US3218808A - Artificial reef and sand breakwater and method of constructing same - Google Patents

Description

Nov. 23, 1965 c. J. SMITH ETAL 3,218,808

ARTIFICIAL REEF AND SAND BREAKWATER AND METHOD OF CONSTRUCTING SAME Filed July 25, 1961 2 Sheets-Sheet 1 WATER L/NE w M m m M M m ,m w w M N I 5 u M D m d T w l ....v E E gna/.2.... m H M T H n ..1 0:.. ...,.....:....v

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M W m f w w mf M E M m um T WKN UDO W my my M150 BY THEIR' ATTORNEYS. Hmm/5, /f/ECH, RUSSEL/ KIS/QN Nov. 23, 1965 c J. SMITH r-:TAL

. 3,218,808 ARTIFICIAL REEF AND SAND BREAKWATER AND METH Filed July 25, 1961 OD OF CONS TRUCTING SAME 2 Sheets-Sheet 2 BY THE/l? ATTORNEYS. HAee/s, KnscH, Russen KaR/v United States Patent O 3,218,803 ARTlFCAL AND SAND BREAKWATER AND METHQD F CONSTRUCTENG SAME Charles Il. Smith, Los Angeles, and .lames W. Dunham,

Seal Beach, Calif., assignors to Seaway Enterprises, luc.,

Beverly Hills, Calif., a corporation of California Filed duly 25, 1961, Ser. No. 125,684 4 Claims. (Cl. 61-4) The instant invention relates generally to the construction art and more particularly to a novel artificial reef and sand breakwater in a coastal area characterized by littoral drift predominantly in one direction, and to a method of constructing the same.

With the increased popularity `of boating which requires mooring and harbor facilities, and the scarcity of desirable beach property for residential and business purposes, it has become advantageous to consider the utilization of less `desirable coastal areas for such purposes and the construction of artificial boat harbors and filled land areas.

However, a construction of this type presents many engineering problems, particularly in a coastal or shore line area where there is an appreciable littoral current, as on the west coast of the United States. Thus, on most beaches of the west coast, for example, the movement of the breakers onto and away from the beach churns up the sand and moves it along the shore predominantly in a downcoast or northwest-to-southeast direction. Consequently, if a jetty, breakwater, or causeway were to be indiscriminately extended into the ocean in such areas of predominant downcoast drift, the sand carried by the littoral current would soon accumulate on the upcoast or updrift side, and erosion would occur on the downcoast or leaward side.

It is an object of the present invention, therefore, to provide in an area having a littoral drift predominantly in one direction a novel artificial reef and sand breakwater construction and a method of building same which will not adversely affect the downdrift coastal area as by eroding the sand from the beaches. More particularly. it is an object to provide such an artificial reef and sand breakwater construction in an offshore position and to provide for a small boat harbor and building area in back thereof without causing erosion problems at the lower or downdrift coastal areas.

Another object is to provide an artificial reef and sand breakwater construction in an offshore position which will not adversely affect the flow of the littoral current along it. More particularly, it is an object to provide such a construction whereby the littoral current and movement of sand along the new littoral berm will remain substantially the same as along the pre-existing beach berm upstream of the new construction.

Yet another object is to provide an artificial reef and sand breakwater construction which has an end groin at the downcoast or downdrift end thereof which includes means for bypassing the sand carried by the littoral current to the end groin so as not to adversely affect the downdrift coastal areas. More particularly, it is an object to provide such an artificial reef and sand breakwater construction with an end groin which includes means for transporting the sand which accumulates at the end groin adjacent the downdrift end of the new beach berm to a position on the coast downstream of the end groin whereby the sand will be acted upon by the normal wave action.

A further object is to provide novel methods for constructing such an artificial reef and sand breakwater whereby the resultant structure can be constructed in a minimum amount of time using materials which are 3,218,808 Paten-.ted Nov. 23, 1965 close at hand. More particularly, it is an object to provide such novel methods of constructing an artificial reef and sand breakwater whereby both portions thereof can be constructed substantially simultaneously Without the sand portion being destroyed by wave action during the topping-out operation.

Further objects and advantages of the present invention will be apparent from the following detailed description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is shown.

