5.0
SEDIMENT BUDGET SITES
Shoreline erosion is a natural process that occurs throughout the study boundaries, the
entire Great Lakes system and many the world’s beaches and bluff coastlines. Although
water levels on Lake Ontario have fluctuated significantly in the last 10,000 years
following the last glaciation in North America, they have stabilized in the last few
thousand years to the present measured range. Consequently, natural processes have
been eroding the study shoreline (lake and river) long before European settlement began.
Refer to Figure 5.1 for a typical eroding bluff in Northumberland Regional Municipality,
north shore of Lake Ontario.
Figure 5.1
Eroding Bluff Shoreline East of Cobourg, Northumberland County (Aug. 9, 2003)
Natural background erosion is vital for the creation of new sand and gravel deposits in
the nearshore zone, which ultimately supplies the beach/dune environments and barrier
beaches around the lake with new sediment. Refer to the discussion in Section 6.0 of this
report on barrier beaches and dunes. Consequently, shoreline erosion is an important
natural process on Lake Ontario and it started long before the construction of the Moses
Saunders Power Dam. The sediment budget Performance Indicator was created to
educate the study participants and riparian community on the benefits of the natural
background erosion rate.
When evaluating shore erosion and the creation of new sand and gravel sources in a
regional content, the concept of sediment budgets is often used. Like a financial budget,
a sediment budget is an accounting system for all the sand and gravel within a defined
study boundary (spatial extents). Littoral cells are closed sediment compartments that
define the limits of all sand movement, both along the shore and onshore/offshore.
Consequently, the limits of a littoral cell make good spatial boundaries for a sediment
budget analysis.
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The rationale for this performance indicator was a means to describe the beneficial
components of shoreline erosion. For example, when storm waves strike a bluff
shoreline (such as the conditions in Figure 5.1), the force of the attacking wave energy
often exceeds the resisting properties of the soils, resulting in erosion and shoreline
recession. If the eroding shoreline belongs to a riparian, there is a loss to the owner, as
his total acreage decreases. Generally, shoreline recession is not reversible, and
consequently the riparian will not be able to reclaim the lost land. However, for many
parts of study area, erosion is a critical natural process that provides new supplies of sand
and gravel to nourish barrier beaches and dune environments. The sediment budget for
Sites #12 and #13 are described below.
5.1
Site #12 – CND8 Sediment Budget
A sediment budget investigation was completed for the north shore of Lake Ontario
classified as CND8 for the purpose of this study. This shoreline unit generally consists of
the Northumberland County and the shoreline communities between Port Hope in the
west and Prequ’ile Provincial Park in the east. Refer to Figure 5.2.
Figure 5.2
Regional Map of the CND8 and Limits of Sediment Budget Calculations
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For the purpose of this analysis, the community of Port Hope was considered the western
limits of the littoral cell. Historically, it is possible the cell boundary extended further to
the west. Presently, there are three large coastal structures within the boundaries of this
sediment budget, including the Port Hope Harbour, Cobourg Harbour and industrial port
at Ogden Point. These three structures define three sub-cells in the modern littoral cell.
This region is the sediment supply zone of the littoral cell, as shoreline erosion generates
new supplies of sand and gravel for the littoral system.
It should be noted that a detailed sediment bypassing analysis was not completed at these
three locations. However, for the purpose of the demonstration sediment budget, it is
assumed the sediment bypassing these structures. As such, this analysis could also be
considered a “pre-settlement” sediment budget between Port Hope and Presqu’ile.
Presqu’ile Provincial Park was the historical downdrift sediment sink for this littoral cell.
The present feature associate with the park began as a low crested sand spit when Lake
Ontario water levels stabilized in their present range. Refer to Figure 5.3. Sand and
gravel transported to the east was deposited between the mainland and bedrock
peninsula, and progressively built additional breach ridges. Eventually these ridges
attached to the bedrock peninsula and the modern beach was deposited.
original
spit
modern
beach
bedrock
peninsula
Figure 5.3
Progressive Beach Ridges at Presqu’ile Provincial Park
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An oblique digital photograph of the beach is presented in Figure 5.4. The tips of the
forested beach ridges can be seen in the top right hand corner of the photograph. The
modern beach is wide, flat and features a low vegetated dune.
Figure 5.4
Beach and Dunes at Presqu’ile Provincial Park, Looking East (August 9, 2003)
The provincial park protects the valuable dune and marsh habitat, which is used by shore
birds and other marsh species of animals and plants. The sandy beach is also a popular
summer vacation destination.
Historically, updrift erosion provided new sources of sand and gravel for the littoral
system, which was ultimately transported in an easterly direction to the park. The future
health of the beach and dune environment at Presqu’ile will require a continuous supply
of new sand and gravel from the littoral cell.
5.1.1
Rates of Sediment Supply for Different Regulation Plans
As documented in Section 3.0 of the report, the amount of shoreline recession on Lake
Ontario can be influenced by water level regulation. For example, of the legacy plans
utilized for the erosion modeling in Section 3.0, pre-project resulted in the highest bluff
recession rates at the detailed study site, while the lower new basin supplies and thus
lower lake levels associated with the climate change scenarios resulted in the lowest bluff
recession rates.
Based on this finding, the shoreline classification for CND8 was used in conjunction with
erosion rate modifiers developed from the detailed sites to quantify the impacts of water
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level regulation on sediment supply to the littoral zone of Lake Ontario. The principal
steps in the investigation are summarized below:
•
Erosion rate modifiers were developed for each of the legacy plans and climate
change scenarios based on the results from the detailed study sites discussed in
Section 2.0. For example, if the pre-project hydrograph doubled the recession
rate compared to 1958DD, then the modifier for pre-project would be 2.0. For the
climate change scenarios, the multipliers were all less than 1.0, since they resulted
in less bluff erosion compared to 1958DD;
•
The long term AARR for the 1 km reach classification was extracted from the
FEPS database for the littoral cell boundaries. The AARR was modified for each
of the legacy plans and climate change water levels based on the erosion rate
modifiers;
•
Since the lakebed in Northumberland is shelving limestone bedrock, the primary
source of sediment input is the eroding cohesive shoreline above Chart Datum.
