Coastal Risk Assessment and Adaptation Options at Miseners Long Beach, Lower East Chezzetcook Nova Scotia

Transcription

1 Coastal Risk Assessment and Adaptation Options at Miseners Long Beach, Lower East Chezzetcook Nova Scotia April 2018 Prepared for: Nova Scotia Department of Natural Resources Prepared by:

2 Final Report DK VL Draft Report DK VL Issue or Revision Reviewed By: Date Issued By: This document was prepared for the party indicated herein. The material and information in the document reflects CBCL Limited s opinion and best judgment based on the information available at the time of preparation. Any use of this document or reliance on its content by third parties is the responsibility of the third party. CBCL Limited accepts no responsibility for any damages suffered as a result of third party use of this document. Report Cover Photo (CBCL): Tidal breach through Miseners Long Beach, 12 March 2018

3 Contents Executive Summary... iii CHAPTER 1 Introduction... 1 CHAPTER 2 Site Information Site Surveys Topo-Bathymetric Surveys Post-January 2018 Breach CBCL Site Visit 9 February Latest Status Historical Air Photos Long-Term Barrier Beach Response to Rising Sea Levels Studies by Geological Survey of Canada Acknowledgments Historical Information Pre-Breach Lake Water Levels Future Evolution Water Levels: Tide, Storm Surge, Sea Level Rise Vulnerability to Seawater Intrusion Freshwater Inflows vs. Tidal Influence Seawater Intrusion Relative Risk Index CHAPTER 3 Storm Surge and Wave Modeling Storm Surge Impacts Regional Model Scenarios for Local Model Flood Risk vs. Elevation Wave Impacts Offshore Wind and Wave Climate Nearshore Wave Transformation Model CHAPTER 4 Options for Coastal Adaptation Comparative Flood Risks for Dyke Options Conceptual Costing of Dyke Options CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach i

4 4.3 Alternative Approaches CHAPTER 5 Conclusions and Recommendations Summary Natural Evolution Dyke Options Alternatives Recommended Next Steps CHAPTER 6 References Appendices A B Historical Air Photos. Offshore Wind and Wave Inform CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach ii

5 EXECUTIVE SUMMARY Background Miseners Lake is located in Lower East Chezzetcook, Nova Scotia. The gravel barrier beach separating the lake from the Atlantic Ocean is under jurisdiction of the Nova Scotia Department of Natural Resources (NSDNR) as part of a Provincial Park. Its status as a protected area was first established in 1976 as a means to stop extraction of sand and gravel from the beach. There is no Park infrastructure beyond the parking lot at the western end of the beach. The barrier beach is increasingly prone to storm-induced breaches, causing the lake to become tidal on occasions. Two cycles of a breach followed by natural closure occurred in early These breaches cause great concern to lakeshore residents regarding the potential for increased coastal flooding and seawater intrusion into drinking water wells. Present Study Scope NSDNR has hired CBCL to investigate the implications of long-term coastal change for potential increased erosion and property flooding, as well as recommendations for future coastal damage mitigation. As a basis for timely decision making, this study is based on the best available information at the time. The initial coastal storm surge modeling is indicative of conditions at the site, and based on the information gathered in a short period of time, with the assistance of NSDNR staff as well as and historical and ongoing monitoring by the Geological Survey of Canada (GSC). Natural Beach Evolution The barrier beach fronting Miseners Lake is expected to continue to erode and migrate landward due to long-term sea level rise. This will result in more frequent overwash events, and increase the likelihood that a tidal breach would become permanent. With a permanent breach and increased barrier beach erosion, the extreme storm surge elevations in the lake may increase by an approximate 0.5 m. In the long term the western islands may provide natural headland anchor points for the beach, and it is expected that the islands and future beach will continue to provide some level of wave protection to properties on the west side of the lake. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach iii

6 Dyke Options Gravel fill may be imported for: Short-term repair of the current breach area. Long-term reinforcement of the 1.3 km long barrier beach in the form a gravel dyke. Cumulative coastal flood risk probabilities were estimated for various scenarios, as illustrated in Figure A. While dyke options can mitigate the impact of ocean storm surge on the lake, lake level is expected to rise in conjunction with sea level. In addition, seawater intrusion is expected to remain a growing concern even with dyke options, due to the fresh/seawater interface rising with sea level. In summary, dyke options can only delay, not eliminate, long-term impacts of sea level rise on flooding and seawater intrusion. Figure A: Timeline to Reach 50% Coastal Flood Risk Based on its surveyed grade elevation, a property is estimated to have a 50% probability of flooding at least once between today and its color-coded time horizon. For a given property elevation, the probability of flooding increases with the time, regardless of beach repair or erosion scenario. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach iv

7 Alternatives Alternatives to the dyke options include options at the property level which would typically include either: (1) Relocation of assets at risk. (2) Flood proofing of individual properties through a combination of: Abandon drinking water wells, use tank (communal or individual units) with imported drinking water. Raise living quarters and electrical equipment. Place fill on property lot and raise homes. Raise access road if required. Shoreline protection or berm if required (we note that natural sheltering from lake islands is expected to present an opportunity for individual property-scale shore protection). Recommended Next Steps The cost of dyke options should be considered relative to value of assets to be temporarily protected. Alternative options may then be further explored. The findings and recommendations are based on information collected to date at the time of writing, with uncertainties associated with data gaps and modeling approximations inherent to this type of study. We recommend that they be revisited by NSDNR as new information becomes available. Updates from GSC s research should be incorporated in the understanding of the coastal system. Notably, soon-to-berecovered tide gauge observations from the winter should be analyzed to improve the understanding of the local dynamics, most notably water levels evolving over several breach-closure cycles. Finally, we emphasize that the challenges posed by rising sea levels as presented in this report apply to many other dynamic coastal areas around the Province. This case represents a good illustration of the necessity to establish Province-wide coastal management policies towards practical and financially sustainable solutions. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach v

