component 1 - review of ice study work - nalcor … · component 1: review of ice study work ......

•)) SNC• LAVALIN

Lower Churchill Project

COMPONENT 1: REVIEW OF ICE STUDY WORK

SLI Document No. 505573·300A-4HER·0001·00

Nalcor Reference No. MFA-SN-CD-2116-CV·RP-0001-01 Rev. 81

Date: 26-Mar-2012

Prepared by: Daniel Damov I Stephanie Warren

Senior Hydraulics Engineer I Junior Hydraulics Engineer

Checked by:

Approved by:

Approved by:

Component 1: Review of Ice Study Work Revision Nalcor Doc. No. MFA-SN-CD-2110-CV-RP-0001-01 B1 Date Page

SLI Doc. No. 505573-300A-4HER-0001 00 26-Mar-2012 i

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REVISION LIST

Revision

Remarks

No By Chec Appr. Appr. Date

00 SW, DD MT GS NB 26-Mar-2012 Issued for final client acceptance.

PC SW, DD - LT 03-Feb-2012 Issued for client review and comments.

PB SW, DD - FC 22-Sep-2011 Issued for client review and comments.

PA SW, DD - FC 14-Sep-2011 Issued for internal review and comments.


SLI Doc. No. 505573-300A-4HER-0001 00 26-Mar-2012 ii

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TABLE OF CONTENTS

Page No.

1 INTRODUCTION ................................................................................................................ 1

2 OBJECTIVES OF THE TECHNICAL REPORT .................................................................. 2

3 TYPICAL MID-WINTER ICE CONDITIONS ........................................................................ 3 3.1 Frazil Ice .................................................................................................................... 3

3.1.1 Active Frazil Ice .............................................................................................. 4 3.1.2 Passive Frazil Ice ........................................................................................... 4

4 ICE FORMATION AND ICE FORMATION CRITERIA ........................................................ 5 4.1 Thermal Ice Cover...................................................................................................... 5 4.2 Dynamic Ice Cover ..................................................................................................... 5

5 PREVIOUS ICE STUDIES .................................................................................................. 7

6 1989 - 1992 ICE SURVEY VIDEOS .................................................................................... 8 6.1 Ice Progression at Muskrat Falls - Winter 1988-1989 ................................................. 9 6.2 Ice Progression at Muskrat Falls - Winter 1989-1990 ................................................12 6.3 Ice Progression at Muskrat Falls - Winter 1990-1991 ................................................15 6.4 Ice Progression at Muskrat Falls - Winter 1991-1992 ................................................19 6.5 Ice Progression at Muskrat Falls – Unknown Dates ..................................................22 6.6 Summary of Ice Observation Surveys .......................................................................23

6.6.1 Conditions Downstream of Lower Muskrat Falls ............................................24 6.6.2 Conditions Between the Two Falls ................................................................24 6.6.3 Conditions Upstream Upper Muskrat Falls ....................................................24

7 HYDROMETRIC DATA AND SURVEYS ...........................................................................25 7.1 Environment Canada Hydrometric Stations ...............................................................25 7.2 Historical Winter Water Levels at Muskrat Falls ........................................................29 7.3 Statistical Analysis of Maximum Winter Water Level and Ice management During

Phase 1 Construction ................................................................................................35

8 ICE MANAGEMENT DURING PHASE 2 CONSTRUCTION .............................................40 8.1 Downstream Maximum Winter Water Level Analysis ................................................41

9 PRELIMINARY RECOMMENDATIONS ............................................................................49

10 PATH FORWARD .............................................................................................................50

Appendices Appendix A - Temperature, Discharge and Maximum Winter Water Level at Muskrat Falls


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List of Figures Figure 3-1: Frazil Ice Observed on the Churchill River near Muskrat Falls in March, 2011 ......... 4 Figure 6-1: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - January

24, 1989 .................................................................................................................. 9 Figure 6-2: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - February

6, 1989 ...................................................................................................................10 Figure 6-3: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - February

15, 1989 .................................................................................................................10 Figure 6-4: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - March 13,

1989 .......................................................................................................................11 Figure 6-5: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - April 4,

1989 .......................................................................................................................11 Figure 6-6: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - May 1,

1989 .......................................................................................................................12 Figure 6-7: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – December

18, 1989 .................................................................................................................12 Figure 6-8: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - February

7, 1990 ...................................................................................................................13 Figure 6-9: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – February

21, 1990 .................................................................................................................14 Figure 6-10: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – March

30, 1990 .................................................................................................................14 Figure 6-11: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - April 30,

1990 .......................................................................................................................15 Figure 6-12: Ice Conditions at Muskrat Falls (at the lower falls looking downstream) – May 9,

1990 .......................................................................................................................15 Figure 6-13: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – February

6, 1991 .................................................................................................................16 Figure 6-14: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – February

18, 1991................................................................................................................16 Figure 6-15: Ice Conditions at Muskrat Falls (below the upper falls looking upstream) – March 4,

1991 .....................................................................................................................17 Figure 6-16: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – March

18, 1991................................................................................................................18 Figure 6-17: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – April 1,

1991 .....................................................................................................................18 Figure 6-18: Ice Conditions at Muskrat Falls (below the upper falls looking upstream) – April 12,

1991 .....................................................................................................................19 Figure 6-19: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – April 29,

1991 .....................................................................................................................19 Figure 6-20: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – February

4, 1992 .................................................................................................................20 Figure 6-21: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – March 4,

1992 .....................................................................................................................21


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Figure 6-22: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – March 16, 1992................................................................................................................21

Figure 6-23: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – April 7, 1992 .....................................................................................................................22

Figure 6-24: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – May 11, 1992 .....................................................................................................................22

Figure 6-25: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - photo taken possibly sometime from March 4 – April 29, 1991 .......................................23

Figure 6-26: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - photo taken possibly sometime from March 4 – April 29, 1991 .......................................23

Figure 7-1: Station 03OE007 – Churchill River at the Foot of Lower Muskrat Falls Historical Water Levels ..........................................................................................................27

Figure 7-2: Station 03OE014 – Churchill River 6.15 kms Below Lower Muskrat Falls ...............28 Figure 7-3: Photo Taken of One of the Water Monitoring Station Charts. ..................................29 Figure 7-4: Average Discharge 15 Days Prior to the Occurrence of the Maximum Winter Water

Level Plotted Against the Maximum Winter Water Level ........................................33 Figure 7-5: Sample Data for Maximum Winter Water Levels Observed at Muskrat Falls ...........37 Figure 7-6: Probability of Exceedance of Maximum Water level Downstream of Muskrat Falls .38 Figure 8-1: Velocity and Froude Number for WL 25 m and Discharge 2,200 m³/s Between

km 42.85 and km 95 of the Churchill River .............................................................41 Figure 8-2: Muskrat Falls Downstream Rating Curve with and without Ice Cover (in natural

conditions) ..............................................................................................................43 Figure 8-3: Profile for HEC-RAS Ice Dam Simulation with WL = 9.03 m ....................................45 Figure 8-4: Profile for HEC-RAS Ice Dam Simulation with WL = 15.85 m ..................................46 Figure 8-5: Profile for HEC-RAS Ice Dam Simulation with WL = 20.79 m ..................................47 Figure 8-6: Downstream Water Level Versus Percent Blockage at Muskrat Falls .....................48 List of Tables Table 6-1: Summary of Available Ice Survey Videos for Muskrat Falls ....................................... 8 Table 7-1: Summary of Water Survey of Canada Water Monitoring Stations Near Muskrat Falls

