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Report To: Planning and Development Committee
Date of Meeting: February 1, 2021 Report Number: PDS-007-21
Submitted By: Faye Langmaid, Acting Director of Planning Services
Reviewed By: Andrew C. Allison, CAO Resolution#: PD-029-21, PD-113-21
File Number: PLN15.2.2 By-law Number:
Report Subject: Cedar Crest Beach — Property Loss Study
Recommendations:
1. That Report PDS-007-21 be received; and
2. That all interested parties listed in Report PDS-007-21 and any delegations be
advised of Council's decision.
Municipality of Clarington
Report PDS-007-21
Report Overview
Page 2
This report provides background information on the Cedar Crest Beach — property loss study
requested by Council, including the final Port Darlington West Embayment Shoreline
Change Assessment report prepared by Zuzek Inc. (January 25, 2021). The final report
details a historical shore trend analysis, field data collection, and results of modelling. It
identifies both positive and negative impacts associated with the artificial littoral barriers that
bound this reach of Lake Ontario shoreline and the other factors that contribute to both
shoreline recession and accretion within the embayment situated between the St. Marys
Cement headland and the Port Darlington jetties, in Bowmanville.
1. Background
1.1 The reach of Lake Ontario shoreline that is the subject of this report, referred to
hereafter as the Port Darlington West Embayment, extends from St. Marys Cement
eastward to the piers at the mouth of Bowmanville / Soper Creek (approximately
1,800 m). The area is subject to multiple natural hazards, including lake flooding,
erosion and dynamic beach, and riverine flooding from the adjacent Westside Creek
and Bowmanville / Soper Creek watersheds and marsh systems. The Port Darlington
West Embayment is shown in Figure 1.
Figure 1: Key Map — Port Darlington West Embayment
Municipality of Clarington Page 3
Report PDS-007-21
1.2 Report CAO-006-19, dated June 17, 2019, outlines the history and background of the
actions that have been taken over the past 4 years by the Central Lake Ontario
Conservation Authority (CLOCA) and the Municipality with regard to the multiple natural
hazards which are present. As a result of Report CAO-006-19, Council passed
Resolution #C-275-19 on July 2, 2019. This resolution had several requests of staff. An
outline of these requests and the actions taken were reported in CAO-010-19.
1.3 The purpose of this report is to address the following action from Resolution #C-275-19:
That Clarington Staff provide a report to Council on the quantum of waterfront
property and public beach that have been lost along Cedar Crest Beach Road since
the St. Marys / Votorantim dock expansion took place due to erosion and all other
environmental factors and report back to Committee in September 2019.
1.4 Section 3.8 of CAO-010-19 outlines the work by Municipal and CLOCA staff with regard
to review of historical records, aerial photographs, subdivision plans and land ownership
records, a review of which clearly demonstrates ownership of a "beach" has not been
public. Unlike the beach at Port Darlington West Beach Park, dedication of a beach
block was never part of the subdivision plan along Cedar Crest Beach Road.
1.5 Report PSD-012-20, dated April 27, 2020, outlines the steps that occurred relating to
approval of the scope of work, budget ($30,000) and consulting firm to complete the
assignment. On May 25, 2020, Council approved resolution #C-235-20, approving the
approach for consultant selection and providing for the award of contract for the
completion of the requested study to Zuzek Inc., and directing staff to report back to
Council with the results of the study, once completed.
1.6 The scope of the assignment undertaken by Zuzek Inc. builds off the technical
investigations completed recently for the Lake Ontario Shoreline Management Plan
(Zuzek Inc., 2020). The Lake Ontario Shoreline Management Plan was originally
prepared in 1990 for the Central Lake Ontario, Ganaraska Region and Lower Trent
Conservation Authorities. It provided shoreline management direction for each
authority's respective shoreline area, extending approximately 135 km along the north
shore of Lake Ontario. In 2018, an update of this plan was jointly initiated by these three
Conservation Authorities, with support from the affected municipalities. The final Lake
Ontario Shoreline Management Plan (Zuzek, 2020) was endorsed by the CLOCA Board
on January 19, 2021.
1.7 The technical report prepared by Zuzek Inc., Port Darlington West Embayment
Shoreline Change Assessment (January 25, 2021), is provided as Attachment 1.
Municipality of Clarington
Report PDS-007-21
Page 4
2. Summary of the Shoreline Change Assessment Findings
2.1 The following sections present a synopsis of the approach and key findings from the
assessment undertaken by Zuzek Inc. Refer to the complete technical report
(Attachment 1) for detailed information on the data collection, modelling and analysis
methods. A summary of the study conclusions is found in Section 4.0 (Attachment 1).
2.2 The scope of the shoreline change assessment included the following:
• Review of construction history in the area for potential littoral barriers;
• Analysis of shoreline change for the regional study area;
• Analysis of sediment bypassing at the potential littoral barriers that were
identified;
• Study of development history impacts on shoreline evolution; and
• Preparation of a technical report.
2.3 To inform the analysis, a field investigation was undertaken to gather comprehensive
local data on the nearshore conditions for the Port Darlington West Embayment. A
collection of historical aerial imagery from 1954 to 2018 was also provided by the
Municipality and CLOCA for the analysis.
2.4 The assessment considered the entirety of the Port Darlington West Embayment. The
natural conditions and historical development within this area influence how the
shoreline adjacent to Cedar Crest Beach Road has evolved. To provide for comparison
it was important to establish an understanding of how the shoreline functioned prior to
development. Accordingly, the assessment also undertook modelling of local conditions
based on three scenarios, as follows:
• Scenario A: Pre-1800's (historical natural shoreline);
• Scenario B: Mid-1800's to mid-1970's (Port Darlington jetties present; St. Marys
Cement dock not yet constructed); and
• Scenario C: Post-1970's (current conditions).
2.5 The analysis of shoreline change for the Port Darlington West Embayment identifies that
the study area shoreline was a dynamic barrier beach system prior to development of
the shoreline with roads and buildings. Further, it confirms that Cedar Crest Beach has
been receding since at least 1954 and continues to do so today. A comparison to
similar, near by, undeveloped and uninterrupted shoreline areas showed that these
areas have also been receding over the same time period (1954 to 2018). The technical
report prepared by Zuzek Inc. indicates that "recession is the predominant natural long-
term shoreline trend for the north shore of Lake Ontario."
Municipality of Clarington Page 5
Report PDS-007-21
2.6 Based on the volume of sediment accumulated on the fillet beach immediately west of
the St. Marys Cement headland, the assessment estimates that this headland has
reduced the volume of sand and gravel transported into the Port Darlington West
Embayment by approximately 660 m3/year. Notwithstanding, the results of scenario
modelling demonstrated that multiple factors would have limited the likelihood of the
accumulation of large volumes of sediment along Cedar Crest Beach prior to
construction of the dock and prior to construction of the Port Darlington jetties. These
include current direction and speed, shoreline orientation, and a low total -load of
sediment suitable for transport.
2.7 Overall, the assessment indicates that several environmental and physical factors have
contributed to beach loss along the western half of the Port Darlington West
Embayment. These include:
• A natural long-term shore recession trend along the north shore of Lake
Ontario;
• Shoreline orientation that is not conducive to sediment deposition;
• Reduction in sediment supply due to the construction of the St. Marys Cement
headland;
• The construction of homes too close to the water's edge on top of a dynamic
eroding low-lying barrier beach; and
• The construction of vertical shoreline protection structures that are not
conducive to beach building.
2.8 Positive impacts identified in the assessment which are associated with the constructed
artificial littoral barriers that border the Port Darlington West Embayment include:
Stabilization of the eastern half of the Port Darlington West Embayment due to
the Port Darlington jetties, contributing to the existence of the beach at Port
Darlington West Beach Park; and
Protection of the eroding bluff shoreline within the footprint of the St. Marys
Cement headland, which contributes to the stability and anchoring of the
western boundary of the Port Darlington West Embayment.
