Dam safety: BC Hydro a world leader in flow management
Unlike California's Oroville Dam, all our spillways are engineered concrete
Evacuations resulting from damaged spillways at a dam in northern California have raised questions as to what BC Hydro has done to ensure a similar situation doesn't happen at our dams in B.C.
Following the end of the drought in California, the spillway at the Oroville Dam has been recently used for the first time in many years. Last Saturday, the California Department of Water Resources reduced flows from the main spillway at the Oroville Dam after erosion resulted in a hole in the spillway.
The water then rose in the reservoir until it freely overflowed a concrete weir into an emergency spillway. As the water flow began to erode the exposed earth near the head of the emergency spillway, counties and cities near Lake Oroville and the surrounding area issued evacuation orders over concerns that this erosion threatened to undermine the concrete weir and allow large, uncontrolled releases of water from Lake Oroville.
Most of BC Hydros major spillways have been used in the past year for various reasons, so we're confident they'll work in emergency situations. Some of our larger spillways saw their last major spill about 4½ years ago; these have all been closely inspected following their use, and repaired when required. We've spent about $2 million on general maintenance on the concrete in many of our spillways in this time frame, with another $.5M planned for this coming year.
In addition, we've recently completed a major rehabilitation of the spillway at the Bennett Dam, at a total cost of about $64M, to replace areas of damaged concrete and to provide safe access for the work, and future repairs. We're confident that our spillways are ready when needed, and the concrete damage that occurred at the Oroville main spillway will not happen here.
We also have "free overflow spillways" like the concrete weir at the head of the emergency spillway at Oroville. But all of our structures are very different than at Oroville, where the emergency spillway immediately downstream from the weir wasn't lined with concrete, and allowed water to flow over the unprotected ground. All of our spillways are fully engineered concrete structures.
Because spillway gates must be reliable, we're upgrading them across B.C.
Most spillways have massive gates that can be used to adjust the flows. These gates must be reliable; they absolutely must open when required to release the rising water behind the dam, even though at some dams, this may only be required once or twice in a decade.
BC Hydro initiated a major program of reliability upgrades to our spillway gates back in 2005. Projects at 10 of our 22 sites with gated spillways have now been completed, with the next two projects underway, at a cost of about $360M to date.
At our Ruskin Redevelopment Project, we’re completely replacing the spillway piers and gates to improve reliability and post-seismic performance. At John Hart, a recently initiated project will be constructing a totally redundant free overflow concrete spillway to improve operational safety.
In addition to all this work, system wide procedural improvements and revised operational, maintenance, inspection and regular testing procedures have been implemented and sustained for about 10 years. We're now recognized as a leading agency in the stewardship of spillways.
BC Hydro also prides itself in promoting collaborative research into new methods of analysis to better the safety of dams and spillways. We have worked together with Ontario Power, the US Corps of Engineers and a major utility in Sweden (Vattenfall) over the past few years in the development of an authoritative book on the operational safety of hydro facilities, focusing on spillway discharge. This has just been published, and provides the most up-to-date thinking in regard to safe spillway design and operations.
Some of this new thinking is evident at Site C, a third dam on the Peace River in northeast B.C., which will go much further than most previous developments with its design. It has two main concrete spillways, so that if one becomes damaged, flow can be diverted to the other one. In addition, there's a third free overflow concrete spillway for added redundancy.
BC Hydro's Dam Safety Program
Our highest responsibility is public safety, so BC Hydro continuously monitors and assesses our dams. We rely on 24/7 instrumentation monitoring, weekly inspections, bi-annual engineering reports and regular expert reviews of all our dams by international, independent experts.
A 2013 independent audit by international experts found BC Hydro has a strong dam safety program and a robust risk assessment process consistent with international best practices. The next audit is planned for 2018.
We have 80 regulated dams at 41 sites throughout B.C. Over the next 10 years, BC Hydro is investing about $1.5 billion in dam safety across the province, including about $700 million on upgrading the three older dams on the Campbell River system on Vancouver Island alone. This $1.5B does not include the ongoing work to rebuild the Ruskin spillway and left abutment (about $190M).
In addition, the John Hart Redevelopment project is replacing the seismically deficient intake and surface penstocks with a robust intake and underground tunnel that significantly increases seismic withstand.
All this work follows on the heels of previous dam upgrade projects, including:
- $400 million on spillway gates at various dams around B.C., a program that started in 2005 and is ongoing
- $19 million to complete the Elsie Dam Safety Upgrade (Port Alberni) in 2004
- $65 million to completely rebuild the Coquitlam Dam (completed in 2008)
- $34 million on the Ruskin right abutment seismic and seepage upgrades (2012-15)
- $20 million on the Strathcona Dam intake tower project (2009-10)
Our monitoring and assessment of dam safety includes:
- Real-time monitoring using thousands of measurement devices and tools
- Weekly site inspections at every dam by trained inspectors
- Inspections twice a year at every dam by a dam safety engineer
- Inspections by an independent dam safety consulting engineer every five to ten years
- Special inspections after landslides, earthquake, high winds, spillway discharges, floods.