The cost of doing nothing to address the potential for future overland flooding in Sundre is estimated as high as $14 million if the Red Deer River overflows its banks again, according to an engineering study conducted for the town.
McElhanney Consulting Services's report assesses expected overland routing of flood flows and potential impacts to Sundre, overall risk, and reviews mitigation options.
The engineering and cost benefit report was required to be completed before the Town of Sundre could apply for Flood Recovery Erosion Control Program grant funding from the provincial government to implement flood mitigation measures. The program provides funding to address municipalitys' immediate repairs from the June 2013 floods and includes long-term community mitigation projects.
The report backed construction of a berm for overland flow protection but advised against using a swale/canal to redirect water away from Sundre.
When Sundre councillors weighed in on the report earlier this winter, Myron Thompson said the report also dismisses dredging the Red Deer River, which he disagrees with.
“I need an explanation on this. What do you mean dredging doesn't do any good?” said Thompson.
“Let's get after in good fashion that Sundre can be saved from flooding. We need to get that river back to where it was.”
Coun. Paul Isaac said government officials were dredging in Bragg Creek and Eckshaw.
Nearly 60 projects have been approved through the Flood Recovery Erosion Control Program – including Mountain View County's Little Red Deer River project near Water Valley and Red Deer County's road erosion control projects. But Sundre's projects, including a joint bid with Mountain View Country to construct a berm, as backed by the McElhanney report, haven't been approved yet.
“What does Sundre have to do to get the government's attention? Do we have to drown?” said Isaac.
There is potential for future overland flooding in Sundre again, according to the report.
The majority of the town is built on an alluvial floodplain created by the river, the report states.
“This area is on the west side of the current location of the Red Deer River. It is likely that the river originally aligned itself along the north side of the floodplain, which is delineated by a significant increase in bank height and slowly meandered to the south by depositing material along the north margin of the river and eroding the south bank,” reads the report.
Because the current location of the river is at the southern extreme of the overall floodplain, the bank on the north, left side is poorly defined and easily overtopped in some locations, according to the report.
The flooded area to the north of the river, according to the report, becomes unbounded indicating the potential for the entire flood plain to be wetted.
The report also reviews Sundre's history of overland flooding in modelling potential future flooding.
In 2013, the Red Deer River flooded low-lying areas around town. In 2005, the Bearberry Creek breached its banks causing extensive damage to Sundre and surrounding areas. The Red Deer River breached its north bank and discharged down a depression towards Sundre in both 1952 and 1966.
Potential future flood paths are presented in the report and include three reaches along the river where flooding may occur.
Reach 1 may connect with Bearberry Creek to the north of Highway 27. It has not been subject to overland flooding in the past, but highway commercial and general residential are the main areas that would be affected.
The breakout point is farthest from the commercial centre of town, so officials hope that any breach of the bank would be identified early on. This would allow for response techniques such as the deployment of temporary diking to be carried out before the floodwaters reach town.
There is also a good chance that a breach at this location would result in water heading back towards the main stem of the river.
Reach 2 appears to reach town through connection to a quarry area on the west side. It would likely have the most impact on infrastructure and is expected to move through the industrial area to the west of town and continue east towards the river through businesses and residential areas.
“The industrial/commercial area supports businesses such as mechanical and fabricating shops, the town office as well as above-ground oil storage tanks. Water may move through these areas and be exposed to associated industrial materials, potentially affecting water quality before it flows towards the smaller business and residential area in town, and eventually entering the Red Deer River,” reads the report.
However, it has a low probability of overland flooding and there is no historical evidence of an actual breach at the potential breach location. If there were a breach, it would likely enter a secondary channel and be directed back to the river.
Reaches 1 and 2 have the potential to affect industrial, highway commercial, general and low density residential uses.
Reach 3 does not access town directly, but reconnects with the river upstream. It stays south of most of the town infrastructure, but crosses over at least one north-south road. There was damage to this road from the 2013 flood.
Reach 3 is the most likely area for the river to breach its banks.
“The probability was not assigned as a high risk since high flows were experienced in the Red Deer River in 2013 without a breach occurring at this location,” reads the report.
“This could have been a result of the partial construction of the berms.”
A flood in reach 2 is estimated to cost $14 million in damage and response costs to the town and to Mountain View County. The cost for reaches 1 and 3 would range from $5.4 million to $8.5 million. Costs are based on average property values as well as potential cost of response.
The study suggests developing temporary berms around buildings to reduce direct impacts of floodwaters.
“However, preventing water from being exposed to the contaminants that may be present in these areas may not be as simple. Even slow-moving water, which doesn't erode foundations or buildings, can pick up contaminants from yard sites, storage areas and associated soils, and then move this material to downstream areas,” reads the report.
With backing from the report, town officials and Mountain View County officials applied for joint provincial funding for construction of a 3.9-kilometre setback berm along the north bank of the Red Deer River. The berm would protect both the town and the county.
Town of Sundre officials have also applied for a $200,000 grant through the Flood Recovery Erosion Control Program to construct a 100-mm gas line that would service the residents and businesses on the east side of Sundre.
An existing gas line is located under the Highway 27 bridge over the Red Deer River, but officials say if another flood comes through town, the line could be damaged.
“During the floods of 2013, only after flood water subsided, it was evidenced that this gas main had sustained significant damage relative to its protective insulation due to the amount of debris flowing under the bridge,” explained Dave Dubauskas, the town's chief administrative officer, in a letter to request the funding.
“Additionally, a section of the gas main had been dislodged as one of the pipe supports for the gas main was completely torn off the bridge, leaving the gas main hanging precariously under the bridge.
“Had the gas main severed or broke, the results could have been a gas leak, fire or explosion causing potential damage to the only bridge in Sundre.”
The gas line is the only service to the east side of town, so if flow in it was disrupted, approximately 50 residential homes, a trailer park consisting of about 25 permanent trailers, about 30 businesses and Tall Timber Leisure Park would be without gas service, he added.
“Additionally, a leak would cause loss of gas supply to residents on the west side in the vicinity of the bridge due to low pressure,” he said.
“The potential population without gas in the event of this type of occurrence would be in the order of 1,375.”
Officials are proposing that gas servicing to the east side by provided from the east side. This would allow for the gas line under the bridge to be shut off during a flood event, without impacting east side residents.
“Presently the Foothills Gas Co-op has an existing gas main on the east side of Sundre that they are willing to allow the town to connect to such that this servicing can be provided,” he said.