8 CHAPTER 1 INTRODUCTION Miseners Lake is located in Lower East Chezzetcook (LEC), Nova Scotia (Figure 1.1). The gravel barrier beach separating the lake from the Atlantic Ocean is under jurisdiction of the Nova Scotia Department of Natural Resources (NSDNR) as part of LEC Provincial Park. Its status as a protected area was first established in 1976 as a means to stop extraction of sand and gravel from the beach. There is no Park infrastructure beyond the parking lot at the western end of the beach. The barrier beach is sensitive to storm-induced breaches, which turn the lake into a barachois 1. Based on available information from NSDNR, recent breaching history can by summarized as follows: Breach in January 2010, which was artificially repaired. Breach on 4-5 January 2018 adjacent to the previously repaired section; Natural closure on January 18 th 2018 Breach on March 3 rd. Natural closure on April 4-5, The recent natural cycle of successive breaches and closures are characteristic of a very dynamic system. This demonstrates that while breaches may close through natural processes or artificial repairs, the system remains prone to future breaching. NSDNR has hired CBCL to investigate the implications of long-term coastal change for potential increased erosion and property flooding, as well as recommendations for future coastal damage mitigation. The scope of the present study includes: Review of existing information. Lake bathymetric survey. Coastal modelling of storm surge and wave impacts under scenarios of progressive barrier beach erosion. Assessment of long-term flooding implications and recommendations. 1 A barachois is a term used in Atlantic Canada to describe a coastal lagoon separated from the ocean by a sand or shingle barrier beach. Salt water may enter the barachois during high tide. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 1

9 As a basis for emergency decision making, the report is based on the best available information at the time of this rapid assessment. Initial coastal modelling is therefore indicative of conditions at the site, and limited to the information gathered in a short period of time. Figure 1.1: Site Location and Park Information CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 2

10 CHAPTER 2 SITE INFORMATION 2.1 Site Surveys Topo-Bathymetric Surveys Post-January 2018 Breach Geological Survey of Canada (GSC) Natural Resources Canada staff conducted UAV (drone) surveys on 10 January 2018 in addition to complementary ground surveys. These surveys produced a Digital Elevation Model (DEM) presented in this report (Figure 2.2.a). The breach at the approximate time of the survey is visible on the middle-east side of the beach (Figure 2.1.a). NSDNR completed ground surveys of specific shoreline features and property elevations on 17 January Finally, CBCL conducted a bathymetric survey after ice out on 27 March The topo-bathymetric observations were compiled and presented in Figures 2.2.a (topo-bathymetry of the beach) and 2.2b (property elevations) CBCL Site Visit 9 February 2018 CBCL staff visited the site the morning of 9 February 2018 at low tide, with moderate low swell conditions. Photos are shown on Figure 2.1.b. Sediment size ranges from sand on the lower beach face to cobble on the ridge, which has a steep slope on some sections (close to natural angle of repose). Beach cusps were observed, and the beach face presents characteristics that are thought to be conducive to their formation including, but not limited to: steep beach face slope, surging waves approaching normally to the shore, sediment sizes ranging from sand to cobbles, and a dominant long wave period (which in this case would be long swell). There were no open tidal breaches at the time of the CBCL site visit, however evidence of multiple recent overwash events was visible. Of these, three overwash platforms were at elevations estimated at less than 0.5 m above the high water line delimited by the thin snow cover. At these three locations, even a moderate storm event occurring at high tide would likely cause additional wave overwash towards the lake. The location of the recent overwash events did not appear to fall within a common beach area with defined limits. Two overwash sites were on the west side close to the islands, including one in front of the inhabited island (Figure 2.1.a), located behind a deposit of large boulders in the lower intertidal area (these boulders therefore did not appear to mitigate against breaches, as their crest likely sits too low below high tide to provide enough wave energy attenuation during a surge event). The third overwash site was at the January 2018 tidal breach (closed at the time of this visit). CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 3

11 Figure 2.1.a: NSDNR Photos of Initial Breach, 8 January 2018 CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 4

12 Figure 2.1.b: Photos of Naturally Filled-in Breach (CBCL 9 February 2018) CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 5

13 2.1.3 Latest Status The breach re-opened in early March 2018 (Figure 2.1.c, top two photos) in the same general area as the January occurrence. It closed naturally early April. It was closed at the time of writing this report (Figure 2.1.c, bottom). Figure 2.1.c: Photos of Most Recent Breach and Closure Cycle CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 6

14 Figure 2.2.a: Topo-Bathymetric Information Nautical chart. GSC-NSDNR topographic surveys (Post-breach, 10 January 2018). CBCL bathymetric survey (28 March 2018). All elevations on bottom map are referenced to CGVD28. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 7

15 18 ELEVATION OF LAKESIDE BUILDINGS (CGVD28) COUNT < 2 2 to to 3 3 to to 4 > 4 ELEVATION RANGE (m) FIG 2.2.b FIG 4

16 2.2 Historical Air Photos CBCL collected historical air photos from NSDNR and georeferenced these to more recent satellite imagery, to describe historical shoreline change at Miseners Long Beach. Based on georeferenced air photos, the historical shoreline retreat rate of the beach is estimated at m/year from 1945 to 2003 (Figure 2.3.a). This rate estimated from air photos is consistent with GSC studies described in section 2.3. The processes of barrier beach migration and crest erosion are not specific to Miseners Long Beach, and many similar situations occur throughout Nova Scotia. An overview of satellite pictures can rapidly reveal many cases with similar coastal conditions, such as the three shown on Figure 2.3.b. These examples serve to add context to this investigation, and demonstrate that the situation at Miseners Long Beach is not necessarily unique in its nature. The similar low gravel barrier situation at Story Head beach, can also be related to excessive historical sediment extraction (pers. comm. Robert Taylor GSC). The observed migration of barrier beaches can be explained by rising sea levels as described in the following section. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 9

