2. Description of the Project

Transcription

1 2. Description of the Project The proposed Project consists of a run-of-river waterpower facility with an installed capacity of 3 to 4 megawatt (MW). The main structural components of the project, the proposed construction methodology and the proposed operational regime for the facility are outlined below. Drawings SK-001 through -005 in Appendix A present the general layout of the facility. The details described in the following sections, particularly those relating to the mechanical and electrical components which form the water to wire package (i.e., turbine type and number, generator, control equipment, etc), are based on the preliminary engineering conducted to date. The final equipment will be selected following tendering of the water to wire package to equipment suppliers. Detailed design of the facility will proceed following selection of the water to wire package supplier. Once the detailed design of the facility has been completed, the design drawings will be forwarded to regulatory agencies as part of the permitting process for this project. The general components of the Project are discussed in Section 2.1, while Section 2.2 outlines the proposed construction of the facility including all temporary works required to construct the Project and the methodology that will be employed. Operational aspects of the Project are discussed in Section 2.3, long-term maintenance activities are discussed in Section 2.4 and decommissioning is discussed in Section Project Components/Structures The arrangement of the proposed development is based on a gross head of about 18.8 m. The facility will have the following permanent components: powerhouse with either one or two Kaplan type turbines, intake channel with one or two penstocks to supply water to the powerhouse, tailrace channel to transfer water back to the river, concrete overflow spillway with temporary diversion works, and conduit to pass ecological flows, head pond, to provide generating head for the water power turbine, small switchyard and feeder line to transfer power from the facility to the adjacent 115-kV transmission line, and access road from the adjacent secondary road with small turn around/parking area. These permanent components are discussed in the following sections. Construction of fish habitat enhancements in several areas of the Trout Lake River will also be undertaken. Drawings SK-001 through -005 in Appendix A display the general layout of the facility. The conceptual design of the development is described in the following subsections. H , Rev. 1, Page 2-1

2 2.1.1 Powerhouse The powerhouse is separate from the dam and will be excavated into the rock slope downstream of the intake structure and along the east bank of the Trout Lake River at the base of the North Channel of Big Falls (see Appendix A, Drawing SK-002). In order to minimize the footprint of the powerhouse and due to the steep angle of the penstock, a Kaplan turbine unit was recommended as the optimum configuration in the feasibility study (Hatch, 2008b). This selection could change following the award of the water-to-wire package. The powerhouse is predominantly constructed of concrete with a steel superstructure above the equipment room floor. A powerhouse crane is installed for routine maintenance and normal lifts. A mobile crane would be used through a hatch in the roof for heavy, infrequent lifts. A typical cross section and a plan view of the powerhouse are shown on Drawing SK-005 in Appendix A. The powerhouse will contain most of the water-to-wire equipment including turbine(s), generator(s), hydraulic power unit, cooling and lubrication system, generator switchgear, station service equipment, compressed air system, ventilation system with fans and louvers, blow unit heaters, drainage and dewater pumps, fire alarm and security panels. The turbine(s) (as recommended in the feasibility study) would be a double-regulated type axial flow Kaplan turbine with adjustable wicket gates and movable runner blades, connected directly to the generator unit (see powerhouse cross section on Drawing SK-005 in Appendix A). The generator(s) will be a horizontal, synchronous, 60-Hz, 3-phase, air-cooled generator. The powerhouse, with total dimensions of approximately 11 m x 15 m (165 m 2 ), will be comprised of an access floor and a generator and turbine floor. Additional areas in the powerhouse include a maintenance workshop, control and telecommunications rooms, personnel facilities and a ventilation room (Drawing SK-005 in Appendix A). Recently, it has been decided that the project may benefit from two smaller units, compared to one larger unit. If the final design is one unit, it will have a turbine runner diameter of 2.0 m and be equipped with six blades. The unit would have a rated capacity of 3-4 MW and a maximum flow capacity of 24 m 3 /s. If the final design uses two units, these will have turbine runner diameters of 1.5 m, six blades and each have a rated capacity of 1.5 to 2.0 MW and a maximum flow capacity of m 3 /s (total 27 m 3 /s and 3-4 MW). Flow passing through the turbine(s) is discharged to the tailrace via a draft tube. Each turbine will be paired with a generator and possibly a gearbox. If a gearbox is used, an oil-water separator will be provided in the powerhouse to ensure oil is not accidentally discharged to the environment in the event of accidental spillage. A cooling water system, drawing water from the Trout Lake River, will also be included. Gate slots will be provided at both the intake and the draft tube (upstream and downstream ends of the powerhouse, respectively) to allow for dewatering of the turbine for maintenance. H , Rev. 1, Page 2-2

