Churchill River Diversion
For a high level overview of this and other hydro projects see Hydroelectric Development in Northern Manitoba.
- 1 Background
- 2 Location
- 3 Components and Principal Works
- 4 Construction
- 5 Operations
- 6 Mitigation and Rehabilitation
- 7 References
The Manitoba portion of the Churchill River originally had a hydroelectric potential of more than 3,000 MW. Instead of harnessing this hydroelectric potential by building hydropower stations along the river itself, a considerable economic advantage was gained by diverting most of the Churchill River water into the Burntwood and Nelson River systems to use at the generating stations planned on these rivers.
Following joint federal-provincial studies, Manitoba Hydro, in February 1966, announced its intention to divert the Churchill River as part of an overall plan of northern hydro development.
The Churchill River basin lies to the north of the Nelson and Saskatchewan River basins, with its headwaters in east-central Alberta. The river flows across Saskatchewan in an easterly direction, at an average distance of about 150 mi (240 km) north of the Saskatchewan River. In its lower reaches through Manitoba it runs in a north-easterly direction, roughly parallel to and at a distance of about 100 mi (160 km) from the Nelson River.
The Churchill River Diversion (CRD) centers on Southern Indian Lake, which is a widening in the Churchill River in the northwestern part of Manitoba (Map 1). The project is not a single location but a collection of works that are collectively described as the CRD. The Missi Falls Control Structure (CS) regulates the amount of water allowed to flow out of Southern Indian Lake, down the Churchill River (the natural outlet of Southern Indian Lake). Water is diverted from Southern Indian Lake through the South Bay Diversion Channel, into the Rat River, and through the Notigi CS to the Burntwood River and then to the Nelson River (Map 1).
Components and Principal Works
The components of the CRD are comprised of two control structures, an excavated channel, and two mitigation structures as shown in Map 1. Following, are descriptions of each of these components.
Missi Falls Control Structure
The Missi Falls CS (Map 2; Photo 1) regulates the amount of water allowed to flow out of Southern Indian Lake, down the Churchill River (the natural outlet of Southern Indian Lake). The Missi Falls CS is located 106 mi (170 km) north of the City of Thompson. The control structure is capable of discharging 113,000 ft3/s (3,200 m3/s) at a forebay elevation of 847.5 ft (258.32 m). The principal works include a sixbay gated spillway, the South Channel Dam, the North Channel Dam, the Main Dam, the South Dyke, and an electrical services building. The Missi Falls CS was built between 1973 and 1976.
South Bay Diversion Channel
The South Bay Diversion Channel (Photo 2) diverts water from the South Bay of Southern Indian Lake into Issett Lake which flows into the Rat, Burntwood, and then Nelson Rivers. The channel is approximately 200 ft (61 m) wide at its base and 5.8 mi (9.3 km) long. The South Bay Diversion Channel was opened in 1976.
Notigi Control Structure
The Notigi CS (Photo 3; Map 3) regulates the amount of water diverted to the Nelson River via the Rat River and Burntwood River. The Notigi CS is located on the Rat River between Notigi Lake and Wapisu Lake. The control structure is capable of discharging 66,000 ft3/s (1,869 m3/s) at a forebay elevation of 847.5 ft (258.32 m). Principal works consist of a three bay spillway, an adjacent electrical service substation building, the Main Dam and a Saddle Dam. The Notigi CS was built between 1974 and 1975. In addition, the structure provides a crossing for PR 391.
Manasan Falls Ice Control Structure
The Manasan Falls Ice Control Structure is a passive control structure designed to reduce the risk of inundation (flooding) in the City of Thomson due to ice. The control structure is located on the Burntwood River approximately 5 mi (8 km) upstream of the City of Thompson. Principal works consist of an ice boom across the river, a by-pass channel with a concrete overflow weir, and a flood channel protected with a fuse plug dyke. The project was initially constructed in 1976 followed by rehabilitation in 1986 and the incorporation of additional safety features in 1988. An aerial view of the structure is shown in Photo 4.
The Churchill Weir (Photo 5) is a mitigation structure designed to increase water levels on the Churchill River to ensure a potable source of water, to enhance recreation and to enhance aquatic habitat. The structure was built 6 mi (10 km) south of the Town of Churchill, upstream of Mosquito Point and the salt water intrusion zone in the Churchill River estuary. The principal works consist of an overflow section and two dyke sections. The overflow section is 7,500 ft (2,300 m) long with a 1,000 ft (300 m) fishway segment at the lowest point of the weir. The west dyke is 450 ft (140 m) long and the east dyke is 3,850 ft (1,170 m) long. The east dyke incorporates the Goose Creek fishway and an emergency flood relief section. These works were essentially completed in October 1999.
