Note: Descriptions are shown in the official language in which they were submitted.
CA 02778848 2012-05-25
SHORE LINE EROSION CONTROL
This invention relates to an apparatus for control of erosion at the
shore line of a body of water.
BACKGROUND OF THE INVENTION
There has been some severe erosion taking place on lake shores in
sandy beach areas in Canada and the United States and this has become a wide
scale problem.
One of the problems with traditional erosion protection designs using
conventional revetments is the large width of space required to complete a
design
on sandy beaches. If the shoreline of the beach area where the erosion is
taking
place is populated with cottages and is used as recreational space for
swimming and
sun bathing there is a conflict for beach usage. Sun bathers want more beach
during the summer and cottage owners see their frontage being eroded away. For
traditional revetments to function requires the placement of armor rock in
front of the
cliff or eroding area in order to dissipate the kinetic energy of the waves as
they
move towards the bank or cliff zone. In some cases up to forty or fifty feet
of sandy
beach may be required for the placement of this rock. In many cases this is
not an
acceptable use of the beach.
SUMMARY OF THE INVENTION
According to the invention there is provided an apparatus for control of
erosion at the shore line of a body of water at or near an edge of the surface
of the
body of water comprising:
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a frame for mounting at the shore line with a base for engaging into the
ground and an adjustable upper portion for extending upwardly from
the ground;
at least one curved sheet mounted on and located by the frame;
the curved sheet having a lower edge arranged relative to the frame so
as to be located at a position below the ground surface;
the curved sheet or sheets having an upper edge arranged relative to
the frame so as to be located at a position above the water or beach surface;
the curved sheet or sheets having a concave front surface extending
from the bottom edge upwardly to the upper surface and curved so that an angle
of
the surface to horizontal planes increases from the horizontal planes adjacent
to the
bottom edge to horizontal planes adjacent to the upper edge.
The height of the upper edge of the curved sheet is located at a
position above the water surface which is sufficient to reach the level of the
adjacent
cliff level so that this can vary depending upon the height of the cliff. In
some cases
where the required height is less than the typical sheet height of 9.6 feet, a
single
sheet can be used. In some cases the sheet is connected to a second curved
sheet
if the eroded shoreline is at a height higher than one curved sheet.
Preferably the curved sheet is substantially vertical at the upper edge.
Preferably the frame is a bolt together structure formed of a plurality of
horizontal rails supporting the curved sheet including a bottom rail at or
adjacent to
the bottom edge and a top rail at or adjacent to the top edge and the rails
are
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connected to upstanding supports which extend from the rails downwardly to the
base. The height of the frame is preferably adjustable to accommodate
different
heights of cliff and the required height of the sheets. This can be done by
bolting
together additional pieces or by adjustable coupling of one frame member to
another.
Preferably the base includes a receptacle in the form of a heavier
gauge corrugated galvanized flat base sheet for receiving ballast such as
rocks to
hold down the frame in the ground. That is, the base is held down against the
sand
by heavy rock such that any lateral forces pushing from the cliff side are
counterbalanced by this rock by at least a factor of two.
Preferably there is provided a plurality of curved panels arranged side
by side with the curved sheet panels being corrugated with channels which
extend
longitudinally from the bottom edge to the top edge. Such panels are readily
available from grain bins or similar constructions with the corrugations
providing
sufficient stiffness to maintain the curvatures of the panels.
Preferably the curved panels are coated with a sand colored coating at
least on the concave front surface.
After installation the void behind the curved sheet is filled with a
drainage material. No armor rock is required in front of the curved sheet to
provide a
very short width profile on the beach.
A hand railing can be attached to the frame at or adjacent to the upper
edge to provide a safe walkway behind the revetment along the splash apron.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a side view of revetment design showing curve S1 and the
splash apron.
Figure 2 is an isometric view of the assembled apparatus separated
from the installation showing the components.