3 Roller-type gates will be included for either the intake or draft tube to allow emergency closure of the units and stop-log bulkheads will be provided for the other set of gate slots. The powerhouse is designed as an unmanned station, therefore, minimal provisions are supplied in terms of sanitary facilities. Non-potable water will be utilized where water is required by drawing from the river. A small parking area/turn around will be located immediately adjacent to the powerhouse. Station power will be obtained from the local 115-kV lines located approximately 250 m east of the site at the main access road. Additional services such as communications will be provided through a phone/data line, cellular, satellite, or other connection Intake Channel Water will be conveyed from the head pond to the powerhouse via a 210-m long open cut intake channel to the concrete intake structure, where it will enter 120-m long, 2.8-m diameter steel underground penstock that will convey it to the powerhouse (see Drawing SK-002 for general layout and longitudinal profile of these features). The 210-m long open cut channel will initially be used to convey the water along a section of relatively flat land to the intake structure. The channel is anticipated to be excavated within overburden and be concrete lined to prevent erosion and create suitable hydraulic flow conditions. The invert of the channel varies from elevation m at the upstream edge to elevation m at the intake structure. This will result in an average excavation depth of 4.5 m in the overburden. The base of the channel measures 1.5 m in width with side slopes of 2:1 (horizontal:vertical). The top width of the intake channel varies from 22 m to 27 m. The intake structure is located at the east end of the intake channel, and will consist of a reinforced concrete structure founded on bedrock (see Drawing SK-002 for general layout and Drawing SK-004 for plan and profile views of the structure). The intake structure is located at the top of the slope to the powerhouse and provides a transition between the open intake channel and the steel underground penstock. The intake structure houses the trash racks, emergency closure gate and service bulkhead slots. The intake structure will be constructed completely in the dry with no requirement for cofferdams. An inclined trash rack located at the entrance to the intake will prevent any floating debris and ice from entering the penstock and ultimately the turbine. The trash rack bar spacing will be a maximum of 150 mm, with actual bar spacing being based on the minimum opening of the runner or maximum opening of the wicket gate (whichever is smaller) furnished by the turbine manufacturer. The trash rack will be arranged in two sections with a central concrete pier. Monitoring of the differential pressure across the trash racks will be provided in order to assess the degree of blockage by debris. Debris will be removed by use of a mobile crane equipped with a grapple. One single leaf bulkhead gate will be installed in the intake structure to facilitate dewatering for the inspection and maintenance of the intake roller gate. An intake gate will be installed to allow flow of water in the penstock. The gate will be designed to close automatically under emergency conditions when the generating unit is under full flow conditions. The gate will be operated by a wire rope hoist mounted on a tower and bridge frame located on the intake H , Rev. 1, Page 2-3

4 deck. Normal and back-up emergency power supplies will be provided for the hoist and its controls. Controls for the hoist will be provided on the intake deck for local operation and in the powerhouse control room for remote operation. Provision shall be made for remote operation and monitoring through the SCADA system of the facility. The steel penstock will be approximately 120 m long and will have a diameter of 2.8 m. The penstock will be buried for the majority of its length using a cut and cover construction technique within overburden and rock. Proper bedding material is required within the rock cut in order to remove the requirement for additional support saddles. The penstock has two bends between the intake structure and powerhouse which require the use of concrete anchor blocks. Two penstocks may be installed if a 2-unit configuration is selected in final design. No burp pipe to release water to the environment in the event of a facility shut down will be provided. Should pressure relief of this nature be determined to be necessary during the final design, water will remain contained within the system and will not be discharged to the environment Tailrace A tailrace will be constructed downstream from the powerhouse draft tube to convey flow from the powerhouse back to the Trout Lake River. The tailrace will be an open channel approximately 18 m long and 5 m wide at the invert, excavated in bedrock to an invert elevation of m over a 3 m distance from the powerhouse outflow, followed by a 15-m long transition grading up at a 25% slope to the natural riverbed elevation at the end of the tailrace. Approximately 950-m 3 rock will be excavated from the tailrace area Overflow Weir A new concrete overflow weir, founded on bedrock, will be constructed just upstream of the crest of Big Falls with a fixed crest elevation of m (CGVD28), in order to maintain the head-pond water level. The weir will consist of a central overflow section, flanked by higher wingwalls on either side. The weir will be approximately 4 m high on average (8 m high in centre of channel) and designed to pass the Inflow Design Flood (IDF) flow of 117 m 3 /s (the 1-in-100-yr return period flood flow). The overflow section of the weir will be 64 m long with a width of 5 m at the base, the right wingwall will be 28.3 m long with a width of 3.4 m at the base and the left wingwall will be 24 m long with a width of 5.9 to 6.4 m at the base. Several cross sections through the structure are provided on Drawing SK-003 (Appendix A). Three 4-m wide sluice ways with sill elevations of m will be constructed into the left side of the overflow weir (looking downstream). These sluiceways will be used to temporarily divert flows around the overflow weir working area during the construction period. This section will then be modified to pass the required bypass flows to the falls. This will be achieved by notching of the weir, installation of a pipe and valve system, or stop log sluice structure, to be determined during the detailed design stage of the project, prior to permitting Head Pond The inundation area for the proposed facility will extend approximately 1.7 km along the Trout Lake River upstream of the dam (see Figure A1, Appendix A). The total head-pond area will H , Rev. 1, Page 2-4