3. Next Steps
3.1 It is important that shoreline management be both sustainable and holistic. The updatec
Lake Ontario Shoreline Management Plan (Zuzek Inc., 2020) recently released by the
Central Lake Ontario, Ganaraska Region and Lower Trent Conservation Authorities
provides updated hazard limits and management recommendations for several
shoreline reaches within the Municipality, including but not limited to the Port Darlington
Municipality of Clarington Page 6
Report PDS-007-21
West Embayment. CLOCA and Ganaraska Region Conservation Authority Staff will
present the results of the broader study to Council, in the near future.
3.2 The development of an implementation strategy to respond to all identified shoreline
vulnerabilities and risks, increase community resilience, and protect from coastal
hazards will be needed. Such a strategy should establish priorities, roles and
responsibilities, and opportunities to collaborate on actions, and be developed in
consultation with all stakeholders.
4. Concurrence
This report has been reviewed by the Director of Public Works who concurs with the
recommendations.
5. Conclusion
5.1 Council and residents are seeking more specific information on how the St. Marys
Cement dock and other environmental factors have contributed to beach loss along
Cedar Crest Beach, in Bowmanville. The purpose of retaining a consultant with coastal
engineering expertise was to assist with a technical analysis of shoreline recession
along Cedar Crest Beach and the contributing factors. A comprehensive assessment
was undertaken by Zuzek Inc., including a historical shore trend analysis, field data
collection and modelling.
5.2 The technical report prepared by Zuzek Inc. provides a more complete understanding of
the factors that have and will continue to influence the evolution of the shoreline along
Cedar Crest Beach Road. It quantifies the interruption of sediment transport resulting
from the construction of the littoral barriers within this shoreline area, including the St.
Marys Cement headland and the Port Darlington jetties, and identifies several other
factors which also contribute to beach loss and the on -going shoreline recession trend
along Cedar Crest Beach. Positive impacts associated with the human -made littoral
barriers that bound the Port Darlington West Embayment are also identified. Benefits
include shoreline stabilization that has contributed to the establishment of the public
beach at Port Darlington West Beach Park and to the stability of the western boundary
of the Port Darlington West Embayment.
5.3 The technical report prepared by Zuzek Inc. contributes to a growing understanding of
natural and human -made factors that are influencing the evolution of the Lake Ontario
shoreline throughout Clarington and helps to better inform management decisions.
Following the upcoming release of the updated Lake Ontario Shoreline Management
Plan, a strategy that prioritizes actions to increase the resilience of Clarington's
waterfront will be needed. The Lake Ontario Shoreline Management Plan will be the
subject of a future report to Council.
Municipality of Clarington Page 7
Report PDS-007-21
5.4 It is respectfully recommended Council receive Staff Report PDS-007-21.
Staff Contact: Amy Burke, Acting Manager, Special Projects, 905-623-3379 x 2423 or
aburke@clarington.net.
Attachments:
Attachment 1 — Cedar Crest Beach Shoreline Change Assessment (Zuzek Inc., January 25,
2021)
Interested Parties:
The following interested parties will be notified of Council's decision:
Steve Brake, Director of Works
Sean Bagshaw, Manager of Infrastructure, Works Department
Chris Darling, Central Lake Ontario Conservation Authority
Perry Sisson, Central Lake Ontario Conservation Authority
Chris Jones, Central Lake Ontario Conservation Authority
Ruben Plaza, St. Marys Cement
Don Huff, ECO Strategy
Jeff Mitchell, President, Port Darlington Community Association
Victoria Caballero
Patrick Corcoran
Alison Fellowes
Gord Giffin
Joan Giffin
Susie Plumpton
Corinne Racioppa
Tony Racioppa
Rick Rossi
Bill Sims
Brad Winton
Roberta Winton
Attachment 1 to Report
PDS-007-21
Port Darlington West Embayment
Shoreline Change Assessment
Prepared for:
Municipality of Clarington
January 25, 2021
Prepared by:
Contact the Author:
Peter J. Zuzek
905-719-8980
pzuzek@zuzekinc.com
Zuzek inc.
CAVE WORLD
View of Cedar Crest Beach Shoreline (top) and St. Marys Cement Headland
(bottom) from the Port Darlington Navigation Channel on August 7, 2020
p%� �Oa
PETER J. ZJZ£K
PRACTiSMG MEMUR
Disclaimer:
Zuzek Inc. prepared this report for Municipality of Clarington. The standard of care typically
applied to such an assignment was followed using available data to produce the report. Zuzek
Inc. assumes no responsibility for the use of this report by a third party. Furthermore, if used by
a third party, they agree that the information is subject to change without notice and Zuzek Inc.
assumes no responsibility for the consequences of such use or changes in the information. Under
no circumstances will Zuzek Inc. be liable for direct, indirect, special, or incidental damages
resulting from, arising out of, or in connection with the use of the information in this report by a
third party.
1031.01 Port Darlington West Embayment
Shoreline Change Assessment
TABLE OF CONTENTS
1.0 INTRODUCTION............................................................................................ I
1.1 Scope of Investigation..................................................................................................1
1.2 History of SMC Headland...........................................................................................2
2.0 SHORELINE CHANGE.................................................................................. 3
2.1 1863 Map.....................................................................................................................3
2.2 1878 Map.....................................................................................................................4
2.3 1954 to 2018 Shoreline Trend.......................................................................................4
2.4 SMC Headland Fillet Beaches.....................................................................................6
2.5 Port Darlington Fillet Beaches.....................................................................................7
2.6 Regional Shoreline Trends...........................................................................................7
3.0 DATA COLLECTION AND MODELLING.................................................14
3.1 Bathymetric Survey and Sonar Data Collection.........................................................14
3.1.1 Profile Data and Substrate Mapping......................................................................................................15
3.2 Numerical Modelling of Waves and Sediment Transport..........................................22
3.2.1 Offshore Wave Climate.........................................................................................................................22
3.2.2 Longshore Sediment Transport Potential (CERC-Formula)..................................................................23
3.2.3 Detailed Wave, Hydrodynamic and Sediment Transport Modelling.....................................................24
3.3 Influence of Development History on Shoreline Recession.......................................34
4.0 CONCLUSIONS.............................................................................................36
4.1 Early 1800s (prior to the Port Darlington Jetties).....................................................36
4.2 Mid-1800s to Late-1970s (Port Darlington Jetties).....................................................36
4.3 Late-1970s to Present (Jetties and SMC Headland)...................................................37
4.4 Summary of Benefits and Impacts of Shoreline Alterations.......................................37
REFERENCES......................................................................................................... 39
APPENDIX A — Historical Shoreline Change Data
List of Tables
Table 3.1 Offshore Wave Conditions Corresponding to a Variety of Return Periods ............................... 23
List of Figures
Figure 1.1 Port Darlington West Embayment..............................................................................................1
Figure 1.2 Original SMC East Headland (image courtesy of SMC)............................................................ 2
Figure 2.1 Map of Lake Ontario Ports and Harbours in 1863..................................................................... 3
1031.01 Port Darlington West Embayment i
Shoreline Change Assessment
Figure 2.2 1878 Map of Study Area Overlaid on 2018 Aerial Photograph ................................................. 4
Figure 2.3 1954 to 2018 Waterline Comparison..........................................................................................
5
Figure 2.4 Bluff Recession West of SMC Headland...................................................................................
5
Figure 2.5 Pre-lakefill Shoreline Recession and Current Fillet Beaches .....................................................
6
Figure 2.6 Port Darlington Fillet Beach Volume Estimates........................................................................
7
Figure 2.7 Shoreline Trend Data for Reach 1, Lake Ontario SMP (Zuzek Inc., 2020) ...............................
