Flood maps released Wednesday show the McKernan and Parkallen neighbourhoods would likely experience major flooding in a “one-in-100-year” storm.
The City of Edmonton’s preliminary maps show parts of McKernan could see more than 1.25 metres of water pooling above the surface in a big rainstorm.
“The flood maps are saying very clearly that this is a location where flooding will occur and the sanitary sewer systems in this area are saying they will be surcharged,” or overloaded, said Chris Ward, branch manager of utility services.
“This is locations where we have somewhere in history built residential subdivisions basically at the bottom of an old lake bed after draining it and not filling it in.”
In Parkallen, water levels could reach 0.5 to 0.75 metres, according to the maps, part of a city-wide, flood-mitigation assessment begun as the result of flooding in 2012.
The assessment looked at drainage infrastructure in 160 of Edmonton’s mature neighbourhoods, most of which were built before 1989 and have not had any flood-mitigation upgrades. While the systems were build to the standards of their day, times and needs have changed.
“The Edmonton of decades past had a much smaller population, with less demand on the system, and experienced different, less-severe rainstorms than we see today,” Ward said. “City staff have started a proactive study of urban flood mitigation measures so that we can be better prepared in the years ahead.”
Ward said some mitigation work has already been done or is underway. In McKernan, for example, there is a large storm tunnel close by and the city has considered connecting it to relieve flood pressures.
In Parkallen, Ward said a dry pond is planned, with construction scheduled to begin in 2019-2020.
Bob Barton has lived in McKernan for 42 years. He said he’s been through at least two bad floods over the years. About a decade ago, he was forced to gut his basement following a flood.
“The first time, it was bad. It flooded the basement and it was sewer backup. We had about three or four inches. The next time, in 2004 I think it was, it was big, bad. It was over my boots’ height. It was coming in the basement windows. It was a mess.”
Luckily, his insurance company covered the costs. He’s also taken steps himself to mitigate further flooding.
“Putting in the downspouts,” he said. “Last year, I regraded the lot. I brought in seven yards of soil and regraded the lot.”
Even though the release of the city flood maps could affect his property value, Barton said homeowners and buyers have a right to know.
“I think it’s right. I think people should have the ability to find out the issues about the property if they’re looking at buying,” he said.
The city anticipates more infrastructure upgrades will be required to ensure neighbourhoods can deal with increasing pressure on the drainage system.
City administration will present a strategy to council in the mid-2017.
Potential fixes include improving overland drainage routes, constructing new storm water management dry ponds and building new underground storage tunnels and sewers.
In addition to the residential neighbourhoods, 33 industrial parks will be studied in the flood mitigation programs.
Implementation of the project is expected to start in 2019, but because of the large scope of the project, it will likely be implemented over decades, the city said.
All of the maps released by the city are posted below. More information can be found on the city’s website.