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NATIONAL SHORELINE STUDY SHORE PROTECTION GUIDELINES yv m lviiz TC 223 U55 1971 DEPARTMENT OFTHE ARMY CORPS OF ENGINEERS WASHINGTON, D.C. THE NATIONAL SHORELINE STUDY How will the shore be used ? SHORE MANAGEMENT GUIDELINES What is its condition? REGIONAL INVENTORY REPORTS What can be done ? to preserve or enhance the shore, by using- Engineering techniques SHORE PROTECTION GUIDELINES REGIONAL INVENTORY REPORTS Management techniques SHORE MANAGEMENT GUIDELINES SHORE PROTECTION GUIDELINES A PART OF THE NATIONAL SHORELINE STUDY CONDUCTED BY THE CORPS OF ENGINEERS August 1971 DEPARTMENT OF THE ARMY CORPS OF ENGINEERS WASHINGTON, D.C. In 1968, the 90th Congress authorized this National appraisal of shore erosion and shore protection needs. This National Shoreline Study and the existing Federal shore protec- tion programs recognize beach and shore ero- sion as problems for all levels of government and all citizens. To satisfy the purposes of the authorizing legislation, a family of 12 related reports has been published. All are available to concerned individuals and organizations in and out of government. REGIONAL INVENTORY REPORTS (one for each of the 9 major drainage areas) assess the nature and extent of erosion; develop conceptual plans for needed shore protec- tion; develop general order-of-magnitude estimates of cost for the selected shore protection; and identify shore owners. SHORE PROTECTION GUIDELINES de- scribe typical erosion control measuresand present examples of shore protection facili- ties, and present criteria for planning shore protection programs. SHORE MANAGEMENT GUIDELINES provide information to assist decision makers to develop and implement shore management programs. REPORT ON THE NATIONAL SHORE- LINE STUDY, addressed to the Congress,- summarizes the findings of the study and recommends priorities among serious prob- lem areas for action to stop erosion. US Department of Comm e NOAA Coastal Services Center Library 2234 South Hobson Avenue Charleston, SC 29405-2413 3H F\ 19 n Page Page INTRODUCTION ............ 4 MANMADE EFFECTS ON THE SHORE . 25 GENERAL NATURE OF THE PROBLEM 7 Encroachment on the Sea ....... 25 Natural Protection ........... 30 Natural Beach Protection . . . . . . . 7 Shore Protection Methods . . . . . . . 30 Dunes . . . . . . . . . . . . . . . . . 7 Comprehensive Protection . . . . . . . 30 Barrier Beaches, Lagoons, and Inlets 7 Bulkheads, Seawalls and Revetments . . 30 Origin and Movement of Beach Sands 7 Breakwaters . . . . . . . . . . . . . . 33 Today's Beach Conditions . . . . . . . 9 Groins . . . . . . . . . . . . . . . . . 41 Jetties . . . . 45 FORCES OF THE SEA . . . . . . . . . . 13 Beach Restoration and Nourishment . . . 47 Tides and Winds . . . . . . . . . . . . 13 REGIONAL PROTECTIVE PRACTICES 55 Waves 13 Currents and Surges . . . . . . . . . . 14 General . . . . . . . . . . . . . . . . . 55 Tidal Currents . . . . . . . . . . . . . 15 New England Region . . . . . . . . . . 55 Middle and South Atlantic and THE BEHAVIOR OF BEACHES . . . . 16 Gulf Regions . . . . . . . . . . . . 56 Puerto Rico and Virgin Islands . . . . . 56 Beach Composition . . . . . . . . . . 16 Pacific Coast Region . . . . . . . . . . 56 Beach Characteristics . . . . . . . . . . 17 Alaska Region . . . . . . . . . . . . . 56 Breakers . . . . . . . . . . . . . . . . 17 Hawaiian Islands . . . . . . . . . . . . 57 Effects of Wind Waves . . . . . . . . . 17 Great Lakes Region . . . . . . . . . . 57 Littoral Transport . . . . . . . . . . . 17 Formation of Deltas . . . . . . . . . . 19 CONSERVATION OF SAND . . . . . . . 58 Effects of Inlets on Barrier Beaches . . . . . . . . . . . . . . . 20 CONCLUSION . . . . . . . . . . . . . . 59 Impact of Storms . . . . . . . . . . . 21 Beach Stability . . . . . . . . . . . . . 21 ILLUSTRATIONS ILLUSTRATIONS Figure Page Figure Page 1 Research Facilities - Coastal 12 Unimproved Tidal Inlet Showing Engineering Research Center . . . . 6 Barrier Beach and Pattern of Offshore Bar and Shoals - 2 A. Sand Dunes along the South North Carolina . . . . . . . . . . 23 Shore of Lake Michigan . . . . . . . 8 B. Sand Dune, Honeyman State 13 Residential Development Encroach- Park, Oregon . . . . . . . . . . . . 8 ing on Dune Areas and Resulting Backshore Damage to Townsends 3 Barrier Islands Separated by Tidal Inlet, N.J . . .. . . . . . . . . . . . 24 Inlets -Wrightsville Beach, N.C. About 1940 . . . . . . . . . 10 14 Backshore Damage at Sea Isle City, New Jersey, after March 1962 4 Barrier Beach Island Developed Storm . . . . . . . . . . . . . . . 25 as Recreational Park - Jones Beach State Park, Long Island 15 Backshore Damage at Ocean City, New York, 3 July 1955 . . . . . . 11 Maryland, after March 1962 Storm . . . . . . . . . . . . . . . 26 5 Large Waves Breaking over a Breakwater . . . . . . . . . . . 12 16 A. Steel Sheet Pile Bulkhead . . . . 27 B. Timber Sheet Pile Bulkhead . . . 28 6 Wave Characteristics . . . . . . . . . 14 17 Bulkhead of Precast Concrete 7 Water Particle Movement under Sheetpiles at Daytona Beach, Wave Action . . . . . . . . . . . 15 Florida . . . . . . . . . . . . . . 29 8 Beach Profile -Related Terms . . . 16 18 Vertical-face Concrete Seawall Built 25 Years ago at Watch 9 Schematic Diagram of Storm Wave Hill, Rhode Island . . . . . . . . 29 Attack on Beach and Dune . . . . 18 19 Concrete Combination Stepped 10 Longshore or Lateral Movement of and Curved-Face Seawall, San Littoral Drift . . . . . . . . . . . 20 Francisco, California . . . . . . . 31 11 River Delta at Mouth of San Juan Creek, California . . . . . . . . . 22 2 Figure 29 Jetties at Cold Spring Inlet, New Jersey, Entrance to Cape May Harbor . . . . . . . . . 45 30 Shark River Inlet, New Jersey, where Sand Impounded at Jetty was Transported across Inlet by Truck . . . . . . . 46 4, 31 Fixed Bypassing Plant - South 'iP Figure Page Lake Worth Inlet, Florida . . . . . 48 20 Concrete Stepped-Face Seawall 32 A. Masonboro Inlet, North Carolina, July 1966 . . . . . . . . 49 in Harrison and Hancock Counties, Mississippi . . . . . . . 32 B. Weir Jetty at Masonboro Inlet, North Carolina, February 21 Seawall at Galveston, Texas . . . . . 34 1966 . . . . . . . . . . . . . . . 50 22 Stone Revetment - Cape Henry, 33 Concrete Stepped-Face Seawall, Virginia . . . . . . . . . . . . . . 36 Harrison and Hancock Counties, Mississippi (prior 23 Interlocking Concrete Block to placement of beach fill) . . . . 51 Revetment at Benedict, Maryland . . . . . . . . . . . . . 37 34 Restored Beach at Presque Isle Peninsula, Erie, Pennsylvania . . . 52 24 Interlocking Concrete-Block Revetment at Jupiter 35 Wrightsville Beach, North Carolina Island, Florida . . . . . . . . . . 38 after Completion of Beach Restoration and Hurricane 25 Sand Bypassing at Santa Barbara, Protection Project . . . . . . . . 53 California . . . . . . . . . . . . . 39 36 Dunes formed by trapping wind- 26 Sand Bypassing at Channel blown sand with fences and Islands Harbor, California . . . . . 40 grasses, Outer Banks, North Carolina . . . . . . . . . . . . . . 54 27 Groin System - Willoughby Spit, Virginia . . . . . . . . . . . 42 37 Weekday use of artificially nourished beach, north of 28 Groin System at Miami Beach, Haverhill Avenue, Hampton Florida - April 1962 . . . . . . . 44 Beach, New Hampshire . . . . . . 54 3 INTRODUCTION SHORE These guidelines are for general use by those who are interested in suitable and economical methods of shore protection. They will be of E U M ES value to those who may be knowledgeable in one or more of the shoreline processes but want additional information on the many forces that may affect a specific shore area. However, the general nature of this material precludes its use as a technical reference for preparing detailed design of protective measures. The guidelines will be of particular interest to officials who want to avoid the pitfalls of approving inadequate or ineffective measures which may appear inexpensive, but would prove costly on a long-range basis. They will be able to better understand alternative proposals because this reference covers basic points which should be considered in any analysis that leads to the selection and recommendation of a specific type of shore protection. The discussion of shore processes and nat- ural protective features stresses the hazards which individual property owners face when they build within the zone of shoreline fluctua, tions. Examples show what happens when owners attempt to take advantage of the apparent full area of their shore lots by building out close to the high water line; when they level the dunes to obtain a better view of the ocean, or to permit easier passage to the beach. 