................................................................................................................................26 Table 7-2: Winter Water Levels Above Upper Muskrat Falls (Station 03OE001) .......................30


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List of References

No. Description 1 EIS0017 – Further Clarification and Updating of the 2007 Ice Dynamics Report, Hatch,

November 2008 2 Effects of Ice Progression During Construction of Muskrat Falls Hydropower

Development, J.L. Cheung and Ch. Guillaud, CSCE, 5th Canadian Hydrotechnical Conference, 26-27 May 1981

3 GI1070 – Ice Study (Gull Island and Muskrat Falls), Hatch, January 2008 4 Historical Water Data, Water Survey of Canada, www.ec.gc.ca/rhc-

wsc/default.asp?lang=En&n=4EED50F1-1 5 Ice Dynamics of the Lower Churchill River, Hatch, October 2007 6 Ice Observations Muskrat Falls to Cache River Videos, Nalcor Energy, 1989-1992 7 Lower Churchill River Ice Studies 1977-1978, Shawmont Newfoundland Limited, May

1978 8 Lower Churchill River Ice Observation Program 1988-89, Newfoundland and Labrador

Hydro, 1989 9 Lower Churchill River Ice Observation Program 1989-90, Newfoundland and Labrador



Hydro, 1992 12 MF1330 – Hydraulic Modeling and Studies 2010 Update – Report 1: Hydraulic Modeling

of the River, Hatch, October 2010 13 MF1330 – Hydraulic Modeling and Studies 2010 Update – Report 4: Muskrat Falls Ice

Study, Hatch, March 2011 14 Muskrat Falls Final Feasibility Study - Ice Studies, LaSalle Consulting Group Inc.,

October 1998 15 Muskrat Falls Power Development & 345 kV Transmission Intertie to Churchill Falls,

SNC-Lavalin Inc., March 1980 16 Report on Lower Churchill River Ice Observations and Studies, Shawmont

Newfoundland Limited, June 1979 17 Station 03OE001 Charts, Water Survey of Canada, Environment Canada, 1943-2007 18 Water Treatment Plant Design, American Water Works Association, 2004


SLI Doc. No. 505573-300A-4HER-0001 00 26-Mar-2012 1

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1 INTRODUCTION

SNC-Lavalin Inc. has signed an agreement with Nalcor Energy (the Client) to deliver

engineering, procurement and construction management services for the Lower

Churchill Project (LCP) in Newfoundland and Labrador, Canada.

As part of the LCP, the Muskrat Falls Hydroelectric Development is located on the

Churchill River, about 291 km downstream of the Churchill Falls Hydroelectric

Development which was developed in the early 1970’s. The installed capacity of the

project will be 824 MW (4 units of 206 MW each).

Ice management is a very important aspect of construction and operation of the

Muskrat Falls hydroelectric plant. Various studies have been conducted over a

number of years to try and better understand the ice conditions in the area of the

project. It is extremely important to have a good understanding of past and present

conditions to better predict what might occur during construction. These predictions

allow one to take appropriate precautions and develop mitigative measures to

manage potential problems due to ice.

It is SNC-Lavalin’s mandate to review previous ice investigations and verify the

conclusions developed from these studies. The following report is a summary of this

review and verification process. Recommendations as well as the path forward are

presented based on the analysis.



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2 OBJECTIVES OF THE TECHNICAL REPORT

The main objectives of the present report are:

• To present the challenges related to managing ice conditions at Muskrat Falls;

• To present the status of knowledge;

• To present preliminary recommendations for managing ice conditions during

construction for Phase 1 (construction of gated spillway);

• To present preliminary recommendations for managing ice conditions during

construction for Phase 2 (temporary diversion through gated spillway); and

• To present the path forward in strengthening the recommendations.



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3 TYPICAL MID-WINTER ICE CONDITIONS

The Churchill River varies along its length from very narrow channels with high

velocity flows and rapid conditions to large lakes with relatively low velocity flows.

During the winter, the narrow channels remain open with only a small amount of

shore ice. The large lakes typically become ice covered and experience ice jams at

many of the inlets. Frazil ice generated in the open water area is responsible for the

formation of the ice jams.

3.1 FRAZIL ICE

Frazil ice consists of very small ice crystals which are formed in super-cooled water,

water with its temperature below 0°C. It is generated when open water comes into

contact with cold air. This causes the temperature of the water to decrease rapidly

and the water to become super-cooled.

The meteorological conditions which encourage frazil ice formation are

(AWWA, 2004):

• A clear night sky with an air temperature of -12.5°C or less;

• A daytime water temperature of 0.222°C or less;

• A cooling rate greater than 0.006°C per hour; and

• A wind speed greater than 16.1 km/h at the water surface.

There are two different types of frazil ice, active and passive. Both types are

described in the following sections.



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Figure 3-1: Frazil Ice Observed on the Churchill River near Muskrat Falls in March, 2011

3.1.1 Active Frazil Ice

Active frazil ice is defined as freshly formed frazil ice crystals dispersed in super-

cooled water and growing in size. In this condition, frazil ice will adhere to

underwater objects such as intake trash racks or rocks. When the frazil ice is

attached to the riverbed, it creates “anchor” ice.

Normally, frazil ice remains active for a period of about 10 to 15 minutes after the

water goes under an ice cover, i.e. the time required for the water to return to 0°C or

slightly above. Active frazil ice however, has been observed more than one hour

after travelling under an ice cover.

3.1.2 Passive Frazil Ice

Passive frazil ice occurs once the temperature of the water returns to 0°C or above

and the frazil ice crystals stop growing; they become inactive (passive). Passive

frazil ice losses most of its adhesive properties and is less troublesome than active

frazil ice. River ice jams and reduction of the discharge capacity can be created by

an extensive amount of passive frazil ice.



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4 ICE FORMATION AND ICE FORMATION CRITERIA

There are different types of ice and different criteria required for the formation of

each type. There have been two types of ice cover observed at the Muskrat Falls

site, thermal ice cover and dynamic ice cover. The way in which these ice covers

form is described in the following sections.

4.1 THERMAL ICE COVER

A solid layer of ice will appear over the surface of the water once the temperature is

below 0°C. This thermal ice cover will appear when the flow velocity is low (less than

0.65 m/s) and the Froude number is less than 0.08. Frazil ice does not normally

form when a thermal ice cover is present, because the ice cover isolates the water

from cold air.

4.2 DYNAMIC ICE COVER

When the velocity of flow is greater than 0.65 m/s, dynamic ice cover can occur.

