Engineering Design Basis GA

Sea to Sky Power Corporation Skookum Power Project Engineering Design Basis

Document No. 421.100 December 2010 Draft Rev. B Prepared by:

103-1718 Commercial Drive, Vancouver, BC V5N 4A3 Tel: 604-254-3914 Fax: 604-254-3928 E-mail: [email protected] GEA Project No. 10005

In association with:

Kerr Wood Leidal Associates Ltd.

Skookum Power Project Engineering Design Basis i

GEA Gygax Engineering Associates Ltd. December 2010 BGCE Engineering Inc. KWL Kerr Wood Leidal Associates Draft Rev. B

CONTENTS

Executive Summary 1 1 Introduction 3

1.1 Purpose and Scope 3 1.2 Project Overview 4 1.3 Acknowledgements 5

2 Description of Facilities 7 2.1 Intake 7 2.2 Penstock 7 2.3 Powerhouse and Tailrace 8 2.4 Roads and Site Works 9

3 Site And Environmental Conditions and Parameters 11 3.1 Geotechnical Conditions 11

3.1.1 General 11 3.1.2 Intake Site 11 3.1.3 Penstock Alignment 12 3.1.4 Powerhouse Site 12

3.2 Seismicity 12 3.3 Climate 13

3.3.1 Temperature 13 3.3.2 Snow and Rain 14 3.3.3 Wind 15

3.4 Hydrology and Flows 15 3.4.1 Baseline Hydrology 15 3.4.2 Minimum Instream Flow Requirements 16 3.4.3 Flood Hydrology 17

3.5 Geohazard Risk and Sedimentation 19 3.5.1 Geohazards 19 3.5.2 Sedimentology 19

3.6 Mapping, Surveys and Controls 19

Skookum Power Project Engineering Design Basis ii


3.6.1 LIDAR Mapping 19 3.6.2 Ground Surveys 20

3.7 Site Access 20 4 Facility Sizing 21

4.1 Penstock Sizing 21 4.2 Power Generation Model 21 4.3 Turbine/Generator Sizing 22

5 Power Generation Equipment Design 23 5.1 Turbine 23

5.1.1 Pelton Turbines 23 5.1.2 Turbine Inlet Valve 24

5.2 Generator, Switchgear, and Substation 24 5.3 Control System 25 5.4 Grounding 25

5.4.1 Powerhouse Ground Grid 25 5.4.2 Grounding of the Penstock 25 5.4.3 Grounding of the Intake 25

6 Project Works Design 25 6.1 Design Approach 27

6.1.1 Facility Classification 27 6.1.2 Required Performance Levels 27 6.1.3 Material Parameters 28

6.2 Hydraulic and Hydromechanical Design 33 6.2.1 Performance Requirements 33 6.2.2 Intake Flood Passage, Controls and Isolation 36

6.3 Penstock 37 6.3.1 Penstock Design Premises 37 6.3.2 Transient Pressure Analysis 39 6.3.3 Structural Analysis 39 6.3.4 Penstock Structural Design 43 6.3.5 Corrosion Protection 45 6.3.6 Penstock Restraint and Interface with Roads 45

Skookum Power Project Engineering Design Basis iii


6.3.7 Surface Water Management 46 6.3.8 Erosion and Flood Protection Works 47 6.3.9 Construction and Filling 48 6.3.10 Penstock De-watering 48

6.4 Access Roads 48 6.4.1 Public or Stakeholder Access during Construction 48 6.4.2 Permanent Multi-Stakeholder Roads 49 6.4.3 Permanent Project Roads 49

6.5 Intake and Powerhouse Structures 50 6.5.1 Limit States 50 6.5.2 Design Parameters 52 6.5.3 Key Design Details 55

6.6 Powerhouse Building Services 58 7 Governing Design Codes, Standards and References 59

Skookum Power Project Engineering Design Basis 1


EXECUTIVE SUMMARY

On 31 March 2010, Sea to Sky Power Corporation (SSPC) was awarded an Electricity Purchase Agreement by BC Hydro under the Clean Call for Power for the Skookum Power Project.

The proposed hydropower project is a 25 MW run-of-river plant located on Skookum Creek, a tributary of the Mamquam River, near Squamish, BC. The creek drains an area of 67 km2 at the proposed intake site. With the drainage area extending into Garibaldi Park to the north and east, glacial melt-water contributes considerably to the flows.

The proposed intake is located at about 805 m above sea level (masl) at a location where the valley narrows significantly and the creek steepens considerably. The project is licensed to divert a maximum of 9.9 m3/s from the creek. The design foresees a design flow of 9 m3/s led through a 6.3 km penstock to the powerhouse, located at about 340 m below the intake at EL 460 masl, on the left bank of the creek some 150 m upstream of its confluence with the Mamquam River. The project proponent, SSPC, has signed an energy purchase agreement with BC Hydro that foresees an average annual energy production of 95 GWh at a capacity factor of just over 40%.

Currently, SSPC is undertaking the preliminary engineering and environmental investigations required to support a Water Development Permit Application. The preliminary engineering for the power generation works and transmission line will be completed in early 2011 and further define the scope of permanent works and facilities to allow more accurate costing and economic modelling.

This Design Basis document establishes criteria for the design and construction of the project. The current version of this document describes the project in the midst of the preliminary design phase and summarizes basic project site data, specified design criteria, relevant design guidelines, codes, and other key project information as they are know at this time. The document provides a foundation for the further development of the design and, in its final form, will serve as reference information for construction, operation and maintenance.

The main project characteristics are summarized overleaf.



Table 1: Project Summary Data

Intake

Design Flow

Instream Fisheries Release (IFR)

Intake type

Normal max. headpond level

Intake forebay operating water level

Headworks construction

Spillway

200 Year Flood Discharge

200 Year Flood Level

9.0 m3/s

0.54 to 1.36 m3/s

Coanda weir

EL 806.00m

EL 803.50m

concrete

Coanda weir plus twin overshot spillway

275 m3/s

EL 808.00m

Penstock DN 2000 to 1800 mm, steel (HDPE possible for low-pressure portion)

Powerhouse

Building Type

Plan Dimensions

Crane

Main Floor Elevation

free-standing, concrete substructure, steel superstructure

20 m x 30 m

travelling bridge crane 20 to 40 tonne hook height to main floor 11 m

EL 461.00 m

Generation

No./Type of Units

Rated Capacity

Runner Elevation

Gross Head

Control Room Location

Runner Maintenance Provision

2 x 12.5 MW

multi-jet vertical axis Pelton

12.5 MW

EL 460 m

343.5 m

powerhouse

runner removal through tailrace and hatch

Isolation Systems open sluice gate to dry Coanda screen turbine inlet valves



1 INTRODUCTION

1.1 PURPOSE AND SCOPE

Sea to Sky Power Corporation (SSPC) has engaged Gygax Engineering Associates Ltd. (GEA) to provide the civil engineering services required for Preliminary Design. GEA is performing these services in association with BCE Engineering Inc. and Kerr Wood Leidal Associates Ltd. This Engineering Design Basis establishes criteria for the design and construction of the Skookum Creek Hydroelectric Project. It is a living document that is continuously being updated as design progresses. In its current form, this Design Basis Report summarizes the project engineering mid-way through the Preliminary Design process and in support of the Water Development Permit Application. Therefore, the information contained herein should be considered preliminary and subject to further confirmation and refinement.

The overall objective of the Preliminary Design Phase is to define the scope of permanent works and facilities to allow more accurate costing and economic modelling. SSPC intends to construct the project on an owner-contractor alliance basis and the final preliminary design deliverables, expected to be complete in early 2011, will facilitate establishing this as well.

This document describes the project at the current state of completion of the preliminary design phase and summarizes basic project site data, specified design criteria, relevant design guidelines, codes, and other key project information. The basic project features outlined in this Design Basis are intended to provide a foundation for the development of the detailed design and, in its final form, will serve as reference information for construction, operation and maintenance.

The scope of this document includes the main project works, including the intake, penstock and powerhouse as well as the power generation equipment comprising the turbine inlet valve, turbine, generator, control, switch gear, transformer and associated electrical and mechanical works. The following components of the project are being completed by others and are not included in the scope of this document:

Power line to connect the plant to BC Hydro at the Cheekeye Substation;

Switchgear, substation and generation controller;

Powerhouse balance of plan mechanical and electrical;

Access roads between the powerhouse and intake that are not integrated with the earthworks required to install the penstock; and



Access roads below the powerhouse.

