In addition to Fanshawe, Wildwood and Pittock Dams, the UTRCA owns and/or operates and maintains 10 other dams in the upper Thames River watershed. These dams and reservoirs are primarily recreational facilities, but their structural components and operations must be monitored to ensure they can withstand flood conditions and that upstream and downstream properties are not at risk from flooding. Actual operations are undertaken by the local public utilities or engineering department under the direction of the UTRCA.
The role of the UTRCA’s hydrology staff is:
• to assess maintenance needs,
• to arrange scheduled maintenance,
• to provide project management, and
• to undertake flood forecasting and monitoring activities for these facilities.
Reservoir operations focus on the safety of the structures and the residents of the watershed, but other factors play an important role, too. The needs of reservoir users and of the watercourse downstream play an important role in determining reservoir releases. Similarly, environmental concerns related to water quality as well as the health and migration of aquatic life add more and more complexity to the operational decisions.
• Springbank Dam (London)
• RT Orr Dam – R Thomas Orr Dam is located on the Avon River in Stratford east of the Huron Street bridge. This dam was built in 1964 at a cost of $260,000, creating Lake Victoria. This lake is a focal point for the Festival City. The lake is approximately 1.6 km long with an average width of 112 m, and covers 16 Ha. The upstream drainage area is 89 square kilometres of mainly agricultural land.
• Mitchell Dam – Mitchell Dam is located on the North Thames River in Mitchell north of the Highway 8 bridge over the Thames River. The dam was constructed in 1963 at a cost of $260,000. Mitchell Dam has a drainage area of 166 square kilometres and creates an 18.6 hectare reservoir (see information on repairs to Mitchell Dam, fall 2015).
• Centreville Dam – owned by Township of Southwest Oxford, maintained by UTRCA
• Dorchester Dam – owned/maintained by UTRCA
• Dorchester Mill Pond Dam – owned/maintained by UTRCA
• Embro Dam – owned/maintained by UTRCA (see information on Class EA for Harrington and Embro Dams)
• Fullarton Dam – owned/maintained by UTRCA
• Harrington Dam – owned/maintained by UTRCA (see information on Class EA for Harrington and Embro Dams)
• Shakespeare Dam – owned/maintained by UTRCA
In addition to the above structures, there are 225 smaller barriers throughout the Thames River watershed.
In 2007, Dam Safety Reviews were completed for all structures and Embankment Stability Assessments have been completed for most. The UTRCA has been proactive with the completion of the Dam Safety Reviews to meet the MNRF’s Ontario Dam Safety Guidelines. It is anticipated that the Ontario Dam Safety Guidelines will become legislation in the next few years.
The Dam Safety Reviews showed that there are dams in the upper Thames watershed that have the potential to fail. Failure of dams leads to sedimentation problems, impacts on fish habitat and possible fines from Fisheries and Oceans Canada. In addition, liability issues would need to be resolved and could possibly involve litigation.
The UTRCA’s goal is to work with the local municipality to implement safety measures and/or remove structures so that dams are not left in an unsafe condition.
Dam Safety Background
As part of their mandate under the Lakes and Rivers Improvement Act, the Ontario Ministry of Natural Resources and Forestry (MNRF) introduced dam safety and flood emergency contingency planning requirements that are based, in part, on the Canadian Dam Association Guidelines. These have been formalized in the form of a draft document entitled “Ontario Dam Safety Guidelines” (ODSG).
According to the draft ODSG, a dam safety review “. . . involves a phased process beginning with the collection and review of existing information, proceeding to detailed inspections and analyses, and culminating with formal documentation.”
With this as a basis, the objectives of a dam safety review include:
• assessment of the conditions of the dam and its components
• performance of detailed site inspections
• identification of any necessary repairs and/or continuing maintenance needs and costs
• establishment of an emergency action plan to help minimize adverse impacts
• documentation of the results of the safety assessment so that the information is available in times of need and can be readily updated
• assessment of operational methods and equipment.
Specifically, the safety assessment of a dam comprises a procedural evaluation of the ability of a water-retaining structure to safely withstand all forces that could be expected to act on such a structure during its lifetime. A number of criteria have been developed to allow a systematic evaluation and classification of structures with respect to the potential failure risk it imposes. These criteria incorporate a classification system that addresses the following aspects:
• hazard classification
• flood handling capability evaluation
• geological/geotechnical assessments
• dam break flood evaluation [to evaluate incremental hazard potential (IHP) classification] • structural integrity and stability assessment.
Safety around Dams (MNRF webpage)