There are three different ways in which dynamic ice cover forms: bridging,

juxtaposition and shoving.

Ice cover by bridging forms at very low flow velocities and relatively high

concentrations of surface ice by ice cover spontaneously arching across the open

width of the channel.

At relatively low flow velocities, ice floes arriving at the leading edge may simply

come to a stop and not under turn. This is known as ice formation by juxtaposition.

Ice formation via shoving is at a wide range of flow velocities. The ice cover

collapses in the downstream direction and becomes thicker as the forces acting on it

exceed its ability to withstand those forces. The strength of an ice cover formed from

many separate pieces of ice increases with its thickness, so that when shoving takes

place, the strength of the ice cover is increased. An ice cover may repeatedly shove

and thicken as it progresses upstream.



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Ice cover via shoving is the method of formation of the large ice dam which forms

each winter below the Lower Muskrat Falls.



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5 PREVIOUS ICE STUDIES

Part of SNC-Lavalin’s mandate was to review previous studies that have been

conducted on the ice situation in the Churchill River and in particular, at Muskrat

Falls. The ice studies reviewed include:

• Muskrat Falls Power Development & 345 kV Transmission Intertie to Churchill

Falls, SNC-Lavalin Inc., March 1980;

• Effects of Ice Progression During Construction of Muskrat Falls Hydropower

Development, J.L. Cheung and Ch. Guillaud, CSCE, 5th Canadian Hydrotechnical

Conference, 26-27 May 1981;

• Muskrat Falls Final Feasibility Study, Ice Studies, LaSalle Consulting Group Inc.,

October 1998;

• Ice Dynamics of the Lower Churchill River, HATCH, October 2007;

• The Lower Churchill Project, GI1070 – Ice Study (Gull Island and Muskrat Falls),

HATCH, January 2008;

• The Lower Churchill Project, EIS0017 – Further Clarification and Updating of the

2007 Ice Dynamics Report, HATCH, November 2008; and

• The Lower Churchill Project, MF1330 – Hydraulic Modeling and Studies 2010

Update, Report 4: Muskrat Falls Ice Study, HATCH, March 2011.

SNC-Lavalin has reviewed all of the studies named above and verified whether or

not it agrees with the information presented in the documents. SNC-Lavalin has also

performed its own analysis using modeling software (HEC-RAS and Flow 3D) to

validate the results.

Nalcor has also provided SNC-Lavalin with video from the Ice Surveys conducted

during the winters 1989 – 1992. SNC-Lavalin has reviewed these videos and the

observations will be discussed in the following section.



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6 1989 - 1992 ICE SURVEY VIDEOS

The Ice Survey videos for the winters of 1989-1992 were viewed and snapshots of

the ice conditions at Muskrat Falls were recorded. The following table summarizes

the dates for which video was available:

Table 6-1: Summary of Available Ice Survey Videos for Muskrat Falls

Winter Date

1988-89

January 24 February 6

February 15 February 27

March 13 April 4 May 1

1989-90

December 18 January 9

January 24 February 7

February 21 March 14 March 30 April 20 May 9

1990-91


March 4 March 18

April 1 April 12 April 29

1991-92


March 4 March 16

April 7 April 23 May 11



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There were also two videos available with no date stamp and the exact time of the

visit is unknown. It is estimated that these videos were recorded sometime between

March and April, 1992.

6.1 ICE PROGRESSION AT MUSKRAT FALLS - WINTER 1988-1989

The following figures are images taken from the ice survey videos during the winter

of 1988-1989. There appears to be shore ice along the Churchill River upstream of

Upper Muskrat Falls and an ice cover build-up downstream of Lower Muskrat Falls

during the month of January. Shore ice has also formed on the banks of the river

between the falls. The early stages of ice dam formation below Lower Muskrat Falls

are also observed.

Figure 6-1: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - January 24, 1989

By the first week in February, a partial cover has formed on the river between the

falls and the ice dam continues to grow. Open water conditions remain at Upper and

Lower Muskrat Falls throughout the winter.



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Figure 6-2: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - February 6, 1989


As the winter progresses, the partial ice cover between the falls and the ice dam

below Lower Muskrat Falls continues to grow throughout March and even into the

month of April.



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Figure 6-4: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - March 13, 1989

Figure 6-5: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - April 4, 1989

By May 1, the temperatures have risen and the ice has begun to melt. The partial

ice cover between the falls melts and ice dam shrinks in size.



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Figure 6-6: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - May 1, 1989



of 1989-1990. By December 18, 1989, the ice dam downstream of Muskrat Falls

appears to have begun to form as well as a small amount of shore ice on the banks

of the river between the falls.

Figure 6-7: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – December 18, 1989

The quality of the videos taken in January as well as the way in which the area was

surveyed made it very difficult to observe the conditions at Muskrat Falls and acquire

satisfactory images. However, from what can be observed, the conditions appear to



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be very similar to that observed during the winter of 1988-1989 with the increased

progression of the ice dam and an increase of shore ice extending across the river

between the falls.

By early February, 1990, the ice dam below Lower Muskrat Falls is well progressed.

Ice cover development between the falls appears to be slightly behind that observed

in the previous year. February 7 – 21 appears to show a significant progression of

shore ice development between the falls. Open waters conditions are still observed

at Upper and Lower Muskrat Falls.




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Figure 6-9: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – February 21, 1990

The ice cover and dam continue to progress through the month of March.

Figure 6-10: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – March 30, 1990

By the end of April, temperatures have begun to rise and the ice has started to melt.



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Figure 6-11: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - April 30, 1990

Unfortunately, the video for May 9 did not provide a sufficient view of the falls

however it can be observed that at Lower Muskrat Falls the ice dam is continuing to

melt and there is indication of very little ice between the falls.

Figure 6-12: Ice Conditions at Muskrat Falls (at the lower falls looking downstream) – May 9, 1990


Video surveys for the winter 1990-1991 were available starting February 9. By that

time, the ice dam below Lower Muskrat Falls has well progressed. Ice has begun to

form on the banks of the river between the falls and open water conditions exist



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between the falls. The following figures are images taken from the ice survey videos

during the winter of 1990-1991.


More ice forms as the winter progresses.




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It is difficult to determine the conditions between the falls from video taken March 4.

Figure 6-15: Ice Conditions at Muskrat Falls (below the upper falls looking upstream) – March 4, 1991

The peak of the ice in the Churchill River near Muskrat Falls has been observed to

be between the middle to the end of March.



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By April 1, the ice has already begun to melt.

Figure 6-17: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – April 1, 1991



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The ice cover and dam continues to melt through the month of April.

Figure 6-18: Ice Conditions at Muskrat Falls (below the upper falls looking upstream) – April 12, 1991



Video surveys for the winter were available starting February 4. By that time, the ice

dam below Lower Muskrat Falls has started to form. Ice has begun to form on the



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banks of the river between the falls and open water conditions exist between the

falls. The following figures are images taken from the ice survey videos during the

winter of 1991-1992.


More ice forms as the winter progresses. By March 4, the shore ice between the falls extends

the entire way across the river and continues through the month of March.



