U.S. patent number 3,888,209 [Application Number 05/415,690] was granted by the patent office on 1975-06-10 for artificial reef.
Invention is credited to Edmund R. Boots.
United States Patent |
3,888,209 |
Boots |
June 10, 1975 |
Artificial reef
Abstract
A method and apparatus for preventing erosion of a beach,
including an artificial reef for subsurface placement adjacent a
shoreline and made up of a base reef set on the seabed and an upper
reef preformed and mounted to the base reef or formed in situ on
the base reef by a sabellariid marine organism thereby forming a
composite reef to build up accretion of sand on the shore side of
the reef and to prevent erosion of a beach.
Inventors: |
Boots; Edmund R. (Vero Beach,
FL) |
Family
ID: |
23646769 |
Appl.
No.: |
05/415,690 |
Filed: |
November 14, 1973 |
Current U.S.
Class: |
405/25; 119/239;
119/221 |
Current CPC
Class: |
E02B
3/06 (20130101) |
Current International
Class: |
E02B
3/06 (20060101); A01k 061/00 (); E02b 003/04 () |
Field of
Search: |
;61/3,4,5,37
;119/1,4 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"The Reef Builders" by D. W. Kirtley, National History Magazine,
January 1968..
|
Primary Examiner: Wolfe; Robert L.
Assistant Examiner: Corbin; David H.
Attorney, Agent or Firm: Brumbaugh, Graves, Donohue &
Raymond
Claims
I claim:
1. A method for protecting a shoreline against undesirable erosion
by positioning an artificial reef offshore to serve as a favorable
habitat for sabellariid marine organism, comprising the steps of
submerging a plurality of solid one-piece base reefs substantially
end-to-end on the seabed adjacent and oblique to the shoreline,
such that one end of the artificial reef is closer to the shoreline
than the other end, each of said base reefs having an upper crown
portion and a pair of spaced depending sidewalls each forming a
substantially continuous interface surface extending from the
seabed to the top of said reef, the lower ends of said sidewalls
being adapted to be set on the seabed to define a chamber extending
the length of the base reef between the seabed and the interior
surface area of said sidewalls and said crown, said base reefs
having an opening into said chamber in said crown to provide access
to the chamber for sand and water, the mean water level relative to
the seabed at the points of placement of said base reefs being no
less than the height of the artificial reef, and permitting the
sabellariid organisms to form an upper reef on said base reefs.
2. The method of claim 1 comprising the steps of securing a
prefabricated upper reef on at least some of said base reefs, said
upper reef having a cross section of inverted substantially U-shape
open at the bottom with the lower ends thereof engaging an upper
surface of said base reefs and having chamber defined between said
upper surface of said base reefs and the interior surface area of
said upper reef.
3. A method of building an artificial reef for placement on a
seabed adjacent a shoreline, comprising the steps of submerging a
base reef adjacent the shoreline, cultivating a colony of
sabellariid marine organisms on a transplant support in a nutrient
media, transporting said transplant support to the base reef, and
affixing said transplant support to the base reef, the organisms on
said support forming an upper reef on the base reef to increase the
height of the reef.
4. The method of claim 3 comprising the step of applying a nutrient
composition to the surface of said base reef to facilitate growth
on said base reef of said sabellariid marine organisms.
Description
The present invention relates to artificial ocean reefs and in
particular to a composite reef which includes one or more base
reefs built up in height by either a marine organism implanted
thereon or an upper reef element mounted thereon, the composite
reef serving to interrupt the prevailing ocean currents and wave
patterns in the vicinity of the beach to restore balance between
accretive and erosive influences on the beach.
BACKGROUND OF THE INVENTION
The ecological problems of the shoreline have recently been
receiving a great deal of attention, particularly in the form of
studies, national in scope, in which the significance and extent of
the shore erosion has been assessed. For example, it has recently
been determined that of the approximately 85,000 miles of total
shoreline of the United States, significant or critical shoreline
erosion appears over approximately 2,700 shoreline miles.
The erosion of sand beaches is one aspect of the general shoreline
problem referred to above and is especially significant in view of
its commercial impact for certain shore communities.
