:a guide for engineers and contractors/U.S. Army Corps of Engineers. United States.Army.Corps of Engineers. [Washington, D.C.] :U.S. Army. Corps of Engineers,1981. Shore protection United States. Coastal engineering United States. Beach erosion United States. 1/0 "w Al vv J @,; w = 4-:4 -@-- LOW COST SHORE PROTECTION a Guide for Engineers and Contractors TC 223 L6 1981 The U. S. Army Corps of Engineers presents this information as a public service. Inclusion of any shore protection device or method does not necessarily constitute a government recommendation or en- dorsement, nor is it guaranteed that any particular method will be successful for a specific applica- tion. LOW COST SHORE PROTECTION a Gilide for Engineers and Contractor$ US Department of Commerce NOAA Coatital Services Center Library 2234 South Hobson Avenue Charleston, SC 29405-2413 TABLE OF CONTENTS Page INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 5 Low Cost Shore Protection . . . . . . . . . . . . . . . 5 The Shoreline Erosion Control Demonstration Program. . 5 Shoreline Processes . . . . . . . . . . . . . . . . . . 6 THE EROSION PROBLEM . . . . . . . . . . . . . . . . . . . . 15 The Importance of Shoreform . . . . . . . . . . . . . . 15 The Causes of Erosion . . . . . . . . . . . . . . . . . 18 A LOOK AT THE OPTIONS . . . . . . . . . . . . . . . . . . . 21 No Action . . . . . . . . . . . . . . . . . . . . . . . 21 Relocation . . . . . . . . . . . . . . . . . . . . . . 21 Bulkheads and Seawalls . . . . . . . . . . . . . . . . 22 Revetments . . . . . . . . . . . . . . . . . . . . . . 24 Breakwaters . . . . . . . . . . . . . . . . . . . . . . 25 Groins . . . . . . . . . . . . . . . . . . . . . . . . 26 Beach Fills . . . . . . . . . . . . . . . . . . . . . . 28 Vegetation . . . . . . . . . . . . . . . . . . . . . . 28 Infiltration and Drainage Controls . . . . . . . . . . 29 Slope Flattening . . . . . . . . . . . . . . . . . . . 29 Perched Beaches . . . . . . . . . . . . . . . . . . . . 29 Structures and Fills . . . . . . . . . . . . . . . . . 31 Structures and Vegetation . . . . . . . ... . . . . . . 31 THE DESIGN PROBLEM . . . . . . . . . . . . . . . . . . . . . 33 Functional Design . . . . . . . . . . . . . . . . . . . 33 Structural Design . . . . . . . . . . . . . . . . . . . 36 SHORE PROTECTION METHODS . . . . . . . . . . . . . . . . . . 65 Bulkheads . . . . . . . . . . . . . . . . . . . . . . . 65 Revetments . . . . . . . . . . . . . . . . . . . . . . 77 Breakwaters . . . . . . . . . . . . . . . . . . . . . . 96 Groins . . . . . . . . . . . . . . . . . . . . . . . . 110 Beach Fills . . . . . . . . . . . . . . . . . . . . . . 118 Vegetation . . . . . . . . . . . . . . . . . . . . . . 121 Perched Beaches . . . . . . . . . . . . . . . . . . . . 133 PROPRIETARY DEVICES AND SPECIALTY MATERIALS . . . . . . . . 135 OVERVIEW OF THE DESIGN PROBLEM . . . . . . . . . . . . . . . 139 Characterization of the Site . . . . . . . . . . . . . 139 Water Levels . . . . . . . . . . . . . . . . . . . . . 139 Wave Conditions . . . . . . . . . . . . . . . . . . . . 140 Selection of Devices . . . . . . . . . . . . . . . . . 143 3 TABLE OF CONTENTS (Continued) Page PERMIT REQUIREMENTS . . . . . . . . . . . . . . . . . . . . 145 OTHER HELP . . . . . . .. . . . . . . . . . . . . . . . . . . 147 Corps of Engineers Offices . . . . . . . . . . . . . . 147 State Coastal Zone Management Offices . . . . . . . . . 148 Other Sources of Information . . . . . . . . . . . . . 153 Suggested Reading . . . . . . . . . . . . . . . . . . . 154 GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . 161 LITERATURE CITED . . . . . . . . . . . . . . . . . .. . . . . 171 4 LOW COST SHORE PROTECTION a Guide for Engineers and Contractors INTRODUCTION The purpose of this report is to familiarize engineers and contractors with various established methods of low cost shore protection. It is written for the individual who is knowledgeable in general civil engineering design and construction, but not a specialist in coastal engineering or shoreline protection. This report can be used 'without other references, but many topics are discussed with only minimal detail, so some additional reading may be necessary to gain a better understanding of the text. The Suggested Reading section at the end of the report lists a full range of readily available books, reports, and publications that are recommended for additional background study. LOW COST SHORE PROTECTION In distinguishing between low cost and cheap, one should remember that practically any method of shore protection, if pro- perly implemented, is expensive. significant investments are required to achieve the durability needed to resist even small waves. Low cost simply means that the various measures are com- mensurate with the value of individual residential or commercial properties. The total cost of implementation will vary with the different alternatives, but in all cases, there should be a suit- able (and affordable) range of solutions. The methods described in this report are usually appropriate for use only in sheltered waters. That is, they are generally not intended for open coast sites where they would be exposed to the undiminished attack of large oceanic waves. Use of most of these structures in such areas is definitelV not recommended and entails a considerable risk of failure. THE SHORELINE EROSION CONTROL DEMONSTRATION PROGRAM From 1975 to 1980, the U. S. Army Corps of Engineers conducted a program to develop and demonstrate low cost methods of shore protection. This program was mandated by Section 54 of Public Law 93-251, the Shoreline Erosion Control Demonstration Act of 1974. Working with the Soil Conservation Service, the Corps desig- nated 16 demonstration sites throughout the Atlantic, Gulf, and 5 Pacific coasts, Alaska and the Great Lakes. These sites were chosen because they represented a broad cross section of shoreform. and environmental conditions. This would permit wide application of the results obtained to other sites located throughout the country. At each of these sites, various structures and kinds of vegetation were established to evaluate their effectiveness in the local environment. Twenty-one additional supplemental sites were also chosen where existing shore protection devices had previously been established by others. The devices at all 37 sites were intensively monitored over a period of months. Data that were collected included daily visual observations of wave heights and directions, quarterly surveys of beach and offshore profiles, quarterly color aerial photos, quart- erly sediment sampling and gradation analyses, and monthly site visits with ground level photos. SHORELINE PROCESSES Before developing a comprehensive solution for a client, it is first necessary to understand the coastal processes that are con- tributing to the erosion problem. The following sections present basic information about shoreline processes that will serve as a foundation for later discussions. These sections are not exhaus- tive in their depth of coverage and cannot replace detailed and widely accepted texts such as the Shore Protection Manual [U.S. Army Corps of Engineers (1977c)]. Wave Action While waves are always present on the open coast, they are not continuous in sheltered waters. Nonetheless., they are still the major cause of erosion in these areas. Several basic wave charac- teristics are important. The wave height is the vertical distance between the wave crest and trough, the period is the time (in seconds) it takes two successive wave crests to pass a stationary point, and the wavelength is the distance between successive crests (Figure 1). Using linear wave theory (the simplest case), these characteristics are given by the expressions; L = CT (1) where L = wavelength in feet, C = wave celerity (speed) in feet/second, and T = wave period in seconds; C = 21 tanh 2Ttd (2) 27E L ) where d = water depth in feet; 2 and g = acceleration due to gravity, 32.2 feet/second 6 WAVELENGTH WAVE CREST WAVE HEIGHT STILLWATER LEVEL WAVE TROUGH WAVE PERIOD IS. THE TIME REQUIRED FOR SUCCESSIVE CRESTS TO PASS A STATIONARY POINT. Figure 1 Characteristics of Waves 2 (_In d ) and L =-q-T tanh L (3) 2n As a wave moves through deep water (depths greater than one- half the wavelength), the celerity and wavelength remain essen- tially constant, because for d/L > 0.5 (deep water); the expression tanh [2nd/L] approaches unity. Therefore, since the period remains constant, the celerity and wavelength also do not vary. However, when a wave approaches the shallower water near the shore (where d/L <0.5), Equations (2) and (3) cannot be simplified by ignoring tanh [2nd/L]. From Equation (2), the celerity decreases with depth; the wave slows as it enters shallower water. The same is true with the wavelength, L, as can be seen from Equation (3), where it appears on both sides of the equation and an iterative solution is required. As the wave continues to move in shoaling water, its profile begins to steepen and its gently rolling shape changes to a series of sharp crests with intervening flat troughs. At some point, this process can continue no longer and the wave breaks at the shore. The break point is a function of the wave height, period, water depth and bottom slope, but as a first approximation, assume that the wave breaks when the height is about 0.78 times the depth. For example, a 5-foot high wave breaks in a water depth of about 6.4 feet. IILLWATE@R \@@@WA 7 Important wave properties are demonstrated when a train (series) of regular waves meets a solid barrier such as an offshore breakwater (Figure 2). Wave diffraction occurs when the waves pass the breakwater and wave energy is transferred along their crests to the quiet area in the shadow of the structure. This causes waves to form in the shadow zone that are smaller than in the adjacent unprotected zone. DIFFRACTION ZONE \ Small Waves) BREAKWATER UNPROTECTED ZONE (Large Waves) REFLECTION ZONE Crossing Waves) Figure 2 wave Diffraction and Reflection Wave reflection occurs on the offshore side of the breakwater. While waves passing the structure are diffracted, the portions striking the breakwater are reflected like a billiard ball from a cushion. If the structure is a smooth vertical wall, the reflec- tion is nearly perfect; and if the wave crests are parallel with the breakwater, the reflected and incident waves will reinforce each other to form standing waves twice as high as the incident waves. This could cause considerable bottom scour at the toe of, and offshore from, the structure. I f the waves approach at an angle, no standing waves will form, but the resulting water sur- face, with crossing wave crests, will be rough, and choppy. These short-crested waves could also cause, considerable bottom scour. The final important wave characteristic is evident when waves 8 break either on a beach or structure - The uprush of water after breaking is called runup and it expends the wave I s remaining en- ergy. The runup height depends on the roughness and steepness of the structure or beach and the characteristics of the wave. In general, increased roughness reduces runup. ,Sediment Transport The large variety of littoral (shoreline) materials include rock, boulders, cobbles, gravels, sand, silt, and clay. A number of classification systems have been developed to identify the'se materials, and typical scales of sizes are given in Figure 3. Rock characterizes cliff shorelines, such as along the coasts of northern California. Boulders are often present at the base of such cliffs because of rock fracturing and weathering. Cobbles and gravels are prevalent beach materials in the Pacific Northwest, Alaska, and the Great Lakes area. Sand, the most common shoreline material, is found in virtually all coastal areas. -Silts and clays generally occur on bluff shorelines or marshes, such as along the Great Lakes and various bays. Littoral materials are derived from the deterioration and erosion of coastal bluffs and cliffs; the weathering of rock mater- ials found inland and transported to the shore by rivers and streams; the disintegration of shells, coral or algae to form carbonate materials; and the production of organic material (gen- erally peat) by coastal marshes and wetlands. Failure or erosion of a bluff causes material to be deposited at the base. Waves sort this material and carry the fine-grained silts and clays offshore where they settle to the bottom. The original deposit is eventually reduced to sand and gravel fractions which form a beach. Eventually, if no other littoral material is carried to the site by waves, even the sand and fine gravel will disappear down the coast or offshore, leaving only coarse gravels behind. However, a new supply of material may be deposited on the beach by a fresh failure of the bluff, and the process begins again. In many cases, therefore, the littoral materials comprising beaches are often derived from erosion of the shoreline itself. Rivers and streams that carry sediments eroded from the inland land mass are a second source of littoral material, particularly during floods. Material from this source is predominantly smaller than sand, particularly for large rivers. These silts and clays are largely deposited far offshore. Smaller rivers that flow through sandy drainage areas may carry significant quantities of sand during floods. However, the total contribution of sand by rivers and streams is probably considerably less than from erosion of the shores themselves. Coral reefs, shells, and other plant or animal matter are a third material source. They gradually break and weather into 9 American Society for Colloids Clay Silt Fine Coarse Gravel Testing Materials Sand Sand American Association of Colloids Clay Silt Fine Coarse Fine medium Coarse Boulders State Highway Officials Sand Sand Gravel Gravel Gravel Silt very Fine Ve U.S. Department of Clay Fine Coarse Fine Gravel Coarse Gravel Cobbles Agriculture Sand Sand Sand Civil Aeronautics Clay Silt Fine Sand Coarse Sand Gravel Administration Unified Soil Classification (Corps of Engineers, Fines (Silt or Clay) Fine Sand Medium Coarse Fine Coarse Cobbles Department of the Army, Distinction Based On Plasticity Sand Sand Gravel Gravel and Bureau or Reclamation) 0 co 0 WIM T 0 0 U.S. Standard Sieve Sizes I I I Phi Scale Figure 3 Common Soil Classification Systems [After Winterkorn and Fang (1975)] carbonate sands which are, for instance, the primary components of beaches south of Palm Beach, Florida. Swamps, marshes, and coastal wetlands produce peats and other organic matter, also a source of littoral material. Too light to remain in place under continued wave action, they are ultimately washed offshore unless stabilized. Littoral materials are transported along the shore by wave action. Approaching from deeper water, the shoreward portion of a wave moves in progressively more shallow water than the section farther of fshore. This portion begins to slow, which causes the wave to bend (refract) until breaking at an angle to the beach. This creates considerable turbulence that temporarily suspends the bottom sediments and carries them up the foreshore (beach face) in the general direction of wave advance. The motion stops a short distance up the beach, and then reverses direction back down the slope. However, the downrush does not retrace the same path, but rather, moves directly down the foreshore in response to gravity. The next wave repeats the process, moving the material downdrift along the beach. Littoral transport occurs not only by rolling bedload, as above, but also by the movement of suspended sediment. The waves generate a longshore current that flows through the area where they break (breaker zone). Alone, it is generally too weak to move appreciable quantities of sediment; however, the turbulence from breaking waves suspends sediments that can then be moved downdrift by the longshore current. This sediment generally settles out within a short distance, but the next wave provides additional movement. Therefore, longshore transport is caused by the zig-zag movement of bedload up and down the beach, and the turbulence and action of the wave-induced longshore current. Water Level Variations The water surface elevation itself constantly changes with time. The stillwater level, or the water level with no waves present, changes because of three processes; astronomical tides, storms, and periodic lake level variations. Astronomical Tides. Tides are generated by the gravitational attraction between the-earth, moon, and sun, and are classified as diurnal, semidiurnal, or mixed. Diurnal tides have only one high and one low each lunar day. Semidiurnal tides have two approxi- mately equal highs and two approximately equal lows daily. Mixed tides are intermediate between them and typically have two highs and lows that occur each day. However, in contrast to semidiurnal tides, there is a large inequality, or difference in height, be- tween either successive high or successive low waters. (Figure 4). Most Atlantic coast tides are semidiurnal and the heights of suc- cessive highs or lows are approximately equal. Gulf and Pacific coast tides tend to be mixed, and in most cases, there is a dis- tinct inequality between successive highs or lows. 11 0 6 12 18 0 6 12 18 0 6 12 hours - 12 ft. I - I I -10 -Tidal Day -8 Tidal Period 6 -4 -2 -0-Datum --2 --4 ft. SEMIDIURNAL 0 6 12 18 0 6 12 18 0 6 12 hours -12 ft. Flo Iad Tide bb Tide -10 High Tide,,, -8 -6 -4 @40 - O-Daturn --2 --4 ft. Tide DIURNAL 0 6 12 18 0 6 12 18 0 6 12 hours -12 f t. Tidal Day igher High WateF -10 1 [-Tidal Period -8 Lo er Hi Water -6 Tidal Rise -4 -2 -0-Dotum --2 Tidal Range Higher Low Water Lower Low Water f t. I ---1- 1 1 1 1 , 1. 