Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakwater, McNabs Island

8/18/2019 Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakwater, McNabs Island

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141019.00 ● Final Report ● July 2014

ISO 9001

Registered Company Prepared by:Prepared for:

Halifax Harbour Wave Agitation

Risk Study at Maughers Beach

Breakwater McNabs Island


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141019 MBEACH 2014 REVISIONS FINAL.DOCX/VLED: 17/07/2014 13:27:00/PD: 17/07/2014 13:27:00

1489 Hollis Street

PO Box 606

Halifax, Nova Scotia

Canada B3J 2R7

Telephone: 902 421 7241

Fax: 902 423 3938

E-mail: [email protected]

www.cbcl.ca

ISO 9001

Registered Company

15 July 2014

Erica Copeland, P.Eng.

Project Engineer

Portfolio Management Division, Real Property Safety and Security

Fisheries and Oceans Canada

PO Box 1000, 50 Discovery Drive, Dartmouth, NS B2Y 3Z8tel: (902) 426-5003

fax: (902) 426-6501

email: [email protected]

Dear Mrs. Copeland:

RE: Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakwater – Final

Report

We are pleased to submit our final report assessing wave agitation risks in Halifax Harbourrelated to sea level rise and the condition of the breakwater at Maughers Beach on McNabs

Island. Should you have any questions or require clarification of any matter raised in this

submission, please contact me at your convenience.

We appreciate your consideration of our services for this very interesting project, and we

look forward to working with you again.

Yours very truly,

CBCL Limited

Vincent Leys, M.Sc., P.Eng.

Coastal Engineer

Direct: (902) 421-7241, Ext. 2508

E-Mail: [email protected]

Project No: 141019.00

mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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CBCL Limited Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakwater i

Contents

EXECUTIVE SUMMARY ........................................................................................................................ i

CHAPTER 1 Introduction .............................................................................................................. 1

1.1 Background ......................................................................................................................... 1

1.2 Objectives ........................................................................................................................... 1

1.3 Work Scope ......................................................................................................................... 3

CHAPTER 2 Coastal site Characterization ...................................................................................... 4

2.1 Bathymetry and Topography .............................................................................................. 4

2.2 Geomorphology and Recent Erosion .................................................................................. 5

2.3 Site Observations ................................................................................................................ 6

2.4 Water Levels ....................................................................................................................... 6

2.4.1 Tides ........................................................................................................................ 6

2.4.2 Historical Water Levels ........................................................................................... 8

2.4.3 Sea Level Rise Projections ....................................................................................... 9

2.4.4 Impact of Sea Level Rise on Extreme Event Frequency .......................................... 9

2.5 Offshore Wave Climate ..................................................................................................... 10

2.5.1 Data Sources ......................................................................................................... 10

2.5.2 Wind and Wave Height Statistics .......................................................................... 11

2.5.3 Extreme Value Analyses ........................................................................................ 11

2.6 Nearshore Wave Climate .................................................................................................. 12

2.6.1 Numerical Wave Model ........................................................................................ 12

2.6.2 Storm Wave Conditions ........................................................................................ 14

2.6.3 Nearshore Currents .............................................................................................. 15

2.6.4 Impact of Existing Shore Protection Damage ....................................................... 16

CHAPTER 3 Wave Climate Changes Due to Isthmus Erosion and Sea Level Rise ........................... 17

3.1 Potential Isthmus Damage Scenarios ............................................................................... 17

3.1.1 Damage Caused by Individual Storms .................................................................. 173.1.2 Cumulative Damage .............................................................................................. 18

3.1.3 Hypothetical Damage Evolution ........................................................................... 19

3.2 Impacts on Wave Climate in Halifax Harbour ................................................................... 21

3.2.1 Extreme Events ..................................................................................................... 21

3.2.2 Operational Conditions ......................................................................................... 21


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CHAPTER 4 Socio-Economic Considerations ................................................................................ 26

4.1 Objectives ......................................................................................................................... 26

4.2 McNabs and Lawor Islands Provincial Park ...................................................................... 26

4.2.1 Location ................................................................................................................ 26

4.2.2 Future of the Park ................................................................................................. 26

4.3 Provincial Park Amenities Potentially Impacted by Beach Erosion .................................. 27

4.4 MacNabs Island as a Tourism Product .............................................................................. 28

4.4.1 Tourism Demand-Supply Balance ......................................................................... 29

4.4.2 Travel Market ........................................................................................................ 29

4.4.3 Supply Side ............................................................................................................ 29

4.5 Sea Level Rise and Isthmus Erosion Impacts .................................................................... 31

4.6 Potential Mitigation .......................................................................................................... 32

CHAPTER 5 Conclusions ............................................................................................................. 33

CHAPTER 6 References ............................................................................................................... 35

Appendices

A Statistics on Offshore Wind and Wave Climate (44.5N-63.4W) and Water Levels

B Map of McNabs Island


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CBCL Limited Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakwater i

EXECUTIVE SUMMARY

The Department of Fisheries and Oceans Canada (DFO) maintains a lighthouse at the entrance of Halifax

Harbour, Nova Scotia. The lighthouse is located on an islet at the end of a cobble isthmus on the West

side of McNabs Island, extending from the end of Maughers Beach. The isthmus, which has previously

been used to access the lighthouse, is lined with an armour stone breakwater that is deteriorating due

to wave attack and overtopping. The lighthouse is now serviced by helicopter; therefore land access

along the isthmus is no longer required for operations. Before finalizing any decision on repair orreplacement of the breakwater, DFO would like to determine the impact of continued breakwater

deterioration on the surrounding geography, including the impact on operations for all stakeholders.

A numerical wave model was used to quantify the wave climate changes in Halifax Harbour that would

be caused by further breakwater deterioration and subsequent isthmus erosion, along with Sea Level

Rise (SLR) impacts. Existing and future wave agitation was investigated at key sites including Garrison

Pier in McNabs Cove (the Island’s main access point), Outer Halifax Harbour, Point Pleasant Shoal and

Halifax’s Container Terminals. Three scenarios were examined:

(1) Partial loss of Maughers Beach breakwater with overtopping(2) Breakwater deterioration and breach through isthmus

(3) Full breakwater deterioration and isthmus eroded down to a submerged bar

The modeling exercise indicated that SLR alone will cause a generalized increase in wave heights over

time around McNab’s Island and in Halifax Harbour. It also indicated that further breakwater

deterioration causing subsequent isthmus erosion would add to the SLR impact on wave climate in

McNabs Cove but not elsewhere in the Harbour. While it is not possible to give accurate predictions on

time frames, the modeling used provides qualitative conclusions with associated order-of-magnitude

timelines based on a hypothetically assumed isthmus damage evolution.

If the breakwater is repaired and regularly maintained (Scenario 1), the extreme wave height increase by

year 2100 is estimated at 0.2 m at Garrison Pier (SLR only, assumed at 1.0 m by 2100). The increase in

extreme wave heights at other sites examined (Outer Harbour, Point Pleasant Shoal and Halterm

Terminals) due to SLR was estimated at 0.06 to 0.1 m by year 2100.


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If the breakwater and isthmus fully deteriorate (Scenario 3), modeling indicates that extreme wave

heights will be further increased by less than 0.02 m by 2100 in the Outer Harbour, Point Pleasant Shoal

and Halterm Terminals. At Garrison Pier, this increase in wave heights by 2100 for Scenario 3 is 0.2 m.