The degradation of sand beaches through natural erosion is a
complex problem. The most pervasive and persistent influence on
alteration of the beach appears to be the continuous assault by the
ocean, particularly those ocean currents developed during severe
storms. An additional contribution to beach erosion is often made
by the so-called littoral currents adjacent the beach which move in
a direction parallel to the shoreline.
Under normal circumstances the movement of beach sand onto and off
of the beach reaches an equilibrium state in which sand is
deposited on and removed from the beach in a substantially regular
cyclical process. This process appears to vary with weather
conditions which affect the intensity and direction of the
prevailing wave and wind action.
Critical beach erosion normally results when this natural balance
is upset in some way, and there is a resulting net movement of sand
away from the beach. Such interference with the natural
accretion-degradation cycle typically results when sea walls or the
like are emplaced on the shore in order to protect a commercial or
residential development from the sea. During a storm, for example,
aggravated ocean waves impinge upon the sea walls and are deflected
downwardly thereby to carry sand off the beach and into the ocean.
In the absence of normal protective sand dunes, nothing remains on
the shore with which to replace the sand that has been removed from
the beach in this manner. Over a period of time the result may be a
net flow of sand from the beach. Such erosion by severe storms
frequently exceeds the economic capabilities of the nearby
communities to replenish the beach materials.
Even under normal weather conditions, the ocean turbulence at the
shoreline causes a suspension in the water near the shoreline of
sand and shell fragments. These suspended materials may be
transported along and substantially parallel to the shore by a
phenomenon known as the littoral or longshore current. This current
results from interference between incoming waves, which generally
approach the shore obliquely, and backwash from the beach.
Normally beach materials transported in this fashion are being
picked up and deposited at various locations along the shore. Over
a sufficient period of time, the littoral transport of beach
materials would not be expected to create an erosion problem.
However, this natural balance of ecological forces acting on the
beach may be interrupted by the presence of artificial or natural
interference with the normal ocean current and wave action adjacent
the beach. For example, river currents emptying into the sea can
cause the littoral material to be deposited outwardly away from the
land. Dredging operations near the shoreline can also cause the
littoral material to settle out of the water away from the beach.
In addition, man-made formations which project outwardly from the
shore frequently act to disrupt the movement of the longshore
currents thereby causing an unnatural deposition of littoral
material away from the shoreline. The effect of these occurrences
in a particular location is frequently a net flow of sand away from
the beach. A critical erosion situation may thereby quickly
develop.
Many different attempts have been made heretofore to develop a
solution to these problems. One approach has been to ignore the
erosion process and to replenish an eroding beach periodically with
sand and other suitable materials from some other source. This
approach is expensive and is only suitable in situations where sand
may be readily obtained from nearby inlets, bays or other areas
without damaging the regional ecology. Where such a supply of beach
material is not readily available, the cost of obtaining the
necessary sand is generally prohibitive.
Another approach which has been attempted heretofore is the
construction of artificial groins or the like which may be spaced
along the shoreline oriented substantially perpendicularly to the
shoreline. The use of such groins not only significantly degrades
the appearance of the beach but is generally only effective when
large amounts of sand are being transported by the longshore
currents. In addition, construction of such groins, while tending
to induce the accretion of sand on the updrift side, frequently
results in serious erosion of the beach on the downdrift side. The
net result of such erosion is generally a requirement for
substantial amounts of sand from other areas with which to
replenish the eroded area. The cost of such groins, along with the
added cost of importing sand from another source, makes this
solution to the problem impractical for most communities.
Still another approach for preventing beach erosion is the
construction of artificial breakwaters. Such breakwaters may take
the form of massive stone structures which are placed in the sea
outwardly from the beach area and substantially parallel to the
shore. Generally, these breakwaters serve to interrupt wave action
before the wave actually reaches the shore, thereby to induce a
relatively calm area on the beach side of the breakwater. As a
result of the induced calm, the suspended sand in transit may be
deposited inwardly of the breakwater. Beaches which are located
downdrift of the breakwater, however, may be deprived, as a result
of the breakwater, of sufficient amounts of naturally deposited
beach materials with which to offset the natural forces of sand
depletion. Thus, as to such downdrift beaches, the normal
deposition of the suspended materials is interrupted with the
result that there is frequently a net movement of sand away from
the beach.
SUMMARY OF THE INVENTION P
An object of the present invention is to provide a practical method
and apparatus for offshore reef construction which serves to
correct an imbalance in the natural accretion-degradation cycle so
as to prevent substantial erosion of a beach area by the net
movement of beach materials away from the shore.