This section of the Engineering Design Basis includes an introduction and overview of the project, while Section 2 provides a more detailed description of proposed project facilities. Site conditions are described in Section 3. Section 4 addresses facility sizing and optimization, while the basis of the power generation equipment design is given in Section 5. Parameters for project works design are given in Section 6. Governing design codes, standards and references used are presented in Section 7.

1.2 PROJECT OVERVIEW

The proposed Skookum Creek HEP is a 25 MW run-of-river plant located on a tributary of the Mamquam River, near Squamish, BC. The creek drains an area of 67 km2 at the proposed intake site. With the drainage area extending into Garibaldi Park to the north and east, glacial meltwater contributes considerably to the flows.

The proposed intake is located at about 805 m above sea level (masl) at a location where the valley narrows significantly and the creek steepens considerably. A maximum of 9 m3/s will be diverted from the creek by a Coanda screen intake, with headpond level controlled by an Obermeyer gate. This intake arrangement was developed to address the highly variable flow regime, substantial annual bedload movements and the constricting topography of the intake site.

From the intake, diverted flows will be led through a 6.3 km penstock along the left bank of the creek to the powerhouse, located at about 340 m below the intake at EL 460 masl, on the left bank of the creek some 150 m upstream of its confluence with the Mamquam River. The first 4.3 km of the penstock will see low pressures as it slopes between 0.5 and 0.7%. Considerable construction challenges are posed by the terrain on this stretch, which is characterized by 20 to 40 till slopes higher up transitioning to very steep rock slopes lower down. A considerable portion of the low-pressure penstock will be in the rock slopes, where exposed bedrock bluffs alternate with slopes with thin till caps. The final two kilometres of the penstock sees slopes varying between 10 and 30% on average. Along this high-pressure stretch, the pipe will be buried along the uphill side of existing logging roads.

The project proponent, Sea to Sky Power Corporation (SSPC) has signed an energy purchase agreement with BC Hydro that foresees an average annual energy production of 95 GWh at a capacity factor of just over 40%.



1.3 ACKNOWLEDGEMENTS

This document is a compilation of information developed by many persons involved with the project. The Project Civil Engineering Team, reporting to Peter Zell, Clean Energy Consulting Inc. Project Manager, comprises as key staff Adrian Gygax of Gygax Engineering Associates Ltd. (Team Leader); Mark Pritchard of BGC Engineering Inc.; David Roche and Stephen Mills of Kerr Wood Leidal Associates Ltd.; Gabe Sentlinger of Aquarius Research and Development; Rob Adams (Knight Pisold); and Shelley Higman (EBA Engineering Ltd.). All of these individuals have contributed to this document.

Adrian Gygax, P.Eng., Struct.Eng.

Gygax Engineering Associates Ltd.

Mark Pritchard, MASc, P.Eng., P.Geo.

BGC Engineering Inc.

David Roche, P.Eng.

KWL Engineering Inc.



2 DESCRIPTION OF FACILITIES

2.1 INTAKE

The intake will withdraw water from the creek while maintaining a normal headpond elevation of about EL 806 metres above mean seal level (masl) in order to keep flooding of the upstream wetlands to a minimum. The current concept foresees controlling headpond level with an Obermeyer type flap gate to divert water over a Coanda-effect screen intake, about 20 m long. This intake type has been selected on the advice of Barkley Group, the project environmental and fisheries consultant. In order to maintain the backwater pool at EL 806, the topography of the site dictates arranging the intake screen along the left creek bank parallel to the natural stream channel.

A bottom-hinged flap gate or Obermeyer gate controlled spillway, 4 m tall by 15 m wide, will be constructed within the current natural channel thalweg and provide for headpond level control and most of the flood passage. A second 5 m tall and 7.5 m wide Obermeyer gate will control flows through a sluiceway adjacent to the Coanda screen weir. The sluiceway will be closed except during annual flood flows. The relatively small Coanda screen by-pass flow will be discharged into a side-channel spillway. From the Coanda screen collection channel, flows will be directed to a forebay that will re-establish laminar flow and provide adequate submergence to the penstock inlet.

An in-stream flow release bypass system will pass the minimum IFR flows directly from the headpond to the side-channel spillway, ensuring that fish passing across the Coanda screen will always find a wetted channel.

2.2 PENSTOCK

For the first 4.4 km from the intake, the penstock alignment follows the left flank of the Skookum Creek valley. The terrain in this area are generally characterised by native till and colluvium slopes in the upper elevations and exposed rock or rock with a shallow till or colluvium cap at lower elevations. Slopes in many areas steepen towards lower elevations. Till slopes reach inclines of 40, while those of rock are generally in the 50 to 60 range. In this stretch, penstock pressures are low. The penstock alignment roughly follows the boundary between moderate to steep till mantled slopes and steeper rock slopes at 0.5% to 0.7% grade, but a significant portion is in rock slopes. The design foresees minimizing the penstock gradient to avoid the steep rock slopes closer down to the valley bottom as much as possible. Two major tributary crossings, requiring pipe bridges, are crossed within the first two kilometres of the alignment. At roughly 2.1 km from the intake, a zone of rock bluffs is reached, where the typical full-bench concept will be expensive and difficult to construct,



therefore it is proposed to raise the penstock alignment by some 10 m to pass above this challenging terrain. This would require a rising single-span pipe bridge some 30 m long, followed by a stretch of short spans between individual concrete pedestals built on top of the rock bluffs, and finally, a 70 m long three-span pipe bridge over the largest gully. The resulting siphon will be maintained at no more than 75% of standard atmospheric pressure relative to the emergency operation hydraulic grade line (i.e. including valve fail-safe-to-close transients). This solution is under development and will require ground-truthing in the spring.

A decommissioned logging road is located a few to a few tens of meters above the penstock alignment and following re-construction will provide access to the intake and to spur roads leading down to the penstock bench during construction.

The remaining 2 km of steeper gradient higher pressure penstock will follow semi-active or active logging roads that traverse down a till mantled ridge to a till terrace where the powerhouse location is proposed. The penstock pipe will generally be placed on the upslope side of the road.

The penstock will mostly be of 1.8 m steel pipe, although 2.0 m is currently foreseen for the first 950 m or so. The low-pressure section will be of double-welded bell and spigot or butt-welded construction; medium and high-pressure stretches will require butt-welded construction. Between the intake and about km 1.0 of the low-pressure penstock, pipe restraint will be provided by burial and soil restraint. Beyond km 1.0, the penstock will be placed on suitable bedding materials on the excavated bench with pipe restraint at significant bends provided by ground-anchored ring girders, and protected against up slope geohazards. This is discussed further in Section 6.3.

Along the higher-pressure section, the penstock pipe will be placed on suitable bedding materials in the trench, backfilled with compacted pipe fill and covered with select fill to at least 1.2 m above the crown. Cross drains and trench drains will be provided. Pipe restraint will be provided by soil-structure interaction wherever possible, to minimize the need for anchor blocks. The design approach will be one of displacement control and stress limitation for the various governing performance levels.

2.3 POWERHOUSE AND TAILRACE

The powerhouse will be located beside Skookum Creek, about 150 m upstream of the forest mainline service road bridge. The building will be located on a narrow natural bench, about 5 m above the creek bed, but as this is only 10 to 15 m wide, considerable excavation into the uphill slope will be required. This slope tops out at a large bench about 20 m above the creek. The building will comprise a concrete substructure and a steel superstructure. The excavation will be laid back to safe, permanent slopes with drainage berms and left open. Access will be from the upper bench by means of a spur off the forest service road along



which the penstock alignment runs. This will allow a natural screen of trees to be left in place and reduce the visual impact of the powerhouse when seen from the bridge.

A service crane will be provided, capable of rotor removal. The powerhouse will comprise an open machine hall also housing the indoor electrical gear and a containerized control room. Laydown and maintenance will be accommodated within the machine hall. Sanitary facilities will comprise a single unisex electro-flash toilet washroom and a wash-up sink. The exterior powerhouse traffic access area will be gravel surfaced and generally sloped to provide natural drainage to swales and percolation drains.

Two vertical axis multi-jet pelton turbines are currently foreseen. The powerhouse floor level will be set at least 1 m above the 1:200 year return period design flood event, but it appears likely that main floor, plunge pool invert and runner elevations will be dictated by the requirement of restricting fish access up the tailrace as well as the impracticalities of constructing the powerhouse excavation below normal river levels.

The tailrace will be a steep slush-grouted rip-rap glacis below a tailpool sill.

2.4 ROADS AND SITE WORKS

The existing roads that would be used for site access range from active forest service roads, through semi-deactivated forest service roads (ATV and trail bike access) to a decommissioned forest road over the final 2.5 km to the intake.

