Comprehensive Study Report

This section summarizes the information on the background and purpose of the project, alternative approaches and the proposed options, and a description of the proposed facility. The information is taken from Chapters 1, 3 and 4 of Volume 1 of the draft-design report and the supplement to that report prepared by the proponent.

2.1. Background and purpose of the project

Hydro-Québec is planning to build a new hydroelectric facility at the Grand-Mère site on the Saint-Maurice River.

The Grand-Mère hydroelectric power station, built between 1913 and 1916, is becoming obsolescent and experiencing operating problems. Furthermore, the design flow is inadequate, and this causes a bottleneck situation on the river and prevents optimization of the output from the Saint-Maurice complex facilities located downstream (Shawinigan I and II, La Gabelle).

The existing generating station, located on the right bank of the river (western bank), has nine Francis turbine units with an installed capacity of 150 MW. Its peak design flow is 880 m³/s. The facility has a sending-end substation on its roof and spillways with a maximum capacity of 5 925 m³/s.

From an analysis of the state of the present facility, the proponent identified four serious problems revealing the need for major repairs in order to ensure effective operations at the site. The problems are associated with the following elements:

• The turbine-generator units require major repairs owing to their age (50 years) and their advanced state of deterioration. This equipment will reach the end of its useful life in early 2000;
• The sending-end substation, which has exhibited operating problems caused mainly by its lack of flexibility and its low electrical capacity;
• The spillways' concrete structures, which are in an advanced state of deterioration, coupled with gate operating and maintenance problems, increase the need for action to make the works safe. In addition, based on a review of the criterion related to the discharge capacity of the facility, work needs to be done to enable the spillways to withstand the additional loads created by exceptional floods;
• The power station creates a bottleneck situation on the Saint-Maurice River, impeding optimization of the maximum usable flow at the facilities of the Saint-Maurice complex, all of which have a much lower design flow than does the Grand-Mère station.

Out of the three options studied (abandonment, upgrading or construction of a new generating station), the proponent considers construction to be the most acceptable solution from an economic, social and environmental viewpoint, and this option is also in keeping with Hydro-Québec's strategic plan.

In preparing its project proposal, the proponent assessed three possible construction scenarios for the power station, the spillways and the sending-end substation, and five construction options for the access roads leading to the structures.

The proposal for a new hydroelectric facility at Grand-Mère fits in with Hydro-Québec's 1998-2002 strategic plan, whose orientations include maintenance of present electricity rates and consistent service quality in the area of energy supply in Quebec. This means ensuring the sustainability of the bulk power system so as to provide a safe and reliable supply of electricity over the coming years. The project is part of the upgrading program run by Production d'Hydro-Québec, which is aimed at maintaining the facilities in good operating condition in order to ensure maximum generating system availability at the lowest possible cost.

There are many advantages to upgrading an existing facility, both economic and environmental, and this approach is consistent with the recommendations formulated by various groups during the consultations on the 1993 development plan, which urged Hydro-Québec to make every possible improvement to the existing system on a priority basis before undertaking new projects to satisfy demand.

2.2. Alternative approaches to carrying out the project

2.2.1. Determining the facility's future

In the process of studying possibilities for upgrading generating facilities, Hydro-Québec analysed the following options from a technical, economic, financial and environmental standpoint:

• Upgrading of the existing facility;
• Replacement of the existing facility by a new one, built at the same location on the river or nearby;
• Decommissioning of the present facility.

The option of decommissioning was not selected for the comparative analysis, however, since the criterion of establishing a new generating station at a cost of under 3¢/kWh made this option uncompetitive. In addition, the repairs required to the existing spillways for reliability and safety reasons would increase the decommissioning costs.

In light of the results of the comparative analysis, the proponent determined that construction of a new facility at the Grand-Mère site was the most advantageous solution (Table 1). It addresses the problem of the facility's obsolescence and the bottleneck situation at the outlet of the generating station.

