Limestone Generating Station

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For a high level overview of this and other hydro projects see Hydroelectric Development in Northern Manitoba.

Background and Construction[edit]

Background Studies in the 1960s and early 1970s envisioned a four phase development at Kettle Rapids and downstream, namely the sites at Kettle Rapids, Long Spruce Rapids, Lower Limestone Rapids and Gillam Island, to harness the abundant hydroelectric potential of the Nelson River. The first phase of development included the following components:

  • a generating station at Kettle Rapids;
  • a High Voltage Direct Current (HVdc) transmission line from Kettle Rapids to the City of Winnipeg;
  • control works to divert the Churchill River into the Nelson River via the Burntwood River; and
  • control works to regulate the outflow of Lake Winnipeg into the Nelson River.

The second phase of development included the Long Spruce Generating Station (GS) which was Manitoba Hydro’s fourth generating station built on the Nelson River. The third phase of development included the Limestone GS.

Location[edit]

The Limestone GS is located at a site previously known as Limestone Rapids or Upper Limestone Rapids (Photo 1), upstream of where the Limestone River empties into the Nelson River. It is approximately 14 mi (23 km) immediately downstream of the Long Spruce GS, 34 mi (55 km) from the Town of Gillam and 466 mi (750 km) north of the City of Winnipeg.

Photo 1: Upper Limestone Rapids Looking Downstream at the North Shore, 1976

Initial Construction[edit]

Prior to the commencement of construction on the Limestone GS, a number of supporting infrastructure components were constructed as part of the adjacent Henday CS (see HVDC Transmission System). A permanent gravel access road and a construction power line were extended from the Long Spruce GS area to the Limestone GS area in the early 1970’s, with the road later becoming PR 290. A rail spur from the Hudson Bay Railway line (now HBR; Canadian National Railway [CNR] at the time) near the community of Bird (now Fox Lake Cree Nation [FLCN]) was also constructed to the Henday CS site. Construction of the Limestone GS Stage I cofferdam began in 1976. However, while the cofferdam construction was underway and nearly complete in 1978 (Photo 2), construction of the Limestone GS was suspended indefinitely by Manitoba Hydro as a result of a lower than expected forecast in the provincial demand for electricity. Cessation of the Limestone GS construction brought to an end the busiest period of electrical development activity ever to occur in Manitoba.

Photo 2: Stage I Cofferdam Construction – 1978

Reinitiated Construction[edit]

In August 1985 construction of the Limestone GS was resumed by Manitoba Hydro as a result of the approval by the National Energy Board for an export sale for up to 500 MW of firm power from 1993 to 2005 to the Northern States Power Company of Minneapolis, Minnesota. As a result of the initial construction activities between 1976 and 1978, the project was able to re-commence development work directly on the principal structures as much of the supporting infrastructure required for construction activities was already in place.

A new rail spur extending the Henday rail spur was added to the Limestone GS work area. There was an airstrip in the community of Bird for some portions of the project but it was not used for construction. The temporary construction camp, work areas, a temporary townsite named Sundance, and the opening of the Limestone River Quarry as a source of rock fill for the Stage I cofferdam were re-established. The entire construction workforce either lived in camp or in the Sundance townsite. Those living in camp stayed for several weeks at a time and travelled to their homes during their days off. Solid waste was disposed of at a local solid waste disposal site and wastewater was treated at a local lagoon.

The Stage I cofferdam constructed in 1978 was originally designed to an elevation of 70.0 m above sea level. During the period from 1979 to 1985 this cofferdam was overtopped on two occasions due to high water levels caused by ice jams (Photo 3). This new information led to the requirement to increase the height of the Stage I cofferdam to a nominal elevation of 73.0 m prior to re-commencing construction (Figure 1). The materials for construction came from local areas, rock came from the Limestone River Quarry and the site excavations, granular and impervious materials came from local borrow areas.

Photo 3: Nelson River Overtopping the Stage I Cofferdam – 1979
Figure 1: Limestone Generating Station during Construction

The generating station was constructed in two primary stages, the first being the construction of the north dam, the powerhouse, and the spillway all contained within the Stage I cofferdam (Photo 4). The second stage began with the full closure of the river, the diversion of water through the spillway, and the completion of the south dam across the river (Photo 5). Following five years of construction activity the first unit went into service in 1990, with the station becoming fully operational by 1992 when the tenth and final unit went into service.

Photo 4: Principal Works Construction – 1987
Photo 5: Stage II Closure – 1989

Project Components[edit]

Principal Works[edit]

The generating station spans a total of 0.8 mi (1.3 km ) across the Nelson River and consists of a closecoupled intake/powerhouse with ten generating units, concrete wing walls, two main earthfill dams (north and south) and a seven-bay gated spillway (Photos 6, 7; Map 1).