1 MIXED Figure 4 Types of Tides Wiegel 53)] rN H Pe,,od-, r Aote 12 In addition, the tidal range, or difference in elevation between the high and low waters, tends to fluctuate throughout the month. These tidal range variations are caused by changes in the distance between the earth and moon (perigean and apogean tides), the declination of the moon (equatorial and tropical tides), the declination of the sun, and the phase of the moon (spring or neap tides). (See GlossarV.) The tides are highest during spring, perigean and tropical tides and are particularly high when these are approximately in phase. Tides are also present on the Great Lakes, but they are small and not significant for practical problems of shore protection design. Some key tidal datums, shown on Figure 5, are important be- cause of their wide use. Not shown are datums for the Great Lakes, where all levels are ultimately referenced to the International Great Lakes Datum (see GlossarV). Each lake has a designated chart datum [Low Water Datum (LWD)] based on the IGLD. MHHW A A A A A A MHW It 11 It 11 11 It R A It I MSL A A A MTL MLW 11 If V_ V MLLW V V V 5 9 13 D A Y S Figure 5 Illustration of Tidal Datums [After Harris (1981)] Storm Ef fects. The passage of storms tends to increase the stillwater level through two principal mechanisms: atmospheric pressure effects, and stress caused by storm winds blowing across the water. Atmospheric pressure differences across a large water body cause a rise in the water level in the lower pressure area (inverse barometer effect). Water surface rises of one or two feet are common in niany areas under this effect. Enclosed water bodies (such as the Great Lakes) can also respond to storm forces by seiching. This occurs when storm winds or pressure effects drive the water surface higher at the downwind end of a lake. The passage of the storm front releases this water, and causes a periodic oscillation within the basin that will con- tinue for several cycles. On the Great Lakes, seiching is most pronounced on Erie, because its long axis more closely matches predominant storm tracks and its relatively shallow depths lead to higher storm setup levels. 13 Wind stress also tends to drive the water on shore to above normal heights (storm setup). This continues until the tendency for the water to flow back to its normal level balances the forces driving it on shore. The high winds associated with storms also generate large waves, with their effects being felt in addition to the elevated storm surge levels. Lake Level Variations. Water levels in the Great Lakes are also subject to periodi-C changes. Records of lake levels dating from 1836 reveal seasonal and annual changes which are due to variations in precipitation annually, and from year to year. Lake levels (particularly Ontario and Superior) are also partially con- trolled by regulatory works operated jointly by Canadian and U. S. authorities, and these may result in minimizing lake level changes. Average monthly lake level elevations showing data for the past calendar year and present year-to date, and a forecast for the next six months, are published monthly by the U. S. Army Corps of Engi- neers, Detroit District (see Other Help Section). 14 THE EROSION PROBLEM THE IMPORTANCE OF SHOREFORM The land-sea boundary in characterized by many shapes and con- figurations. Geologists have devised elaborate classification systems to describe these various features. For the purposes of understanding basic shoreline processes and for designing appro- priate corrective measures, however, it will only be necessary to informally classify shorelines as either bluffs, low erodible plains (including sandy beaches), or wetlands. Many shorelines, of course, contain two or even all three of these basic features. Bluff Shorelines A distinction will be drawn between bluffs and cliffs. Cliffs will be defined as shorelines composed of relatively sound rock. These rarely undergo severe or sudden erosion problems, but may experience slow, steady retreat over a long period of years. Such shorelines generally cannot be treated with low cost solutions because available alternatives are usually less durable than the cliff rock itself. On the other hand, bluffs are composed of sediments such as clay, sand, gravel, or erodible rock and erosion problems are often present along these kinds of shorelines. The most prevalent causes of bluff erosion are toe scour by wave action, surface runoff, and drainage and infiltration problems that lead to slope stability failures. An important factor to consider is whether a bluff is high or low. While no precise definition is possible, many writers have described high bluffs as those being greater than 20 or 30 feet high or, using a different criterion, a low bluff might be clas- sified as one that can stand alone, while a high bluff must either be protected, or otherwise treated, to remain standing. In evaluating conditions at a site, it is necessary to deter- mine which of the above processes is primarily responsible for the erosion problem. Slope stability problems that are not aggravated by toe undercutting should be treated using established civil engineering techniques of slope stability analysis and design. Typical solutions could include vertical or horizontal drains, slope regrading and terracing, surface drainage controls, elimi- nation of unnecessary surcharges at the top of the slope, and buttressing the toe. . Wave action at the toe which undermines the bluf f can be treated using a low cost shore protection device. Important fac- tors in selecting a device will include the relative steepness of the offshore bottom slope, and whether a sand beach is present at the base of the bluff. These are often derived from bluff materi- als that have fallen from above, and they provide a buffer against 15 normal wave action and may serve as a suitable foundation for various protective devices. During severe wave activity, however, waves can reach the bluff itself and erode or undercut the toe. Depending on the strength and characteristics of the bluff materi- als, this may cause the bluff to fail in a relatively short time. The slope of the offshore bottom is also important. I f the offshore slopes are steep, deep water is closer to shore, larger waves can reach the bluff, and maintenance of a protective beach is more difficult. Conversely, flat offshore slopes inhibit heavy wave action at the bluff and provide for potentially better protec- tive beaches. Low Erodible Plains and Sand Beaches These are the most common shoreforms throughout most areas of the United States. They are primarily composed of sands and grav- els that gently rise from the water's edge and seldom attain a height of more than five to ten feet above the stillwater level. Figure 6 is a definition sketch of an ideal ized beach profile. Waves approach from offshore, finally breaking and surging up the foreshore. Above the foreshore, the profile flattens considerably to form a broad berm which is not reached by normal wave activity. The beach berm will sometimes be backed by a low scarp leading to a second berm and eventually to a bluff or sand dune. The profile will reach some equilibrium shape in response to normal water levels and wave activity. This equilibrium will be disturbed and erosion will begin if the long-term water level rises or predominant wave heights increase. For a water level - NEARSHORE(littoral) ZONE UPLANDW- BEACH (extends through breaker zone) BACKSHORE __F70RE- OFFSHORE SHORE BLUFF or RM ESCARPMENT SURGE BEACH SCARP BREAKERS HIGH WATER LEVEL LOW WATER LEVEL CREST OF BERM----/ PLUNGE POINT BOTTOM Figure 6 An Idealized Beach Profile [After U.S. Army Corps of Engineers (1977c)) 1.6 rise, a new equilibrium profile will eventually form with the same shape as the old, but shifted landward and upward. Similarly, increased wave activity causes a nearshore bar to grow as the beach erodes. Eventually, as this bar grows and the depths of water decrease, the larger waves will break farther offshore. This weakens their attacks on the beach and equilibrium is restored. At open coast sites, the return to normal water levels and waves will initiate a healing process that may return the profile to essentially its initial position. This is because the flat swells tend to move sand back to the beach from the nearshore bar. At sheltered sites, however, these swells are not present, so the healing process never occurs, and storm-caused erosion losses tend to be permanent. Changes in the sediment supply from updrift will also cause movement of the profile. A decrease in the supply will cause the beach to erode, and the profile will retreat landward, while still maintaining the same shape. Conversely, an increase in the supply will cause accretion and the profile will advance toward the water. Wetlands and Marshes Although they are treated separately in this section, wetlands and marshes usually occur in combination with sand beaches or low erodible plains. For federal regulatory purposes, wetlands are defined as: "Those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and under normal circumstances do support, a pre- valence of vegetation typically adapted to life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas." [U. S. Army Corps of Engineers (1977b)] Marsh plants are primarily herbaceous (lack woody stems) and include grasses, sedges and rushes. The species present depend on location and whether the marsh is low (regularly flooded) or high (irregularly flooded). Until recently, marshes were considered undesirable and regu- larly drained and filled for new development or agriculture. Their value has now been recognized as an important environmental re- source, but they also protect the shore by absorbing the energy of approaching waves and trapping sediment that is being carried along by currents. These shore protection qualities are particularly important when the marsh fronts a sandy beach or other area where erosion is to be prevented. In that case, the marsh provides a front line of defense for the shore. While it may not provide full protection, it may, at least, partially dampen wave action and allow for less massive and costly backup protection. 17 THE CAUSES OF EROSION Wave Action Wave action is the most obvious cause of shoreline erosion. Littoral Material Supply Stable shorelines are in a state of dynamic equilibrium. Waves keep the littoral materials in constant motion in the down- drift direction, and the shoreline remains stable provided there is an equal supply of material from updrift. When the updrift supply is deficient, the shoreline erodes. A substantial portion of the littoral material supplied to shorelines is the result of updrift erosion. If large amounts of the updrift shoreline are suddenly protected, material is lost to the littoral system. This decreases the supply to the downdrift shore, resulting in erosion problems unless that land is also protected. Determining the longshore transport direction is sometimes necessary. This is usually a difficult task because it depends on wave directions that can vary considerably with the seasons. Summer winds (and waves) may be from one predominant direction, while winter storm winds may be from an entirely different quad- rant. When the winds and waves change direction, the transport direction also changes (transport reversal). The gross longshore transport rate is the quantity of sand (usually in cubic yards per year) that moves past a fixed point in either direction. The net longshore transport rate is the quantity that moves in the predominant direction minus the quantity that moves the other way. The net transport rate is specified by both quantity -and direction (e.g., 10,000 cubic yards per year to the east). Transport rates are important when considering accretion .devices such as breakwaters and groins because it is necessary to judge the effects of device construction on the littoral system, particularly with respect to potential downdrift damages. A pre- cise estimate will not usually be possible, but it may be feasible to examine similar structures or harbor works that have been con- structed in the past for evidence of accretion over known periods of time. If nothing else, this should reveal the predominant transport direction and a crude measure of the possible transport rate. This should be an acceptable level of precision for small scale, low cost devices. Slope Stability Slope stability analysis is covered in standard geotechnical engineering textbooks [e.g., Lambe and Whitman (1969) and Winter- 18 korn and Fang (1975)]. Major stability problems are most likely at high bluff shorelines where the heights are 20 feet or more. Except where toe protection is needed, slope stability problems on high bluffs tend to be beyond the range of low cost solutions. 19 A LOOK AT THE OPTIONS Three basic choices are possible in response to an erosion problem: no action, relocation of endangered structures, and posi- tive corrective measures. The latter includes devices that di- rectly armor the shore, those that intercept and dissipate wave energy, and those that retain the earth slopes against sliding. Each alternative requires an evaluation of the planned land uses, money and time available, and other effects that may result from the decision. NO ACTION This is a decision-aid that can be used to evaluate different alternatives. Because even low cost solutions can require sub- stantial investments, it is preferable to closely estimate poten- tial losses using this alternative, particularly if no dwellings are directly threatened, and only undeveloped land or inexpensive structures are in danger. Also, erosion problems are sometimes caused by temporary factors (e.g., unusually high Great Lakes levels) that may abate. The resulting erosion, therefore, may slow before any action is taken. This could eliminate the immediate need for protective devices, or it could mean choosing a smaller scale, less expensive, device. RELOCATION In most cases, some action is necessary. It may be less expensive to relocate endangered structures than to invest in shore protection. Relocation can be to an entirely different site or it can be a setback farther from the water at the present site. The required setback must be carefully evaluated because the consid- erable expense of moving a building could be wasted if the setback is insufficient. The first step is to evaluate the long-term erosion rate. This is difficult because reliable historical data on past shore- line positions is often lacking. Possible sources of data include a time sequence of aerial photographs or shoreline maps. If the property owner has occupied the site for many years (say 25 or more), and has observed slow shoreline retreat during that time, the annual erosion rate could be approximated by dividing the total amount of retreat by the number of years of observation. For instance, if the shoreline steadily receded 300 feet in 30 years, the estimated average erosion rate is about 10 feet/year. A set- back of 100 feet could produce an additional 10 years of life for a structure, provided erosion continues at the same rate. Conversely, if the shoreline was stable for years and suddenly retreated 300 feet in only 5 years, relocation on the same site may be risky and not generally advisable unless considerable setback room is available. 