Table 1. Result of the comparative analysis of the two project completion options

	New Facility	Upgrading
Technical criteria
Power gain	81 MW	10 MW
Energy gain	234 GWh	63 GWh
Economic criteria
Construction	$451.3M	$426.1M
Cost of equivalent service	-	$133.5M
Total investment	$451.3M	$559.6M
Loss of production during construction	-	$6M
Maintenance and operating cost	$31M	$58.1M
Total	$482.3M	$623.7M
Financial criteria
Installed capacity	220 MW	150 MW
Peak power	215 MW	144 MW
Mean annual power output	1209 GWh	1038 GWh
Cost of equivalent service (in 2004 dollars)	$482.3M	$623.7M
Financial cost based on a rate of 11%	2.89 ¢/kWh	3.25 ¢/kWh
Internal rate of return at a supply rate of 2.81 ¢/kWh over a 30-year horizon	9.9%	4.7%
Environmental criteria	Acceptable	Acceptable

2.2.2. Development options

Following its decision to replace the existing facility, Hydro-Québec prepared various development options and compared them from a technical, economic and environmental standpoint. Three scenarios for the power station and the spillways, three scenarios for the sending-end substation and five scenarios for the access roads to the works were assessed.

The options retained are those that make up the proposed project. In terms of the generating station and the spillways, the selected option entails no dredging or in-stream excavation, less cofferdam work is involved, the overall cost is lower and the impacts on wildlife and river use are of lesser magnitude than with the other two options. The selected access road option was preferred for safety considerations and because it is located away from residential areas and requires a much smaller volume of fill than the other options. As for the sending-end substation, the technical criteria (sufficient reliability, no strengthening of the roof) and the economic criteria (lower cost) rendered the option of building a traditional type of sending-end substation more favourable, while the environmental criteria (visual impact) supported a sending-end substation design that does not have aboveground lines running between it and the generating station.

The selection of a disposal site for the excavated material from the project was made on the following basis. Owing to the high cost of haulage, serious environmental impacts and practical problems associated with urban traffic, the existing disposal sites could not be used for excavated material. However, two other potential disposal sites were identified: a lot located immediately south of the work camp installations, beside the Saint-Maurice River; and a sandpit just east of the Canadian National (CN) railway tracks, on the left (east) bank of the river. The analysis of these two options was based on the value of the vegetation communities that will be destroyed and on the visual impact of the spoil disposal site. The sandpit site, owned and operated by Excavation Gaston Trépanier, proved to be a more suitable choice for spoil disposal purposes than the forested lot beside the Saint-Maurice River.

DFO is satisfied with the proponent's analysis of the scenarios and considers that the proposed options are those involving the least environmental impacts.

2.3. Project description

2.3.1. Infrastructure

The new facility will be composed of many new works (generating station, spillways, sending-end substation, protective structures) as well as some existing works (generating station, left and right gravity dam) (Figure 1).

The new generating station, to be built on the left bank, will be equipped with three Kaplan turbine units giving it an installed capacity of 220 MW and a design flow of 1 040 m³/s. This aboveground plant with a built-in water intake will be supplied by a short tailrace canal that begins downstream from the present spillway, which will be partly demolished.

There will be three new spillways, with a total capacity of 8 225 m³/s at a peak operating level:

• A main spillway with a discharge capacity of 4 462 m³/s;
• A control structure with a capacity of 2 185 m³/s;
• A secondary spillway with a capacity of 1 578 m³/s.

These works will be designed so that any exceptional flood can flow over them, producing an upstream water level that is equal to or lower than the level at the existing facility (0 to 1.21 m lower).

A conventional type of sending-end substation will be built on the left bank about 150 m from the new generating station. With a capacity of 69 kV, it comprises eight line feeders, two of which are intended to meet future needs. The sending-end substation and the transformer substation, to be located on the roof of the new generating station, will be connected by means of three circuits of underground cables. Although the sending-end substation will initially operate at a capacity of 69 kV, it will be equipped to raise the voltage to 120 kV in response to increased demand requirements.

Figure 1. New Grand-Mère facility

Source: Hydro-Québec. New Grand-Mère hydroelectric facility. Information Bulletin, Number 3 - summer 1998.

A 1.45-km-long access road will be built, including an intersection with Highway 153. Some short temporary roads will also be constructed to provide access to the different work sites and structures, the spoil and waste disposal site and the CN railway tracks, where shipments of heavy equipment, such as power transformers for the new station, will be received.

The project includes decommissioning the existing power station building and dismantling the associated installations (turbine-generators, equipment, etc.), in-stream backfilling (base of the draft tubes, downstream retaining wall, the downstream ends of the rockfill dike), work associated with the protective structures (right gravity dam, concrete wall, rockfill dike on the right bank) as well as razing the existing spillway and weir. The present station's water intake will serve as a retaining structure for the forebay of the new Grand-Mère hydroelectric facility.