Another object of the present invention is to provide an offshore
submerged reef structure in a form which may be transported to and
implaced in the desired offshore location and built up to a desired
height.
Still another object of the present invention is to provide a means
and method for securing an offshore reef structure to the ocean
floor.
A further object of the present invention is to provide an offshore
reef structure which will tend to entrap sand and other materials
within an internal cavity thereof so as to become substantially
self-stabilizing.
A still further object of the present invention is to provide an
offshore reef structure which is an artifical habitat for a reef
building marine organism known as phragmatopoma lapidosa, or
sabellariid.
Yet another object of the present invention is to provide a method
for implanting a sabellariid colony on an artificial reef structure
submerged adjacent a shoreline.
Another object of the present invention is to provide a system of
sabellariid reefs adjacent a shoreline and oriented so as to
facilitate the accumulation of sand in the beach area.
These and other objectives of the present invention can be achieved
by constructing one or more artificial reefs within the ocean along
the shoreline. Although such reefs would ordinarily be too heavy
and cumbersome to be handled and set in place or, if built of
lighter weight materials, destroyed by the impact of the ocean
currents and waves, the present invention provides a composite reef
made up of a heavy and durable base reef element built up in size,
and particularly in height, by an upper reef element composed of a
marine organism implanted thereon or a preformed upper reef element
mounted thereon. In this manner a heavy, durable artificial reef
can be built up in situ to a size and height that would ordinarily
be too cumbersome to handle and set in place.
The base reef element is preferably secured to the ocean floor by
pile members or stakes which are passed through the base element
and driven into the ocean floor. The base reef element may serve as
the habitat for an implanted marine organism, such as a sabellariid
organism, which over the years will continue to grow and build up
the size and height of the reef. On the other hand, if the
artificial reef is used in deeper waters where an increase of
height in the base reef is required immediately to permit the reef
to be effective, a preformed upper reef element may be mounted on
the base reef element and the marine organism may be implanted on
the upper reef element or eliminated entirely.
The base reef element is preferably of inverted U-shaped cross
section having openings therein to permit sand and other
particulate matter normally held in suspension in the sea water to
deposit and settle within the reef structure to afford it greater
anchorage and stability.
The composite artificial reefs are preferably arranged
substantially end-to-end and relative to the shoreline so as to
interfere with the destructive shoreline currents by deflecting the
incoming waves. This deflection interrupts the rhythm and intensity
of the incoming waves and thereby minimizes the adverse effects of
the waves on the beach. In addition, the interruption permits sand
and other suspended particles in the ocean water to settle out and
accumulate on the shore side of the reef .
BRIEF DESCRIPTION OF THE DRAWINGS
For a further understanding of the present invention, reference may
be had to the accompanying drawings, in which:
FIG. 1 is a perspective view of a base reef element adapted for
securement to the ocean floor;
FIG. 1a is a perspective view of the underside of the base reef
element of FIG. 1;
FIG. 2 is a schematic sectional view of one embodiment of the
artificial reef anchored in position adjacent the shoreline and
showing accumulated beach material on one side thereof;
FIG. 3 is an elevated view of a portion of a beach protected by a
reef system of the present invention;
FIG. 4 is a cross sectional view of the reef of FIG. 1; and
FIG. 5 is a cross sectional view of the base reef element having a
preformed upper reef element mounted thereon.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, and in particular to FIG. 1, there
is illustrated a base reef, generally indicated by reference
numeral 10, which is adapted for use in an artificial reef system.
The base reef 10 is preferably of substantially inverted U-shaped
cross section having a relatively flat, downwardly sloped surface
11 on its outer seaward side. The base reef 10 rests on the lower
terminal edges 12 and 13.
The base reef 10 is provided with a plurality of openings 14 and 15
spaced along the top 16 of the base reef. The openings 14 are each
adapted to receive a concrete pile or stake 17 which secure the
reef to the ocean floor.
The base reef 10 is placed in the ocean with the sloping portion 11
facing away from the shoreline. Thus, the surface 11 intercepts and
deflects the incoming wave currents up and over the top of the
reef. The slope of the surface 11 ensures that the vertically
downward component of force imparted by the impact of a wave moving
substantially horizontally against the reef acts to urge the base
against the ocean floor. The horizontal component of force imparted
by the wave impact is, as a result of the slope of the surface 11,
insufficient to unseat the reef.