Access to each of the components consist of the following:
- Missi Falls CS: by winter trail, air and water;
- South Bay Diversion Channel: by winter trail, air and water;
- Notigi CS: initially by winter trail along the 138 kV transmission line. PR 391 was constructed at the same time, originally as a gravel all-weather road between the City of Thompson and the community of Leaf Rapids;
- Manasan Falls Ice CS: by a temporary construction road; and
- Churchill Weir: by Hudson Bay Railway line, local roads and air.
Of the CRD components, only the Notigi CS is connected to the provincial transmission grid. The Notigi CS is connected by a 12 kV line to the 138 kV line, WL43, from Mystery Lake to the Laurie River #1 GS. Electrical power required for the operation of the Missi Falls CS is supplied by a house unit.
All of the CRD components were undertaken utilizing local materials. For construction dates, see the description of the components above.
Temporary construction camps and work areas were established near the sites. Construction power for each of the components was provided by:
- Missi Falls CS: diesel generators;
- Notigi CS: a tap from the 138 kV line between Mystery Lake and Laurie River #1 G.S. (WL43);
- South Bay Diversion Channel: diesel generator (likely);
- Manasan Ice CS: diesel generator; and
- Churchill Weir: a tap to the 138 kV Radisson to Churchill (RC60) line, or may have been by a generator.
Workforce: The Notigi CS is not normally manned. Operation of the spillway gates is directed by the Energy Operations Planning Department, with operations staff from the City of Thompson traveling to the Notigi CS by PR 391 to operate the gates as required.
The Missi Falls CS is not normally manned. Operation of the spillway gates is directed by the Energy Operations Planning Department, with operations staff from the City of Thompson being dispatched to the Missi Falls CS to operate the gates as required. Operation of the spillway gates occur at least six times a year, generally in the spring and fall.
The Missi Falls CS is accessible by water by boats launched from the Notigi CS or by air. There is an airstrip 1.2 mi (2 km) from the Missi Falls CS site, but the site is also commonly accessed by helicopter. There is a staff house at the Missi Falls CS with a water and sewer system.
Water Regime: The Missi Falls CS and the Notigi CS operate to control outflow from Southern Indian Lake as part of the CRD. The majority of flow is typically diverted through the Notigi CS, while a smaller portion flows through the Missi Falls CS. The discharge at both the Missi Falls CS and the Notigi CS typically remain constant for long periods of time up to several months in duration. For more details on CRD operations and their effect on the water regime see Water Regime, Section 4.3.3.
Licence: Manitoba Hydro operates the CRD in accordance with a Province of Manitoba Water Power Act License. Authorizations granting temporary amendments to this licence first began for the 1979/1980 winter operating season to optimize CRD operations. Variations to these amendments occurred until 1986. Every year since then, these amendments have been unchanged and have been referred to as the Augmented Flow Program. For further information see the Manitoba Government Water Power Licensing website at http://www.gov.mb.ca/waterstewardship/licensing/water_power_licensing.html
Mitigation and Rehabilitation
As a result of the increased flows in the Burntwood River at the City of Thompson, it was necessary to modify the city's water intake system and to rebuild the floatplane base. As a result of the decreased river flows on the Churchill River, modifications were required to the water supply works for the Town of Churchill. As a result of flooding of approximately 3.1 mi2 (8.1 km2) of Indian Reserve land, remedial works and other mitigation measures were required in the area of Nelson House.
Construction of the South Bay Diversion Channel in the 1970’s resulted in residual construction debris and the contamination of soil at the former South Bay Construction Area. In 2003, environmental drilling investigations were initiated at the former diesel generating and transformer station sites at South Bay. Remediation subsequently took place at the former transformer station in 2005, comprising of the excavation of approximately 2,100 ft3 (60 m3) of impacted soils and the removal of construction debris. In 2005 and 2006, thirteen sites were assessed for buried metal debris using a geophysical electromagnetic survey to quantity and locate historical construction debris; eight areas of buried debris were confirmed by the survey. In 2007, an environmental drilling investigation comprising 127 test pits and/or test holes was conducted at eighteen sites to determine the presence or absence of impacted soil; approximately 919,100 ft3 (26,030) m3 of petroleum hydrocarbon impacted soil was identified at three sites. To treat the impacted soils, a soil treatment facility is required. Manitoba Hydro and O-Pipon-na-Piwin Cree Nation are currently investigating the suitability of a parcel of land close to South Bay for the construction of the facility. Once the suitability of the land is confirmed, the soil treatment facility will be constructed and remediation of impacted soil and removal of debris will commence. At the Missi Falls CS, no significant environmental work has been completed. Investigations are planned when South Bay Remediation concludes.
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