9
Figure 2.8 Barrier Beach Recession Rates at Cranberry Marsh.................................................................10
Figure 2.9 Summary of Reach 3 Shoreline Change Rates (Zuzek Inc., 2020)..........................................11
Figure 2.10 Reach 7 Shoreline Change Rates............................................................................................
12
Figure 2.11 1954 to 2018 Shoreline Recession Data for Carr's Marsh.....................................................13
Figure 3.1 Survey Boat (left) and Transducer Mount (right).....................................................................14
Figure 3.2 Boat Tracks West and East of Port Darlington.........................................................................14
Figure 3.3 Bathymetric Data Points Colour Coded by Depth....................................................................15
Figure 3.4 Profile 1 (top), Sonar Imagery (middle), Underwater Pictures of Cobble Lag (bottom) ..........
17
Figure 3.5 Profile 6 at Southwest Corner of SMC Headland.....................................................................18
Figure 3.6 Profile 8 (top), Sonar of Wharf Armour Stone and Concrete Caisson (middle), Mud Lake
Bottom(bottom)..........................................................................................................................................19
Figure 3.7 Profile 13 (top), Sonar Imagery of Transition from Cobbles and Sand Substrate (middle),
Underwater Picture of Cobble Lag (bottom left) and Sand Substrate (bottom right) .................................
20
Figure 3.8 Gentle Nearshore Slope and Natural Beach Conditions at Profile 14......................................
21
Figure 3.9 Eroding Bluff Shoreline East of Port Darlington.....................................................................
21
Figure 3.10 Cobble -Boulder Lag Deposit in Nearshore between Line 19 and 20.....................................
22
Figure 3.11 Alongshore View of West Beach...........................................................................................
22
Figure 3.12 CMS -Wave Model Domain and Bathymetry.........................................................................
25
Figure 3.13 CMS -Wave Model Results for Three Scenarios and Both SW and ESE Waves ...................
26
Figure 3.14 CMS -Flow Model Results Showing Nearshore Currents for all Three Scenarios and the SW
(230 deg) Waves.........................................................................................................................................
29
Figure 3.15 CMS -Flow Model Results Showing Nearshore Currents for all Three Scenarios and for ESE
(100 deg) Waves.........................................................................................................................................30
Figure 3.16 CMS -Flow Model Results Showing Simulated Sediment Transport Capacity and Direction
for all Three Scenarios and SW (230 deg) Waves......................................................................................32
Figure 3.17 CMS -Flow Model Results Showing Simulated Sediment Transport Capacity and Direction
for all Three Scenarios and for ESE (100 deg) Waves...............................................................................
33
Figure 3.18 Map from 1878 and 1954 Aerial Photograph.........................................................................
35
1031.01 Port Darlington West Embayment ii
Shoreline Change Assessment
1.0 INTRODUCTION
Cedar Crest Beach is located on the north shore of Lake Ontario immediately west of Port
Darlington and east of the St. Marys Cement (SMC) facility in the Municipality of Clarington.
Refer to Figure 1.1. The Port Darlington navigation channel has been stabilized with jetties
since at least 1860, a period of 160 years. Lake filling to create the main SMC Headland
occurred between 1974 and 1979, with the western portion constructed in the late 1990s. This
report summarizes the shoreline change assessment for the Port Darlington West Embayment
completed by Zuzek Inc. and SJL Engineering Inc.
Figure 1.1 Port Darlington West Embayment
1.1 Scope of Investigation
The scope of the shoreline change assessment is summarized in the following bullets and builds
off the technical investigations completed recently for the Lake Ontario Shoreline Management
Plan (Zuzek Inc., 2020):
• Review of construction history for potential littoral barriers.
• Shoreline change analysis for the regional study area.
• Sediment bypassing analysis at potential littoral barriers.
• Study of development history impacts on shoreline evolution.
• Reporting.
1031.01 Port Darlington West Embayment P.l
Shoreline Change Assessment
1.2 History of SMC Headland
Operation of the SMC plant in Bowmanville began in 1967/68, with the lake filling for the main
eastern pier occurring from 1974 to 1979. Prior to the construction of the SMC Headland, the
shoreline consisted of an eroding bluff and small embayment protected by a barrier beach. The
newer western portion of the headland was constructed in the late 1990s (Municipality of
Clarington, 2017). An aerial picture of the original eastern headland following construction is
provided in Figure 1.2. The influence of the SMC Headland on sediment bypassing will be
investigated in the study, along with Port Darlington jetties.
Figure 1.2 Original SMC East Headland (image courtesy of SMC)
1031.01 Port Darlington West Embayment p.2
Shoreline Change Assessment
�z
2.0 SHORELINE CHANGE
Section 2.0 of the report summarizes the findings of the shoreline change assessment for local
conditions in the Port Darlington West Embayment, the adjacent shoreline, and regional trends.
Evaluating the long-term shoreline change trends at the site and the north shore of Lake Ontario is
necessary to put the observed changes in context, evaluate potential sources of new sand and
gravel to the embayment, and evaluate long-term shoreline trends at other similar sites.
2.1 1863 Map
By the early to mid- 1800s, Lake Ontario featured an extensive series of harbours and ports, which
facilitated trade and commerce in the region and provided recreational opportunities for the
growing population of the province. A map published in 1863 by Chewett & Co. of Toronto for
the ports on the lake is presented in Figure 2.1 (Public Archives Canada).
In 1863, the jetties at Port Darlington sheltered the interior embayment, as noted on the inset map
of Figure 2.1. The Cedar Crest Beach shoreline to the west was depicted as a narrow undeveloped
barrier beach.
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Figure 2.1 Map of Lake Ontario Ports and Harbours in 1863
1031.01 Port Darlington West Embayment p.3
Shoreline Change Assessment
2.2 1878 Map
A second historical map of the area was obtained from the Atlas of Durham and Northumberland
Counties. It was geo-referenced with Geographic Information Software (GIS) using coordinates
of known features, such as Lots and Concessions and the street network. Refer to Figure 2.2. The
jetties in the historical map correspond to the current navigation channel to the existing port lands.
The atlas also indicates that the Port Darlington Harbour Company was created in 1837,
suggesting almost a 200-year history in the area.
2018 Air Photo with 1878 Map Overlay '
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R �r A F � � - # � • � r'++-- � { � R4 F,i' t ^� I�i{k,� ''aS. �e�`y4 ! V
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Figure 2.2 1878 Map of Study Area Overlaid on 2018 Aerial Photograph
From the historical 1878 map, it is important to note that the Cedar Crest Beach shoreline, west of
Cove Road, was depicted on the map as a barrier beach and an inlet over 100 in wide. While the
cartographic accuracy of these historical maps is not consistent with modern technology, there is
clearly a large inlet to the current embayment and marsh region. This finding is significant, as it
demonstrates that the study area shoreline was a dynamic barrier beach system with a large inlet
prior to development of the shoreline with a road and permanent buildings.
2.3 1954 to 2018 Shoreline Trend
Aerial imagery of the study area was available for nine temporal periods from 1954 to 2018. A
map with the geo-referenced aerial photographs is provided in Appendix A with the 2018 waters
edge overlaid to evaluate shoreline changes. A summary of the changes from 1954 to 2018 is
provided in Figure 2.3. The 1954 shoreline position was corrected to account for differences in
water level between the 1954 and 2018 images.
Adjacent to the west jetty at Port Darlington, the shoreline has been migrating slowly lakeward,
noted as a zone of accretion in Figure 2.3. The central portion of the Port Darlington West
Embayment has been stable from 1954 to 2018 (no significant recession or accretion trend). The
1031.01 Port Darlington West Embayment p.4
Shoreline Change Assessment
shoreline for the western portion of the embayment has been receding from 1954 to 2018, with an
average long-term recession rate of 0.17 m/yr.