4 Illustrations and text emphasize that a por- tion of the beach area belongs as much to the sea or lake as to the land, and that the beach area may be periodically inundated or eroded. The descriptions explain why the degree of inundation, which shorefront property owners and managers may anticipate, depends upon the dimensions of beach height and width relative to the intensity of water motion in the adjacent sea during severe storms; and that these dimensions depend largely on whether the shore has been eroding or is stable or It is national policy that any beach protec- accreting. The discussion is designed to help tion works supported by the Federal Govern- create acceptance of the fact that a beach ment must have a detailed assessment of its erodes where the rate of littoral material (sand) potential impace on the environment in the supplied naturally to the shore is less than the interests of avoiding adverse effects and restor- rate at which natural forces of waves, currents, ing or enhancing environmental quality. Altern- and winds are removing it from the shore. ative actions must be explored and both long and short-range implications to man, including The guidelines cover several ways to reduce his physical and social surroundings, must be shorefront damages, such as: a) conservation - evaluated. preserving and enhancing natural protective features such as dunes, vegetation and natural Part of the value of the guidelines is its sand supply; b) structural - preventing sea combination of many basic findings from waves from reaching erodible shore formations research, study and observation of the complex by use of structures such as offshore break- phenomena related to the coastal environment. waters, seawalls, dune or bluff armoring; and c) While the discussion points out the limitations also structural to restore or enhance natural of available information, it contributes to a processes - by restoring and maintaining pro- better understanding of why research will lead tective beaches and dunes by direct placement to continuing improvements in design for of sand from inland or ocean sources, and present or yet to be developed protective either periodically augmenting a deficient nat- measures. It indicates what may be expected ural sand supply or providing structures such as from continuing the quest for knowledge by groins to reduce sand losses. the Corps of Engineers through research at its Coastal Engineering Research Center (CERC) in Washington, D.C., as called for by Federal statute (P.L. 88-172) and as an adjunct to its function of planning and construction of Fed- eral projects for shore improvements (Figure 1). A technical report for use by prrofessional engineers or other technically trained persons involved with shore protection problems has resulted from this research effort. The title is "Shore Protection, Planning and Design", Technical Report No. 4, U.S. Army Coastal Engineering Research Center. This report is periodically updated to include current knowl- edge. The most recent edition (1966) is pres- ently available from the U.S. Government Printing Office, Washington, D.C. 20402, for $4.75. 5 34 iog Dunes GENERAL Winds blowing inland over the foreshore and berm move sand behind the beach to form NATURE dunes (Figure 2). Grass, and sometimes bushes and trees, grow on the dunes, and the dunes (OF THE become a natural levee against the sea attack. PROBLEM Dunes are the final protection line against the sea, and are also a savings bank for the storage of sand against a stormy day. Natural Beach Protection And stormy days do come. Strong winds Many beaches of the United States, which blow high waves before them. These waves are have a high value as a natural resource, are so huge that the nearshore slope weakens them being destroyed through erosion associated only slightly. The thrust of the wind and the with manmade developments. waves toward shore raises the elevation of the sea and large waves pass over an offshore bar Where the land meets the ocean, nature has without breaking. If the storm occurs at high provided the shore with a natural defense tide, the storm surge and the tide superelevate against the attack of the waves. The first the waves and some of them may break high on defense against the waves is the sloping near- the beach or even at the base of the dunes. shore bottom which dissipates the energy or After a storm or stormy season, the natural defenses are again reformed by normal wave weakens the force of the deepwater waves. Yet and wind action. some waves continue toward the shore with force and energy still at tremendous levels until they near the beach. There they break, and Barrier Beaches, Lagoons and Inlets unleash most of their destructive energy. This Nature provides an additional protection for process of breaking often builds in front of the the mainland in the form of barrier beaches beach another defense in the form of an (Figures 3 and 4). Nearly all of the Atlantic offshore bar which helps to trip following Coast from Long Island to Mexico is comprised waves. The broken waves reform to break again of barrier beaches. These are essentially long and may do this several times more before narrow islands or spits built parallel to the finally rushing up the foreshore of the beach. shoreline by wave action and changes in sea At the top of wave uprush a ridge of sand is level. The barrier beaches thus formed and the formed and serves as a defense against uprush entrapped shallow lagoons of varying widths of following waves. Beyond this ridge, or crest separate the mainland from the sea. During of the berm, lies the flat beach berm which is severe storms these barrier beaches absorb the reached only by higher storm waves. brunt of the seawave attack, and even when their dunes are breached, the major damage is the cutting of an inlet which permits sand to enter the lagoon; there is no major damage to the mainland from the sea waves. Figure 1. Research Facilities - Coastal Engineering Research Origin and Movement of Beach Sands Center The sands of the beaches and nearshore slopes are small, resistant rock particles that 7 441@ X 'R@ V, 7-0 j -W, wn@ Figure 2-A. Sand Dunes along the South Shore of Lake Michigan Figure 2-B. Sand Dune, Honeyman State Park, Oregon A up the estuaries. Coastal villages were pop- ulated by fishermen. Few people had the time or the money to spend vacations at the beach. As time progressed, and particularly after World War 1, all of this changed rapidly. The technical revolution brought trains, the auto- mobile, gasoline-powered pleasure boats, large ships with deep drafts, and the new leisure. Coupled with the population explosion, these developments resulted in hordes of people descending onto the shore. Dunes were destroyed to make way for hotels, boardwalks, roads, and houses. Break- waters and jetties were built to aid large and small craft to harbor. In nearly every instance, these harbor structures interrupted the along- shore movement of sand and starved adjacent downdrift beaches. The rivers were dammed to provide the expanding population and industry with hydro- electric power, water supplies, and flood con- trol. These dams have essentially stopped the supply of sand previously reaching the beaches have been carried to the oceans from eroding from large parts of the major river basins. uplands. Some sand particles have traveled In many places, dunes were bulldozed away many miles from inland mountains. Other sand merely to provide picturewindow views of the is derived from erosion along the shore. When ocean. the sand reaches the shore, it is moved along- shore by waves and littoral currents. This Today's Beach Conditions transport by littoral currents is a constant process and moves great volumes of sand Today, we find that although there are still alongshore. In most places this movement many beautiful beaches for outdoor enjoy- changes direction as the direction of wave ment, in most areas there is less and less sand attack changes. The natural defenses of the land against the sea, the erosion by storm waves, and the littoral transport of the sand have shaped and reshaped the sandy beaches for millions of years. From the beginning of recorded history through the early years of this century, man has met the sea at the shore with few problems. He has built ports and used the seas for commerce and warfare. In the early days of settlement of this country, harbors were either landlocked or far 9 A NAM 4r Figure 3. Barrier Islands Separated by Tidal Inlets - Wrights- ville Beach, N.C., About 1940 reaching them and they erode. Causes for our shrinking beaches are in general the normal geologic changes and changes made by man. Considering a very long-term basis, the slow rise in sea level, if it continues, will submerge part of the present beaches. However, this rise is so slow that changes occurring in the course beaches and stop erosion of the bluffs which of a normal human lifetime will not be would normally furnish sand to the beaches. noticeable without measurement by precise Therefore, there is less material available for gages. Changes which occur on a shorter-term replenishment of the moving sands. basis, and which are of greater urgency, are those caused by development of the shore by Flood control and water supply dams are man for various purposes. As shore areas are necessary to the everyday life and safety of developed, attempts are made to stabilize the