For perspective, replacing and maintaining the breakwater would delay the inevitable increase in wave

impacts due to SLR by approximately 30 years at Garrison Pier (2100 versus 2070, under the modeling

assumptions).

The frequency of smaller wave events was also examined, which is relevant for visitor boat traffic and

berthing at Garrison Pier. The acceptable wave climate for berthing typically used for DFO Small Craft

Harbours is defined by a 0.4 m significant wave height upper limit for 10 to 20 m-long vessels, which

would apply to summer island visitor vessels. Modeling indicated that the acceptable wave height

threshold for berthing (0.4 m) at Garrison Pier is presently exceeded approximately 4 days per year, and

would be exceeded on average:

11 days/year assuming 1.0 m SLR and regular breakwater maintenance (potentially in year

2100)

11 days/year assuming 0.6 m SLR and breakwater left to deteriorate (potentially in year 2070)

18 days/year assuming 1.0 m SLR and breakwater left to deteriorate (potentially in year 2100).The downtime periods typically occur during the winter off-season, therefore not affecting summer

visitor traffic.

Pros and Cons of Maintaining the Isthmus Breakwater

Breakwater should be repaired and maintained

because:

Breakwater should be left to deteriorate

because:

The impact of SLR on wave agitation in McNabs

Cove would not be further exacerbated;

Garrison Pier could remain the main Park access

point with future visitor centre development asplanned (vision in 2005 McNabs Island

Management Plan) for an additional 30 years;

and

The public could safely access the lighthouse

islet.

Increase in wave agitation due to deterioration is limited

to McNabs Cove and Garrison Pier only (not Halifax

Harbour), and would primarily affect winter off-season;

Increase in wave impacts due to SLR is inevitable aroundthe island. Breakwater maintenance would only delay

the process for a limited time and area;

Capital and ongoing maintenance expenses are

significant;

Alternative landing sites on the Island are suitable SLR

adaptation options (Ives Cove, Timmonds Cove); and

The isthmus area offers an opportunity to educate Island

visitors on coastal processes.

Based on the modeling results, we offer the following conclusions: The deterioration of the breakwater and the resulting erosion will not impact the islet on which

the lighthouse is located and therefore will not impact departmental operations.

The deterioration of the breakwater and the resulting erosion is expected to cause a relatively

low impact on the local wave climate and in the worst case scenario will only moderately delay

the impact of sea level rise.


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CBCL Limited Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakwater 1

CHAPTER 1 INTRODUCTION

1.1 Background

The Department of Fisheries and Oceans Canada (DFO) maintains a lighthouse at the entrance of Halifax

Harbour, Nova Scotia. The lighthouse is located on an islet at the end of a cobble isthmus on the West

side of McNabs Island, extending from the end of Maughers Beach (Figure 1). The isthmus extends from

the converging ends of both Maughers Beach to the Northeast of the lighthouse, and Hangmans Beachto the Southeast. The isthmus, which has previously been used to access the lighthouse, is lined with an

armour stone breakwater that is deteriorating due to wave attack and overtopping. Significant damage

was caused to the breakwater by Hurricane Juan in September 2003.

The lighthouse is now serviced by helicopter; therefore land access along the isthmus is no longer

required for operations. Before finalizing any decision on repair or replacement of the breakwater, DFO

would like to determine the impact of continued breakwater deterioration on the surrounding

geography, including the impact on operations for all stakeholders.

1.2

ObjectivesThe objectives of the study are as follows:

Determine the potential evolution of breakwater damage and isthmus erosion under extreme

storms and sea level rise;

Quantify the wave climate at target locations under existing and future conditions, accounting for

the impacts of sea level rise, breakwater damage and isthmus erosion; and

Consider potential socio-economic impacts of higher wave agitation in McNabs Cove for the McNabs

Island Park, and in the Outer Harbour if it is impacted by breakwater failure.


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1.3 Work Scope

Coastal Site Characterisation (Chapter 2)

There is a wealth of historical information on the lighthouse and beach and their shore protection works

dating back to the early 20th century. The information includes surveys, ground and air photos,

numerous design reports and construction drawings. Historical information was summarized by PWGSC

in a 2007 design study report. The characterization was further augmented in this assessment by the

following investigations: Site visit;

Water level analyses;

Offshore wind and wave climate; and

Development of a nearshore wave transformation model.

Impacts of isthmus erosion and sea level rise on wave climate (Chapter 3)

A numerical wave model was used to quantify the wave climate changes in Halifax Harbour that would

be caused by further breakwater deterioration and subsequent isthmus erosion, along with Sea Level

Rise (SLR) impacts. Existing and future wave agitation was investigated at key sites including Garrison

Pier in McNabs Cove (the Island’s main access point), Outer Halifax Harbour, Point Pleasant Shoal andHalifax’s Container Terminals. Three scenarios were examined:

(1) Partial loss of Maughers Beach breakwater with overtopping

(2) Breakwater deterioration and breach through isthmus


Socio-Economic Considerations (Chapter 4)

Maughers Beach is one of the most popular day-use areas on McNabs Island and is a natural attraction

for visitors. Based on a review of currently available literature and Island visitor data, this study presents

a cursory commentary on the economic value at stake if commercial, tourism and recreational activities

in the area were to be affected by the deterioration of the Maughers Beach isthmus. The scope for this

desktop task is of a preliminary nature, and does not stand as a detailed impact assessment.

Conclusions are presented in Chapter 5.


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CHAPTER 2 COASTAL SITE CHARACTERIZATION

2.1 Bathymetry and Topography

Regional soundings from the Canadian Hydrographic Service (CHS) Navigation Charts 4202 and 4203

(Halifax Harbour) were obtained in electronic format from DFO. High-resolution multibeam soundings

from 2009 were provided by PWGSC for the Maughers Beach and McNabs Cove area. Soundings and

GPS cross-section survey points in Chart Datum (CD) are displayed on Figure 2.1. The Maughers BeachIsthmus Breakwater and lighthouse presently shelters McNabs Cove. The detailed topography of the

isthmus and lighthouse area is shown on Figure 2.2.

Figure 2.1 Local Multibeam and GPS Cross-Section Survey Coverage (Chart Datum)


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Figure 2.2 Topography of Maughers Beach Isthmus and Lighthouse Area

Based on 15 Oct 2012 Topographic survey provided by PWGSC

2.2 Geomorphology and Recent Erosion

The geomorphology and coastal processes of the island were studied in detail by Dr. Gavin Manson

(1999, 2008). McNabs Island is comprised of a series of connected glacial till drumlins derived from

shale, sandstone and mudstone from the Carboniferous age. Beaches are formed by deposition of

material from eroding drumlin bluffs. The highest rates of erosion occur on the exposed southwestern

side of the Island, which supplies sediment to the beaches to the North. Hangmans Beach to the

southeast of the Maughers Beach isthmus is an exposed and steep cobble beach footing an eroding cliff.

Eroded material feeds the beach and is transported by breaking waves towards the isthmus to the

Northwest. The large natural cobble berm crest is typically 5 to 6 m CD, sloping down as the peninsula

narrows toward the isthmus until it meets the armourstone crest at 4.0 m CD or less. On the Northeast

side of the isthmus, Maughers Beach is protected from the large southerly waves, and therefore

supports a gentler beach of finer sediment, including from wind-blown transport.

