Flood protection options

This summer the City of Grand Forks and Regional District of Kootenay Boundary evaluated flood mitigation and land use options with technical, stakeholder and community input. The options presented provided permanent solutions that reduce the risk over time while building community capacity and resilience.

This evaluation included:

  • Preparation of land use and flood mitigation options by Don Dobson, P.Eng. Recommendations were based on aerial and ground surveillance, GIS / map analysis and interviews with response and infrastructure personnel.
  • Peer review of preliminary options in a technical review meeting by professional engineers and a flood management / recovery expert.
  • Planning and operational review by City of Grand Forks and Regional District of Kootenay Boundary emergency management, planning, and operations personnel.
  • Technical workshop with regional stakeholders, government agency representatives, flood recovery team members and RDKB Board and City Council.
  • Presentation of revised options to Council, four neighbourhood-specific meetings and three open community meetings.
  • Community survey and four neighbourhood meetings to review impacts of options on property owners and businesses.
  • River Study from Don Dobson with options for Council and RDKB Board consideration.

Johnson Flats / Rural Residential

The neighbourhood is surrounded on three sides by the Kettle River. The area has some unofficial flood protection works, i.e. discontinuous berms along the portions of the riverbank but no bank armouring. During the high flows on May 10th there was bank erosion in the northwest sector and overbank flow into the neighbourhood through an area where there was no berm. There was also overbank flows into the neighbourhood along the bank at the south end where there was no berm and overflow from the east in the northeast sector. Floodwaters flowed into the remnant oxbow in the north central area and flowed back into the river through the channel connecting the oxbow to the river.

Flood damages in the neighbourhood range from none to total destruction. Undamaged residences were either situated on a local elevated piece of land or, had been constructed in accordance with the City’s Floodplain Bylaw at the current flood construction level. Other residences that were situated on lower lands and/or predated the Floodplain Bylaw, had water depths in and around the building ranging from a few centimeters to 1‐ 2 m.

Dwellings that are situated within the designated 1:200 year floodplain and were not constructed to the flood construction level (FCL) are at risk of being damaged in the future when the area floods. Areas of specific concern are those properties in the northwest near the initial overbank flow, those in the south affected by the overbank flow from the south and those at north end of 12th Street near the old oxbow that are located on low lying land.

Option selected:

  1. Use the existing floodplain bylaw for low risk areas where water was less than 50 cm deep with greater than 5 percent annual probability as determined by the floodplain study. Require and support residents in raising their dwellings to the new flood construction level.
  2. Limited bank protection for west edge and portions of south edge to prevent land and infrastructure losses. Elevate 12th St to maintain emergency access, and install additional drainage along it.
  3. Buy-out the highest risk areas at north end of 12th St and other residences lower than the 1:20 year floodplain level.

South Ruckle

The South Ruckle neighbourhood is located within an oxbow section of old river channel. The ground in the South Ruckle area slopes to the east away from the river with the lowest ground around the eastern perimeter of the neighbourhood which is likely the deepest part of the original channel. It is in this area where the floodwaters were the greatest depth and where flooded dwellings suffered the greatest damage.

There are no flood protection berms along the riverbank in the neighbourhood but there was a section of bank protection works, i.e. riprap constructed by the City northwest of 66th Avenue. The neighbourhood is bounded by the railway tracks to the north, east and south that services the Interfor sawmill. Floodwaters overtopped the east bank of the river and flowed into the neighbourhood and were constrained either by the natural banks of the old oxbow or by the railway grade.

The damages to residences ranged from none to total destruction. The undamaged buildings were on localized higher ground and/or more recent construction built according to the Floodplain Bylaw. The dwellings that were flooded to depths less than 0.5 m were typically in the western areas and those that were destroyed were situated on the eastern side of the old oxbow where the ground was lowest. The properties to the east were also impacted by the railway grade that prevented overflow to the east. There were four known dwellings with no flood damage, 24 with water depths 0.5 m or less and ~60 dwellings with water depths >0.5m. A resident of South Ruckle provided additional data based on visual assessment of all the properties in the neighbourhood. He estimated that ~38 dwellings had little to no damage; 12 dwellings had moderate damage and 36 dwellings were likely severely damaged.