people, yet these dams often alter the flow of 10 water which brings sand from inland to the deeper water from where most of it may never shore. They may in some instances trap sand return to the shores. Unless means are provided that would move to the sea by the action of to overcome these losses of beach sand from normal flows. Improvements of inlets and river the shore zone, or methods are devised to mouths for navigation cause interruptions of reduce the effects of development, stabilizing the sand movement or shifting of the sand to beaches will become an ever-increasing prob- lem. In addition to sand losses and beach changes induced by works of man, there are natural coastal processes which produce sand losses, such as diversions into deep submarine canyons and accumulating shoals inside unim- proved inlets and at major headlands. Figure 4. Barrier Beach Island Developed as Recreational Park - Jones Beach State Park, Long Island, N. Y. 3 July 1955. NE "@7 g@ 7,, Nil F woo R AIL- MOO* E@ Figure 5. Large Waves Breaking over a Breakwater (Photo from Portland Cement Association) 12 Waves The familiar waves of the sea are "wind waves" generated by the winds blowing over the water. They may vary in size from ripples on a pond to giant waves in the oceans as high as 100 feet (see Figure 5). Wind waves cause most of the damage to our seacoasts. Another type of wave, the tsunami, is created by earthquakes or other large disturbances on the ocean bottom. Tsunamis have caused spectac- ular damage at times, but fortunately they do not occur frequently. Wind waves are of the type known as 00 F oscillatory waves, and are usually defined by CTp ri P, FF:D their height, length, and period (see Figure 6). Wave height is the vertical distance from the top of the crest to the bottom of the trough between crests. Wave length is the horizontal distance between successive crests. Wave period Tides and Winds is the time between successive crests passing a given point. The forces of the sea originate in the sun and the moon. The sun causes air movements or When waves move over the water, only the winds, and helps the moon create the tidal rise form and energy of the waves move forward, and fall of the ocean surface. Advance of the wave form causes oscillatory motions of the individual water particles Air movements originate with temperature (Figure 7). changes. The sun heats the earth, the waters of the earth, and the air around the earth, but this These particles describe circular orbits in deep heating is not uniform. The air in some parts of water with each particle returning to its origi- the earth is heated more than that in other nal position after passage of the wave. The places. The warmer, lighter air rises, causing a diameters of the circles decrease with depth zone of reduced pressure; winds result as from a diameter at the surface equal to the colder, denser air moves into this zone. wave height. In shallow water the orbital movements become flattened, and at the The moon, and to a lesser extent the su n, bottom are merely horizontal oscillations to creates the tides of the sea. Together they and fro as the wave form passes. generate the tides because they attract the water masses of the earth in the same way that The height, length, and period of wind waves the earth attracts objects near its surface. are determined by the fetch (the distance the Because of this gravitational force of attraction wind blows over the sea in generating the and the fact that the sun, moon, and earth are waves), the speed of the wind, and the length always in motion with relation to each other, of time that the wind blows. Generally, the the waters of the ocean basins are set in longer the fetch, the stronger the wind, and the motion. Once the water masses of the oceans longer the time that the wind blows over the have been set in motion, they create the tides. water, the larger the waves will be. The wind The tidal motions of the water masses are a generates waves of many heights, lengths, and form of wave motion. periods simultaneously as it blows over the sea. 13 01 Wave crest L Wave length Direction of Wove travel Hz Heig Wove crest ove trou T da depth ough Still water level ,Ocean bottom WAVE CHARACTERISTICS Figure 6. Wave Characteristics If winds of a local storm blow toward the The wind creates currents because, as it coast, the generated waves will reach the local blows over the surface of the water, it creates a beach in essentially the form in which they "stress" on the surface water particles, and are generated. Under these conditions, the starts these particles moving in the direction in waves are rather steep, that is, the wave length which the wind is blowing. Thus, a surface is only from 7 to 20 times the wave height. If current is created. When such a current comes the waves are generated by a distant storm, to a barrier, such as a coastline, the water tends they may travel through hundreds or even to pile up against the land. In this way "wind thousands of miles of calm areas before reach- tides" or "storm surges" are created by the ing the shore. Under these conditions the waves wind. The amount of "storm surge" depends "decay" - the short, steep waves are elimi- on the wind velocity and direction, the fetch, nated, and only relatively long, low waves and the water depth. In violent storms this reach the shore. Such waves have lengthsfrom wind surge may raise the sea level as much as 30, to 500 or more times the wave height and 20 feet. In the United States, the larger surges are called "swells" or "ground swells". occur on the Gulf Coast because of the lesser depths on that coast compared to those on the Currents and Surges Atlantic and Pacific Coasts. Storm surges may also be increased by the funneling effect in Currents are created in oceans and adjacent converging estuaries. bays and lagoons when the water in one area becomes higher than the water in another area. Waves create a current known as the "long- The water in the higher area flows toward the shore current" when they approach the beach lower area, creating a current. Some causes of at an angle. As they break on the beach they differences in the elevation of the water in the set up a current which moves parallel to the oceans are the ordinary tides, the blowing shore in shallow water. The longshore current wind, waves breaking on a beach, and streams is frequently noticeable to swimmers and which flow into the ocean. Changes in water bathers in the surf when they find themselves temperature cause changes in water density and being moved slowly along the beach. This produce currents such as the Gu If Stream. current, under certain conditions, may turn 14 and run out to sea in what is known as a "rip particular place, then water must flow into and current". Rip currents are often referred to by out of the area. The most important currents bathers as "undertow", and when strong that the tides generate are those at inlets to enough they may endanger swimmers by carry- lagoons and bays or at entrances to harbors. At ing them seaward to deeper water rather most such places, the water flows in when the unexpectedly. tide in the sea is rising (flood tide) and then flows out as the tide in the sea falls (ebb tide). The rivers and streams which flow into the ocean are currents themselves, and they carry In addition to creating currents, the tides are the sediments which have been eroded from constantly changing the level at which the the land. waves attack the beach. Tidal Currents The tides are a rise and fall in the water level. If the water level is to rise and fall at any Figure 7. Water Particle Movement under Wave Action DIRECTION OF ORBITAL MOVEMENT OF WATER PARTICLES IN DIFFERENT PARTS OF A DEEP-WATER WAVE. Small motion of water below L/2 Wave direction BEACH GRASS SHOWS THE DIRECTION OF MOVEMENT OF WATER PARTICLES UNDER VARIOUS PARTS OF A SHALLOW-WATER WAVE. 15 Coastal Area Zone of Nearshore Currents Upland Beach or Shore Backshore Foreshore Inshore or Shoreface Offshore (extends through breaker zone) Bluff or escarpment L Berms Beach scarp High Water Level Breakers Crest of Berm Low Water Level Plunge Point Bottom Figure 8. Beach Profile - Related Terms Beach Composition The sediments of a beach are determined by the forces to which the beach is exposed and the type of material available at the shore. Most beaches are composed of very fine to very THE BEHAVIOR coarse sand. This sand is supplied to the S beaches by the streams, and by the erosion of OF BEACHE the shores by waves and currents. Mud does not usually remain on beaches because the waves create much turbulence in the water along the shore and the fine materials which compose muds are kept in suspension in the shore area. It is only after moving away from the beaches into quieter or deeper water that these fine particles settle out and deposit on the bottom. Many beaches along the New England Coast are composed of rather large stones, frequently called "shingle" or "gravel". Some beaches on water bodies where wave action is very mild are composed of mud. ""7 Bluff or eS"rp@met Grasses usually grow in the mud, thus these shores are marshes. 