The following recent observations were provided by Cathy McCarthy of the Friends of McNabs Island

Society. “In 2003 Hurricane Juan opened a tidal inlet into McNabs Pond, cutting Maughers Beach in two

sections and destroying the boardwalk and cribwork to the lighthouse along the isthmus. Garrison Pier

suffered minor damage. An oil pipeline along Garrison Road was exposed and leaking. It was capped and

remained capped until the pipeline, the pump house and storage tanks were removed in 2010. During

this remediation work, the vegetation along Garrison Road was removed. Erosion along the road has

been an issue since then”. Anecdotal observations would also indicate that recent erosion along

Garrison Road is more likely related to the destabilization of the road bed during remediation works in

2010 than to the deterioration of the isthmus breakwater since 2003.


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2.3 Site Observations

A visual assessment of the site and surrounding shorelines was conducted on the morning of March 7th,

2013. Photos are shown on Figure 2.3. The predicted tide was 0.3 m CD (low) at 10:29 am. Offshore

wave buoy records (see section 2.5.1) indicate heavy seas, with wave heights ranging from 3.4 m

(significant wave height) to 5.6 m (maximum wave height) with a 9 s peak period. Heavy swells were

observed along the cobble beach and isthmus.

Cribwork behind the armour protection was destroyed by Hurricane Juan over a distance of 100 m, with

only ruins now visible. A 60 m-long western section remains standing, with various degrees of

settlement and localized damage from amour stone pushed onto the deck. The armour stone section in

front of the remains of the crib exhibits the most damage and the smaller stones have been washed

onto the North side of the isthmus. Even at low tide, some overtopping was visibly occurring across the

damaged section of the armour stone. The site can be accessed by the public from Maughers Beach and

safety hazards include unstable rocks and crib ruins combined with overwash during heavy seas.

A limited armour stone sampling exercise was conducted during the field visit. Eight stones deemedrepresentative were sized within a safe and stable area at the eastern end of the breakwater. Based on

measurements along three axes and assuming a rock density of 2,650 kg/m 3, the median weight of the

sample was approximately 4 tonnes, which is in the lower range of the 4-6 t range specified on the

historical drawings provided by PWGSC. The median stone weight over the whole structure would be

difficult to determine with certainty due to difficult access and potentially unstable conditions.

2.4 Water Levels

Water levels are a critical factor for coastal wave damage assessments because they determine the

maximum wave breaking height at near-shore locations in shallow waters. Extreme water levels, being a

combination of tide, storm surge and relative sea level rise (SLR), allow larger waves to travel further in

the near-shore region. A tide gauge is in operation at the Bedford Institute of Oceanography (BIO). The

continuous tide gauge record for Halifax Harbour is available from 1919 to present, which was analysed

in detail for historical SLR trend and extreme value analyses of storm peaks.

2.4.1 Tides

Local astronomical tides are semi-diurnal, with two high waters and two low waters occurring during

each 25-hour lunar day. The tidal range is 2.1m for a large tide and 1.5m for a mean tide, and the mean

water level is at 1.0m above Chart Datum (source: Canadian Hydrographic Service 2013 Tide and Current

Tables). Tidal levels are listed in Table 2.1.


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Approaching the site

from the Southeast

along Hangmans

Beach.

Looking West from

eastern end of the

breakwater.

Overtopping at low

tide.

Looking East at the

most damaged

breakwater section

from the remaining

crib deck.

Figure 2.3 Site Photos, 7 March 2013


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1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 20200.75

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

M e a n s e a l e v e l [ m C

D ]

Annual means

92-year trend10-year trends

Table 2.1 2013 Water Levels in Halifax Harbour (metres above existing Chart Datum)

Storm event return period (years) Metres Chart Datum Metres CGVD28

100 3.0 2.2

50 2.9 2.1

10 2.7 1.9

5 2.6 1.8

1 2.4 1.6

Tidal Elevations as published by CHS

Higher High Water Large Tide 2.2 1.4

Higher High Water Mean Tide 1.8 1.0

Mean Water Level 1.0 0.2

Lower Low Water Mean Tide 0.3 -0.5

Lower Low Water Large Tide 0.0 -0.8

Lowest Low Water (recorded extreme) -0.8 -1.6

2.4.2 Historical Water Levels

SLR along Eastern Canada’s coast has been occurring since the end of the last ice age, about 10,000

years ago, when PEI was still linked to the mainland of Nova Scotia and New Brunswick. The tide gauge

observations in Halifax show a historical SLR rate of 0.32 m in the last 92 years (Figure 2.4). Forbes et al

(2009) estimate that 0.16 m of this trend is due to land subsidence due to post-glacial motion of the

local Earth’s crust, based on observations from a GPS station at the BIO. It is interesting to note that 10-

year trends over the last 30 years have progressively accelerated.

Figure 2.4 Historical Mean Sea Level in Halifax Harbour

Storm surge is due to meteorological effects on sea level, such as wind set-up1 and low atmospheric

pressure, and can be defined as the difference between the observed water level during a storm and the

predicted astronomical tide. Extreme total water levels (including tide, storm surge and historical SLR)

1 Wind set-up refers to the increase in mean water level along the coast due to shoreward wind stresses on the water surface.


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were derived from statistics on the Halifax tide gauge data (1919-2013). An extreme value distribution

(‘Weibull’) was optimally fitted to a series of statistically independent peaks greater than 2.4 m,

following the so-called ‘Peak-Over-Threshold’ extreme value analysis technique (Appendix A Figure A.5).

The method is based on the premise that the process investigated is stationary2. To satisfy this

requirement, the tide gauge time-series was de-trended, and its mean was set to the 2013 mean sea

level (i.e. the past SLR trend was taken out). Extreme water levels are listed in Table 2.1.

2.4.3 Sea Level Rise Projections

The rate of global mean sea level is accelerating in the 21st century due to global warming impacts,

notably the melting of polar ice caps. Projections for Halifax Harbour were developed by Forbes et al in

2009, based on scenarios by IPCC AR4 (2007) and Rahmstorf (2007). Since then, SLR projections have

been updated based on climate research and recent trends, including the melting of arctic sea ice and

ice caps. The Intergovernmental Panel on Climate Change (IPCC AR5, 2013) recently indicated that the

current consensus is as follows:

The likely range of global mean sea level rise for 2081-2100 relative to 1986-2005 was estimated

from 0.26 m (lower bound value for low emission scenario) to 0.98 m (higher bound estimate for

high emission scenario); There is currently insufficient evidence to evaluate the probability of specific levels above the

assessed likely range; and

There will be regional differences, with the northeastern coast of North America potentially

experiencing a sea level rise rate higher than the global average (Sallenger et al., 2012).

Time-dependent mathematical projections of global mean SLR for use in infrastructure projects were

developed by the US Army Corps of Engineers (2011). Projections were classified into a low, medium

and high category. Numerical projections starting in 2012 were computed from the equations

recommended by USACE, and are presented on Figure 2.5. A crustal subsidence factor of 0.16 m/century

for Halifax (Forbes 2009) was added to the projection. The calculation resulted in a year 2100 value of

1.06 m ± 0.48 m, which was used for the present study. It matches the estimates by Daigle and Richards

for coastal municipalities in NS and PEI including Halifax (2011). Projections should be revisited at least

every decade based on up-to-date scientific observations and climate model projections.

2.4.4 Impact of Sea Level Rise on Extreme Event Frequency

In terms of extreme water levels, the difference between a 10-year storm (currently 2.7 m CD) and a

100-year storm (3.0 m CD) is only 0.3 m. Given the SLR projections, extreme water levels with a low

return period today will be very common in a few decades (Figure 2.6). This needs to be considered in

coastal structure design and future damage predictions (section 3.1).

