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

Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakw Bre akwater ater McN McNabs abs Isl Island and

141019.00 ISO 9001 Registered Company

Prepared for:

●

Final Report

●

July 2014

Prepared by:

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 3Z8 tel: (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 Final Report

1489 Hollis Street

Canada B3J 2R7

We are pleased to submit our final report assessing wave agitation risks in Halifax Harbour related 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.

Telephone: Tele phone: 902 421 7241 7241

We appreciate your consideration of our services for this very interesting project, and we look forward to working with you again.

PO Box 606 Halifax, Nova Scotia

Fax: 902 423 3938 E-mail: [email protected]

Yours very truly,

www.cbcl.ca

CBCL Limited

ISO 9001

Vincent Leys, M.Sc., P.Eng. Coastal Engineer Direct: (902) 421-7241, Ext. 2508 E-Mail: [email protected]

Registered Company

Project No: 141019.00

141019 MBEACH 2014 REVISIONS

FINAL.DOCX /VL

ED: 17/07/2014 13:27:00/PD: 17/07/2014 13:27:00

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

2.5

2.6

2.4.1

Tides ................................... .................. ................................... ................................... ................................... ................................... ................................ ............... 6

2.4.2

Historical Historica l Water Levels .................................... .................. ................................... .................................. ................................... ..................... ... 8

2.4.3

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

2.4.4

Impact of Sea LLevel evel Rise on Extreme Event Frequency ................................. ............... ........................... ......... 9

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

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

3.2

3.1.1

Damage Caused by Individual Storms ................................. ............... ................................... ................................. ................ 17

3.1.2

Cumulative Damage ................................... ................. ................................... .................................. ................................... ......................... ....... 18

3.1.3

Hypothetical Hypothetica l Damage Evolution Evolutio n ................................. ................ .................................. ................................... ......................... ....... 19

Impacts on Wave Climate in Halifax Harbour .................................. ................ ................................... ................................. ................ 21 3.2.1

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

3.2.2

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

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Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakwater i

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 Demand-Suppl y 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 B

Statistics on Offshore Wind and Wave Climate (44.5N-63.4W) and Water Levels Map of McNabs Island

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Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakwater ii

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 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 deteriorating due to wave attack and overtopping. overtopping. The lighthouse is now serviced by helicopter; therefore 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 deterioration on the surrounding geography, including the impact on operations for all stakeholders. stakeholders. A numerical wave model was used to quantify the wave climate changes in Halifax Harbour that would be caused by further breakwater deterioration 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. 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 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 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 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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Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakwater i

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 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 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

Breakwater should be left to deteriorate

because:

because:

The impact of SLR on wave agitation in McNabs

Increase in wave agitation due to deterioration is limited

Cove would not be further exacerbated;

to McNabs Cove and Garrison Pier only (not Halifax

Garrison Pier could remain the main Park access

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

point with future visitor centre development as



Increase in wave impacts due to SLR is inevitable around

planned (vision in 2005 McNabs Island

the island. Breakwater maintenance would only delay

Management Plan) for an additional 30 years;

the process for a limited time and area;

and 





The public could safely access the lighthouse islet.

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 climate and in the worst case scenario scenario will only moderately moderately delay the impact of sea level rise.

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Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakwater ii

CHAPTER 1

1.1

INTRODUCTION

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 Beach to 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 o perations for all stakeholders.

1.2

Objectives

The 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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Halifax Harbour Wave Agitation Risk Study at Maughers Beach Breakwater 1

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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 20 th 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: investigations: Site visit; Water level analyses; Offshore wind and wave climate; and Development Development of a nearshore wave transformation 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 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. 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 deterioration and isthmus eroded down to a submerged bar 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, nature, and does not stand as a detailed impact assessment. assessment. Conclusions are presented in Chapter 5.

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CHAPTER 2

2.1

COASTAL SITE CHARACTERIZATION

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 Beach Isthmus 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 deemed representative representative 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 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 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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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

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

Tidal Elevations as published by CHS

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 10year trends over the last 30 years have progressively accelerated.

1.15 1.1

Annual means 92-year 92-year trend 10-year 10-year trends

] 1.05 D C 1 m [ l e v e 0.95 l a e s n 0.9 a e M

0.85

0.8 0.75 1920

1930

Figure 2.4

1940

1950

1960

1970

1980

1990

2000

2010

2020

Historical Mean Sea Level in Halifax Harbour

Storm surge is due to meteorological meteorological effects on sea level, such as wind set-up 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 stationary 2. 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 accelerating in the 21 st 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 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; 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 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 oc curring 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 i n time. Statistical properties such as mean and variance must remain co nstant in time and not follow trends.

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High

2 y r u t n 1.8 e c - / 1.6 ) m m 7 5 1.4 ( 1 . e s 0 i f r l o 1.2 e e v c e n 1 l e a d e i s s 0.8 e b v u i t s 0.6 a d l e n a R l s 0.4 e d u 0.2 l c n I 0 2010

Figure 2.5

Intermediate (used for assessment) Low

2030

2050

2070

2090

211 0

Sea Level Rise Projections Used in the Present Study

100 WL = 3.1 m CD

] s r a e y [ d o i r e p 10 n u r t e R

WL = 2.9 m CD (Hurricane Juan) WL = 2.7 m CD

1 2010

Figure 2.6

2.5

2020

2030

2040

2050

2060

2070

2080

2090

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

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 (grid point 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). 