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By April 7, the ice has begun to melt as shown on Figure 6-23.



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The ice cover and dam continues to melt through the month of April and by May 11

the ice only remains on the banks of the river between the falls.

Figure 6-24: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) – May 11, 1992

6.5 ICE PROGRESSION AT MUSKRAT FALLS – UNKNOWN DATES


of unknown dates. There is evidence to suggest that the videos were possibly taken

sometime during March – April 29, 1992. In either case, it appears as though there



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is shore ice between the falls and the ice dam below Lower Muskrat Falls is well

progressed.

Figure 6-25: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - photo taken possibly sometime from March 4 – April 29, 1991

Figure 6-26: Ice Conditions at Muskrat Falls (below the lower falls looking upstream) - photo taken possibly sometime from March 4 – April 29, 1991

6.6 SUMMARY OF ICE OBSERVATION SURVEYS

The following summarizes the observations of the ice conditions near Muskrat Falls

during the winters 1988-1992.



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6.6.1 Conditions Downstream of Lower Muskrat Falls

It has been observed that an ice jam occurs downstream of the Lower Muskrat Falls.

Each year, a large ice dam forms in this area. From the ice observation surveys, it

can be stated that formation of the ice dam begins as early as mid-December. Its

formation is well progressed by mid-February. As the temperatures increase, the ice

dam begins to melt by the end of April but still can be observed well into the month of

May.

The formation of this ice dam has an impact on the water level at the Muskrat Falls

site. It creates a backwater effect causing the water level downstream of Lower

Muskrat Falls (and between the falls) to rise. This backwater effect is evident in the

available water level data from Environment Canada during the period. Station

03OE007 was located at the foot of Lower Muskrat Falls and recorded data from

1980 to 1995. The data shows a gradual increase in the water level beginning

usually in the middle of January and continuing until the end of March. This

corresponds with the formation and melting of the ice dam. Sometimes the rise in

water level is significant enough to flood Lower Muskrat Falls.

6.6.2 Conditions Between the Two Falls

It can be observed from the videos that there is a significant amount of ice between

Upper and Lower Muskrat Falls. The velocity of the water between the falls is

significantly lower than at the falls. This allows a partial ice cover to develop by

juxtaposition starting along the shore. However, a solid ice cover is not observed to

form in this area.

6.6.3 Conditions Upstream Upper Muskrat Falls

Upstream of Upper Muskrat Falls, ice is observed to form on the banks of the river.

It extends out further from the north bank where the velocity of the water is slower

than from the south bank. This ice can be due to the accumulation of frazil ice

and/or the formation of a thermal ice cover. The main flow channel of the river

remains in open water conditions.



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7 HYDROMETRIC DATA AND SURVEYS

The following section describes the hydrometric information available and presents

some analysis of the water survey data for Muskrat Falls.

7.1 ENVIRONMENT CANADA HYDROMETRIC STATIONS

Much of the water data for the studies mentioned previously was obtained from

Environment Canada and the Water Survey of Canada (WSC). WSC is the national

authority responsible for the collection, interpretation and dissemination of

standardized water resource data and information in Canada. There are five

different monitoring stations of interest to the project1 which are summarized in the

following table:

1 The station 03OE014 (Churchill River 6.15 km below Lower Muskrat Falls) has been in

operation since 2008



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Table 7-1: Summary of Water Survey of Canada Water Monitoring Stations Near Muskrat Falls

Station ID Station Name Latitude Longitude Data Type

Reported Monitoring Period

03OE001 Above Upper Muskrat Falls 53°14’53”N 60°47’6”W Flow2 Monitored manually from 1948 – 1952. Since then, it has been monitored continuously with a recorder

03OE004 Below Muskrat Falls 53°14’46N 60°42’38”W Water Level

Monitored continuously with a recorder from 1978 – 1980

03OE005 Between Upper and Lower Muskrat Falls

53°14’39”N 60°46’24”W Water Level


03OE007 At the Foot of the Lower Muskrat Falls

53°14’57”N 60°46’8”W Water Level


03OE014 Churchill River 6.15 kms Below Lower Muskrat Falls

53°14'15"N 60°40'30"W Water Level

Monitored continuously with a recorder since 2008

2 Obtained indirectly from water level measurement interpretation.



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All of the interpreted data from these monitoring stations is available online through

Environment Canada’s website. Figure 7-1 below highlights the daily observed

water levels at Station 03OE007 Churchill River at the Foot of Lower Muskrat Falls.

Figure 7-1: Station 03OE007 – Churchill River at the Foot of Lower Muskrat Falls Historical Water

Levels

Figure 7-2 below highlights the daily observed water levels at Station 03OE014

Churchill River 6.15 kms Below Lower Muskrat Falls.

0

2

4

6

8

10

12

14

16

18

Jan-01 Jan-31 Mar-01 Mar-31 Apr-30 May-30 Jun-29 Jul-29 Aug-28 Sep-27 Oct-27 Nov-26 Dec-26

Dai

ly O

bser

ved

Wat

er L

evel

(m)

STATION 03OE007CHURCHILL RIVER AT FOOT OF LOWER MUSKRAT FALLS

1978 1979

1980 1981

1982 1983

1984 1985

1986 1987

1988 1989

1990 1991

1992 1993

1994 1995



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Figure 7-2: Station 03OE014 – Churchill River 6.15 kms Below Lower Muskrat Falls

SNC-Lavalin was interested in obtaining the raw data from monitoring station,

03OE001, to see how it compared with the online data as well as that found in

previous studies. SNC-Lavalin was successful in obtaining original water level charts

from the station and was able to compare the data in the charts to that of the studies

as a secondary verification. The records, although incomplete, provide valuable

information allowing some interpretation to be made about the missing data.

0

2

4

6

8

10

12

14

16

18

Jan-01 Jan-31 Mar-01 Mar-31 Apr-30 May-30 Jun-29 Jul-29 Aug-28 Sep-27 Oct-27 Nov-26 Dec-26

Dai

ly O

bser

ved

Wat

er L

evel

(m)

Station 03OE014CHURCHILL RIVER 6.15 KM DOWNSTREAM OF MUSKRAT FALLS

2008

2009

2010

2011



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Figure 7-3: Photo Taken of One of the Water Monitoring Station Charts.

7.2 HISTORICAL WINTER WATER LEVELS AT MUSKRAT FALLS

Since the commissioning of the Churchill Falls Hydroelectric Development, the

discharge and the water levels observed in the Churchill River have been quite

different than what was observed prior to the 1970’s. Prior to the commissioning of

Churchill Falls (1954 – 1972), the average discharge recorded at station 03OE001

during the winter (December to February) was approximately 760 m³/s, which

corresponds to a water level of 14.5 m. After the commissioning of Churchill Falls

(1975 – 2009), the average discharge during the winter is about 1,820 m³/s,

corresponding to a water level approximately 16.4 m.

The below table is a summary of historical winter water levels and discharges at

station 03OE001 based on:

• Nalcor Ice Survey Reports;

• Environment Canada’s Water Survey of Canada charts; and

• The flow data published on the Environment Canada website.