Although this configuration of the reef is preferred because it
provides increased stability to resist anticipated wave forces
without excessive or unmanageable weight, nevertheless other
configurations may be suitable provided that the resulting unit is
not too heavy to prevent it from being handled and set in
position.
The reef is preferably constructed of prestressed concrete,
although other non-corrosive materials, such as ordinary reinforced
concrete or asphalt, might also be utilized. Prestressed concrete
is preferred because of its strength. It is also light enough to
keep the total weight of each base reef within manageable
limits.
As shown in FIG. 1a, each of the individual base reefs 10 has a
plurality of substantially vertical integrally formed wall sections
or baffles 18a, 18b and 18c which provide support for the
undersurface of the arch. These wall sections divide the interior
of the reef into chambers 19 and 21.
A vertical bore communicating with the openings 14 extends through
each of the wall sections. The bores permit passage of the
anchoring piles downwardly through the wall sections and into the
seabed to secure the reef to the ocean floor. The close tolerance
between the piles and the interior surface areas defining the
boreholes serves to stabilize the reef against rocking and swaying
about the piles.
The openings 15 formed in the reef establish flow communication
between the chambers 19 and 21 and the media surrounding the reef
structure. Sand and other materials normally suspended in the ocean
water pass through these openings and these materials settle to the
bottom and gradually fill the chambers.
The holes 15 also permit the water pressure within the chambers 19
and 21 to correspond substantially to the pressure of water flowing
across the base reef unit. A pressure imbalance might otherwise
occur as impacting waves are deflected by the reef and flow across
the crown thereof. Such an imbalance might, over a period of time,
develop instability in the reef.
The lower edges 22a and 22b of the two end walls 18a and 18b,
respectively, are above the terminal edges 12 and 13 of the base
reef. The lower edge 22c of the middle partition 18c is
substantially coplanar with the terminal edges 12 and 13 of the
reef and, therefore, rests on the seabed. This arrangement prevents
the flow of water between the chambers 19 and 20 so that water
within each of the chambers becomes relatively quiescent. Under
these conditions, materials suspended in the water beneath the reef
will more readily settle out and accumulate within the chambers.
The accumulation beneath the reef gradually increases with the
passage of time to stabilize the reef.
The walls 18a and 18b close the ends of the reef. The closed ends
are preferred because the reef will tend to be better stabilized.
For example, where wall sections are recessed inwardly from the
ends of the base reef, a horizontal ledge is defined by the
undersurface of the arch adjacent each end. Wave turbulence
developed during a storm may result in the application of an upward
force against each such ledge. In the course of time, such a force
might loosen the anchorage of the reef.
The piles or spikes 17 can be prefabricated from reinforced
concrete and formed with a shank portion 17a and a larger head 17b.
The piles or spikes can also be made of corrosion resisting steel,
steel treated for corrosion resistance or other suitable
non-corrosive material. The spikes are inserted through the reef
and driven into the ocean floor until the relatively wide diameter
head 17b engages the top of the reef. In this way, each base reef
10 may be essentially "nailed" to the ocean floor.
It may not be desirable to bring to bear against the head 17b the
driving forces required to insert the spike into the ocean floor.
Thus, in accordance with an alternate embodiment of the invention,
the reef units may be fastened to the seabed by means of augered
piles. In this technique a hollow drill is passed successively
through each of the holes 14 in the reef and thence into the seabed
for a predetermined distance. Concrete or other suitable material
is introduced through the hollow drill into the holes drilled in
the ocean bed. The drill is withdrawn while the material is still
fluent so that the material will fill the holes drilled in the
ocean bed and the passages through the walls 18a, 18b and 18c. The
concrete may then be suitably capped off at the top of the reef and
allowed to harden forming the piles or spikes which anchor the
reef.