Photo 6: Limestone Generating Station Area – Looking South
Photo 7: Limestone Generating Station – 2009
Map 1: Limestone Generating Station General Arrangement

Project Data[edit]

  • Turbine generator units:
    • Type: 10 vertical-shaft fixed-blade propeller turbines
    • Capacity: 1350 MW (63rd Annual Report, March 2014)
  • Powerhouse:
    • Length: 948.2 ft (268.5 m)
    • Waterfall drop (head): 120.5 ft (31.2 m)
    • Discharge capacity: 176,573 ft3/s (5,000 m3/s)
  • Main dams (North and South dams):
    • Length: North Dam = 230 ft ( 70.0 m); South Dam = 2,362 ft (720 m)
    • Maximum Height: North and South dams = 131 ft (40.0 m)
  • Spillway:
    • Number of bays: 7
    • Length (7 bays): 444.9 ft (113 m)
    • Discharge capacity: 339,021 ft3/s (9,600 m3/s)
  • Reservoir/forebay elevation:
    • Full supply level: (Maximum Operating Forebay Elevation, Open Water) - 279.9 ft (85.313 m)
    • Normal minimum operating forebay elevation: 270.0 ft (82.296 m)
    • Flooded Area: 0.8 mi2 (2.1 km2)

Transmission Components[edit]

In conjunction with the construction of the Limestone GS two transmission projects were undertaken, and are described below.

Related Transmission[edit]

A 25 mi (40 km) 138 kV transmission line was built in 1989 from the Radisson Converter Station to the Limestone GS to act as an emergency backup to the generating station.

Generation Outlet Transmission[edit]

The Limestone GS outlet transmission consists of five 138 kV transmission lines built in 1990 from the Limestone GS to the existing Henday Converter Station. This allowed the power to be moved from the Limestone GS onto the High Voltage Direct Current (HVdc) transmission system to southern Manitoba.

Mitigation and Rehabilitation[edit]

As part of the re-initiation of construction activities for the Limestone GS, the project underwent the first environmental assessment for a Nelson River generating station. The environmental assessment included consultation with the Town of Gillam and the FLCN. Most of the recommendations for monitoring potential adverse effects on the biophysical environment and enhancing beneficial effects to the local area were implemented during project construction and operation. Only minimal mitigation was recommended because the environmental effects of the project were assessed to be minimal, largely because the Limestone GS resulted in a relatively small amount of flooding. Select borrow areas underwent pilot revegetation initiatives.

The Limestone/Bird waste disposal ground was in use until approximately 1999. The site was cleaned up to meet regulatory requirements in 2000 and Manitoba Hydro planned to transfer the site to the FLCN, however, the transfer has not been finalized.

Operations[edit]

Access: Access to the site is by PR 290, which was designated as a provincial road following construction. The rail spur line, stores work area, and various buildings remaining from construction continue to be used for operational purposes.

Workforce: The station has approximately 30 to 35 staff comprised of the following: operating staff, maintenance staff (electrical, mechanical, utility), support staff (administration, stores) and supervisory staff. The operators are located on site for 24 hours per day, seven days per week. The remaining of the maintenance staff are on site during normal business hours during the weekdays. The majority of the staff working at the Limestone GS drive in from the Town of Gillam. There are no staff accommodations on site at the Limestone GS. Additional support and technical services are located in the nearby Town of Gillam.

Public Safety: The Limestone GS has a portage around the site and the following public safety features:

  • A water release siren is used before adjusting discharge to warn the public in the area;
  • Life rings are provided at the spillway; and
  • Warning signs are provided (in English and Cree) at site to warn the public of: dangerous swift moving waters, steep drop off, overhead power lines, stay off Ice, falling ice, slippery rocks, and rapidly changing water conditions.

Water Regime: The Limestone GS is operated as a run-of-river generating station with flow patterns matching water releases from the Long Spruce GS upstream, which are driven by water releases at the Kettle GS further upstream. The Kettle GS is operated with a daily and weekly cycling pattern that allows Manitoba Hydro to match energy production to consumption patterns. For more details on the Limestone GS, the Long Spruce GS, and the Kettle GS operations and their effects on the water regime, see Water Regime, Sections 4.3.4.3 and 4.3.4.4.

License: Manitoba Hydro operates the Limestone GS in accordance with a Province of Manitoba Water Power Act license. For further information see the Manitoba Government Water Power Licensing website at: http://www.gov.mb.ca/waterstewardship/licensing/water_power_licensing.html.

Rehabilitation[edit]

The facilities built during construction were not totally decommissioned following construction. Several facilities remain and are used for operations or as potential future work areas. There has been some restoration work undertaken in the surrounding borrow areas. The former metal waste disposal ground was decommissioned in 1995.

References[edit]

Manitoba Hydro & the Province of Manitoba, December 2015, Regional Cumulative Effects Assessment Phase II: Part II Hydroelectric Development Project Description in the Region of Interest. Retrieved April 1 2016 from, https://www.hydro.mb.ca/regulatory_affairs/rcea/pdf/rcea_phase2_part_ii_hydroelectric_development_project_description.pdf