DETAILED DESCRIPTION
The apparatus for control of erosion at the shore line of a body of water
at an edge of the surface of the body of water includes a frame 10 for
mounting at
the shore line with a base 20 for engaging into the ground and an adjustable
upper
portion 12 for extending upwardly from the ground. On the frame is mounted a
row
of panels 13 mounted side by side on and located by the frame. The panels form
a
curved sheet 14 of the top part of the structure which has a lower edge 15 and
an
upper edge 16. The sheet can be formed of a single panel 14 or can include a
second panel 14A connected at the bottom edge 14B of the upper panel as
required.
The lower edge 15 is located at a position below the ground surface at a
bottom and
forwardmost point forming a toe 15A. The curved sheet 14 together with the
lower
sheet 14A has a concave front surface 14C extending from the bottom edge 15
below the ground surface continuing upwardly to the upper surface 16 and
curved so
that an angle of the surface to horizontal planes increases from the
horizontal planes
CA 02778848 2012-05-25
adjacent the bottom edge to horizontal planes adjacent to the upper edge where
the
curved sheet is substantially vertical.
The frame is a bolt together adjustable structure formed of a plurality of
horizontal rails 17 supporting the curved sheet or sheets including a bottom
rail 17C
5 at or adjacent to the bottom edge of the bottom and a middle rail 17B at or
adjacent
to the bottom edge 15 and a top rail 17A at or adjacent to the top edge 16 and
the
rails are connected to upstanding adjustable supports 18 including the rear
longest
posts 18A, middle posts 18B and the short front posts 18C which extend from
the
rails downwardly to the base. The top sheet 14 is also supported by curved
beams
19 which follow the curvature behind the sheet and extend downwardly and
forwardly to the lowermost rail 17C at the top of the posts 18C.
The base attached at the bottom of the posts 18 includes a receptacle
in the form of a galvanized flat base sheet 20 also formed from corrugated
panels for
receiving ballast such as rocks to hold down the frame in the ground. The base
sheet 20 is carried on a plurality of beams 22- connected to the bottom of the
posts
18A, 18B and 18C so that the frame forms a rigid structure attached to the
base
sheet 20 and carrying the sheet 14 and the lower sheet at its elevated
position
above the base sheet.
The active part of the curved sheet 14 is that from just above ground or
beach level to the top edge 16. The curved panels are coated with a sand
colored
coating on the concave front surface.
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After installation the void V behind the curved sheets is filled with a
drainage material. No armor rock is required in front of the curved sheet to
provide a
very short width profile on the beach. A railing 21 can be attached to the
frame at
the top rail 17A to provide a safe walkway behind the revetment.
The Southern basin of Lake Winnipeg similar to other North American
lakes is a prime candidate for this new design. The first observation that
should be
made is that the footprint of this design will take up considerably less sandy
beach
than a traditional design as there is no need to provide armor rock in front
of this
configuration. The design is comprised of a galvanized curved sheet of
corrugated
steel such that a line tangent. at the top edge of the curved steel sheet is
almost
vertical. A second observation is the flexibility of the design which can be
easily
adjusted by overlapping the curved sheets and adjusting MedifyiRg the support
structures 18.
The novel revetment design is provided for eliminating bank and cliff
erosion on sandy beaches and has a very small width footprint on the beach.
The
main structure of the design incorporates curved corrugated steel sheets
coated with
a special sandy colored polyurethane. The curvature of the sheets can be
designed
as a part of a parabola or a circle. The curved sheets are supported by a
superstructure that leans slightly towards the erosion cliff and has a
corrugated
sheet as the base to link to the structure. The base sheet is held down
against the
sand by heavy rock such that any lateral forces pushing from the cliff side
are
counterbalanced by this rock by at least a factor of two. The design has the
toe of
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the curved sheet buried three feet below the sand surface with the tangent at
the
upper edge of the curvature creating an almost vertical line when the circle
equation
is used. The design also has pea gravel or drainage rock filling the void
behind the
curved steel right up to the cliff or bank. The design does not require any
armor rock
in front of the curved, hence the very short width profile on the beach. It is
also
possible to attach a railing on the upper edge to provide a safe walkway
behind the
revetment at a designed elevation depending on the cliff or bank height at the
specific location.