Briefly stated, the sand breakwater extends from the existing headland as a continuation of the shore line thereof to an end groin downstream of the headland, the alignment of the new breakwater maintaining throughout the length thereof substantially the same rate of littoral drift as that prevailing at the headland from which the breakwater extends. Spaced seawardly of the break- Water and substantially parallel therewith is an artificial reef, one end of the reef being opposite the headland and the other end being at the end groin, the crest of the reef being below low tide datum at least a distance equal to the maximum breaker depth. Construction of the reef and breakwater can proceed from either end but the topping out of the breakwater should lag behind the reef construction by at least three design wave lengths to prevent the breakwater from being adversely affected by wave action.

In the drawings:

FIG. 1 is a schematic plan view of an artificial reef and sand breakwater constructed in accordance with the teachings of the present invention, shown in conjunction with a small boat har-bor and building area;

FIG. 2 is an enlarged fragmentary vertical sectional view taken on the line 2-2 in FIG. 1;

FIGS. 3-5 are schematic plan views, in sequence, illustrating the steps which are followed in constructing the artificial reef and sand breakwater starting from the headland end; and

FIGS. 6-8 are schematic plan views, in sequence, illustrating the steps which are followed in constructing the artificial reef and sand breakwater starting from the end groin.

For best results, the site for the artificial reef and sand breakwater should be in a coastal area characterized by littoral drift or current with the movement in one direction strongly predominant over the movement in the opposite direction.

Also, the site should take advantage of a re-entrant curve of the shore line downcoast from a headland so that, as the crest of the new beach is extended off shore in the downcoast direction, the alignment is such as to maintain throughout the length of the struct-ure the same rate of littoral drift or current iiow as that prevailing at the headland from which the breakwater extends.

As will be described more fully hereinafter, the water area between the new breakwater and the existing beach must be wide enough to peirnit the required harbor development, and should preferably be wide enough to provide an adequate source of sand for dredging and transporting by hydraulic methods to sand-fill portions of the structure lying above the average breaker depth plane at low tide.

Referring to the drawings more particularly by reference numerals, l0 indicates generally a novel artificial small boat harbor and associated land-ll areas constructed utilizing the teachings of the present invention and being formed adjacent an existing shore line 12 or .beach -berm crest and a projecting headland 14.

In this development it is assumed that the `littoral drift 3 is from the top to the bottom (FIG. l) `as indicated by the directional arrow 16.

Extending from adjacent the headland 14 substantially parallel with the original shore line or crest of the beach berm 12 is a submerged artificial reef 18 which terminates at an end groin 20. Inwardly of the reef 18 is a sand breakwater structure having a beach berm 22 which is also substantially parallel with the original shore line, and, in the present illustration, a road or freeway 24 is atop the breakwater structure.

Adjacent the road 24 is a land-fill area 26 which provides space for a plurality of small-boat basins 2S. It will be apparent that this land-fill can also be used for the erection of business establishments, residences, and high-rise apartments, but these have been omitted from the drawing in the interests of simplicity.

Inwardly of the land-fill area is a harbor area 30 with an entrance 32 between the end groin 20 and a jetty 34 which projects from the beach downstream of said end groin. It is to be understood that when the terms up, down, upcoast, and downcoast are used throughout this specification they are to be considered in relation to the littoral drift as indicated by the directional arrow 16.

Provided at the end groin intermediate the artificial reef 18 and the new berm crest 22 is a fixed sand bypassing plant 36 for transporting sand through a submerged pipe 38 to the downstream side of the jetty 34. As will be discussed more fully hereinafter, the discharge end of the pipe 38 must be a suflicient distance below the end groin so that the sand discharged therefrom will be subjected to normal wave action and be carried down the coastline by the normal littoral current or drift.

Whether or not an operable breakwater is constructed without mishap depends largely upon the location of the breakwater structure and upon the sequence of operations andthe controlled rates of placement of the component parts of the structure. Although other approaches may achieve the desired result, set forth below is the preferred construction and the preferred construction procedures.