2 The ‘Peak-Over-Threshold’ procedure selects statistically independent storm peaks occurring more than 48 hours apart. An

extreme value distribution is then fitted to the population of storm peaks for extrapolating extreme events and their associated

return periods. The procedure is statistically valid for stationary processes, i.e. processes with a probability distribution that

does not change when shifted in time. Statistical properties such as mean and variance must remain constant in time and not

follow trends.


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1

10

100

2010 2020 2030 2040 2050 2060 2070 2080 2090

R e t r u n p e r i o d [ y e a r s ]

WL = 3.1 m CDWL = 2.9 m CD (Hurricane Juan)

WL = 2.7 m CD

Figure 2.5 Sea Level Rise Projections Used in the Present Study

Figure 2.6 Influence of Sea Level Rise on Return Periods of Extreme Water Levels in Halifax

2.5 Offshore Wave Climate

2.5.1 Data Sources

Inputs to the wave study are based on two data sources located 15.5 km offshore from Maughers

Beach:

Environment Canada wave buoy C44258 observations collected at 44.502N – 63.403W, from

February 2000 to February 2013; and

The MSC50 wind and wave model hindcast from January 1954 to December 2009. It contains hourly

time series of wind (speed, direction) and wave (height, period, direction) at 44.5N – 63.4W (gridpoint 6984 in 56m water depth). The dataset is a state-of-the art hindcast, i.e., data computed from

all existing wind and wave measurements that were re-analysed and input to a 0.1-degree

resolution ocean wave growth model that includes the effect of depth and ice cover. The MSC50

hindcast was developed by Oceanweather Inc. and is distributed by Environment Canada (Swail et

al., 2006).

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2010 2030 2050 2070 2090 2110

R e l a t i v e s e a

l e v e l r i s e ( m ) -

I n c l u d e s l a n d s u b s i d e

n c e o f 0 . 1 5 7 m / c e n t u r y

High

Intermediate (used for assessment)

Low


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Detailed comparisons revealed that the MSC50 wave heights are on average 0.09 m greater than buoy

observations, with a standard deviation of 0.34 m. To compensate for any potential inaccuracies in the

MSC50 model, the hourly dataset used for the study was assembled by merging the above two, using

the buoy observations when available and complementing with MSC50 data outside of the buoy

observation period. We note that for the purposes of this study, once the offshore wave information is

transformed to the depth-limited nearshore sites of interest, the differences in offshore data sources

are not consequential due to wave breaking.

2.5.2 Wind and Wave Height Statistics

Complete statistics are presented in graphical and tabular format in Appendix A. Wind and wave

climates are typically represented as ‘roses’, i.e., plots of frequency of given wind speed or wave height

by direction. The roses show that prevailing winds are from the northwest, west and southwest

directions with seasonal variations. Summer winds are generally below 30 km/h and from the

southwest. Winter winds are much stronger and predominantly from the northwest. Waves offshore

Halifax of significant height3 over 3 m typically come from the south, southeast and southwest

quadrants, with higher occurrences in the late fall and winter.

2.5.3 Extreme Value Analyses

Return periods for extreme significant wave heights (1, 10, 50, 100-year) 4 were estimated based on an

analysis of 67 storm peaks of significant wave height over 6 m, using the “Peak-Over-Threshold”

method. The best fitting Weibull statistical distribution was used to derive extreme values. A most

probable peak period (‘Tp’) and wind speed were derived from extreme wave heights based on the joint

frequency distributions from the storm peaks. Results are listed in Table 2.2. In the near-shore wave

transformation modeling presented in the next section, these extreme values were used as offshore

boundary conditions for the wave model.

Table 2.2 Extreme Return Values for Offshore Significant Wave Heights, Associated Peak Period

and Wind Speed

Return PeriodSignificant Wave

Height

Associated

Peak Period Wind Speed

Years Metres Seconds m/s km/hour

1 6.1 10.6 18.1 65

5 7.9 11.6 20.4 73

10 8.7 12.0 22.2 80

50 10.4 12.8 27.8 100

100 11.2 13.1 31.2 112

3 The significant wave height (Hsig) is the common parameter for characterizing the energy in a wave field. Hsig represents the

average of the third highest waves over a given time period, and is a good approximation of the ‘typical’ wave height that

would be reported from visual observations. The maximum wave height within a wave field is greater than the significant wave

height by a factor of 1 to 2 typically, depending mainly on water depth, wave field parameters, and duration of observations.4 The N-year return value represents the value that is exceeded on average once every N years.


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2.6 Nearshore Wave Climate

2.6.1

Numerical Wave Model

Model Description

A numerical wave model for near-shore transformation was used to transfer the offshore wave climate

to nearshore sites of interest. The Danish Hydraulic Institute’s MIKE 21 Spectral Wave (SW) model wasused over a flexible mesh domain with high resolution in the project area. The model has a wide base of

users worldwide and extensive recognition from the coastal science and engineering community. It is

particularly suited for near-shore wave transformations and harbour investigations. The model

simulates the following physical phenomena:

Refraction and shoaling due to depth variations;

Dissipation due to depth-induced wave breaking;

Dissipation due to bottom friction (a typical bottom roughness of 0.04m was used);

Dissipation due to white-capping;

Non-linear wave-wave interaction;

One-time reflection from vertical walls; however the model cannot simulate wave agitation due tomultiple reflections of harbour resonance (e.g. in between the piers at Halterm Terminals). These

processes can be resolved with a finer scale phase-resolving model; and

The output radiation stresses from the breaking waves can be used in the hydrodynamic (HD)

module of MIKE21 to study near-shore currents and localized water level changes due to wave setup

(typically in the order of 10% of breaking wave height).

Modeling Methodology

The MIKE21 model domain used in the study was based on the nautical chart and a local bathymetric

survey. It includes 7,483 elements of varying size, with smaller sizes to provide high resolution in the area

of interest (Figure 2.7). The model was run in steady-state mode to evaluate operational and extreme

conditions under various scenarios of SLR and isthmus breakwater damage (Chapter 3). Extreme offshore

wave heights were assumed to coincide with extreme water levels of the same return period, as the joint

distribution of offshore wave heights and peak water levels indicates a clear correlation (Table A.4 in

Appendix A). The coupled MIKE21 SW-HD was also used to verify that water level statistics from tide gauge

observations at BIO are applicable to Maughers Beach under storm conditions.

Model Confidence Interval

The offshore wave conditions and the bathymetry are known with very good accuracy. However there

are no site-specific measurements to validate the nearshore wave model results, as is oftentimes the

case with coastal studies. The model breaking wave coefficient γ = Hmax/depth is considered the primary

calibration parameter. It is lowest for gentle bed slopes, and highest for steep slopes. It typically ranges

from 0.6 to 1.4, with an average value of 0.8 generally recommended for modeling studies (USACE

2006). Wave height estimates presented in this report are based on the 0.8 value. Model sensitivity tests

to the γ parameter were conducted. The confidence interval for modeled nearshore wave heights

presented in this study is estimated at ±25%.