Also note that it is important that the toe or bottom edge of the lower
sheet near the front rail 17C of the curved sheet is buried at least three (3)
feet into
the sand with some associated rocks being placed at this level as shown. The
base
of the structure at the three (3) foot level is comprised of 10 gauge
galvanized
corrugated steel sheets linked to upward facing support members. These members
are connected to and support the curved sheets. The splash apron area as
depicted
behind the curved sheets is filled with pea gravel or two (2) inch drainage
rock fill to
allow rain water and water that possibly overflows the top of the curved steel
to
easily percolate back down the back of the entire structure. This design
ensures no
water remains behind the structure that could freeze and cause sheet movement
in
freezing winter weather.
For an average cottage lot frontage of seventy-five (75) feet, the
individual curved sheets each cover forty-four (44) linear inches requiring
about 21
sheets. They are bolted together to create an impervious continuum. The curved
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sheets are spray coated with a polyurethane, fire retardant, sandy colored
product
which creates a very tough, sand paper surface. The thickness of the sprayed
product will vary along the sheet being approximately two hundred and forty
(240)
mils near the bottom to about ninety (90) mils near the top. The reason for
this is that
there will be more sand/water sediment movement at the bottom of the curve
during
storm conditions than at the top of the curve leading to increased wear.
This design assumes the waves have "broken" prior to encountering
the barrier. As the wave action moves up the curved sheet at 2 to 5 meters per
second, its kinetic energy is dissipated as the force of gravity eventually
equals the
weight of the water and it stops upward movement. It is anticipated that
during windy
and waving conditions the water movement may not only be upward but may
propagate sideways along many sheets. Wind and wave movement from the lake
will dictate whether this occurs and in which direction water moves. One of
the
interesting aspects of this design is its flexibility. By combining two (2)
sheets, one
overlapping the other, the curved length or generated chord can be varied
considerably. This allows the design to be matched to the cliff height and
desirability
of erosion protection. It is suggested that the minimum height could be set to
four (4)
feet and the maximum chord length set to about sixteen (16) feet. These values
are
currently based on the corrugated sheet sizes that are readily available and
manufactured in industry.
In the design it is necessary to determine the amount of rock required
in the base section to counteract the moment of force caused by the cliff
pushing
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against the upper portion of the structure. A factor of two has been selected
as the
target and further study will determine the exact rock tonnage required.
The curve of the steel sheets is important in this design. Two types of
curves can be implemented although one type would require a manufacturing
modification. The curvature can be a section of a circle or can be a section
of a
parabola. An equation of the form
y=axe+bx+c (1)
represents the generic formula for a parabola. If, for example, an erosion
barrier for
a fifteen (15) foot high cliff design is required, the following equation has
been
determined for the parabola with a=0.96, b=-5.81,c=8.80 and x defined in feet.
This
gives
y=0.96x2-5.81x+8.80 for 35x510 (2)
Based on this equation the toe of the parabola would start at about x=3
feet. The advantage of the parabola curve is the rapid, somewhat exponential
change in the slope of the curve as it rises almost vertically. A tangent to
the curve
at the 15 foot level never becomes fully vertical but remains at a very steep
slope.
This would mean that the kinetic energy of any water mass moving up the curve
CA 02778848 2012-05-25
would soon be balanced by its own weight, stop, fall back on itself or move to
the left
or right.
The second curve, a circle, has the general equation as follows.