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Detailed comparisons revealed 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 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 ‘r oses’, 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 Associated

Return Period

Significant Wave Height

Peak Period

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 12. 8

27.8

100

100

11.2

13.1

31.2

112

Wind Speed

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 o ver 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 fiel d 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 was used 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 transformations and harbour investigations. investigations. The model simulates the following physical phenomena: Refraction and shoaling due to depth variations; Dissipation due to depth-induced depth-induced wave breaking; Dissipation due to bottom friction (a typical bottom roughness of 0.04m was used); Dissipation due to white-capping; white-capping; Non-linear wave-wave interaction; One-time reflection from vertical walls; however the model cannot simulate wave agitation due to multiple 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 o f 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. co nditions. Model Confidence Interval

The offshore wave conditions and the bathymetry are known with very good accuracy. However there are no site-specific measurements measurements to validate the t he 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. 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

Wave buoy and MSC50 data, 44.5N-63.4W

Point Pleasant Shoal

Outer Harbour

Garrison Pier

Maugher Maugherss Beach breakwater

Model output locations

Figure 2.7

MIKE21 Wave Model Domain

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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 the influence 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 o f energy refracts around the lighthouse islet into McNabs Cove.

1-year storm

Figure 2.8

100-year storm

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 is transported 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.

1-year return storm

Figure 2.9

100-year return storm

Nearshore Currents during Extreme Storm Conditions

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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 with the 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

3.1

WAVE CLIMATE CHANGES DUE TO ISTHMUS EROSION AND SEA LEVEL RISE

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 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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4-tonne armour stone 5-tonne armour stone

12 ] 2 ^ 11 0 5 n 10 D / a e r 9 a d 8 e d o r 7 E = S [ 6 e g a m 5 a d r 4 e t a w 3 k a e 2 r B 1

6-tonne armour stone Failure (underlayer exposed) [S=8] Intermediate damage [S=4] Initial damage [S=2]

1.8

2

2.2

2. 4

2.6

2.8

3

3. 2

3.4

3.6

3.8

4

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

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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Damage development at new breakwater (S_2013 = 0) 10 ] 2 ^ 0 5 n D / d e d o r e _ A = S [

8

6 4-tonne armour stone, with SLR

e g a 4 m a D e v i t a l u 2 m u C 0 2010

4-tonne armour stone, no SLR 5-tonne armour stone, with SLR 5-tonne armour stone, no SLR 6-tonne armour stone, with SLR 6-tonne armour stone, no SLR 2020

2030

2040

2050

2060

2070

2080

2090

2100

Likely damage development development at existing breakwater breakwater without repairs (assumed S_2013=4) 10

e g a m 8 a D e v i t a l u 6 m u C 4 2010

4-tonne armour stone, with SLR 5-tonne armour stone, with SLR

2020

2030

2040

2050

2060

2070

2080

2090

2100

Years from present

Figure 3.2

Breakwater Damage Development 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 differentiate between the impacts of isthmus erosion and SLR on its own, a fourth scenario was modeled assuming complete breakwater 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 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 failure Armour 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 elevation = 1.5 m throughout throughout Potential time-scale = 10-50 years years Assumed sea level rise within potential damage time-scale time-scale = 0.3 m

Scenario 2 – Breach •

• •

Assumed crest elevation elevation = -0.5 m along 60 m distance Potential time-scale = 50-100 50-100 years Assumed sea level rise within potential damage time-scale time-scale = 0.6 m

Scenario 3 – Erosion to gravel bar •

• •

Figure 3.3

Assumed crest elevation elevation = -1.0 m along 120 m distance Potential time-scale 100 years + Assumed sea level rise within potential damage time-scale time-scale = 1.0 m

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 operationa l 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 generalized increase in wave heights over time around McNab’s Island and in Halifax Harbour. It also indicated 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. 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. 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 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). 3.2.2 Operational Conditions

The frequency of smaller wave events was also examined, which is relevant for visitor boat traffic and 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). L arger 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 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. However impacts on winter shoreline erosion in McNabs Cove would be relevant yearround. 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 for mooring 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

Service / offloading Mooring basin

Vessel Length

Threshold Hsig

0 – 10.7 m

0.3 m

10.7 – 19.8 m

0.4 m

0 – 19.8 m

0.5 m

Frequency of Occurrence (developed for year-round fishing harbours)

1.0-2.5 % = 3.6 to 9 days per year

Note: the frequency of occurrence criteria (maximum 9 days per year) developed for year-round fishing harbours would be too stringent 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

Breach, 0.6 m SLR

Loss of shore protection, 0.3 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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Garrison Pier 1.4 1.3 ] m1.2 [ t h 1.1 g i e H1.0 e v a 0.9 W . g i S 0.8 e m0.7 e r t x E 0.6

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

0.5 0.4 1

10

1 00

Storm Return Period [years]


