The threat of land slumping behind his house has prompted Jim Cole to seek a development permit from city hall to demolish the building and backfill the excavated basement.
During its March 14 regular meeting, city council voted unanimously to approve the demolition permit application for 216 Grandview Street West based on the results of a geotechnical report from Feb. 17 that Ground Engineering Consultants Ltd. provided the homeowner.
Geotechnical report
The engineering firm assessed the area on Feb. 16 to determine whether the proposed demolition would affect the lot’s slope stability, the geotechnical report said. The document noted that landslides are active in the area, with the most recent slope movement in February 2017 east near Skipton Road.
“Basically, there is instability anywhere along the Moose Jaw River valley walls where the river undercuts the toe of the slope … ,” said the report. “This process will continue over the long term. South of this property, there is a retaining wall constructed out of waste concrete which supports Grandview Street. … the wall is failing, and at some point, will have to be replaced.”
A test hole drilled near Grandview Street West in 1980 showed the soil is a surficial sand layer underlain by a till stratigraphic unit that extends 77-feet down to the bedrock shale.
The house is 7.5 metres north of Grandview Street, while the basement is far enough from the street that the fill weight would not affect the slope stability, added the report. Filling the basement and grading the lot would keep to a minimum surface water infiltration on the top edge of the slope.
City hall’s perspective
Under the zoning bylaw, residents cannot backfill, grade, deposit earth or other material, or excavate in a slump zone unless they obtain a favourable geotechnical report that authorizes the specific development and can provide it to council, explained Michelle Sanson, director of planning and development.
A geotechnical report must also confirm that any action would not affect the existing slope stability of that site, neighbouring properties, drainage courses or public utilities before council issues the development permit, she continued.
The one-unit dwelling is in the s2 slump hazard overlay district, an area considered low to moderate risk of land falling away. There is also an s1 slump hazard overlay in the community that is considered moderate to high risk for collapse.
The slump zones are near the Moose Jaw River, Thunder Creek and Spring Creek lower valleys, a council report said. The purpose of these zones is to provide for orderly development and safe construction in areas subject to slope instability.
Cole has no plans to re-develop the lot now, although if he does in the future, he will need another geotechnical report, Sanson said. City hall suggested that Cole attain the report now, but he wasn’t prepared.
A future update to the zoning bylaw will remove the need for council to approve demolition permits in slump zones, she added, since removing a structure would not require the same level of administrative analysis as a new building, structure or addition.
Reflecting on the forthcoming update, Coun. Heather Eby said she understood the reason for the change but thought it was important for these slumping issues to come to council as a reminder of this problem along Grandview Street.
“If it hadn’t come to us, we would not have known about it. It would have been out of sight, out of mind,” she added. “It’s good information for councillors and for the community, and I don’t think bringing it to council creates that much more work or time in the process.”
The next regular council meeting is Monday, March 28.