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Table 7-2: Winter Water Levels Above Upper Muskrat Falls (Station 03OE001)

Nalcor Ice Survey Reports EC Website Environment Canada (EC) Scroll Charts EC Website

Winter Date of Max. Observed WL

Max. WL Observed

(m)

Max. Discharge Observed

(m³/s)

Date of Max. Observed WL

Max. WL Observed

(m)

Max. Discharge Observed

(m³/s)

74 – 75 January 3 16.12 1270 January 13 16.06 1300 75 – 76 January 22 17.00 1700 January 25 16.93 1700 76 – 77 January 22 17.11 1790 January 21 17.04 1750 77 – 78 March 18 19.673 2120 March 17 19.663 1950 78 – 79 February 23 20.133 2100 February 16 18.813 2070 79 – 80 January 28 17.22 1930 March 21 17.21 1940 80 – 81 February 20 17.57 2180 March 8 17.893 2010 81 – 82 December 12 17.64 2260 January 5 17.46 2060 82 – 83 January 24 16.90 1780 January 5 16.75 1440 83 – 84 December 24 17.21 1990 January 1 17.26 1980 84 – 85 February 10 17.19 1970 February 9 17.20 1920 85 – 86 January 29 17.17 1960 January 29 17.20 1960 86 – 87 - 17.10 - February 7 17.10 1910 87 – 88 - 17.49 - March 30 17.22 1320 88 – 89 - 16.93 - January 28 16.78 - 89 – 90 February 28 18.283 2080 March 1 17.35 2050 90 – 91 January 25 18.133 1980 January 24 17.24 1870 91 – 92 December 9 17.773 1640 January 24 16.78 1680

92 – 93 - - - March 26 17.26 1960

93 – 94 - - - March 28 17.75 1020 94 – 95 - - - February 10 17.22 1960 95 – 96 - - - March 27 17.20 764 96 – 97 - - - January 13 17.37 2090 97 - 98 - - - March 11 17.46 2070 98 - 99 - - - January 8 17.21 1990 99 - 00 - - - February 28 16.93 2140 00 - 01 - - - March 25 16.52 1900 01 – 02 - - - February 28 17.32 2060 02 – 03 - - - January 23 17.30 2050 03 – 04 - - - January 17 17.69 2240 04 - 05 - - - January 22 17.13 1930 05 - 06 - 17.52 - March 4 17.58 2190 06 - 07 - - - January 6 17.05 1880

3 Highlighted values represent the maximum values observed throughout the period of record.



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From 1974 to 1992, Nalcor had ice surveys conducted over the Churchill River at

Muskrat Falls and other areas. The water level data reported from those surveys in

Table 7-2 is the observed water level above Upper Muskrat Falls. The maximum

recorded winter water level and the date it occurred is shown in column 3 and was

referenced from Table 3.1 in the “Lower Churchill River Ice Observation Program

1991-92”, Newfoundland and Labrador Hydro, November 1992.

It should be noted that the maximum water levels for 1977-78 and 1978-79 were

those reported in Volume II of the engineering report No. 11.99.10, “Muskrat Falls

Power Development and 345 kV Transmission Intertie to Churchill Falls” by SNC-

Lavalin Inc. In the 1979 Ice Observation Report by Shawmont Newfoundland Ltd.,

the maximum water level observed was 20.51 m in 1978 and 20.02 m in 1979. This

is quite different than what is reported in the above table. The reason for this

difference is unknown but may be due to conversion of the water levels to geodetic

datum or any corrections applied to the data due to a malfunctioning hydrometric

station.

As was previously mentioned, SNC-Lavalin was able to obtain original water level

charts from Station 03OE001 – Churchill River Above Upper Muskrat Falls. The

maximum winter water level as recorded from these charts is shown also in Table

7-2 in column 6. It should be noted that this is raw, uncorrected data and therefore

may be subject to some errors. Although this gauge has historically been very

reliable, Environment Canada has experienced some problems in the past with loss

of nitrogen pressure due to the low temperatures, ice build up on the gauge itself and

the gauge line sticking to the well walls. Therefore, the data on occasion reflected

incorrect water levels and/or there was missing data. Areas on the charts where

there were issues with the gauge were easily identified with periods of rapid

fluctuations in water level, flat lines or gaps and were not considered as part of the

valid record.

The Water Survey of Canada publishes daily flows for station 03OE001 on its

website. The flows corresponding to the dates of the maximum observed water



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levels from both the Nalcor Ice Survey Reports and the Environment Canada Charts

are presented in columns 4 and 7 of Table 7-2.

For the most part, the water levels reported by each data source are similar with

negligible differences. It should be noted that in 1978 and 1979, the Ice Survey

Reports as well as the Environment Canada charts, indicate water levels about 2 to 3

m above the average observed in other years. There is also a difference between

the Ice Survey data and Environment Canada charts for both of these years. It is

indicated that the Ice Survey data is based on water levels recorded at station

03OE001 at the time of the survey. The Environment Canada chart data is based on

the levels as read directly from the scroll charts from station 03OE001 (no data

processing). The chart for 1979 indicates that for a period, the station well was

frozen and the gauge was stopped. It is possible that the water reached higher

levels and the information was not recorded.

The Ice Survey Reports also indicate water levels approximately 1 m higher than

what was observed on the Environment Canada charts during the winters of 1990,

1991 and 1992. This may be due to the fact that reliable data at station 03OE001

was not available during these years as the gauge was malfunctioning. Therefore,

the actual maximum water level may have been higher than what was indicated on

the Environment Canada charts.

Further analysis has been carried out in an attempt to understand why such high

water levels occurred only during the winters of 1978 and 1979.

The temperature, discharge and maximum winter water level for Muskrat Falls were

analysed to see if there is any correlation between each which could help explain the

events of 1978 – 1979. The temperature and the discharge are likely to be the most

important factors to play a role in influencing the water level. The average

temperature and discharge for December to February from 1975 – 2007 were

calculated as well as the average 15 days prior to the occurrence of the maximum

water level. Graphs were plotted to determine possible trends between the air

temperature, the discharge and the observed maximum water level.



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There were generally no trends observed in the data except for the graph illustrating

the 15 day average for discharge prior to the occurrence of the maximum water level

versus the maximum water level (see Figure 7-4). It is evident in this graph that as

the discharge increases so does the water level. This observation is logical and

expected. However, it appears that the years 1978 and 1979 were subject to critical

ice conditions induced by other causes as well. Please see Appendix A for the

remainder of the graphs.

Figure 7-4: Average Discharge 15 Days Prior to the Occurrence of the Maximum Winter Water

Level Plotted Against the Maximum Winter Water Level

The maximum water level observed in 1994 was not out of the ordinary in terms of

average water levels, however it was for the lower than normal discharge.

Observations from the hydrometric station located between the two falls and at the

foot of Lower Muskrat Falls, do not indicate a significant increase of the water level

downstream of the Upper Falls.