The decommissioned road has had all bridges removed and abutments pulled-back, culverts have been removed and replaced with swales and the downslope fills have been pulled up onto the bench along about 30% of the alignment. This road will require re-establishment for access to the intake, for construction access to the penstock route, and also to conduct the detailed site investigations (alignment surveys, intake drilling) that will need to take place in late spring 2011 in advance of detailed design. The design for re-establishing this road will be carried out by a forest road consultant under direct contract to SSPC and is outside the scope of this Design Basis.

Where the penstock is located within, or beside, existing, re-established or new roads, the backfill design will require due consideration of drainage and traffic loads. At the intake and powerhouse areas, site grading, drainage, restoration and traffic area designs will be required. Both the powerhouse and the intake will be fenced to prevent public access.



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3 SITE AND ENVIRONMENTAL CONDITIONS AND PARAMETERS

3.1 GEOTECHNICAL CONDITIONS

3.1.1 GENERAL

The project area is located near the southern edge of the Garibaldi Volcanic Complex in the Coastal Range of British Columbia. The headwaters of Skookum Creek are near Mt. Garibaldi, and the morphology of the upper reaches of the drainage is strongly influenced by volcanic flows, cinder cones, and glaciation. The portion of Skookum Creek Valley in the area of the proposed hydropower project has a left (east) valley slope predominantly controlled by the underlying granitic Cloudburst Pluton, Ref. [32], and a right bank defined by the east margin of the approximately 9,000 year old dacite Ring Creek Volcanic Flow. Slopes traversed by the penstock route along the left valley slope vary from moderate to steep with a general pattern of steepening downslope. Conditions along the penstock route vary from till greater than 3 m thick to rock bluffs, and the route crosses several tributary creeks. Near and at the powerhouse, facilities will be on a till terrace bounded by Skookum Creek and the Mamquam River.

3.1.2 INTAKE SITE

The intake site is located predominantly on an exposure of granodiorite. This very strong, widely jointed rock is exposed in the left bank, thalweg, and for the majority of the height of the right bank affected by the intake right abutment. Overlying the granodiorite on the right bank is dacite of the Ring Creek Volcanic Flow. The granodiorite provides excellent foundation conditions for the intake structures, but may require consideration of joint seepage potential and uplift or overturning restraint in detailed design. The geotechnical conditions at the contact between the granodiorite and the Ring Creek Volcanic are not yet known. As the Ring Creek Volcanic flowed over the existing ground surface at the time of deposition, it is possible that this contact could contain sediments or organic materials that could form a preferential path for seepage. Although the depth of this deposit that is expected to form the upper part of the right abutment of the intake structure will likely be less than 2 m, detailed design will need to consider foundation and seepage cut off conditions in this area. The Ring Creek Lava itself has columnar jointing, and on surface exposures is quite dilated. The right bank slope at the intake is steep and generally has a discontinuous veneer of colluvium composed of blocks from the lava flow. Seepage through the lava flow itself, and local stability of excavations into the steep face of the flow will need to be considered in detailed design.



Overburden in the immediate vicinity of the intake area is limited to the dacite colluvium veneer described on the right bank, an interpreted thin (1 to 2 m) blanket of till outside of the active channel on the left bank, and alluvial sediment accumulated in the river channel upstream of the erosion resistant barrier formed by the granodiorite exposure at the intake area.

A seismic geophysic survey is planned for late fall, 2010 to confirm overburden thickness. The results from this survey will be used to determine requirements for additional investigations as appropriate, such as drilling. Intake design will incorporate assessment of rock mass conditions, seepage, and static and seismic stability of the intake structure for normal, emergency, and survivability conditions.

3.1.3 PENSTOCK ALIGNMENT

The penstock alignment will begin in granodiorite bedrock, and transition to till mantled bedrock slopes. Up to about km 1.0, the penstock alignment will be predominantly in till, but from km 1.0 to km 4.4 the alignment will have bedrock cut slopes that will average about 6 m to 9 m in height, with a maximum height of about 20 m in one location. Past about km 4.4, the penstock route follows existing logging roads traversing a till mantled slope to the powerhouse. Geotechnical characteristics, and terrain stability and geohazards along the route have been assessed separately (BGC, 2010). Terrain stability and geohazard concerns include debris flows, debris slides/flows and rock fall and occur primarily between the intake and km 4.4. Mitigation against these hazards affecting the environment, or the construction of the facilities affecting these hazards, will be considered in design. Additional detail of hazard inventory and risk assessment and mitigation proposed can be found in Ref. [6] (BGC, 2010).

3.1.4 POWERHOUSE SITE

The powerhouse is situated on a till terrace bounded by the Mamquam River and Skookum Creek. Exposures along Skookum Creek are a relatively homogeneous deposit of moderately dense, sub-rounded sand through boulder size material. Drilling and seismic geophysics surveys are planned to characterize the foundation and groundwater conditions. Powerhouse design will incorporate static and seismic foundation stability, slope stability as necessary for temporary or permanent excavation slopes, and seepage inflow control as necessary for excavation planning.

3.2 SEISMICITY

A site-specific seismic risk assessment was obtained for the powerhouse and intake sites from the National Research Councils seismic zoning website. The spectral parameters are



almost identical for both intake and powerhouse, varying only in the third decimal place, and will be considered applicable for penstock as well.

Site classes are inferred from visual observations during the site reconnaissance and will be confirmed based on actual site investigation data. The seismic parameters for the proposed 2% probability of exceedance in 50 years (equivalent to a typical return period interval of 1 in 2475 years) are:

Peak ground acceleration PGA = 0.32 g

Importance factor I = 1.0

Site Class:

Intake Class A Powerhouse Class C

Spectral parameters, as given by the Geological Service of Canada website, vary little within the confines of the project site and to two significant figures are:

Period, T 0.2 s 0.5 s 1.0 s 2.0 s

S(T) 0.70 0.51 0.29 0.16

3.3 CLIMATE

3.3.1 TEMPERATURE

3.3.1.1 Design Temperature Ranges

The 2006 BC Building Code (Appendix C, Division B) provides 1% and 2.5% exceedance design temperatures for Squamish, located at 5 m above sea level (masl) and the nearest Environment Canada station to the project site. These temperatures represent values commonly used for the design of heating and cooling systems, with the assumption that these design conditions should be occasionally (but not regularly or greatly) exceeded.

The BCBC design temperatures are based on hourly ambient temperature records and do not include the effects of wind or solar radiation.

Transposing the Squamish BCBC design temperatures to the project site using conservative lapse rates (change in temperature versus elevation), yields the results in Table 2 below.



Table 2: Design Temperature Range

Location Elevation (m asl) January

(C) July (C)

Powerhouse Site 460 -14 25

Intake Site 805 -15 21

If necessary, site-specific values can be obtained directly from Environment Canadas Atmospheric Environment Service during detailed design.

3.3.1.2 Average Summer and Winter Temperatures

To provide an idea of more typical summer and winter temperatures, 1971 - 2000 climate normal average daily maximum (July-August) and minimum (January) temperatures for Squamish have been transposed to the project facility elevations using conservative lapse rates. The results are given in below.

Table 3: Average Daily Temperatures

Location Elevation January, C August, C

(m als) Daily Minimum Average Daily Max.

Daily Minimum Average

Daily Max.

Powerhouse Site 460 -4 -3 -2 10 15 20

Intake Site 805 -5 -5 -5 9 13 17

The above data will be used to estimate average-day heating and ventilation loads, as well as in establishing construction requirements such as maximum weld-up temperatures and concrete curing procedures.

3.3.2 SNOW AND RAIN

Based on the BCBC values for Squamish and a snow load versus elevation relationship developed for the southern Coast Mountains modified for Squamish 1, the following design snow and rain loads are applicable:

1 Sr = 3.2 + 0.008 (Elevation) in kPa.



Powerhouse:

Ground snow load Ss = 7 kPa Associated rain load Sr = 0.8 kPa Depth of snow pack 2.5 m

Intake:

Ground snow load Ss = 10 kPa Associated rain load Sr = 0.8 kPa Depth of snow pack 3.5 m

Depth of snow for the above has been calculated using a unit weight of 3 kN/m3.

3.3.3 WIND

Based on BCBC wind values for Squamish, the following values are applicable at both the powerhouse and intake sites.

Table 4: Design Wind Speeds and Pressures

Reference Velocity Reference Pressure Return Period

vref (m/s) vref (km/hr) qref, (kPa)

50 years 29.4 106 0.56

The above wind speeds are derived from , where V is in m/s for qref in Pa.