5
(x-xo)2+(y-yo)2=r2 (3)
where xo and yo are the coordinates of the center of the circle and r
represents the
radius. As an example, for the design of an erosion barrier curvature based on
a
10 circle for a fifteen (15) foot cliff height, the following equation would
be used
x2 + (y - 15)2 = 225 (4)
with center at xo = 0 and yo = 15. It creates a more gently inclining curve
and has a
vertical tangent line' occurring only once in the right hand quadrant. Given
that the
current manufacturing process for curled sheets is based on circles, the
current
design will focus on equation (3) rather than equation (1). Parabolic designed
curves
can be implemented in the future by modifying the curling equipment to adjust
the
amount of curl occurring in real time as the sheet passes through the curling
machine. For now, emphasis will be on the circle designed curvature for the
erosion
barrier.
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An important consideration is the length and thickness of the steel
sheets that are available from industry for the structure. Steel sheets are
roll formed
and cut to a maximum length of 116.5 0.3 inches, with a width of 45.5 +0.5,-
0.3
inches, and a variety of thicknesses ranging from gauge 3 (0.2391 ") to gauge
30
(0.0120"). Assuming a fifteen (15) foot high erosion barrier is to be designed
based
on a curvature given by the circle with equation (4) the length of the arc
subtended
by 90 degrees as shown in Figure 1 is calculated as 23.5612 feet. However,
only the
part of the curve subtended by 70.5 degrees (representing the arc labeled S1
in
Figure 1 from Toe to the Top edge of the curvature) is required for the
design.
Essentially, this reduces the footprint of the barrier on the beach by five
(5) feet and
would require only 18.46 feet of curled steel or 221.56 inches. For the
design, two
(2) corrugated steel sheets would be required with an overlap of two (2)
inches. One
sheet would be 116.5 inches in length and the second sheet would be cut to
107.5
inches. A thickness of 0.1046 inch or 12 gauge would be used. The corrugated
steel
base would be comprised of 88 inch sheets with a suggested thickness of 0.2092
inch or 5 gauge. Support members are anchored to these base sheets.
Sections of the barrier would be fabricated 88 inches wide and then
placed in a ready made 3 foot trench at approximately 88 inches apart. On the
higher structures as shown here, the curved sections for the upper portion of
the
barrier are then be installed and secured in place. The lower curved sections
would
not be installed at this time. Rock is then be placed on the base support
corrugations to as high as possible with a bucket no wider than 6.5 feet as it
must
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pass through the support structure. The rock weight should be at least two
times the
possible lateral forces created by the cliff forces behind the structure
pushing
towards the lakeshore. Section by section is then added until complete at
about 75
feet. During this time sensors for measuring structural integrity can be
installed at
the back of the upper and mid sections of the curved sheets and support
members.
Wiring can be installed in EMT to prevent cable damage. Once completed and the
necessary rock installed, the lower curved sheets would be installed using
self
tapping screws at the bottom and nuts and bolts at the mid sections as the
structure
is gradually fabricated. The area behind the structure would then be filled
with pea
gravel or drainage rock.
Based on the current cost of the components a maximum price range
should be within the $30,000 to $35,000 maximum for a 75 foot frontage giving
an
installed cost range of $400 to $465 per running foot. Of course, if a number
of
cottage owners band together then it is presumed that pricing could be better.
It is
anticipated that the metal component of the structure could be supplied in
kits from
the manufacturer for a specific locations design height and width requirement.
This design can use curved corrugated steel sheets with a sandy
colored polyurethane coat. The only component of this design that will wear
would
be the polyurethane isomer coating depending on the frequency of storms and
the
amount of sand carried by the water that would continually move across the
lower
section of the curved portion of the sheets. This would be examined after
every
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storm that impacts the structure to see how much, if any, of the coating has
disappeared.
Ultra-violet sun rays that impact on the coating may cause some signs
of fading but is anticipated that the coating should be good for at least 10
to 12
years, after which a new coating might be required. Damaged areas could be re-
coated or have a kit supplied to repair small areas.