The 1 km shoreline classification was used to determine the type of shoreline
geology, percentage of sand in the soil, the average height of the bank or bluff and
the percentage of shoreline protection for each 1 km reach. This information was
used in conjunction with the AARR for each regulation plan to calculate the
annual volume of sand and gravel entering the nearshore zone from shoreline
recession.
The results are summarized in Figure 5.5. Shoreline recession associated with preproject generated over 11,000 m3/yr of sand and gravel on average, while the current
regulation plan, 1958DD, produced 7,300 m3/yr. The climate change water levels
produced significantly less, especially the 2090 water levels, which rarely exceed chart
datum and thus result in very little shoreline recession.
The results from the sediment supply calculations summarized in Figure 5.5 provide two
very important pieces of information when considering historic, present and future
sediment budgets for Lake Ontario. First, it is quite possible the long term recession
rates for the cohesive shorelines around the lake were higher prior to the regulation of
Lake Ontario. Higher rates mean more sediment was produced from the natural
background recession rate. Conversely, since regulation began in the 1960s, less sand
and gravel is generated from shoreline erosion and thus available for the nearshore
sediment budget. In other words, there is less sand available to maintain and build
beaches.
In the future, if supplies of water to the Great Lakes watershed and thus by extension lake
levels decrease due to the impacts of global warming, the rates of shoreline erosion for
the cohesive bank and bluff sites around the lake will also decrease. This will result in
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less sand and gravel entering the littoral system and thus available to build new beaches
Annual Sand and Gravel from bluffs (m 3/yr)
30,000
Sub-cell C
25,000
Sub-cell B
11,158
20,000
Sub-cell A
8,751
15,000
7,293
7,074
10,000
4,594
3,355
5,000
510
0
Pre-Project
1958D w/o
Deviations
1958D w
Deviations
Plan 1998
Climate
Climate
Climate
Change 2030 Change 2050 Change 2090
Legacy Plan
and maintain existing ones.
Figure 5.5
5.1.2
Hypothetical Annual Inputs of Sand and Gravel for Different Regulation Plans
Economic Function to Quantify the Value of Eroded Sediment
In order to assess the economic implications of regulation plans that alter the long term
background recession rate, a preliminary economic function was developed. The
function assumes the sand and gravel supplied to the nearshore zone from erosion is an
important commodity and has value for the nearshore environments of Lake Ontario.
Specifically, the sand is required to maintain existing beaches, such as the one at
Presqu’ile Provincial Park.
The function assumes the value of the eroded sediment can be quantified by the cost to
truck this material to the shoreline from upland sources. For example, if a particular
parcel of land contributes 10 m3 of new sand and gravel a year and it costs $20/ m3 to
ship the equivalent amount of sand to the site from an upland quarry, then the value of
the eroded sediment is $200 per year.
This non-market assessment technique is depicted graphically in Figure 5.6. In this
example, we assume Plan A generates 10 m3 of sand and gravel a year for a given stretch
of shoreline and the cost to truck the sand to the lakeshore is $20/ m3 or $200/truckload.
Plan B causes twice as much shoreline recession and thus new sand and gravel generated
is worth $400.
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There are some limitations to this performance indicator if applied to the entire lake
without consideration to the local conditions. For example, if the new sand and gravel
generated from bluff recession is deposited into a navigation channel, it may represent a
cost for a local port authority, since dredging would be required to remove the sediment.
Figure 5.6
5.1.3
Economic Function for Sediment Budget Performance Indicator
Benefits and Costs of Regulation for the Port Hope to Presqu’ile Littoral Cell
For the case study described in Section 5.1, we have assumed that all of the eroded
sediment between Port Hope and Presqu’ile has a beneficial economic value, since
ultimate this sediment built the historical sand spit and modern beach at the Provincial
Park.
The volume of sediment generated for each of the legacy plans and climate change
scenarios was converted to a dollar amount using a unit cost of $20/ m3. These dollar
amounts were then normalize to 1958DD, since it is the baseline for the comparison as
the present regulation plan. The results are presented in Figure 5.7. Pre-project
generates an average annual benefit of approximately $100,000, while the benefits from
1958D without deviations represent approximately $35,000 in benefits.
The climate change scenarios generate significantly less sediment per year, which is
expressed as a cost in Figure 5.7. These annual costs range from $67,000 to $170,000
per year. As mentioned previously, climate change lake levels and reduced sediment
supplies will have a negative impact on sand and gravel beaches, particularly sites that
feature a cohesive or bedrock lakebed. The preliminary economic function developed for
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the sediment budget performance indicator could be used to quantify the costs of this
reduction.
150,000
Economic Benefit and Cost
100,000
Benefits
CND Dollars
50,000
0
Pre-Project
1958D w/o
Deviations
1958D w
Deviations
Plan 1998
Climate
Climate
Climate
Change 2030* Change 2050* Change 2090*
-50,000
-100,000
Costs
-150,000
-200,000
Figure 5.7
Economic Benefits and Costs of Eroded Sediment for Legacy Plans and Climate
Change Scenarios (results normalized to 1958DD)
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5.2
Site #13 – Eastern Lake Ontario Sediment Budget
The Eastern Lake Ontario site is a dynamic coastal environment that features bedrock
headlands, eroding drumlins, barrier beaches, modern and relic dunes, and shifting inlets,
such as the one presented below in Figure 5.8. In many locations, natural shoreline
processes are constrained and often negatively impacted by shoreline development. For
example, refer to the residential development constructed on top of a former barrier
beach in Figure 5.9. Shoreline armoring is required to protect the homes from flooding
and erosion hazards, and thus the barrier beach can no longer function as a dynamic
system.
Figure 5.8
Inlet at Lakeview Wildlife Management Area, August 6, 2003
Figure 5.9
Development on Barrier Beach at South Pond, August 6, 2003
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A regional map of Shore Unit US7, which roughly corresponds to the Eastern Lake
Ontario (ELO) site, is presented in Figure 5.10. The 1 km shoreline reaches are also
plotted on Figure 5.10, along with a summary of the classification in the legend. For
example, the shoreline along the open lake and inside the major ponds is classified as
32% baymouth barrier, 33% open shoreline wetlands (mostly associated with interior
ponds and rivers), 31% low bank and 4% coarse cobble/gravel beaches.