5 be 15.8 ha. The newly inundated area will be about 6.3 ha, adding to the existing wetted area of 9.5 ha. The water levels immediately upstream of the dam will be increased by approximately 3.8 m. The Normal Operating Level (NOL) of the facility will be approximately m (CGVD28) Transmission and Interconnect Requirements The station switchyard and main transformer will be installed outside, to the southeast of the powerhouse. Switchyard dimensions will be approximately 20 m by 10 m (200 m 2 ). The switchyard will include a generator step-up transformer, surge arrestors, HV circuit breaker and disconnect switch, segment of a 44-kV power line and metering, protection and control equipment. The switchyard will be fenced off and locked to prevent unauthorized access for safety considerations. The transformer will be installed in the switchyard, above an enclosed crushed stone filled basin filled in order to contain spills and provide fire protection. Power generated by the station will be transmitted to the provincial grid via a new approximately 200-m long 115-kV transmission line from the powerhouse switchyard to the existing 115-kV distribution line, owned by Hydro One Networks Inc. (HONI). The existing line is located approximately 200 m east of the powerhouse location along the east side of South Bay Road (Drawing SK-001) forming part of the distribution system between Ear Falls and Pickle Lake. An up to 38-m wide right-of-way (ROW) will be cleared for the transmission line throughout its length. The ROW may be narrower, depending on line height, existing tree canopy conditions and configuration of the pole structure. The permanent access road to the powerhouse will be constructed within the transmission line ROW. Therefore, no grubbing (i.e., removal of stumps) will be required within the transmission line ROW other than for the access road. No stream crossings are required along the proposed transmission line route. Future maintenance of the new transmission line section (owned by Horizon Hydro) will likely include cutting every 10 to 15 years to eliminate tree growth that could potentially affect the transmission line. Mechanical means, rather than herbicide, will be used as required. 2.2 Project Construction and Schedule Construction of the project will commence after the completion of the detailed design and receipt of all required environmental permits and approvals, and is currently anticipated to occur in fall The construction period will be approximately 12 to 18 months long, with operational start-up scheduled to occur in late 2014 or early 2015 (see Figure 2.1). Construction activities are briefly described below. The first construction activities will be the access road from South Bay Road to the intake and overflow weir, and the powerhouse locations (see Appendix A, Drawing SK-001). Works and laydown areas will be constructed to provide designated locations for site trailers and equipment and material storage. Site preparation will commence with the removal of vegetation and topsoil in working areas and associated land grading to prepare for construction. Staging and construction laydown areas can be developed anywhere in the H , Rev. 1, Page 2-5