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Halterm

Container Terminal

Outer

Harbour

Garrison

Pier

Model output

locations

Point

Pleasant

Shoal

Maughers Beach

breakwater

Wave buoy and MSC50

data, 44.5N-63.4W

Figure 2.7 MIKE21 Wave Model Domain


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1-year storm100-year storm

2.6.2

Storm Wave Conditions

Examples of modeled wave fields for extreme storm conditions are shown on Figure 2.8. As waves

approach the site, the numerous shoals and narrowing of the Outer Harbour cause waves to bend

towards the shoreline (refraction) and ultimately break, reducing the amount of energy propagating into

Halifax Harbour. Refraction is controlled by wave period and water depths, i.e. longer waves refract

more. Breaking is controlled by the water/wave height ratio, so larger waves break further offshore

while greater storm surges allow higher waves nearshore. As waves propagate, refraction reduces theinfluence of variations in the offshore directionality, while breaking reduces the influence of offshore

wave height for a given water level.

At the Project site, a limited amount of wave energy overtops the breakwater and further dissipates over

the shoals in its lee. A larger amount of energy refracts around the lighthouse islet into McNabs Cove.

Figure 2.8 Sample Modeled Wave Heights for Extreme Storm Condition


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2.6.3

Nearshore Currents

Nearshore currents were simulated using MIKE21 HD driven by radiation stresses generated by breaking

waves in MIKE21 SW. Simulated currents during the 1-year and 100-year return storm are shown in

Figure 2.9. Breaking waves generate a strong northwestward longshore current along Hangmans Beach,

then flowing around the lighthouse and ebbing out over the shoal in the lee of the lighthouse. This

explains the formation of this shoal, made of material eroded from the cliffs along the southwestern

shore of the Island, and transported by the longshore current described. The finer sandy material istransported further east of the lighthouse towards Maughers Beach by the remaining wave energy

refracted around the lighthouse. Strong overwash currents of 1 to 2 m/s are expected to occur during

large storms over the damaged breakwater. Such current velocities combined with breaking waves

contribute to destabilizing the existing armourstone, particularly over its damaged section. The area of

influence of the breach currents ranges from 50 to 150 m away to the North into McNabs Cove,

depending on the intensity of the storm.

Figure 2.9 Nearshore Currents during Extreme Storm Conditions

1-year return

storm

100-year return

storm


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2.6.4

Impact of Existing Shore Protection Damage

The immediate impact of the existing shore protection damage is to allow an overwash current during

extreme events, as described above. The wave model was also used to investigate the potential role of

the existing breakwater deterioration on recent erosion trends near Garrison Pier. Simulated extreme

events under present water level conditions were compared between existing breakwater condition

with overwash, and repaired breakwater without overwash. It is estimated that under existing water

levels, the extreme Hsig at Garrison Pier increased by 1.4% due to present deterioration, compared withthe repaired breakwater case. Therefore the present level of breakwater deterioration is not severe

enough to impact wave climate at Garrison Pier. The impact on wave climate should deterioration be

left to continue is examined in the following Chapter.


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CHAPTER 3 WAVE CLIMATE CHANGES DUE TO ISTHMUSEROSION AND SEA LEVEL RISE

3.1 Potential Isthmus Damage Scenarios

This section predicts the evolution of damage to the armoured isthmus using the shallow water

breakwater design and damage formulations by Van Der Meer (CIRIA 2007). The damage formulation is

applied using the long-term trends of extreme events based on the most likely (intermediate) sea level

rise (SLR) scenario presented in section 2.3.3.

3.1.1 Damage Caused by Individual Storms

Joint statistics on water level and offshore wave heights show that storm surges and large offshore

waves generally peak at the same time (Appendix A, Table A.4). In addition, the wave model shows that

breaking wave heights at the toe of the breakwater in 2m CD water depth are controlled by the water

level. This is due to the effect of shoals along the western shores of McNabs Island where large offshore

waves break before reaching the isthmus. Therefore breakwater damage levels, typically a function of

wave parameters, can be correlated to the storm water levels.

The Van Der Meer equation predicts the amount of damage of a given storm to the face (S,

dimensionless) of a breakwater as related to the median rock size, i.e., S=A eroded / Dn502

, where Aeroded (m2)

is the area of the armour stone face that is damaged and Dn50 is the median diameter of the armour

stone.

The equation results for breakwater damage level after one storm are shown on Figure 3.1. Historical

design drawings provided by PWGSC indicate the present armour stone weight range is 4-6 tonnes.

Limited site observations indicate that in some areas, placed armour stone weight may be on the lower

end of the specified range (i.e. 4 tonne – see section 2.3). However this local observation cannot be

generalized to the whole structure.


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1

2

3

4

5

6

7

8

9

10

11

12

1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

B r e a k w a t e r d a m a g e [ S = E r o d e d

a r e a / D n 5 0 ^ 2 ]

Extreme Water Level [m CD] - Determines breaking wave height

4-tonne armour stone



Failure (underlayer exposed) [S=8]

Intermediate damage [S=4]

Initial damage [S=2]

Figure 3.1 Maughers Beach Breakwater Damage vs. Extreme Water Level during One Event

3.1.2

Cumulative Damage

Extreme water levels (and therefore near-shore wave heights) with a low return period today will be

very common in a few decades due to SLR. Therefore, the design parameter of return period becomes a

moving target and the common engineering practice of designing for the N-year storm and expecting a

given probability of occurrence within the design life time is rendered invalid by SLR. CBCL Limited has

developed statistical analysis tools for coastal design that account for gradual SLR, and applied them to

the isthmus breakwater. The following analysis is based on the Van Der Meer approach to calculating

cumulative breakwater damage in shallow water after a series of storms (CIRIA 2007). Inputs include the

90-year time-series of extreme water levels corrected for future SLR. It is assumed that at the peak of

each storm maximum breaking waves are depth limited using a standard depth/wave height coefficient

of 0.8.

The evolution of damage level S in time is shown on Figure 3.2. The top panel shows the hypothetical

example of a new, undamaged, breakwater of 4t, 5t, and 6t armour stone, respectively. The equations

predict that without SLR damage would be significantly lower and 5t and 6t armour stone would protect

the structure for the next 100 years. However with SLR, damage will develop at a faster rate.

The existing damage level at the breakwater is not uniform, ranging from minimal damage near the ends

(S=2) to failure near the middle (S=8). The cumulative damage value over time will vary with the existing

(i.e. initial) damage along the structure. Based on an assumed damage level of at least 4 averaged over

the existing structure (bottom graph), complete failure (S=8) is expected within less than 50 years in

areas where 4 tonne is the prevailing stone weight.


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0

2

4

6

8

10

2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

C u m u l a t i v e D a m a g e [ S = A_

e r o

d e d

/ D n 5 0 ^ 2

]

Damage development at new breakwater (S_2013 = 0)

4-tonne armour stone, with SLR

4-tonne armour stone, no SLR





4

6

8

10

2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

C u m u l a t i v e D a m a g e

Years from present

Likely damage development at existing breakwater without repairs (assumed S_2013=4)



Figure 3.2 Breakwater Damage Development

3.1.3 Hypothetical Damage Evolution

The wave climate in the lee of the breakwater may change with progressing deterioration of the

isthmus. Modeling scenarios below were developed assuming that the shore protection along the

isthmus is left to deteriorate without maintenance, while the armour stone along the lighthouse islet is

properly maintained (Figure 3.3). The time frame for scenario 1 – loss of shore protection – is based on

the damage analyses presented above. The next stages, beyond a few decades, would likely include a

breach through the isthmus (scenario 2) gradually developing into a submerged bar (scenario 3). In

addition, in order to differentiate between the impacts of isthmus erosion and SLR on its own, a fourth

scenario was modeled assuming complete breakwater repair (no overwash) and a 1.0 m SLR.