The majority of the lake bottom is classified as sandy (85%), with exposed bedrock and
silty/mucky organic sediment comprising the remaining 15%. When shoreline protection
structures were evaluated, 75% of the 1 km shoreline reaches were completely
unprotected, while the remaining 25% of the reaches had some percentage of protection,
such as armor stone revetments.
A second map of the study area is presented in Figure 5.11 and includes the place names
and geomorphic features that will be discussed throughout the report.
The studies completed to investigate the regional sediment budget for the ELO site will
be summarized, including a review of the post glacial history, modern geology and
geomorphology, sediment sources, sediment sinks, transport patterns, harbor bypassing,
and the overall sediment budget findings. The analysis at this detailed study site will
conclude with a discussion of water level regulation impacts on the ELO site.
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Figure 5.10
US7 Shore Unit Map and 1 km Reach Classification
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Figure 5.11
Eastern Lake Ontario with Place Names (from Woodrow et al., 2002)
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5.2.1
Post Glacial Evolution at ELO Site
The Eastern Lake Ontario site has been evolving since the retreat of the Pleistocene
Glaciers over 12k YBP (years before present). For example, following the final retreat of
the glacial ice, Lake Iroquois formed on top of the modern Lake Ontario Basin when the
ice sheet stalled at Brockville. Water levels of Lake Iroquois were over 100 m higher
than the present conditions and the lake drained southeast through Syracuse and Rome.
Once the continental glacier retreated further north, Lake Ontario was cutoff from further
meltwater sources. Lake Erie drainage via the Niagara River had not yet been
established. Therefore, the level of Lake Ontario decreased dramatically below the
modern condition.
Between 10k and 6k YBP, the level of Lake Ontario slowly started to increase. The
present drainage into and out of Lake Erie was evolving and slowly the supply of water
to Lake Ontario increased. By 5k YBP, the level of Lake Ontario breached the sills on
the St. Lawrence River and began draining down its modern outlet to the Gulf of St.
Lawrence.
Lake levels higher than the modern condition may have occurred approximately 4k YBP
during a period known as the Nipissing Transgression. This high water period was short
in duration, with levels then falling below the present range. From 4k YBP to present,
there has been a slow rise in lake levels to the modern condition.
5.2.2
Modern Geology and Geomorphology
Section 5.2.2 will review the modern geomorphic features within the study area and the
geologic properties of the sediments and soils.
Regional Littoral Cell
On a regional scale, the Eastern Lake Ontario barrier complex is a very large pocket
beach that is controlled or anchored by the Stony Point bedrock headland in the north and
Nine Mile Point in the south. In the north, the bedrock outcrops just north of Stony
Creek, which drains Black Pond and the tributaries that feed the marsh. A picture of the
shelving bedrock recorded during the August 2003 aerial survey of the shoreline is
presented in Figure 5.12.
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Figure 5.12
Shelving Bedrock Immediately North of Black Pond and Stony Creek
A photograph of the eroding bedrock shoreline in the Nine Mile Point area, east of
Oswego, is presented in Figure 5.13. At this particularly location, there are no beaches,
just vertical eroding bedrock cliffs. In other locations, the bedrock in the nearshore zone
is shallower and gravel beaches are present along the shoreline.
Figure 5.13
Eroding Bedrock Cliff Near Nine Mile Point
These two bedrock zones define the spatial boundaries of the ELO littoral cell. All
sediment supply is limited to sources within the cell and movement is confined within its
boundaries.
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Lakebed Geology
Extensive surveying of the lake bottom (surface and sub-surface) was completed for the
Eastern Lake Ontario Sand Transport Study (Woodrow et al., 2002), which was
completed by Woodrow et al (2002). One of the products of this study, which is
reproduced in Figure 5.14, is a regional map of the lakebed sediment distribution.
In the Nine Mile Point area, while bedrock is exposed along the waterline, it is capped on
the lake bottom with a broad sheet of glacial till. This till sheet extends north to
approximately the mouth of the Salmon River. From the Salmon River north to Black
Pond and Stony Creek, the lake bottom is covered with a broad sand sheet that extends
offshore 4-5 km. The thickness of the sand sheet ranges from 1 to 5 m.
Offshore of the sand sheet, laminated silts and clays were identified. Presumably this
clay plan continues onshore and is the foundation under the nearshore sand, the dunes
and marshes.
North of Black Pond and Stony Creek, the bedrock foundation of Stony Point was
recorded and the spatial extent is noted in Figure 5.14.
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Figure 5.14
Surficial Lakebed Mapping for ELO (from Woodrow et al, 2002)
Several sources for the large sand sheet on the bed of the lake at the ELO site were
proposed in Woodrow et al (2002), including glacial processes and post-glacial beach
ridges when Lake Ontario was at different elevations. Within the littoral cell, new sand
sized sediment is introduced to the littoral system when the drumlins found along the
shoreline erode, however, this is not thought to be a major source. In summary, the
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majority of the sand has been in this littoral cell for thousands of years and the position of
the sandy barriers and dunes is modified waves, currents and wind.
Shoreline Conditions
The shoreline conditions for the ELO site are described with the assistance of the oblique
digital photographs captured on August 6, 2003. Additional relevant site photographs are
provided in Sections 6.2 and 6.3.
The mouth of the Salmon River is protected with a long armor stone jetty that extents in a
northwest direction from the south shore of the inlet. A smaller east-west jetty was
constructed along the north banks of the outlet, as seen in Figure 5.15. Small fillet
beaches have developed north and south of the jetties. The beach material is primarily
sand, with trace deposits of pebbles and cobbles.
Figure 5.15
Salmon River Jetties and Adjacent Beaches
North of the Salmon River jetties, a broad marsh is sheltered from Lake Ontario waves
by a barrier beach and dune ridge, as seen in Figure 5.16. This area is protected as part of
the Deer Creek Wildlife Management Area.
The Rainbow Shores community is located north of Deer Creek. Much of this
development is located on top of an eroding drumlin, which separates the Deer Creek
marsh from South Pond. Refer to Figure 5.17.
The southern half of North Pond is presented in Figure 5.18. The southern barrier beach
features some large relic dunes, as does the north barrier. These dunes are heavily
vegetated and have been developed with seasonal and permanent residences. Shore
protection has been constructed in some locations to protect from flooding and erosion
hazards.