1000

1200

1400

1600

1800

2000

2200

15 15.5 16 16.5 17 17.5 18 18.5 19 19.5 20

Dis

char

ge (

m°/

s)

Max. Water Level (m)

Station 03OE001 - Above Upper Muskrat FallsAverage Discharge (15 days before event) vs. Max. Water Level

1978

1979

1994



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One explanation of the phenomenon occurring in 1978 - 1979, as reported in the

Nalcor Ice Survey Reports, is that flow releases from the Churchill Falls power plant

were kept very high during those periods (approximately 25%+ higher than the

previous winters). 1978 was the first winter in which all generating units at the

Churchill Falls powerplant were available for full production. These high flows in turn

caused the Churchill River to remain open between Muskrat Falls and Gull Lake

where in other years an ice cover had formed at Sandy Island Lake and Gull Lake.

The ice cover normally formed over these lakes vastly reduces the amount of frazil

ice which is transported downstream to Muskrat Falls. As a result, there was a larger

than usual accumulation of ice, causing a backwater effect, completely flooding both

Upper and Lower Muskrat Falls. This is a plausible explanation. However, similar

discharges and air temperatures were observed in other years which did not result in

the same water levels. That suggests that other causes also influenced the

phenomenon.

A further explanation may be a change in the bathymetry downstream of Muskrat

Falls. Bathymetric data reveals that there is a large hole downstream of Lower

Muskrat Falls where the water is very deep. This hole is believed to be caused (at

least partially) by erosion of the riverbed due to ice action. It is possible that prior to

the commissioning of Churchill Falls, when the river discharge was much lower in

winter, the water depth was shallower. During the first years after the Churchill Falls

Project was commissioned, the storage capacity downstream of the falls was limited

for the increased amount of frazil ice reporting to the falls. As a result, a backwater

effect started to form more intensely, triggering a gradual riverbed erosion.

Therefore, such high water levels occurring during these two years can be

associated to this initial lack of storage. Erosion on the riverbed may have been

sufficient after this period that the next time a similar discharge occurred, the river

was able to better adapt to the new conditions. This does not imply that such

conditions could not occur again in the future since the erosion is most probably

ongoing.



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Based on historical water level data, it is inferred that the water level downstream of

Muskrat Falls peaks in the winter due to backwater from ice jamming. The water

levels upstream of Muskrat Falls peak during the spring flood.

7.3 STATISTICAL ANALYSIS OF MAXIMUM WINTER WATER LEVEL AND ICE MANAGEMENT DURING PHASE 1 CONSTRUCTION

A number of sources were studied which provided water levels at Muskrat Falls. The

maximum water level observed in winter (January to March) was recorded for

various years and plotted on the graph shown in Figure 7-5. On this graph, the dark

blue line indicates the maximum winter water level for 1964 to 2007 as observed on

the Station 03OE001 charts obtained from Environment Canada’s archives. The red

line indicates the maximum winter water level for 1969 to 1996 as observed on the

Station 03OE001 tables obtained from Environment Canada’s archives4. The green

line indicates the maximum winter water level for 1975 to 1992 as reported in the

Nalcor Ice Survey Reports. The purple line indicates the maximum winter water level

downstream of the falls for 1984 to 1987 and 1989 to 1991 as reported in the SNC-

Agra 1998 report, Muskrat Falls Final Feasibility Study. Finally, the light blue line

indicates the maximum winter water level downstream of the falls for 1977 to 1992

estimated from the interpretation of the Nalcor Ice Survey Reports.

The higher than normal water levels observed in 1978 and 1979 were described in

Section 7.2. As noted, the estimated water level downstream of Lower Muskrat Falls

in 1978 and 1979 was interpreted from the observations published in the Ice Survey

reports for Muskrat Falls. These reports state that the backwater effect caused by

the ice accumulation downstream of the falls caused both Upper and Lower Muskrat

Falls to completely flood. This provided suitable conditions for a stable ice cover to

form upstream of Muskrat Falls. In order for both falls to be flooded and a stable ice

cover to form, both Upper and Lower Muskrat Falls should be at the same water

level, approximately 20 m in this case.

4 The charts are the raw data or scrolls printed directly from the station and have no corrections

applied. The tables have corrections applied to the raw data.



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Statistical analysis was performed to evaluate the probability of exceedance of the

maximum winter water level downstream of Muskrat Falls under the existing natural

conditions. Four different distribution laws were applied; log normal, log normal

(3 parameters), log Pearson III and Gumbel. The log normal distribution has been

chosen to determine the water level which structures for Construction Phase 1 will be

designed for. The results of the statistical analyses are presented in Figure 7-6.



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Figure 7-5: Sample Data for Maximum Winter Water Levels Observed at Muskrat Falls

0

5

10

15

20

25

63 –

64

65 –

66

67 –

68

69 –

70

71 –

72

73 –

74

75 –

76

77 –

78

79 –

80

81 –

82

83 –

84

85 –

86

87 –

88

89 –

90

91 –

92

93 –

94

95 –

96

97 -

98

99 -

00

,01

-02

03 -

04

05 -

06

Wat

er e

leva

tion

(m

)

Winter Water Levels Sample

Environment Canada Station 03OE001 Charts (m)

Environment Canada Station 03OE001 Tables (m)

Ice Observation Reports (Upper Falls)

SNC-AGRA 1998 Report

Estimated Downstream of Falls



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Figure 7-6: Probability of Exceedance of Maximum Water level Downstream of Muskrat Falls

1

10

100

Wat

er le

vel (

m)

Year

CHURCHILL RIVER - WINTER MAX WATER LEVEL D/S OF MUSKRAT FALLS

Log Normal

Log Normal 3 param

Log Pearson III

Gumbel

Probability of exceedance

1.001 1.01 1.1 2 5 10 100 1000 10000

0.999 0.99 0.909 0.5 0.2 0.1 0.01 0.001 0.0001

100000

0.00001



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For the results of these statistical analyses, it is noted that the observed maximum

water level downstream of the falls follows log normal distribution. The

corresponding water elevation for a design return period of 1:40 years is 20.0 m. It is

also noted that from Nalcor’s observation reports, at this elevation, a thermal

upstream ice cover starts to form. This is an indication for a physical limitation of the

possibility of further rise in the water level in the area of the falls. Therefore, during

Construction Phase 1 of the Muskrat Falls Hydroelectric Development, the riverside

cofferdam and the cofferdams upstream and downstream the spillway and the

powerplant, will be designed for a water elevation of 20.0 m with one metre of

freeboard.



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8 ICE MANAGEMENT DURING PHASE 2 CONSTRUCTION

Based on previous ice studies and the statistical analysis of available water level

data at Muskrat Falls, SNC-Lavalin has validated a recommended approach to ice

management during Phase 2 Construction. This approach includes the minimization

and control of frazil ice.

The amount of frazil ice generated between Gull Lake and Muskrat Falls can be

minimized by forming a stable ice cover. This stable ice cover can be formed by

raising the water level upstream of Muskrat Falls. Increasing the water level in the

river will reduce the water velocity (to less than 0.65 m/s) and promote the formation

of a thermal ice cover.