21 BULKHEADS AND SEAWALLS The terms bulkhead and seawall are often used interchangeably. In a strict sense, however, bulkheads are retaining walls whose primary purpose is to hold or prevent sliding of the soil while providing protection from light-to-moderate wave action. Seawalls, on the other hand, are structures whose primary purpose is to protect the backshore from heavy wave action. Their massive size generally places them beyond the low cost range. Also, they are not generally needed in sheltered waters where large waves are not generated (except perhaps in the Great Lakes). Bulkheads can be used to protect eroding bluffs by retaining soil at the toe, thereby increasing stability, or by protecting the toe from erosion and undercutting. They are also used for reclama- tion where a fill is needed in advance of the existing shore. Finally, bulkheads are used for marina and.other structures, where deep water is needed directly at the shore .(Figure 7). Construction of a bulkhead does not insure stability of a bluff. If a bulkhead is placed at the toe of a high bluff steep- ened by erosion to the point of incipient failure, the bluff above the bulkhead may slide, burying or moving the structure toward the water. To increase the chances of success, the bulkhead should be placed lakeward of the bluff toe, and if possible, the bluff should be graded to a flatter, more stable slope. Bulkheads protect only the land immediately behind them and offer no protection to adjacent areas up- or downcoast, or to the fronting beach. In fact, their vertical faces reflect wave energy which may cause increased scour and could lead to a loss of any existing fronting beach. If the downdrift beaches were previously supplied by erosion of the land now protected, they may erode even more quickly. If a beach is to be maintained adjacent to a bulk- head, additional structures such groins or detached breakwaters may be required. Bulkheads may be either cantilevers or anchored (like sheet piling), or gravity structures (like sand-filled bags). Cantilever bulkheads require adequate embedment to retain soil, and are used where low heights are sufficient. Toe scour reduces their effec- tive embedment and can cause failure. Anchored bulkheads are usually used where higher structures are needed. They also require adequate embedment (although less than cantilever bulkheads) to function properly, but they tend to be less susceptible to toe scour. Gravity structures eliminate the need for heavy pile driving equipment and are often appropriate where subsurface conditions hinder pile penetration. However, they require strong foundation soils to adequately support their weight, and they normally do not sufficiently penetrate the ground to develop reliable soil resis- tance on the offshore side. Therefore, they depend primarily on shearing resistance along the base of the bulkhead to support the 22 RETAIN BLUFF LAND RECLAMATION DOCKING STRUCTURE Figure 7 Uses of Bulkheads applied loads. Gravity bulkheads also cannot prevent rotational slides in materials where the failure surface passes beneath the structure. Their use, therefore, is generally limited to rela- tively low heights where their cost is comparable to cantilever sheet pile bulkheads. 23 REVETMENTS A revetment is placed on a slope to protect it and adjacent uplands against scour (Figure 8). It depends on the underlying soil for support, so it must be built on a stable slope. An un- stable bank must first be properly graded before construction. Fill material, when needed to achieve a uniform grade, must be adequately compacted. OVERTOPPING APRON ARMOR LAYER M H W TOE MLW PROTECTION GRADED STONE FILTER Figure 8 Typical Revetment Section Revetments protect only the land immediately behind them and provide no protection to adjacent areas. Erosion may continue on adjacent shores, and near the revetment may be accelerated by wave reflection from the structure, although not as seriously as with vertical-faced bulkheads. Also, the downdrift shore may experience increased erosion if it was formerly supplied with material eroded from the now protected area. If a beach is to be maintained in front of a revetment, additional structures such as groins or detached breakwaters may be required. A revetment consists of an armor layer, filter and toe. The armor must resist the waves, and the slope must be sufficiently flat to provide stability. Typical armor materials include quarry- stone and 'various concrete blocks. The filter supports the armor against settlement, provides drainage of groundwater through the revetment, and prevents the retained soil from being washed through the armor layer by waves or groundwater seepage. Toe protection prevents displacement of the seaward edge of the revetment. Overtopping by green water (not white spray) may cause erosion at the top of the revetment. Problems from overtopping can be minimized by choosing a structure height that is greater than the 24 expected runup height, or by providing an overtopping apron at the top of the revetment. Flanking is another potential problem that can be prevented by tying each end of the revetment into adjacent shore protection structures or the existing bank. However, if the bank recedes, the ends will have to be periodically extended to maintain contact. BREAKWATERS Breakwaters are constructed offshore to dissipate the energy of approaching waves and form a protected shadow zone on their landward sides. (Figure 9). The ability of waves to transport sediment is a function of the wave height-squared, so a relatively modest decrease in incoming wave heights can have a major effect on sediment transport. For instance, if incoming waves are reduced to 70% of their original height after passing a breakwater, their ability to move sediment will decrease to 0.70 x 0.70 or 49% of their original capacity. Therefore, longshore-moving littoral drift will tend to accumulate behind the structure. The ability of a breakwatpr to trap sand is a function of its distance offshore, length parallel to shore, porosity, and spacing (where more than one breakwater is used). ORIGINAL SHORELINE DOWNDRIFT EROSION 1_@RESULTING SHORELINE -.Ole (NATURAL ACCRETION) APPROACHING WAVE CRESTS BREAKWATER Figure 9 Plan View of a Breakwater """rM 0 C @Al 1A1 A 'I 25 If accretion continues until the breakwater is joined to the shore, the resulting system would act as a large groin that would totally block the sand supply to the downdrift beach. This could cause significant erosion damages. Therefore, the area landward of the breakwater.should be partially filled with sand after construc- tion is completed. This may allow sand to continue past the struc- ture and on to the downdrift beach without causing serious erosion problems. Breakwaters are either fixed or floating. Fixed breakwaters are large masses of heavy material that rest on the bottom. Float- ing breakwaters are constructed of buoyant materials such as logs, hollow concrete boxes and scrap rubber tires. The latter are most popular because of their durability and ready, no-cost availa- bility. Floating breakwaters are generally effective in sheltered waters where short-period (less than five seconds) waves are dis- sipated as they pass floating structures. Such waves have short lengths that may be less than the width of the breakwater. GROINS Groins are constructed perpendicular to shore and extend, finger-like, out into the water. Used singly or in groups known as groin fields, they trap sand or retard its longshore movement (Figure 10). Sand tends to accumulate on the updrift side of a WAVE CRESTS NO rE. rhe resulting shoreline will gradually transition to Ineel the original shoreline on either side of the groin field BREAK POINT FOR LARGE WAVES X*M RESULTING SHORELINE (pre-f illed) ORIGINAL RESULTING SHORELINE SHORELINE (natural accretion) Figure 10 Effects of Groins 26 groin while erosion occurs downdrift. This will cause the shore- line to rotate and aline itself with the crests of the incoming waves, gradually decreasing the angle between the waves and the shore. In turn, the longshore transport rate will decrease and the shoreline will stabilize. The fillets of sand that collect on the updrift sides of the groins act as protective buffers. Storm waves attack these accumulations first, before reaching the unprotected backshore. Without the sand fillets, groins cannot protect the shoreline from wave action, nor are they effective where the waves approach perpendicular to shore. Groin installations also require an ade- quate sand supply and are not effective where the littoral mater- ials are finer than sand. Silts and clays tend to move in suspen- sion and are not retained by groins on the beach. When a groin is first built, the sand trapped on its updrift side is no longer available to downdrift beaches and erosion may result. When the updrift fillet is completely formed, the sand will pass around or over the groin to the downdrift shore, but at a slower rate than before it was built. If erosion of the downdrift shore is unacceptable (it usually is), an alternative is to build more than one groin and fill the area between with sand. This minimizes the downdrift damages and limits the erosion at the groin's shoreward end. Groins can be built either high or low with respect to the existing beach profile. High groins effectively block the supply of sand to downdrift beaches, provided sand cannot pass through them. Low groins, built to be overtopped by waves either during storms or at a given tide level, permit sand to pass over them and nourish downdrift beaches. A groin's length must be sufficient to create the desired beach shape while still allowing sand to pass around its outer end. If a groin extends seaward past the breaker zone, the sediment moving around the structure may be forced too far offshore to return to the adjacent downdrift beach. If it is too short, it may not trap enough sand to provide the desired beach. The correct spacing of individual groins within a field is often difficult to determine and is a function of their length and the desired final shoreline shape. If groins are too far apart, excessive erosion can occur between them. If spaced too closely, they may not function properly. This is particularly true for long groins where sand passing around their ends must follow a curved path back to the beach. If the groins are too close toqether, the sand will be unable to reach the beach before it is again forced seaward by the next downdrift groin. A groin must be built to resist wave forces, currents, the impact of floating debris, and earth pressures created by the dif- ference in sand levels on both sides. As with other structures, 27 groins must resist toe scour, and must be constructed to prevent failure due to flanking (erosion at their landward end). BEACH FILLS Beach fills are quantities of sand placed on the shoreline by mechanical means, such as dredging from offshore deposits or over- land hauling by trucks. The resulting beach provides some protec- tion to the area behind it and also serves as a valuable recrea- tional resource. The beach fill functions as an eroding buffer zone. Its useful life will depend on how quickly it erodes; a rapid succes- sion of severe storms can completely eliminate a new fill in a short time. The owner must then be prepared to periodically re- nourish (add more fill) as erosion continues. Beach fills gener- ally have relatively low initial costs but periodic maintenance costs needed for adding new fill. VEGETATION A planting program to establish desired species of vegetation is an inexpensive approach to shoreline protection and erosion control. Depending on where stabilization is desired, species from one of two general groups should be selected to insure adequate growth. Found on parts of shorelines flooded periodically by brackish water, species of grasses, sedges, and rushes occur in marshes of moderate to low energy shorelines. once extensive and widely dis- tributed, marsh areas were viewed in the past as useless and were subjected to filling and diking. However, their destruction has lessened as their importance in the ecosystem and to shoreline protection has been realized. upland species (shrubs and trees but particularly grasses) are especially adapted to growing in the low-nutrient, low-moisture environment of the higher beach elevations, where they are subject to abrasion by windblown sand particles. Used to trap sand and stabilize the beach, upland vegetation also improves the beauty of a shoreline, prevents erosion during heavy rain, diminishes the velocity of overland flow, increases the soil's infiltration rate, and provides a habitat for wildlife. Even though vegetation provides significant help in stabiliz- ing slopes and preventing erosion, vegetation alone cannot prevent erosion from heavy wave action or prevent movement of shoreline bluffs activated by groundwater action. In these instances, struc- tural devices augmented with vegetation are recommended. The effectiveness of vegetation is also limited by character- istics of the site. For instance, the site requirements which 28 determine the effectiveness of 'a tidal marsh planting include: elevation and tidal regime, which determine the degree, duration, and timing of plant submergence; slope of the site; exposure to wave action; type of soil; salinity regime; and oxygen-aeration times. Plants which are specially adapted for higher beach eleva- tions must tolerate rapid sand accumulation, flooding, salt spray, abrasion by wind-borne sand particles, wind and water erosion, wide temperature fluctuations, drought, and low nutrient levels. Appro- priate species also vary with geographical location, climate, and distance from the water (vegetative zone). INFILTRATION AND DRAINAGE CONTROLS Infiltration and drainage controls are often needed to achieve stability along high bluff shorelines. Although many factors lead to slope stability problems, the presence of groundwater is one of the most important, since the majority of slope failures and land- slides occur during or after periods of heavy rainfall or increased groundwater elevations. Infiltration controls prevent water from entering the ground, while drainage controls remove water that is already present in the soil. Infiltration can be controlled by appropriate ditches and swales, and by sealing the ground surface. Surface cracks that develop when a slope begins to f ail can be an easy path for water to enter, exert hydrostatic pressures, and lead to further insta- bility. Such cracks should be promptly filled with compacted, relatively impermeable soil (preferably clay) to reduce the poten- tial for such detrimental effects. Drainage of the subsurface can be accomplished using vertical or horizontal drains. Standard design techniques and methods are described in civil engineering references such as Winterkorn and Fang (1975). SLOPE FLATTENING A bluff slope may be flattened to enhance its stability when adequate room exists, and there is no interference with the desired land use. Freshly excavated slopes should be planted to prevent erosion from surface runoff. It may also be necessary to build a revetment or bulkhead at the toe of the slope to protect against wave action. PERCHED BEACHES A perched beach (Figure 11) combines a low breakwater or sill and a beach fill perched, or elevated, above the normal level. 