Figure 2.3 1954 to 2018 Waterline Comparison
Between the Darlington Nuclear Generating Station and the SMC Headland, changes in the
position of the glacial till bluff crest were also measured. The bluff has been eroding at an average
annual recession rate of 0.22 m/year from 1954 to 2018. Refer to Figure 2.4.
Figure 2.4 Bluff Recession West of SMC Headland
1031.01 Port Darlington West Embayment p.5
Shoreline Change Assessment
2.4 SMC Headland Fillet Beaches
Prior to the construction of the SMC Headland, the bluff shoreline corresponding to the footprint
of the headland was receding and contributed approximately 178 m3/year of sand and gravel to the
shoreline. Refer to Figure 2.5 (top panel). With a net sediment transport direction of west to east
(Zuzek Inc., 2020), this material would have historically been transported eastward into the Port
Darlington West Embayment.
Figure 2.5 Pre-lakefill Shoreline Recession and Current Fillet Beaches
The spatial extent of the east and west fillet beaches associated with the existing SMC Headland
are mapped in the bottom panel of Figure 2.5. From the late 1990s to 2016, the west fillet beach
has trapped approximately 14,000 m3 of sand and gravel, or 660 m3/yr. From the late 1970s to
2016, the smaller east fillet beach has trapped roughly 7,000 m3 of sediment or 180 m3/yr.
Based on this shoreline change assessment, the SMC Headland has reduced the volume of sand
and gravel transported into the Port Darlington West Embayment by roughly 660 m3/yr.
Conversely, roughly 180 m3/yr has been retained within the embayment (in the SMC Headland
east fillet beach) that would otherwise have been transported out of the embayment to the east or
west.
1031.01 Port Darlington West Embayment p.6
Shoreline Change Assessment
2.5 Port Darlington Fillet Beaches
As noted in Section 2.1, the Port Darlington jetties have been in place since at least the mid-1800s,
with the Harbour Company being established in 1837. The west jetty has been trapping sand and
gravel that was moving west to east along the shoreline for at least 160 years. As seen in Figure
2.6, the volume estimate for the west fillet beach is approximately 55,000 m3, which translates into
an annual accretion rate of 340 m3/year. This is likely an underestimation of the total volume of
eastward transport, as additional sand and gravel have accumulated in the navigation channel.
This additional volume was not estimated, and historical dredging records were not investigated.
Figure 2.6 Port Darlington Fillet Beach Volume Estimates
2.6 Regional Shoreline Trends
Extensive information on regional shoreline change trends was recently developed for the Lake
Ontario Shoreline Management Plan (Zuzek Inc., 2020), which provides important context on the
historical trends for the Port Darlington West Embayment. Three sites with similar shoreline
conditions were evaluated. Where appropriate, waterline corrections were applied to the shoreline
data in the Shoreline Management Plan.
The 1954 to 2018 shoreline trend data for Reach 1 of the Shoreline Management Plan study, which
includes the Cranberry Marsh and Lynde Shores Conservation Area, is presented in Figure 2.7.
This reach is not only close in proximity to the Port Darlington West Embayment, but it also has a
similar shoreline orientation (SW to NE), features barrier beaches protecting coastal wetlands, and
has a jettied navigation channel at its eastern extent (Whitby Harbour). The central portion of the
reach, which features beaches, has a long-term recession rate of 0.23 m/yr from 1954 to 2018.
Refer to Figure 2.8 for the actual waterline comparison at the barrier beach. As evident from this
comparison, even in a natural undeveloped state, barrier beaches along the north shore of Lake
Ontario erode and have been receding since at least 1954.
Reach 3 from the Lake Ontario SMP is another relevant example, as it features the sandy
shorelines and barrier beaches fronting the Oshawa Second Marsh and Darlington Provincial Park.
1031.01 Port Darlington West Embayment p.7
Shoreline Change Assessment
These beaches also have a long-term recession rate of 0.36/m/yr, on average, from 1954 to 2018.
Refer to Figure 2.9.
The final shoreline change example from the Lake Ontario SMP comes from Reach 7, which
covers the shoreline from Port Hope to Cobourg. The central portion of Reach 7 (Figure 2.10)
features a sand and cobble beach shoreline fronting a large natural area, including Carr's Marsh.
The long-term recession rate for the beach portion of the shoreline ranges from 0.9 m/yr to
upwards of 1.3 m/yr, as seen in Figure 2.11.
The shoreline change measurements from these other beach sites with similar shoreline
characteristics has shown recession is the predominant natural long-term shoreline trend for the
north shore of Lake Ontario. Prior to the construction of the Port Darlington jetties and the SMC
Headland, the shoreline of the Port Darlington West Embayment and the adjacent cohesive bluffs
would have featured a similar long-term recession rate.
1031.01 Port Darlington West Embayment p.8
Shoreline Change Assessment
Pringle Creek
+Port Whitby
• Whitby
Harbour.
CLOCA
-i�77CIC50R5
Point
TOP OF B L U FF TRANS ECTS (1954 to 20181
No. Erosion Transects 85
Max Length (m) 16.1
Avg Length [mj 6.4
AARR (m/yr) 0.10
S.D- (Standard Deviation) 0.05
AARR + 1 5.0. (m/yr) 0.1S
WATERLINE TRANSECTS (1954to 2018)
Legend
Total No. Transects 192
Annualized SCR (m/yr) 0.23
Bluff Transects: Trend
Net Trend Erosion
Erosion
No. Erosion Transects 190
Waterline Transects: Trend
Ann uaIized SCR (m/yr) 0.23
� Erasion
No. Accretion Transects 2
Annualized SCR (m/yr) -0.10
Accretion
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1031.01 Port Darlington West Embayment P.9
Shoreline Change Assessment
Shoreline Comparison at Lynde Shores
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1031.01 Port Darlington West Embayment p.10
Shoreline Change Assessment
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1031.01 Port Darlington West Embayment p.I I
Shoreline Change Assessment
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1031.01 Port Darlington West Embayment p.12
Shoreline Change Assessment
Figure 2.11 1954 to 2018 Shoreline Recession Data for Carr's Marsh
1031.01 Port Darlington West Embayment p.13
Shoreline Change Assessment
3.0 DATA COLLECTION AND MODELLING
Field data collected for the investigation and detailed local -scale numerical modelling are
discussed in Section 3.0 of the report.
3.1 Bathymetric Survey and Sonar Data Collection
A detailed bathymetric survey of the nearshore zone in the Port Darlington West Embayment
was completed on August 7, 2020. Figure 3.1 provides a picture of the survey boat (left) and
SOLIX transducer mounted on the back of the boat (right). The SOLIX is a single -beam
bathymetric system for recording lake bottom depths and sonar images of the bottom substrate.
The survey track used to navigate the boat is presented in Figure 3.2 and the resulting colour -
coded depth data collected with the SOLIX is plotted in Figure 3.3.
IV
Figure 3.1 Survey Boat (left) and Transducer Mount (right)
Figure 3.2 Boat Tracks West and East of Port Darlington
i
1031.01 Port Darlington West Embayment p.14
Shoreline Change Assessment
41
� y
7
L
_ m
1
o �
5 �
Figure 3.3 Bathymetric Data Points Colour Coded by Depth
3.1.1 Profile Data and Substrate Mapping
The key findings from the profile data and substrate mapping are summarized below:
• Profile 1 West of SMC Headland: Located along the eroding bluffs west of the SMC
Headland, Profile 1 features a steep bluff face with crest elevations over 30 m above the
lake (Figure 3.4, top). The nearshore profile is very flat, featuring a nearshore slope of
approximately 1:100 (V:H). The sonar imagery captured a significant cobble lag deposit
that blankets the lake bottom. Refer to the middle panel of Figure 3.4, which includes a
plan view map showing the boat location (left), a cross-section of the sonar image under
the boat (middle), and an image of the lake bottom 25 in to the right and left of the boat
(right). Underwater pictures, also presented in Figure 3.4, verify the interpretation of the
sonar.