16 energy of the wave, which causes a great turbulence in the water, and stirs up the bottom materials. After breaking, the water travels forward as a foaming, turbulent mass, expending its remaining energy in a rush up the beach slope, then falling under the influence of the force of gravity, the water runs back down the beach slope to the sea. Effects of Wind Waves Wind waves affect the beaches in two major ways. Short steep waves, which usually occur during a storm near the coast, tend to tear the beach down (Figure 9). However, when the local weather is fair, the long swell which comes ashore from distant storms tends to rebuild the beaches. On most beaches, there is a constant change caused by the tearing away of the beach by local storms followed by gradual rebuilding by swells from distant storms. A series of violent local storms in a short time can result in severe erosion of the shore, if there is not enough time between them for swells to rebuild the beaches. Alter- nate erosion and accretion of beaches is Beach Characteristics seasonal on some beaches; the winter storms tear the beach away, and the summer swells The characteristics of a beach are usually rebuild it. Beaches may also follow longterm described in terms of the average size of the cyclic patterns. They may erode for several sand particles that make up the beach, the years, and then accrete for several years. range and distribution of sizes of those parti- cles, the elevation and width of berm, the slope Littoral Transport or steepness of the foreshore, and the general slope of the inshore zone fronting the beach The longshore current is very important in (see Figure 8). Generally the larger the sand coastal processes because it carries sand which particles which make up the beach, the steeper has been stirred into suspension by the turbu- the beach will be. Beaches with gently sloping lence of the breaking waves. The sand moved in foreshores and inshore zones usually have a this way is known as "littoral drift". Onshore preponderance of the finer or smaller sizes of and offshore sand movements are caused by sand. low swells and steep waves respectively, and coupled with littoral drift help explain the Breakers major shoreline changes on the open coasts of the world. This onshore-off shore process as- The primary agent causing onshore, off- sociated with storm wave events is illustrated in shore, and alongshore movement of sand is the Figure 9, while Figure 10 illustrates an on- breaking wave or "breaker". As a wave moves shore-offshore path for motion of sand parti- onto the shore, it finally reaches a depth of cles associated with each individual wave. water which is so shallow that the wave collapses, or "breaks". This depth is equal to The direction and violence of the wave about 1.3 times the wave height. Thus a wave 3 attack determine the direction and magnitude feet high will break in a depth of about 4 feet. of the littoral transport at a given time. For Breaking results in a sudden dissipation of the instance, on a coast facing to the east, violent 17 Dune Crest Berm .... ....... M.H.W, Profile A Normal wave action M.L.W. o M.H.W. Profile B - Initial attack of storm waves M.L.W. ACCRETION de P f i I Storm Tide M.H.W. R 0 S 0 N Crest t Profile C Star wave at oc M.L.W. Lowering of foredune Crest Recession- ACCRETION Prof ileA Oy 0 IV M.H.W. Profile D - After storm wave attack, M.L.W. normal wave action ACCRETION 1'@7` Profile A -=@H. W. Storm Tde est 'tR eCcre 3sion 18 place to place. In landlocked water of limited extent, such as the Great Lakes, the rate of littoral transport can normally be expected to be no more than about 150,000 cubic yards per year. For the open coasts of the oceans, the net rate of transport may be from 100,000 to 2 million or more cubic yards per year. The rate storm waves from the northeast would produce depends on the local shore conditions and a high rate of littoral transport toward the alignment as well as the energy and direction of south. Conversely, mild wave action out of the wave action in the area. southeast would result in a much smaller rate of littoral transport to the north. However, if Formation of Deltas the southeast waves existed for a much longer time than did the northeast waves, the effect of The fresh water from rivers and upland the southeast waves might well be more im- streams flows to the sea, in some cases directly, portant in moving sand than that of the and in other cases through estuaries, bays or northeast waves. In reality, most shores show lagoons. Sediments brought down by rivers changes in the direction of littoral transport as flowing directly into the ocean are deposited at the weather patterns change. However, most the river mouth in the form of a delta (Figure shores consistently have a net annual littoral 11). Sand in these deltas is placed in suspension transport in one (same) direction. Determining by the waves, and is carried onto the beaches the direction and the average net annual toward which the longshore current is moving. amount of the littoral drift is important in In this way, sediments brought down by rivers developing shore protection plans. and streams feed the ocean beaches. When the f resh water from the river flows through the The average annual net rate of littoral estuary, bay or lagoon into the ocean, the river transport at a given place is fairly regular from sediment is frequently deposited in the pro- year to year unless man changes the shore, and tected area and only the water reaches the eliminates or reduces the supply of sand. The ocean. In such cases, the sand is not supplied to average annual rate varies considerably from the ocean beaches. Figure 9. Schematic Diagram of Storm Wave A ttack on Beach and Dune 19 Effects of Inlets on Barrier Beaches Inlets have important effects on adjacent shores by interrupting littoral transport of sand and trapping the littoral drift. As littoral drift moves into the inlet, it narrows the inlet. Increased tidal currents caused by the constric- tion then pick up the littoral drift from the inlet. On the ebb current, the sand is carried a short distance out to sea and deposited on an outer bar (see Figure 3 and 12). When this bar becomes large enough, the waves begin to break on it, and this sand again begins to move along the bar toward the beach. However, on the flood tide, when the water flows through the inlet into the lagoon, the littoral drift in the inlet is carried a short distance into the lagoon and deposited. Such sand creates shoals in the landward end of the inlet known as "middle ground shoals" or "inner bars". Later ebb flows may bring some of the material in these shoals back to the ocean, but some is BACKSHORE CREST OF BERM WATER LEVEL PATH OF SAND GRAINS DIRECTION OF WAVE-INDUCED CURRENT IN THE SURF ZONE MATERIAL PLACED IN SUSPENSION BY BREAKERS IS MOVED LATERALLY BY THE LONGSHORE CURRENT, VPATH OF SA7ND GRAI-NS OF OUTSIDE SURF ZONE BED LOAD MOVES IN A ZIGZAG PATTERN 20 always lost from the littoral drift stream and thus from the downdrift beaches. In this way, inlets frequently store sand and cause narrower beaches by reducing the supply of sand to those beaches. Also, by temporarily interrupt- ing transport of sand, inlets may cause alter- nate periods of erosion and accretion on the downdrift shores. Impact of Storms the water, are then subjected to the forces of the waves and are often completely destroyed. Hurricanes or other severe storms moving Low-lying areas next to the ocean or lagoons over the ocean near the coast will change and bays are often flooded by such storm beaches drastically. Such storms generate large, surge. Storm surges are especially damaging if steep waves. These waves take sand from the they occur at the same time as high tide. beach and carry it offshore; they move much more sand than do ordinary waves. In addition, The berm, or berms of the beach are built the strong winds of the storm often create a naturally by waves to an elevation approximat- storm surge. This surge raises the water level ing the highest point reached by normal storm and exposes higher parts of the beach not waves. While the berms tend to absorb the ordinarily vulnerable to waves. Structures, in- major forces of the waves, overtopping permits adequately protected and located too close to waves to reach the dunes or bluffs in back of the beach and damage unprotected manmade features. When storm waves erode the berm and carry the sand offshore, the protective value of the berm is reduced and large waves can overtop the beach. The width of the berm at the time of a storm is thus an important factor in the amount of upland damage the storm can inflict. In spite of the changes in the beach that result from storm-wave attack, a gently sloping beach of adequate width and height is nature's most effective method of dissipating wave energy. Beach Stability Although a beach may temporarily be eroded by storm waves and later restored by swells, Figure 10. LonKshore or Lateral Movement ofLittoral Drift. Movement in all three zones is in a direction and at a rate dependent on the lonKshore component of wave enerKy. 