29 SPLASH APRON MHW ROCK SILL BEACH FILL FILTER CLOTH CROSS- SECr101V 4-A MHW BEACH FILL ROCK SILL PLAN VIEW Figure 11 Perched Beach This alternative provides a broad buf fer against wave action while offering a potentially excellent recreational site. The sill can be constructed of various materials, but it must be impermeable to the passage of the retained beach sand by using, for instance, a filter cloth behind and beneath the structure. The cloth prevents the fill from escaping through any large voids in the sill and also stabilizes the structure against settlement. While a graded stone core could also be used in a rock sill in place of filter cloth, the limited height of such sills generally precludes use of multi- layered structures of this kind. The figure also shows a splash apron which is provided to prevent scour and erosion of the beach fill from overtopping waves. Al 30 Perched beaches can be provided where offshore slopes are mild enough to permit the use of a sill in shallow water at a reasonable distance from shore. STRUCTURES AND FILLS In addition to perched beaches, fills can also be incorporated in groin systems and with breakwaters. in fact, auxiliary fills are almost mandatory in most cases, otherwise serious erosion problems can occur downdrift. STRUCTURES AND VEGETATION While vegetation is one means of controlling shoreline ero- sion, its most serious deficiency is its restriction to areas of limited fetch because it cannot become established in heavy wave environments. Vegetation can be used in areas experiencing con- siderably heavier wave activity, however, if it is placed in the shadow of a structure such as a breakwater. The use of temporary structures is particillarly appealing because they provide protec- tion while the plants need it, and can then be removed later when the plantings have matured. 31 THE DESIGN PROBLEM FUNCTIONAL DESIGN Shoreform Compatibility Certain approaches are better suited to particular shoreline configurations than others. It is important to choose a method appropriate to the dominant shoreform at the site. Bluff Shorelines. The no action alternative can be appro- priate for blufFs---slr-nce it does not disrupt natural shoreline pro- cesses and requires no investment for protective structures. Eventually, however, the property may be totally destroyed by ero- sion. While relocation does not disrupt shoreline processes, and it can permanently eliminate any threat to buildings, it can cost as much as or more than a protective structure. Bulkheads are ideally suited, either for full-height retention of low bluffs, or as toe protection for high bluffs. Constructed of readily avail- able materials and easily repaired if damaged, they are parti- cularly useful where offshore slopes are steep. They can, however, induce toe scour and loss of beach material. Revetments are mar- ginally effective in bluff situations. Low bluf fs that can be flattened to a stable slope may be effectively protected by revet- ments, but high bluffs generally cannot be regraded. Revetments can protect the toes of high bluffs, either alone, or in conjunc- tion with another device. Breakwaters reduce wave energy reaching the bluff but do not provide positive toe protection. They may build or maintain a beach (if an adequate sand supply exists) which provides some protection against normal waves, but would be inef- fective against storm waves. Use of breakwaters generally requires gentle offshore slopes. Groins protect only to the extent they can build or hold a beach. since they require a sand supply, they would not work in an area of clay or silt bluf fs unless sand were imported. Beach fills provide some protection against normal wave action but would be ineffective during storms. Vegetation would provide little protection until well established and even then, does not positively protect against large storm waves. Drainage controls are mandatory if groundwater adversely affects slope sta- bility. However, they provide no toe protection and can be expen- sive. Slope flattening provides a permanent solution for slope stability problems, but does not protect against continued wave action. It also requires adequate room at the top of the bluff for the slope. A perched beach would protect against normal waves but would be ineffective during storms. A combination approach can be the best solution. For instance, drainage controls should be used as needed, possibly with slope flattening. Toe protection could be provided with a revetment and a fronting sand beach to provide additional protection (provided offshore slopes are mild). Vegeta- tion planted on the regraded slope would prevent erosion from runoff,, and other species could be used to stabilize the beach fill. Sand Beaches. The no action and relocation alternatives are applicable as they were for bluffs. Bulkheads are generally inap- 33 propriate unless an elevated featurej, such as a promenade or parking lot, is needed. Vertical bulkheads induce toe scour and wave reflections, and could cause erosion of the beach fronting the bulkhead. Revetments are better for protecting features directly behind the beach since they absorb wave energy better and are more flexible when settlement occurs. They have an adverse aesthetic effect on the beach, however, and they can limit use or access to the shore. Use of revetments by a single landowner is often a problem because they are subject to flanking. Breakwaters are also well suited because they trap and hold sand moving along-, on- or offshore. They can cause extensive downdrift damages, however, because the trapped sand cannot reach adjacent beaches. They are also expensive to build. Groins can effectively build beaches on their updrift sides but can also cause accelerated downdrift ero- sion. Their functional behavior is complex and difficult to pre- dict. Beach fills retain the natural form and character of the beach and enhance its recrdational potential. Local sources of suitable sand are not always available, however, and fills require periodic renourishment. Vegetation, effective in many sheltered areas, has low initial costs and enhances the natural appearance and beauty of the shoreline. Unfortunately, foot and vehicular traffic damage plantings. Drainage controls and slope flattening are not applicable. Perched beaches can be used in some areas where fills alone would be too large to be economical, or where larger wave action is a problem. Combination approaches are often excellent, such as a perched beach that is further stabilized by vegetation. Wetlands. Structures built near wetlands are usually placed at a low bluf f or beach behind the marsh. For protection of the marsh itself, vegetation is the only appropriate alternative. To assist in establishing plantings, however, small temporary break- waters may be required. Beach fills or perched beaches may also be used to provide , a suitable substrate for planting in some areas. Applicability to Shoreline Uses Some methods lend themselves more readily than others to particular shoreline uses. It is important to choose a method that performs its function and does not interfere with the planned use of *the shoreline. No action obviously does not enhance shoreline uses, although continued erosion may have an adverse impact. Relocation involves similar considerations. Bulkheads create an access problem unless stairs are provided. Vertical structures may also cause wave reflections that can erode the remaining beach material. Bulkheads are necessary when some water depth for boat- ing activities is needed at the shore. Revetments of randomly placed rough stone may hinder access to the beach. Smooth struc- tures, such as concrete blocks, cause less difficulty for walkers. Breakwaters provide an area sheltered from waves, but they can hinder circulation and cause water quality problems. Beaches built behind breakwaters have enhanced recreational potential. Rough stone structures may provide an improved habitat for certain fish 34 species but may be hazardous to climbers. High structures may also intrude on the view of the water and be aesthetically undesirable. Groins may hinder travel along the beach, but any sand they trap improves the beach conditions. Beach fills enhance recreational uses of the shore, but increased turbidity during construction can temporarily harm certain fin and shellfish species. Vegetation greatly improves the natural habitat but hinders other uses of the beach because traffic through the plantings must be restricted. Drainage controls have little impact on shoreline uses and slope flattening reduces the available land at the shore. Perched beaches provide a recreational beach. A vertical sill may 'pose a hazard to bathers because of the sudden step to deeper water, but it may provide improved access for fishing. A rock sill may pro- vide a natural habitat for fin and shellfish and may not be as hazardous to bathers. Conditions in the General Area Conditions in the local area can strongly influence the selec- tion of an alternative. One of the most important considerations is the possible effects on downdrift properties. Accretion devices (breakwaters and groins) trap sand moving along the beach and tend to starve the downdrift shoreline. If this would cause damages to neighboring properties, the area behind the breakwater or updrift from the groin must be partially filled so that littoral material bypasses the structure, and downdrift damages are avoided. shoreline composition is also important. Accretion devices do not function in areas where little sand is in transit because they do not sufficiently calm the water to permit settlement of silts and clays. Slopes and soil composition are also important for determining appropriate plant species. Finally, climatic and other environmental conditions must be considered. Plant species obviously must be planted where the climate permits survival and growth. Salinity is critical for many species which can only tolerate changes of salinity within a narrow band. Warm salt water more easily corrodes steel and other metals than cold fresh water. Warm salt water is also the habitat of marine borers that attack submerged timber structures. On the other hand, fresh water lakes freeze in the winter, subjecting structures to large forces and abrasion from ice sheets. In some areas this may require more sturdy construction than would be required for resisting wave action at the site. Summary The factors relating each available alternative to shoreform and shoreline use are summarized on Tables 1 and 2. 35 Table METHODS APPLICABLE TO VARIOUS SHOREFORMS Alternative* High Bluffs Low Bluffs Beaches Wetlands No Action Rarely Rarely Rarely Rarely Relocation Sometimes Sometimes Sometimes Sometimes Bulkheads Usually Almost always Sometimes Rarely Revetments Sometimes Almost always Almost always Rarely Breakwaters Rarely Rarely Almost always Sometimes Groins Almost.never Almost never Almost always Almost never Beach Fills Almost never Almost never Almost always Rarely Vegetation Almost never Almost never Sometimes Almost always Infiltration and Drainage Controls Almost always Usually Almost never Almost never Slope Flattening Rarely Usually Almost never Almost never Perched Beaches Rarely Rarely Almost always Sometimes Applicability is for the alternative used alone in the given situation. Combination devices are not included. Table 2 COMPATIBILITY OF ALTERNATIVES WITH SHORELINE USES Alternative Strolling Bathing Fishing Boating No Action Sometimes Sometimes Usually Usually Relocation sometimes Sometimes Sometimes Sometimes Bulkheads Usually Sometimes Almost always Almost always .Revetments Usually sometimes Usually Usually Breakwaters Almost always Almost always Almost always Usually Groins Usually Almost always Almost always Usually Beach Fills Almost always Almost always Usually Almost always Vegetation Almost never Almost never Almost always Rarely Infiltration and Drainage Controls Almost always Almost always Almost always Almost always slope Flattening Almost always Almost always Almost always Almost always Perched Beaches Almost always Almost always Almost always Usually STRUCTURAL DESIGN If the chosen alternative involves construction of a physical shore protection device, several key problems must be resolved before an adequate structural design is completed. The first step is an evaluation of the potential water level and design wave height at the site. Other considerations include toe protection, filtering, flank protection, structure height, and various environ- mental factors. 36 Water Levels A design water level must be determined before the wave height used to design structures can be found. In tidal waters, the elevation of the mean spring or diurnal tide is a sufficient star- ting point for low cost protection. Table 3 is reproduced from Tide Tables published by the National ocean Survey (See Water fe__Veli___1T_nthe OTHER HELP Section). For instance, at Station 37, 6R-ford, Maryland, the mean tide range is 1.4 feet, the spring range is 1.6 feet, and the mean tide level is +0.7 feet above chart datum (MLW). The average spring tide, therefore, is +1.5 feet above MLW (Figure 12). An increment should be added to account for storm setup effects. Local experience should dictate, but values of two or three feet are probably reasonable for storm setup. Attention should be drawn to the use of Mean Low Water (MLW) as datum in the previous discussion. This has been the datum used by the National Ocean survey in the past for east coast navigation charts. In the future, however, the NOS will begin to adopt Mean Lower Low Water (MLLW) as datum for all nautical charts in the United States. This change will occur gradually as charts are periodically revised and reissued. On the Great Lakes, the Monthly Bulletin of Lake Levels for the Great Lakes (see Water Leve_ls-@1_nthe Other Help Sec on) sum- i-ar-ii-eswat-e-F-Tevels for the previous year and the current year to date, as well as projected lake levels for the next six months. For each lake, a curve is also given for the long-term average lake level (1900 to the present) (See Figure 13). A suggested design water level is the greater of (a) the water level midway between the long-term average and the recorded maximum average monthly water level or (b) the highest monthly water level that has oc- curred during the preceding year. For instance, on Lake Michigan, the highest average water levels occur in July when they are about 2.0 feet above chart datum (576.8 feet). (Low Water Datum (LWD) is +576.8 feet IGLD for Lake Michigan.) The maximum observed monthly water level for July on Lake Michigan was observed in 1974 at +4.2 feet. A water level midway between them is +3.1 feet. The maximum observed monthly water level during the previous year was +3.0 feet, so the chosen water level should be the greater of the two or +3.1 feet (579.9 feet). Storm setup or seiche values should be added to obtain a final water level. Figure 14 contains suggested values from Help Your- self [U. S. Army Corps of Engineers (1978d)] superimposed on a map of the Great Lakes. The design lake level, therefore, will be the sum of the lake level found in the previous step and the storm setup value. Wave Heights Waves at a site are generated either by wind action or moving vessels. At most locations, however, wind action is more critical 37 POSITION DIFFERENCES RANGES No. PLACE Time Height Mean Tide Lot. Long. Mean Spring Level . I . I feet feet feet VIRGINIA - Continued Chesapeake Bay, Eastern Shore Con. N. W. on HAMPTON ROADS, p.88 Time meridian, 75'W. 1959 Occohannock Creek ------------------- 37 33 75 55 +2 02 +2 32 -0.8 0.0 1.7 2.0 0.9 1961 Pungoteague Creek ------------------- 37 40 75 50 +2 22 +2 37 -0.8 0.0 1.7 2.0 0.8 1963 Onancock, Onancock Creek ------------ 37 43 75 45 +2 52 +3 09 -0.7 0.0 1.8 2.2 0.9 1965 Watts Island--7 --------------------- 37 48 75 54 +2 59 +3 02 -0.9 0.0 1.6 1.9 0.8 1967 Tangier Sound Light ----------------- 37 47 75 58 +2 51 +2 48'*0.64 *0.64 1.6 1.9 0.8 1969 Muddy Creek Entrance ---------------- 37 51 75 40 +3 14 +3 43 -0.3 0.0 2.2 2.6 1.1 MARYLAND Chesapeake Bay, Eastern Shore 1971 Ape Hole Creek, Pocomoke Sound ------ 37 58 75 49 +3 24 +3 48 -0.2 0.0 2.3 2.8 1.1 Pocomoke River 1973 Shelltown ----------------------- 37 59 75 38 +3 29 +4 06 -0.1 0.0 2.4 2.9 1.2 1975 Pocomoke City ------------------- 38 05 75 34 +5 46 +6 05 -0.9 0.0 1.6 2.0 0.8 1976 Snow Hill, city park ------------ 38 10 75 24 +7 32 +7 43 -0.6 0.0 1.9 2.3 1.0 1977 Janes Island Light ------------------ 37 58 75 55 +3 51 +3 50 -0.7 0.0 1.8 2.2 0.9 1979 Crisfield, Little Annemessex River- 37 59 75 52 +3 47 +3 55 -0.5 0.0 2.0 2.4 1.0 1981 Long Point, Big Annemessex River ---- 38 03 75 48 +4 16 +4 36 -0.4 0.0 2.1 2.5 1.0 1983 Teague Creek, Manokin River --------- 38 06 75 50 +4 35 +4 55 -0.4 0.0 2.1 2.5 1.0 1985 Ewell, Smith Island ----------------- 38 00 76 02 +3 56 +4 21 *0.64 '0.64 1.6 1.9 0.8 1987 Solomons Lump Light ----------------- 38 03 76 01 +4 13 4-4 15 -0.8 0.0 1.7 2.0 0.8 1989 Holland Island Bar Light ------------ 38 04 76 06 +4 13 +4 20 *0.56 *0.56 1.4 1.7 0.7 1991 Sharkfin Shoal Light ---------------- 38 12 75 59 +4 43 +4 56 -0.3 0.0 2.2 2.6 1.1 1993 Great Shoals Light, Monie Bay ------- 38 13 75 53 +4 57 +5 12 -0.2 0.0 2.3 2.8 1.2 Wicomtco River 1995 Whitehaven ---------------------- 38 16 75 47 +5 24 +5 37 -0.1 0.0 2.4 2.9 1.2 1997 Salisbury ----------------------- 38 22 75 36 +6 18 +6 14 +0.5 0.0 3.0 3.6 1.5 Nanticoke River 1999 Roaring Point ------------------- 38 16 75 55 +4 57 +5 25 -0.2 0.0 2.3 2.8 1.2 2001 Vienna -------------------------- 38 29 75 49 +7 30 +7 36 -0.2 0.0 2.3 2.8 1.2 2003 Sharptown ----------------------- 38 32 75 43 +8 16 +8 18 0.0 0.0 2.5 3.0 1.3 2005 Fishing Point, Fishing Bay ---------- 38 18 76 01 +5 01 +5 24 0.0 0.0 2.5 3.0 1.2 2007 Hooper Strait Light ----------------- 38 14 76 05 +4 52 1+4 57 -0.8 0.0 1.7 2.0 0.8 on BALTIMORE, P.80 2009 Hooper Island Light ----------------- 38 15 76 15 -5 07 -5 23 +0.4 0.0 1.5 1.8 0.7 2011 Barren Island ----------------------- 38 20 76 16 -4 52 -5 07 +0.2 0.0 1.3 1.5 0.6 Little Choptank River 2013 Taylors Island, Slaughter Creek- 38 28 76 18 -3 27 -3 14 +0.2 0.0 1.3 1.5 0.6 2015 Woolford, Church Creek ---------- 38 30 76 10 -3 25 -3 10 +0.3 0.0 1.4 1.6 0.7 2017 Cherry Island, Beckwiths Creek- 38 34 76 13 -3 21 -3 11 +0.2 0.0 1.3 1.5 0.6 2019 Hudson Creek -------------------- 38 35 76 15 -3 49 -3 31 +0.3 0.0 1.4 1.6 0.7 2021 Sharps Island Light ----------------- 38 38 76 23 -3 51 -4 00 +0.2 0.0 1.3 1.5 0.6 Choptank River 2023 Choptank River Light ------------ 38 39 76 11 -3 17 -3 18 +0.3 0.0 1.4 1.6 0.7 2025 Cambridge ----------------------- 38 34 76 04 -2 54 -2 50 +0.5 0.0 1.6 1.8 0.8 2027 Choptank ------------------------ 38 41 75 57 -2 13 -1 58 +0.5 0.0 1.6 1.8 0.8 2029 Dover Bridge -------------------- 38 45 76 00 -0 57 -0 56 +0'.6 0.0 1.7 2.0 0.8 2031 Denton -------------------------- 38 53 75 50 +0 13 +0 22 +1.1 0.0 2.2 2.5 1.1 2033 Greensboro ---------------------- 38 58 75 49 +1 18 +1 08 +1.4 0.0 2.5 2.9 1.2 2035 Wayman Wharf, Tuckahoe Creek ---- 38 53 75 57 +0 53 +0 25 +1.3 0.b 2.4 2.8 1.2 Tred Avon River I I I I I 2037 Oxford -------------------------- 38 42 76 10 1-3 05- -3 00 +0.3 0.01 1.4 11.6 0.7 1 2039 Easton Point -------------------- 38 46 76 06 -2 59 -2 50 +0.5 0.0 1.6 1.8 0,8 2041 Deep Neck Point, Broad Creek -------- 38 44 76 14 -3 10 -3 01 +0.3 0.0 1.4 1.6 0.7 2043 St. Michaels, San Domingo Creek ----- 38 46 76 14 -3 08 -3 06 +0.3 0.0 1.4 1.6 0.7 2045 Avalon, Dogwood Harbor -------------- 38 42 76 20 -3 08 -3 03 +0.2 0.0 1.3 1.5 0.6 2047 Poplar Island ----------------------- 38 46 76 23 -3 12 -3 18 +0.1 0.0 1.2 1.3 0.6 2049 Ferry Cove, Eastern Bay ------------- 38 46 76 20 -3 01 -3 04 -0.1 0.0 1.0 1.2 0.5 Table 3 Sample Tide Table [U.-S. Department of Commerce (1976)] 38 + 1.1MLW + 1.4' M LW (MEAN HIGH WATER) 0. 7' 0.8' (MEAN SPRING RANGE 2) MLW (MEAN TIDE LEVEL) 0.7' (MEAN TIDE RANGE - 2) +0.0' MLW Figure 12 Reference Water Levels at Oxford, Maryland 39 1980 1981 1982 MAY OCT NOV DEC MMAY JUN @ JUL AUG S OCT NOV ' JANTFEB W..JUN Ft. @--- ---.,-T - -.-, -,I --- - - -TE-C F 67iiik-l -APRI"--' N,,!, @FIII IIIAAI .......... . .... . ......... ..... . ......... ............ . .. . . .... . .......... . ..... ...... . . . . ............ . ....... ..... ...... . ........... ........... T97 wn 5 _1973 1,@73 ......... . . . ........ .... ... . . . ...... i 4973@1971 L03 1973 @ 4,- - - +4 . ... ......... .. in --- - -- . ....... 1977 .-7:. -4 . . ............ a .3; .... ...... . . ..... .... . . . .. ......... -.1 . . ........... ....... . . .. . ..... ....... ...... . . . .... .... 12 1-42 ....... ... -4- ...... ............ . ... ... . .... ... . ..... . .. ......... +1 -4- +1 7=11, -4.1--,@- .. . ......... ......... . .. .......... .......... ... .... . . . ....... ............ . ..... iRS 1934 . . ... ........ 19 4 r9jw 19341 0 0 LO -7- 3- 95 . . ....... . n -5 -.1 1.4 ioj6 - T 77ii=i=,17-2@-- ..... ......... 1980 1981 1982 JUN JAN FEB MAR APR MAY AUG JUN i JUL AUG 1 SEP OCT NOV DEC JAN FEB MMART PR KAY UN SEP RT V_@EC JWIFEBMARI@F@ IIAIT .. ....... . . . . ........ . ......... . . ......... . . . . . ........... ... .......... -F-I ........... i, -- pi 1974 4 . ............ . im +4 +4 1P.I. 77- -IV3 1: 19 3 52 ly/3 . ........... .... II AS2 V 1973 lo-3-ft,§ ........... ....... . .......... ...... . .. .......... + . .......... . .... 3 +3, F77P . . ......... ... ..... ........... E@ 0 -. . . . ........... ...... ............ .. ............ ......... . -7. . ... . . ......... +2 . . ....... ........ ..... ..... .. ............ . ...... ... . . . . ............. .... ........... _J I . ......... --- :777; -4- t +1 ....... ... ........ ... -- . . . . . ....... ............ ..... ........ . . ............ ....... . . ............ .. . . ......... CA'R -DATU 5-T 8 (1 ....... .... . . ...... -.... ....... . .. 0@ 0@717 ...... ....... .... ...... . ....... .. . ........ ....... . ...... . ... ........... -1 -1064 ID9, . . . . . ......... LAKE-8 MI 1064-" '1964 17,7 i=q.=7T- 19@4 _TM 19- 196S 41.96 2196E =F17 .. ........ ... EXAMPLE CHOOSE GREATER OF.' (a) Midway between long term average (Thin Line) and highest recorded monthly level. These are points (a) W Highest water level recorded in previous 12 months (Thick Line). These ore points (b). LEGEND Actual monthly water levels for post 15 months =No Projected monthly water levels for next 6months - Average monthly water levels; 1900 to present , @QAT E) Extreme monthly high and low water levels I tR 4 Figure 13 Design Lake Levels [After U.S. Army Corps of Engineers (1981a)j 40 NOTE' Values of storm setup are in feet. S /.0) X, . .0 (/.0) 41 (0-9) (0.8) (2.2 (08) f-I* -P 00 -0) ONTARIo 0 0) X, - (0.7) 0-0) (4.8) VL < .j 2,0 (2.0 0.7) 0) 03 (19) P E N N. I N D I A N A 0 H I o Figure 14 Storm Setup values for the Great Lakes [After U. S. Army Corps of Engineers (1978d)] for design. The design wave will be the lesser of (a) the maximum height generated by wind acting along the critical fetch or (b) the maximum breaker height that can reach the site during design water level conditions. In other words, if the wind can produce a larger wave than can be supported at the site, the available depth will control, not the wind. The height of wind-driven waves depends on several factors: wind speed, duration, fetch length and depth. When considering wind speed, it is important to realize that there must be sustained wind action to effectively generate waves. Brief gusts reaching high velocities do not last long enough to cause wave growth. The fastest-mile is a convenient way to characterize both wind speed and duration. The maximum fastest-mile is the highest speed that occurs with a sufficient duration for the wind to travel one mile. In other words, a 60 mile/hour wind must last for one minute to travel one mile, whereas a 30 mile/hour wind must last for two minutes. Figures 15 and 16 are maps of the continental United States, including Alaska, which display the maximum fastest-mile wind speed contours for 10- and 25-year return periods. For exam- ple, the 10-year fastest-mile wind speed at New York City is 60 mph, and at Charleston, South Carolina it is 75 mph. A brief review of the concept of return period is needed because the public ,tends to be confused about its meaning. For instance, when told that a device will withstand the 10-year wave at a site, most people will probably conclude that the structure will be safe for the next ten years. Or, if design wave conditions have occurred recently, they may assume that these will not occur again for another ten years. Neither of these perceptions is correct. What is really meant can be illustrated by an example. For instance, if over a long time (e.g., 100 years), 10 episodes with waves of a certain size were observed, the return period for that wave height, based on the available statistics, would be 10 years (100 years of record/10 observed episodes). Return periods can be used to assess the risk involved in a particular decision. The probability, P, that-a particular-event with return period, Tr,, will occur during a period of time, 1, is given by, P 1 1 x 100 (4) TJ I Table 4 contains probabilities of occurrence (percentages). for events with 10- or 25-year return periods as a function of various project durations. For example, consider an individual who wishes to protect his shoreline for 10 years. Using methods explained later, the designer chooses a 10-year design wave. The chance of experiencing the design wave during a structure's 10-year life is 65 percent. If this is an unacceptable level of risk, the designer may then provide protection against a larger design wave, say 25 years. In that case, there is an 34-percent chance of the 25-year 42 90 0 0 60 80 0 c 7 ...... .......... . ........ 6 0 7 ............ 0 80 .......... 5 1, . ........ .* 0 5 ......... 9 6 i......... 6 0 70 0 0 70 8 90 60 80 40 8 [After Thom (1968)) Figure 15 Fastest-Mile Wind Speeds:10-year Return Period 10 7 00 70 80 80 70 ............ ...... 80 ...... 6 0 0 ...... ....... 100 ........... 5 00 50 0 0 0 ........ 100 70 8 90 10 90 0 96 [After Thom (1968)] Figure 16 Fastest-Mile Wind Speeds:25-year Return Period 43 wave occurring during the structure's 10-year life. If this is an acceptable level of risk, the design can proceed on that basis. Table 4 PERCENT CHANCE OF DESIGN EVENT OCCURRENCE Project Life Design Condition Return Period (years) (years) 10 25 10 4 2 19 8 5 41 18 10 65 34 15 79 46 20 88 56 25 93 64 30 96 71 40 99 80 50 99 87 Returning to the problem of the design wave, the critical fetch must be identified before it is possible to calculate the wave height. Fetch length is the distance across water that wind blows to generate waves. At a constant wind speed, the longer the fetch, the larger the generated waves, up to an equilibrium point beyond which there is no further wave growth unless the wind speed increases. Figure 17 shows a proposed site for a shore protection project. The critical fetch must be determined in order to esti- mate the design way height. The longest fetch is labeled Q in the figure. Line @b , although shorter than Line crosses significantly deeper water. In general, greater depths along the fetch will cause greater wave heights because of decreased bottom frictional effects. The fetch lines on Figure 17 have been divided into a series of equal length segments. As shown on the figure, by noting the depth at each division point, the average depth along the fetch can be determined. Care should be taken, however, to avoid including depths which are the result of small-scale depressions or rises that are not typical of the area, but which the fetch line happens to cross. Small features such as rocks would not significantly affect wave growth and should be excluded in favor of a depth that is more typical to that area. The average depth must also be adjusted to correspond with the design water level. If, for in- stance, the design water level is +2.8 fee MLW, then the average fetch depth would be 10. 0 feet for Line 1 and 14.4 feet for Line The final step in determining wind-driven wave heights is to refer to Tables 5, 6, 7, 8, and 9, and select the tables that bracket the average fetch depth. The wave height can then be found by using the fetch length and the fastest-mile wind speed. In the 44 FETCH LINE 4 2 DEPTHS DEPTHS 5 6 3 10 12@ 7` 6 5 W9 18 S#'. .9- 1 12 10 1.5--@jfa 2 6 1 18 6 .. . 9' 11 '2 `- 11 &.... 9 3 18 PA R '14- SCA 10 27 10 14 w 10 12 do 2 4 12 5 13 12 12 %-2 1 0 Marke, Avg: 7.21 MLW Avg: 11.6' MLW ......... 13 14 Fetch Length: Fetch Lengt 'I 2r* NAUTICA h: V5 2.80 nm 2. 10 nm Pile PA t:PiI*-PA'Z--- 10 12 ii, 12: 3.20 mi 2.40 mi -7 9 36 bleto 1. R V,, 2 J@ 16. 4 3 wg@ R - - 2 4 14 -4@ 3 W LrI 9 Ito I 14 9 R 9 0 . ....... 8 10 Z,- --% 9 lu S* 12 -5 _7 M 2 10 el GI 4 3 3 2 .4 7 4143 3% ."2 20..' 18, 4 3 15 15 Film U Doi?,. V; 3 14 Z7 Eel n 3 @-t`fsft note 6) 8 ..-6 4 R,i2,, R 19, 5 3 -4- ::9 atI%I- A?'PA": @6: 3 7 s1k 4 4 2' A 19 W 4 NO -E 8 2- PA . ..... 9 Bridge Creeki privately 14see 15ft 4 M 1 2 F . 4@ : 4 tained channet is marked b Piles PA 13 21 beacorls I thru Figure 17 Identification of Fetch Lengths at a Site Table 5 WIND-GENERATED WAVE HEIGHTS AND (PERIODS) FETCH LENGTHS WITH AVERAGE DEPTHS = 5 FEET Wind Speed Fetch Length (miles) (mph) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 6.o 7.0 8.0 9.0 10.0 10 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 (1.0) (1.0) (1.0) (2.0) (2.0) (2-0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) 20 0.5 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 (1.0) (2.0) (2.0) (2.0) (2-0) (2.0) (2-0) (2.0) (2.0) (2.0) (2.0) (2-0) (2.0) (2.0) (2.0) 30 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 (2.0) (2.0) (2-0) (2.0) (2.0) (3.0) (3-0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) 0.0) (3.0) 40 l.'O 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 (2.0 (2.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) 50 1.5 1.5 1.5 1.5 1.5 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 (2.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3-0) (3.0) (3.0) 55 1.5 1.5 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 (2.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.01 (3.0) (3-0) (3.0) (3.0) 60 1.5 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0@ 2.0 2.0 2.0 2.0 2.0 (2.0 (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) 65 1.5 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 (3.0) (3.0) (3.0) (3.0) (3.0) (3-0) (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4:0) (4.0) 70 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) 75 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) 80 2.0 2.0 2.0 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 (3-0) (3.0) (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) Table 6 WIND-GENFRATED WAVE HEIGHTS AND (PERIODS) FETCH LENGTHS WITH AVERAGE DEPTHS = 10 FEET Wind Speed Fetch Length (miles) (mph) 0.5 1.0 1.5 2.0 2.5 3 0 3 5 4 0 4 5 5 0 7 0 8 0 9 0 10.0 10 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1.0 1.0 1.0 (1.0) (1.0) (1.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2-0) (2-0) (2-0) (2.0) (2.0) (2.0) 20 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2-0) (2.0) (3.0) (3.0) (3.0) (3.0) 30 1.0 1.5 1.5 1.5 1.5 1.5 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 (2.0) (2.0) (2.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3-0) (3.0) (3.0) (3-0) (3.0) 0.0) (3.0) 40 1.5 1.5 2.0 2.0 2.0 2.0 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 (2.0) (2.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3-0) (4.0) (4.0) (4.0) 50 1.5 2.0 2.5 2.5 2.5 2.5 2.5 2.5 3.0 3.0 3.0 3.0 3.0 3.0 3.0 (2.0) (3A) (3.0) (3.0) (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4-0) (4.0) (4.0) (4.0) (4.0) 55 2.0 2.5 2.5 2.5 2.5 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 (3.0) (3.0) (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) 60 2.0 2.5 2.5 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.5 3.5 3.5 (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4-0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) 65 2.0 2.5 3.0 3.0 3.0 3.0 3.0 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) 70 2.5 3.0 3.0 3.0 3.5 3.5- 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 (3.0) (3.0) (3.0) (4.0) (4-0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) 75 2.5 3.0 3.0 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4-0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) 80 2.5 3.0 3.5 3.5 3.5 3.5 3.5 3.5 3.5 4.0 4.0 4.0 4.0 4.0 4.0 (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4-0) (4.0) (5.0) (5.0) (5.0) (5.0) (5.0) (5.0) (5-0) 46 Table 7 WIND-GENERATED WAVE HEIGHTS AND (PERIODS) FETCH LENGTHS WITH AVERAGE DEPTHS = 15 FEET Wind Speed Fetch LeZ!th (miles) (mph) 0 5 1 0 1 5 2 0 2 5 3 0 3 .5 0 4 5 5 0 6 0 7 0 8 0 9 0 10.0 10 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1.0 1.0 1.0 1.0 (1-0) (1.0) (1.