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Figure 5.16
Marsh and Barrier Beach at the Deer Creek Wildlife Management Area
Figure 5.17
Portion of Rainbow Shores Development Located on Top of an Eroding Drumlin
Figure 5.18
Eroding Relic Dunes Along the Southern Barrier Beach at North Pond
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The inlet to North Pond is presented in Figure 5.19. Since this inlet was created, a series
of successive interior beach ridges have formed along the margins of the inlet. The
reduced channel width and sediment is a problem for recreational boaters. Maintenance
dredging is now routinely required to provide safe access to Lake Ontario.
Figure 5.19
Modern Inlet to North Pond
The Montario Point community is located between Cranberry Pond and South Colwell
Pond. Refer to the oblique photograph in Figure 5.20. The higher elevations between the
two marshes is associated with the drumlin field, however, there is no drumlin present at
the waterline as at Rainbow Shores. The beaches in the community consist of pebbles,
cobbles and boulders.
Figure 5.20
Montario Point Community and Cranberry Pond
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North of Montario Point, the shoreline alternates between natural areas and shoreline
development. The marshes are sheltered from Lake Ontario by barrier beaches and drain
via sandy inlets. A picture of the shoreline development located on the dunes north of
Southwick State Park is presented in Figure 5.21. The natural conditions at the inlet to
Black Pond are presented in Figure 5.22.
Figure 5.21
Development on the Dunes North of Southwick Beach State Park
Figure 5.22
Black Pond Inlet and Barrier Dunes
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Formation of Barrier Beaches, Dunes and Marsh
Carbon dating of sediment cores extracted from the lake bottom offshore of Eastern Lake
Ontario indicate the formation of the sand sheet began approximately 8,400 years ago
(Woodrow et al, 2002). As lake levels increased to their modern range, it is possible
barrier beaches and dunes existed at locations now occupied by the lake bottom.
Peat samples were extracted from the base of the Rainbow Shores marsh immediately
above the clay/mud surface for carbon dating. The results indicate the marsh began to
form approximately 2,400 years ago. Since some form of a protective barrier would be
required for the accumulation of organic material in the marshes and ultimately the
formation of peat deposits between the high ground associated with drumlins, it can be
inferred that the barrier beaches were also forming at this time. The barrier beach dunes
in Figure 5.18 are an example of a very old relic dune at ELO.
Carbon dating of plant debris within the dunes at Black Pond suggest the material was
approximately 1,300 YBP. Organic material in the dunes at Southwick Beach State Park,
which is a younger dune system, dated approximately 350 YBP. The dunes along the
inlet to Lakeview in Figure 5.8 are a good example of a young dune system.
5.2.3
Sediment Sources and Sinks
Three potential sources of new sand and pebbles/cobbles within the littoral cell are
discussed based on the data collected and generated for this study, including: beach and
dune erosion, lakebed erosion and isostatic rebound. Sediment sinks, such as inlet
migration, fillet beaches and aeolian transport into the dune systems will also be
reviewed.
Beach and Dune Erosion
A historical 1960s aerial photograph was geo-referenced against the 2002 detailed
orthophotograph collected for this study. This region of the lake was a difficult area to
register photographs, since the vast tracks of open natural areas don’t provide suitable
low level ground control points, such as road intersections. In some locations, it was
simply not possible to register the 1960s photographs with acceptable error limits
(horizontal registration error less than predicted change in the shoreline change reference
feature, such as the toe of dune).
Once registered, the toe of the dune in 1960 was digitized. This feature is commonly the
edge of active vegetation for stable or accreting beaches or the base of the eroding dune
scarp. Since the lake level difference between the two photographic series was only
0.13 m, the lines were not corrected for water level differences. For example, if we
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assume a 1:10 (V:H) beach slope the 0.13 m difference in lake levels only corresponds to
a horizontal positional shift of 1.3 m or 0.03 m per year.
The toe of the dune in 2002 was provided by the mapping contractor that generated the
2002 orthophotograph. Shore perpendicular transects were drawn with Baird Shoretools
to measure shoreline change rates and then annualized for the 42 year period. The
individual transects were grouped together into the 1 km shoreline reaches and are
presented in Figure 5.23. A positive shoreline change rate (SCR) indicates dune erosion,
while a negative SCR indicates dune accretion. Place names are added to the figure to
provide reference.
Deer Creek
Brenne Beach
Fillet Beach
South of Salmon R.
0698
0699
0721
Montario Point
0661
SCR (m/yr)
Rainbow
Shores
N & S Colwell
Pond
0654
0.50
Lakeview
Wildlife
Management
Area
1.00
Southwick Beach SP
1.50
Jefferson Park
Sunset Bluff
Eastman
2.00
-1.00
0722
0697
0696
0695
0694
0693
0692
0691
0664
0663
0662
0653
0652
0631
0630
0629
0628
0627
-0.50
0626
0.00
0625
Shoreline Change Rate (m/yr)
2.50
South Pond
Recession of Dunes/Barrier Beach
Former Inlet to North Pond
3.00
N. Barrier at North Pond
3.50
Accretion of Dunes
-1.50
Shoreline Reach
Figure 5.23
Shoreline Change Rates from 1960 to 2002 (based on toe of dune measurements)
Before the results are described, it should be mentioned that there are many challenges
when measuring SCR at dynamic sandy environments such as ELO. For example, when
measuring rates of change based on the active edge of dune vegetation, factors other than
erosion and accretion trends can affect the presence or absence of dune vegetation (e.g.
human disturbances). Also, the embryo dunes where the vegetation is most commonly
found can inflate (grow) in volume very quickly, especially during low water periods.
Conversely, one storm at high lake levels could completely erode an embryo dune
stabilized with vegetation. Therefore, the antecedent conditions prior to the aerial
photography are very important. Fortunately, for this analysis the lake levels were very
similar for both photographic series.
The ideal method for measuring rates of change for a dynamic sandy environment such as
ELO would be a full 3D volumetric analysis. For example, a 3D surface of the nearshore
zone, beach, dunes and backslope and/or swale would be generated for both time periods.