South Ruckle may be at risk of flooding in 2019, depending upon the size of the freshet from bank overflow in those areas where overflow occurred in 2018. Since the ground slopes towards the east away from the river, any overflow will flow towards the low ground and pool flooding those low lying dwellings. The fact that many of the dwellings were not constructed to the required FCL, any flooding could cause more damages in 2019.

Even with temporary protective works many dwellings in the South Ruckle neighbourhood are at risk from flooding in the future during high flows in the Kettle River since many of them are not constructed at the required FCL. Permanent flood protective works in combination with raising dwellings to the FCL can lower the risk to acceptable levels.

Option selected:

  1. Use the existing floodplain bylaw for low risk areas where water was less than 50 cm deep with greater than 5 percent annual probability as determined by the floodplain study. Require and support residents in raising their dwellings to the new flood construction level.
  2. Install river bank protection from 63rd Ave to 66th Ave to prevent further loss of land; build a setback dike aligned with 9th St and 66thwith an internal drainage system.
  3. Buy-out the highest risk and lowest lying dwellings along south and east edge of South Ruckle equivalent to less than the 1:20 year floodplain level and for properties at immanent risk of loss to erosion.

North Ruckle

North Ruckle is a single family home residential neighbourhood of 62 homes across the river from downtown Grand Forks. The neighbourhood was flooded as a result of flood waters (including backwater from the confluence of the Kettle and Granby Rivers) overtopping the dikes and sections of the dike upstream of the 2nd Street Bridge being compromised. Only those dwellings that were constructed in accordance with the Floodplain Bylaw remained undamaged. Damages to many of the older homes were severe due to water depths greater than 0.5 m. Based on a review of the satellite data and ground elevations it appears that of the 62 dwellings only one to two were not damaged during the flood likely because they were constructed according to the bylaw. Most of the remaining dwellings has floodwaters with a depth of at least 0.5 m and deeper. The worst damages were in the 1st and 2nd Street area where water pooled at a meter or more deep for several weeks after the flood and a number of dwellings were seriously damaged.

There was flooding around the Rockwool plant as a result of floodwaters crossing the North Ruckle neighbourhood, 68th Avenue and 2nd Street before exiting the floodplain near the river bank. The Interfor property had been raised using fill when the mill was rebuilt. The mill property was not flooded.

Option selected:

  1. Elevate 2nd St and 68th Ave; dike along path east of Rockwool; remainder north of 68threstored to functional floodway / riparian habitat with portions rezoned to compatible open space use.
  2. Complete buy-out of all areas north and east of dike. Removal of infrastructure and restoration of floodplain and compatible open space uses.

Downtown

Downtown Grand Forks was impacted by floodwaters from the Kettle River that flowed in through City Park, from floodwaters from the Granby River that overtopped the banks near the Highway 3 (Yale) Bridge, the backwater effect from the synchronized peaks in the Kettle and Granby where water flowed into the downtown from the rivers at the confluence. The flooded areas extended from approximately 75th Avenue near the Granby west to between 3rd and 4th streets and then in City Park and the floodplain south of 72nd Avenue past 7th Street to the Kettle River. Many businesses and dwellings were damaged, and several businesses remain closed.

Option selected:

  1. Build a dike as per alignment in the River Study. Elevate Riverside Drive north of Highway 3 in lowest lying areas. Provide repairs and improvements for storm system.
  2. Build flood walls to protect high value buildings that have no room for other options.
  3. Buy-out house west of City Park and along dike alignment just north of the Kettle River and the Forks. Obtain first right of refusal for single family residence on Riverside just south of Hwy 3.