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) 20 0.5 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 2.0 2.0 (2.0) (2.0) (2.0) (2.0) (2-0) (2-0) (2.0) (2.0) (2.0) (2.0) (2.0) (3.0) (3.0) (3-0) (3.0) 30 1.0 1.5 1.5 1.5 2.0 2.0 2.0 2.0 2.0 2.0 2.5 2.5 2.5 2.5 2.5 (2.0) (2.0) (2.0) (3-0) (3.0) (3-0) (3.0) (3-0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) 40 1.5 2.0 2.0 2.0 2.5 2.5 2.5 2.5 3.0 3.0 3.0 3.0 3.0 3.0 3.0 (2.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) 50 2.0 2.0 2.5 2.5 3.0 3.0 3.0 3.5 3.5 3.5 3.5 3.5 3.5 3.5 4.0 (2.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4-0) (4.0) (4.0) (4.0) (4.0) (4.0) 55 2.0 2.5 3.0 3.0 3.0 3.5 3.5 3.5 3.5 3.5 4.0 4.0 4.0 4.0 4.o (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) 60 2.0 2.5 3.0 3.5 3.5 3.5 3.5 4.0 4.o 4.0 4.0 4.o 4.o 4.0 4.5 (3.0) (3.0) (3.0) (4.0) (4-0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5.0) 65 2.5 3.0 3.5 3.5 3.5 4.0 4.o 4.0 4.0 4.0 4.5 4.5 4.5 4.5 4.5 (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4-0) (4.0) (4.0) (5.0) (5.0) 70 2.5 3.0 3.5 4.0 4.0 4.0 4.0 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5.0) (5.0) (5.0) (5.0) 75 2.5 3.5 3.5 4.0 4.0 4.5 4.5 4.5 4.5 4.5 4.5 5.0 5.0 5.0 5.0 (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5-0) (5.0) (5.0) (5-0) 80 3.0 3.5 4.0 4.0 4.5 4.5 4-.5 4.5 5.0 5.0 5.0 5.0 5.0 5.0 5.0 (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5-0) (5.0) (5.0) (5.0) (5.0) (5.0) (5.0) Table8 WIND-GENERATED WAVE HEIGHTS AND (PERIODS) FETCH LENGTHS WITH AVERAGE DEPTHS = 20 FEET Wind Speed Fetch Leuth (miles) .5 4.0 (mph) 0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 5 5 0 7 0 8 0 9 0 10.0 10 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1.0 1.0 1.0 1.0 1.0 (1.0) (1.0) (1.0) (2.0) (2-0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2-0) (2.0) (2.0) (2.0) 20 0.5 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 1.5 1.5 2.0 2.0 2.0 (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) 30 1.0 1.5 1.5 1.5 2.0 2.0 2.0 2.0 2.5 2.5 2.5 2.5 3.0 3.0 3.0 (2.0) (2.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (4.0) (4.0) 40 1.5 2.0 2.0 2.5 2.5 2.5 3.0 3.0 3.0 3.0 3.5 3.5 3.5 3.5 3.5 (2.0) (3.0) (3.0) (3.0) (3-0) (3.0) (3-0) (4-0) (4.0) (4.0) (4.0) (4-0) (4.0) (4.0) (4.0) 50 2.0 2.5 2.5 3.0 3.0 3.5 3.5 3.5 3.5 4.0 4.0 4.0 4.0 4.5 4.5 (3.0) (3-0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) 55 2.0 2.5 3.0 3.0 3.5 3.5 4.0 4.0 4.0 4.0 4.5 4.5 4.5 4.5 4.5 (3.0) (3.0) (3.0) (4.0) (4.0) (4-6) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5.0) (5.0) 60 2.0 3.0 3.0 3.5 4.0 4.0 4.0 4.0 4.5 4.5 4.5 5.0 5.0 5.0 5.0 (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5.0) (5.0) (5.0) (5-0) 65 2.5 3.0 3.5 4.0 4.0 4.5 4.5 4.5 4.5 5.0 5.0 5.0 5.0 5.0 5.5 (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5.0) (5.0) (5-0) (5.0) (5-0) 70 2.5 3.5 4.0 4.0 4.5 4.5 4.5 5.o 5.0 5.0 5.0 5.5 5.5 5.5 5.5 (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5.0) (5.0) (5.0) (5.0) (5.0) (5.0) (5.0) 75 3.0 3.5 4.0 4.5 4.5 5.0 5.0 5.0 5.0 5.5 5.5 5.5 5.5 6.0 6.0 (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5.0) (5.0) (5.0) (5.0) (5.0) (5.0) (5.0) (5-0) 80 3.0 4.0 4.5 4.5 5.0 5.0 5.5 5.5 5.5 5.5 5.5 6.0 6.0 6.0 6.o (3-0) (4.0) (4.0) (4.0) (4.0) (5.0) (5.0) (5.0) (5.0) (5-0) (5.0) (5.0) (5-0) (5.0) (5.0) 47 Table 9 WIND-GENERATED WAVE HEIGHTS AND (PERIODS) FETCH LENGTHS WITH AVERAGE DEPTHS = 25 FEET Wind Speed Fetch Length (miles) (mph) 0 5 1 0 1 5 2 0 2 5 3 0 _3 5 4 0 4 5 5 0 6.0 7.0 8.0 9.0 10.0 10 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1.0 1.0 1.0 1.0 1.0 (1-0) (1-0) (1.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2-0) (2.0) (2.0) (2.0) 20 0.5 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 1.5 2.0 2.0 2.0 2.0 (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (2.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) 30 1.0 1.5 1.5 2.0 2.0 2.0 2.0 2.5 2.5 2.5 2.5 2.5 3.0 3.0 3.0 (2.0) (2.0) (2.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3-0) (3-0) (4.0) (4.0) (4.0) 40 1.5 2.0 2.0 2.5 2.5 3.0 3.0 3.0 3.0 3.5 3.5 3.5 4.0 4.0 4.0 (2.0) (3.0) (3.0) (3.0) (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4-0) (4.0) (4.0) (4.0) 50 2.0 2.5 3.0 3.0 3.5 3.5 3.5 4.0 4.0 4.0 4.5 4.5 4.5 4.5 5.0 (3.0) (3.0) (3.0) (3.0) (4.0) (4.0) (4-0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5-0) 55 2.0 2.5 3.0 3.5 3.5 4.0 4.o 4.0 4.5 4.5 4.5 5.0 5.0 5.0 5.0 (3.0) (3-0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5-0) (5.0) (5.0) (5.0) 60 2.0 3.0 3.5 3.5 4.0 4.0 4.5 4.5 4.5 5.0 5.0 5.0 5.5 5.5 5.5 (3.0) (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5-0) (5.0) (5.0) (5.0) 65 2.5 3.0 3.5 4.0 4.5 4.5 4.5 5.0 5.0 5.0 5.5 5.5 5.5 6.0 6.0 (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5.0) (5.0) (5.0) (5-0) (5.0) (5.0) (5.0) 70 2.5 3.5 4.0 4.5 4.5 5.0 5.0 5.0 5.0 5.5 5.5 6.0 6.0 6.0 6.5 (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5.0) (5.0) (5.0) (5-0) (5.0) (5.0) (5.0) 75 3.0 3.5 4.0 4.5 4.5 5.0 5.5 5.5 5.5 6.0 6.0 6.0 6.5 6.5 6.5 (3.0) (3.0) (4.0) (4.0) (4.0) (4.0) (5.0) (5.0) (5-0) (5.0) (5.0) (5.0) (5.0) (5.0) (5-0) 80 3.0 4.0 4.5 5.0 5.0 5.5 5.5 6.0 6.0 6.0 6.5 6.5 6.5 7.0 7.0 (3.0) (4.0) (5.0) (5.0) (5-0) (5.0) (5.0) (5.0) (5.0) (5.0) (5.0) (5-0) (5-0) (6.0) (6.0) example, fetch line 1 was 3.@ miles long with an average depth of 10.0 feet (design wa@er level at +2.81 MLW). Assuming a 10-year, fastest-mile wind speed of 65 miles/hour, the wave height would be 2 , with an average depth of 14.4 3.0 feet (Table 6). Along Lineo feet, the wave height would be 3.5 feet (interpolating between Tables 6 and 7), despite the fact that its fetch length is only 2.4 miles. This should be used for design. The wave periods are given in parentheses on the tables below the wave heights. In both cases, the wave period is 4.0 seconds. Alternate, more precise, methods of determining the wave height and period by using shallow water wave forecasting equations are given in U. S. Army Corps of Engineers (1977c) (1981b) and (1981c). The two later references will eventually supersede the first and are preferred by many coastal engineering specialists. Their use, however, involves more elaborate procedures so, for the sake of brevity and simplicity, only the equations from the first reference will be given. Either the tables or the equations are adequate for design of low cost shore protection. The wave height, H, is, 48 0.0125 (@F 0 42 H = 0.283 U 2 tanh 0.530 d) 0.75 tanh 2) (5) 9 @U2 tanh 0.530 @d 0.71 U 2) and the period, T, is 0.077 (_qFy .25 U (gdY.375 U 2 T = 2.40 1- tanh 0.833 - tanh (6) 9 U2 (_gd tanh 10. 833 U 2T*375 where U = the wind speed in feet/second; F = the fetch length in feet; d = the depth in fee@; and g = 32.2 feet/second . Note: The above equations are in dimensionless form and can be used with any consistent set of units. Wave heights so determined should then be checked against the maximum possible breaking wave at the design water level. This should be evaluated using Figure 18 and the depth at the toe of the structure, or if appropriate, the minimum depth offshore from the structure. With the design water depth at the toe of the struc- ture, d ; the wave period, T; and the fronting bottom slope, m; the s breaker height, H can be found as a function of d For @n- ,b' stance, if d s = 3.0 feet, m = 1:33, and T 4.0 secone?s,' d /gT 0.00582, and H /d = 0.98; therefore H 3.0 x 0.98 = 2N (say 3. 0) feet. TR minimum depth along 'feibch line is near Cedar Point where the depth is 1 foot at MLW, and 3 .@)feet under the design water level. This would not control for this case (it is greater than d ), but it should be checked in every instance. Fetch line ('D &es not cross similar shoal areas. If the wind-driven wave height was 3.5 feet, it should not be used for design because only a 3.0-foot wave can be supported-B-ased on the available minimum depth at the structure. The final design wave height, therefore, should be 2.9 (3.0) feet in this case. To restate the rule, the design wave height should be the lesser of the maximum wind-generated wave along the fetch, or thei-m-a-'ilimum possible. breaking wave at the structure or at points offshore. Figure 19 gives appropriate locations for measuring the depth at the structure, d s 49 3.5 I- ff +I-f+i- - -------- -- Ow 3.0 breaker travel III distance 6 Hb Design SWL Uff . ............. :j ..4. d, Nearshore slope 2.0 af Hb d 1.5 Ln J. T: T, MINE song= 1.0 MEIN noun 0.5 ---------- 0 -------- 0 0.002 0.004 0.006 0.006 0;010 0.012 0.014 0.016 0.018 0.020 d 9T' Figure 18 Dimensionless Design Breaker Height Versus Relative Depth at Structure el [Wegg (1972)] ds ds M REVETMENTS BULKHEADS ds M GROINS d S PERCHED BEACHES BREAKWATERS Figure 19 Depth at Structure for Various Devices Strength Shore protection structures must be strong, and this can only be achieved by using either massive and heavy components that cannot be dislodged by waves, or smaller components that interlock to form a large mass. The problem with small interlocking units, such as concrete blocks, is that they exhibit little reserve strength. That is, once damages occur, they generally progress to complete failure. Flexibility Flexibility is also desired because it allows structures to compensate for settlement, consolidation and toe scour. The revet- ment shown on Figure 20 illustrates this point. The massive indi- vidual concrete slabs could not be moved by waves, but the struc- ture failed because it was not able to adjust to erosion that occurred around the ends and through cracks between the slabs. Toe Protection @ds M __""4@ds M r Toe protection is supplemental armoring of the beach surface in front of.a structure which prevents waves from scouring or 51 21 June 1979 Ong, 7 August 1979 4W Figure 20 Flexibility as a Structural Requirement undercutting it. Failure to provide toe protection invites almost certain failure. A typical example is shown on Figure 21. Filterin Filtering, although one of the most important technical design details of shore protection structures, is probably the most ne- 52 BULKHEAD BULKHEAD (WITH TOE PROTECTION) (NO TOE PROTECTION) SCOUR AT FILTER TOE CLOTH Figure 21 Typical Example of Toe Protection glected, and leads to more failures than any other cause. The con- sequences of not providing proper filtering are illustrated on Figure 22. Without filtering, the soil particles are easily trans- ported through the armor layer, which continues to settle as the bank erodes. A properly designed f ilter blocks the passage of the soil particles while still allowing for hydrostatic pressure relief beneath the structure (Figure 23). A filter layer can be provided through the use of either graded aggregates or a synthetic filter fabric. Filter criteria for graded filters are covered in standard references such as Winterkorn and Fang (1975). Bertram (1940) developed one widely used criterion as given below: D15 (filter) < 4 to 5 < D15( filter) (7) D85 (soil) D15 (so") The left side of the equation is intended to prevent piping of fine-grained soil through the filter. That is, the 15-percent size of the filter material, D (percent finer by weight), must be no more than 4 or 5 times D85 size of the protected soil. The 53 MLWV INI TIA L POSITION Soil and water posses through GRA DED gaps between stones STONE MLW FIL TER 4_/-Soil particles cannot penetrate filter. Water easily flows throug @Groundwater structure f low MLW V FIAIA L S)`NrHE r/C POSMON Erosion FIL TER continu'es CLOTH SSW M L W Synthetic filter cloth Water can pass throuah filter cloth but soil particles cannot Figure 22 Figure 23 Inadequate or No Filtering Proper Filter Design right side of the equation provides for adequate permeability of the filter (several times greater than the adjacent soil). It requires the D size of the filter to be-at least 4 or 5 times the D f the soil. This criterion should provide adequate permea- bility for structural bedding layers, but may be insufficient for groundwater drains. . Several organizations have developed further restrictive criteria for filters. For instance, the Bureau of Reclamation allows no filter aggregates larger than 3.0 inches, and the Corps of Engineers specifies that, D 50 (filter) < 25 (8) D50 (soil) In other words, the D of the filter cannot be greater than 25 50 times the D of the soil. This is intended to insure that the gradation cUves of the filter and soil are generally parallel. 54 For perforated or slotted pipe, the D of the filter must be greater than the hole width or slot diameteP D85 (filter) > (1.0 to 1.2) (9) Hole Diameter D85 (filter) > (1.2 to 1.4) (10) Slot Width These and other criteria for graded filters are illustrated on Figure 24. The above criteria also apply to the armor layer in relation to the filter layer. That is, the armor layer must retain the filter layer as the filter retains the soil. In some cases, two filter layers may be required to provide the necessary transition from the soil to the armor. Synthetic filter fabrics, available in woven and non-woven varieties, can be used in place of graded stone filters. Woven cloths, manufactured of high strength nylon or other synthetic fibers, provide a uniform mesh with a constant opening size which can be matched to the soil characteristics. Non-woven cloths, manufactured from masses of somewhat randomly oriented fibers bonded together by chemicals, heat or pressure, come in various standard thicknesses. Unlike woven cloths, however, they lack uniform-sized openings, their principal advantage being lower cost. Guidance on the selection of filter fabrics is contained in Plastic Filter Fabric [U. S. Army Corps of Engineers (1977a)]. Selection is based on the equivalent opening size (EOS), which the Corps defines as "the number of the U. S. Standard Sieve having openings closest in size to the filter fabric openings". Material will first be retained on the sieve whose number is equal to the EOS. The EOS of commonly used filter fabrics is given in Table 10. The appropriate filter fabric should be selected as follows: For granular soils with less than 50 percent by weight fines (minus No. 200 materials) 85% Passing Size of Soil > Opening Size of the E57ssieve - For other soils, the EOS should not be less than 70 (0.0083 in.). Furthermore, to reduce problems with clogging, no fabric should be used whose EOS is greater than 100 (openings smaller than the mesh of a No. 100 sieve). Also, no filter fabric should be used alone if the underlying soil contains more than 85 percent of particles finer than the No. 200 sieve. In those cases, 55 CLEAR SQUARE OPENINGS US STANDARD SiEVE NUMBERS 10. Sn2"Ihe' r'WW,W 1 Be- 1@@ 30 40 50 70 100 200 HYDROMETER ANALYSIS II I TYPICAL MATERIALS FILTER SHEET ASPHAL so SAND, ASTMOK)73D 10 K CONCRE AVERAGE SAN 00@ PROPERT IES: M12 CU FTIMIN W ASTMD633 ASPHALT SAND .15 .35 .03 .03 :ONCRETE SAND .3 .75 24 .07 CONCRETE GRAVEL WTONO4 7 12 2.5 > 50 It W ICONCRETE GRAa 2.. 70 314 25 35 2.5 ASTM 3 3 U. C 21/2"TO I Ve* 40 52 56 1.5 V4"TO NO.4 W Al 2" TO 3/4" r 2 1/2"TO I W if- APPROXIMATE FINEST LIMJT 20 OF FILTER MATERIALS 0 100 8 6 4 3 2 108 6 -4 3 2 16 6 4 3 2 .1 8 64 3 2 .0 1 1) 643 2 .001 GRAIN SIZE MILLIMETERS COWES [@SE --I FINE I CO-A-RSTT-MOIUM I FINE SILT OR CLAY(PLAS OR NON- GRAVEL SAND PTr TIC, LAS 100 4 810 16 30 4D50 70 100 200 RELATION OF FILTER AND BASE \,.fINEST LIMIT OF SAN D R BASE OF PLASTIC CLAY Ncol!@!!@ ESN 658 WITH LOW PERMEABILITY, so ALT A CONCRETE SAND FILTER k I ["KWILTERS MAY BE USED. OR BASE OF )-60- NONPLASTIC SILT',- ROCK FLOUR VARVED SILT, IN D D500 z THIS RANGE USE U. COARSEST MATERIAL ASPHALT SAND TO BE USED FILTER. z AGAINST C014CRE74 U INEST BASE W SAND FILTER LAYER 1K i I 1@ , .1( 1 MOST FAVORA FOR CONCRET IT BLE SAND FILTER, Q. 20 COMPOS E FILTER -. X@ @4 - VIb'SAND FOR 70% SAM; 30% GRAVEL DI! F 30%GR&'El-FILTERA N I I' - - . 9\ - D 0 1 N I I I I . I I 1111-@-Jx I I I I 106-8 6 4 3 2 108 6 4 3 2 18 6 4 3 2.1 8 6 4 3 2.01 8 6 4 3 2 .001 General requirements: D 1. To avoid head loss in filter: 015B > 4, and permeability of filter must be large enough to suffice for the partic- ular drainage system. ;,0 F D _ D 50 B < 25, ;1 E 2. To avoid movement of particles from base: D85 B < 5, 11 5B < 20 For very uniform base material (C. < 1.5): DIS F/D85 D may be increased to 6 For broadly graded base material (C. > 4): ' DIS F/1315 B may be increased to 40 3. To avoid movement of filter in drain pipe perforations or joints: N5 F/slot width > (1. 2 to 1. 4) D85 F/hole diameter > (1.0 to 1. 