Outer Harbour

3.0 ] 2.9 m2.8 [ t h 2.7 g 2.6 i e H2.5 e 2.4 v a 2.3 W . 2.2 g i S 2.1 e 2.0 m e 1.9 r t x 1.8 E 1.7 1.6

2.6 ] 2.5 m2.4 [ t h 2.3 g i e 2.2 H e 2.1 v 2.0 a W1.9 . g 1.8 i S e 1.7 m1.6 e r t 1.5 x E 1.4 1.3 1

10 Storm Return Period [years]

10 0

1


10 0

Halterm Terminals ] 2.7 m2.6 [ t 2.5 h 2.4 g i e 2.3 H e 2.2 v a 2.1 W2.0 . g 1.9 i S e 1.8 m1.7 e r t 1.6 x E 1.5 1

Figure 3.5


100

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

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Garrison Pier

Outer Harbour

100.00

100.00

Existing Conditions

Existing Conditions

Loss of Shore Protection - 0.3 m SLR


Breach - 0.6 m SLR

Breach - 0.6 m SLR Erosion to Gravel Bar - 1.0 m SLR

Erosion to Gravel Bar - 1.0 m SLR 10.00

Repaired Breakwater - 1.0 m SLR

10.00

] % [ e c n e d e 1.00 e c x E

] % [ e c n e d e 1.00 e c x E

0.10

0.10

0.01


0.01 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.1

0.3

0.5

Hsig threshold [m]

0.7

0.9

1.1

1.3

1.5

Hsig threshold [m]


Halterm Terminals

100.00

100.00

Existing Conditions

Existing Conditions



Breach - 0.6 m SLR

Breach - 0.6 m SLR




] % [ e c n e d e 1.00 e c x E

] % [ e c n e d e 1.00 e c x E

0.10

0.10

0.01


0.01 0.1

0.3

0.5

0.7

0.9

1.1

1.3

1.5

1.7

0.1

0.3

0.5

Hsig threshold [m]

Figure 3.6

0.7

0.9

1.1

1.3

1.5

Hsig threshold [m]

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

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CHAPTER 4

4.1

SOCIO-ECONOMIC CONSIDERATIONS

Objectives

As demonstrated, sea level rise (SLR) will cause increased storm wave heights in Halifax Harbour, particularly in exposed nearshore areas. Further breakwater 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 to McNabs 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 o wned 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. 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 I slands’ significant natural and cultur al heritage elements and values. 2. To provide opportunit o pportunities ies for a variety of high-quality outdoor recreation activities. 3. To provide opportunities for exploration, education, 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 Interpretation and education for park visitors will be largely self-directed, facilitated facilitated by brochures, brochures, onsite interpretive panels, and publications. Special-event Special-event programming will complement 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 implementing trails, shelters and interpretation 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 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

4.4

Park Amenities Potentially Affected (adapted from Figure 4, Management Plan Development Concept)

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 7 supporting local, regional and provincial tourism efforts” . 7

Park Management Plan, page 3.

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As a tourism product, McNabs 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 Balance

Critical to all tourism development and its planning are the ma ny 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 Management Plan 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 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 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. 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.

Attractions

Transporation

Services

Promotion

Figure 4.2

Information

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.

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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

Sea Level Rise and Isthmus Erosion Impacts

4.5

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 outlined losses on the supply side of the I sland’s tourism equation may need to be compensated by alternate infrastructure. 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 o f tourism infrastructure infrastructure located near Garrison Pier along McNabs Cove. The 2005 Management Plan envisions the cove as the key piece of Island infrastructure infrastructure development.

4.6

Potential Mitigation

There are several potential mitigation measures to address risks from SLR and from the possibility that the breakwater may be left to deteriorate. deteriorate. Most important would be the investigation investigation into other potential landing sites for incoming boats from Halifax. A recent study by Dalhousie University Community Design students presented at the 23 rd 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. development. The planned McNabs Cove interpretation 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 I sland’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 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 breakwater deterioration 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 (3) Full breakwater deterioration 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 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 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. 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 m -long vessels, which would apply to summer island visitor vessels. Modeling indicated indicated that the acceptable wave height

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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

Breakwater should be left to deteriorate

because:

because:

The impact of SLR on wave agitation in McNabs

Increase in wave agitation due to deterioration is limited

Cove would not be further exacerbated;

to McNabs Cove and Garrison Pier only (not Halifax

Garrison Pier could remain the main Park access

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

point with future visitor centre development as



Increase in wave impacts due to SLR is inevitable around

planned (vision in 2005 McNabs Island

the island. Breakwater maintenance would only delay

Management Plan) for an additional 30 years;

the process for a limited time and area;

and 





The public could safely access the lighthouse islet.

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.

Prepared by: Vincent Leys Coastal Engineer

Reviewed by: Alexander Wilson Water Resources Engineer

This document was prepared prepared for the party indicated herein. The material and information 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 party use of this document.