GIS software would be used to calculate volumetric changes along the shoreline,
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expressed as m3/m, for example. This methodology would be ideal for tracking changes
in the shoreline due to inlet migration, dune blowouts and depositional features due to
aeolian processes. Unfortunately, there was insufficient information in the 1960s dataset
to complete this type of analysis.
The results in Figure 5.23 will be described from north to south. Reaches 625 and 626
correspond to the Jefferson Park, Sunset Bluff and Eastman communities. The long term
trend for the beach and dunes in this region is a slow recession rate. Southwick Beach
State Park featured a small accretion rate of 0.07 m/yr.
The trend for reaches 628 to 652 is an accretion rate of 0.42 m/yr. This region
corresponds to the Lakeview Wildlife Management Area. The natural setting for this
stretch of coastline plus the lack of development make it an idea location for embryo
dune growth and a healthy barrier beach system. Reach 653 and 654 represent the wide
barrier system in front of North and South Colwell Pond. This natural area also features
a healthy accretion rate of 0.47 m/yr since 1960.
Reach 662 to 664 correspond to the northern barrier beach and dunes that shelter North
Pond. There is a progressive increase in the long term recession rate for this region, from
0.13 to almost 3.0 m/yr (increasing in a southerly direction). The most extreme rates at
Reach 664 are related to the current inlet location. In 1960 the inlet was located further
south. With the development of the modern inlet, the toe of the dune has migrated
significantly inland, which is captured in the 2002 orthophotograph.
In 1960, the inlet to North Pond was located at Reach 691. This feature has since filled
with beach sediment creating a triangular wedge of sand south of the modern inlet. The
toe of the dune at Reach 691 has migrated lakeward 1.2 m/yr since 1960.
The rate of shoreline change for Sandy Island Beach, South Pond and Rainbow Shores is
captured in the results for Reaches 693 to 697. The trend between 1960 and 2002 is
recession and it decreases from 0.55 m/y in the north to 0.10 m/yr in the south at
Rainbow Shores. There are several possible reasons for this long term trend of shoreline
recession, including disruption of the natural barrier beach processes by the housing
developments, construction of shoreline protection structures and the natural tendency for
shoreline erosion along this drumlin section of the shoreline. The impacts of the regional
sediment transport patterns may also influence the long term shoreline change rates along
this stretch of shoreline in ELO. Refer to Section 5.2.5 for additional details.
Reach 698 represents the Deer Creek WMA. The long term trend for this stretch of
shoreline is a slow accretion rate (0.14 m/yr). At Brennen Beach, the accretion trend
increases to 0.46 m/yr. The shoreline position and dune stability at Brennen is partially
influenced by the north jetty at the Salmon River. South of the south jetty at the Salmon
River, the growth of a small fillet beach in captured with the rates at Reach 721, which
documents 0.37 m/yr of accretion since 1960. In Reach 722, which does not appear to be
influenced by the jetties, the long term trend is accretion of 0.2 m/yr.
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In summary, the beaches south of the Salmon River jetties are a sediment sink, as are the
conditions for a few kilometers north of the river. The eroding drumlins and barrier
beaches from Rainbow Shores north to South Pond are a source of new littoral sediment.
However, it should be mentioned that only a fraction of the eroded material in the
drumlins remains on the beaches. The percentage of sand is unknown but is generally in
the range of 10 to 20 percent for a glacial till. The eroding drumlins also supply the
rounded pebbles, cobbles and boulders found on the beaches throughout ELO. For
example, refer to the conditions 5.24.
Figure 5.24
Eroding Drumlin at Rainbow Shores (note pebble/cobble sized material in the till)
The deposition at Reach 691 along the southern barrier at North Pond represents a long
term sediment sink for the littoral cell. Although the shoreline change rates document
erosion for the northern barrier, this does not translate into new sediment for the littoral
cell, since the eroded sediment is deposited in the pond and used to build the flood delta
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inside the marsh (the arrow head shaped depositional feature at the inlet). This is
discussed further in the section on inlet migration below.
At Montario Point, the shoreline has been very stable since 1960. It appears the beach
and nearshore are well armored with the cobles and pebbles eroded from the glacial till.
It is also interesting to note that these cobbles do not appear to migrate significantly north
to the beach at North and South Colwell Pond or to the south along the northern barrier
beach at North Pond. This cobble deposit is either very isolated on the beach or the net
direction of longshore drift is very close to zero at this location.
From South Colwell Pond north to the limits of Southwick Beach State Park, including
Lakeview WMA, the dunes have been accreting or inflating since 1960. This dune
growth and shoreline stability is at least partly attributed to the natural state of the
shoreline, which is capable of responding dynamically to periods of high and low lake
levels. Plus, since the dam became operational in 1960, the regulation plan has worked
to eliminate the natural high lake level conditions that would have occurred under the
pre-project scenario. These natural highs combined with storm events may have lead to
more dune erosion events, which would have been followed by recovery during average
and low levels. Collectively this region is a net sediment sink for the littoral cell.
The Jefferson Park, Sunset Bluff and the Eastman communities featured an average long
term recession rate of 0.15 m/yr. In many locations, these homes were constructed on top
of the dunes, permanently disrupting the natural function of the sand system. This reach
of shore is a small net provider of sediment and may have supplied some of the material
for the dune accretion further to the south.
2001 SHOALS Lakebed Profiles
The SHOALS bathymetry collected in 2001 provided complete coverage for the ELO
nearshore environment, from the waterline to depths often greater than 10 m. A total of
36 shore perpendicular profiles were extracted from the 3D bathymetry grid. The reach
profiles will be described from 619 in the north to 732 in the south. Collectively, they
provide a vivid story of the lake bottom geology and morphology.
Figure 5.25 plots five profiles that are strikingly different in their shape and geology.
Reach 619 corresponds to the southern limits of the bedrock at Stony Point. The profile
is very flat and features a slope of approximately 1:100 (H:V) from the waterline to the 6
m depth contour. Reach 622 is located just south of black pond and the profile
morphology suggests this is still a bedrock profile with a shallow nearshore sand deposit.