As mentioned above, the site should be characterized by littoral drift with the movement of the current in one direction predominant over movement in the opposite direction. Also, the alignment of the breakwater (and the artificial reef) must be such as to maintain throughout the length of the structure the same rate of littoral drift as that prevailing at the headland from which the breakwater extends. Stating it differently, the angle between the breakwater and the breaker crests of the predominant wave trains should continue to open on the downcoast or downdrift side throughout the length of the structure, even :under the refraction effects of the new littoral berm created in the process. Thus, the breakwater structure 22 should constitute an extension ofthe existing shore line at the headland 14 and should be substantially parallel with what might be called the straight portion of the existing shore line or berm crest 12 downstream of the headland. The artificial reef 18 should also be substantially parallel with the breakwater and inasmuch as substantially all of the littoral drift that affects the beach regimen occurs between the two-fathom depth and the shore, the upcoast or upper end of the reef 18 should be opposite the headland 14 at a point where the natural bottom is at least two fathoms deep and should extend continuously to the end groin 20. The exact location of the lreef is determined by ascertaining the depth seaward at which the seasonal variation in the depth of the natural bottom does not exceed one foot. This may vary from two to four fathoms, and is determined by periodic soundings of the bottom for at least a year prior to breakwater construction.

In order to ascertain the depth of the crown of the artificial reef below low tide datum, the height of a socalled design wave or reference wave is determined by examining wave-prediction charts and ascertaining the breaker height at low tide for the average of the highest one-third waves of all of the waves in a given series in the most severe storm in an average year. This breaker height of the design wave is then multiplied by 1.3 to ascertain the approximate depth of the so-called maximum breaker depth plane. This is the minimum depth below tide datum for the crown of the artificial reef 18, i.e. it may be somewhat deeper. In addition, the crown of the reef should be at least two feet above the natural bottom at the shallowest portion of the reef, which portion would usually occur opposite the headland. Consequently, the upper end of the reef will be located opposite the headland at a point where the bottom is at least two feet below the maximum breaker depth plane, and, as mentioned above, at a point where the seasonal variation in the bottom does not exceed one foot.

Knowing the approximate location of the breakwater structure based upon the aforementioned criteria as to littoral drift, the length of the design or reference wave at the depth of the proposed breakwater site is then determined based on the predicted wave period of the aforementioned design wave at the surface as ascertained during the most severe storm of an average year, and by utilizing the formulas:

a at). c2-27rtanh L andL-CT where c equals velocity of wave propagation, g equals acceleration due to gravity, d equals depth from tide datum to bottom, T equals wave period, and L equals wave length at depth d. For example, if the design wave were found to have a l2-second period, it would have a length of 735 feet in deep water but only a length of 350 feet in five fathoms of water. As will be discussed more fully hereinafter, the length of the design wave at the depth of the proposed breakwater is important because, regardless of Whether the construction proceeds from the upper or headland end or from the downcoast or groin end, the artificial reef must be built up to its crown elevation at least three design wave lengths ahead of the sand breakwater crest or topping-out phase of the construction as measured along the breakwater axis.

Assuming that the construction were to begin at the upper or headland end, the construction of the artificial reef 18 would start opposite the headland 14 at the point determined by the aforementioned criteria, which, we will assume is the fourteen-foot depth, and suicient rock 0r the like would be dumped in a mound initially two feet high but increasing in height along the selected line (FIG. 3) to bring the crest or crown of the reef up to the aforementioned maximum breaker depth plane which is assumed to have been determined to be twelve feet or two fathoms below low tide datum.

The base 40 of the sand part of the breakwater structure would then be iilled in behind or on the landward side of the artificial reef (FIG. 4), as with Sand obtained by dredging, up to the normal bottom profile but no higher than the average breaker depth below low tide datum, the last-mentioned depth being determined in the same manner as the maximum breaker depth plane except that it is based on the average of all waves throughout an average year rather than on the highest one third of a particular series during the most severe storm such as used in determining the maximum breaker depth plane. As a practical matter, the initial portion of the base fill 40 would be placed using overland end-dump equipment until sufficient quiet water were available for the operation of the dredge 41. The positioning of the base fill 40 can proceed along with the construction of the reef regardless of the relationship therebetween because wave action should not adversely affect the base fill at the aforementioned depth. However, if it is desirable to make certain that the base fill will not be affected by wave action, the construction of the base fill should proceed no closer than two design wave lengths behind the leading reef construction.

If material for the base fill 40 is being taken from the bottom between the breakwater site and the existing shore line, sufiicient borrow material should be reserved in the dredging area to complete the topping out process of the breakwater, which will now be described.

