How vulnerable is Langley to a major flood?

This is the second of three stories on the annual flood risk in the Fraser Valley’s biggest cities. We also examined the Fraser’s flood danger in Chilliwack and Abbotsford. Find those stories here: Chilliwack | Abbotsford. We also wrote about the threat to Mission’s waterfront here.

Flooding is a major risk in the Fraser Valley. After all, floods helped create the valley in the first place. But not all cities are equally vulnerable. And some floodplains are more at risk than others.

November’s flooding shone a light on the region’s vulnerability to a major flood. But which areas in which towns are most at risk? And what is needed to prevent—or at least reduce the risk or scale of—a future devastating flood?

We don’t have all the answers. But we have some, thanks to experts who have been studying the issue, creating reports, and pushing for change for years. We will unpack these over the coming weeks and months for each community. First up: Langley.

On Jan. 10, Doug McFee warned the Township of Langley council of the challenges faced in protecting properties in the Fort Langley area.

“It’s clear that we can’t engineer our way out of flooding. We’ve tried that and it hasn’t worked,” said McFee, the chair of the Salmon River Enhancement Society.

Much of Langley is built above the Fraser’s floodplain, leaving the majority of its rapidly growing population not susceptible to a freshet flood. But having been deliberately built 195 years ago to service river traffic, Fort Langley is vulnerable when the Fraser swells in the spring.

The area surrounding the historic fort, along with Glen Valley and Walnut Grove are the three most vulnerable areas in Langley to flooding of the Fraser.

The Fraser Basin Council has modelled various scenarios of freshet floods based on the historical data and present day conditions. The models indicate where flooding is most likely. And a subsequent Fraser Basin Council analysis of dikes suggests why many places are vulnerable.

Walnut Grove and Katzie

In many of the models, a broad swath of land west of Derby Reach Regional Park is one of the first places to be inundated.

In the event of a 100-year flood, the most northwestern part of the area could see itself under upwards of two metres of flood water. The area is unprotected.

From the Katzie First Nation reserve lands just east of the Golden Ears Bridge, the waters could stretch southeast beyond Allard Crescent, submerging hundreds of acres of farmland used to grow cranberries and other crops. The waters could extend east to Derby Reach. Water could rise as high as three metres across the area.

A 100-year flood event does not mean such a flood could only happen once every 100 years, or that it will happen 100 years after the last flood. Instead, it means there is a 1% probability that a flood of this magnitude could happen in any year (or a 9.6% chance over 10 years)—although climate change is likely increasing the odds of such events.

The Fraser Basin Council also modelled more severe 200-year and 500-year floods. In those scenarios, the analysis found much of the same defenseless area in north Walnut Grove could be overwhelmed, just with a lot more water. The 500-year event could submerge many parts of the area under three metres, along with industrial lands just south of the Golden Ears Bridge.

The West Langley dike runs for 2.2km along the Fraser east of the Golden Ears Bridge before cutting inland for nearly one kilometre south of Katzie First Nation. A review of the dike found it to be “unacceptable,” and unable to stop a flood of the scale of that which occurred in 1894.

According to a 2015 dike assessment report commissioned by the province that evaluated all Lower Mainland dikes, the West Langley dike is “too low.” Engineers rated the crest (or height) of the West Langley dike the lowest possible grade: one out of four. They also found the dike geometry to be “substandard” and “seismically unstable.”

Fort Langley

A severe flood has the potential to turn Fort Langley into an island and could cause damage along the waterfront.

A 100-year and 200-year event would see McMillian Island submerged entirely. But inland, the overflow wouldn’t extend far beyond the banks of the Fraser. The map indicates the Fort Langley National Historic Site is likely spared.

However a more severe flood could see water breach the banks of the Salmon River.

In his presentation earlier this month, McFee noted the challenges posed by the local topography. The Salmon River, which drains into the Fraser just west of Fort Langley, follows a sinuous trail stretching several kilometres from Trinity Western University. But throughout its length the elevation remains consistent at three meters (barely above the height of the Fraser.)

“Water flows downhill, there is no real downhill going on here,” McFee said.The Fort Langley dike covers the shortest distance. Just opposite McMillian Island, it runs for about one kilometres along the Fort Langley golf course. The crest of the dike was also evaluated as “unacceptable.” Like the West Langley dike, it is “too low.”

Glen Valley

Further upstream, about 8km east of Fort Langley, is the Glen Valley. The vast area of farmland in the valley straddles the border joining the Township and Abbotsford, where three segments of dike work to keep water away from the area.

In the event of a 100-year flood, the modeling shows there are a half-dozen sizable farms and businesses at risk. The waters wouldn’t spare Glen Valley Regional Park, which could be submerged under two to three metres.

As water rises, it is expected to start to collect in fields along the westernmost dike protecting the area’s broad flood plain. The dikes may hold for a while. But they would be unable to stop a severe flood on the magnitude of the 1894 disaster. And when those dikes breach, it could be catastrophic, with the model showing upwards of three meters of water across almost the entire of the area. The farmland would drown.

Like the other dikes, the Glen Valley dike was also found to be “unacceptable.” In addition to the dike being “too low,” the report indicated that the dike and river bank has experienced erosion damage and require repair.

Elsewhere

It isn’t only areas skirting along the Fraser that are susceptible to flooding.

The Nicomekl River flows through the centre of Langley City. Several smaller channels feed into the 34km long river, but only five of those kilometres are situated in Langley. The river runs east west through the central part of the City before pouring into Surrey and finally Boundary Bay and the Strait of Georgia. The river is controlled by sea dams located just south of King George Boulevard off Elgin Road.

The City has zoned a broad area bordering the Nicomekl as floodplain to limit development, but it remains concerned about the potential risk to lowlands. It believes the floodplain can support a minimal flood event, but the area east of 203 Street is vulnerable to a major one that would extend “well into existing developed urban areas.” And despite current flood control measures the river continues to overflow when it rains.

Langley City doesn’t have dikes but Surrey has several flanking the Nicomekl. So how those dikes function and how the water behaves in the neighbouring city plays a large part in how it will impact the Nicomekl in Langley.

A KPU engineering study prepared decades ago under the Canada-British Columbia Floodplain Mapping Agreement found that “the Serpentine-Nicomekl lowlands are subject to a major flood threat from the sea which could result in a very rapid inundation of inhabited land.”

The engineers also warned Surrey, the Langleys and the Ministry of Transportation that changes to the road profile within the Serpentine-Nicomekl floodplain could have major impacts on flood levels.

Sea levels are projected to rise and Surrey’s drainage system is complex. How those rising sea levels will affect a future flood event in Langley remains to be seen.