2) 4. To avoid segregation filter should contain no sizts latter than 3*- 5. To avoid internal movement @bf fines, filter should have no more than 57. passing No. 200 sieve. CO FT @3 FO % I F@ INE S FOR SAI Figure 24 Design criteria for Protective Filters [U.S. Navy, Naval Facilities Engineering Command (1971)] 56 Table 10 FILTER FABRIC EQUIVALENT OPENING SIZES Fabric EOS Filter X 100 Laurel Erosion Control Cloth 100 Monsanto E2B 80 Polyfilter X 70 Mirafi 140 50 Nicolon 66424 50 Nicolon 66429 40 Polyfilter GB 40 Nicolon 66487 30 [U.S. Army Corps of Engineers (1977a)] *Note: Manufacturer's product lines are subject to change. Check with the supplier to verify current products and specifications. an intermediate sand layer may provide the necessary transition layer from the in-situ soil to the filter fabric. The Corps of Engineers also limits the gradient ratio of the filter fabric to a maximum of 3. This is defined as the hydraulic gradient through the fabric and the one inch of soil immediately above the fabric (i ) divided by the hydraulic gradient over the two inches of soil 16e`tween one and three inches above the fabric (i 2). Gradient Ratio < 3, (12) 12 - Where i and i are measured by a constant head permeability test conduct@d as s@lcified by the Corps in the earlier cited reference. Flank Protection Flank protection is important because any shore protection structure, such as a revetment or bulkhead, is vulnerable as ero- sion continues around its ends. if not prevented by flank protec- tion, the land eventually erodes from behind the structure, which then fails to function adequately. Figure 25 illustrates what happens when flank protection is not provided. Return sections can be provided either during the original construction or later, as erosion progresses. For instance, sheet pile bulkheads along low bluffs can easily be tied into the exist- ing bank during the initial work. This is not generally possible for high bluffs. Revetments must nearly always be progressively lengthened as erosion continues. They should be tied to the exis- ting bank or high ground during initial construction, however. 57 F><1 EXISTING RELINE BULKHEAD--,,, Z (initial Construction) "M"*'@@@BREA7KING@@ WAVES RETREATED SHORE@@...___ ...................... . . . . .................................... BULKHEAD--\ BREAKING WAVES (Without Flonk Protection) A% ........................... RETURN BULKHEAD RETURN WALLS WALLS BREAKING WAVES (With Flonk Protection) Figure 25 Flank Protection RETURN WAL LS 58 Structure Height Waves breaking against an inclined structure will run up to an elevation higher than the stillwater level depending on the rough- ness of the structure. Smooth concrete surfaces experience higher runup than rough stone slopes. Vertical structures also cause splashing and can experience overtopping. If possible, the struc- ture should be built high enough to preclude severe overtopping. White spray does little damage, but solid jets of "green" water should be avoided. The required height of the structure will depend on the computed runup height based on the wave and structure characteristics. Detailed guidance is presented in Stoa (1978) and (1979). The runup height, R, can be found by a more. approximate method as given below. First, find the wavelength at the structure by using either Figure 26 or Equation (3) with the known depth at the structure and the design wave period. The definition sketch for runup is shown on Figure 27. For SMOOTH impermeable slopes, the runup, R'. is given in Seelig (1980) by, (C2 \fH/ds+ C3) R = HC 0.12 1! (13) 1 ( H )' where: L = the local wavelength from Figure 26 or Eq. (3), d = the depth at the structure (feet), R = the approaching wave height (feet), and Cl. C 2" C3 = coefficients given below. Structure Slope* C1 C2 C3 Vertical 0.96 0.23 +0.06 1 on 1.0 1.47 0.35 -0.11 1 on 1.5 1.99 0.50 -0.19 1 on 2.25 1.81 0.47 -0.08 1 on 3.0 1.37 0.51 +0.04 Interpolate linearly between these values for other slopes. For ROUGH slopes, Seelig (1980) gives the runup as, R 0.69 @ ) H (14) 1 + 0.5 where: tan 0 (15) NFH-/ L 0 L0= 5.12 T 2 (16) and 6 = the structure slope (e.g., tan e 0.25 for a slope of 1V on 4H). 59 14 13 12 10 9- 12 14 10 8- 8 0 4 Z 7- 3 w 2 CL 6- 5- WATER DEPTH, d 4 (f t.) 3- 2 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 Wavelength, L (ft.) Figure 26 Local Wavelength Given Depth and Period [After Giles and Eckert (1979)] R L ds M if -0 Figure 27 Wave Runup Definition Sketch For STEPPED slopes, Stoa (1979) recommends using 70 to 75 percent of the smooth slope runup if the risers are vertical, and 86 percent if the edges are rounded. A rough approximation of the runup height can be obtained from Table 11. However, the values in the table tend to represent the upper bound of the available data and may result in over design. Equations (13) and (14) or the methods given in Stoa (1978) and (1979) are recommended. If it is impossible or undesirable to build a structure to the recommended height, a splash apron should be provided at the top of the structure. These are generally constructed of rock and they prevent the ground at the top from being eroded and undermining that portion of the structure. Environmental Factors Many different materials can be used to construct shore pro- tection structures, including rock, concrete, timber, metal and plastics. The choice often depends on the desired permanence of the protection. Durable materials usually cost considerably more than shorter-lived materials used for temporary protection. The choice of materials is important because the coastal environment is a harsh testing ground for all man-made structures. Aside from wave forces, which are formidable in and of themselves, a host of z M 61 R m R m SWL wn 1.5 2.25 H 10 2.5 1 .75 H SMOOTH FACE 4.0 1 .50H m E- .1 TR SWL, -ai-F - 5 1.25H H -L 2.5 1.00H 10 4.0 0.75H ROUGH FACE SWL V m 1.5 2.OOH L STEPPED FACE -SWL V HF 2.00 H 10 V4FRT/CAL FACE W L TH 10 SWI SWL Sw@L 1@ 'o Table 11 Wave Runup Heights 62 chemical, biological and other factors can degrade structural materials. A brief review of these follows. Corrosion and Freezina. Corrosion is a primary problem with metals in bra h and saline water. This is particularly true in the splash zone, where the materials are subjected to continuous wet-dry cycles. Plain carbon steel, for instance, probably has a life of less than five years under some conditions. Corrosion- resistant steel marketed under various trade names is useful for some applications. Aluminum sheet piling can also be used in many areas in place of steel. Stainless, galvanized, or other cor- rosion-protected steel, or wrought iron can be used for bolts and other fasteners. However, care should be taken not to mix dis- similar metals in structures where they directly contact each other. The resulting galvanic action will.quickly corrode the more active metal of the pair (e.g., aluminum is more active than stain- less steel). Concrete can be degraded by chemical reaction with salt water and by freeze-thaw cycles. Guidance on producing suitable high quality concrete is presented in Mather (1957). Aggregates should be durable and not reactive with cement. Dense (cement rich) mixes should be used, typically about 7 bags of portland cement per cubic yard. Types II or V should be used in salt water, while Types I or II are, acceptable in fresh and brackish water. Potable water should generally be used, but brackish or salt water may sometimes be acceptable for mass concrete. Fresh water, however, should always be used for reinforced concrete. Maximum water content should be no more than 5 1/2 gallons per bag of cement, including the moisture content of the aggregates. Finally, air entrainment (typically 4 to 7% of the concrete volume) is necessary to minimize damages from freeze-thaw cycles. Marine Borer Activity. Timber structures submerged in brack- ish and salt water are subject to damage from marine borers. Any wood or timber used for bulkhead or other construction in areas of moderate borer activity should be treated with 20 pounds of creo- sote or 2.5 lbs. of preservative salts per cubic foot of timber. Where borer activity is severe, 20 pounds of creosote and 1.5 pounds per cubic foot of preservative salts in a dual-treatment process is recommended for all lumber. Timber piles should be dual-treated with 20 pounds of creosote and 1.0 pound of preserva- tive salts per cubic foot in such areas [American Wood Preservers' Association (1977)]. Ultraviolet Light. The ultraviolet component of sunlight rapidly degrades untreated synthetic fibers such as those used for filter cloth or sand bags, totally deteriorating them in less than one season if heavily exposed. Any fabric used for shore protec- tion devices should be stabilized against ultraviolet light. This typically involves adding carbon black to the synthetic compound which gives the finished product a black or dark color in contrast to the white or light gray color of unstabilized cloth. Even filter cloth covered by a structure should be stabilized since 63 small cracks or openings in the. structure could admit enough light to destroy the cloth. Abrasion. Abrasion damage occurs in all structures where waves move coarse sediments such as sand and gravel back and forth across their faces. Coarse gravels and cobbles can also cause impact damages when hurled by large waves. Little can be done to prevent abrasion damages beyond the use of durable rock and con- crete as armoring in critical areas such as along the sand line of sheet pile groins. It is here that such structures typically experience the greatest amount of abrasion. Ice Forces. Ice forces are primarily a problem on cold region waterbodies such as the Great Lakes. Ice covers will typically vary with the size and location of the waterbody, and local cli- matic conditions. Large bodies, such as the Great Lakes, usually develop partial ice covers, while smaller embayments within them may be totally covered. The ice covers are never totally stationary and movement creates several categories of ice forces on structures. For in- stance, dynamic forces result from wind and current-driven ice sheets or floes. Vertical-faced structures will experience large horizontal forces, while inclined faces will tend to reduce the total force acting on the structure. Static ice forces result from thermal expansion and contraction of relatively stationary ice sheets. Fractured ice forces arise from broken pack ice driven against a structure. Uplift and drawdown forces are associated with the adhesion of floating ice sheets to structures. Water level fluctuations caused by seiches, tides, or reser- voir operation can result in significant damage to pile-supported structures. Water level recession can cause considerable downward loadings that force the piles deeper into the bottom. Conversely, water surface rises will pull the piles upward. I As this occurs, the soil will collapse beneath the pile tips and will prevent return to their original positions. A series of such actions can jack the piles completely out of the bottom. Possible preventative measures include air bubbler systems and pile sleeves, but these must be evaluated on an individual case basis. Relatively comprehensive summaries of current methods. for evaluating ice forces on structures are given in Neill (1976), Wortley (1978) and the U. S. Army Corps of Engineers (1980b). Vandalism and Theft. The final factor is the susceptibility of the structure to vandalism. If this may be a problem, materials should be selected which cannot easily be cut, carried away, dis- mantled or otherwise damaged. For instance, sand-filled fabric bags are easily slashed by knives, small concrete blocks can be stolen, and wire mesh baskets can be opened with wire cutters and the contents scattered. 64 SHORE PROTECTION METHODS This section will examine specific devices, including struc- tures and vegetation, in more detail. Where past performance data are available, these will be incorporated in the discussion. BULKHEADS Because bulkheads normally have vertical faces for ease of construction and cost efficiency, wave reflections are maximized, increasing the potential for overtopping and scour in front of the structure. Since scour can be a serious problem, toe protection is necessary for stability. Typical toe protection consists of quarrystone large enough to resist movement by wave forces, with an underlying layer of granular material or filter cloth to prevent the soil from being washed through voids in the scour apron. Sheet Pile Bulkheads Wave Height Range: Above five feet. Sheet piling is available in different materials, including steel, aluminum and timber. These are used in structures that may be either cantilevers or anchored (Figure 28). Detailed design procedures are available in standard references such as the Steel Sheet Piling Design Manual [U. S. Steel Corporation (1975)]. Fill Cop Fill,_/_'@ CCap Original Sheet Pile ground surface" Wale Sheet Pile //777- Originall -777W07 Tie-Bock ground surface Anchor- (dead man) Li ANCHORED CANFILEVER Figure 28 Cantilever and Anchored Sheet Pile Bulkheads 65 A cantilever bulkhead derives its support solely from ground penetration; therefore, the sheet piles must be driven deep enough to resist overturning. Cantilever bulkheads are susceptible to failure due to toe scour because this reduces the effective embed- ment of the piling. An anchored or braced bulkhead gains additional support against seaward deflection from embedded anchors or from battered structural piles on the seaward side. Anchors are commonly a row of piles or deadmen driven or buried a distance behind the bulk- head. Connections between the anchors and wall should be wrought iron, galvanized or other suitably corrosion-protected steel. Plain carbon steel should not be used for long-term protection. Horizontal wales are generally located in the upper one-third of the wall height above the dredge line. For low bulkheads, they may be at or near the top of the structure. The wales distribute to the anchors, the lateral loads on the structure. An anchor system is not well suited to sites with buildings close to the shoreline because of the distance needed between the bulkhead and anchors. In that case, brace piles may be used in place of anchoring. Subsurface conditions determine the type of sheet piling that can be used. Steel sheet piling can be driven into hard soil and some soft rock. Aluminum and timber sheet piling can only be driven or jetted into softer soil. The advantages of sheet pile bulkheads are their relatively long and maintenance-free lives, and their uniform appearance. Their disadvantages include the special pile-driving equipment required to install them. Treated Timber. Well-designed and built timber structures have long been i7e-cognized as viable and economical materials for bulkhead construction (Figure 29). Figure 30 illustrates the common types of timber sheeting used. As mentioned earlier, only specially treated timber should be used for marine construction. A plan view and cross section of a typical timber bulkhead are shown on Figure 31. The actual dimensions will vary. depending on site conditions. Granular material is preferred for backfill. If anchor piles are used, backfilling should begin over them, and then proceed to the bulkhead. The joints between sheets should be kept as tight as possible. The use of filter fabric is advisable as an added pre- caution to prevent loss of soil through cracks. Supplemental drain holes should be placed at regular intervals to further facilitate the movement of water from behind the structure, and th@se must always be backed with filter.cloth or properly graded crushed-stone T'Ilters. only corrosion-resistant or protected metals should be used for hardware and fasteners. Wrought iron anchor rods with turn- buckles and bolts have good durability. Galvanized fasteners are also recommended. Carbon steel should not be used unless protected 66 @3" __ ;qo- Figure 29 Timber Sheet Pile Bulkhead (Photo Courtesy of Koppers Company, Inc.) 716* DEEP BY 518.DEEP BY 1 314* WIDE GROOVE. 