17 Figure 2.3.a: Summary of Long-Term Shoreline Change based on Historical Air Photos at Miseners Long Beach (see Appendix A for individual photos) CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 10

18 Figure 2.3.b: A Few Examples of Other Eroding Barrier Beaches Fronting Private Waterfront Land along the Eastern Shore CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 11

19 2.3 Long-Term Barrier Beach Response to Rising Sea Levels In a big-picture sense, as emphasized by the GSC studies described in section 2.4, the Atlantic coast of Nova Scotia has been retreating landward for thousands of years due to Sea Level Rise (SLR). The process varies in intensity depending on specific shoreline condition. Large storms, such as those experienced in January of this year, represent just one small step in the long-term process. Conceptual models of long-term shoreline response to rising sea levels have been proposed as summarized in various publications including, but not limited to Dean and Dalrymple (2002) or Davidson Arnott (2005). Most of the simpler models apply to sandy coasts, which would be too simplistic in the case of Miseners Long Beach with a wide range of sediment sizes including coarse gravel. While conceptual models may vary, the conservation of sediment volume within the nearshore profile remains a common basis for evaluation. Assuming there is no significant new sources of sediment, the beach profile must translate landward and upward to conserve sand volume, as illustrated on Figure 2.4. In the case of a low-elevation backshore or a barrier beach, some of the sediment eroded on the ocean side is transferred to the backshore (referred to as washover deposit) to maintain an equilibrium profile across the barrier. In the present case, it appears that there is insufficient overwash material to build up the barrier on the lake side, where material is lost to deeper areas behind the breach. Therefore barrier beaches such as at Miseners are more susceptible to erosion than land-fronting beaches. In cases where the bay depth exceeds the ocean depth, it becomes impossible for the barrier to migrate and still maintain its original form. In these situations, the barrier would migrate landward while narrowing and losing elevation, to become eventually completely submerged. For natural barrier beaches to be able to keep up with sea level rise, the following conditions must be met: Have a relatively shallow platform on the bay side to slow migration and retain sediment in the system. Enough sediment supply in the foreshore to keep up with the required profile shift. The above conditions do not appear to be fully met at Miseners Long Beach, as evidenced by the gradual lowering of its crest observed by GSC, as presented in the next section. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 12

20 Figure 2.4: Schematic of Theoretical Long-Term Barrier Beach Response to Rising Sea Levels For a given set of similar wave, storm surge and sediment conditions, shoreline response to SLR will vary depending on beach configuration. The response is governed by the conservation of sediment volume during wave overwash and breaching events moving seaside material landward. Areas with a low elevation backshore (B) or lagoon (C) capture higher volumes of overwash material, which slows down natural rebuilding of the crest and results in higher rates of landward migration. Adapted from: Dean and Dalrymple (2002), Davidson-Arnott (2005). CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 13

21 2.4 Studies by Geological Survey of Canada Acknowledgments CBCL wishes to thank the GSC s Scientists Robert Taylor and Vladimir Kosltylev, who have shared longterm research on the site reported in several publications Historical Information In summary, the Atlantic coast of Nova Scotia has been retreating landward for thousands of years because of Sea Level Rise (SLR). The process varies in intensity depending on specific shoreline condition. Shoreline changes caused by large storms, such as those recently experienced, represent one small step in the long-term process. Robert Taylor provided the following information specific to the site, with key figures reproduced on Figure 2.5. Observations over the last 20 years (Figure 2.5.a) indicate decreasing rates of natural rebuilding at Miseners Long Beach. In 2010 a breach was repaired using approximately 80 gravel bags (Figure 2.5.c) placed on the backshore sediment platform formed by shallow washover lobes. The repair survived a storm that followed shortly after. The beach then naturally rebuilt itself over the summer, however the sediment volumes that were moved to the crest in the rebuilding process resulted in less volume on its sides. The 2018 breach occurred on the eastern side of the 2010 repair. Unfortunately, there appears to be limited backshore platform on the lake side of the 2018 breach, therefore some of the sediment washed in on the flood tide has likely fallen to the bottom of the lake. It may therefore take a greater volume of material than it took in 2010 to either repair it, and/or for natural rebuilding to take place Pre-Breach Lake Water Levels Mr. Taylor notes that the lake s pre-breach typical level was approximately 1.3 m CGVD28, which is close to ocean high tide (see Table 2.1). The maximum oscillation in lake levels measured was 0.58 m (excluding breach conditions). The highest lake level observed during GSC surveys was 1.6 m CGVD28 during Hurricane Hortense. Peak water levels observed from the Halifax tide gauge at the time were 1.9 m CGVD28, so the maximum pre-breach lake level was approximately 0.3 m below the peak storm surge Future Evolution The GSC have been monitoring the evolution of Miseners Long Beach and Story Head, the next barrier beach to the west of the site. Both systems are gravel bars that migrate landward with SLR. Story Head is a comparatively low gravel bar, with high rates of migration and erosion. Miseners Long Beach has been a high gravel barrier, with historical lower migration rates, i.e. approximately m/year in the last 30 years. However, the recent history of breaches at Miseners, as well as the observed decrease in crest elevation, indicates that the Miseners Long Beach is likely moving closer to the low gravel barrier case with accelerated rate of migration. It will be prone to increased storm wave overwash and destruction as it moves landward. 2 Based on available information at the time of this study, storm surge levels measured by the Halifax tide gauge are deemed a reasonable approximation of storm surge levels along Miseners Long Beach - see section 3.1. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 14

22 The presence of backshore platforms to anchor the migrating crest will be critical for natural resilience. The decreasing rate of natural rebuilding indicates that there is a finite sediment amount in the system with limited natural supply. Therefore it is unlikely that natural beach building can keep up with accelerated SLR in the long-term. Breaches will result in sediment volumes being sucked into the lake, some if it being lost in areas of steeper lakeside slopes providing no backshore platforms. This will reduce both the nearshore sand buffer to support the seaward slope of the beach, and the material available for crest building. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 15