• Profile 6 SW Tip of SMC Headland: Profile 6 captures the shoreline and lake bottom
conditions at the southwest corner of the SMC Headland (Figure 3.5). The lake bottom is
very deep, 8 in at the toe of the armour stone protecting the headland. The middle panel
of Figure 3.5 captures the edge of the armour stone and the transition to the lake bottom.
Based on the intensity of the sonar signal and flat slope of the lake bottom (middle and
bottom panel of Figure 3.5), the substrate features soft/muddy material. There is no
1031.01 Port Darlington West Embayment p.15
Shoreline Change Assessment
evidence of a sandy bypassing shoal or bed features that indicate the sand is being
transported around the headland.
• Profile 8 SE Tip of SMC Headland: Profile 8 records the conditions at the southeast
corner of the SMC Headland. Like Profile 6, the lake bottom is very deep at the pier
(-10 m) and progresses quickly to a depth of 15 in. There is no evidence of a sand lake
bottom, sandy bypassing shoal or bar system that could facilitate the movement of
sediment around the headland. In contrast, the sonar imagery suggests the lake bottom
features soft/muddy sediment.
• Profile 13 Cedar Crest Beach Road: The land elevation is low (< 3m) along Cedar
Crest Beach Road and drops off quickly at the waters edge (see Figure 3.7, top), which
mostly features shoreline protection structures. A cobble lag deposit was mapped on the
lake bottom except close to shore, where the bottom substrate changes to sand. Refer to
the middle panel in Figure 3.7. The substrate mapping was confirmed with underwater
pictures, as seen in the bottom images of Figure 3.7.
• Profile 14 Cove Road: Profile 14 in Figure 3.8 is typical of the beach and nearshore
conditions along Cove Road. The homes are set back further from the waters edge and a
wide beach transitions to a shallow gently sloping nearshore. The slope at the waters
edge (approximately 150 in on the x-axis) is much gentler than Profile 13 (175 in on the
x-axis of Figure 3.7, top panel) which is typical of the nearshore along Cedar Crest
Beach.
• Profile 20 Eroding Bluffs East of Port Darlington: Profile 20 is typical of the
shoreline and nearshore conditions east of Port Darlington (Figure 3.9). Steep eroding
bluffs define the shoreline, and the nearshore profile is flat, featuring a slope similar to
Profile 1 (1:100) between the waters edge and the 4 in depth contour. The sonar mapped
an extensive cobble -boulder lag deposit between Lines 19 and 20. Refer to Figure 3.10.
No significant sand deposits were identified with the mapping.
At West Beach, a mixed sand -cobble beach transitions to a narrow sandy nearshore, followed by
an extensive cobble -lag deposit. Refer to Figure 3.11. There are no major sand deposits in the
study area other than the fillet beaches and the largest sand deposit (West Beach) only exists
because of the artificial littoral barrier formed with the construction of the Port Darlington jetties
160 years ago. Immediately offshore of the SMC Headland and in depths greater than 10 in, the
lake bottom consists of soft sediments (mud).
In summary, the sonar mapped large areas in the nearshore of the Port Darlington West
Embayment and the shoreline to the east and west dominated by cobble -lag deposits. Sand is
generally limited to the waters edge and accumulations in the small fillet beaches adjacent to the
littoral barriers.
1031.01 Port Darlington West Embayment p.16
Shoreline Change Assessment
pl
40.0
—202QAug-075OLIX S.—Y
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a
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0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300
Distance (m)
Figure 3.4 Profile 1 (top), Sonar Imagery (middle), Underwater Pictures of Cobble Lag
(bottom)
1031.01 Port Darlington West Embayment p.17
Shoreline Change Assessment
p6
20.0
—2O20.Aug-07 S OLD(S"-,y
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Figure 3.5 Profile 6 at Southwest Corner of SMC Headland
1031.01 Port Darlington West Embayment p.18
Shoreline Change Assessment
20.0
15.0
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Distance (m)
Wd maass 0 ► „
Figure 3.6 Profile 8 (top), Sonar of Wharf Armour Stone and Concrete Caisson (middle),
Mud Lake Bottom (bottom)
1031.01 Port Darlington West Embayment p.19
Shoreline Change Assessment
20.0
15.0
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i
0 100 200 3D3 4D3 500 600 700 aO0 900 1000 1100
Distance (m)
E® t] )'45:20 0 111 1 .
Figure 3.7 Profile 13 (top), Sonar Imagery of Transition from Cobbles and Sand Substrate
(middle), Underwater Picture of Cobble Lag (bottom left) and Sand Substrate (bottom right)
1031.01 Port Darlington West Embayment p.20
Shoreline Change Assessment
20.0
15.0
10.0
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5.0
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......... i.. .. .. ..
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Figure 3.8 Gentle Nearshore Slope and Natural Beach Conditions at Profile 14
20.0
15.0
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Figure 3.9 Eroding Bluff Shoreline East of Port Darlington
1031.01 Port Darlington West Embayment p.21
Shoreline Change Assessment
Figure 3.10 Cobble -Boulder Lag Deposit in Nearshore between Line 19 and 20
Figure 3.11 Alongshore View of West Beach
3.2 Numerical Modelling of Waves and Sediment Transport
Numerical simulations of waves, currents, and longshore sediment transport potential were
investigated with a high -resolution coastal model for the study area. The results are summarized
in the following sections.
3.2.1 Offshore Wave Climate
The offshore wave climate affecting the north shore of Lake Ontario in the vicinity of Cedar
Crest Beach was assessed with the Wave Information Study (WIS) database. The WIS is a
United States Army Corps of Engineers (USACE) sponsored project providing hourly wave
climatologies for all major shorelines throughout the United States. Included in this study was a
45-year wave hindcast for Lake Ontario covering the period from 1970 to 2014. In a wave
hindcast, historical wind fields are used to drive a wave generation and propagation model to
1031.01 Port Darlington West Embayment p.22
Shoreline Change Assessment
produce a timeseries of historical waves around the perimeter of the lakes. The model is then
calibrated to measured wave buoy data, where available, to verify the predictions. The WIS
database is the most accurate and complete wind -wave dataset available for Lake Ontario.
Offshore waves were assessed from WIS station 991178, located at a depth of 36 in (below chart
datum), and approximately 5.4 km south of Port Darlington. A statistical analysis of storm
events was conducted on the offshore wave data for the period from 1960 to 2014 inclusive.
Storm events are the primary cause of coastal erosion, flooding events, and the transport of sand
and gravel along the north shore of Lake Ontario. As such, it is important to understand the
wave characteristics and particularly the directionality of storm events impacting the Cedar Crest
Beach shoreline and surrounding areas.
Significant storm events were isolated from the offshore WIS dataset and ranked. The events
were binned based on peak wave direction. Of the ranked events, 74% were shown to arrive
from 230 degrees (+/- 10 deg) and 23% from 100 degrees (+/- 10 deg). The remainder of storm
events (less than 5%) arrive from a variety of other southerly directions. The wave climate can
therefore be characterized as having two principal directions (bimodal) from which significant
wave energy is produced. Due to the general shoreline orientation along the north shore of Lake
Ontario, the dominant SW wave direction (230 deg) will produce west to east longshore
sediment transport along the shoreline. Conversely, the secondary ESE wave direction (100 deg)
will produce east to west longshore sediment transport.
Further statistical analyses of the offshore waves were completed to determine the magnitude of
storm events associated with a variety of return periods. The significant wave heights
corresponding to the top 45 storm events (one per year, on average) were fit to several statistical
distributions for extreme value analysis. The offshore significant wave height associated with a
variety of return periods were then calculated from the best fitting distribution and are listed in
Table 3.1. The significant wave height corresponding to each storm event in the storm list was
also plotted against the corresponding peak wave period (Tp) to determine an appropriate
relationship between wave height and wave period during major storm events, with the results
listed in Table 3.1.