CBCL Limited


CHAPTER 6

REFERENCES

CIRIA, CUR, CETMEF 2007. The Rock Manual. The use of rock in hydraulic engineering (2 nd edition). C683, CIRIA, London. Daigle R., Richards W. 2011. Scenarios and guidance for adaptation to climate change and sea level rise – NS and PEI municipalities. Report commissioned by the Atlantic Climate Solutions Association. www.atlanticadaptation.ca DHI Software 2012. MIKE, Coastal Hydraulics and Oceanography Oceanography – User Guide. Danish Hydraulic Institute. Forbes D., Manson G., Charles J., Thompson K., Taylor R. 2009. Halifax Harbour Extreme Water Levels in the Context of Climate Change: Scenarios for a 100-year Planning Horizon. Geological Survey of Canada Open File 6346. Gunn C. and Var T. 2002. Tourism Planning: Basics, Concepts, Cases. Routledge. ISBN-10: 0415932688. IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. http://www.climatechange2013.org/images/report/WG1AR5_SPM_FINAL.pdf Manson G. 1999. Recent and Historical Coastal Change Under Rising Sea Level, McNabs Island Area, Halifax NS. Submitted in partial fulfillment of the degree of Master of Science, Dalhousie University. Manson G. 2008. McNabs Island Geology and Coastal Processes. In: Discover McNabs Island, Second Edition. ISBN 978-0-9699518-2-7. McCarthy, C. 2001. McNabs Island Visitor Survey Final Report. Information Series PKS 2005-1. McCarthy, C. 2009. Trail Rebuilding on McNabs Island Continues. The Rucksack, volume seventeen, Issue 4, Fall/Winter 2009 – 2010, page 10. Nova Scotia Department of Economic and Rural Development and Tourism. 2011. 2010 Nova Scotia Visitor Exit Survey.

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Nova Scotia Department of Natural Resources. 2005. Park Management Plan Mcnabs And Lawlor Islands Provincial Park. Information Series PKS 2005-1. Public Works and Government Services Canada, 2007. Preliminary Design Report-Capital Restoration and Repair of Maughers Beach Protection Works, McNabs Island, Halifax Regional Municiplaity. P/N 325016. Prepared for DFO Waterways Program Rahmstorf, S. 2007. A semi-empirical approach to projecting future sea-level rise. Science, 315(5810), 368-370. Sallenger, A. H., K. S. Doran, and P. A. Howd, 2012: Hotspot of accelerated sea-level rise on the Atlantic coast of North America. Nature Climate Change, Advanced on line publication. Swail V.R, Cardone V.J., Ferguson M., Gummer D.J., Harris E.L., Orelup E.A. and Cox A.T. 2006. The MSC50 Wind And Wave Reanalysis. 9th International Workshop On Wave Hindcasting and Forecasting September 25-29, 2006 Victoria, B.C. Canada. Available from www.oceanweather.com (accessed 30 October 2007). Tourism Industry Association of Nova Scotia. 2011. Tourism Plan. U.S. Army Corps of Engineers (USACE). 2006. Coastal Engineering Manual. Engineer Manual 1110-21100. U.S. Army Corps of Engineers (USACE). 2011. Sea Level Changes Considerations for Civil Works Programs. Circular No. 1165-2-212, 1 Oct 2011. Washington, DC 20314-1000.

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APPENDIX A

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

Figure A.1 Annual Directional Frequencies of Wind Speed Note: Calm represents all occurrences of wind speed < 1 m/s

Figure A.2 Annual Directional Frequencies of Significant Wave Heights Note: Calm represents all occurrences of Hsig < 0.5 m

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Figure A.2 Monthly Directional Frequencies of Wind Speed Note: Calm represents all occurrences of wind speed < 1 m/s

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Figure A.3 Monthly Directional Frequencies of Significant Wave Heights Note: Calm represents all occurrences of Hsig < 0.5 m

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Table A.1

Frequency of Exceedance for Hourly Wind Speed by Direction Values given in % of time, 1% = 3.6 days / year

Wind speed m/s 30 25 20 15 10 5 0

Direction from

km/hr 108 90 72 54 36 18 0

0 0 0 0 ..0 00 01 15 0 ..1 13 32 23 0 .9 .9 83 83 9 3 ..5 56 61 18 4 ..9 98 82 21

Table A.2

22. 5 0 0.0002 0 ..0 00 07 77 0 ..1 10 00 00 0 .8 .8 09 09 1 2 ..9 96 69 91 4 ..2 27 70 09

45 0 0 0 .0 .0 1 11 12 0 .0 .0 9 91 13 0 .6 .6 35 35 8 2 .5 .5 0 02 22 3 .6 .6 9 98 85

67.5 0 0 0.0 0 04 42 0.1 1 15 52 0 .5 .5 38 38 1 2.1 5 57 74 3 .3 .3 7 76 67

90 0 0 0.0 0 02 29 0.0 7 72 26 0 .4 .4 96 96 5 1.8 1 12 21 3 .0 .0 4 47 76

112.5 0 0.0002 0 .0 .0 0 01 18 0 .0 .0 6 63 34 0 .4 .4 50 50 4 1 ..8 86 61 19 3 .3 .3 7 73 30