Time frames for scenarios 2 and 3 were assigned based on judgment in order to use a corresponding SLR

estimate, because there are no numerical models that can reliably predict long-term geomorphologic

changes in seabeds of very coarse material. Therefore, the results presented here should be considered

an educated guess and their use limited to planning-level exercises.


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Existing conditions – Intermediate armour

stone failureArmour stone crest elevation along the isthmus

(excluding lighthouse) varies between

4 m and 1.5 m over a 15 m distance (failure

area since Hurricane Juan)

Scenario 1 – Loss of shore protection• Assumed crest elevation = 1.5 m throughout

• Potential time-scale = 10-50 years

• Assumed sea level rise within potential

damage time-scale = 0.3 m

Scenario 2 – Breach• Assumed crest elevation = -0.5 m along 60

m distance

• Potential time-scale = 50-100 years



Scenario 3 – Erosion to gravel bar• Assumed crest elevation = -1.0 m along 120

m distance

• Potential time-scale 100 years +



Figure 3.3 Modeling Scenarios for Isthmus Damage


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3.2 Impacts on Wave Climate in Halifax Harbour

The numerical wave model was used to quantify the wave climate changes in Halifax Harbour that

would be caused by further breakwater deterioration and subsequent isthmus erosion, along SLR

impacts. Existing and future wave agitation were investigated at the key sites including Garrison Pier in

McNabs Cove (the Island’s main access point), Outer Halifax Harbour, Point Pleasant Shoal and Halifax’s

Container Terminals. Both extreme events and operational conditions were investigated.

3.2.1 Extreme Events

Modeled 50-year return wave fields for each of the scenarios are shown on Figure 3.4. Extreme

significant wave heights vs. return period at sites of interest are shown on Figure 3.5. The modeling

exercise indicated that SLR alone will cause a generalized increase in wave heights over time around

McNab’s Island and in Halifax Harbour. It also indicated that further breakwater deterioration causing

subsequent isthmus erosion would add to the SLR impact on wave climate in McNabs Cove but not

elsewhere in the Harbour. While it is not possible to give accurate predictions on time frames, the

modeling results provide qualitative conclusions with associated order-of-magnitude timelines based on

a hypothetically assumed isthmus damage evolution.










assumptions).

3.2.2 Operational Conditions


berthing at Garrison Pier. Wave height occurrence percentages were computed for each site of interest

based on MIKE21 SW model results and offshore statistics. A series of 986 model runs was conducted to

include all combinations of input parameters (wind speed, offshore Hsig, Tp, direction and tidal water

level). Each input condition was assigned a probability based on the offshore wave climate. Results are

shown on Figure 3.6. Each graph presents the frequency of exceedance of wave height thresholds, in

percentage of the time (1% is 3.6 days/year, and 0.01 % is 1 hour per year).

The acceptable wave climate for berthing typically used for DFO Small Craft Harbours (Table 3.1) is

defined by a 0.4 m significant wave height upper limit for 10 to 20 m-long vessels, which would apply to

summer island visitor vessels. ‘Murphy’s on the Water’ is the main passenger boat operator using

Garrison Pier, with vessel sizes ranging from 24 to 65 feet doing approximately 20 trips per year (pers.

comm. Peter Murphy, Murphy’s on the water). Larger boats (‘Harbour Queen’ or ‘Haligonian’) taking big

groups are used 2 to 3 times a season, during good weather.


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Modeling indicated that the acceptable wave height threshold for berthing (0.4 m) at Garrison Pier is

presently exceeded approximately 4 days per year, and would be exceeded on average:


2100)


18 days/year assuming 1.0 m SLR and breakwater left to deteriorate (potentially in year 2100).

The downtime periods typically occur during the winter off-season, therefore not affecting summer

visitor traffic. However impacts on winter shoreline erosion in McNabs Cove would be relevant year-

round.

The increase in wave agitation at other sites in Halifax Harbour will be due almost entirely to SLR. At the

Outer Harbour, Point Pleasant Shoal and Halterm Terminals, the impact of isthmus erosion would be

negligible in the context of SLR.

Finally, it is noted that the Navy once used the McNabs Cove area in the lee of the lighthouse formooring purposes5. Local wave agitation conditions will become worse than they were previously, which

would compromise the viability of this site if it becomes contemplated again for use in the future.

Table 3.1 Operational Wave Agitation Guidelines (DFO Planning Guidelines for Commercial

Fishing Harbours)

Location Vessel Length Threshold HsigFrequency of Occurrence

(developed for year-round fishing harbours)

Service / offloading0 – 10.7 m 0.3 m

1.0-2.5 % = 3.6 to 9 days per year10.7 – 19.8 m 0.4 mMooring basin 0 – 19.8 m 0.5 m

Note: the frequency of occurrence criteria (maximum 9 days per year) developed for year-round fishing

harbours would be too stringent for seasonal tourist operation.

5 UTM Coordinates 457500 E - 4939500 N (Figure 2.1), or 500 m to the Southwest of Garrison Pier. The mooring sites ‘Navy A’

and ‘Navy B’ were indicated on the 1989 edition of CHS Chart #4203, however the current version of the chart (dated year

2000) does not show them.


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Existing

conditions

Loss of shore

protection,

0.3 m SLR

Breach,

0.6 m SLR

Gravel Bar,

1.0 m SLR

Repaired

breakwater

1.0 m SLR

Figure 3.4 Modeled 50-Year Return Wave Heights for Future Scenarios of SLR and Isthmus

Damage


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0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1 10 100

E x t r e m e S i g . W a v e H e i g h t [ m ]

Storm Return Period [years]

Garrison Pier

Existing

Loss of Shore Protection - 0.3m SLR

Breach - 0.6m SLR

Erosion to Gravel Bar - 1.0 m SLR

Repaired Breakwater - 1.0 m SLR

1.61.71.81.92.02.12.22.32.42.52.62.72.8

2.93.0

1 10 100

E x t r e m e S i g . W a v e H e i g h t [ m

]


Point Pleasant Shoal

1.3

1.41.5

1.61.7

1.81.9

2.0

2.12.2

2.32.4

2.52.6

1 10 100

E x t r e m e S i g . W a v e H e i g h t [ m

]


Outer Harbour

1.51.61.71.81.92.02.12.22.32.42.52.62.7

1 10 100

E x t r e m e S i g . W a v e H e i g h t [ m ]


Halterm Terminals

Figure 3.5 Projected Increases in Extreme Wave Heights from Sea Level Rise and Isthmus Erosion


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0.01

0.10

1.00

10.00

100.00

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

E x c e e d e n c e [ % ]

Hsig threshold [m]

Garrison Pier

Existing Conditions

Loss of Shore Protection - 0.3 m SLR

Breach - 0.6 m SLR



0.01

0.10

1.00

10.00

100.00

0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5


Hsig threshold [m]

Outer Harbour

Existing Conditions


Breach - 0.6 m SLR



0.01

0.10

1.00

10.00

100.00

0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5


Hsig threshold [m]

Halterm Terminals

Existing Conditions


Breach - 0.6 m SLR



0.01

0.10

1.00

10.00

100.00

0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7


Hsig threshold [m]

Point Pleasant Shoal

Existing Conditions


Breach - 0.6 m SLR



Figure 3.6 Projected Increases in Wave Agitation from Sea Level Rise and Isthmus Erosion


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CHAPTER 4 SOCIO-ECONOMIC CONSIDERATIONS

4.1 Objectives

As demonstrated, sea level rise (SLR) will cause increased storm wave heights in Halifax Harbour,

particularly in exposed nearshore areas. Further breakwater damage and isthmus erosion at Maughers

Beach would add to the SLR impact in McNabs Cove but not elsewhere in the Outer Harbour where the

impact would be minimal. Sites impacted in McNabs Cove include Garrison Pier, the landing wharf toMcNabs Island Park. Maughers Beach is also one of the most popular day-use areas on McNabs Island

and is a natural attraction for visitors.