If the construction were to start from the headland or upcoast end, the laying down of the reef 18 and bottom portion or bottom fill 40 of the breakwater would proceed in the order previously described. Then, when an adequate length of reef and base ll had been constructed to insure uninterrupted completion of the topping-out operation on the breakwater proper, coarse top material 42 with substantial quantities of rock would be deposited on the base fill, as by overland hauling with end dumping equipment (FIG. 5), until sufficient quiet water existed in the protected embayment to permit uninterrupted dredging operations. As mentioned hereinabove, it is important to have the topping out of the breakwater proper follow no closer than three design wave lengths behind the forming of the artificial reef in order to prevent the breakwater material from being swept away by wave action.

After there is sufficient quiet water in the embayment to permit dredging, the remainder of the breakwater is topped out by utilizing hydraulic dredges or the like with sufficient capacity to handle about 30,000 cubic yards of material per day, which material would be placed in position by a bracket line extending progressively in the general direction of the construction at a distance of about fifty feet seaward of the planned alignment of the beach or breakwater crest. This operation would be carried out without interruption to the end groin.

On the other hand, if the pumping capacity of the dredges were adequate for the purpose, and most of the material needed for the base fill could be obtained by hopper dredges working in an oft-shore area, it is preferable to start the breakwater construction from the downcoast end at the end groin so as to obviate the more costly truck-haul method as would be required when starting from the upcoast or headland end. Thus, work would begin with placement of base till 40 at the end groin using hopper dredges 44 (FIG. 7) and proceed in the upcoast or updrift direction in order to provide a safe working area for the pipeline dredges as quickly as possible. The pipeline dredges 41 would begin the topping-out operation (FIG. 8) as soon as adequate protection were afforded by the new breakwater or whenever a protected area were available from which to commence pipeline dredging operations. As in the case of downdrift construction, the nal topping-out should continue at such rate that the top material 42 being deposited is not swept away by breaking waves faster than it can be placed. However, in the case of the upstream construction, the newly formed shoreline downdrift of the topping out operation would be under erosion by wave action throughout the construction process, unaided by littoral drift from the updrift beaches as would be the case with the downdrift construction. Consequently, the rate of placement must be at least twice the natural rate of littoral drift prevailing in the area in excess of the minimum rate that could be used for the downdrift construction. Another disadvantage of the updrift construction is that the natural drift of sand along the coast updrift of the construction will terminate in thev wave shadow behind the new breakwater, building out the shore line to some extent and possibly requiring additional dredging to remove excess deposited material. Because of the eroding action of the waves tending to strip the new beach, the bracket line should be placed somewhat further seaward than in the downstream plan. It is believed that the bracket line should be placed 100 feet seaward of the planned alignment of the beach crest, so that as the accelerated erosion occurs, the new beach line will retrograde eventually to the planned alignment where it will then be held in relative equilibrium by natural littoral drift after the entire structure is completed.

After the sand breakwater has been completed, a nar- 6 row rock blanket 46 (FIG. 2) should be placed on top of the sand ill immediately inwardly of the articial reef 18 to prevent the sand from being Washed into deep water by wave turbulence.

Completion of the breakwater ll behind the topped-out breakwater structure sufficient to provide a wide berm behind the beach crest can be undertaken at any time following the completion of the topping-out operation of the breakwater itself. The width of this berm must be adequate to absorb seasonal recessions of the beach crest without permitting waves to breach the new sand spit and is preferably of a size and shape to provide for suitable small boat basins and residential and business buildings as desired.

As mentioned hereinabove, a primary object of the present invention is to provide a new crest or beach berm 2.2 which will maintain the same littoral drift of sand as at the old beach berm 12 and at the headland from which the breakwater extends. Thus, as the sand moves downcoast between the artilicial reef 18 and the new crest 22, it will accumulate or build up at the end groin 20 in the vicinity of the sand bypassing plant 36. Therefore, the movable arm or dredge portion of the plant 36 would be moved back and forth between the reef and beach berm to remove the excess sand and transmit it through the pipe 38 to be discharged at the jetty 34 which is downstream of the end groin a sufiicient distance whereby the discharged sand will be subjected to normal wave action and be carried down the coast by littoral drift or current in the usual manner. It is to be understood, however, that a mobile plant on a trestle or a pipeline dredge Working behind a breakwater built opposite the downcoast end could be used in place of the fixed bypassing plant 36 with similar results.