135 0 0.0002 0 .0 .0 0 02 20 0 .0 .0 6 66 65 0 .5 .5 06 06 5 2 ..1 10 01 17 3 .6 .6 6 62 25

157. 5 0 0.0004 0 .0 .0 0 02 20 0 .0 .0 6 64 43 0 .5 .5 18 18 0 2 ..2 28 86 61 4 .0 .0 4 48 82

202. 5 0 0.0004 0 .0 .0 0 03 31 0 .0 .0 5 55 59 0 .8 .8 40 40 0 5 ..3 30 02 20 8 .4 .4 8 82 25

225 0 0 0.0 0 03 35 0.0 7 78 83 1 .1 .1 04 04 4 6.8 5 57 71 10 10 ..6 64 43 38

247.5 0 0 0 ..0 00 06 64 0 ..1 15 53 31 1 .3 .3 12 12 8 6 ..2 26 68 83 9 ..5 55 58 81

270

292.5

Total exceedence % 0 0 0 0.0018 0 ..0 00 01 18 0 ..0 06 63 30 0 ..1 15 53 33 2 ..1 14 47 79 1 .3 .3 29 29 9 1 8. 8.1 46 46 4 4 ..6 64 41 14 67 7..5 3 36 67 6 ..3 32 22 27 10 00 0

315

337. 5

0

0

0

0

0 0

0 ..0 00 03 35

0 ..0 00 03 37

0 .0 .0 0 06 61

0 ..3 30 02 27

0 ..4 40 03 37

0 .2 .2 2 20 07

2 .1 .1 98 98 6

3 .3 .3 67 67 0

2 .3 .3 43 43 6

6 ..6 61 14 49

8 ..3 32 23 35

6 .6 .6 8 89 93

9 ..2 29 98 86 1 0 0..59 8 82 2

8 .5 .5 8 85 54

Frequency of Exceedance for Significant Wave Height by Direction

Hsig m 11 10.5 10 9.5 9 8.5 8 7.5 7 6.5 6 5.5 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0

180 0 0.0002 0 .0 .0 0 01 18 0 .0 .0 7 74 46 0 .7 .7 11 11 9 3 ..5 58 87 79 6 .0 .0 5 51 11

Direction from

ft 36.1 34.4 32.8 31.2 29.5 27.9 26.2 24.6 23.0 21.3 19 19.7 18.0 16 16.4 14.8 1 3.1 11.5 9.8 8.2 6.6 4.9 3.3 1.6 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.001 0.003 0.018 0.124 0.768 1.363 1.377

Table A.3

22.5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.001 0.009 0.034 0.153 0.706 1.317 1.334

45 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00 1 0.01 4 0.06 8 0.27 8 0.95 0 1.57 4 1.60 1

67.5 0 0 0 0 0 0 0 0 0 0 0 0 0 0.001 0.002 0. 0.006 0.026 0.091 0.227 0.668 1.587 2.195 2.243

90 0 0 0 0 0 0 0 0 0 0.000 0.002 0.005 0.009 0.017 0.038 0. 0.072 0.158 0.394 0.900 1.679 2.707 3.628 3.725

112.5 0 0 0 0 0 0 0 0.000 0.002 0.007 0.014 0.032 0.059 0.124 0.222 0. 0.386 0.668 1.110 1.900 3.133 4.889 6.737 7.112

135 0 0 0 0 0 0 0 0.0 01 0.0 06 0.0 11 0.0 21 0.0 39 0.0 81 0.1 44 0.2 27 0. 0.3 98 0.6 93 1.2 20 2.2 14 4.0 25 7.1 58 1 0. 0.18 8 10 10.72 2

157.5 0 0.0002 0.001 0.001 0.001 0.001 0.002 0.004 0.006 0.010 0.020 0.035 0.076 0.154 0.295 0. 0.506 0.831 1.357 2.382 4.224 7.577 12 1 2.062 12 12.584

180 0 0 0 0 0 0.000 0.003 0.005 0.007 0.010 0.016 0.033 0.070 0.140 0.283 0. 0.526 0.948 1.685 2.972 5.378 10 10.456 17 1 7.575 18 18.244

202.5 0 0 0 0 0 0 0 .001 0 .002 0 .003 0 .006 0 .013 0 .025 0 .052 0 .089 0 .192 0. 0.393 0 .822 1 .552 3 .087 6 .138 13 13.248 21 2 1.757 22 22.323

225 0 0 0 0 0 0 0 0 0 0 0 0 0 0.002 0.019 0.078 0.223 0.551 1.431 3.466 7.102 9.676 9.815

247.5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.000 0.013 0.102 0.342 0.933 1.915 2.689 2.744

270 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.000 0.016 0.126 0.480 1.115 1.577 1.601

292.5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.006 0.069 0.387 1.065 1.446 1.461

315 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0 02 0.0 33 0.3 02 1.1 02 1.4 89 1.5 01

Total exceedence % 0 0 0 0.0002 0 0.001 0 0.001 0 0.001 0 0.001 0 0.005 0 0.012 0 0.023 0 0.043 0 0.087 0 0.169 0 0.347 0 0.672 0 1.277 0 2.366 0 4.386 0.003 8.116 0.025 15.828 0.234 31.602 0.991 63.337 1.452 96.725 1.465 99.853