This section provides commentary on the socio-economic and cultural value at stake if tourism and

recreational activities in the area were to be affected by SLR and the continuous erosion of the isthmus

at Maughers Beach.

4.2 McNabs and Lawor Islands Provincial Park

4.2.1

Location

McNabs and Lawlor Islands are located at the mouth of the Halifax Harbour. Designated in 2002,

McNabs and Lawlor Islands Provincial Park encompasses 430 hectares of land, 28 of which are owned by

the federal government as part of Parks Canada’s Fort McNabs National Historic Site. The Islands are

home to a multitude of important natural and cultural heritage resources and offer opportunities for

outdoor recreation and interpretation.

4.2.2 Future of the Park

In 2005, the Nova Scotia Department of Natural Resources released a Park Management Plan for the

McNabs and Lawlor Islands Provincial Park, which defines a vision and management plan that is

intended to guide park management decisions until 2030. Five principal management objectives for

McNabs and Lawlor Islands Provincial Park have been adopted. The objectives are:

1. To preserve and protect the Islands’ significant natural and cultural heritage elements and values.

2. To provide opportunities for a variety of high-quality outdoor recreation activities.

3. To provide opportunities for exploration, education, and appreciation of the Islands’ heritage values

through interpretation, information, and outdoor education programs.

4. To have the park play an important role in supporting local, regional, and provincial tourism efforts.


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5.

To provide basic services and facilities to enhance visitor enjoyment of the park.

Park development plans are limited to McNabs Island and are primarily focused on providing facilities

and services that support day-use activities, wherever possible, using already existing facilities. New

facilities ought to be placed in locations with minimal impact on heritage resources, natural landscapes

and views corridors.

Interpretation and education for park visitors will be largely self-directed, facilitated by brochures, on-

site interpretive panels, and publications. Special-event programming will complement individual

interpretation activities. The majority of cultural heritage sites will not be actively managed.

To be implemented in four phases, the Park Management Plan stipulated that the park was going to be

operational three years after the adoption of the plan in 2005, with the Parks and Recreation Division of

the Department of Natural Resources playing the lead role in facilitating the implementation of the plan.

According to the Friends of McNabs Island Society, funding from the Department has been slow in the

first years after implementation6 . However, the society has been successful with fundraising efforts to

fill some of the void, and has started implementing trails, shelters and interpretation panels.

4.3 Provincial Park Amenities Potentially Impacted by Beach Erosion

The Park Management Plan lays out the number of park amenities and facilities which, as a whole will

define the park’s visitor experience. Figure 4.1 depicts the amenities that could potentially be impacted

directly or indirectly by the erosion of Maughers Beach.

Garrison Pier in McNabs Cove is one of two main public access points to the Island, the second being

Range Pier at Wreck Cove. In 2002, major repairs to Garrison Pier were completed and further

enhancements are planned. Garrison Pier is serviced by a number of ferry and charter boat operators

offering drop-off and pick-up as well as group charters.

McNabs cove is a key piece on the development road map for the park and is a dedicated recreation

development zone that is expected to become one of the most used areas on McNabs Island. The main

day-use area will be situated close to Garrison Pier. A visitor services centre providing information,

change rooms, toilets, food and a picnic area will be located to the east of the ferry access point.

Loosing Garrison Pier as the main ferry access and potentially relocating it to a more sheltered location

will shift the centre for visitors’ day use activities as most facilities and services envisioned in the 2005

Management Plan are concentrated in the west central portion of the Island.

6 The Rucksack, page 10.


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Figure 4.1 Park Amenities Potentially Affected (adapted from Figure 4, Management Plan

Development Concept)

4.4 MacNabs Island as a Tourism Product

McNabs Island Provincial Park is part of Nova Scotia’s Provincial Parks system that includes over 300

individual park properties throughout the province. Like its sister parks, McNabs Island Park will, when

fully in operation, be an invaluable tourism resource and its visitors will generate economic benefits

through spending in nearby communities.

The five principal park management objectives for the park all revolve around the protection and

preservation of significant natural and cultural resources for the purpose of making them accessible and

appreciated by visitors. One of the principal objectives particularly emphasizes the Park ’s role “in

supporting local, regional and provincial tourism efforts” 7.

7 Park Management Plan, page 3.


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As a tourism product, McNabs Island Provincial Park needs to offer a satisfying visitor experience. In

order to be successful, the park has to balance several parts of the supply side and match them with the

tourism market demand. While the park has been modestly successful in operating as a local tourism

product, removing critical infrastructure such as access points, beaches or interpretive facilities might

sway the demand-supply equation in a direction where the park loses its attraction as a destination.

4.4.1

Tourism Demand-Supply BalanceCritical to all tourism development and its planning are the many characteristics of visitors’ tourism

demands. All physical development and programs offered in McNabs Island Provincial Park must meet

the interests and needs of travellers. If not, economic rewards may not be obtained and the cultural

landscape of the park may be eroded. Whenever demand and supply are out of balance, planning and

development should be directed toward improving the supply-demand match.

4.4.2 Travel Market

People in the travel market are those who have the interest and ability to travel to McNabs Island

Provincial Park. McNabs Island development is mainly geared towards visitors interested in natural and

cultural heritage, outdoor recreation, and nature-based tourism. Even though the 2005 ManagementPlan anticipates that visitors will be largely drawn from the local area, it is plausible that available

tourism infrastructure on the Island coupled with targeted marketing strategies could increase the

number of other Nova Scotians and out-of-province park users. Conversely, a lack of attractions for

those interested in natural and cultural heritage as well as outdoor recreation will result in lower

visitation.

A 2001 McNabs Island Visitor Survey found that 82% of visitors resided in the Halifax Regional

Municipality. 12% of visitors came from other parts of Nova Scotia, and the remainder from other

Canadian provinces and international origins. By far the most popular activity in which these visitors

were looking to engage was walking and hiking on trails, followed by nature study, camping and

picnicking.

The 2010 Nova Scotia Visitor Exit Survey prepared for the Nova Scotia Department of Economic and

Rural Development and Tourism provides useful information on a tourism market segment currently

underrepresented among McNabs Island visitors. Visitors to Nova Scotia are vital contributors to the

provincial economy where tourism is a $1.8 billion industry that accounts for roughly 32,000 jobs. In

2010, visitors to Nova Scotia spent approximately $98 per person per day during their visit. Total

expenditures were highest among overseas visitors followed by those from Western Canada, and lowest

among visitors from Atlantic Canada.

Like visitors to McNabs Island, many tourists travelling to Nova Scotia (40%) do so to participate in

outdoor activities, most commonly coastal sightseeing, hiking and beach exploring.

4.4.3 Supply Side

As outlined in Section 4.3, several elements of the supply side of McNabs Island tourism equation are

going to be impacted by SLR and the potential erosion of Maughers Beach. The supply side includes all

those programs and land uses that are designed and managed to provide for receiving visitors. In the


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literature, the supply side is typically described as including the five major interdependent components

shown in Figure 4.2.

Figure 4.2 Components of Tourism System Supply Side

Table 4.1 lists all categorized components of the supply side of McNabs Island tourism with those

elements highlighted that are potentially affected by SLR and the Maughers Beach erosion.

