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RESERVOIR REFORMATION
Tuesday, February 15, 2011
Flood control reservoirs were in vogue fifty/sixty years ago. In some cases they were given credence for summertime stream flow augmentation; Luther Lake being a primary example. Flood control reservoirs where an answer to the increasing occurrence and scale of flooding problems in some built up areas of southern Ontario. Historically, numerous marshes and extensive swamps and forests had provided this flood control function; but much of these had been lost, indeed are still being lost, to drainage and clearing for agriculture, urban development and transportation corridors.The Grand River and Upper Thames Valley Conservation Authorities were the biggest of the reservoir builders. The “opening up” of vast watersheds above cities like Cambridge and London had resulted in a spring melt rush of waters, sometimes augmented by a heavy rainfall event, through naturally and artificially constricted flood plains within these metropolises. Though the Saugeen River has a comparable watershed, it still retains a goodly percentage of its natural water retention characteristics. Flooding along the Saugeen is infrequent, localized, and usually the result of temporary ice jams.
The Grand River Conservation Authority contains Conestogo Lake, Belwood Lake, Guelph Lake and Luther Lake. Guelph Lake was created in the 1970’s and to my knowledge is the last of the major flood control reservoirs. The Upper Thames Valley Conservation Authority has Fanshaw Lake, Wildwood Lake and the Gordon Pittock Reservoir at Woodstock. The Upper Thames proposed a major reservoir near Fullarton in the 70’s but it never came to be. There are other mini reservoirs like Mountsberg near Milton and Parkhill near its namesake town, plus small recreation reservoirs in municipalities both large and small; such as Toronto and Strathroy. Another flood control reservoir of significance is the Binbrook Reservoir, near its namesake town; also known as Lake Niapenco; called so after the Niagara Peninsula Conservation Authority wherein it lies.
Flood control reservoirs are created by placing large water control and management works, commonly known as dams and floodgates, at river flood plain constrictions and flooding the valleys above, often for quite a distance upstream. The exception is Luther Lake. Being at the height of several smaller watersheds, all within the Grand River watershed, Luther Lake is not in a deep valley. Much of this impoundment is quite shallow by typical reservoir standards. The Luther impoundment rapidly evolved into a great marsh and was known for many years as Luther Marsh. Like a marsh in the middle of a prairie, it attracted a host of aquatic species, especially water birds. Over time, due to prolonged flooding and aggressive reforestation around the perimeter, in addition to woody species evolution across abandoned fields and pastures, the Luther impoundment became more characteristic of a lake in the middle of a forest.
The typical, as intended, annual water retention regime for any flood control reservoir is to store water in late winter and early spring to a maximum design level; and then release this water over the summer and fall so as to make room for next spring’s anticipated runoff. As such, flood control reservoirs are big lakes in the spring and small lakes with a lot of empty perimeter by late fall. Large expanses of the upper ends of these reservoirs become barren mud flats on an annual basis, devoid of water with the exception of the original watercourse. The upper extremities of reservoirs are shallow by way of natural and historic topographical gradients. When inundated, they are like shallow wetlands, offering marsh like conditions to indigenous wildlife. However, this marshy condition is annually temporary; natural aquatic vegetation communities never gain a permanent foothold and wildlife values suffer accordingly.
When Ducks Unlimited Canada came to Ontario in 1975, two of its earliest “landowners”, now known more accurately as “partners”, were the Niagara Peninsula and Upper Thames Valley Conservation Authorities. Both had visions of maintaining, on a year round basis, the shallow aquatic conditions at the upper end of the Binbrook and Wildwood Reservoirs. Both realized that the loss in flood storage volume within these shallow areas was insignificant given the flood routing capacity of the remainder of each reservoir. The Authorities were looking to make something more of their reservoirs, adding some diversity and values---natural, aesthetic and social, to the overall feature. Both Authorities called on Ducks Unlimited Canada for assistance in locating, designing, constructing and maintaining a permanent wetland feature within the upper echelons of their respective reservoirs.
The means of maintaining a shallow, year-round flood in the upper reaches of a reservoir is to isolate the selected area from the primary reservoir and its annual fluctuations. Constructing another dam across an optimal location will serve this purpose. This was done at both Wildwood and Binbrook. Now, flood control reservoirs typically have large watersheds and the volume of runoff waters that are being conveyed through the main dam must also be conveyed through any management works placed at the top end of the reservoir. Comparable floodgate controls are prohibitively expensive. The solution is a long overflow spillway section at the end of each dam to convey spring melt and major rainfall events. Small, economical, variable-level control structures allow the management of marsh levels, including occasional dewatering should this ever be required, during periods of low runoff, typically throughout the late spring, summer and fall.
The Binbrook and Wildwood marshes where outfitted with very similar small, variable-level structures. However, the big overflow spillways are quite different. At Binbrook, the spillway has a broad, relatively flat concrete crest with a concrete cut off wall underneath, running the entire length of the crest. The upstream ingress and downstream egress of the spillway crest are protected from erosion by armour stone. The Wildwood spillway is a wall of interlocking steel sheet piling. Armour stone along each side and downstream of the piling inhibits erosion.
Wildwood Lake is on a tributary of the Upper Thames River known as Trout Creek. As its name suggests, this waterway likely contained a robust population of native Brook Trout back in early settlement days. It runs clear most of the time and this clarity positively influenced the establishment of aquatic vegetation communities, regardless of water depths, in the permanent wetland in the upper reservoir. The Binbrook Reservoir lies in the upper reaches of the Welland River watershed. The inherent clay soils and more intensive human activity on this watershed result in more turbid waters, especially during runoff events. As such, the establishment of native wetland vegetation communities has not been as extensive as at Wildwood. However, the permanent aquatic condition has been of considerable benefit to fish and wildlife making Binbrook another wetland restoration and management success story.
Not all flood control reservoirs lend themselves to the type of conservation action implemented at Wildwood and Binbrook. The physical features have to be just right. The primary purpose and function of the reservoir must not be adversely compromised. The Board Of Directors and staff of the Conservation Authority; and all partners for that matter, must have the kind of vision and be of a mindset that will allow such action to be considered and to take place. And it is always helpful to have a partner, such as Ducks Unlimited Canada, to help facilitate the success story.
I was born on the Bruce Peninsula on July 20, 1951 and raised on a farm just south of the village of Lions Head, which is located about halfway up the peninsula on the Georgian Bay shoreline. I graduated from Georgian College of Applied Arts and Technology in Barrie in 1973 as a Resources Engineering Technologist. I was hired by Ducks Unlimited Canada (DUC) in April of 1975 as the first DUC employee in Ontario. Throughout almost 29 years I was involved with the implementation of more than 500 wetland projects and project complexes in southwestern and south central Ontario. Some of these habitat projects included important waterfowl and migratory bird habitat along the eastern shoreline of Lake St. Clair. Just three weeks short of completing 29 years with DUC, I accepted an early retirement opportunity effective March 31, 2004.