The amount of frazil ice generated upstream of Muskrat Falls will be controlled by

creating a headpond.

There have been various studies performed on this subject. In 1998, LaSalle

recommended a water level of 24 m be maintained. It is noted that the location of

the dam in this study was considered at the upstream falls. In 2011, HATCH

recommended a water level of 25 m be maintained. HATCH confirmed this value by

performing simulations using HEC-RAS, a 1D flow analysis software. This

recommendation was made for the dam location at the lower falls as presently

retained.

SNC-Lavalin also conducted its own analysis using HEC-RAS and verified HATCH’s

model. With a water level of 25 m and a discharge of 2,200 m³/s (maximum flow

observed between 1973- 2011), the simulation shows that stable ice conditions can

be maintained for over 20 km upstream of Muskrat Falls, however there would be no

ice cover maintained between the falls as both the velocity of the water and Froude’s

number would be greater than that required to maintain a thermal ice cover. Also, at

this water level, it is indicated that a stable ice cover would not be maintained at two

narrow sections further upstream where rapids conditions are present as well as

between Sandy Lake and Gull Lake. This is illustrated in the following graph:



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Figure 8-1: Velocity and Froude Number for WL 25 m and Discharge 2,200 m³/s Between km 42.85 and km 95 of the Churchill River

By increasing the water level in winter to 26 m, the impact on the water velocity and

Froude number will not change significantly at a discharge of 2,200 m3/s; however,

the volume available to store frazil ice from upstream will increase slightly, but it

should not be significant, since most of the river will already be covered by ice.

An upstream winter water level of 25 m is proposed to be retained for the

construction Phase 2 of the project.

8.1 DOWNSTREAM MAXIMUM WINTER WATER LEVEL ANALYSIS

The open water elevation downstream of Muskrat Falls is around El. 3.0 m and stays

relatively stable for the ranges of the normal river flows. In winter, this same

elevation rises due to the ice jam and has reached observed water elevations as

high as El. 20.0 m as presented in Figure 7-5.

It was noted from the hydrometric station data at Station 03OE007 (Churchill River at

the Foot of Lower Muskrat Falls) and at Station 03OE014 (Churchill River 6.15 kms

below Lower Muskrat Falls), that an increase in water level is observed during

0

0.1

0.2

0.3

0.4

0.5

0

0.5

1

1.5

2

2.5

40 45 50 55 60 65 70 75 80 85 90 95

Frou

de

Nu

mb

erV

elo

city

(m

/s)

Distance (km)

Ice VerificationWL 25 m - Discharge 2,200 m³/s

Velocity Target Velocity Velocity w/ Ice CoverFroude Number Target Froude Froude w/ Ice Cover

Location of dam

Rapids Location of upstream Muskrat Falls

Sandy Lake

Gull Lake



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November and December each year (see Figure 7-1 for Station 03OE007 and Figure

7-2 for Station 03OE014). This backwater is most probably due to the formation of a

thermal ice cover in the downstream river reach and is not related to the ice jam at

the foot of the falls. It should be noted that Station 03OE014 is located far enough

downstream of Muskrat Falls that water levels at this location should not be

influenced by the presence of a hanging dam downstream of Muskrat Falls therefore,

the increase in water level at this location is most definitely due to the presence of a

thermal ice cover.

A hydrodynamic analysis with HEC-RAS was carried out to verify this hypothesis.

Water levels were simulated with a 0.5 m thermal ice cover generated downstream

of Muskrat Falls from the mouth of the Churchill River as far upstream as Muskrat

Falls. Manning roughness coefficients of 0.03 to 0.06 (recommended by USACE)

were assumed for the ice cover. The effects of using various Manning coefficients

were evaluated as it is likely this value will vary throughout the winter. Based on the

preliminary results, a rating curve for downstream of Muskrat Falls during ice

conditions was established and is presented in Figure 8-2.



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Figure 8-2: Muskrat Falls Downstream Rating Curve with and without Ice Cover (in natural conditions)

From this rating curve, the range of water levels during winter downstream of

Muskrat Falls is between El. 3.0 and 6.0 m. This corresponds to winter observed

river flow between 700 m³/s and 2,300 m³/s.

As presented in section 8, to eliminate the frazil ice, the upstream water elevation will

be increased and maintained at elevation 25.0 m. The thermal ice cover that will

form with this rise will eliminate to a greater extent the frazil ice that is causing the

present ice jams downstream of the falls by trapping it in the created upstream

reservoir. An analysis with HEC-RAS was carried out to establish a relationship

between the size of the hanging dam and the downstream water level. The analysis

was carried out for various river discharges and the results for a discharge of 2,000

m³/s is illustrated in the following figures. The computed water profiles at a

0

1

2

3

4

5

6

7

8

0 1000 2000 3000 4000 5000 6000

Elev

atio

n (m

)

Discharge (m³/s)

Downstream Rating Curve

Downstream Rating Curve - Thermal ice Cover



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discharge of 2,000 m³/s for various degrees of obstruction are shown on Figure 8-3,

Figure 8-4 and Figure 8-5.

The results of the analysis expressed in terms of backwater level versus river

percentage of blockage due to the hanging dam obstruction for a river discharge of

2,000 m³/s is shown on Figure 8-6. The results indicate that for river obstruction by

hanging dam up to 50% there is little impact on the backwater level. Beyond 50%

obstruction, the backwater level starts increasing significantly faster.

This threshold increase occurs at water elevation 8.0 m. Therefore, for design

purposes, it was selected that water elevation 8.0 m be applied since it provides a

confident estimate of the maximum winter water level during temporary diversion of

Phase 2 construction. All infrastructure susceptible to being influenced by the

downstream water elevation should be designed considering this water elevation.

While it is not believed that an obstruction of 50% will be obtained once the winter

headpond is achieved and the thermal ice cover upstream of Muskrat Falls is

produced, it is believed that there may be some accumulation of frazil ice

downstream of Muskrat Falls during the time period in which the thermal ice cover is

forming. Therefore, there may be some raise in the water level due to this. Also,

based on analysis, it is also noted that there is an increase in water level due to the

presence of a thermal ice cover downstream of Muskrat Falls.

A water level of 8 m (i.e. 50% obstruction) was chosen because this is a threshold

value based on the analysis. The influence on water level is relatively small up until

this point. The results show that obstructions greater than 50%, result in larger

increases in water level. We can consider obstructions up to 50% as an added

factor of safety.