Construction of the new facility and modification of the existing works will be carried out in three stages, which entail two phases of diversion of waters from the Saint-Maurice River. The work will include the installation of cofferdams, concreting, in-stream excavation and the use of explosives.

The excavation work will generate a large volume of rockfill, estimated at 1 500 000 m³. Since the amount of material that can be used in the project has been estimated at 1 059 000 m³, the surplus fill will amount to about 500 000 m³.

The proponent has opted to dump this rockfill in part of an operational sandpit located on the left bank of the river, on the other side of the CN tracks. An access road will have to be built along the tracks, and the existing railroad crossing will have to be modified to permit the passage of heavy vehicles. Hydro-Québec is still negotiating with the site owner to obtain an easement in perpetuity for the operational part of the sandpit where the surplus rockfill is to be dumped.

2.3.2. Facility management

The new power station will be designed to adjust rapidly to an operating flow of between 200 and 1 040 m³/s during the winter. From mid-March to mid-December, the station will be managed as it is now; the water in the reservoir will be maintained near the maximum level in order to optimize the facility's output.

In winter (mid-December to mid-March), Hydro-Québec will adjust its production schedule so that the power station contributes to peak production, concurrently with the stations located downstream. In a given day, these stations will operate at flows of up to 1 040 m³/s during one or two peak periods and at reduced flows of 200 to 400 m³/s during off-peak periods.

The peak generating schedule for each day will be adjusted according to demand and technical constraints. Three operating modes will exist: 1) a mode to meet hourly peak demand in the morning and evening during periods of maximum demand (15 days); 2) a peak operating mode with optimal output (60 days) and 3) a normal mode the rest of the time (15 days). When operating in maximum hourly peak mode, the Grand-Mère station's turbines will handle flows of 255 m³/s during the off-peak period (13 hours) and flows of 1 040 m³/s during peak periods (11 hours). In optimal peak mode, the station will handle flows of 225 m³/s during the night (7 hours) and flows of 830 m³/s the rest of the day (17 hours).

The proponent has stated that it will endeavour to optimize the hourly peak mode to help maintain the stability of the ice cover.

The water-level fluctuations attributable to this new mode of operation will differ in each section of the river affected by the project. Figures 2 and 3 show the location of the different forebays and afterbays involved.

During the cold season, the daily water-level fluctuation range in the Grand-Mère forebay will be about 0.7 m before the ice cover forms, compared with 0.9 m afterward. These fluctuations, albeit greater than the existing variations (0.3 m), nonetheless fall within the reservoir's minimum and maximum operating levels (101.19 m and 102.56 m).

Two management modes for water-level fluctuations will be adopted in the stretch of river between the Grand-Mère and Shawinigan power stations. In this sector, the water-level fluctuation ranges observed between the dam and the Hêtres Rapids will be the largest recorded in relation to the different forebays and afterbays affected by the project. After the project is completed, the maximum fluctuation range, currently about 0.5 m at the Hêtres Rapids, will increase to 1.43 m, whereas at the power station the range will increase from 0.8 m to about 2 m, depending on whether or not the ice cover has formed. These flow variations will make it necessary to install an ice boom, from October or November to the following spring, immediately upstream of the Hêtres Rapids to improve the stability of the ice cover in this sector.

The water-level variations observed in the downstream reach, comprised between the Hêtres Rapids and the Shawinigan power station, will be of similar amplitude or smaller than the maximum fluctuations already recorded between the two sites.

Depending on the generating mode in effect, slight increases or decreases in the existing maximum fluctuation ranges will also occur in the stretch of river between the Shawinigan and La Gabelle dams following adoption of the new winter operating modes. With the exception of the upper reservoir at La Gabelle, which requires a 0.5 m decrease in the minimum operating level, the water-level fluctuations in the other forebays and afterbays of the power stations affected by the project will fall within the current range of maximum water-level fluctuations under normal operating conditions.

Figure 2. Local and extended study area

Source: Hydro-Québec. New Grand-Mère hydroelectric facility, 1998, Figure 2.1.

Figure 3. Zone of influence

Source: Hydro-Québec. New Grand-Mère hydroelectric facility, 1998, Figure 2.2.

2.4. Cost and completion schedule

The cost of the new Grand-Mère hydroelectric facility is estimated at $454 million and meets the proponent's cost-effectiveness criterion (production cost less than 3¢/kWh). The construction work is scheduled to begin in March 2000, with the commissioning of the new power station slated for the spring of 2004.