23 L2a L2a 2018 breach Average rate of crest lowering = 0.5 to 1 m in 20 years ( ) 2010 breach A. Evolution of longshore profile of the beach crest repair B. Observed natural crest rebuilding from 2011 to 2017 Figure 2.5: C. Post-breach changes at L2a in 2010 (the dyke provided a levee against which the new beach was built and will continue to build upon). Observed Profile Changes Source: Robert Taylor, GSC CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 16

24 2.5 Water Levels: Tide, Storm Surge, Sea Level Rise Water levels are the main factor influencing coastal flooding hazards. Still water levels are measured as the sum of: Tide The local tide is semi-diurnal, with a maximum range of 2.2 m. Storm Surge Storm surges are created by meteorological effects on sea level, such as wind set-up 3 and low atmospheric pressure, and is defined as the difference between the observed water level during a storm and the predicted astronomical tide. The storm surge on the ocean side of Miseners Long Beach is expected to be comparable to that measured from the Halifax tide gauge (see modeling section 3.1). Therefore, long-term storm surge statistics are based on Halifax tide gauge data (which spans 1919 to present) corrected to present mean sea level. Wave Run-up Wave runup is the vertical distance a wave travels up the shoreline above the still water level. It includes two components: - Set-up, which is defined as the rise in mean water level due to wave breaking. - Swash 4 distance up the beach of individual waves. Sea-Level Rise (SLR) Nova Scotia coastlines are experiencing Sea Level Rise (SLR) which will accelerate due to climate change, causing increased risks of coastal erosion and flooding. As a result, extreme water levels with a low return period today will be very common in a few decades. Table 2.1: Present-Day Static Water Levels at Halifax (Wave Run-up not Included) Present Extreme Water Levels m CGVD28 m CGVD13 Hurricane Juan storm surge Upper-bound levels if storm residual (1.5 m) surge coincides with HHWLT 100-year storm surge residual (1.15 m) year Storm water levels 50-year for probabilistic 25-year analyses 10-year year year Present Tidal Water Levels metres Halifax m CGVD28 m CGVD2013 Chart Datum = CD =CGVD HHWLT - Higher High Water Large Tide HHWMT - Higher High Water Mean Tide MWL - Mean Water Level LLWMT - Lower Low Water Mean Tide LLWLT - Lower Low Water Large Tide Note: highest recorded was during Hurricane Juan at 2.9 m Halifax Chart Datum = 2.1 m CGVD28 3 Wind set-up refers to the increase in mean water level along the coast due to shoreward wind stresses on the water surface. 4 The swash zone forms the land-ocean boundary on the beach face along the surf zone. The landward edge of the swash zone is highly variable in terms of geomorphology, and may terminate in dunes, cliffs, marshes, ephemeral estuaries and a wide variety of sand, gravel, or rock barriers. This influences the exchange of sediment between the land and ocean, which ultimately forms the coastline. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 17

25 Metres rel. to 2010 SLR Projections SLR projections from the recent scientific literature applicable to Halifax were compiled by CBCL Limited and are presented in Figure 2.6, based on the following existing information. NOAA 2017 Extreme GMSLR NOAA 2017 High GMSLR DFO 2016 High for Halifax DFO 2014 High for Halifax, and NOAA 2017 Intermediate GMSLR NOAA 2017 intermediate-low GMSL Figure 2.6: Annual Mean Sea Level: Past Observations from Halifax Tide Gauge Tide Gauge and Projected Sea Level Rise for Halifax Note: storm surge and wave run-up are not included. The Intergovernmental Panel on Climate Change s Fifth Assessment Report (IPCC AR5 2013) estimated that the upper-bound Global Mean SLR could be in the order of 1.0 m by year This upper-bound projection was for Representative Concentration Pathways RCP8.5 scenario, i.e. business-as-usual, highemission case. At the time there was insufficient evidence to evaluate the probability of specific levels above this 1.0 m projection. DFO then developed the online Canadian Extreme Water Level Adaptation tool, based on the study by Zhai et al. (2014) accounting for local factors. CAN-EWLAT is a science-based planning tool for climate change adaptation of coastal infrastructure related to future water-level extremes. It was developed to provide SLR allowances for DFO harbours across Canada. Allowances are estimates of changes in the elevation of a site that would maintain the same frequency of inundation that the site has experienced historically. CAN- EWLAT was used as a benchmark to forecast relative SLR at Halifax. For the year 2100, the tool estimates an upper-bound relative SLR of approximately 1.1 m for the IPCC 2013 RCP8.5 scenario. However, studies subsequent to the IPCC 2013 and DFO 2014 study suggests that previous Global Mean Sea Level (GMSL) predictions are too modest. These studies updated the scientifically supported upperend GMSL projections, including recent studies of the potential for rapid ice melt in Greenland and Antarctica. DFO s Han et al. study (2016) revisited mean sea level rise scenarios to include a High Scenario of 1.97 m projected SLR to year 2100 relative to 2010 for Halifax. Subsequently, a 2017 NOAA publication (Sweet W. et al, 2017) present a year 2100 GMSL forecast range discretized into six GMSL CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 18