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Figure 8-3: Profile for HEC-RAS Ice Dam Simulation with WL = 9.03 m

0 10 20 30 40 50-50

-40

-30

-20

-10

0

10

20

30

Ice Conditions Plan: Retry_8 m WL_5 2012-01-23

Main Channel Distance (km)

Ele

vatio

n (m

)

Legend

WS 1830

Ground

Ice Cover

Churchill Lower

km 42.85 – Lower Muskrat Falls

Flow

Percent Blockage = 54% Q = 2,000 m³/s D/S WL = 9.03 m



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0 10 20 30 40 50-50

-40

-30

-20

-10

0

10

20

30



Ele

vatio

n (m

)

Legend

WS 2000

Ground

Ice Cover

Churchill Lower

Flow

km 42.85 – Lower Muskrat Falls




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0 10 20 30 40 50-50

-40

-30

-20

-10

0

10

20

30



Ele

vatio

n (m

)

Legend

WS 2000

Ground

Ice Cover

Churchill Lower

Flow

Km 42.85 – Lower Muskrat Falls




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Figure 8-6: Downstream Water Level Versus Percent Blockage at Muskrat Falls

0

5

10

15

20

25

0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% 90.00% 100.00%

Dow

nstr

eam

WL

(m)

Percent Blockage (%)

Muskrat FallsDownstream WL vs. Percent Blockage

Q = 2,000 m³/s

Design winter water level for Phase 2 construction (WL = 8 m).



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9 PRELIMINARY RECOMMENDATIONS

Based on SNC-Lavalin’s review of past ice studies as well as analysis of simulations

run by SNC-Lavalin, the following preliminary recommendations have been made:

• During Phase 1 Construction, i.e. before the diversion through the spillway

structure, a downstream water level of 20 m should be considered for the

protection of the spillway and the powerhouse. This level corresponds to a 1 in

40 year return period;

• During Phase 2 Construction, the upstream water level should be maintained at

25 m in winter, to promote the formation of a thermal ice cover on most of the

river between the project site and Gull Lake and eliminate to a greater extent the

frazil ice generation;

• During Phase 2 Construction, a downstream water level should be considered at

8 m; and

• For the long term operation of the system, a specific downstream rating curve

should be considered during the winter season, since it is related to the increase

of headlosses in the river due to the formation of a thermal ice cover downstream

of Muskrat Falls. It will reduce the available head during the winter season. This

should be confirmed in a future study.

These recommendations do impact the layout of the project. During Phase 1, the

cofferdams will have to be constructed to protect the construction site against a

water level of 20 m. During Phase 2, the upstream cofferdam, power intake

cofferdam, upstream RCC cofferdam and the concrete wall between the upstream

cofferdam and the approach channel will all have to be raised to meet the 25 m

water level requirements. The downstream cofferdams during Phase 2 construction

should consider a downstream water elevation of 8.0 m.



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10 PATH FORWARD

Going forward, SNC-Lavalin has made recommendations for the future in order to

further verify the recommendations made in this report. These recommendations are

as follows:

• Future ice observation programs needed according to Nalcor’s Ice Review Panel

recommendation:

• Aerial surveys, temperature data, satellite data, bathymetry downstream of

the falls, etc.

This information is a valuable record and important in helping expain current river

conditions as well as any changes that may occur in the future, especially during

construction and operation;

• If possible, find and compare bathymetric data downstream of Lower Muskrat

Falls for periods before and after the 1978-79 and 1979-80 winters. This will be

beneficial since one of the most logical explanations to date of the extremely high

water levels experienced in the winters of 1978-79 and 1979-80, is of

morphological changes in the river due to erosion. Comparing bathymetric

information before and after these periods, if available, would help verify this

explanation;

• Any new monitoring equipment to be installed at Muskrat Falls should be

installed prior to winter 2011-12 (between the falls and downstream of the falls):

• Water level gauges, cameras, etc.

The installation of this equipment would aid in the facilitation of remote

observations and improve the monitoring water levels and the formation of the

ice dam at Muskrat Falls;

• Further discuss and consider carrying out of LiDAR survey of the 2011-2012 ice

dam. This will help to determine the exact extents of the ice dam that currently

forms. The total depth and size of the dam has only been determined based on

surface observation and the results of hydraulic analysis software;



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• Further discuss and consider the monitoring of ice in the Mud Lake area. The

formation of an ice cover at Mud Lake is extremely important to the residents as

it is their only means of travel from the community during the winter season when

they cannot travel by boat. It is important to have an understanding of the ice

processes in this area and the effects of various stages of the project on it;

• Continued observations at the Gull Island site, assuming that Gull Island

construction will follow Muskrat Falls. It is important to understand the ice

processes at Gull Island, particularly how they may change during the

construction and operation of Muskrat Falls. Continued observations will help in

the determination of this; and

• If an update of the energy study is required, it should take into account a revised

downstream rating curve for the winter season. Preliminary studies have shown

that the amount of available head may decrease during the winter season. This

would have an impact on the energy study and therefore should be accounted

for.

SNC-Lavalin will proceed with the design of the infrastructure according to the

findings and the recommendations for design ice conditions presented in this

document. SNC-Lavalin will also adapt the design of the structures should there be

need for modification due to any new information. However, SNC-Lavalin remains

confident that the adopted ice conditions for design are conservative.


SLI Doc. No. 505573-300A-4HER-0001 00 26-Mar-2012 A

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Appendix A Temperature, Discharge and Maximum Winter Water Level

Above Upper Muskrat Falls


SLI Doc. No. 505573-300A-4HER-0001 00 26-Mar-2012 A-1

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-20

-19

-18

-17

-16

-15

-14

-13

-12

-11

-10

1000 1200 1400 1600 1800 2000 2200

Tem

pera

ture

(°C)

Discharge (m³/s)

Station 03OE001 - Above Upper Muskrat FallsTemperature vs. Discharge

Average for December to February

1978

1979



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-30

-25

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-15

-10

-5

0

500 700 900 1100 1300 1500 1700 1900 2100 2300

Tem

pera

ture

(°C)

Discharge (m³/s)

Station 03OE001 - Above Upper Muskrat FallsTemperature vs. Discharge

15 Day Average Prior to Max. Water Level

1978 1979



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-20

-19

-18

-17

-16

-15

-14

-13

-12

-11

-10

15 15.5 16 16.5 17 17.5 18 18.5 19 19.5 20

Tem

pera

ture

(°C)


Station 03OE001 - Above Upper Muskrat FallsAverage Temperature (Dec. to Feb.) vs. Max. Water Level

19781979



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-30

-25

-20

-15

-10

-5

0

15 15.5 16 16.5 17 17.5 18 18.5 19 19.5 20

Tem

pera

ture

(°C)


Station 03OE001 - Above Upper Muskrat FallsAverage Temperature (15 days before event) vs. Max. Water Level

19781979



SNC-Lavalin Inc.

1000

1200

1400

1600

1800

2000

2200

15 15.5 16 16.5 17 17.5 18 18.5 19 19.5 20

Dis

char

ge (

m°/

s)


Station 03OE001 - Above Upper Muskrat FallsAverage Discharge (Dec. to Feb.) vs. Max. Water Level

19781979



SNC-Lavalin Inc.

1000

1200

1400

1600

1800

2000

2200

15 15.5 16 16.5 17 17.5 18 18.5 19 19.5 20

Dis

char

ge (

m°/

s)


Station 03OE001 - Above Upper Muskrat FallsAverage Discharge (15 days before event) vs. Max. Water Level

1978

1979

1994

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