6 vicinity of the powerhouse and intake subject to the appropriate approvals. All land in this area is owned by the provincial Crown. Topography indicates that the terrain is more level toward the area of the proposed intake, suggesting that this area might be more suitable for use as a laydown area. A construction methodology for the overflow weir has been identified but may be modified by the selected contractor. A rock-fill cofferdam with an impervious barrier will be installed along the left bank (looking downstream) to construct the left side of the spillway, including diversion bays, in the dry. Flow in the river will be directed toward the right side of the channel during that period. Once the left hand side of the structure is complete, the cofferdam will be shifted to the right hand side of the channel, with all flow in the river being diverted through the newly constructed diversion bays. Once the overflow weir is complete, the cofferdams will be removed and flow will be routed over the new structure. Final design of the cofferdams will be submitted to MNR and Transport Canada following the detailed design process. The intake channel will be constructed in the dry behind an earth plug that will remain at the shoreline. The normal water level of the river is below the invert of this channel. A small sand bag cofferdam may be constructed at the upstream end of the intake channel to prevent submergence in the event of extreme high water in the Trout Lake River during the construction period. Removal of the plug and installation of any required erosion protection will be done prior to the raising of the head pond. Powerhouse construction will occur behind a rock plug at the shore of the Trout Lake River. Some minor topping of the rock plug with rock fill or sand bags will be required to ensure adequate freeboard during flood periods. No in-water cofferdam will be required in order to construct the powerhouse. A tailrace will be constructed downstream from the powerhouse draft tube to convey flow from the powerhouse back to Trout Lake River. The first 3-m long section of tailrace will be constructed behind a rock plug (i.e., the existing bedrock along the shoreline). Excavation and grading of the remaining portion of the tailrace will be done in the wet behind turbidity curtains. Following the completion of construction of the main project components, the final features will be installed including the proposed transmission line, completion of interior powerhouse works and site rehabilitation (e.g., removal of all equipment and debris, final grading and landscaping). H , Rev. 1, Page 2-6

7 Project Schedule MNR Crown Land RFP Applicant of Record EA Notice of Commencement Notice of Modification Notice of Transition PIC and Open Houses Notice of Inspection Notice of Completion Statement of Completion Permitting Tendering Design Equipment Manuf/Install Construction Site Clearing Access Roads Weir Construction Canal Excavation Intake Penstock Powerhouse Substation Transmission Line Connection (HONI) Commissioning COD Jan Mar Apr Jun Jul Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb H340773_April_4_2013_rm Figure 2.1 Horizon Hydro Inc. Trout Lake River Hydro Project Project Schedule

8 Back of figure H , Rev. 1, Page 2-8

9 Equipment used during the construction process could potentially include: pick-up trucks excavators (some equipped with hoe rams) dump trucks bulldozers crane backhoe concrete trucks welding machines cutting torches grinding tools vibro hammer diesel pile hammer rock drill compressor generator concrete vibrator truck-mounted concrete pump. 2.3 Hydraulic Characteristics and Project Operation The proposed facility will be operated in a run-of-river manner and will utilize natural inflows without any manipulation of reservoir storage. This means that the facility will adjust its generation to match inflow and it will not re-regulate river flow (i.e., which would introduce fluctuations in the upstream reservoir and affect downstream flows and levels). As the turbines are operated in synchrony with natural reservoir inflows, the river downstream of the southern portion of the falls will see no change in flow or level. The NOL of the head pond will be just below (~7 cm) the spillway crest. This provides a buffer such that higher river flows can be accommodated (at least for a while) without changing the operational flow rate. A minimum operating level 27 cm below the weir crest has been identified as the lower limit of the facility s compliance zone (as per the Water Management Plan and LIRA approval). As the station will be remotely operated, this provides adequate time to react to natural inflow changes, while remaining within the compliance zone. However, there will be natural water level fluctuations (upward) associated with increases in river flow, as is the case in any river system. Flood flows will not be changed or affected by the project, and will be passed through the project and into the downstream reach. A 1:100-yr flood at 117 m 3 /s will be selected as the spillway design flood in accordance with the MNR dam safety guidelines. The estimated hydraulic characteristics of the proposed development are shown in Table 2.1. H , Rev. 1, Page 2-9

