Construction of a dam on Trout Creek, upstream of the Town of St. Marys, was proposed in 1948 as the first major project of the UTRCA after its formation in 1947. Originally designed as a flood control reservoir, there was considerable opposition and the project was shelved. It was thought that improving certain land use practices would be more effective at improving flood control.
The Upper Thames Valley Conservation Report (1952) modified the plans for the dam, proposing that in addition to providing flood protection to downstream communities, the reservoir supplement flows during the drier summer months.
Construction began at the dam site in 1962 and finished in 1965. The cost of the dam and land base at that time was close to $3.5 million. Present annual maintenance costs are about $50,000.
The dam can reduce flood flows on Trout Creek by up to 95%, and on the North Thames below St. Marys by 10%. Flows from the reservoir increase dilution of treated sanitary sewage, providing up to 75% of the flow in the North Thames below St. Marys and, during long dry periods, up to 30% of the flow on the Thames below London. During dry periods, the dam and reservoir provide additional water quality and aquatic habitat benefits.
Operating the Dam
Wildwood is operated in a coordinated manner with reservoirs at Fanshawe (London) and at Pittock (Woodstock). This optimizes flood control and low flow augmentation efforts for the North Thames River in St. Marys and for the Thames River watershed in general.
Facts about Wildwood Dam & Reservoir
• Completed: 1965
• Cost: $2,180,000 (1965 dollars)
• Who paid: Provincial government 37.5%, Federal government 37.5%, UTRCA 25% (benefitting watershed municipalities)
• Drainage area: 141 square kilometres
• Normal summer length – 9.3 km
• Average width – 460 m
• Normal water surface area – 385 ha
• Normal lake storage available for summer flow augmentation – 1780 hectare-metres
• Spring runoff storage – 2470 hectare-metres
• Maximum water level – 326.4 metres above sea level (masl)
• Early summer holding level – 324.8 masl
• Winter holding level – 318.2 masl
Dam & Berm
• Crest length – 640 m
• Distance from crest to river bed – 16.5 m
• Elevation of crest – 328 masl
• Size of gates (4) – 3.65 m2
• Capacity of each gate – 70 cubic metres/second (cms)
• Size of regulating valves (3) – 45 cm diameter
• Capacity of each valve at maximum water level – 1.2 cms
• Maximum total discharge capacity – 565 cms
Wildwood Dam is designed for both flood control and flow augmentation purposes. The outflow from the dam is controlled by three main operating features:
• Four large sluice gates provide coarse control of flows from the dam. These gates are used mainly during the spring runoff period (March- April) and during the fall and early winter when the soil may be frozen or saturated and runoff from snow melt or rainfall is potentially high.
• Three small valves located in the core of the dam below the winter water level provide fine control of outflow during the summer and other times when often even less flow enters into the reservoir. The valves also allow discharges of cooler water from the bottom of the reservoir during the summer. By using the valves, the reservoir can be further lowered for maintenance purposes.
• Concrete baffle walls above the gates provide some automatic control during the early summer months when the reservoir level is at or close to its highest level. Water can spill over the walls when the reservoir rises following summer storms.
By agreement with the Ministry of Environment a minimum volume of water is released downstream during the summer months. An annual operating cycle guideline was established within the original design intent for the dam and reservoir. The cycle indicates continuous changes in water levels during the year. The fluctuations provide optimum year round flood control capability to protect downstream communities without endangering the safe operation of the dam, and benefits water quality downstream during dry summer conditions.
Safety around Dams (MNRF webpage)