21 @ NI vlr'@ - .1N -61 4 X oe, Figure 12. Umimproved Tidal Inlet Showing Barrier Beach and Pattern of Offshore Bar and Shores- North Carolina and erosion and accretion patterns may occur seasonally, the long-range condition of the beach - whether eroding, stable or accreting - depends on the rates of supply and loss of littoral material. Erosion or recession of the shore occurs when the rate of loss exceeds the rate of supply. The shore is considered stable (even though subject to storm and seasonal changes) when the rates of supply and loss are equal. The shore accretes or progrades when the rate of supply exceeds the rate of loss. Figure 11. River Delta at Mouth of San Juan Creek, California (March 1969) 23 7 -, 441@ (n tO Pleasure Ave. House House End of Dune Crest of Dune Breach in Dune Figure 13. Residential Development Encroaching on Dune Areas and Resulting Backshore Damage (Townsends I::-_- I @@Housej Inlet, New Jersey, March 1962) 24 Encroachment on the Sea During the early days of the United States, natural beach processes continued to mold the shore as in ages past. As the country developed, activity in the shore area was confined princi- pally to harbor areas. Between the harbor areas, the shore developed slowly as small, MANMADE isolated, fishing villages. As the national econ- EFFECTS omy developed, improvements in transporta- ON THE tion brought more people to the beaches. The SHORE fishing villages gave way to the massive and permanent type of resort such as Atlantic City and Miami Beach. Figure 14. Backshore Damage at Sea Isle City, New Jersey, after March 1962 Storm 25 Numerous factors control the growth of development at beach areas, but undoubtedly the beach is the resort's basic asset. The desire of visitors, residents, and industries to find accommodations as close to the ocean as possible has resulted in man's encroachment on the sea. There are numerous places where the beach has been gradually widened by natural processes over the years; lighthouses and other structures which once stood on the beach now stand hundreds of feet inland. In their eager- ness to be as close as possible to the water, Figure 1-5. Backshore Damage at Ocean City, Maryland, after developers and property owners often forget March 1962 Storm Note wave uprush in foreground that land comes and goes, and that land which reaching backshore development. 26 Figure 16A. Steel Sheet Pile Bulkhead XV 7, A- A 01 A P,Y!N,o 35 Ar A j, CA4 @-t TP, DUNDALK DOCK, BALTIMORE, MARYLAND A splash apron may be added next to coping channel to Dimensions and details to be reduce damage due to overtopping. determined by particular site conditions. Coping channel Top of bulkhead Sand fill Sl e I on 20 'Former ground surface Tie- rod 67Timber block Tide Range Timber strut Timber wale Timber Wale $-Round timber piling Steel shear piling Water level datum 27 ;ps Figure 16B. Timber Sheet Pile Bulkhead Top Elevation of Bulkhead Average Height of H, ghest Yearly Storm Vides Plus Wow Heiahts. ALE TIE "00 STRUT RIPRAP 0 Water Le 1) Datum SECTION 4 ELEVATION a A A, PILE WAL SHEETING NOTE: Dimensions a Details To Be 3 0 Determined By Particular Site Conditions. WA j?ANGH0ft PILES PLAN "00 PILE Ur 0 IN 4= 0 rAN.HO. TMES 28 Now we Figure IZ Precast Concrete Sheetpiles, DaYtona Beach, Florida. The sheetpiles are 8 x 30 inches and 15 J@et, 3 inches long. The concrete cap is 15 inches wide x 12 inches deep. Photo fronz Portland Cement A ssociation Figure 18. Vertical-face Concre te Seawall built 25 years ago at Watch Hill, Rhode Island. Seawall, combined with heavy rock riprap, protects the residence on hill at right. Photo front Portland Cemen t A Fyociation. J,.Na& fl-4 J- ?i nature provides at one time may later be onto the beach and into the sea, storm waves reclaimed by the sea. Yet once the seaward overtop the beach and damage backshore struc- limit of a development is established, this line tures. Measures designed to stabilize the shore must be held if large investments are to be fall into two general classes: a) a structure to preserved. This type of encroachment has prevent waves from reaching erodible materials; resulted in great monetary losses due to storm and b) an artificial supply of sand to the shore damage and ever-increasing costs of protection. to make up for a deficiency in sand supply through natural processes, with or without Natural Protection structures such as groins to reduce the rate of loss of littoral material. While the sloping beach and beach berm are the outer line of defense to absorb most of the Comprehensive Protection wave energy, dunes are the last zone of defense in absorbing the energy of storm waves that Separate protection for shore reaches of succeed in overtopping the berm. Although eroding shores (as an individual lot frontage) dunes erode during severe storms, they are very within a larger zone of eroding shore, is often substantial enough to afford complete difficult and costly. Such protection often fails protection to the land behind them. Even when at the flanks as the adjacent unprotected shores breached by waves of an unusually severe continue to recede. Partial or inadequate pro- storm, dunes gradually rebuild naturally to tective measures may even accelerate erosion of provide protection during future storms. Con- adjacent shores. Coordinated action under a tinuing encroachment on the sea with man- comprehensive plan which considers the made development has very often taken place erosion processes over the full length of the without proper regard for this protection pro- receding shore segment is much more effective vided by dunes. Great dune areas have been and economical. leveled for real estate developments, and be- cause such developments were left unpro- Bulkheads, Seawalls and Revetments tected, great damage has resulted during storms. Dunes are frequently lowered to permit Protection on the upper part of the beach, easy access to the beach. This allows storm fronting backshore development, is required as waters to flood the area behind the dunes a partial substitute for the natural protection (Figure 13). Where there is inadequate dune or that is lost when the dunes are destroyed. similar protection against storm waves, the Shorefront owners have resorted to armoring storm waters may wash over low-lying land, of the shore by wave-resistant walls of various moving or destroying everything in their path, types. A vertical wall in this location is as illustrated by Figures 14 and 15. Sometimes sometimes known as a bulkhead, and serves as those waters cut new inlets through barrier islands. Shore Protection Methods Where beaches and dunes serve to protect the shore developments, additional protective structures may not be required. However, in some localities where development encroaches 30 Figure 19. Concrete Combination Stepped and Curved-face Seawall San Francisco, California I H-beams 20@O"o.c.- 1 20LO" 2'6" 33" Top of wall Promenade r7" Scupper to 0" 7 21, H-beoms 20'0"O.c. 1'-7"square pedestal pile SECTION A -A 2*6" Ion Beach line g 10 Extreme high tide. A Cross.alls A. O"concrete r- ..It between I sheetp! ing I .I. and b m b Mean sea level --1, 81"underdroin 4--0.. 4 0 and outlet -11 Cross walls are to stop at C C SECTION B-B this line.. L 10.1 Twosbulb piles replace 5 4 -0`1 14"0" 7 L pecle tol pilepwhen sheetpiles @'l .-I conflict with edestal pile. D 6"tubing-___@ j17" B I I B _4 L Interlocking D sheetpiles SECTION b 3._I.,x 3LI.. pedestal D - D SECTION C-C lu, L 31 a secondary line of defense in major storms. Bulkheads are constructed of steel, timber, or concrete piling. Typical steel and timber pile bulkheads are shown on Figures 16A and 16B, and a concrete pile bulkhead is shown on Figure 17. For ocean-exposed locations, bulk- heads do not provide a long-lived permanent solution, because eventually a more substantial wall is required as the beach continues to recede and larger waves reach the structure. Unless combined with other types of protec- tion, the bulkhead eventually evolves into the massive seawall capable of withstanding the direct onslaught of the waves. Extensive sea- 7-g, -@7 A @B - A -k M V, j- M 10�51 V M _M @71 M It 2 5 -0 9 Treads(9 18N-_134! H fill ? -, '0" 0 T .. 1@; Section of 1*_1 I Rib A-A 71 Origina I grourl surface(voriabill W =0. 