10 Table 2.1 Estimated Hydraulic Characteristics Headwater level (1:100-yr flood) m Headwater level (1:2-yr flood) m Head pond NOL el m* Minimum operating level el m Spillway crest elevation el m Tailwater level downstream at powerhouse el m Rated operating gross head 18.8 m Long-term average flow 16.8 m 3 /s Minimum plant flow 2 m 3 /s Maximum plant flow 27 m 3 /s *This estimate was based on an assumed rated flow of 24.5 m 3 /s. Normally power generation will be under remote control. Periodic visits by the operator will be required for visual inspection, routine checks and maintenance for normal operation of all powerhouse equipment and the mechanical equipment at intake. As in any unattended powerhouse, facilities for operating personnel in the powerhouse will be minimal. 2.4 Dam Safety A preliminary review of dam safety aspects has been undertaken according to the Ontario LRIA Administrative Guide (OMNR, 2010). The assessment is based on the relative volume and areas of the proponent s head pond versus Bruce Lake, which is the first location where a breach of the proponents weir could have potential incremental impacts to property or life, and where the flood wave from a dam breach would be significantly attenuated. The area of Bruce Lake, shown in Figure 2.2, is conservatively estimated, on the low side, to be 1914 ha. Downstream of Bruce Lake is Pakwash Lake, which has approximately three times the area of Bruce Lake. Bruce Lake and Pakwash Lake are connected by a short channel that does not cause a large drop in water level between the two lakes, thus during high floods the two lakes are most likely at the same, or very near to the same, elevation. The combining of the area and volume of these two lakes has a significant attenuating affect on flood hydrographs as floods enter and exit Bruce and Pakwash lakes. The area of the head pond is 15.8 ha, which is 121 times smaller than Bruce Lake. A simple ratio of areas indicates that a release of water from the head pond equivalent to the height of the weir (5 m), would increase the level of Bruce Lake by m if the entire volume of the head pond was stored in Bruce Lake. This would not be the case as the combining of Bruce and Pakwash lakes and the release of water downstream from Pakwash Lake would result in a lower incremental flood wave in Bruce Lake. The conservatively estimated m increase in water level on Bruce Lake is less than 0.61 m (2 ft), thus according to the LRIA 2 x 2 rule for calculation of loss-of-life it appears that there is no potential for incremental loss-of-life from a breaching of the proponents weir for sunny-day or for flood conditions. H , Rev. 1, Page 2-10

11 Figure 2.2 Bruce Lake Area The following information on the Griffith Mine Perimeter Dykes is taken from Report on Dykes Constructed by the Griffith Mine (OMNR, May-1986). The freeboard on the perimeter dykes during sunny-day conditions is m, based on m and m the minimum elevation of the perimeter dyke and the average Bruce Lake water level respectively. The estimated m water level increase in Bruce Lake water level is significantly less than the freeboard on the Griffith Mine Perimeter dykes, thus a sunny-day breaching of the proponents weir would not have any impact on the perimeter dyke. During the 1:100-yr flood event the elevation of Bruce Lake is predicted to be m which overtops the perimeter dyke by 0.8 m, the dyke has been designed for overtopping. Thus, the incremental increase in Bruce Lake water level from a breach of the proponents head pond is assessed to have minimal impact during the 1:100-yr flood and higher flood events. Downstream of Bruce Lake the incremental increase in water levels from a breaching of the proponents weir would be less than m, thus their appears to be only potential for small impacts from a breaching of the weir. Therefore, the preliminary HPC for the weir has been assessed to be LOW according to the LRIA Administrative Guide (August 2010) for both sunny-day and flood conditions. The Highway 105 bridge crosses the connecting channel between Bruce and Pakwash Lakes. No negative effects on the bridge structure are anticipated to occur due to the incremental increase in water levels discussed above. H , Rev. 1, Page 2-11

12 2.5 Facility Maintenance Activities Facility maintenance activities include normal activities that are conducted on a regular basis to ensure that equipment is maintained in good operation. Common repairs that could be expected over the life of the facility are also included in this category. Facility maintenance activities include: oil changes for gearboxes, transformers and other oil filled equipment, manual trash rack debris removal, transmission line corridor and road side vegetation maintenance, facility cleaning (e.g., floor sweeping, mopping, bathroom cleaning), minor concrete repairs on powerhouse or on spillway crest and downstream face, and access road grading and/or application of dust control. A comprehensive facility inspection program will also be developed and implemented to ensure the facility is functioning properly and remedial works will be implemented as necessary based on the results of inspections. 2.6 Decommissioning Waterpower projects are designed for long life spans, typically in excess of 50 years and ongoing maintenance, repair and upgrade programs can extend the life of facilities to over 100 years. As such, decommissioning of the facility is highly unlikely to happen in less than 50 years. Furthermore, it is more likely that a water project facility such as this would be redeveloped at the end of its lifespan as opposed to decommissioned due to the benefits of green energy and constantly increasing demand for energy in Ontario. If, however, facility decommissioning is to occur, an environmental assessment process based on the environmental knowledge, standards, and legislative requirements in place at that time would need to be undertaken as required and all necessary permits and approvals would have to be obtained prior to implementation of the decommissioning. H , Rev. 1, Page 2-12