3.4 HYDROLOGY AND FLOWS

3.4.1 BASELINE HYDROLOGY

Skookum Creek drains a rugged south-facing watershed ranging in elevation from about 440 m to over 2,500 m above sea level. Above the proposed intake site (approximate EL 805 m) the watershed measures approximately 67 km in area, primarily consisting of second- and third-growth forest. The high elevation of the watershed and its proximity to the Salish Sea produce a transitional runoff regime with both a dominant fall flood season (rain-on-snow) and a significant freshet. Discharges in the late summer are supported by meltwater from high-elevation glaciers that cover over 8% of the watershed.

Hydrometric data has been collected on Skookum Creek since 2003. Data are processed and results analyzed by Aquarius Research and Development (ARD) of Bowen Island, BC. The hydrometric data are subjected to a baseline regression against concurrent data



collected at nearby long-term Water Survey of Canada stations. The resulting regression relationship is used to produce a synthetic streamflow series over 20 years in length, which is sufficient to provide reasonable estimates of long-term runoff statistics. The hydrometric data collection process and hydrologic review are summarized in a pair of reports prepared by Aquarius R&D (Sentlinger, 2010). A review and summary report on these studies prepared by KWL concludes that the approach taken by ARD is generally consistent with accepted industry practices, and that the results provide a reasonable indication of streamflow on Skookum Creek.

The streamflow statistics provided in Table 5 below are obtained from the long-term synthetic flow series for Skookum Creek, as produced by ARD.

Table 5: Estimated Mean and Median Streamflow Data for Skookum Creek at the Intake

Period Median Discharge (m/s) Mean Discharge (m/s)

January 1.2 3.2 February 0.7 1.2

March 1.0 1.4 April 2.3 3.2 May 6.7 8.8 June 13.6 14.3 July 9.2 10.6

August 5.0 6.0 September 2.7 3.2

October 2.2 5.3 November 2.4 6.0 December 1.1 2.3

Annual 3.1 5.5

For Skookum Creek, the median discharges range from 0.7 m3/s in February to 13.6 m3/s in June. Mean discharges range from 1.2 m3/s in February to 14.3 m3/s in June. The median discharges are less than 1.2 m3/s for the months of December through March and the mean discharges were less than 3.2 m3/s for the months of December through March. The annual median discharge is 3.1 m3/s and the annual mean discharge is 5.5 m3/s.

3.4.2 MINIMUM INSTREAM FLOW REQUIREMENTS

The proposed project will directly decrease the instream flows between the proposed intake and powerhouse tailrace by diverting flow through the intake for power generation. The minimum instream flow requirements (IFR), as presented in Table 8, were developed to



provide a balance between project economics and stream health by the environmental consultant, Barkley Group.

The turbines in the power plants cannot operate when the creek discharges are less than 3% of the project design flows. During these low flow periods water will continue to be diverted from the creek through the Coanda intake, but all flows will be immediately returned to the creek via the IFR outlet described below.

The IFR flows will be discharged directly from the headpond back into the creek channel through a discharge pipe set into the weir. The discharge pipe will be sized to draw the largest required IFR flow from the forebay with the minimum forebay water level. The smaller IFR flows will be controlled by closing a gate valve on the discharge pipe to pre-set settings.

In addition, the project will be operated in a manner that minimizes the rate of downstream flow increases below the powerhouse during project start-ups and shutdowns (i.e. flow ramping). Flow ramping will be monitored at established compliance points downstream of the tailrace.

Table 6: Instream Flow Requirements and Flow Ramping Requirements

Time of Year Life Stage History IFR Day Ramp Rate Night Ramp Rate

16 September to 22 October

DV spawning 1.36 m3/s 0 to m3/hr to m3/hr

23 October to 30 April

Overwintering 0.54 m3/s 0 to m3/hr to m3/hr

1 May to 15 September

Rearing, RB spawning and egg incubation

0.81 m3/s 0 m3/hr 0 to m3/hr

3.4.3 FLOOD HYDROLOGY

A flood frequency analysis was conducted on the synthetic flow series generated for the Skookum Creek intake. The series of annual maximum peak flows was analyzed with Environment Canadas CFA 3.1 software package, and the results validated by regional analysis. Average maximum daily flows for return periods up to the 200-year event, as estimated by the flood frequency analysis, are shown in Table 7. A 10% allowance for climate change effects is incorporated in all discharges.

Peak instantaneous flows corresponding to 2 year, 10 year, 50 year, 100 year, and 200 year return period flood events are also presented in Table 7. These were obtained by multiplying the daily average flows by a representative peaking factor of approximately 2.0. (Ref. [2]).



Table 7: Recommended Clear-Water Design Floods at the Skookum Creek Intake

Return Period (years) Average Daily Flow (m/s) Instantaneous Flow (m/s)

2 46 92 5 62 124

10 75 150 50 105 210

100 120 240 200 135 275

The flood flows range from 46 m3/s for the two-year return period daily average flood discharge to 275 m3/s for a 200-year maximum design event. The present-day mean annual flood is approximately 51 m/s. A 10% allowance for climate change should be added to the mean annual flow (MAF) for comparison with the flood quantiles reported in Table 7.

To proceed with the preliminary design, initial estimates of flood flows have been made. These will be firmed-up by more detailed HEC-RAS modelling as design progresses. Table 8 shows the initial estimates of clear water levels prior to the construction of the project, i.e. under current natural conditions. It is interesting to note that the 200 year return period event produces a water depth of about 6 m above the creek bed at the intake site. Table 9 shows the initial estimates of intake flood levels post-construction. Due to a natural constriction about 50 m below the intake, which acts as a natural hydraulic control at high flows, the 200 year return period flood level is not influenced by the presence of the intake at all. The intake structures and embankments will be designed for this flood level and, where appropriate, 1 m of freeboard will be provided. The powerhouse flood levels are not influenced by its presence.

Table 8: Design Flood Elevations Prior to Project (m above sea level)

10 year 100 year 200 year

Intake* 804.50 808.00

Powerhouse 456.90 * Before construction

Table 9: Design Flood Elevations With Project (m)

10 year 100 year 200 year

Intake** 806.00 808.00 **With project



3.5 GEOHAZARD RISK AND SEDIMENTATION

3.5.1 GEOHAZARDS

A terrain stability and risk assessment has been undertaken to inventory potential existing terrain hazards to the penstock route, assess the risk they pose to the penstock, and propose preliminary mitigation strategies. This assessment is documented in Ref. [6]. Terrain stability hazards (geohazards) to the penstock include:

Debris slide/flow from open slopes or up slope access road fill slope failures,

Channelized debris flows in creeks that cross the alignment, and

Rock fall from natural bluffs.

In addition to these current geohazards, construction could create the geohazards of rock fall from cut slopes, debris fall from erosion of soil cut slopes and cut slope slides.

3.5.2 SEDIMENTOLOGY

Sedimentation in Skookum Creek is under study by EBA Engineering Consultants Ltd., with interim results published in Ref. [25]. Sediment sources identified comprise colluvial, alluvial and glacial processes. Total sediment transport values are summarized as follows:

Table 10: Summary of Total Sediment Transport (m3)

Source Annual Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Bedload 81000 4500 3950 3500 3900 12300 11800 11100 3100 4150 9600 8250 3950

Suspended Sediment 12050 700 600 500 600 1850 1750 1700 450 600 1450 1250 600

Total 92150 5200 4550 4000 4500 13550 13550 12800 3550 4750 11050 9500 4550

3.6 MAPPING, SURVEYS AND CONTROLS

3.6.1 LIDAR MAPPING

Terra Remote undertook the LIDAR (Light Detection And Ranging) mapping on 6 and 8 July 2007. The data collection specifications provided include a relative accuracy of better than 0.10 m at two standard deviations. The mapping datum was UTM NAD 83 and the geoid



that was used was Canada 2000 (HT2). Nanoose Bay, Whistler and Chilliwack CACS reference sites were used to correct the positioning of the bases.

3.6.2 GROUND SURVEYS

Ground surveys were conducted at the intake and powerhouse sites in September 2010 to improve detail and ground-truth the LIDAR. The ground survey results were also processed to UTM NAD 83 and geodetic elevations.

Prior to construction, a ground level survey will be required to establish geodetic controls for the project, preferably at the intakes, approximately every 500 m along the penstock routes, at the creek crossings and at the powerhouse.

There is presently no survey control in the project area.

3.7 SITE ACCESS

Access to the project area is by means of the Mamquam Forest Service Road, wich passes within 150 m of the powerhouse site. A branch forest service road leads uphill and is accessible to 4 wheel drive vehicles for the first 1.8 km.