337.5

Significant Wave Height and Peak Period Joint Probability of Occurrence

H s ig m

ft

0-2

2 -4

4 -6

6 -8

Peak period [s] 8-10 10-12

12-14

14-16

Total occurence

16-18

11

36.1

0

0

0

0

0

0

0

0

0

0

10.5

34.4

0

0

0

0

0

0

0

0.0002

0

0.0002

10

32.8

0

0

0

0

0

0

0.0002

0.0002

0

0.0004

9.5

31.2

0

0

0

0

0

0

0

0

0

0

9

29.5

0

0

0

0

0

0

0

0

0

0

8.5

27.9

0

0

0

0

0

0

0.0004

0

0

0.0004

8

26.2

0

0

0

0

0

0

0.0013

0.0029

0

0.0042

7.5

24.6

0

0

0

0

0

0.0007

0.0053

0

0.0004

0.0064

7

23.0

0

0

0

0

0

0.0029

0.0079

0.0007

0.0002

0.0116

6.5

21.3

0

0

0

0

0

0.0081

0.0092

0.0026

0.0002

0.0202

6

19.7

0

0

0

0

0

0.0200

0.0213

0.0018

0.0002

0.0432

5.5

18.0

0

0

0

0

0. 0.0029

0. 0.0432

0. 0.0340

0. 0.0020

0. 0.0002

0. 0.0823

5

16.4

0

0

0

0

0.0176

0.1132

0.0467

0.0011

0

0.1786

4.5

14.8

0

0

0

0

0.0794

0.1753

0.0630

0.0079

0

0.3256

4

13.1

0

0

0

0.0004

0.2025

0.2973

0.0992

0.0070

0

0.6064

3.5

11.5

0

0

0

0.0070

0.4363

0.4769

0.1487

0.0180

0.0011

1.0881

3

9.8

0

0

0.0002

0.1450

0.8135

0.8143

0.2192

0.0303

0.0011

2.0236

2.5

8.2

0

0

0.0408

0.6836

1.3387

1.3770

0.2442

0.0522

0.0004

3.7369

2

6.6

0

0

0.3754

2.1585

2.5838

2.2260

0.3027

0.0700

0.0031

7.7195

1.5

4.9

0

0.0156

2.7679

4.4481

5.0093

3.0257

0.4094

0.1150

0.0066

15.7975

1

3.3

0

1.2671

8.5536

8.7469

9.3315

3.1457

0.5094

0.2034

0.0110

31.7685

0.5

1.6

0

0

Total occurence %

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0

3.8104

4.7904

13 13.6647

7.8794

2.1126

0.7204

0.3475

0.0204

33 33.3458

0.1474

0.2534

0.2565

0.8192

1.2542

0.3060

0.1174

0.0759

0.0107

3.2407

0 ..1 1 47 47 4

5 ..3 3 46 46 5

1 6. 6.7 84 847

3 0. 0.6 73 73 4

2 8. 8.9 49 49 0

1 4. 4.1 44 44 9

2 ..9 9 59 59 9

0 ..9 9 38 38 5

0 ..0 0 55 55 7 1 00 00 ..0 0 00 00 0


Table A.4

Offshore Hsig m ft

Significant Wave Height and Tide Gauge Water Level Joint Probability of Occurrence Values given in % of time, 1% = 3.6 days / year < 0.25

0 . 2 5 -0 . 5

0 .5-0.7 5

0. 75-1.0

Water Level from Halifax Tide Gauge [m CD] 1.0 -1.25 1.25 -1.5 1.5-1. 75 1 .75-2. 0 2.0 -2.25