26 rise scenarios: a Low (0.3m), Intermediate-Low (0.5m), Intermediate (1.0m), Intermediate-High (1.5m), High (2.0m) and Extreme (2.5m). A key finding was that along regions of the Northeast Atlantic (Virginia coast and northward), regional SLR is projected to be greater than the updated global average for almost all future scenarios (e.g. by 0.3 to 0.5 m with the Intermediate scenario by year 2100). Given these findings, the 2014 DFO estimates based on IPCC AR5 RCP8.5 can now be considered Intermediate projections, with High and Extreme SLR scenarios to range 1.0 to 1.5 m higher than previously anticipated. Figure 2.7 demonstrates the potential sea level rise that can be expected at Halifax. Recommended SLR Scenarios for Planning For planning purposes where long-term risk management is paramount, the following approach is recommended, as per NOAA 2017: Define a scientifically plausible upper-bound scenario, which in the present case would be the high (or extreme) GMSLR projection, and use it as a guide for overall risk and long-term adaptation strategy. Define an intermediate GMSLR projection as baseline for shorter-term planning. The two scenarios above can be thought of as providing a general planning envelope. For the present project, the extreme scenario can be used for guiding the selection of minimum site elevations required for siting of future and potentially vulnerable permanent infrastructure. The intermediate scenario may be used for defining the elevation of coastal protection structures and potentially roads, which could be built for a shorter design life and/or have built-in flexibility to allow incremental raising. 2.6 Vulnerability to Seawater Intrusion Freshwater Inflows vs. Tidal Influence The watershed area of the lake is estimated at 530 ha. The annual average daily freshwater flow into the lake is estimated at a modest 0.17 m 3 /s (based on prorated flow rates using observations from the Sackville River). The tidal volume flowing through the January 2018 breach is estimated to be at least 50 times more than freshwater inflows over a tidal cycle, based on hydrodynamic modeling presented in the next section. The ratio will grow larger towards tidal influence if the breach widens and/or deepens. This explains why the lake water turned salty relatively quickly after the breach occurred, as evidenced by freshwater fish kill reported by lakeshore residents Seawater Intrusion Relative Risk Index The risk of seawater intrusion was assessed by NSDNR (Kennedy 2012) in a province-wide study based on available information. Municipal water service is not available to residents of Lower East Chezzetcook, who have relied on private wells as the only practical means of obtaining a water supply. The NSDNR study estimated that over 90% of these wells intercept fractured bedrock aquifers. Seawater intrusion into coastal aquifers, driven by overpumping and rising sea levels, is therefore a key issue for water resource management. The approach uses available datasets, such as digital elevation models, civic address points and well logs data. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 19

27 Relative vulnerability was assessed based on the following derived criteria: Distance to the coast. Land slope. Development density. Non-residential groundwater use. Static water level. The results were compiled in a GIS database for the area of interest as shown on Figure 2.8. It indicates that the Project area s relative vulnerability to seawater intrusion was ranked as highest, even before the breach. Rising sea levels are expected to push back the interface between fresh and seawater. That is, even if an artificial rock dyke was built along the whole barrier beach, seawater penetration into the lake and adjacent groundwater wells appears inevitable in the long-term. Figure 2.8: Illustration of Seawater Intrusion Vulnerability Process (Left) and Local Relative Index Pre-Breach (Right) In (b left), the water supply wells are at greater risk due to lower freshwater head above sea level (H), a lower hydraulic gradient (i) and increased drawdown (s). Source: Reference: Kennedy G, CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 20

28 CHAPTER 3 STORM SURGE AND WAVE MODELING 3.1 Storm Surge Impacts CBCL used the industry-standard MIKE21 coupled hydrodynamic and wave model available from the Danish Hydraulic Institute (DHI). The model was used to investigate storm surge and wave climate at the site under various hypothetical beach damage scenarios Regional Model The storm surge model was calibrated to a known event, i.e. Hurricane Juan on 29 September This event generated the record high water level observed by the Halifax tide gauge (2.9 m Chart Datum total water level). Hurricane track, wind and atmospheric pressure data were input into the model to simulate the storm surge. The modelled peak storm surge residual (i.e. above astronomical tide) at the Halifax tide gauge was 1.5 to 1.6 m, which is consistent with the tide gauge record of a 1.5 m peak for this event. Model results (Figure 3.1) indicate that storm surge estimates from the Halifax tide gauge are consistent with the values that would be experienced at the site along the beach including wave setup (excluding wave runup) Scenarios for Local Model Outputs from the regional storm surge model were used as boundary conditions for a local model with high resolution at Miseners Long Beach and Lake. The local model was used to run two scenarios described on Figure Short-term scenario, based on the January 2018 breach configuration (Figure 3.2 top). 2. A long-term scenario based on an eroded barrier with lower beach crest, enlarged middle inlet, and beach partly anchored by the west islands (Figure 3.2 bottom). There are no industry-accepted numerical models that can reliably predict long-term geomorphologic changes in seabeds of very coarse material. Therefore the long-term scenario is considered hypothetical and the intended use should be limited to the present planning-level exercise. If timeframes had to be assigned, given the GSC s assessment that Miseners Long Beach is moving toward a low barrier configuration resembling adjacent Story Head, the potential time frames for scenario 2 may be in the order of 50 to 100 years, respectively. We have therefore tested a SLR of 0.5 to 1.0 m for this scenario in the model. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 21

29 Figure 3.1: Snapshot of Modeled Hurricane Wind Fields (top) and Peak Storm Surge along Eastern Shore (Bottom) During Hurricane Juan CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 22

30 Short-term scenario Jan 2018 Breach assumed to remain open Hypothetical long-term erosion scenario Lower beach crest, enlarged middle inlet, beach partly anchored by the west islands Figure 3.2: Miseners Lake Model Bathymetry for Two Scenarios Under Investigation Note: Modeling the progressive erosion of the barrier itself is outside the scope of the study. Instead, the modeling exercise examines implications on wave impact and flooding for the configurations shown. Sample storm surge model result maps are presented on Figure 3.3.a, with a sample time series in Figure 3.3.b. The model indicates that peak water levels in the lake are expected to exceed beach-side levels by 0.1 and 0.2 m approximately for the breach and long-term erosion scenarios, respectively. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 23

31 Figure 3.3.a: Sample of Modeled Peak Water Levels and Hydrodynamic Circulation at Miseners Lake for Hurricane Juan Simulation CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 24

