Flood Protection Infrastructure
The City of Chilliwack has an extensive diking network to protect the community from floods on the Fraser and Vedder River systems. The City inspects and maintains the dikes and related infrastructure on a routine basis to keep the system functioning as designed.
In 2014, BC Ministry of Forests Lands and Natural Resource Operations completed a study which updated the estimated flood water elevations for the Fraser River. The elevations are based on a Fraser River freshet of the same magnitude that occurred in 1894, which is the flood of record.
The new predictions for flood water elevations are similiar to hose determined by Northwest Hydraulic Consultants in 2008 and significantly higher than previously estimated in 1969 and 2001. Since the 1969 modeling had been the basis for designing the Fraser River diking systems, many sections of the diking network require substantial upgrades.
Chilliwack is not the only community affected by the new flood modeling results. The new study revealed estimated flood water levels higher than previously estimated in 1969 for almost every location along the Fraser River from Chilliwack to Richmond.
In Chilliwack, some dike sections are sufficiently high, but many of the dikes need to be raised. Most of the dikes are high enough to meet the new estimated flood water elevations, but they lack sufficient freeboard. The provincial standard for Fraser River dikes is to meet the flood profile plus have 0.6 meters (2 feet) of additional freeboard. In the worst locations, however, the dike crests would be overtopped by water levels associated with the 1894 flood of record if they are not raised. In these locations, the dikes need to be raised by up to 0.8 meters.
While our dikes require raising to withstand a flood of the same magnitude as the 1894 event, the chance of the 1894 flood recurring in any given year is very low. It is more likely that a flood of smaller magnitude would occur, and Chilliwack’s dikes are high enough to withstand fairly large floods, similar to the flood of 1948. The City of Chilliwack has been undertaking extensive dike upgrade projects over the past decade. A summary of recent project is provided below.
Recent Flood Protection Projects:
Recent flood protection projects include drainage pump stations, dike raising, riverbank erosion protection works and improvements to the dike's seepage control system. These works help protect the integrity of the dike system.
West Dike (Right Bank) Upgrade
This $1.5 Million-dollar project provided for raising the West Dike (Right bank between the Great Blue Heron Reserve and 1.1km West) by approximately one meter to increase flood protection for the Vedder River 1:200 year flood event with 0.75m of freeboard and the Fraser River 1:500 year flood event with 0.6m of freeboard. Emergency Management BC through the National Disaster Mitigation Program provided funding contribution in the amount of $960,000.
The Design-Build team of Timbro Contracting and Onsite Engineering commenced construction in early September 2022 and achieved substantial completion November 1, 2022.
Fraser River Erosion Protection (2022)
The City of Chilliwack received provincial funding in the amount of $750,000 through the Union of BC Municipalities to complete Fraser River Erosion protection under the Community Emergency Preparedness Fund. This funding approval is for Phase 2 of the river bank armouring downstream of the CHIP intake. The $900,000 project included rock armouring of 210 linear meters of riverbank. By stabilizing the riverbank the diking will offer a higher level of protection to the community.
2022 Vedder River Sediment Removal
The Vedder River Management Area Committee (VRMAC) plans and designs sediment removals from the Vedder River and Canal to maintain floodway capacity. Left unmanaged, the naturally depositing sediment would result in increased flood water levels and reduce the effectiveness of the dike system.
The atmospheric river event in November 2021 resulted in over 440,000 cubic metres of sediment to be deposited in the Vedder River and Vedder Canal. This is extraordinary in that the long-term sediment deposit rate has been declining in the past decade to under 40,000 cubic metres per year.
VRMAC identified a total of eleven sites for sediment removal in 2022, including five City of Chilliwack sites.
Although 151,000 cubic metres of sediment at eleven sites has been identified, only 110,000 cubic metres will be removed which represents the long-term average deposit rate and the amount prescribed in our agency applications.
Council at the regular meeting of July 19, 2022 awarded the tender for the “2022 Vedder River Floodway Sediment Removal” to Jakes Construction Ltd. to remove up to 110,000 cubic metres of sediment from the Vedder River and Canal at unit prices as provided in their tender submittal in the amount of up to $500,000 (plus applicable taxes).
The City did not receive provincial (Water Sustainability Act) approval until Aug 29, 2022 and therefore not able to begin sediment removals until Aug 31, 2022. Between Aug 31 and September 13, 2022 approximately 35,000 cubic metres of sediment was removed from five (5) locations (Railway, Greendale, Salad, Powerline and Boundary bars). Environmental design, monitoring and post removal assessment is being completed by a qualified environmental professional.