Thus, it is apparent that there has been provided a novel artificial reef and breakwater and methods of constructing the same, which fulill all of the-objects and advantages sought therefor. The novel reef and breakwater will not adversely affect the littoral drift of said down the new beach berm because the amount or degree of littoral drift will be the same as previously existed at the old beach berm and at the headland from which the structure extends. Furthermore, the sand which accumulates at the end groin is bypassed to a position down the coast where the discharged sand will be acted upon by normal wave action so that downcoast areas will not be adversely affected. In addition, the novel methods of constructing the reef and breakwater described herein permit the reef and breakwater constructions to proceed substantially simultaneously whereby the entire structure can be completed much sooner than if the articial reef were completed before the sand portion of the breakwater were to be started.

It is to be understood that the foregoing description and the accompanying drawings have been given only by way of illustration and example and that changes and alterations in the present disclosure which will be readily apparent to one skilled in the art are contemplated as within the scope of the present invention.

We claim:

l. An articial reef and sand breakwater construction at a headland in a coastal area having a body of water therealong with a known low tide datum plane, a known maximum breaker depth plane, and a known seasonal variation in the depth of the natural bottom, and -said body being characterized by a littoral drift with a predominant downcoast direction along said headland and a natural existing downcoast shoreline, comprising:

an elongated sand breakwater having a crest extending continuously above the water downcoast offshore from the headland shore line and defining a seawardly disposed beach berm continuing substantially in line with the headland shore line to an end groin a predetermined distance downcoast of the headland,

the alignment of the beach berm of the break- Water maintaining throughout its length substanitally the same rate of normal littoral drift as that prevailing at the headland shore line;

an elongated, submerged, permanent artificial reef with a crown positioned seawardly of the crest of the sand breakwater and extending continuously substantially equidistant therefrom and seawardly thereof from a point opposite the headland shore line to said end groin,

the end of the `submerged reef opposite the headland being located on the natural bottom where the seasonal variation does not exceed about one foot, the crown of the reef being below the low tide datum plane a distance greater than the maximum breaker depth plane and projecting above said bottom; said end groin extending transversely from said reef and across the downcoast end of said sand breakwater; and, means adjacent the end groin for transporting sand accumulated immediately upcoast of the groin to the water at said natural existing shore line downcoast of the end groin where the beach is subject to normal wave action and the said predominant littoral drift.

2. An artificial reef and sand breakwater as delined in claim 1 wherein the said distance of the crown of said reef below the low tide datum plane is at least 1.3 times the average breaker height at low tide of the highest one-third of the waves in a given series in the most severe storm in an average year.

3. An artificial reef and sand breakwater as defined in claim 1 wherein the crown of said reef is at least two feet above the natural bottom.

4. The method of constructing a sand breakwater having one end thereof at a headland and the other end at a groin downcoast of the headland and an artificial, submerged reef seawardly of said breakwater and substantially equidistant therefrom at a predetermined water depth in a coastal area having a known maximum breaker depth plane and a known low tide datum plane and at said predetermined depth a known length of a reference wave taken as the average of the highest one-third of the waves in a given series in the most severe storm in an average year, said sand breakwater having a crest above the low tide datum plane and a bottom fill below the 10W tide datum plane, the breakwater and reef being positioned to maintain throughout the length of the breakwater substantially the same littoral drift prevailing at the headland, including the steps of starting at one end, at said headland or groin, and

building a permanent reef on the bottom toward the other end, spaced from the coast and in substantial alignment with the littoral drift prevailing at said headland, and with the crown thereof below maximum breaker depth, for a distance of at least two of said reference Wave lengths, then starting at the same end and laying down a bottom ll for the sand breakwater, below the low tide datum plane, shoreward of the reef and also toward said other end while continuing the building of said reef, the construction of the bottomiill nearest said other end lagging behind the construction of the end portion of the reef nearest said other end by a distance at least as great as two of said reference wave lengths at said predetermined depth as measured along the breakwater to prevent said bottom ll from being adversely affected by wave action during the construction thereof; and topping out the sand breakwater by placing material on the bottom lill to bring the crest of the sand breakwater above the low tide datum plane, starting at said same end and continuing toward said other end, the construction of the crest of the breakwater nearest said other end lagging behind the construction of the end portion of the reef nearest said other end by a distance at least as great as three of said reference wave lengths at said predetermined depth as measured along the breakwater to prevent said breakwater from being adversely affected by wave action during the construction thereof.