32 Typical pre-breach lake el. 1.3 m (source: GSC) Figure 3.3.b: Modeled Timeseries of Water Levels for Hurricane Juan Simulation with January 2018 Breach Note: Modeled lake water levels were not validated by field observations. Tidal range may vary and model should be revisited after recovery of tide gauge by GSC in the late spring of In contrast, with a closed barrier beach (or artificial dyke), the peak storm surge lake level is estimated to be approximately 0.3 m below beach-side level based on limited historical observations by GSC (see section 2.4.3). Based on the limiting existing information, it is reasonable to assume that SLR will increase water levels on the ocean and lake side concurrently, and that this 0.3 m estimated difference will likely remain applicable in the long-term under a closed barrier scenario. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 25

33 3.1.3 Flood Risk vs. Elevation The model results were used to generate risk curves for lake flooding, presented in Figure 3.4. Each chart shows the cumulative probability of flood level exceeding a given elevation over a chosen lifetime, depending on the SLR scenario (intermediate on left-hand column, high on right hand column). These curves form the basis for flood risk maps presented in Chapter 4. Figure 3.4: Estimated Cumulative Probabilities of Storm Surge Lake Levels Under Two SLR Scenarios For example, with an artificial dyke repair, a property at ground elevation 2.1 m is expected to have a probability of flooding of 10% between today and the 2030's for the intermediate Sea Level Rise scenario. For a given property elevation, the probability of flooding increases with time, regardless of beach repair or erosion scenario. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 26

34 3.2 Wave Impacts Waves are the most important factor for coastal erosion hazards and impacts to beaches. Large offshore waves occur with every major storm. Near the coast, approaching wave crests bend towards the shoreline, become steeper, and ultimately break. The height of a breaking wave is limited by the water depth. Breaking waves are higher during high tides and storm surges. Sea-level rise will also tend to cause higher waves at the shore Offshore Wind and Wave Climate The MSC50 offshore wind and wave model hindcast from January 1954 to December 2015 contains hourly time series of wind and wave parameters at a location offshore the project site. 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). Directional statistics are presented in Appendix B, showing the site is exposed to prevailing offshore swells that can reach up to 12 m during extreme events. The MSC50 data includes records of Hurricane Juan, which was used as a base storm for numerical modeling as follows Nearshore Wave Transformation Model The offshore extreme wave data was input into the model to assess local wave heights at the project site after nearshore transformations including. Refraction (the slowdown and bending of wave crests as they feel the bottom). Shoaling (the changes in wave height entering shallow water). Breaking (when shallow waters cannot support wave heights greater than approximately 0.8 times the water depth). Setup (the increase in still water level in the surf zone due to energy transfer from wave breaking). The MIKE21 wave model was not calibrated to wave observations close to the beach. Therefore, the model could not be fully calibrated and validated to event-specific observations. In previous studies, experience has shown that the validated MSC50 offshore data provides satisfactory preliminary indicative output of wave climates in the nearshore, prior to more detailed investigations. The results should therefore be treated as an indicative sample of the anticipated wave climate under the described input conditions. Sample results for Hurricane Juan are shown on Figure 3.5, and indicate gradually increasing wave heights into the lake in scenarios with progressing erosion. It is emphasized that the model plot showing potential wave heights under long-term erosion scenario is based on the hypothetical bathymetry shown on Figure 3.2 (bottom). In reality the wave heights reaching the property shorelines in the longterm will depend on the actual barrier crest elevation relative to storm surge levels, which cannot be determined with confidence at this point based on the existing information. Further, the uniform eroded barrier (used in this exercise for demonstrative purposes) will realistically be irregular in nature, influencing the wave heights at a local scale. In conclusion, the wave model indicates that the islands are expected to continue provide some wave sheltering to the area with low-elevation properties on the west side of the lake. If required in the long- CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 27

35 term, this natural sheltering represents a potential opportunity to work on local property scale to implement shoreline stabilization such as rock revetments or hybrid solutions combining rock and stabilizing vegetation. Single open breach scenario, Existing sea level Hypothetical long-term erosion scenario Islands are expected to - continue provide wave sheltering to west lakeshore properties, and - provide anchor points for future beach With 0.5 m SLR With 1.0 m SLR Figure 3.5: Sample Modeled Peak Wave Heights during Hurricane Juan for Various Scenarios CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 28

36 CHAPTER 4 OPTIONS FOR COASTAL ADAPTATION 4.1 Comparative Flood Risks for Dyke Options Options can be broadly defined into two categories: A. Coastal engineering intervention on the barrier beach involving either (A1) short-term breach repair, or (A2) long-term reinforcement of barrier beach with rock material. B. Leave the beach to evolve naturally, and intervene at the property level as necessary Details for category B will be expanded upon further in the report. In this section, the implications of structural Options A1 and A2 on flood risks were summarized on maps (Figures 4.1 and 4.2). These maps are based on the modeled risk curves presented in section Due to long-term sea level rise, the following two problems will continue to occur regardless of the option chosen: Seawater intrusion. Increasing flood risk. Options involving partial or full rebuilding of the barrier beach using imported gravel material will mitigate risks in the short-term, but would only act as delaying the inevitable erosive processes. Therefore cost implications need to be understood before making a decision. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 29

37 INTERMEDIATE SEA LEVEL RISE, SINGLE BREACH INTERMEDIATE SEA LEVEL RISE, ARTIFICAL DYKE Single Single Breach Breach Artifical Artifical Dyke Dyke HIGH SEA LEVEL RISE, SINGLE BREACH HIGH SEA LEVEL RISE, ARTIFICAL DYKE Single Single Breach Breach Artifical Artifical Dyke Dyke Estimated Flooding Timeline After 's 2080's 2070's 2060's 2030's 2040's 2030's 2020's By 2020 FIG LE CHEZZETCOOK: ESTIMATED FLOODING TIMELINE FOR 10% CUMULATIVE PROBABILITY NOTES: Based on its surveyed grade elevation, a property is estimated to have a 10% probability of flooding at least once between today and its color-coded time horizon. For a given property elevation, the probability of flooding increases with the time, regardless of beach repair or erosion scenario. Ü m 8.5x11 MAR