Between 800 and 1,500 m on the x-axis a shoal is observed for the Reach 622 profile
with a crest elevation of 7.0 m. Interestingly, this shoal is also observed in the profiles
for Reaches 623 and 624, however at a higher elevation (2.2 to 3.6 m below Chart
Datum). It is not known whether these shoals are bedrock or glacially features, such as
drumlins. The field observations, aerial photographs and digital oblique photographs all
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categorize the shoreline for Reaches 622 to 624 as sandy with wide beaches and dunes.
Therefore, the bedrock must dip to the east and south, where it is eventually buried by
glacial sediments and the large ELO sand sheet.
The final profile in Figure 5.25 represents the conditions for Reach 625, which extends
offshore of the Eastman residential community. The profile geometry is dramatically
different than the adjacent reaches, since this profile records the full extent of the Eastern
Lake Ontario sand sheet. When compared to the adjacent reaches (623 and 624), it
appears the sand between the 2 and 6 m depth contour is anchored by the shoal for
profiles 623 and 624. This feature prevents sediment from leaking (moving) in an
northerly direction out of the littoral cell when wave generated currents are moving in a
northerly direction.
Figure 5.26 presents the profiles for Reaches 626 to 631, which corresponds to
Southwich Beach State Park and the Lakeview WMA. All the profiles feature a
prominent nearshore bar and trough feature, are very flat, and strikingly similar in shape
from the waterline to the 10 m depth contour. They appear to be in equilibrium with the
local wave climate.
The lakebed profiles between North and South Colwell Pond and the north barrier beach
at North Pond are presented in Figure 5.27. Again, a prominent nearshore bar is
documented and the lakebed morphology is very similar for this group of profiles. The
origin of the depression for Profile 633 at 600 m on the x-axis is unknown (i.e. physical
feature or surveying error).
Figure 5.28 presents nine profiles for the shoreline from the southern barrier beach at
North Pond to Brennan Beach. Although the general morphology is similar for this
group of profiles, there is considerably more variability than the profiles to the north.
Also, the nearshore conditions are much deeper, particularly for profiles 695 and 696,
which correspond to the Rainbow Shores development. Shoreline protection has been
constructed to protect many of the homes along with stretch of shoreline. Reach 699,
which is located at Brennan Beach, appears to record the glacial till lakebed below the 6
m depth contour (approximately 700 m on the x-axis). This area marks the transition
from the sandy lakebed to glacial till (refer to Figure 5.14).
The lakebed profiles for a ten kilometer stretch of shoreline south of the Salmon River
Jetties are presented in Figure 5.29. They capture the variability associated with the
glacial till lake bottom for this region of Eastern Lake Ontario.
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0
0619
-1
0622
-2
Depth (m)
0623
-3
0624
-4
0625
-5
-6
-7
-8
-9
-10
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
Distance (m)
Figure 5.25
2001 SHOALS Lakebed Profiles from Stony Point to Jefferson Park Community
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0
-1
0626
0627
0628
0629
0630
0631
-2
-3
Depth (m)
-4
-5
-6
-7
-8
-9
-10
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
Distance (m)
Figure 5.26
2001 SHOALS Lakebed Profiles from Southwick State Park to Inlet at Lakeview WMA
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0
-1
0652
-2
0653
-3
0654
Depth (m)
-4
0661
-5
0662
-6
0663
-7
0664
-8
-9
-10
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
Distance (m)
Figure 5.27
2001 SHOALS Lakebed Profiles from Inlet at Lakeview WMA to Inlet to North Pond
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0
-1
0691
-2
0692
0693
-3
0694
Depth (m)
-4
0695
-5
0696
-6
0697
-7
0698
-8
0699
-9
-10
0
200
400
600
800
1000
1200
1400
1600
1800
Distance (m)
Figure 5.28
2001 SHOALS Lakebed Profiles from South Barrier Beach at North Pond to Brennan Beach (adjacent to north jetty at Salmon River)
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0
0720
-1
0721
-2
0722
-3
0723
Depth (m)
-4
0728
-5
0729
-6
0730
-7
0731
-8
0732
-9
-10
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
Distance (m)
Figure 5.29
2001 SHOALS Lakebed Profiles from South Fillet Beach at Salmon Inlet to 7.5 km south of Salmon River
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Lakebed Change
A bathymetric survey of ELO was completed in 1948 by NOAA. These soundings were
compared to the 2001 SHOALS survey to document over 50 years of lakebed evolution
at the site. Plus, the findings help identify zones of lakebed erosion and thus sediment
supply regions for the littoral cell.
Starting in the north, Figure 5.30 compares the 1948 NOAA soundings to the SHOALS
survey at Reach 628, which corresponds to the Lakeview WMA. Since a large survey
vessel was likely deployed in 1948, the soundings were generally limited to depths below
the 1.0 m contour. Between the 2 and 6 m depth contour in Figure 5.30, the lakebed has
been stable for the last 50 years, with no significant deposition or erosion areas.
The profile offshore of Montario Point, presented in Figure 5.31, documents a different
trend. Although the lakebed has been stable from the 4 to 7 m depth contour, between
the 4 and 2 m depth contour the data documents downcutting or lakebed erosion. This
may be related to the permanent erosion of the glacial sediments that outcrop at the
waterline at Montario Point.
Reach 664 corresponds to the location of the modern inlet to North Pond. Refer to the
profile comparison in Figure 5.32. There has been significant lakebed erosion between
the 1 and 5.5 m depth contour (below Chart Datum). This erosion may be partly
associated with the changes to the barrier for the modern inlet.
Reach 693 is located along the southern barrier at North Pond. Figure 5.33 presents the
profile comparison between 1948 and 2001. Lakebed erosion is focused between the 2
and 4 m depth contours.
The lakebed conditions at the Deer Lake WMA are represented by the profile comparison
findings for Reach 698, as plotted in Figure 5.34. At this location, the lake bottom below
the 2 m depth contour has been stable for the last 50 years.
