UTRCA Position on Watercourse Barriers
Dams and weirs in the UTRCA watershed serve various purposes, including flood control, water augmentation, power generation, stormwater management, and recreation. However, many of these structures are aging and require rehabilitation or major maintenance to continue to safely operate. In some cases, they may no longer be needed or no longer fulfill their intended functions. In such cases, decommissioning barriers can restore natural river conditions and enhance environmental flow as well as eliminating the need for ongoing operation and maintenance efforts. Unless there is a strong justification for
retaining a dam, decommissioning can significantly improve the health of the watercourse.
Reasons to Decommission a Barrier
Decommissioning a barrier may include removal of all or part of the structure, bypassing the structure, and restoring the watercourse. Decommissioning barriers in river systems offers several compelling benefits:
- Restoring the range of native species: Many barriers disrupt natural river flow and hinder the movement of native fish and aquatic organisms. Decommissioning such barriers can restore the natural range of native species, promoting ecosystem health and preserving biodiversity.
- Improving aquatic habitat: Dams and weirs can alter the natural flow patterns of rivers and create impoundments that can lead to problems, such as temperature fluctuations and nutrient and sediment accumulation.
- Reducing water pollution: Barriers can create stagnant water conditions, promoting algae growth and pollutant accumulation. Decommissioning barriers can help reduce water pollution by allowing for better water circulation and improving the overall water quality within the watershed.
- Restoring sediment movement: Barriers can cause sediment to accumulate upstream. This deprives downstream areas of sediment, leading to bank erosion and reduced channel stability and negatively impacting fish spawning grounds.
- Eliminating impoundments: Artificially impounded rivers have altered characteristics that can lead to temperature fluctuations, nutrient accumulation, and algae blooms, and create favourable conditions for invasive species. Structure failure could lead to downstream damages, water quality impairment, massive sediment release, habitat loss, and other impacts.
- Restoring seasonal flows: Riverine plants and animals rely on seasonal flow fluctuations for various life stages, such as reproduction and growth. Barriers can disrupt this natural variation, affecting floodplain ecosystems and aquatic habitats.
- Impacts on river-adapted species: The Thames River watershed supports diverse aquatic, semi-aquatic, and riparian-dependent species. Native species are vulnerable to changes caused by damming, potentially leading to their disappearance from impacted areas.
- Impacts on species at risk: Barriers are identified as one of the primary threats to many at-risk reptiles, mussels, and fish in species-at-risk recovery strategies and management plans, including the Recovery Strategy for the Thames River Aquatic Ecosystem (draft 2004).
- Safety-related considerations: Barriers may become unsafe due to age and lack of maintenance which can heighten the risk of failure. They may also become too costly to maintain properly. These barriers may present safety concerns, elevated flood risk, and potential liabilities.
Reasons to Retain a Barrier
Some barriers serve beneficial purposes, such as:
- preventing the spread of invasive species,
- protecting sensitive upstream species,
- creating recreational opportunities not possible without the impoundment created by the dam, or
- providing flood control, flow augmentation, or hydropower generation.
Where purposes such as these are still valid, these should be weighed against the environmental improvements that could be realized if the dam were decommissioned.
Linkages to Other UTRCA Policies, Management Plans, and Strategies
- The (SWA) is a 20-year plan aimed at improving the ecological condition of the Thames River and its connected lakes. The plan is a collaboration of First Nations, federal and provincial agencies, municipalities, and conservation authorities. The SWA recognizes watercourse barriers as threats to aquatic communities and emphasizes barrier removal projects for water quality improvement and stream health.
- There are permitting and legislative requirements when decommissioning a constructed barrier. Property owners must obtain permits for dam decommissioning. Environmental impacts of decommissioning must be mitigated.
How the UTRCA can Encourage and Support Barrier Decommissioning
- Continue to assess and prioritize decommissioning barriers owned and/or managed by the UTRCA.
- Continue to pursue opportunities to encourage and support owners in decommissioning constructed barriers.
- Continue to provide barrier owners with technical advice on proper operation and maintenance of constructed barriers.
- In collaboration with partners, develop educational materials on barriers and their impacts.
- Investigate methods to mitigate environmental impacts of barriers that are not decommissioned.
UTRCA Board Position
On October 18, 2023, the UTRCA Board of Directors adopted the following position:
“Constructed barriers such as weirs and dams should be considered for decommissioning whenever possible to improve watercourse health and reduce flood risks.”
This position incorporates legal advice, allowing UTRCA staff the flexibility to identify the various considerations for each dam. For example, flood control, low flow augmentation, thermal impacts, sedimentation, barrier to invasive species, fisheries migration, and other pertinent factors can be weighed for each structure.
Case Studies
Hodge’s Pond, Oxford County
Cedar Creek restoration at the former Hodges Pond site
In 2016-2018, the UTRCA worked with Stewardship Oxford, Ducks Unlimited, and Oxford County to decommission the Hodges Pond Dam, located on Cedar Creek near Woodstock. Built in the 1800鈥檚, the concrete dam was originally part of a mill. The 3.3 meter high dam created a barrier within the 95 km2 watershed. Its decommissioning reestablished the aquatic connection between approximately 90 km of Cedar Creek upstream of the site, and the Thames River downstream.
Originally built as a mill pond, the reservoir had become a sediment-filled shallow lake with low oxygen levels and a high bacteria count.
Cedar Creek now bypasses the dam structure, which remains as a cultural reminder, partly buried with earth. A stable cascade was created along the new channel using stones. The stone cascade also acts as a deterrent for invasive species such as Eurasian Carp, preventing them from moving upstream. Woody and herbaceous vegetation has been planted to protect the streambanks and shade the creek.
The restoration efforts undertaken over the past few years have resulted in a remarkable transformation of the area. Cedar Creek has been restored to its original watercourse, and strategically placed rocks and logs now provide shade for fish and basking spots for turtles. Through the gradual removal of accumulated silt, the pond has been converted into a series of connected pools adorned with native plants. Decommissioning the dam has allowed Cedar Creek to flow freely, leading to cooler water temperatures, enhanced pollution absorption, and improved aquatic habitat.
Overall, the restoration efforts have been a success, significantly improving water quality and revitalizing the natural ecosystem. As a result, a diverse range of aquatic species in the area has benefited from these positive changes.
Video links: , , , the .
Springbank Dam Failure and the Benefits to Spiny Softshell Turtles
Spiny Softshell Turtle hatchlings | Photo by Scott Gillingwater
Located on the main branch of the Thames River in London, Springbank Dam was constructed at this site in 1929 to replace a dam that had washed out several years before. While the original dam had been built to provide water power, the 1929 dam had a recreational function, creating a reservoir for boating and fishing for six months of the year.
In 2008, a hinge on Springbank Dam failed during commissioning following a lengthy rehabilitation project, rendering the dam inoperable. With the structure no longer creating a seasonal barrier, the Thames River resumed its natural flows within the footprint of the former reservoir. A free-flowing system formed, allowing sediment to mobilize and a low-flow channel to become better defined. Lateral sand bars developed along the margins of the river. Mid-channel bars in wider, multi-threaded sections of the river formed island features that divert flows and accumulate sediment under low-flow or normal flow conditions.
London City Council voted to permanently decommission Springbank Dam.