38 INTERMEDIATE SEA LEVEL RISE, SINGLE BREACH INTERMEDIATE SEA LEVEL RISE, ARTIFICAL DYKE Single Single Breach Breach Artifical Artifical Dyke Dyke HIGH SEA LEVEL RISE, SINGLE BREACH HIGH SEA LEVEL RISE, ARTIFICAL DYKE Single Single Breach Breach Artifical Artifical Dyke Dyke Estimated Flooding Timeline After 2090's 2090's 2080's 2070's 2060's 2030's 2040's 2030's 2020's By 2020 FIG LE CHEZZETCOOK: ESTIMATED FLOODING TIMELINE FOR 50% CUMULATIVE PROBABILITY NOTES: Based on its surveyed grade elevation, a property is estimated to have a 50% probability of flooding at least once between today and its color-coded time horizon. For a given property elevation, the probability of flooding increases with the time, regardless of beach repair or erosion scenario. Ü m 8.5x11 MAR

39 4.2 Conceptual Costing of Dyke Options A conceptual cross-section of the gravel fill that may be required was developed based on the topobathymetric information (Figure 4.3). The objective was to obtain order-of-magnitude fill volumes for quarried gravel 5 (typical dimension 200 mm). We note that beach-type round cobble is not available in the required volumes, and the quarried gravel beach response may vary from that observed with the natural cobble. Key inputs and assumptions used for deriving the estimates are listed below each of the following two figures. Figure 4.3 Notes: Not for construction. Concept Cross-Section for Preliminary Estimation of Required Order-of-Magnitude Gravel Dyke Volume Recommended minimum dimensions shown are based on preliminary examination of existing barrier beach sections. Notably, 4.5 m to 5.0 m crest elevation is typical of end section of the barrier east of the breach that appears less prone to overwash. Should this option be pursued further, final dimensions and materials should be determined by a detailed design study. Order-of-magnitude costs were developed and summarized on Figure 4.4. Estimates range from: Several hundred thousand dollars (potentially $ 0.5 million) to effectively repair the existing breach, with the risk of new breaches developing elsewhere. The required volumes were estimated assuming all imported gravel fill. Upwards of $5 million for a 1.3 km gravel dyke with enough backslope to encourage natural rebuilding of the crest without losing elevation with rising sea levels. Final dimensions and costs would have to be determined in a detailed design study that takes into account potential profiles reshaping under long-term sea level rise. 5 The hard armour stone option is not recommended, as it would be both more expensive and would be incompatible with long-term coastal processes of beach building. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 32

40 $10,000,000 $9,000,000 $8,000,000 $7,000,000 $6,000,000 $5,000,000 $4,000,000 $3,000,000 $2,000,000 $1,000,000 construction budget contingencies $- Breach repair el. 4.0 m 1.3 km gravel dyke el. 4.5 m 1.3 km gravel dyke el. 5.0 m Figure 4.4: Opinion of Probable Order-of-Magnitude Cost for Gravel Barrier Repair Options Notes: Imported gravel fill volumes estimated based on sketch from Figure 4.3 with existing topo-bathymetric information collected post-breach in January Based on conservative estimation of gravel unit cost of $80/m3, which accounts for the required supply, stockpile and placement of the material. This opinion of probable costs is presented on the basis of experience, qualifications, and best judgement. It has been prepared in accordance with acceptable principles and practices. Market trends, non-competitive bidding situations, unforseen labour and material adjustments and the like are beyond the control of CBCL limited. As such we cannot warrant or guarantee that actual costs will not vary from the opinion provided. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 33

41 4.3 Alternative Approaches Risk is defined as the combined likelihood of hazards (e.g. storm surge, wave attack) and impacts (e.g. infrastructure damage from flooding or erosion). Strategies for reducing coastal risk involve reducing hazards and/or reducing impacts, as summarized in Figure 4.5, with details in Table 4.1. For Miseners Long Beach, it is recommended that the cost of dyke options presented in the previous section be considered relative to: (1) The value of property and infrastructure to be protected. (2) The feasibility and cost of alternative options. 1. PROTECT Build-up and defend shoreline with artificial structures 2. ACCOMMODATE Modify existing practices to tolerate and/or minimize risk 3. MANAGED RETREAT Let nature take its course and relocate assets Figure 4.5: Schematic of Alternative Approaches to Sea Level Rise Adaptation CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 34

42 Table 4.1: Approaches for Coastal Risk Mitigation at Miseners Long Beach and Lake Area Approach Description Application to Miseners Long Beach Hazard Reduction Approaches (coastal engineering interventions) Historically the most common form of coastal adaptation. Short-term breach repair. Protect i.e. Aims to allow for current land use to Longer-term gravel dyke construction. Advance or hold remain unchanged. Localized shore protection or berms of the the line Expensive over the long-term, especially properties to be impacted. with the expected increase in the rate of sea-level rise. Consequence Reduction Approaches (let the beach evolve naturally) Floodproof individual properties through a combination of: Abandon drinking water wells, use tank Allows for continued use of coastal land. (communal or individual units) with Accommodate i.e. Changes the current use of coastal land imported drinking water. Raise the line or infrastructure to become water Raise living quarters and electrical dependent or tolerating. equipment. Place fill on property lot and raise homes. Raise access road if required. Make decisions about what assets to relocate and what areas are going to be allowed to be overcome by natural processes. Managed Retreat Long-term strategy for adaptation in high-risk areas. Make decisions on what to relocate and what areas are going to be allowed to be overcome by natural processes. Discourage/prevent development in risk Avoid areas before they become developed. Do not allow any new development around the Added benefits include environmental lake. protection and increased public access to the coast. Generate climate information. Planning Collect/map local data. Interpretive panels on coastal processes. Disseminate information to stakeholders Encourage collection of data by local and the public. volunteers (e.g. Friends of associations). Incorporate local climate change Develop policies for coastal beach parks. information into community plans or policies. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 35