111 2%.I.Soil pipe wee 0 an GuttlLsvel hole CL 41 s Wh Detail of sheet pile !2 32 wall structures have been built principally in Massachusetts, Florida, Mississippi, Texas and California. Seawalls may have vertical, curved or stepped faces (see Figures 18, 19, 20 and 21). While seawalls may protect the upland, they do not hold or protect the beach which is the greatest asset of shorefront property. In some cases, the seawall may be detrimental to the beach in that the downward forces of water, created by the waves on striking the wall, rapidly remove sand from the beach. The Galveston seawall, shown on Figure 21, in- cludes a stone apron to minimize scouring of the beach and undermining the wall. A revetment armors the slope face of a dune (the latter discussed in the next section) are or bluff with one or more layers of rock or more expensive and are usually built only in concrete. This protection dissipates wave the more openly exposed sites. Their estimated energy with less damaging effect on the beach cost begins at, say, $200 per foot and ranges than waves striking vertical walls. A rock considerably above $500 per foot for massive revetment built at Cape Henry, Virginia, is structures far from rock sources. shown on Figure 22. A light concrete-block revetment designed for a less exposed location Breakwaters in Chesapeake Bay is shown on Figure 23. A concrete-block revetment in a more exposed Beaches and bluffs or dunes can be pro- location fronting on the Atlantic Ocean at tected by an offshore breakwater that prevents Jupiter Island, Florida, is shown on Figure 24. waves from reaching the shore. However, off- shore breakwaters are more costly than on- Adequately designed bulkheads and revet- shore structures, and are seldom built solely for ments usually cost about $75 to $150 per foot this purpose. Offshore breakwaters are con- of shore protected, depending upon exposure structed mainly for navigation purposes. A to wave action, total length, and proximity to breakwater enclosing a harbor area provides sources of construction material. The cost of shelter for boats. Breakwaters have both bene- this type of protection might exceed $400 per ficial and detrimental effects on the shore. All foot in some areas. Seawalls and breakwaters breakwaters reduce or eliminate wave action Figure 20. Concrete Stepped-face Seawall in Harrison and Hancock Counties, Mississippi 33 igg @-g 1W 34 and thus protect the shore immediately behind processes. When placed on the updrift side of a them, Whether offshore or shore-connected, navigation opening, the structure impounds the elimination of wave action reduces littoral sand, prevents it from entering the navigation transport, obstructing the free flow of sand channel, and affords shelter for a floating along the coast and starving the downstream dredge to pump the impounded material across beaches. At a harbor breakwater, the sand the navigation opening back into the stream of stream generally can be restored by pumping sand moving along the shore. This method is the sand through a pipeline from the side used at a harbor near Port Hueneme, Cali- where sand accumulates to the starved side. fornia, shown on Figure 26. This type of operation, in use for many years at Santa Barbara, California, is illustrated by Figure 25. Even without a shore arm, an offshore breakwater stops wave action and creates a quiet water area between it and the beach. In the absence of wave action to move the sand stream, the sand is deposited and builds the shore seaward toward the break- water. The buildup actually serves as a barrier and completely dams the sand stream, depriv- ing the downdrift beaches of sand. Although this type of construction is generally detri- mental to downstream beaches, there is one case in which it may be used to aid the beach Figure 21. Seawall at Galveston, Texas. Top elevation is 15.6 f@et mean sea level. (Stone at toe and groins reduce loss of sand) 35 20 25 Riprop (1000 Ibs to 6000 lbs', averaging 4000 lbs.),chinked EL. + 15.0' with one man stone. Lo du s graded 5\011e CP-, 12 to 4 15.0 ft. EL + 50' Crushed stone unscreened 21 inches and under. Natural beach 2 slope One man eo'o 7 EL.+ 2 Figure 22. Stone Revetment at Cape Henry, Virginia 36 N, 4- A, Wood railing 3 18..-7 2F Concr te sidewalk Original ground line S-d x6" thick Concrete Block [19tails Woven plastic filter cloth 6" Loyer fto I fstone Stone toe protection 2 2 M. L.W. Hardpan 2"x6" Timber n sandy bottom too or cut off wall would be required @11 Figure 23. Interlocking Concrete-Block Revetment at Benedict, Maryland 1 6 i#C4 7W, 37 2@ + -i@@ + 14.Oft. 12@' Reinforced concrete wavescreen Asphalt grouting If + 10.0ft. Plastic f! ter cloth Interlocking blocks 0.5" to 1.0"Gravel on plastic filter cloth, Reinf. conc. cap 16" t1l 10 + 1.5 ft. 14 8" thick to on stones 36 5 M.S.L. O.Oft. Plastic filter cloth as far down as possible. I '. . = -- i - tlig A t Plan View Prestressed concrete piling U') 7 -1 Section A -A 10" block Section A -A 1 0 f ? 3 4 5 ft. -T 14" block Scale .1 Figure 24. Interlocking Concrete-Block Revetment at Jupiter Island, Florida 38 SANTA BARBARA "A P, PAL t4 A 14J N CCEP . Q WEST BREAKWATER J .... ..... 71- 11@z Q, Figure 25. Sand Bypassing at Santa Barbara, California. Sand dredged from inside the breakwater is pumped to downdrift beach. 39 no, 4 -1-To W. CTIO U.S. NAVAL CONSTRUu N BATTALION CENTER Future Por I eeder beach Development Hueneme area Harbor I\b Existing seawall 10 49 Exist ing east jetty Silver Strand I , Existing entrance channel 6......... . Hueneme s'and @,--.@xisting wesir jetty submarIne Trop n/rGnce'viianne'l- ... .. Canyon .... .. ..... Breakwate i_ 24!` .... ..... ... ....-30 4 2300' 40 The basic purpose of a groin is to interrupt alongshore sand movement to accumulate sand on the shore or to retard sand losses. Trapping of sand by a groin is done at the expense of the adjacent clowndrift shore unless the groin or Groins groin system is filled with sand to its entrap- ment capacity. To reduce the potential for Long ago investigators noted that obstruc- damage to property clowndrift of a groin, some tions on a beach, such as logs or wrecks, would limitation must be imposed on the amount of trap sand moving along the beach and cause the sand permitted to be naturally impounded on beach to widen. Such observations led natu- the updrift side. Since more and more shores rally to devising the groin, a barrier-type are being protected, and less and less sand is structure which extends from the backshore available as natural supply, it is now desirable, into the littoral zone of sand movement. In and frequently necessary, to place sand artific- earlier times, prior to the current extensive ally to fill the area between the groins, thereby development of upstream river basins and ensuring a more-or-less uninterrupted sand major portions of the seacoast, the natural supply to clowndrift shores. supply. of beach sand was plentiful, and in many instances groins succeeded remarkably Groins have been constructed in many ways well. This led to further, excessive, and indis- using timber, steel, concrete or rock, but can criminate use of groins. They often were be classified into basic physical categories as installed without considering all the factors high or low, long or short, and permeable and pertaining to the particular problem. Figure 27 impermeable. illustrates a successfully working groin system. The groin system shown in Figure 28 has had A high groin extending through the zone of only marginal success at improving the beach breaking for ordinary or moderate storm waves because of an insufficient natural supply of initially entraps nearly all of the alongshore sand. However, this system has presumably moving sand within that intercepted area until somewhat reduced the rate of loss of sand and the areal pattern or surface profile of the the rate of shore recession. accumulated sand mass allows sand to pass around the seaward end of the structure to the clowndrift shores. Low groins (top profile no higher than that of desired reasonable beach dimensions) function like high groins, except that appreciable amounts of sand also pass over the top of the structure. Permeable groins permit some of the wave energy and moving sand to pass through the structure. Figure 26. Sand Bypassing at Channel Islands Harbor, Cali- fornia. Sand is periodically dredged from trap and moved through a pipeline across both harbor en- trances to the feeder beach on the far right. Photo was taken Just after dredging. 41 46 -'11114 NS 138 WI or i@ R@v Experience has shown that a short groin in heavy drift areas may fill quickly and have a limited effect on adjacent beaches. High groins, particularly if they extend beyond thebreaker zone for most waves, adversely affect down- drift shores long after their updrift-side im- pounding capacity is reached. This is caused by diversion of littoral drift offshore beyond the end of the groin where its subsequent move- ment deprives downdrift beaches of an ade- quate supply of nourishment. The accreted sand adjacent to the updrift side of a long groin may result in such a different shore alignment from that of the natural ungroined shore that sand movement along that alignment by waves is retarded for many years, Short groins, and groins which have an appreciable degree of permeability, do not cause a pronounced set- back in the shore immediately downdrift of the groin as the littoral transport of sand over and through these structures allows a more Gontin- uous supply to the downdrift area. Present knowledge of sediment transport by waves and currents does not permit satisfactory determi- nation of the optimum degree of permeability for proper functioning of permeable groins. Impermeable groins can be more readily de- signed to serve the desired purpose, and they are more widely used. But groins of any type should not be built unless property designed for the particular site. The effects of the contemplated groins on adjacent beaches should be studied by an experienced engineer. Adequately designed protective groins may cost about $100 to $350 per foot of shore protected dependent upon such factors as exposure to wave action, range of tide, and accessibility of building materiais. This is the cost range for groin structures only - where Figure 2 7 Groin System - Willoughby Spit, Vip%inia beach fill is also required to prevent adverse effect on downdrift shores, the cost increases accordingly. 