The other existing roads in the area range from semi-deactivated forest service roads (ATV and trail bike access) to a decommissioned forest road over the final 2.5 km to the intake. The latter has had all bridges removed and abutments pulled-back, culverts have been removed and replaced with swales and the downslope fills have been pulled up onto the bench along about 30% of the alignment. These roads will require re-establishment for construction and permanent access to the intake.



4 FACILITY SIZING

4.1 PENSTOCK SIZING

At the current state of preliminary design, a penstock consisting of approximately 950 m of 2.0 m diameter and 6260 m of 1.8 m diameter steel pipe is being considered. As design progresses, diameters will be optimized further. An alternative using FRP for part, or all, of the low-pressure section is under review as well. Losses in the penstocks are being estimated using the Darcy-Weisbach method.

A literature review included Hwang (1996, Ref. [30]), with roughness ranging from 0.0048 to 0.045 mm, Miller (1996, Ref. [34]) specifies a roughness of 0.025 mm for new steel pipe and that typical allowances for deterioration over time are between 25 to 50 percent of new pipe values (resulting in a roughness of 0.04 for aged steel pipe with some lining damage).

DESI suggests designing pipes to lose 9% of their hydraulic capacity in non-atypical conditions to account for aging. Applying a roughness value of 0.045 mm results and reducing hydraulic capacity by 9% resulted in a friction factor of 0.013 for Skookum Creek.

The losses analysis was conducted assuming a water temperature in the penstock of 5 degrees Celsius and considered entrance losses, bend losses, friction losses, and contraction losses based on preliminary design. In addition, an assumed 1 m head loss between the turbine inlet valves (TIV) and nozzles was included in the overall loss calculations. This corresponds with the turbine manufacturers typical approach of including all losses from the TIV through the distributor and the nozzles and will be verified during equipment tender review and selection.

4.2 POWER GENERATION MODEL

A power generation model is being developed to determine the power generation profile through the year. The modelling parameters currently being used are:

Daily flows (low, average and high) Conveyance losses, as discussed in Section 4.1 above. Turbine efficiency: 89.5 91.4% Generator efficiency: 90.7 97.1% Station services losses: 50 kW

Transformer and line losses between the switchyard and the point of interconnection will be determined by others. The power generation model results will feed into SSPCs project economic model.



4.3 TURBINE/GENERATOR SIZING

The turbine, generator, and appurtenant works will be sized by the suppliers in order to maximise the annual energy production with the variable flows and net head available. The rated capacity will be approximately 12.5 MW for each unit, but the turbine / generator will be sized to produce 110% of this power on a continuous basis as a design factor.



5 POWER GENERATION EQUIPMENT DESIGN

5.1 TURBINE

5.1.1 PELTON TURBINES

Two vertical axis multi-jet Pelton turbines have been selected as the most cost-effective solution for the project.

The turbine suppliers design will meet the following criteria:

Stainless steel runner and needle valves, runner hung on generator shaft with mechanical seals.

Due to environmental flow ramping requirements, turbine deflectors will be capable of bypassing full turbine flow for up to 8 hours at time without abnormal wear.

The unit synchronous speed to be determined by the turbine and generator designers to provide most economical and efficient supply.

Supply of all standard appurtenances, operating equipment, and instrumentation wired to terminal boxes. Instrumentation shall be sourced within North America.

Turbine components will be designed and tested to withstand surge overpressure up to 120% of maximum gross head, no surge relief will be provided other than deflectors and needle valves.

Hydraulic control, from a single HPU per unit, which supplies actuators for injectors, deflectors, brake and inlet valve. The HPU will have two pumps, with each pump capable of operating the system on its own. Each injector will be provided with proportional valve control. The HPU will be complete with an accumulator of sufficient capacity to force closure of all turbine injectors in the event of a power and/or control loss per IEEE 125.

All hydraulic piping will be stainless steel.

Normal closing times of the needle valves will be set to avoid design-critical transient pressures in the penstock. An initial value, 12 minutes will be assumed.

The needle valves will be designed to fail-safe close in the event of loss of hydraulic power in not less than the time required to keep the transient pressures in the penstock



always above 25% of the standard atmosphere. As an initial value, a closing time of 90 seconds will be assumed.

5.1.2 TURBINE INLET VALVE

There will be one inlet valve per turbine, either of the butterfly or spherical valve types, with the head-loss across the valve taken into consideration in the final selection.

The inlet valves will be hydraulically actuated and equipped with a counterweight sufficient to provide fail-safe closing under full design flow. The hydraulic cylinder will be equipped with orifice ports such that the gravity closure has two speeds. For example, 90% of the closing stroke is completed in 70% of the total closing time with the final 10% stroke completed in 30% of the closing time. This is to always keep the transient in the penstock above 25% of the standard atmosphere. As an initial value, a closing time of 120 seconds will be assumed.

Each inlet valve will be equipped with a bypass valve, suitable for pressurising the turbine. Bypass valves may be hydraulically or electrically actuated, and must be capable of operating without cavitation.

5.2 GENERATOR, SWITCHGEAR, AND SUBSTATION

The electrical equipment for the project is being designed by Others. The following general characteristics form the basis for interfacing design of electrical equipment with the civil works.

Generators: vertical axis, self (air) cooled (open, drip-proof) machines, directly coupled to turbine with runner on generator shaft. A minimum of two bearings (self-lubricating, journal) will be provided, one on either side of generator. A high pressure bearing lift pump will be included if required, so that the minimum turbineable flow is capable of breaking the static bearing friction on start-up. Generation voltage is 4160 V.

Generator bearings: water cooled, using a closed-loop cooling system and a heat-exchanger installed in the tailrace. Two 100% redundant cooling pumps will be provided. All cooling piping will be stainless steel. Bearings will be capable of coasting, without damage, from a normal full load rejection overspeed to a complete stop without cooling water. Deflectors will be engaged successfully to prevent runaway speed. Cooling will be provided by heat exchangers set into the plunge pool.

Medium voltage switchgear will be located within the powerhouses. Switchgear will be of the metal-clad type and will be specified to conform to the following standards:

The outdoor substation will transform the medium voltage power from the powerhouse into 138 kV high voltage for transmission into the BC Hydro network.



5.3 CONTROL SYSTEM

Operation and control of the turbine / generator system and auxiliary equipment will be performed by a high-end Programmable Logic Controller (PLC) designed by Others.

5.4 GROUNDING

Grounding design will be by Others. The following sections describe the grounding system as it impacts the civil works.

5.4.1 POWERHOUSE GROUND GRID

The powerhouse and switchyard grounding grid will primarily consist of bare copper conductors embedded in the concrete foundations, electrically connected to the reinforcing steel. Buried bare-copper perimeter loops will also be included as required to eliminate dangerous step and touch potentials.

All structural steel columns in the powerhouse will be connected to the ground-grid, as will all pieces of electrical equipment, cable-trays, handrails, fences, door-frames and other exposed metallic objects.

5.4.2 GROUNDING OF THE PENSTOCK

It is impossible to completely isolate the penstock from the grounding grid, so the prudent approach is to specifically include the penstock as part of the system. Although coated, the massive surface area of the metallic penstock provides an excellent path to ground and is expected to greatly reduce the overall ground grid resistivity and GPR.

The penstock will be grounded at a single location only, where it enters the powerhouse. The grounding connection will be made using a cathodic isolator that allows AC fault currents to pass into the penstock but blocks DC cathodic protection currents from passing into the powerhouse ground-grid.

Depending on the designed GPR, it is likely that exposed parts of the metallic penstock such as manholes and surge shafts, will need a gradient-control mat connected to them. When required, these gradient-control mats shall be of a material, such as zinc, that is compatible with the cathodic protection system.

5.4.3 GROUNDING OF THE INTAKE

Due to the fact the penstock is of steel, over its entire length from powerhouse to intake, it is impossible to practically separate the intake and powerhouse grounding grids. Therefore, the



intake grounding grid will be solidly connected to the penstock, effectively making it part of the powerhouse grounding grid.

The intake grounding grid will be designed and constructed in a similar manner as the powerhouse grounding grid, to ensure that step and touch potentials are kept within the safe limits.



6 PROJECT WORKS DESIGN

6.1 DESIGN APPROACH

All engineering design will be carried out in SI units. Engineering design will use a Performance Level Design approach. All elevations will be in metres above Geodetic Survey of Canada (GSC) datum CGVD28 and will be tied into local benchmarks using precision survey control during construction.

6.1.1 FACILITY CLASSIFICATION

The power project is designed as a post-disaster facility. The BCBC 2006 classification is Division F Class 3. The design life of the facility is 40 years.