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2.0
1.0
1948
0.0
2001
-1.0
Depth (m)
-2.0
-3.0
-4.0
-5.0
-6.0
-7.0
-8.0
0
100
200
300
400
500
600
700
800
900
1,000
1,100
1,200
Distance from Shoreline (m)
Figure 5.30
1948 to 2001 Lakebed Profile Comparison for Reach 628 (Lakeview WMA)
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2.0
1.0
1948
0.0
2001
-1.0
Depth (m)
-2.0
-3.0
-4.0
-5.0
-6.0
-7.0
-8.0
0
100
200
300
400
500
600
700
800
900
1,000
1,100
1,200
Distance from Shoreline (m)
Figure 5.31
1948 to 2001 Lakebed Profile Comparison for Reach 661 (Montario Point)
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2.0
1.0
1948
0.0
2001
-1.0
Depth (m)
-2.0
-3.0
-4.0
-5.0
-6.0
-7.0
-8.0
0
100
200
300
400
500
600
700
800
900
1,000
1,100
1,200
Distance from Shoreline (m)
Figure 5.32
1948 to 2001 Lakebed Profile Comparison for Reach 664 (North Barrier for North Pond)
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2.0
1.0
1948
0.0
2001
-1.0
Depth (m)
-2.0
-3.0
-4.0
-5.0
-6.0
-7.0
-8.0
0
100
200
300
400
500
600
700
800
900
1,000
1,100
1,200
Distance from Shoreline (m)
Figure 5.33
1948 to 2001 Lakebed Profile Comparison for Reach 693 (South Barrier for North Pond)
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2.0
1.0
1948
0.0
2001
Depth (m)
-1.0
-2.0
-3.0
-4.0
-5.0
-6.0
-7.0
-8.0
0
100
200
300
400
500
600
700
800
900
1,000
1,100
1,200
Distance from Shoreline (m)
Figure 5.34
1948 to 2001 Lakebed Profile Comparison for Reach 698 (Deer Lake WMA)
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Isostatic Rebound
During the last glacial period, the weight of the ice sheets that covered the Lake Ontario
Basin depressed the underlying bedrock. When the continental glaciers melted and
migrated in a northerly direction, the underlying bedrock slowly began to bounce back.
This process is known as isostatic rebound. The measured rate of rebound for the eastern
end of Lake Ontario is 2.3 mm/yr. Over a century, this translates into a rebound rate of
0.23 m.
Without the erosive action of waves and currents in Lake Ontario, in theory isostatic
rebound would raise the lake bottom along ELO by 0.23 m per century. However, as the
profile comparisons have shown, the lake bottom at ELO is in a state of dynamic
equilibrium with the wave climate. In other words, over time the shape of the sand sheet
has evolved in response to lake levels and waves. This observation is at odds with
isostatic rebound, since the nearshore environment should be slowly getting shallower.
If the rebounding lake bottom is eroded by waves and currents, this process may
represent a sediment sink for the littoral cell. For example, consider the following
volumetric calculation. The ELO sand sheet is approximately 28 km in length from the
Salmon River Jetties to the outlet at Black Pond. Waves and currents are generally
focused on a zone of the lake bottom between the 6 m depth contour the and the
waterline. This region is approximately 1 km in width. Collectively, this zone of active
sediment dynamics is 28,000,000 m2. When the annual rebound rates is applied (2.3
mm/yr), approximately 64,000 m3/yr of new sediment is added to the littoral zone. In
other words, for the profile morphology to maintain its equilibrium form, waves and
currents must erode this sediment and this process generates sediment for the littoral cell.
Over periods of multiple decades, sand is eroded from the lake bottom to maintain the
equilibrium profile shape and this new sediment is transported alongshore and onshore to
build beaches and dunes. Therefore, in a regional context, the rebounding lake bottom
represents a source of sediment for the littoral cell.
Sediment Supply from the Salmon River
An oblique view of the Salmon River Jetties was provided in Figure 5.15. The mouth of
the river has been modified by the armor stone jetties. Upstream dams have modified the
natural flow regime and sediment delivery from this watershed. Prior to these
modifications, when the river drained naturally to the lake, the watershed may have been
a source of new sand sized sediment for the coastal zone. The gradients of the river and
nature of the surficial sediment has not been investigated to determine the feasibility of
the watershed as a sediment source prior to anthropogenic modifications.
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Sediment Deposition Associated with Inlet Migration
An image of North Pond and the modern barrier beach is provided in Figure 5.35. On the
pond side of the barrier, the multiple arrow head features record a long history of inlet
migration and sediment. The implications of these processes and the associated
depositional features is investigated.
Figure 5.35
1948 to 2001 Lakebed Profile
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For example, the former inlet is located to the south of the modern entrance to North
Pond. From the aerial photograph it is clear channel sedimentation and aeolian processes
have deposited a significant volume of sand into North Pond to fill the old inlet. If the
present inlet was to close and a new channel opened further to the north, over time a
similar feature would develop.
To investigate the implication of this channel migration and evolution on the regional
sediment budget, two historical bathymetry datasets were compared to the 2001
bathymetry collected for this study. Profile B runs parallel to the back side of the barrier
ridge and documents the history of inlet migration below lake level.
Figure 5.36
Profile B Comparison from 1878 to 2001 at North Pond (0 on the x-axis corresponds
to south)
It should be noted that 0.0 m on the x-axis in Figure 5.36 corresponds to the southern
corner of North Pond. In most cases, the 1878 bathymetry records the maximum depth of
the pond. Based on the contours of the lake bottom, it appears the flood shoal for the
inlet in 1878 was between 2,500 and 3,000 m on the x-axis.
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Some time between 1878 and 1948, the inlet was located along the southern half of the
barrier, likely just north of the large relic sand dunes along the current south barrier. This
inlet location is documented by the flood shoal in Figure 5.36 between 800 and 1,300 m
on the x-axis.
In 1948, the inlet was located between 2,000 and 2,500 m on the x-axis in Figure 5.36. In
Figure 5.35 this corresponds to the word “Profile” along the line for Profile B. Once the
new inlet is opened, sediment is driven into the pond during storm events, particularly
events at high lake levels or storms that feature a large storm surge. This sediment
accumulates in the flood shoal in the pond and is permanently lost from the littoral
system. In other words, there is no physical processes capable of transporting the
sediment back out into the nearshore zone of the lake.
The 2001 bathymetry records the location of the modern flood shoal between 3,400 and
3,800 m in Figure 5.36. In 1878 to 1948, the surveys record depths in the pond ranging
from 2.5 to 5.0 m below chart datum. Today much of the flood shoal is at chart datum or
slightly below. A significant volume of sand has accumulated inside North Pond in this
depositional feature.