43 Figure 28. Groin System at Miami Beach, Florida (April 1962) ---------- F7,@", 4P'-- Isi - N 2 tM REA, 44 44 % 4, _4@ Figure 29. Jetties at Cold Spring Inlet, New Jersey, Entrance to Cape May Harbor. (Note widened beach adjacent to updrift jetty and eroded downdrift shore.) Jetties Another structure developed to modify or control sand movement is the jetty. This structure is generally employed at inlets in connection with navigation improvements (see Figure 29). When sand being transported along the coast by waves and currents arrives at an inlet, it flows inward on the flood tide to form climate, and economic considerations. Jetties an inner bar, and outward on the ebb tide to are considerably larger than groins, since jetties form an outer bar. Both formations are harm- sometimes extend from the shoreline seaward ful to navigation through the inlet, and must be to a depth equivalent to the channel depth controlled to maintain an adequate navigation desired for navigation purposes. To be of channel. The jetty is similar to the groin in that maximum aid in maintaining the channel, the it dams the sand stream. Jetties are usually jetty must be high enough to completely constructed of steel, concrete or rock. The obstruct the sand stream. Jetties aid navigation type depends on foundation conditions, wave by reducing movement of sand into the 45 .1.". W@: oro@ ----,'Rock Groin channel, by stabilizing the location of the channel, and by shielding vessels from waves. Trestle No 3 Adversely, sand is impounded at the updrift jetty as shown on Figures 29 and 30, and the Boord.olk supply of sand to the shore downdrift from the inlet is reduced thus causing erosion of that shore. Prior to the installation of a jetty, nature ------ i Hock Groin supplies sand by transporting it across the inlet intermittently along the outer bar to return to Trestle No 2 < the downstream shore. AVON A rLAIVrIC OCEAN To eliminate undesirable downdrift erosion, ------ Rock Groin some projects provide for dredging the sand impounded by the updrift jetty and pumping it through a pipeline to the eroding beach (see Trestle No. 1 Figure 31). This ensures an uninterrupted flow of sand alongshore to nourish the downdrift beach, and also prevents shoaling of the en- ------ No,fl, Jetty trance channel. At Shark River Inlet, New SH,4,?,,r Jersey, shown on Figure 30, sand was trans- ---------- --- ported across the inlet by truck with beneficial Trestle SOUth Jetty 100'_J results. BELMAR 8oRRqW 4REA 0 - ------- -- 100 A more recent development provides a low @1, _@r Fishing Pier section or weir in the updrift jetty over which sand moves into a predredged deposition basin. Boordwolk By dredging the basin periodically, deposition in the channel is reduced or eliminated. The dredged material is normally pumped across the inlet to provide nourishment for the downdrift shore. A "weir-jetty" at Masonboro Inlet, North Carolina, is shown on Figures 32A and 32B. 46 the beach, material is placed periodically to make up deficiencies in the natural supply. This is most economical for long beaches as the increase of supply benefits the entire beach. Coastal engineers can now determine re- Beach Restoration and Nourishment quired dune and beach dimensions to protect against storms of any given intensity. Dune Beach structures, when properly used, have a heights sufficient to prevent overtopping by place in shore protection. But research has waves, and dune widths sufficient to withstand shown that the best protection is afforded by the erosion of a given storm can be determined. using methods as similar as possible to natural Also, beach dimensions, including height and ones. In other words, a greater degree of width of berm and characteristics of sand effectiveness is obtained by the type of protec- required to maintain beach slopes, can be tion provided by nature, which permits the designed to withstand storms of a specified natural processes to continue unhampered. degree of severity. A project for beach restora- To simulate natural protection, dunes and tion with an artificial dune for protection beaches are rebuilt artificially. Sand from against hurricane wave action, completed at sources behind the beach or offshore is Wrightsville Beach, North Carolina, in 1965, is placed on the shore. Figures 20 and 33 shown on Figure 35. Sometimes structures show views of Harrison County, Mississippi, must be provided to protect dunes, to maintain after and before artificial restoration of the a specific beach shape, or to reduce nourish- beach in front of the seawall with sand ment requirements. In each case, the cost of from the offshore bottom. This project was such structures must be weighed against the completed in 1952 and.thus far has required added benefits they would provide. Thus, minor maintenance. A restored beach at measures to provide and keep a wider protec- Presque Isle, Pennsylvania, is shown on tive and recreational beach for a relatively Figure 34. To ensure continued stability of short section of an eroding shore would require excessive nourishment without supplemental structures such as groins to reduce the rate of loss of material from the widened beach. A long, high terminal groin or jetty is frequently justified at the downdrift end of a beach restoration project to reduce losses of fill into an inlet and to stabilize the lip of the inlet. Figure 30. Shark River Inlet, New Jersey, where Sand Im- pounded at Jetty was transported across Inlet by Truck. 47 4a -4 kx @-a N -0,2 4 01- gr@ j v RK JNK. ..... .......... ............ N ArLANr1c ocEAN SOUTH LAKE woRrH llnEr Updrift Pumping plant Pipeline Downdrift ,/Middle -6und Shoal`- LAKE WORrH 111tracoostal Waterway Figure 31. Fixed Bypassing Plant South Lake Worth Inlet, Florida 48 v 2.0 4w go % 0.3 MY JO.s EXISTING A. J ETTY /1205. fk VA . .......... :..., .. 1.3 ......... "N % -N 0 OA,- .7 A41.1 4. 'a 41 5.9 4.0 A IN 4. 4.7 4.5 '4-0 -5.2 4.3 % N. .r. :..3 4 t % ul CD d. :19 P.5 3@\ 5.4 5.6 % 14.1 %% 11.0 % 43a % ........% 5.1 0*! \ .0 14.5 ................ Soundings inf**t rVerred to MLW 590 0 500 1000 EYED 7 JULY . I AUGUST 1966 3CALE IN FEET Figure 32A. Masonboro Inlet, North Carolina (July 1966) 49 CX F- Figure 32B. Weir Jetty at Masonboro Inlet, North Carolina, February 1966 r 50 Figure 33. Concrete Stepped-face Seawall - Harrison and Hancock Counties, Mississipp4 Figure 20 shows seawall after placement of beach fill. ---- - ------ 0 4", ---------- -4- v*@ 12 KM ... T=M WWIM, g rMe M"M I 51 A, 4, PRESQUE ISLE PENINSULA ERIE, PENNSYLVANIA NOVEMBER 1956 Figure 34. Restored Beach at Presque Isle Peninsula, Erie, Pennsylvania Jmo OBLIQUE VIEW OF PRESQUE ISLE PENINSULA ERIE, PENNSYLVANIA -JUNE 1959 52 'X _;V1 jw@ aor 7 Figure 3S. Wrightsville Beach, North Carolina, after completion of Beach Restoration and Hurricane Protection Project Beach fill for most beach widening or restoration can be expected to cost about $50 to $300 per foot of shore receiving the initial fill, depending on exposure, proximity of suitable fill borrow sites, length of beach, and degree of restoration required. Periodic nourishment may be required at intervals of 1 to 5 years at costs estimated to range from $5 to $15 per foot of shore per year, for straight beaches at least 2,000 feet long. It may be uneconomic, or even impracticable, to attempt nourishment of small segments of beach with- out retaining structures. The above estimates do not include dune rehabilitation and main- tenance. 53 pj !5&-- A. 16A Aw Qg!" Sit .. ...... AWQ MIZ, @d A@' @w ZOOL Figure 3Z Dunes lbrined by trapping windblown sand with Pnees and grasses. Outer Banks, Nor. Carolina. 54 Figure 36. Weekday use of artificially nourished beach, north of Haverhill Avenue, Hampton Beach, New Hamp- shire. 