6.1.2 REQUIRED PERFORMANCE LEVELS

The civil structures will be designed to perform as specified under the following performance levels:

Normal Operation Condition: The facilities operate normally.

Emergency Operation Condition: The facilities operate without damage but components may be at their safe design limit.

Survivability Condition: The facilities may suffer local permanent movement or deformations, as well as repairable damage, but without collapse.

The design of the facilities will consider the component performance limit states appropriate for each performance level.

Where a limit state check requires factored loads, the load factors and combinations stipulated by BCBC will be used. Examples of factored loads include:

Gravity loads due to self weight, usage, and equipment; Creep and shrinkage effects; Rock and soil pressures; Environmental loads due to snow and wind; and Equipment operation loads.



For certain loads and effects, discrete maximum expected specified load levels are defined for the each performance level using explicit stochiastic methods and no further load factors are appropriate. Examples of maximum expected specified loads include:

Water levels. Pipe pressures and thermal effects. Seismic loads.

6.1.3 MATERIAL PARAMETERS

The following is a summary of the principal material parameters assumed appropriate for the basic engineering stage design. More detailed information and requirements can be found in the relevant material specifications and actual test results.

6.1.3.1 Geotechnical Design Parameters

The following parameters are initial estimates suitable for approximate sizing of structures at the preliminary design stage and are based on the regional geology and subsurface lithology described in Section 3. They will be modified as additional site investigation results become available.

Temporary excavations:

Maximum slopes for temporary unshored excavations in soil less than 6 m deep 3H : 4V

All areas adjacent to excavations graded to drain water away from the excavation. Store and stockpile materials more than 2 m or half the excavation depth away from excavation edges.

Backfill pressures:

Select native free-draining granular materials, compacted in controlled lifts, will be used for structural backfills. The following strength parameters are appropriate:

Active soil pressure coefficient ka = 0.26 At-rest soil pressure coefficient ko = 0.41

but not less than the following compaction pressure 20 kPa Passive soil pressure coefficient kp = 3.85 Drained shear strength = 36, c = 0 kPa Total unit weight of backfill material 20 kN/m3



For rigid retaining walls and other structures with soil backfills, the lateral seismic force component on vertical faces of height H [m] will be calculated by the Woods (1973) relationship as:

A force located 0.63H above the back of the wall equivalent to 11.0 H [kN]

Penstock soil support:

The penstock will be of 1800 mm pipe. Subgrade reactions for lateral soil-pipe interaction will be within the following ranges:

Axial Subgrade Reaction 5.4 to 37 MN/m3

Lateral Subgrade Reaction 2.3 to 12 MN/m3 Downward Subgrade Reaction 7.7 to 32 MN/m3

For horizontal subgrade reactions, the values are generally near the lower bounds of the values provided above, and for vertical support reactions are towards the upper range of the values. For this design basis, uplift is considered to have no subgrade reaction, unless the cover is in excess of 4 to 5 m.

Horizontal thrusts are generally limited to Coulomb passive limits. This is usually not a design constraint when thrusts are into the hill, but can be an issue when they act against the road berm. It is usually necessary to maintain at least the passive failure wedge geometry within the berm if soil restraint of the penstock is being used.

Minimum cover for buried penstocks relying on soil support 1200 mm

Penstock bend anchorage:

For anchored bends, double-corrosion protected anchors will be used. Anchor sizes will be based on the following:

Matching performance level for prestress Normal operation Pre-stress level 0.6 ultimate tensile strength Soil-grout transfer strength at prestress level 160 kN/m

Intake and powerhouse foundations:

The intake will be founded on competent granite bedrock.

The powerhouse structures are assumed to be founded on till, alluvium or colluvium. Preliminary design foundation design parameters are:

Frost protection depth 1200 mm



Factored bearing resistance pr = 180 kPa Modulus of subgrade reaction (vertical) kv = 4.8 MPa/m Seismic site classification Class C

6.1.3.2 Concrete Design Parameters

Concrete mix types and corresponding design properties are as follows:

Concrete Mix C15 (for concrete blinding on foundation inverts):

Specified cylinder compression strength at 28 days fc = 15 MPa

Concrete Mix C25 (for mass concrete):

Specified cylinder compression strength at 28 days fc = 25 MPa Characteristic tensile strength fctk,0.95 = 3.0 MPa 5th percentile tensile strength fctk,0.05 = 1.5 MPa Modulus of elasticity Ecm = 21 000 MPa Poissons ratio (cracked section) = 0.17

Concrete Mix C35 (for structural reinforced concrete):

Specified cylinder compression strength fck = 35 MPa Characteristic flexural tensile strength fctk,0.95 = 4.2 MPa 5th percentile tensile strength fctk,0.05 = 2.2 MPa Modulus of elasticity Ecm = 28000 MPa Poissons ratio (cracked section) = 0.17

6.1.3.3 Reinforcement Design Parameters

All reinforcing steel will be CSA G30.18 Grade 400W, weldable. Design parameters are:

Yield strength fy = 400 MPa Ultimate tensile strength ftk = 550 MPa Elongation at yield y > 0.2 % Ductility 50 mm > 12 % Modulus of elasticity Esk = 200000 Mpa

6.1.3.4 Penstock Materials

Penstock steel work, including line pipe, bends, appurtenances and integral stiffeners, ring girders and other supports will be of grades suitable for variable pressure and temperature conditions.



Steel line pipe, longitudinal or spiral welded, fabricated, and tested to API 5L, source material to API 5L, or ASTM A1018 (tested to ASTM A20), and meeting the following additional minimum physical requirements:

Low-pressure penstock: API 5L Grade X42 or A1018 SS Grade 40:

Yield strength fy 275 MPa Ultimate tensile strength fu 380 MPa

High-pressure penstock: API 5L Grade X52 or A1018 HSLAS-F Grade 50:

Yield strength fy 345 MPa Ultimate tensile strength fu 410 MPa

The above pipe steels must also meet all of the requirements below.

Strength ratio fy / fu 0.92 Ductility 50 mm > 22 %

Chemical properties must be below the following limits:

Carbon content 0.25%

Manganese content 1.4%

Phosphorous content 0.035%

Sulphur content 0.035%

Carbon equivalent CE 0.40%

where

In addition, for pipe walls greater than 16 mm, the required impact energy, measured per ASTM A370 at -29 C on three specimens is:

16 mm wall thickness < 25 mm CVaverage = 27 J CVlowest = 20 J 25 mm wall thickness < 38 mm CVaverage = 34 J

CVlowest = 27 J

Plate work, including fabricated appurtenances, integral stiffeners, ring girders and other supports, plate to API 5L X52 or ASTM A1018 HSLAS-F, Grade 50:



Yield strength fy = 345 MPa Ultimate tensile strength fu = 410 MPa Ductility 50 mm > 22 %

Weld material: to match the base metal and process used per CSA W48 Series

Electrode type E49XX or equivalent Minimum Tensile Strength 480 MPa Minimum Yield Point 410 MPa Minimum Charpy Toughness at -29 C 40 joules

Pipe lining:

Line pipe and appurtenances, such as bifurcations, line valves, manholes, etc., will be internally coated with liquid epoxy to AWWA C210.

Pipe coating:

All penstock components will be externally coated with liquid epoxy to AWWA C210. Where pipe is exposed to air, a urethane topcoat will be applied.

6.1.3.5 Backfill Materials

Where the penstock is buried adjacent to a road in a pipe trench, pipe bedding and pipe zone backfill will consist of a 19 mm minus bedding layer that will be more pervious than the remainder of trench fill (bedding sand). Adequate trench drainage will be provided and will consist of a combination of trench dams, perforated drainage pipe, filter fabric and drain rock.

6.1.3.6 Structural Steel

Steel sections and corresponding design parameters are as follows:

I sections, welded wide flange members, structural platework CSA G40.21 Grade 350W:

Yield strength fy = 350 MPa Ultimate tensile strength ftk = 450 to 650 MPa Modulus of elasticity Es = 200000 MPa

Hollow structural shapes (HSS) CSA G40.21 ASTM A 500, Grade C:

Yield strength fy = 345 MPa Ultimate tensile strength ftk = 450 to 600 MPa



Modulus of elasticity Es = 200000 MPa

C and L sections and anchor rods, CSA G40.21 Grade 300W:

Yield strength fy = 300 MPa Ultimate tensile strength ftk = 450 - 620 MPa Modulus of elasticity Es = 200000 MPa

High-strength bolts, ASTM A325:

yield strength fy = 417 MPa tensile strength fu = 830 Mpa

Weld material:

Weld material to match the base metal and process used per CSA W48 Series:

for Grade 350W,350WT and A 500 Grade C steels E49XX equivalent for Grade 300W steels E43XX equivalent

6.1.3.7 Timber

Timber will be Douglas Fir Larch species, possibly locally sourced and visually graded.