2.25 -2.5

2.5-2 .75

Total occurence

> 2.75

11

36.1

0

0

0

0

0

0

0

0

0

0

0

0

0

10.5

34.4

0

0

0

0

0

0

0

0

0.0003

0

0

0

0.0003 0.0003

10

32.8

0

0

0

0

0

0

0.0003

0

0

0

0

0

9.5

31.2

0

0

0

0

0

0

0

0

0.0003

0

0

0

0.0003

9

29.5

0

0

0

0

0

0

0

0

0.0003

0

0

0.0003

0.0006

8.5

27 27.9

0

0

0

0

0.0003

0

0.0012

0.0006

0.0003

0

0.0003

0

0.0027

8

26.2

0

0

0.001

0.001

0. 0.0003

0.002

0. 0.0006

0. 0.0006

0. 0.0003

0

0

0

0. 0.0049

7.5

24.6

0

0.001

0.001

0

0.001

0.0015

0.0015

0.001

0.0009

0.0006

0.0006

0

0.0082

7

23.0

0

0

0.001

0.001

0

0.0012

0.0021

0.0012

0.0012

0.0009

0.0006

0.0003

0.0134

6.5

21.3

0.001

0.001

0.00

0.003

0

0.0046

0.0046

0.0036

0.0021

0.0015

0.0003

0

0.0273

6

19.7

0.001

0.002

0.01

0.007

0

0.0058

0.0027

0.0055

0.0036

0.0015

0.0000

0

0.0416

5.5

18.0

0.003

0.005

0.01

0.012

0.0161

0.0155

0.0112

0.0109

0.0079

0.0015

0.0003

0

0.0954

5

16.4

0.005

0.009

0.02

0.028

0. 0.0261

0. 0.0246

0. 0.0322

0. 0.0264

0

0

0

0

0. 0.1875

4.5

14.8

0.006

0.015

0.04

0.050

0. 0.0595

0. 0.0504

0. 0.0568

0. 0.0389

0

0

0

0

0. 0 .3394

4

13.1

0.015

0.043

0.08

0.1082

0.0896

0.0835

0.0990

0.0647

0

0

0

0.0003

0.6253

3.5

11.5

0.033

0.093

0.15

0.1780

0.1622

0.1698

0.1774

0.1164

0.0352

0.0052

0.0012

0

1.1208

3

9.8

0.073

0.180

0.3187

0.3333

0.2825

0.3302

0.3154

0.1999

0.0620

0.0070

0.0003

0

2.1027

2.5

8.2

0.142

0.369

0.6146

0.6158

0.5390

0.5833

0.5733

0.3163

0.0674

0.0088

0

0

3.8293

2

6.6

0.327

0.878

1.2754

1.2137

1.1062

1.2046

1.1663

0.5350

0.1088

0.0067

0.0006

0

7.8223

1.5

4.9

0.816

2.0505

2.6502

2.3373

2.2452

2.5666

2.2546

0.8720

0.1240

0.0039

0

0

15 15.9202

1

3.3

1.771

4.3573

5.3526

4.4989

4.3856

5.1968

4.3096

1.3167

0.1270

0.0070

0

0

31.3222

0.5

1.6

2.136

4.9294

5.6580

4.7146

4.6545

5.6482

4.3953

1.0913

0.0826

0.0012

0

0

33 33.3116

0

0

0.2048

0.4846

0.5256

0.4241

0.4466

0.5241

0.3661

0.1063

0.0055

0

0

0

3.0877

5 .5 .5 33 33 7

1 3. 3.4 18 18 0

1 6. 6.7 14 14 7

1 4. 4.5 25 25 4

1 4. 4.0 29 29 3

1 6. 6.4 12 12 4

1 3. 3.7 70 70 4

4 .7 .7 07 07 0

0 .6 .6 92 92 7

0 .0 .0 54 54 7

0 .0 .0 04 04 6

0 .0 .0 00 00 9

9 9. 9.8 63 63 9

Total occurence %

Table A.5

Significant Wave Height and Wind Speed Joint Probability of Occurrence

O ffshore Hsig m ft

0-5

Wind Spee d [ m/s] 10-15 15-20

5-10

20-25

Total occurence

25-30

11

36.1

0

0

0

0

0

0

0

10.5

34.4

0

0

0

0

0

0.0002

0.0002

10

32.8

0.0002

0

0.0002

0

0

0

0.0004

9.5

31.2

0

0

0.0002

0

0

0

0.0002

9

29.5

0.0002

0

0.0004

0

0

0

0.0006

8.5

27.9

0.0006

0.0004

0.0002

0.0002

0.0004

0.0004

0.0022

8

26.2

0.0002

0.0004

0.001

0.002

0.0016

0

0.0051

7.5

24.6

0.0004

0.001

0.001

0

0.001

0.0002

0.0081

7

23.0

0.0014

0

0.001

0.006

0.002

0.0002

0.0124

6.5

21.3

0.001

0.003

0.00

0.010

0.008

0.0002

0.0250

6

19.7

0.004

0.004

0.01

0.018

0.008

0

0. 0.0446

5.5

18.0

0.009

0.010

0.02

0.046

0.0063

0.0002

0.0948

5

16.4

0.011

0.023

0.06

0.076

0.0059

0.0002

0.1810

4.5

14.8

0.023

0.054

0.14

0.111

0 .0053

0

0 .3348

4

13.1

0.050

0.129

0.27

0.1684

0.0028

0

0.6209

3.5

11.5

0.096

0.278

0.54

0.1941

0.0047

0

1.1139

3

9.8

0.182

0.631

1.0131

0.2362

0.0037

0

2.0656

2.5

8.2

0.385

1.386

1.7073

0.3045

0.0071

0

3.7894

2

6.6

0.921

3.496

2.9995

0.3450

0.0016

0

7.7631

1.5

4.9

2.595

8.7509

4.2139

0.2504

0.0016

0

15.8115

1

3.3

8.571

19.1310

3.6417

0.0429

0.0002

0

31.3869

0.5

1.6

18.774

14.0660

0.6158

0.0507

0.0010

0

33.5078

0

0

2.5900

0.4500

0.0549

0.0045

0

0

3.0994

3 4. 4.2 15 15 7

48 .4 .41 57 57

15 .3 .30 46 46

1 .8 .8 69 695

0.0 60 60 8

0 .0 .00 16 16

9 9. 9.8 67 678

Total occurence %

CBCL Limited


12 11

) m ( t 10 h g i e h 9 e v a 8 w t n 7 a c i f i n 6 g i S

67 Storm peaks over 6 m Weibull distribution distribution

5 4 1 10

Figure A.4

10

0

-1

10 Probability Probability of exceedence exceedence of 1 event in Tr years (Q = 1/(1.1552 Tr))

10

-2

10

-3

Extreme Value Analysis of Offshore Significant Wave Heights Correlation coefficient coefficient using best-fitting Weibull Weibull distribution R = 0.99743