10, 111 R, COY T E L E P C R-kr5"' OCE. 5 General Within the United States and its possessions there are many types of coast with a great variety of physical characteristics and activity of littoral processes. Under these conditions no one method of shore protection would be the most suitable and economical for all shores. The selection of a method of protection or improvement of a specific shore frontage must be based on adequate knowledge of the shore characteristics and littoral processes for the frontage. New England Region The States of Maine, New Hampshire, Mas- sachusetts, Rhode Island and Connecticut have essentially the only shores of the Atlantic and Gulf coasts of the United States which include rocky headlands. These headlands are stable for all practical purposes and need no protection. However, there are also headlands and bluffs of glacial till and other erodible materials. These headlands and bluffs have in many cases been successfully protected by massive seawalls or revetments. Between the headlands there are frequently short stable pocket beaches, but in other cases, there are substantial lengths of sandy beaches attracting recreational users from great distances during seasonal months. 55 accompanied by high storm surges, are a special problem in these regions. Dunes sufficiently high and massive to withstand the severe wave action at the high water stages surmounting a stabilized beach are normally the most eco- nomical type of protection. (See Figure 37 showing dune formation promoted by sand fences and grasses.) Puerto Rico and Virgin Islands The shores of these islands are similar to the New England Shores with rocky headlands and normally short reaches of sandy beach, and similar protective measures are usually indi- cated. Pacific Coast Region Although the shores of Washington, Oregon These inicude the shore segment from Old and California include many rocky headlands, Orchard Beach to Saco, Maine, the reach from there are also many long sandy beaches, such as Hampton Beach, New Hampshire, to Annis- those on both sides of the Columbia River in quam, Massachusetts, the east shore of Cape Washington and Oregon, and in Monterey Bay, Cod and the shores of Nantucket and Marthas on the Oxnard plain, near Santa Monica, from Vineyard in Massachusetts, and the south shore Long Beach to Newport Bay and south of San of Rhode Island from Point Judith to Westerly. Diego Bay in California. As in New England, Many of the long beaches and even some of the revetments are suitable for headland protec- shorter ones can be improved economically by tion. Beach restoration and periodic nourish- artificial restoration and periodic nourishment. ment have been used successfully for the sand (See Figure 36 showing recreational use of beaches, accompanied by jetties or breakwaters restored and nourished beach.) and sand bypassing at inlets or harbors. Middle and South Atlantic, and Gulf Regions Alaska Region The east coast from New York to Florida The shores of Alaska are extremely diverse. and the Gulf coast from Florida to Texas Long stretches are similar to the New England, consist generally of long, straight reaches of beach. Erodible headlands exist infrequently, as in northern and southern New Jersey. Much of the shore consists of barrier islands with the straight reaches of sandy shore interrupted by many inlets. Instability of the intervening beaches is usually associated with instability of the inlets. Under this condition, long reaches of shore can be most economically restored and stablized by artificial placement of sand and periodic nourishment, accompanied by stabili- zation of the inlets by jetties with provision for bypassing the littoral drift. The bypassing may suffice to stabilize the downdrift problem area, but in some cases, supplemental nourishment from other sources is required. Hurricanes, 56 Gulf and Pacific Coast regions. Normal daily tides of relatively large range occur on the Pacific Coast of Alaska. Although beaches may be restored or widened by artificial placement of sand and maintained by periodic nourish- ment, such treatment is frequently not justified due to the absence of recreational use. Thus, where stabilization of short reaches is justified by protective rather than recreational benefits, revetment is likely to prove the most suitable method of protection. Hawaiian Islands These islands have the usual characteristics of volcanic islands with rocky headlands and relatively short sandy beaches. The fringing offshore coral reef substantially reduces the severity of wave attack on some parts of the shore. However, the north shores are subject to supply only a limited amount of sediment of very heavy wave action caused by North Pacific sufficient size to remain on the beach. Thus, storms, as well as the tsunamis resulting from there is a general deficiency in sand supply. earthquakes in the North Pacific region. An Beach restoration, nourishment, revetments economical method of tsunami protection has and seawalls have all been used. The shore is not as yet been devised. Possibly the removal also interrupted by many inlets and harbors so of development from areas within reach of that erosion of downdrift shores is common. A tsunami waves is the only feasible means of special cause of shore problems is the cyclical preventing damage from future tsunamis. variations in lake level. In addition to seasonal variations every year, there are major periods Great Lakes Region of high lake levels such as those of 1952 and 1969. These high stages inundate the beaches, Shore characteristics vary widely on the and permit larger waves to reach and erode the Great Lakes. Eroding bluffs, in many cases, bluffs. Protection of bluffs usually requires revetments or seawalls. On some of the beaches restoration and periodic nourishment would be feasible. In many cases, sand available for bypassing at inlets may be insufficient and the supply of sand must be augmented from other sources. 57 Experience and study have demonstrated that sand, in our dunes, beaches and nearshore areas, is the principal material available natur- ally near the shore in suitable form to protect our seacoasts. Where sand is available in abun- dant quantities, protective measures are greatly simplified and reduced in cost. When dunes and broad, gently sloping beaches can no longer be provided, it is necessary to resort to alternative structures, and the rec- reational attraction of the seashore is lost or greatly diminished. Sand is a rapidly diminishing natural re- source. Although once carried to our shores in abundant supply by streams, rivers and glaciers, cultural development in the watershed areas has progressed to a stage where large areas of our coast now receive little or no sand through natural geological processes. Continued cultural development by man in inland areas tends to further reduce erosion of the upland with resulting reduction in sand supply to the shore. It thus becomes apparent that sand must be conserved. This does not mean local hoarding of beach sand at the expense of adjoining areas, but rather the elimination of wasteful practices and the prevention of losses from the shore zone whenever feasible. Fortunately, nature has provided extensive storage of beach sand in bays, lagoons, estu- aries and offshore areas which can be used as a source of beach and dune replenishment in those cases where the ecological balance will not be disrupted. Massive dune deposits are also available at some locations, though these must be used with caution to avoid exposing the area to flood hazard. These sources are not always located in the proper places for eco- nomic utilization, nor will they last forever. When they are gone, we must face increasing costs for the preservation of our shores. Off- shore sources will probably become the most important source when means for economic recovery become available. 58 Mechanical bypassing of sand at coastal inlets is one means of conservation which will come into increasing practice. Mining of beach sand for commercial purposes, formerly a common procedure, is rapidly being reduced as coastal communities learn the need for regulat- ing this practice. Modern hopper dredges, used for channel maintenance in coastal inlets, are being equipped with pump-out capability so that their loads can be discharged on the shore instead of being dumped at sea, and it is expected that this source of loss will ultimately be eliminated. On the California coast, where large volumes of sand are lost into deep submarine canyons near the shore, facilities are being considered which will trap the sand before it reaches the canyon and transport it mechanically to a point where it can resume normal beach transport. Dune planting with appropriate grasses and shrubs reduces windborne losses landward and aids in dune preservation. Sand conservation is a very important factor in the preservation of our seacoasts, and it must not be neglected in L"(D N C LU S 00 N long-range planning. Protection of our seacoasts is not a simple problem; neither is it insurmountable. It is a task and a responsibility which has increased tremendously in importance in the past 50 years, and is destined to become a necessity in future years. While the cost will mount as time passes, it will be possible through careful planning, adequate control and sound engineer- ing to do the job properly and within our means economically. Shore protection can no longer be regarded as an individual responsi- bility, but must be undertaken as a cooperative effort on a comprehensive basis, with all levels of government participating. i i i i - 3 6668 4102 1040 1