Glulam members

Grade of flexural members Grade 24f-E Grade of compression members Grade 16c-E

Structural timber members DF-L Select Structural

6.2 HYDRAULIC AND HYDROMECHANICAL DESIGN

6.2.1 PERFORMANCE REQUIREMENTS

6.2.1.1 Design Water Levels

The flood level elevations to be used for design are set out in Section 3.4.



6.2.1.2 Operating Rules

a) Coanda Intake

The Coanda intake has been designed based on operation with continuous headpond level control. Unlike many other projects, the Coanda screen intake will not be used as a primary spillway to pass flood flows at Skookum Creek. At this site, the Coanda intake has been chosen to avoid fish and fry ingestion and for its perceived self-cleaning properties.

Headpond levels will be maintained by adjusting the right-bank Obermeyer gate. At low flows, the head on the Coanda crest will be maintained within 0 to 0.5 m. At moderate flows, spilling over the central pier whose crest is set 0.5 m higher than that of the Coanda - will also be allowed. In all instances, headpond levels will be maintained at or below EL 806.00.

The Coanda spillway will consist of 2 mm screens designed to withdraw 140% of the design flow of 9 m3/s, i.e. 12.6 m3/s. The accelerator plate will be designed for 167% of the maximum operating flow over the Coanda, i.e. 1.67 x 9 m3/s or 15 m3/s. The screen length will be sized to be fully wetted when the flow over the Coanda crest just equals the design withdrawl flow. As the headpond level will be controlled, flow over the Coanda will be kept near optimum during most of the time and back-watering the screen should not be a problem. The void area below the screen will be aerated to maintain atmospheric pressure.

For the above design parameters, a total Coanda weir width of 20 m has been chosen. The site topography dictates that the Coanda weir be located parallel to the thalweg alongside the left bank. To optimize approach velocities with this arrangement, current design foresees three equally sized Coanda bays of 6.7 m width, successively rotated 11.6 with respect to each other to produce a flared plan arrangement that narrows in the downstream direction. Each Coanda bay will have provisions for flash boards so that flow may be concentrated during cold periods to mitigate against frazil ice.

The screens will be designed to withstand loads due to floating debris associated with the 200 year flood event. Since bedload will pass through the adjacent sluiceway, no loading due to saultating boulders is expected.

All dimensions provided by the suppliers have been checked by the Coanda design program developed by Tony Wahl, U.S. Bureau of Reclamation, Water Resources Research Laboratory.

b) Screen Collection Channel and Penstock Forebay

The screen collection channel and penstock forebay have been designed to minimize the potential for surface vortices to form and enter the penstock (i.e. submergence), decrease



turbulence, facilitate the release of entrained air bubbles to the surface before entering the penstock and provide sufficient volume for water level control.

6.2.1.3 Submergence

Two submergence equations were evaluated and compared with four operational hydroelectric projects in British Columbia. The more conservative formula of the two evaluated was used to estimate the minimum required submergence (Knauss, 1987, Ref. [33]):

(h/D) = 2Fr + 0.5

where h is the submergence above the centreline of the horizontal inlet pipe; D is the pipe diameter and FD is the Froude Number at the pipe inlet. The Froude number is defined by the following equation:

FD= [V/(g D) 0.5 ]

Where V is the velocity in the inlet pipe, and g is acceleration due to gravity.

The calculated submergence depth requirement is 2.6 m for Skookum Creek based on a 2 metre diameter inlet pipe. Grating platforms will be installed upstream of the penstock entrance to dissipate any potential surface vortex activity. The water level in the penstock forebay will be controlled by the operation of the needle valves at the turbine for discharges up to the design flow. Automated water level gauges in the penstock forebays and within the IFR collection channels will direct the operation of the needle valves at the turbines to ensure adequate submergence at the penstock entrances is achieved and that IFR flow requirements are met. Water level sensors will be protected (ie stilling well) from disturbances that occur during normal plant operations.

6.2.1.4 Turbulence and Air Bubble Movement

The design of the penstock forebay considered the time required for air bubbles to rise from an estimated depth of 2 metres below the forebay water surface, utilizing equations contained in available literature (Batchelor, 1967, Ref. [6]). The air bubble rise calculations were developed based on an air bubble radius of .25 mm with an associated rise velocity of approximately 0.13 m/s (in still water). As with sediment particles, turbulence can keep air bubbles in suspension and therefore, increased turbulence will reduce the rise velocity of individual air bubbles. The geometry and velocities (



6.2.1.5 Intake Chamber Volume Required for Water Level Control

The turbine control systems will be designed to balance the flow entering the turbines with the flow in the creeks through the use of an automated feedback loop that aims to maintain a constant water level in the penstock forebay. The volume of water in the penstock forebay must be sufficient such that temporary imbalances between turbine flows and creek flows do not cause the forebay water level to drop below the minimum submergence depth.

The proposed head pond for the Skookum intake will encompass approximately 1.6 ha at an elevation of 806 m, based on LIDAR. This is the equivalent of approximately 18 seconds of storage at the turbine design flow of 9.0 m3/s per 0.01 m of head pond drawdown.

The intake forebay was also designed to account for 60 seconds of storage independently of the head pond for one nozzle. Assuming 2-5 nozzle machines the storage required would be 54 m3 without drawing the forebay down below the minimum submergence level.

These assumptions will be revisited once the turbine and control configurations have been selected.

6.2.1.6 Penstock Aeration and Air-entrainment Control

Air vents will be installed immediately downstream of the penstock inlet gate. The air vent will be designed to restrict air speeds to less than 30 m/s during a full penstock draining scenario. In addition, the need for air release valves at the abrupt change in slopes in a pipe system will be reviewed. Particular care will be required for air release at the proposed siphon location. The air release vent will be insulated and vaulted to protect against the elements, animal intrusions and vandalism.

6.2.2 INTAKE FLOOD PASSAGE, CONTROLS AND ISOLATION

The Skookum Creek Hydroelectric Project is designed as a run-of-river facility with minimal live storage of water at the intake location, and hence no influence on the natural flow in the creek upstream of the intake and downstream of the powerhouse.

The intake has been configured to accommodate passage of discharges up to the 200-year flood event. This will be accomplished by opening the two Obermeyer adjustable gates. The larger 15 m gate on the right bank will be used to regulate head pond levels and sluicing while the 7 m gate central will be used only for sediment sluicing as required. The top of the embankments and intake structures have been set above the estimated 200 year instantaneous flood level at the project, which is calculated to be El. 808.00 m. Structures designed not to be overtopped will be designed with 1.0 m of freeboard.



The spillway and sluiceways will be designed to safely pass large debris and sediment that is carried into the head pond for discharges up to the 200-year instantaneous flood event.

The sill of the central sluice passage has been set 1.0 m lower than the right-bank sill (at EL 801.00 rather than EL 802.00), thus allowing maintenance of the right-bank gate at low creek flows.

A penstock inlet slide gate will also be provided to allow emergency isolation of the penstock in the event of a penstock rupture, without the need for the (slow) dropping of the Obermeyer gates.

6.3 PENSTOCK

6.3.1 PENSTOCK DESIGN PREMISES

6.3.1.1 Low-Pressure Penstock (LPP)

From the intake to about km 1.0, the penstock will be incorporated in the reconstructed access road, and soil restraint will be used as discussed for the high pressure penstock. From km 1.0 to about km 4.4, the penstock will be placed on the excavated bench on suitable bedding or concrete sills, spaced at 11 - 12 m centres, with ground anchored ring girder restraint at larger bends. Excavation through steeper rock portions of the penstock will require full-bench excavation and end-haul.

6.3.1.2 High-Pressure Penstock (HPP)

The penstock will be designed to act using soil restraint wherever possible, This restraint will be developed through a combination of specified compacted backfill while ensuring adequate passive reactive forces are developed within the backfill and insitu materials. Where soil restraint cannot be completely relied upon, the design will be supplemented with the addition of concrete or mechanical restraints.

The penstock backfill will be designed to operate under drained conditions during normal operation, for which drainage measures including select free-draining media and subdrains have been incorporated into the design. Subdrain spacings and diameters will be designed to ensure that all reasonable flows intercepted by the trench or from infiltration can be adequately discharged from the penstock trench to maintain drained conditions. However, design will consider the possibility of saturated penstock trench fill during extreme runoff events, and not allow the Emergency Operation Performance Level for the penstock pipe to be exceeded with this condition. Despite measures being taken to prevent penstock trench fill saturation, should this occur the penstock backfill will be designed to be of sufficient thickness to provide a static weight to prevent flotation of the penstock.