A 3D volumetric comparison of the lake bottom in 1878 and 2001 was completed in GIS.
It should be noted that in addition to sedimentation associated with the flood shoals,
deposition of fine sediment, such as silt and clay has also occurred in the pond since the
1878 survey. This deposition is thought to be more concentrated in the eastern (back)
half of the pond.
The annualized rate of sediment deposition in North Pond is approximately 58,000 m3/yr.
Since some of this deposition is associated with the riverine transport and deposition of
fine silts and clays, it is estimated 40,000 to 50,000 m3/yr of sand has been deposited in
the pond, on average, since 1878. This represents a large sediment sink for the littoral
cell.
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Fillet Beaches
There are three zones of deposition associated with the Salmon River Jetties: a small
north fillet beach, sand bars inside the jetties next to the navigation channel and the south
fillet beach. Using a the 1960s vegetation line as a basis for comparison with the 2002
orthophotograph, a series of preliminary calculations were completed to estimate the
volume of sediment in these three sinks. Assuming the deposition has occurred over a
vertical depth of 4.0 m, the estimated accumulation is 100,000 to 150,000 m3.
Dune Blowouts and Aeolian Transport
Dune blowouts and aeolian processes can transport large volumes of beach sand inshore
of the foredune ridge, particularly when the dunes are destabilized by natural or artificial
processes. Once the sand is deposited landward of the foredune ridge, it represents a
permanent sink for the sediment budget. An example of a large aeolian deposit at Sandy
Island Beach is seen in the background of Figure 5.37. The cottage in the figure is
located on the backside of the dunes for the south barrier at North Pond.
An estimate of the volume of sediment transported inshore of the foredune and thus
permanently removed from the littoral system was not completed for this investigation
due to insufficient historical information.
Figure 5.37
Large Depositional Lobe of Sand on the Backside of Sandy Island Beach
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5.2.4
Regional Sediment Transport Patterns
Longshore sediment transport estimates for the ELO site were completed with the
COSMOS model to assess regional trends and rates. A sediment grain size of 0.4 mm
was used for the calculations. The historical wave climate and lake levels from 1981 to
2000 were used as model input. Profile conditions at over 30 of the 1 km shoreline
reaches were used.
A sample of the predictive capabilities of the COSMOS model for a 2D beach profile is
presented in Figure 5.38 for the profile at Lakeview WMA. All the profiles extended
from the dune crest to the 10 m depth contour. The model predicts the distribution and
magnitude of the transport across the profile. As waves break across the nearshore bar
and on the beach, the resulting longshore currents transport sediment. Thus, the
magnitude of the transport is greatest in the shallow nearshore zone and across the bar.
10
5,000
Reach 630 Profile
8
4,000
Potential LST to the South
6
3,000
4
2,000
2
1,000
0
0
-2
-1,000
-4
-2,000
-6
-3,000
-8
-4,000
-10
0
200
400
600
800
1,000
1,200
1,400
1,600
Distribution of LST (m/yr)
Depth (m)
Potential LST to the North
-5,000
1,800
Distance (m)
Figure 5.38
Cross-shore Distribution of Longshore Sediment Transport (Lakeview WMA)
A Lakeview, the shoreline orientation and wave climate result in a large southerly
component, which is mapped in red in Figure 5.38. The northerly component features a
similar cross-shore distribution of LST but the annual volume is significantly less. Thus,
the next direction of LST at Lakeview is to the south.
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The results from the regional sediment modeling are summarized graphically in Figure
5.39. The LST rates are annualized and plotted as the northerly, southerly and net
volumes. The shore perpendicular azimuth is plotted on the Y2 axis in Figure 5.39 to
highlight the influence of shoreline orientation. It should also be mentioned that these
are actual LST rates and they assume the full supply is available to be transported.
In the Jefferson Park and Lakeview area, the dominant direction of LST is to the south,
although there is a small northerly component. Consequently, the net direction is to the
south or center of the Eastern Lake Ontario site. The rate decreases towards the center of
ELO and reaches zero at North Pond. It is also worth noting that since the northern limits
of the littoral cell are bounded by bedrock, the potential supply from the north is zero or
very close to zero. Therefore, although the net LST rate predicted with COSMOS is
approximately 200,000 m3/yr, the supply is very close to zero. Therefore, although the
net direction is to the south, the actual volume of sediment transported in a southerly
direction is likely much closer to zero than 200,000 m3/yr.
South of the Salmon River Jetties, the net direction for LST is to the north. However, as
discussed previously, the lake bottom is glacial till and much of the shoreline is hardened
with shoreline protection. Therefore, the actual supply from the south is likely very close
to zero. From the Salmon River to North Pond, the net LST direction is to the north and
decreasing. In other words, there is a decreasing gradient to the north, with the net LST
rate reach zero at North Pond.
In summary, longshore sediment transport at Eastern Lake Ontario converges from the
north and south at North Pond. Along an open coastline, the convergence of LST from
two directions or a decreasing gradient in LST generally results in the formation of a
depositional feature. However, at ELO the sediment transported to the center of the site
is transported into North Pond via the present and historical inlets and stored in the flood
shoals.
A significant volume of sediment has also accumulated in the barrier beach at North and
South Colwell Pond. Based on a comparison of the modern and 1878 shoreline,
approximately 970,000 m3 of sand has accumulated in this feature or 7,900 m3 per year.
This barrier beach is also a significant depositional zone.
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500,000
Fillet Beach South
of Salmon River
310
300
200,000
LST to the South
290
100,000
280
0
270
-100,000
260
-200,000
LST to the North
Shore Perpendicular Azimuth (deg.)
Deer Creek
North Pond
Lakeview
Wildlife
Management
Area
Jefferson Park
300,000
Montario Point
Longshore Sediment Transport (m3/yr)
400,000
320
250
-300,000
Annual North
Annual South
Net Annual
Profile Azimuth
729
728
723
722
721
699
698
697
696
697
696
695
694
693
692
664
663
664
663
662
661
654
653
652
631
652
631
630
629
628
627
626
625
624
625
240
624
-400,000
Reach Number
Figure 5.39
Regional Longshore Sediment Transport Estimates for Eastern Lake Ontario (average annual rates)
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