DECEW FALLS II
PLANT GROUP: Niagara Plant Group
DRAINAGE BASIN: Lake Erie
NEAREST POPULATION CENTRE: St.Catharines (6.4 km (4 miles), 152 M (500 ft) east of Decew 1)
IN SERVICE DATE:
Unit 1- October 1943
Unit 2- 1948
BUILT BY: Hydro-Electric Power Commission of Ontario
FROM: Dominion Power and Transmission Company
Asset Transferred to Ontario Power Generation: April 1, 1999
NUMBER OF UNITS: 2
CENTRE: Allenburg TS
CONTROL: Remote from SAB II GS
A decision to proceed with the DeCew Falls development was reached in 1941. The decision was influenced by a number of considerations.
First, the setbacks, including the fall of France, which were experienced during the early years of the war, made it evident that the war might last much longer, that Canada would be called upon to speed up the production of munitions and undertake many new industrial tasks, and that as a result the large actual and potential reserves of power which the Hydro-Electric Power Commission of Ontario had available at the outbreak of war might not be sufficient should the war last until 1943 or 1944.
Second, the delays experienced in the St. Lawrence project made it evident that power from this source could not be relied upon and that Hydro-Electric Power Commission of Ontario must plan immediately for increased power production from any source which could be started immediately, and which would afford relief in strategic areas.
Ever since the purchase of the Dominion Power and Transmission Company in 1930, by Hydro-Electric Power Commission of Ontario, the development of further power at DeCew Falls was visualized as economically attractive if operated in conjunction with the Niagara River power plants. It was recognized that the agreement respecting the Ogoki and Long Lac diversions would provide the water required for the operation of a new plant at DeCew Falls. The decision to proceed was therefore made.
In 1986 the spillways at Port Dalhousie were replaced by the construction of the Haywood Generating Station, owned and opreated by the City of St. Catharines Hydroelectric Commision. The original spillways were designed to provide the additional capacity, necessary to carry the increased flow from the DeCew power plants. A channel 215 m (700 ft) long, with control structure and concrete highway bridge was constructed immediately to the east of the navigation channel and Lock No.1 of the Third Welland Canal.
The control structure contained four submerged sluiceways designed to accommodate Taintor gates between piers, with supporting gravity wing walls at each side of the channel. Two of these sluiceways were equipped with motor operated Taintor gates, while the remaining two were closed with stoplogs until further additions at the power plant require installation of control gates.
Under wartime conditions, the resulting demand for power necessitated the installation of a 65 000 hp unit at DeCew Falls operating under a head of 80.8 m (265 ft). Unit 1 was brought from the Abitibi Canyon development where it had been a stand-by unit. Being the right size and speed for the DeCew Falls plant, its transfer to the new development effected a considerable saving in time and materials.
The necessary water to operate the plant was provided by two diversions in the Lake Nipigon area.
The Ogoki River diversion, the construction of which began in November 1940, was completed and officially opened on July 20, 1943. The scheme contemplates the diversion of almost all of the flow from the Ogoki River above Waboose Rapids from the Albany River watershed into Lake Nipigon and the Great Lakes. It was estimated that the diverted waters, on the average, would amount to some 113 cms (4,000 cfs).
At Waboose Rapids, on the Ogoki River, a concrete dam, 15.2 m (50 ft) high, was constructed and this together with the Summit Control dam and a number of earth-fill side dams created a reservoir having an area of approximately 259 km2 (100 miles2). This reservoir extends southerly through Mojikit Lake into a small lake known as North Summit Lake. From North Summit Lake, a channel was cut through a saddle in the height of land to permit the water to flow into South Summit Lake and then by way of a chain of connected lakes and the Jack-fish River to Lake Nipigon.
Waboose dam is, the largest dam in the project. It is of concrete construction, with a total length of 518 m (1,700 ft). Twelve sluiceways, 7 m (23 ft) high and 4.9 m (16 ft) wide, separated by 1.8 m (6 ft) piers, provide for the discharge of water which cannot be impounded or diverted southerly. A spillway, 233 m (765 ft) long is provided to take care of flows that might cause the normal high water level of the reservoir to be exceeded.
The Summit Control dam, constructed at the north end of South Summit Lake, is a concrete dam about 7 m (23 ft) high to the top of the deck. It contains eight 4.9 m (16 ft) sluice-ways, separated by 1.5 m (5 ft) piers and a concrete bulkhead section at each end. There is a total length of approximately 123.4 m (405 ft) of concrete dam, beyond which was constructed at the south end 36.6 m (120 ft) of earth-fill with a concrete core wall.
In addition to the above two main dams, several earth-fill dams were required to close low areas around the reservoir. Two of these are east of and near Waboose dam and are known as auxiliary dams No.1 and No.2. They are compacted earth-fill dams, having a timber sheet piling core, with rock toes and a layer of gravel 61 cm (24 in) thick over the compacted material. Snake Creek dam, near the source of the creek of the same name, is 12 km (7.5 miles) west of Mojikit Lake, into which the creek flows. It provides protection at times of high reservoir levels against the possibility that some diverted water might pass westerly to Pikitiguchi River and pass down that channel to Lake Nipigon. It consists of a gravel fill with a 15 cm (6 in) timber sheet piling diaphragm. Chappais Lake dam, a cut-off dam, is constructed of compacted clay and gravel. It provides against a break through at the height of land to the headwaters of Seymour Creek.
At the point where the Jackfish River passes under the Canadian National Railway, it was necessary to provide a stable channel, which would accommodate the greatly increased flow without endangering the railway A channel, 15 m (50 ft) wide, was excavated in rock to the left of the natural river bed, earth-fill placed to close the old channel, and extensive protection given by placing heavy rip-rap on the slopes. A new bridge was constructed with solid concrete abutments and concrete piers. The bridge is of plate girder design with steel towers varying in height from 9 m to 21 m (30 ft to 70 ft). As a conservation measure, this bridge was constructed of steel salvaged from other bridges dismantled in recent years. The total length is approximately 250 m (800 ft) and the spans vary in length from 21 m to 30.2 m (69 ft to 99 ft).