Table 3.1 Offshore Wave Conditions Corresponding to a Variety of Return Periods
Return Period
(years)
Significant Wave Height
(m)
Peak Wave Period
(s)
1
4.36
8.4
2
4.70
8.7
5
5.12
9.1
10
5.44
9.3
25
5.90
9.8
50
6.27
10.1
100
6.67
10.5
3.2.2 Longshore Sediment Transport Potential (CERC-Formula)
As a component of the recent Lake Ontario Shoreline Management Plan (SMP) undertaken by
Zuzek Inc. (2020), offshore waves at WIS station 991178 were transformed to the shoreline
1031.01 Port Darlington West Embayment p.23
Shoreline Change Assessment
using the Delft3D-Wave model to estimate longshore sediment transport potential calculations at
various locations along the Lake Ontario shoreline. The wave model grid had a spatial resolution
of 50 x 50 metres, making it too coarse for detailed analyses of sediment transport pathways near
the shoreline. However, it was sufficiently accurate to inform broad sediment transport potential
calculations using the CERC formula at various locations along the north shore of Lake Ontario.
One such calculation was made at the center of the embayment where Cedar Crest Beach Road
meets Cove Road. At this location it was determined that sediment transport has the potential to
move in both directions along the shoreline depending on the incident wave direction, away from
the centre of the embayment towards the SMC Headland to the west and the Port Darlington
jetties to the east. This finding is consistent with the bimodal storm population found in the WIS
hindcast data. The net sediment transport direction was to the east and the potential transport
was determined to be low, on the order of 2,000 m3/yr. Potential transport is the theoretical
maximum volume of sediment that can be transported along a shoreline with unlimited sediment
supply on the lake bottom, which is not the case for Cedar Crest Beach, where cobble -boulder
lag deposits dominate the nearshore. Therefore, actual sediment transport rates would be much
lower.
3.2.3 Detailed Wave, Hydrodynamic and Sediment Transport Modelling
To examine sediment transport potential and sediment transport pathways at high resolution,
detailed wave and hydrodynamic models were setup covering the shoreline from the Darlington
Nuclear Generating Station to 2.2 km east of the Port Darlington jetties. The CMS -Wave (wave
model) and CMS -Flow (hydrodynamic and sediment transport) models were used in a coupled
manner, both featuring a spatial resolution of 10 x 10 metres. Bathymetry for both models was
interpolated from depth contours courtesy of the National Ocean and Atmospheric
Administration (NOAA). The CMS -WAVE model domain and bathymetry is presented in
Figure 3.12.
1031.01 Port Darlington West Embayment p.24
Shoreline Change Assessment
Figure 3.12 CMS -Wave Model Domain and Bathymetry
The CMS-Wave/Flow models were used to investigate nearshore currents and sediment transport
pathways resulting from both SW (230 degree) and ESE (100 degree) storm wave directions.
The wave height and wave period used in the simulations was representative of a storm that
would be exceeded 5 to 6 times per year, on average (Hs = 3.0 m, Tp = 7.5 s). The models were
run for the following three scenarios:
A. Pre 1800s (no SMC Headland or Port Darlington jetties, just the historical natural
shoreline),
B. Mid-1800s to mid-1970s (Port Darlington jetties present, but no SMC Headland),
C. Post-1970s (existing conditions including SMC Headland and the Port Darlington jetties).
Running the model for the three scenarios listed above provided a comparison of simulated
nearshore hydrodynamics and sediment transport pathways for each period. This provided the
data to investigate the impacts of the Port Darlington jetties and the SMC Headland on important
physical processes that influence shoreline evolution.
1031.01 Port Darlington West Embayment p.25
Shoreline Change Assessment
Figure 3.13 presents the CMS -Wave model results for all three scenarios and for both SW
(primary) and ESE (secondary) wave directions. Colour contours represent significant wave
height in metres (refer to the legend) while vectors visualize the direction of wave propagation.
Figure 3.13 CMS -Wave Model Results for Three Scenarios and Both SW and ESE Waves
1031.01 Port Darlington West Embayment p.26
Shoreline Change Assessment
From Figure 3.13 it is clear waves arriving from the SW direction (230 deg) begin breaking and
dissipating their wave energy much further offshore than waves arriving from the ESE (100 deg).
The SW waves approach the shoreline from a much more oblique angle resulting in significant
refraction compared to the ESE direction. The result is a much wider surf zone, as is evident in
Figure 3.13.
There is little difference in significant wave height or wave direction between the three scenarios
presented in Figure 3.13, except close to shore where there have been changes in the shoreline
geometry due to the littoral barriers. For example, waves tend to break along the SMC Headland
in Scenario C since the southern tip is in relatively deep water (-10 m). For the SW wave
condition, the headland creates a sheltered zone with relatively low wave energy and significant
wave diffraction on its eastern side.
3.2.3.1 Hydrodynamic Modelling
Figure 3.14 and Figure 3.15 present the results of the CMS -Flow hydrodynamic modelling for all
three scenarios described above, zoomed in on the Port Darlington West Embayment. Contours
are representative of current magnitudes while vectors indicate both the speed (vector length)
and direction of nearshore currents throughout the model domain. Inputs to the hydrodynamic
model included the wave conditions (wave heights, periods, directions, radiation stresses, etc.)
from the wave model simulations presented in Figure 3.13 above, and a constant water surface
elevation of +1.0 in CD (+75.2 in IGLD85'), which is representative of a typical spring/summer
water level.
As seen in Figure 3.14 below, the dominant SW (230 deg) wave direction produces a west to east
longshore current generally running parallel to the waterline for all three shoreline geometry
scenarios. Interestingly, for Scenario A and B (no SMC Headland), the longshore current begins
to diverge from the shoreline at the west end of Cedar Crest Beach Road and travel across the
embayment some distance from the shoreline before dissipating offshore. This implies that
mobilized sediment would potentially follow an offshore bar that bypasses, in part, the Port
Darlington West Embayment during the dominant SW wave conditions for Scenario A and B.
The hydrodynamic modelling also shows an accelerating longshore current along the Cedar Crest
Beach shoreline for Scenario A, which would not be conducive for sediment deposition or
natural beach building. In other words, prior to the construction of the Port Darlington jetties,
the area likely featured narrow beaches adjacent to the receding shoreline. For Scenario B, the
current decelerates at the east end of the embayment as it nears the Port Darlington west jetty,
which has resulted in the formation of the west fillet beach.
With the presence of the SMC Headland in Scenario C there is a decreasing longshore current
that moves towards the Headland from the west, leading to the accumulation of a small west
fillet beach (refer to Section 2.4). Further offshore, the currents are moving across a large
cobble -boulder lag deposit and the SONAR data suggests there is no sand and gravel in this
region to transport towards the tip of the SMC Headland. The currents that do develop along the
south side of the Headland (bottom panel, Figure 3.14) are discontinuous and primarily
associated with wave breaking on the armour stone protecting the slope. These modelling results
are supported with the SONAR data, which did not capture any signs of bedload transport (lake
bottom features such as sand sheets or sand bars). The SONAR mapped a lake bottom consisting
predominantly of soft sediment (silts and clays) or mud.