McGillivray Pump Station Upgrade (2019)
The project increased the capacity of the pump station to reduce or eliminate flooding caused by a 1:100 year return period rainfall event. Construction of the $4.7 Million design-build project commenced in 2018 and was completed in 2019. The work included construction of a new electrical building, new electrical controls with standby generator plus upgrades to the pump intake structure, pump discharge piping and new 600 HP Pump/Motors. The floodbox was also retrofitted including a new automated slide gate. The project was funded $4.2M by the Province of BC.
Fraser River Erosion Protection (2019)
The City of Chilliwack received provincial funding in the amount of $750,000 through the Union of BC Municipalities to complete Fraser River Erosion protection under the Community Emergency Preparedness Fund. This project included two (2) sites, Orchard Slough Check Dam site and 225 linear metres of the riverbank rock armour downstream of the CHIP site.
The check dam on the Orchard Slough will provide increased protection by reducing the potential overbank channel flow directed against the adjacent dike. By stabilizing the slough, the diking will offer a higher level of flood protection to the community.
The East Dike near the CHIP intake is critical infrastructure that provides flood protection to the majority of the Chilliwack floodplain. The Fraser River bank erosion protection near the CHIP intake will increase the stability of adjacent diking, located roughly within 15 m of the river bank. By stabilizing the bank with rock armour, the diking will offer a higher level of flood protection to the community.
Collinson Pump Station Upgrade (2015)
The project increased the capacity of the pump station to reduce or eliminate flooding caused by a 1:100 year return period rainfall event. The project has doubled the pumping capacity of this station, which serves the Greendale area. The work included a new electrical building including MCC and HVAC equipment, 2 new 450HP pump/motor assemblies, new standby generator, underground 600V BC Hydro service to replace the 450V pole line, new intake screens, automated screen cleaner and conveyor. The $2.5 Million project was funded through the Building Canada Fund – Flood Protection Program with 2/3 ($1,666,66) federal/provincial contribution.
East Dyke (Young Road) Dyke Upgrade Project: Approximately 1 kilometre of the East Dyke along Young Road between Cartmell Road and Hope River Road was upgraded in 2015. The project was funded two-thirds through the Provincial-Federal Flood Protection Program and Building Canada Fund and one-third by the City of Chilliwack. Total project cost: $2,340,000.
West Dyke Upgrades (Left Bank): Approximately 4 kilometres of the West Dyke along the Vedder Canal and adjacent to Yarrow were upgraded in 2010. The project was funded two-thirds through the Provincial-Federal Flood Protection Program and Building Canada Fund and one-third by the City of Chilliwack. Total project cost: $2,900,000.
East Dyke Upgrades (Greyell Section): Approximately 5.3 kilometres of the East Dyke near Jesperson and Gill Roads were upgraded in 2010. The project was funded two-thirds through the Provincial-Federal Flood Protection Program and Building Canada Fund and one-third by the City of Chilliwack. Total project cost: $1,200,000.
West Dyke Relief Wells: 80 new relief wells were installed along the West Dyke in 2008 to improve seepage control. The project was funded 100% through the Provincial-Federal Flood Protection Program. Total funding: $1,008,000.
East Dyke (CHIP) Relief Wells: 14 new relief wells were installed along the East Dyke by the Camp Hope Intake (CHIP) to improve seepage control. The project was funded 100% through the Provincial Flood Protection Program. Total funding: $213,000.
Fraser River (CHIP) Bank Protection: Bank protection upgrades were completed along a 300 metre length of the Fraser River bank, downstream of the Camp Hope Intake. This was the second phase of bank protection work, with phase one completed as emergency work in the spring of 2007. The project was funded 100% through the Provincial Flood Protection Program. Total funding: $164,000.
2007 Urgent Mitigative Flood Works:The Provincial Government approved $3,753,000 in funding for urgent mitigative flood works in Chilliwack prior to the 2007 freshet. This funding was used to raise low portions of the East Dyke, which extends from Highway 9 to Young Road as well as the Wing Dyke. A small portion of the funding was also used for localized bank armouring.
Additional flood protection upgrades are planned for the coming years, as the City applies to the new annual Provincial-Federal Flood Protection Program. This program commits $20 million per year to fund flood protection projects throughout the province.