To prevent the migration of fines from either the in-situ materials or between backfill units, the material specification of each unit will be carefully specified to ensure compatibility. Where such compatibility cannot be assured, geotextiles to provide an artificial break between media will be incorporated into the design.

As the penstock is being designed to operate under unsaturated conditions, streams crossed by the penstock will be passed over, or under, the penstock. For intercepted water that is considered insufficient to warrant passage over the penstock, the water will be collected in the subdrain system for discharge at intervals.

Typical sections have been prepared which illustrate the two general arrangements, one where the penstock is buried adjacent to the road; and one where the penstock is placed on an excavated bench. For locations where the penstock is adjacent to the road, the design intent is to allow the minimum approach distance from the edge of the road to vary provided that the interaction of water in the roadside ditch with the penstock backfill is minimized.

For locations where the road ditch encroaches on the penstock trench fill, or the penstock crosses under the road, designs will include additional measures to limit entry of seepage from the road ditch into the penstock fill. This will include ditch liners or impervious soil layers.

6.3.1.3 Geohazard Risk

Protection measures will be required to address the geohazards summarized in Section 3.5.1 above. Protection measures will vary depending on the hazard type and cost benefit of different measures, but will include measures to reduce the likelihood of a geohazard initiating, and defensive measures to reduce the likelihood of an undesirable consequence to the penstock. Examples of measures that reduce the likelihood of a geohazard initiating include:

Reconstruction of the up slope access road bench and drainage measures to:

o reduce debris slide/flow likelihood to the penstock from unstable road fill or from concentration or mis-direction of surface drainage; and

o provide a catchment bench above the penstock for events originating up slope of the access road;

Long-term stable design of soil penstock bench cut slopes to reduce the likelihood of debris fall affecting the penstock.

Rock slope cut design, controlled blasting, and stabilization measures to reduce the likelihood of rock fall from rock cut slopes affecting the penstock.



Examples of defensive measures include:

Burial of the penstock. This will apply for the first 1.0 km and for the high pressure section past about 4.4 km, and will also be used where it is the most cost effective protection against rock fall;

Burial design for minor penstock creek crossings to protect against scour and small debris flows as required, or the use of small pipe bridges;

Over larger creek crossings, the use of pipe bridges that are designed for potential flood and debris flow passage;

Maintaining the penstock on the inside of the penstock bench to provide a buffer platform down slope of the penstock that promotes deposition in the event of up slope debris slide or flow events, rather than scour; and

Anchoring the penstock to resist displacement if impacted by an event.

It is recognized that design of the penstock cross drainage, as well as design to mitigate against up slope geohazards to the penstock, will require close integration of the penstock bench, cross drainage, and earthwork design with road reconstruction design.

6.3.2 TRANSIENT PRESSURE ANALYSIS

Transient analyses will be completed assuming two five-jet Pelton turbines in the powerhouse, for the following scenarios:

Normal Operation Condition: Controlled closure of the needle valves or the turbine inlet valves. As an initial value, a 12-minute closing time is being assumed.

Emergency Operation Condition: Fail-safe closure of needle valves or turbine inlet valves. As initial values, a 90 second closure of the needle valves and 120 second closure of the TIVs are being assumed.

Collapse Prevention Condition: Slam closure of one needle valve during full flow (e.g. valve stem failure).

6.3.3 STRUCTURAL ANALYSIS

6.3.3.1 Penstock Design Loads

The load conditions relevant for design are defined as follows:



Internal Pressure

At the current level of design, the following pressures are being used for penstock design:

Maximum static head P1 = ELintake z [m] where z [m] is the elevation of the section under

consideration.

Normal operating pressure head, including head loss, normal valve actuation surges. P2 = 1.05 P1 [m]

Emergency operation pressure head, including head loss and surge for a fail-safe valve closure P3 = 1.25 P1 [m]

Extreme pressure due to a spear valve stem failure causing slam closure, or governor hunting (see Ref. [28]). P4 2.0 P1 [m]

Vacuum pressure P5 = -100 kPa

As design progresses, transient analyses will be performed providing explicit values in lieu of the preliminary values for P2 and P3, above.

Dead Loads:

Dead loads comprise all permanently acting gravity loads due to self weight of structure, contained water and surcharge soil or rock, and are defined as follows:

Weight of penstock D1 Weight of water contained within penstock D2 Weight of soil or rock surcharge and groundwater D3

Live Loads

Wind load, normal operation L1 = 1/30 year wind loads Wind load, extreme L2 = 1.4 x 1/50 year wind loads Ground snow load, per Section, normal operation L3 = Ss Ground snow load, per Section, extreme L4 = 1.5 x (Ss + Sr) Traffic load, truck loading, per Section 6.5.2.3 L5

Earthquake Loads

Quasi-static earthquake loads, determined for the 2475 year return event EQ

Thermal Loads



Thermal loads will be calculated for the buried and exposed sections of penstock, assuming site temperature variations as provided in Section 3.3.1 and accounting for wind and solar radiation where appropriate.

Thermal analysis will be undertaken for exposed sections of penstock to determine the requirements for minimum flows, insulation, or other protective measures to prevent freezing in the penstock.

Difference between temperature at weld-up and cold water T1 = 15 - 4 = 11C Difference between weld-up and extreme annual maxima T2,1 = 15 - Tmin T2,2 = Tmax - 15

6.3.3.2 Load Combinations

The relevant load combinations for each Performance Level are presented in the table overleaf.

Snow, wind and extreme temperature loads are applicable only to the exposed portions of the penstocks, i.e. the pipe bridges. To date, no specific terrain features, such as fault zone crossings that warrant a more detailed assessment have been identified, so seismic loads can be neglected for buried penstock analyses. For the Normal and Emergency Operation cases, vacuum pressures will be applied as calculated from the transient analyses.



Table 11: Relevant Penstock Load Combinations for Various Performance Levels

Loads

Internal Pressure Dead Loads Live Loads Earthquake Load Temperature

Variation normal

transient emergency

transient water

hammer vacuum pipe internal water soil

1/10 wind

fact. 1/50 wind snow fact. snow traffic normal extreme

Performance Level

P2 P3 P4 P5 D1 D2 D3 L1 L2 L3 L4 L5 EQ T1 T2 Normal Operation

Empty pipe

Normal operation

Filling Emergency Operation

Equipment failure or operator erSSPC

Wind storm

Extreme winter Extreme temperature change

Sudden draining

Survivability Earthquake, plant operating

Earthquake, penstock empty

Slam closure or flow resonance

Note: refers to less than the full specified load may be appropriate.



6.3.4 PENSTOCK STRUCTURAL DESIGN

6.3.4.1 Permissible Steel Stresses

Permissible stresses of the steel penstock are based on current design practice that accounts for the high-grade, high ductility steels now available. Reference is made to CSA S16, CSA Z662, AWWA M11, ASCE 79 and EN/DIN 13480-3 for service and strength limit states. Permissible stress limits will be:

Normal Operation Performance Level:

Service stress limit state fNO 0.5 fy so for fy = 275 MPa (LPP) fpermissible = 140 MPa or for fy = 345 MPa (HPP) fpermissible = 175 MPa

Fatigue limit state, constant amplitude threshold stress range derived from S-N curve for weld detail used Fsrt = 38 MPa

Emergency Operation Performance Level:

Strength limit state fEO 0.75 fy so for fy = 275 MPa (LPP) fpermissible = 205 MPa or for fy = 345 MPa (HPP) fpermissible = 260 MPa

Elastic stability limit state buckling stress per AWWA M11

Survivability Performance Level:

Ductility limit state fsurv 0.8 fu so for fu = 380 MPa (LPP) fpermissible = 305 MPa or for fu = 410 MPa (HPP) fpermissible = 330 MPa

Elastic stability limit state buckling stress per AWWA M11

6.3.4.2 Design Approach

The buried penstock will be designed as an isostatic pipe, with hydrostatic thrusts at bends and axial movements due to temperature changes and Poissons effects controlled by soil-pipe interaction. The design will generally consider the biaxaial stress conditions, with the hoop stress representing the major principal stress and the axial stresses (including those due to bending) the minor principal stresses. Combined stresses will be calculated using the



Hinckey-von Mises relationship for comparison with the permissible stress limits given in Section 6.3.4.1 above.

For straight pipe sections, wall thicknesses will generally be selected based on hoop

Engineering Design Basis GA

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