The reef structure may be adapted to serve as a fixed and stable
habitat for a natural reef building marine organism 25, for
example, of the type known as phragmotopoma lapidosa, or
sabellariid. An article detailing the nature and function of these
organisms has been published by D. W. Kirtley, in the January 1968
issue of National History Magazine and is entitled "The Reef
Builders". These marine organisms act to build a structure
generally consisting of a plurality of cylindrical compartments
glued together by the organism to form a colony of interconnected
tubes. The organism lives within the compartment or tube that it
builds. Each organism has a number of teeth and a plurality of
feeding tentacles with which it grasps fragments of sand or crushed
shell from the water. The fragments are licked clean of incrusting
plants and are coated with a mucus cement-like glandular secretion.
Each fragment is thereafter wedged into the tube structure.
This marine organism has been known to construct large natural
reefs consisting of a honeycomb pattern of tube colonies. These
natural reefs have been found in areas in which there is an
abundance of tube building materials carried by turbulent waters.
Colonies of this organism have been known to build an incrustation
approximately ten inches thick within approximately six weeks.
An artificial reef structure composed of a plurality of individual
base reefs 10 linearly aligned end-to-end along the ocean floor,
such as is illustrated in FIG. 3, will be more readily adapted as a
suitable sabellariid habitat if oriented so as to be substantially
perpendicular to the direction of the prevailing wave flow for the
locale, or that is to say, parallel to the crests of the incoming
waves. This arrangement is preferred since nutrients for the
organism are carried inwardly with prevailing wave crests, and
sabellariid covering a reef which is oriented substantially
parallel to the crest lines of the incoming waves are more
favorably disposed to intercept and absorb a maximum amount of such
nutrient. While in the course of time, the sabellariid 25 may be
expected to grow to cover most of the exterior surface area of the
reef units, as indicated generally in FIG. 2, the greatest
concentration of tube colonies will occur in the more nutritious
environment of the ocean side of the reef.
The natural rough texture of the concrete in the base reefs 10 may
itself establish a surface suitable to sustain implantation of the
organism. The surface of each of the base units may also be
specially prepared to serve as a sabellariid habitat, for example,
by providing a plurality of longitudinal grooves or recesses 31 and
43, as shown in FIGS. 1 and 4. Such grooves may provide a
relatively safe location or shelter within which the organism might
attach itself to the base reefs and begin its tube colony
development. They may also serve to accomodate inserts 32 on which
the organism has already become established. As illustrated in FIG.
5, inserts 32 of a suitable material may be placed in the grooves
31 and 43 and attached to the base reef with the organism
established on the surfaces which protrude outwardly from the
surface of the reef. The grooves 31 may be approximately 1 to 2
inches deep, approximately 6 inches wide and from approximately 3
feet to a length substantially coextensive with the length of the
corresponding base unit.
The sabellariid can be grown on strips 32 of suitable material,
such as concrete, either in a remote "garden" containing a suitable
nutrient media, or in the ocean itself. After sufficient growth of
the sabellariid, the strips of concrete containing the incipient
colonies to be transplanted are transported to the submerged reef
units and fastened to the reef by any suitable means, for example,
by fasteners or by use of an epoxy or waterproof adhesive. The
transplanted colonies of sabellariid are more likely to survive the
relocation when they are placed on the upper regions of the reef,
preferably on the side facing the incoming waves.
Rapid sabellariid growth may be accelerated by providing patches of
jellied food compositions on the surface of the reef near the
developing sabellariid transplants. In the water, the prepared food
substances ooze over and around the sabellariid thus facilitating
growth of the natural structure.
The artificial reef implanted with the sabellariid organism, which
I have characterized as a Sabecon reef, provides considerable
advantages over prior artificial reef structures. The sabellariid
have been known to survive hurricanes and have demonstrated a
remarkable ability for rapid repair of any damage to the tube
colonies. Thus, the Sabecon reef of the present invention requires
little or no supervision and can be expected to maintain itself at
virtually no expense to the shoreline community for repair and
renovation. In addition, utilization of the natural growth
tendencies of sabellariid colonies to develop the size of the reef
permits savings with respect to initial expenditures for
construction of the reef. Since the sabellariid can be relied upon
to grow rapidly to an effective height, the base reefs can be made
smaller and lighter than would otherwise be required, thereby
facilitating their manipulation into proper position on the
seabed.
If the artificial reef is to be placed in relatively deep offshore
waters where added height is required immediately, the additional
height can be obtained by mounting upper reef units 33 to the base
reefs 10, as shown in FIG. 5. The upper reef units 33 are mounted
along the crowns 16 of the base reefs 10 and can be arranged in
end-to-end contiguous relationships, as shown, separated by gaps.