1031.01 Port Darlington West Embayment p.27
Shoreline Change Assessment
Hydrodynamic modelling results presented in Figure 3.15 for the less common ESE (100 deg)
wave direction show an east to west longshore current for all three scenarios. With and without
the presence of the Port Darlington jetties and SMC Headland, this current tends to decelerate
from the centre of the Port Darlington West Embayment near the west end of Cove Road to the
west end of Cedar Crest Beach Road, potentially creating a depositional area in the west half of
the embayment. However, there are two lines of physical evidence that indicate the volume of
sediment available for transport from east to west is low. First, the SONAR data mapped a large
cobble -lag deposit in the nearshore, not sand. Second, there is no sediment trapped in the east
fillet beach at Port Darlington. In other words, 160 years after the construction of the jettied
navigation channel, no measurable volume of sediment has accumulated against the east jetty,
indicating there is little to no supply of sand and gravel from the east, let alone a supply that
could bypass the jetties from the east and enter the Port Darlington West Embayment.
With the construction of the SMC Headland, the east to west current resulting from ESE waves
still decelerates but a counterclockwise eddy also develops against the eastern side of the
headland (bottom panel of Figure 3.15). The convergence of the decelerating current and the
eddy result in a dead zone with low hydrodynamic energy. If sediment was being transported
from east to west, the SMC Headland would actually increase the rate of sedimentation in the
Port Darlington West Embayment by acting as a barrier to further westward sediment transport.
In other words, the Headland is a benefit to the stability of Cedar Crest Beach during ESE
storms.
1031.01 Port Darlington West Embayment p.28
Shoreline Change Assessment
7,
`1 _ -
s_ _
Figure 3.14 CMS -Flow Model Results Showing Nearshore Currents for all Three Scenarios
and the SW (230 deg) Waves
1031.01 Port Darlington West Embayment p.29
Shoreline Change Assessment
Figure 3.15 CMS -Flow Model Results Showing Nearshore Currents for all Three Scenarios
and for ESE (100 deg) Waves
3.2.3.2 Sediment Tran sp ort Mo delling
Figure 3.16 and Figure 3.17 present sediment transport capacity (coloured contours) and
sediment transport direction predictions for the three shoreline scenarios and two wave directions
discussed above. Sediment transport capacity is the maximum total -load (combined bed load
1031.01 Port Darlington West Embayment p.30
Shoreline Change Assessment
and suspended load) that could be mobilized and moved in the water column for the input wave
condition and is measured in kg/m3. The total -load capacity can only be realized if sufficient
sources of sediment suitable for transport are present, such as a continuous sand cover across the
lake bottom. Together, the sediment transport capacity and direction of transport gives an
indication of how sediment would move through the nearshore under each wave direction and
shoreline geometry scenario if a continuous supply of sediment were present (which we know is
not the case in this study area). Areas of decreasing sediment transport gradients (in the
direction of transport) can theoretically be depositional zones, while an increasing gradient in
sediment transport capacity would indicate possible areas of erosion (of the lakebed and beach).
The sediment transport model outputs presented in Figure 3.16 for the dominant SW wave
condition generally affirm the observations made in Section 3.2.3.1 above. In particular, they
illustrate that the introduction of the Port Darlington jetties in the 1800s created a deceleration in
the longshore current and reduction in sediment transport capacity which led to the creation of
the west fillet beach. Without the Port Darlington jetties, the sediment transport capacity is
relatively consistent from west to east along this stretch of coastline meaning the embayment
would not have been a sediment sink. Sediment would move through the embayment, possibly
maintaining narrow beaches along the shore, while the majority of sediment would be
transported further to the east.
Figure 3.16 also indicates that the introduction of the SMC Headland in the late 1970s has
created a barrier to the longshore sediment transport capacity from west to east during dominant
SW wave conditions. However, based on the volume of the west fillet beach adjacent to the
SMC Headland, the supply of sand is very small (annual accumulation rate of 660 m3/year).
There was no physical evidence of sand accumulation in an offshore shoal or being transported
around the Headland.
When the Scenario A and B sediment transport capacity results are compared in Figure 3.17, it
appears that the construction of the Port Darlington jetties in the mid- 1800s had the potential to
trap sediment on the east side of the east jetty. However, after 160 years of existence, there is no
east fillet beach, suggesting the supply of sand from the east is close to zero.
It is also evident from Figure 3.17 that prior to the construction of the SMC Headland, an ESE
wave event could mobilize sediment and transport it to the west away from the Port Darlington
West Embayment. However, the Headland now acts as a barrier to sediment transport to the
west, which is a benefit for the Port Darlington West Embayment.
1031.01 Port Darlington West Embayment p.31
Shoreline Change Assessment
Figure 3.16 CMS -Flow Model Results Showing Simulated Sediment Transport Capacity and
Direction for all Three Scenarios and SW (230 deg) Waves
1031.01 Port Darlington West Embayment p.32
Shoreline Change Assessment
r4
Figure 3.17 CMS -Flow Model Results Showing Simulated Sediment Transport Capacity and
Direction for all Three Scenarios and for ESE (100 deg) Waves
3.2.3.3 General Modelling Conclusions
Overall, the results of the hydrodynamic and sediment transport modelling indicate that under
existing conditions, sediment would tend to move away from the center of the Port Darlington
West Embayment towards the Port Darlington jetties to the east and the SMC Headland to the
west depending on the wave direction. Given that the dominant direction is from the SW by a
significant margin, more material is transported eastward and has built the fillet beach known as
1031.01 Port Darlington West Embayment p.33
Shoreline Change Assessment
Port Darlington West Beach. If the Port Darlington jetties were not in place as was the case pre-
1800s, this sediment would have been transported eastward and would not have accumulated
along the shoreline in this region.
The SMC Headland is a barrier to longshore sediment transport arriving from the west under SW
waves, however, the volume of sand and gravel available for transport is very small as evident by
the size of the west fillet beach. During ESE wave events, the SMC Headland acts as a barrier to
sediment transport from the east, providing some local benefit for Cedar Crest Beach (i.e.,
reduces the loss of sediment to the west).
Finally, for the dominant SW wave direction the shoreline orientation fronting Cedar Crest
Beach Road is not conducive to sediment accumulation, even for the pre -development Scenario
A shoreline. Sand and gravel would move along the shoreline, but it is very unlikely that large
accumulations of sediment existed at this location in the past. This observation is independent of
the presence of the Port Darlington jetties or the SMC Headland and consistent with the findings
of the recently completed Lake Ontario Shoreline Management Plan (Zuzek Inc., 2020).
3.3 Influence of Development History on Shoreline Recession
As outlined in Section 2.2, when the jetties were constructed at Port Darlington, the Cedar Crest
Beach shoreline was a natural barrier beach with a hydraulic inlet connecting the interior
wetlands to Lake Ontario. The 1878 map is reproduced in Figure 3.18. The inlet corresponds
with the current marsh outlet between Cove Road and Cedar Crest Beach Road. Based on our
knowledge of the regional shoreline trends from the recently completed Shoreline Management
Plan (Zuzek Inc., 2020), the cohesive headlands and barrier beach were receding before the
construction of the Port Darlington jetties.
Since their construction, the Port Darlington jetties have trapped enough sand to stabilize the
eastern half of the Port Darlington West Embayment and change the long-term shoreline trend
from recession to accretion. The potential negative impacts to the downdrift shoreline to the east
of the jetties was not investigated.
In the western half of the embayment, the homes were built much closer to the shoreline, as seen
in the 1954 aerial photograph in Figure 3.18 The numerical modelling has shown this segment
of shoreline does not feature an orientation conducive to sediment deposition. Therefore,
regardless of the local modification to the shoreline with the construction of the Port Darlington
jetties and SMC Headland, this portion of the Port Darlington West Embayment continues to
erode.
Several factors have contributed to the recession of the beach for the western half of the
embayment, including:
• A reduction in the volume of sand moving from west to east along the shoreline due to
the SMC Headland.
• Construction of homes on top of the former dynamic barrier beach, as noted in Figure
3.18.
1031.01 Port Darlington West Embayment p.34
Shoreline Change Assessment
• Shoreline armouring with reflective structures that contribute to toe scour and lakebed
downcutting.