Attractions

Transporation

InformationPromotion

Services


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Table 4.1 Categorized Supply Components of McNabs Tourism Product

Attractions Transportation Information Promotion Services

Trail network Garrison Pier Garrison Pier

Interpretation/Information

Kiosk

Park brochure Garrison Pier

Visitor

Services Centre

Maughers

Beach

Recreation Area

Range Pier Fort Ives Interpretation General tourism

literature

Pit toilets

Maughers

Beach

lighthouse

Ives Cove Conrad and Matthew

Lynch Homes Outdoor

Education Centre

Discover

McNabs Island

guidebook

Garbage

collection

Fort Ives Private moorage Wreck Cove Information

Kiosk

Link with

regional

marketing

efforts

Potable water

Wreck Cove

Beach

Picnic areas

Fort McNab

National

Historic Site

Military Road

Campground

Strawberry

Battery

Special events

camping

Fort Hugonin

Conrad and

Matthew Lynch

Homes

Hugonin-Perrin

Estate

Fauna and Flora

4.5 Sea Level Rise and Isthmus Erosion Impacts

As summarized in previous sections, likely impacts from SLR compounded by isthmus erosion in McNabs

Cove include:

Increased wave agitation in McNabs Cove, and

Increased shoreline erosion. Manson (2008) notes that while the breach in the isthmus may

allow increased delivery of sediment to Maughers Beach, in the long term the increase in wave

energy in the area is more likely to cause shoreline erosion than deposition.

Without mitigation, SLR and further deterioration of the shore protection of Maughers Beach isthmus

will impact a relatively well functioning McNabs Island tourism system. Short of influence to alter

market trends, the outlined losses on the supply side of the Island’s tourism equation may need to be

compensated by alternate infrastructure.


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Most supply components would be affected by SLR and the shore protection deterioration. The reduced

availability of Garrison Pier as the main access point to the Island would be primarily felt in the winter

off-season, and its impact would therefore be limited. Also in question would be the viability of tourism

infrastructure located near Garrison Pier along McNabs Cove. The 2005 Management Plan envisions the

cove as the key piece of Island infrastructure development.

4.6

Potential MitigationThere are several potential mitigation measures to address risks from SLR and from the possibility that

the breakwater may be left to deteriorate. Most important would be the investigation into other

potential landing sites for incoming boats from Halifax. A recent study by Dalhousie University

Community Design students presented at the 23rd Annual General Meeting of the Friends of McNabs

Island Society (May 2013), recommended Ives Cove as a short-term, and Timmonds Cove as a long term

alternative landing site to Garrison Pier, regardless of the maintenance strategy for the breakwater.

Both areas were described as accessible by all vessel types. Compounded by the present erosion of

Garrison Road along Maughers Beach, the aforementioned alternative landing sites present more

sustainable and attractive long-term alternatives to Garrison Pier, notwithstanding the future condition

of the breakwater.

Moving the main visitor landing site from the west of the Island to the east, would result in shifting the

centre of overall Island tourism development. The planned McNabs Cove interpretation kiosk and

visitor service centre could be moved and located adjacent to the new access facility. Trail routes would

also have to be realigned to connect a new pier to the Island’s main attractions. The Park could then

promote Maughers Beach and the isthmus as a natural area to educate the public about dynamic

coastal processes.

All of these changes should be well communicated and planned in close collaboration with the Friends

of McNabs Island Society, as many of the Island’s long-term devotees have a strong sentiment for

McNabs Cove as the gateway to the Island.

The impact from SLR on the development of the McNabs Island tourism product was not taken into

consideration in the 2005 Management Plan. SLR and more severe storm events will require the

integration of effective adaptation strategies into an updated Management Plan. A cost-benefit analysis

studying all expenditures and advantages of either a relocation of McNabs Cove tourism infrastructure

or the continuous maintenance of shore protection at the isthmus are recommended to ultimately make

an informed decision on a route forward. Regardless of the option chosen, the shorelines of McNabs

Island Provincial Park will continue to naturally reshape, and the Park’s important role as a local,

regional and provincial tourism asset will remain.


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CHAPTER 5 CONCLUSIONS

Maintaining land access along the armoured isthmus to the Maughers Beach lighthouse (now serviced

by helicopter) is no longer required for operations. Three wave modeling scenarios were examined to

quantify the wave climate changes in Halifax Harbour that would be caused by further breakwater

deterioration and subsequent isthmus erosion, along with Sea Level Rise (SLR) impacts:

(1) Partial loss of Maughers Beach breakwater with overtopping(2) Breakwater deterioration and breach through isthmus


The modeling exercise indicated that SLR alone will cause a generalized increase in wave heights over

time around McNab’s Island and in Halifax Harbour. It also indicated that further breakwater

deterioration causing subsequent isthmus erosion would add to the SLR impact on wave climate in

McNabs Cove but not elsewhere in the Harbour. While it is not possible to give accurate predictions on

time frames, the modeling used provides qualitative conclusions with associated order-of-magnitude

timelines based on a hypothetically assumed isthmus damage evolution.










assumptions).


berthing at Garrison Pier. The acceptable wave climate for berthing typically used for DFO Small Craft

Harbours is defined by a 0.4 m significant wave height upper limit for 10 to 20 m-long vessels, which

would apply to summer island visitor vessels. Modeling indicated that the acceptable wave height


41/51


threshold for berthing (0.4 m) at Garrison Pier is presently exceeded approximately 4 days per year, and

would be exceeded on average:


2100)


18 days/year assuming 1.0 m SLR and breakwater left to deteriorate (potentially in year 2100).

The downtime periods typically occur during the winter off-season, therefore not affecting summervisitor traffic.

Pros and Cons of Maintaining the Isthmus Breakwater

Breakwater should be repaired and maintained

because:

Breakwater should be left to deteriorate

because:

The impact of SLR on wave agitation in McNabs

Cove would not be further exacerbated;

Garrison Pier could remain the main Park access

point with future visitor centre development as

planned (vision in 2005 McNabs IslandManagement Plan) for an additional 30 years;

and

The public could safely access the lighthouse

islet.

Increase in wave agitation due to deterioration is limited

to McNabs Cove and Garrison Pier only (not Halifax

Harbour), and would primarily affect winter off-season;

Increase in wave impacts due to SLR is inevitable around

the island. Breakwater maintenance would only delaythe process for a limited time and area;

Capital and ongoing maintenance expenses are

significant;

Alternative landing sites on the Island are suitable SLR

adaptation options (Ives Cove, Timmonds Cove); and

The isthmus area offers an opportunity to educate Island

visitors on coastal processes.

Based on the modeling results, we offer the following conclusions:

The deterioration of the breakwater and the resulting erosion will not impact the islet on whichthe lighthouse is located and therefore will not impact departmental operations.

The deterioration of the breakwater and the resulting erosion is expected to cause a relatively

low impact on the local wave climate and in the worst case scenario will only moderately delay

the impact of sea level rise.

Prepared by: Reviewed by:

Vincent Leys Alexander Wilson

Coastal Engineer Water Resources Engineer

This document was prepared for the party indicated herein. The material and information in the document reflects CBCL

Limited’s opinion and best judgment based on the information available at the time of preparation. Any use of this document

or reliance on its content by third parties is the responsibility of the third party. CBCL Limited accepts no responsibility for any

damages suffered as a result of third

Documents

Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakwater, McNabs Island