.C. brings high temperatures, more rain, or both. That could cause an extra dose of water from nearby mountains and rivers that feed into the Fraser.

"That is a bit of an added piece of uncertainty," said Campbell.

Meteorologist David Jones of Environment Canada, speaking in a government briefing with Campbell, said that a large low pressure system is preparing to hover over most of B.C.

The system is shaped like a wheel, with large "spokes" of cloud and rain that will sweep up from the south.

The next spoke is to sweep in on the weekend, following a brief spike in temperatures, Jones said.

That is not good news, as it means the current surge of water will be followed by another one sometime towards the end of next week.

It's unknown how high the water levels will get, as it will depend on rainfall and temperatures.

Attorney General Shirley Bond said the province is helping local governments with expertise and heavy equipment.

There are two million sandbags in a provincial stockpile, many of them already being distributed, and eight kilometres of gabion diking have been built in Chilliwack over the past few days.

Firefighters who normally would be gearing up for wildfires at this time of year are on call for flooding, instead, Bond said.

Several local Metro Vancouver Regional Parks have already been affected. Campgrounds at Derby Reach Park were shut down a few days ago when water levels spiked, said Roger Bean of Metro Vancouver Parks, and the loop trail on Brae Island Park isn't accessible.

"You can't get very far down it before you're hip deep in water," Bean said.

Camping has also been shut down at campsites in Glen Valley's riverside parks in Langley and Abbotsford.

Langley City does not have to be concerned about rising levels in the Fraser.

The issue came up at the June 18 council meeting when councillors discussed water management and water shortage plans.

The Nikomekl River and its flood plain are not connected to the Fraser River system and not affected by water level changes. But the river that runs through the City can be affected by the amount of rainfall, so the City always keeps watch, explained engineering director Gary Vlieg.

mclaxton@langleyadvance.com