43 CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS 5.1 Summary Natural Evolution The barrier beach fronting Miseners Lake is expected to continue to erode and migrate landward due to long-term sea level rise. This will result in more frequent overwash events, and increase the likelihood that a tidal breach will become permanent. With a permanent breach and increased barrier beach erosion, the extreme storm surge elevations in the lake may increase by an approximate 0.5 m. In the long term the western islands may provide natural headland anchor points for the beach, and it is expected that the islands and future beach will continue to provide some level of wave protection to properties on the west side of the lake Dyke Options Gravel fill may be imported for: Short-term repair of the breach area. Long-term reinforcement of the 1.3 km long barrier beach in the form a gravel dyke. Cumulative coastal flood risk probabilities were estimated for various scenarios, as illustrated in Figures 4.1 and 4.2. While dyke options can mitigate the impact of ocean storm surge on the lake, lake level is expected to rise in conjunction with sea level. In addition, seawater intrusion is expected to remain a growing concern even with dyke options, due to the fresh/seawater interface rising with sea level. In summary, dyke options can only delay, not eliminate, long-term impacts of sea level rise on flooding and seawater intrusion Alternatives Alternatives to the dyke options include options at the property level which would typically include either: (1) Relocation of assets at risk. (2) Flood proofing of individual properties through a combination of: Abandon drinking water wells, use tank (communal or individual units) with imported drinking water. Raise living quarters and electrical equipment. Place fill on property lot and raise homes. Raise access road if required. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 36

44 Shoreline protection or berm if required (we note that natural sheltering from lake islands is expected to present an opportunity for individual property-scale shore protection). 5.2 Recommended Next Steps The cost of dyke options should be considered relative to value of assets to be temporarily protected. Alternative options may then be further explored. The findings and recommendations are based on information collected to date at the time of writing, with uncertainties associated with data gaps and modeling approximations inherent to this type of study. We recommend that they be revisited by NSDNR as new information becomes available. Updates from GSC s research should be incorporated in NSDNR s understanding of the coastal system. Notably, updated topographic surveys and soon-to-be-recovered tide gauge observations from the winter should be analyzed to improve the understanding of the local dynamics, most notably water levels evolving over several breach-closure cycles. Finally, we emphasize that the challenges posed by rising sea levels as presented in this report apply to many other dynamic coastal areas around the Province. This case represents a good illustration of the necessity to establish Province-wide coastal management policies towards practical and financially sustainable solutions. Yours truly, Prepared by: Vincent Leys, M.Sc., P.Eng. Senior Coastal Engineer Reviewed by: Danker Kolijn Coastal Engineer, P.Eng., M.Sc., M.Eng. This document was prepared for the party indicated herein. The material and information in the document reflects CBCL Limited s opinion and best judgment based on the information available at the time of preparation. Any use of this document or reliance on its content by third parties is the responsibility of the third party. CBCL Limited accepts no responsibility for any damages suffered as a result of third party use of this document. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 37

45 CHAPTER 6 REFERENCES DHI Software, MIKE21 User Guide. Danish Hydraulic Institute. Davidson Arnott R.G.D Conceptual Model of the Effects of Sea Level rise on Sandy Coasts. J. of Coastal Res. 21(6), ISSN Dean R. and Dalrymple R Coastal Processes with Engineering Applications. Cambridge U. Prtess. ISBN Han G., Ma Z., Zhai L., Greenan B., Thompson R Twenty-first century mean sea level rise scenarios for Canada. Canadian Technical Report of Hydrography and Ocean Sciences 313. 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. Kennedy G.W Development of a GIS based approach for the assessment of relative seawater intrusion vulnerability in Nova Scotia. IAH 2012 Congress, Niagara Falls. Shaw, J., Taylor, R. & Forbes, D Impact of the Holocene Transgression on the Atlantic Coastline of Nova Scotia. Géographie physique et Quaternaire, 47(2), Sweet W.V, Kopp R.E., Weaver C.P., Obeysekera J., Horton R.M., Thieler E.R., Zervas C., NOAA Technical Report NOS CO -OPS 083: Global and Regional Sea Level Rise Scenarios for the United States. Silver Spring, Maryland. Taylor R.B., Frobel D., Forbes D.L. and Mercer D. 2008: Impacts of Post-tropical Storm Noel (November, 2007) on the Atlantic Coastline of Nova Scotia, Geological Survey of Canada Open File 5802, 90 pgs. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 38

46 Taylor, R.B., Impacts of the February 9, 2013 Storm Along the Atlantic Coast of Nova Scotia; Geological Survey of Canada, Open File 7597, 26 p. doi: / Taylor, R.B., Frobel, D., Mercer, D., Fogarty, C., and MacAuley, P., Impacts of Four Storms in December 2010 on the Eastern Shore of Nova Scotia; Geological Survey of Canada, Open File, 7356; 53 p. doi: / USACE Coastal Engineering Manual. Engineering Manual Zhai L., B. Greenan, J. Hunter, T.S. James, G. Han, R. Thomson, and P. MacAulay Estimating Sealevel allowances for the coasts of Canada and the adjacent United States using the Fifth Assessment Report of the IPCC. Can. Tech. Rep. Hydrogr. Ocean. Sci. 300: v pp. CBCL Limited Coastal Risk Assessment and Adaptation Options at Miseners Long Beach 39

47 APPENDIX A Historical Air Photos CBCL Limited Appendix

48 Meters 1945

49 Meters 1954

50 Meters 1964

51 Meters 1976

52 Meters 1992

53 Meters 2003

54 Legend 2003_PL 1992_PL 1976_PL 1964_PL 1954_PL 1945_PL Meters Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community

55 APPENDIX B Offshore Wind and Wave Information Location of MSC50 Dataset CBCL Limited Appendix

56 Annual Directional Offshore Wave Height Statistics Annual Directional Offshore Wind Speed Statistics CBCL Limited Appendices

57 Monthly Directional Offshore Wave Height Statistics CBCL Limited Appendices

58 Monthly Directional Offshore Wind Speed Statistics CBCL Limited Appendices