References Cited by the Examiner UNITED STATES PATENTS Re. 19,786 12/1935 Wood 61-4 247,065 9/1881 Knapp 6l-4 324,857 8/1885 Littlefield 61-4 1,274,450 8/1918 Remington 6l-4 1,557,409 10/1925 Bradley. 2,128,012 8/1938 ORourke 61-4 2,158,046 5/1939 Prendergast 61-4 2,191,845 2/1940 Bretting 61-63 2,763,940 9/ 1956 Madgwick.

FOREIGN PATENTS 513,588 10/1939 Great Britain. 676,082 7/ 1952 Great Britain.

OTHER REFERENCES Engineering News Record (publ.) August 1958, pp. 46 and 47.

EARL I. WITMER, Primary Exaz'nmer.

WILLIAM I. MUSHAKE, Examiner.

Claims (1)

1. AN ARTIFICIAL REEF AND SAND BREAKWATER CONSTRUCTION AT A HEADLAND IN A COASTAL AREA HAVING A BODY OF WATER THEREALONG WITH A KNOWN LOW TIDE DATUM PLANE, A KNOWN MAXIMUM BREAKER DEPTH PLANE, AND A KNOWN SEASONAL VARIATION IN THE DEPTH OF THE NATURAL BOTTOM, AND SAID BODY BEING CHARACTERIZED BY A LITTORAL DRIFT WITH A PREDOMINANT DOWNCOAST DIRECTION ALONG SAID HEADLAND AND A NATURAL EXISTING DOWNCOAST SHORELINE, COMPRISING: AN ELONGATED SAND BREAKWATER HAVING A CREST EXTENDING CONTINUOUSLY ABOVE THE WATER DOWNCOAST OFFSHORE FROM THE HEADLAND SHORE LINE AND DEFINING A SEAWARDLY DISPOSED BEACH BERM CONTINUING SUBSTANTIALLY IN LINE WITH THE HEADLAND SHORE LINE TO AN END GROIN A PREDETERMINED DISTANCE DOWNCOAST OF THE HEADLAND, THE ALIGNMENT OF THE BEACH BERM OF THE BREAKWATER MAINTAINING THROUGHOUT ITS LENGTH SUBSTANTIALLY THE SAME RATE OF NORMAL LITTORAL DRIFT AS THAT PREVAILING AT THE HEADLAND SHORE LINE; AN ELONGATED, SUBMERGED, PERMANENT ARTIFICIAL REEF WITH A CROWN POSITIONED SEAWARDLY OF THE CREST OF THE SAND BREAKWATER AND EXTENDING CONTINUOUSLY SUBSTANTIALLY EQUIDISTANT THEREFROM AND SEAWARDLY THEREOF FROM A POINT OPPOSITE THE HEADLAND SHORE LINE TO SAID END GROIN, THE END OF THE SUBMERGED REEF OPPOSITE THE HEADLAND BEING LOCATED ON THE NATURAL BOTTOM WHERE THE SEASONAL VARIATION DOES NOT EXCEED ABOUT ONE FOOT, THE CROWN OF THE REEF BEING BELOW THE LOW TIDE DATUM PLANE A DISTANCE GREATER THAN THE MAXIMUM BREAKER DEPTH PLANE AND PROJECTING ABOVE SAID BOTTOM; SAID END GROIN EXTENDING TRANSVERSELY FROM SAID REEF AND ACROSS THE DOWNCOAST END OF SAID SAND BREAKWATER; AND, MEANS ADJACENT THE END GROIN FOR TRANSPORTING SAND ACCUMULATED IMMEDIATELY UPCOAST OF THE GROIN TO THE WATER AT SAID NATURAL EXISTING SHORE LINE DOWNCOAST OF THE END GROIN WHERE THE BEACH IS SUBJECT TO NORMAL WAVE ACTION AND THE SAID PREDOMINANT LITTORAL DRIFT.

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