• Disruption of natural cross -shore sand transport processes that allow beaches to recover
naturally from periods of high lake levels due to home construction and shore protection
on the beach crest, which in turn reduces the overall resilience of the beach to periods of
high lake levels.
Figure 3.18 Map from 1878 and 1954 Aerial Photograph
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Shoreline Change Assessment
4.0 CONCLUSIONS
Section 4.0 of the report summarizes the study conclusions for the three temporal periods
(Scenario A to C) and the overall impacts of the littoral barriers and shoreline alterations in the
Port Darlington West Embayment.
4.1 Early 1800s (prior to the Port Darlington Jetties)
The Scenario A shoreline is reflective of the early 1800s period prior to the construction of the
Port Darlington jetties. The key study findings pertaining to this period include:
• The regional shoreline change data from the Lake Ontario Shoreline Management Plan
(Zuzek Inc, 2020) suggests the entire study area featured a long-term recession rate based
on the presence of erodible glacial till bluffs and sand barrier beaches fronting coastal
wetlands.
• Without the SMC Headland or Port Darlington jetties, in the early 1800s southwest storm
events generated longshore currents that transported sand and gravel from west to east
along the regional shoreline. There were no `natural' barriers capable of trapping sand
and gravel along this shoreline. Due to the natural shoreline orientation in the Port
Darlington West Embayment, the sediment transport modelling suggests that local
beaches would have been narrow with low potential for sediment retention.
4.2 Mid-1800s to Late-1970s (Port Darlington Jetties)
The mid-1800s to late-1970s represents Scenario B, when the Port Darlington jetties were
present, but the SMC Headland had not been constructed. The major conclusions are:
• Based on the rate of accumulation in the west fillet beach adjacent to the SMC Headland,
approximately 660 m3/yr of sediment was historically transported from west to east into
the Port Darlington West Embayment during this period. In Scenario A (pre-1800s) this
sediment would have moved through the embayment and continued to the east.
However, the presence of the Port Darlington Jetties post-1800s has significantly altered
the physical processes and historical shoreline trends in the Port Darlington West
Embayment by trapping much of this sediment in the west fillet beach. Consequently,
following the construction of the jetties the shoreline trend switched from recession to
accretion for the eastern half of the embayment.
• Without the SMC Headland, the bluff shoreline west of Cedar Crest Beach was receding.
As the bluffs continued to retreat inland (northward), the protection they provided to
Cedar Crest Beach was slowly decreasing and contributing to the instability in the
western half of the Port Darlington West Embayment.
• Sediment arriving from the west during SW storms moved along the shoreline in the
western half of the embayment but likely did not accumulate in this region due to the
shoreline orientation. In other words, a dynamic beach was present along the shore, but it
1031.01 Port Darlington West Embayment p.36
Shoreline Change Assessment
featured a long-term recession trend, as the site conditions were not conducive to the
accumulation of large volumes of sand and gravel.
• Although not a focus of this investigation, the Port Darlington jetties have deprived the
shoreline to the east of their natural supply of sand and gravel.
• The construction of homes close to the shoreline in the western half of the Port
Darlington West Embayment has negatively impacted the beach and its ability to respond
naturally to lake level fluctuations.
4.3 Late-1970s to Present (Jetties and SMC Headland)
The last temporal period, the present, is Scenario C when both the Port Darlington jetties and
SMC Headland are present. Key findings include:
• The SMC Headland reduced the supply of sand and gravel to the Port Darlington West
Embayment during SW wave attack by approximately 660 m3/year, which would impact
the beach stability. However, if present the majority of the sediment would have moved
to the east end of the embayment where the historical long-term recession trend has been
reversed by the presence of the Port Darlington jetties. In other words, it would not have
accumulated along the shoreline of Cedar Crest Beach.
• The presence of the SMC Headland has also protected approximately 1.2 km of eroding
bluff shoreline to the west of the Port Darlington West Embayment, which has and will
continue to contribute to the stability of the shoreline by anchoring the western boundary
of the littoral sub -cell. In other words, without the SMC Headland natural bluff recession
would undermine the stability of Cedar Crest Beach.
4.4 Summary of Benefits and Impacts of Shoreline Alterations
Section 4.4 summarizes the benefits and impacts of the major shoreline alterations in the Port
Darlington West Embayment over the last 200 years:
• The Port Darlington jetties have stabilized the eastern half of the Port Darlington West
Embayment.
• The Port Darlington jetties have also starved the shoreline to the east of its natural supply
of sand and gravel for more than 160 years.
• The SMC Headland has reduced the supply of sand and gravel to the Port Darlington
West Embayment by approximately 660 m3/yr, which is one factor that has contributed to
the loss of the beach for the western half of the embayment. The Headland has also
stabilized the eroding bluffs, which has and will continue to create benefits for the
western half of the embayment.
• The construction of homes on the crest of the barrier beach in the western half of the
embayment has reduced the resilience of the beach to periods of high lake levels. The
1031.01 Port Darlington West Embayment p.37
Shoreline Change Assessment
construction of concrete and armour stone walls has made the problem worse by
reflecting incoming wave energy towards the lake bottom, leading to scour and lowering
of the lake bottom.
In summary, there have been positive and negative impacts associated with the artificial littoral
barriers that define the Port Darlington West Embayment. For example, the eastern half of the
embayment has benefitted significantly by the sediment trapped against the Port Darlington
jetties. The SMC Headland is one of five factors that have contributed negatively to the current
flooding and erosion hazards along Cedar Crest Beach:
• A reduction in sediment supply to the Port Darlington West Embayment due to the SMC
Headland.
• The embayment shoreline features a natural long-term recession trend.
• The shoreline orientation is not conducive to the accumulation of sand and gravel.
• Homes were constructed too close to the waters edge and on top of a dynamic receding
low-lying barrier beach.
• Vertical shore -parallel protection structures were constructed on the beach that are not
conducive to beach building.
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Shoreline Change Assessment
REFERENCES
Municipality of Clarington (2017). Technical Note on History of St. Marys Cement Facility.
Public Archives Canada. National Map Collection. Reproduced with permission.
Zuzek Inc. (2020). Lake Ontario Shoreline Management Plan.
1031.01 Port Darlington West Embayment p.39
Shoreline Change Assessment
APPENDIX A
Historical Shoreline Change Data
Appendix A
1954
P ' _ `,�
+ r �►
1954 Corrected Waterline
W.L. = 75.32 m
h
_ __ __
2018 Waterliner
......... IRS'• _� _+'�
1967
W.L.=74.77m
�� n. :. „'ram
— 1967 Corrected Waterline
2018 Waterline
1978
-• ;� ■ _,
1978 Waterline
W.L.=75.05m
_
—
r 2018 Waterline
i
1988
W.L. = 74.88 m
-
a` 1988 Corrected Waterline
.��'.
'
— Waterline
2018
r
206090
— 2000 Corrected Waterline
74.82 m
— 2018 Waterline
2005 , . ;
2005 Waterline
W.L. = 75.03 m
-
— 2018 Waterline
i
2010 °-
2010 Corrected Waterline
W.L. = 74.66 m #-
2018 Waterline
2017
2017 Corrected Waterline
— 2018 Waterline
_`
Y'No
correction applied to 2017 waterline position
west of outlet because the 2017 waterline
position was impeded by shore protection.
2018 + '"� �_ F
f
— 2018 Waterline
W.L.=75.01m
=
/
Waterline Comparison 1954 to 2018
Note:
Alloth19 7/78 aerial ls by
All other aerials of
0 100
4
` l�
provideded
provided s ( .L.) ffencegton.
mean water levels referenced to IQune-
1 I 1 i
ZUzC f i I C -
Waterline positions were corrected relative to the 2018 photo with a water level of 75.01
m (IGLD'85)
for April
pt for:
for April ofphoto year, except for: (May), 78 (June-
Aug),'88 (May).
p7
—ow wcv�n--