Storm peaks over 2.4 m Weibull distribution distribution 3 2.9 ) 2.8 D C m2.7 ( z

2.6 2.5 2.4 0

-1

10

Figure A.5

10 Probability of exceedence of 1 event in Tr years (Q = 1/(1.3814 1/(1.3814 Tr))

10

-2

Extreme Value Analysis on Water Level Storm Peaks From De-trended Halifax Tide Gauge Data Correlation coefficient coefficient using best-fitting Weibull Weibull distribution R = 0.9881

CBCL Limited


APPENDIX B

Map of McNabs Island Source: The Friends of McNabs Island Society http://www.mcnabsisland.ca

CBCL Limited


McNabs Island The Friends of McNabs Island Society

mcnabsisland.ca

Trainer Farm

Ives Point

P.O. Box 31240, Gladstone RPO Halifax, NS B3K 5Y1 Phone:(902)434-2254

Indian Point

l r aa i n t T n P o i a n a i d I n

2 0

Metres 250

2

Ives Cove

Searchlight Emplacement

2 0 I v e 4 0 s P o i 6 0 n t R d .

Fort Ives

P Woolnough's

Pleasure Grounds

Jack Lynch House

. S t e w o H

P

Yards 500

2 0

Hugonin Battery

2 0

G a r rr r i i s so n o R o a d d

1000 1500 Yards

Track

o a d

L y n c h R o a d

Trail

Contour Interval 20 feet

F r a s e r F a r m T r a i l

2 0 4 0

n s m m i n T i m a i l l r a T e C o v

Point Of Interest

6 0 8 0

Navigation Aid

1 0 0

1 2 0

Findlay v e C o Farm & Pop n s i n m m Bottle Site T i m i a l r a

Teahouse

(closed)

n e L a s e u o h a T T e

Cholera Victims Gravesite - 1866

McLean's Farm Site

1 4 0

Site of Hugonin-Perrin House and Gardens 1 4

Carriage Lane

Findlays Cove

Anchorage

C

T

Toilet

P

Private Property

C

Temporary Camp Site

Timmins Hill

T

t r a n F a r a d R o

Hugonin Point

500

500 Metres

Timmins Cove

a i l a s T r i t t s m m r H e

Matthew Lynch House F o r 6 4 0 0 s O y l 6 t h d Former 0 e 4 Lighthouse M i 8 S 0 Site l i tr t a 0 1 0 e e r 0 y t R

Findlay's Picnic Grounds

0

250

Road

8 0

DavisConrad House

0

F r a s e r F a r 2 m 0 4 T r a 0 i l 6 0

Wharf & Floating Dock (DNR Wharf)

T

4 0 0

Fraser Farm

Bog

0 J e n k Jenkins T i n r s a Hill i l H i l l

Information Kiosk

I

Maps Produced By: Judith Chinn and Francis Kelly

1 2 0

Detention Barracks Site

I

Garrison Pier

N

G a r r i s o n R o a d

McNabs Cove

T

D e t e n t i o n B a r r a c k R o a d

6 0

4 0

h h e a c s B r s e g u M a

Maugers Beach Lighthouse

8 0

e r P u m p W a t e o a d H o u s e R

h r s h M a

Marsh

Hangmans Marsh

g mans Be a c ch

1 0 0

F r o s t F i s h B r o o k

0 2

0 4

H a n

Strawberry Battery

McNeil/Farrel Point

McNabs Pond M c N a b s P o n d T r a i l

2 0

r l

i r a i w a tt T

t e

S

n

i l

o

C

l t b o a m l W T r a i

Wreck Cove

G a r r i s o n R o a Brow Hill Trail d

McNabs House Site

2 0 4 0 6 0

McNabs Cemetery

Fort McNab

0

Bedford Basin

1

2

8 0

T 1 0 0

Range Hill Concrete Rangefinder Platforms S e a r c h l i g h t T r a i l

Searchlight Emplacement

DARTMOUTH

1 0 0

C u l l i t o n F a r m T r a 8 0 i l

t h g 6 l i g 0 h c a r a d S e R o 4 0

2 0

Kilometres

R i f l e R a n g e T Marsh r a i l

Green Hill Cove

i l l n H i a l e e r a e G r v e T C o

2 0 4 0 6 0

H a l i a f x H HALIFAX a r b o u r

8 0

Culliton Point

Green Hill

Thrumcap Hook

Doyles Point

T h r u C m c o v a e p

E a s t e r n P a s s a g e

2 0

Big Thrumcap 4 0

Lawlor Island

McNabs Island

Main Burial Site of Cholera Victims from the S.S. England, 1866

Devils Island

Source of Maps: Friends of McNabs LRIS Natural Resources Canada Copyright 2000

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

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