The upper reefs can also be arranged to bridge and lock together
adjacent base reef units.
As shown in FIG. 5, each of the secondary units 33 is of
substantially inverted U-shaped configuration. When mounted on top
of a base reef, an interior space 34 is defined between it and the
crown 16 of the underlying base reef. When the entire reef is
submerged, water fills the space 34 and thus enters the chambers 19
and 21 beneath the reef through the openings 15 in the base
unit.
Supplemental support from beneath the arch of each of the upper
reef units 33 may be provided by one or more vertical walls 37
extending between the base reef 10 and the undersurface of the
upper reef. The walls 37 are preferably integrally formed with the
upper reef.
The upper reefs 33 are mounted on the base reefs by suitable
mounting means, preferably by the piles or spikes 17 passing
through passages through the walls 37 which passages are aligned
with the openings 14. The secondary reefs may thereby be attached
to the base reefs after the latter have been submerged and set in
place on the seabed.
If desired the upper reef unit 33 may be provided with a plurality
of holes (not shown) to establish communication through the space
34 to the chambers 19 and 21 beneath the base reef 10 and to
equalize the water pressure beneath and above the artificial
reef.
With reference to FIG. 4, each of the base reefs 10 may be provided
with at least a pair of longitudinal recesses or grooves 43 and 44.
The grooves 43 and 44 are substantially parallel and are separated
by the crown 15 of the base reef. The distance between the grooves
is equal to the linear distance between the supporting edges 46 and
47 of the upper reef 33 so that the grooves 43 and 44 can receive
the supporting edges 46 and 47, respectively, when the upper reefs
are mounted on the base reefs. To facilitate maximum stability, the
grooves 43 and 44 may be shaped to conform precisely to the
particular configuration of the base edges 46 and 47. For example,
the groove 44 may be provided with a seat or ledge 48 to engage the
lower end 47 of the upper reef. Forces directed against the seaward
side of the upper reef 33 will be transmitted through the arch of
the reef 33 and tend to urge the end 47 against the seat 48.
The groove 43 may be provided with an outwardly extending lip or
shoulder 49 adapted to engage a corresponding surface 51 adjacent
the end 46 of the upper reef. The interfaces between the ends 46
and 47 of the upper reef and the grooves 43 and 44 of the base reef
assists the upper reef in resisting forces which might otherwise
tend to displace the upper reef laterally relative to the base
reef.
A reef system constructed in accordance with the present invention
may consist of several substantially parallel rows of contiguous
base reefs, as shown in FIG. 3, each preferably submerged with the
upper end thereof below the mean low water level and oriented
substantially perpendicular to the direction of flow of the
prevailing wave crests. The parallel rows of such artificial reefs
may use only the base reef elements with or without sabellariid
implants in shallow waters and composite reefs, consisting of an
upper reef mounted on a base reef, in deeper waters, as shown in
FIG. 3.
The linear rows of reefs may be spaced apart, as indicated by the
reference numeral 35, at distances of approximately 400 feet. This
separation between reefs permits waves reflected from the shoreline
to escape through the downdrift reefs with only minimal
interference. The littoral currents are thereby preserved in part
although their capacity to effect a net flow of sand away from the
beach is attenuated. The spacing 35 is ideally too close to allow a
wave which passes over the outermost reef 40 from regaining its
rhythm before impacting against the next reef on its way toward the
shore. At the same time, the spacing 35 is sufficient so that some
vestige of the prevailing littoral current is retained to preserve
the quality of beach areas downdrift of the reef system. In such a
reef system, the incoming waves will dissipate part of their energy
in passing over each of the rows, building up sand or other
deposits 60 on the shore side of each row, as shown in FIG. 2.
In circumstances of excessive or prolonged ocean turbulence, it may
be desirable to provide a plurality of sand bags or the like (not
shown) to lie against each lineal row of the reef system along the
entire length of the row on the landward side. The presence of the
sand bags inhibits erosion of the seabed adjacent the reef and
thereby helps to ensure long term stability. In addition, the inner
end of each of the reefs may be enveloped within a pile of rocks or
sand bags 61, as shown in FIG. 3, to facilitate stability of the
reef.
* * * * *