1 116' WIDE EACH SIDE TONGUE 0 01 3/4' DEEP BY 1 5/6' SQUARE E!L@ 1 1/4' WIDE OAK SPLINE_____6- I' OFFSET GROOVE 0 0 1 FROM ONE 4*x10' -OR 4*xl2' ROUGH FROM ONE 6'x12' FROM THREE -ROUGH 2'x10' OR FASTENED WITH TWO 2'xl2* ROUGH 112* DIAM. DOLTS AND TWO 30d NAILS AT 18' CENTERS - SPLINED WAKEFIELD TONGUE AND GROOVE Figure 30 Typical Timber Sheet Sections [Winterkorn and Fang (1975)] -FS@E@ FI'll \ '*' JE QE TH WO 'LTS AND T .3 A@ 67 1V I" diam. x 18'-2" Tie Rods with Turnbuckles E@'x 8" x 10'- 0" Wale spaced 10'-0" Wale 6" x 8" 16'-0' NOTE.' Sheet Piling T 8 G Actual dimensions 3"x 12 ' or 3" x 10 depend on site 12' -0" long conditions. Mean High Water 'til"-First Stage of Filling 2 /2" Drain Holes 20'- 0" U -6" x 8" x 8' x 6" Tie 0 10'-0" Figure 31 Plan View and Cross Section of Typical Sheet Pile Bulkhead [American Wood Preservers Institute (1970)] with special coatings, such as coal-tar epoxy or other bituminous materials. Minimize the number of washers under bolt heads and nuts to reduce the length of exposed bolt shanks, and provide a @tight fit between bolted timbers so that the bolt shanks are not exposed in the gaps. Bolt holes should be no more than 1/16 of an inch larger than the shank to insure a tight fit. Finally, washers should be provided under bolt heads and nuts to insure that these bear evenly on the timber members. Steel. Steel sheet piling, probably the most widely used bulkhead material (Figure 32), can be driven into hard, dense soilsf and soft rock. The interlocking feature of the sheet pile sections (Figure 33) provides a relatively sand-tight fit that generally precludes the need for filters. This close fit may also be essen- tially water-tight, so regularly spaced weep holes are recommended. 68 Figure 32 Steel Sheet Pile Bulkhead BETHLEHEM FRODINGHAM Z-SECTIONS LARSSEN U-SECTION Figure 33 Steel Sheet Pile Sections [After Winterkorn and Fang (1975)] These, and lifting holes in the piling, should be backed with properly graded stone filters or filter fabric to prevent the loss of backfill. Aluminum. Aluminum sheet pile sections are similar to steel. Design and installation are accomplished using conventional methods and equipment. Its primary advantages over steel are lighter weight and superior corrosion resistance. Individual sheets can be carried and maneuvered by one man, and most drilling and cutting can be performed with simple hand tools. Its main disadvantage, compared to steel, is that it is less rugged when driven and cannot penetrate logs, rocks or other hard obstructions. Figure 34 is a photograph of an aluminum bulkhead. 69 F 57 771 40'. z7____r -A&L Figure 34 Aluminum Sheet Pile Bulkhead (Photo Courtesy of Koppers Company, Inc.) Asbestos-Cement. Sheet piling made of this material has been tried in several lo ations. Indications are that it often suffers significant and rapid deterioration in a marine environment [Watson, Machemehl, and Barnes (1979) ] and should be used with caution when long life is desired. Post Supported Bulkheads Post supported bulkheads consist of regularly spaced posts, usually timber, driven into the ground with an attached facing material that forms a retaining wall. The posts,. support compon- ents of the bulkhead, resist the exerted earth pressures. As with sheet piling, a post supported bulkhead can be - either a cantilever or anchored. One advantage is that the posts can sometimes be installed using only an auger, and the facing material can then be placed by hand. The cost of the bulkhead depends on the required spacing of the posts, and the type of soil being augured. 70 Hogwire Fencing and Stacked Bags Wave Height Range: Below five feet. Hogwire fencing attached to posts can be used to support sand bags stacked on the landward side of the fence (Figure 35) to form a relatively inexpensive structure. The sand bags are vulnerable to tearing, however, if after being undercut by toe scour, they slide against the hogwire fencing. Figure 35 Hogwire Fencing and Stacked Bag Bulkhead For best performance, use small-mesh wire with a PVC coating, because bare wire fencing tends to cut the bags. Tearing of the front row of bags can be prevented by filling them with a sand- cement mixture. Burlap bags can be substituted for the more expen- sive bags when a sand-cement mixture is used. The material and seams of all sand-filled bags must be resistant to ultraviolet light. Place the bottom bags and fencing in a trench excavated to at least the depth of anticipated toe scour. Anchor or brace the posts, or embed them deeply, allowing for loss of support because of toe scour. Provide adequate drainage of the retained embankment and place stone at the toe of the bulkhead. 71 Treated Timber Wave Height Range: Below five feet. Horizontal, pressure-treated planks can be spiked to the landward side of posts which are anchored to deadmen or piles in the backfill. The planks must be backed by filter cloth or graded stone to prevent soil losses through the cracks. Riprap toe pro- tection should be provided (Figure 36). Ur 1A Z41* J71@0 4% --A Figure 36 Treated Timber Bulkhead Untreated Logs Wave Height Range: Below five feet. Horizontal, untreated logs can be attached to the landward side of posts in areas like the Pacific Northwest where there is an abundance of such logs. The same precautions about adequate toe protection and filtering also apply. However, the large gaps between logs make adequate filter design more difficult. If a filter cloth is used, it should follow the log contours so that it is not excessively stressed by bridging large gaps. However, it is vulnerable to damage or vandalism, which would jeopardize the entire structure because of the resulting loss of retained fill. ,W* @ I'A 72 Used Rubber Tires Wave Height Range: Below five feet. Used tires can be strung over two rows of treated posts set in a staggered pattern, with the tires abutting each other and filled with gravel (Figure 37). The posts can be tied back to logs buried in the backfill with filter cloth placed behind the tires before backfilling. Under wave action, the gravel tends to wash out of the tires, and the backfill can then escape. Although used tires can generally be obtained free, the cost of the structure is pro- bably comparable to other bulkheads because of the required close post spacing. 4 M, V P Figure 37 Used Rubber Tire and Post Bulkhead Railroad Ties and Steel H-Piles Wave Height Range: Below five feet. Steel H-piles can be driven at regular intervals and railroad ties placed between the flanges of adjacent piles to form a bulk- head (Figure 38). The toe of the structure should be protected by armor stone, and proper filtering and granular backfill are needed behind the structure. A 12-inch steel channel, welded to the top of the H-piles, serves to aline the piles and retain the railroad ties. The structure has performed well and would be particularly useful where subsurface rock prevents driving sheet piling. How- ever, its cost is probably higher than other effective devices. 73 Wail %N, rob%, -ViL IL 7V, qh Wa Figure 38 Railroad Ties and Steel H-Pile Bulkhead Miscellaneous Bulkheads Longard Tu es Wave Height Range: Below five feet. A Longard tube is a patented, woven, polyethylene tube, filled with sand at installation (Figure 39) and available in 40- and 69-inch diameters, and lengths up to 328 feet. Like sand-filled bags, performance depends on the fabric remaining intact, and the tube completely filled. When filled, the tube is dense and heavy, yet flexible enough to settle if depressions occur. A properly in- stalled Longard tube is placed on a woven filter cloth extending 10 feet seaward of the tube. A small 10-inch tube, factory- stitched to the seaward edge of the filter cloth, settles under wave action to provide toe protection. The primary advantage of a Longard tube is the ease and speed with which it can be filled once equipment and materials are in place. Repairs are possible using sewn-on patches. The . major disadvantage is its vulnerability to vandalism and damage by water- borne debris. A sand-epoxy coating can be applied to dry tubes after filling to provide significantly greater protection by deter- ring vandals and preventing puncture holes from enlarging. This coating cannot be applied to wet tubes. However, the tube must not be allowed to roll after the coating is applied, as uncoated sur- face areas would then be exposed, and distortion of the tube may 74 Figure 39 Longard Tube Bulkhead .cause the existing coating to flake off. other disadvantages are that a large supply of good quality sand is required to fill the tube, patented filling equipment must be used, and only specially licensed contractors can perform the work. The Longard tube depends on its weight to resist overturning and on friction to maintain its position. It is designed to pro- tect the toe of the bank from wave attack, and not necessarily to resist earth pressures. The tube should not be placed directly against the base of a bank or overtopping waves may continue to cause erosion. It should be placed far enough from the toe so that overtopping waves will form a sand berm between the tube and the bank. Wave energy will be absorbed by this berm, and further bank erosion may be prevented. Placement of other devices or another tube on top, to increase the structure height and prevent overtop- ping, is not recommended. Stacked Used Tires Wave Height Range: Below two feet. Because used tires are readily available at most sites at no cost, many have tried to use them for shoreline protection devices. The bulkhead on Figure 40 was made with scrap tires interconnected (both vertically and horizontally) by galvanized spikes and push- nuts. The tires were stacked in a staggered pattern over a filter cloth, and granular material was used both as backfill in low areas, and as fill in the tires. Three rows of galvanized steel anchors secured the structure to the beach. The structure progres- sively failed because the interconnections between the tires were 75 A Figure 40 Stacked Used Tire Bulkhead inadequate to hold it together. The gravel washed out of the tires, eventually allowing them to be lifted by waves. This system is not recommended in view of better and less costly alternatives. This structure illustrates a common problem with using scrap tires. While their availability is a strong temptation to use them in shore protection devices, tires are extremely rugged, and usu- ally cannot be securely fastened together except by considerable labor and expense. In almost all cases, failure results because interconnections do not perform as expected. Used Concrete Pipes Wave Height Range: Below two feet. This bulkhead is constructed by standing used concrete pipes on end, side-by-side, and then filling them with granular soil (Figure 41). This bulkhead is economical and practical only when there is an available supply of used concrete pipes and where a low structure is adequate. A filter must be provided behind the structure to relieve hydrostatic pressures. If a filter cloth is used, it should be forced deeply into the grooves between pipes to avoid ballooning and bursting the cloth. The wall should not be more than two pipe diameters high without an anchoring system. Also, the pipes should be entrenched to provide stability and toe protection. A con- tinuous concrete cap (not pictured) could be cast across the tops of all pipes to insure performance as a unit. This type of bulk- head may not last long because of possible rapid deterioration of the concrete pipes. 76 Figure 41 Used Concrete Pipe Bulkhead REVETMENTS The armor layer of a revetment maintains its position under wave action either through the weight or interlocking of the indi- vidual units. Revetments may be classified as flexible, semi- rigid, or rigid. Flexible armors, such as quarrystone, riprap, or gabions, retain their protective qualities even if the structure is severely distorted, such as when the underlying soil settles, or scour causes the toe of the revetment to sink. A semi-rigid armor layer, such as interlocking concrete blocks, can tolerate minor distortion, but the blocks may be displaced if they are moved too far to remain locked to the surrounding units. once one unit'is completely displaced, such revetments have little reserve strength and displacement will generally continue to complete failure. Rigid structures may be damaged and fail completely if subjected to differential settlement or the'loss of support by underlying soil. Grout-filled mattresses of synthetic fabric and reinforced concrete slabs are examples of rigid structures. Rubble Rubble revetments are constructed of one or more layers of stone, or concrete pieces derived from the demolition of sidewalks, streets and buildings. Stone revetments are constructed of either two or more layers of uniform-sized pieces (quarrystone), or a gradation of sizes between upper or lower limits (riprap). Riprap 77 revetments are somewhat more difficult to design and inspect be- cause of the required close control of allowable gradations and their tendency to be less stable under, large waves. For that rea- son, graded riprap revetments should be used with caution, but they are acceptable for the majority of low cost shore protection appli- cations. Quarrystone structures are more easily designed and in- spected and are recommended. The primary advantage of a rubble revetment is its f lexibil- ity, which allows it to settle into the underlying soil or experi- ence minor damage and still continue to function. Because of its rough surface, it also experiences less wave runup and overtopping than a smooth-faced structure. The primary disadvantage is that placement of the stone or concrete armor material generally re- quires heavy equipment. To insure good performance, prepare the existing ground to a stable slope. in most cases, the steepest recommended slope would be 1 vertical on 2 horizontal (1:2). Fill material should be added where needed to achieve a uniform slope, but it should be free of large stones and should be firmly compacted before revetment con- struction proceeds. Properly sized filter layers should be pro- vided to prevent the loss of the slope material through voids in the revetment stone. If using filter cloth, an intermediate layer of smaller stone below the armor layer may help distribute the load and prevent rupture of the cloth. No individual armor unit should be longer than three times its minimum dimension. In other words, avoid using plate-like or cyl- inder-shaped pieces; stones should be angular and blocky, not rounded. The toe of the revetment should be located one design wave height (but at least three feet) below the existing grade line to prevent undercutting. In lieu of deep burial, a substantial sacrificial berm of additional rubble (with filtering) should be provided at the toe. Quarrystone and Riprap Wave Height Range: Above five feet (Quarrystone). Below five feet (Riprap). Stone revetments are a proven method of shoreline protection (Figure 42). They are durable and can be relatively inexpensive where there is a local source of suitable armor stone. Quarried stone should be clean, hard, dense, durable, and free of cracks and cleavages. Figure 43 shows a typical cross section of a stone revetment. The weight of the armor stones should be determined by the following formula as given in the Shore Protection Manual [U. S. Army'Corps of Engineers (1977c)]. w H 3 r W 1)3 cot 0 (17) KD (Sr 78 AIL W'd ELMO&.,,- Figure 42 Quarrystone Revetment where W = weight of an individual armor stone (pounds); wr= unit3weight (saturated surface dry) of the rock (lbs/ feet H = wave height (feet); S = specific/grav4ty of the armor stone (wr/w ); where3 w r 64.0 lbs feet for salt water and 62.4 'Us/feet Yor fresh water; cot 0 = Slope of the structure expressed as horizontal units/l vertical; KD= Stability coefficient from Table 12. Table 12 Stability Coefficients for Stone Revetments Armor Unit KD Quarrystone Smooth rounded 2.1 ngul Rough a ar 3.5 Graded riprap 2.2 79 FIRST UNDERLAYER (STONE WEIGHT=W/10) ARMOR (2 LAYERS) (STONE WEIGHT =W) NOTE.' Use either stone or filter fobric(Both are shown to illustrate their use -only one is needed) GRADED STONE MLW FILTER (IF USED IN PLACE OF FILTER FABRIC) TOE PROTECTION- BURY AT LEAST THREE FEET OR ONE DESIGN WAVE FILTER FABRIC (IF j HEIGHT BELOW THE (IF USED IN PLACE OF BOTTOM GRADED STONE FILTER Figure 43 Typical Quarrystone Revetment Tables 13, 14, and 15 contain solutions for Equation 17 with an illustrative example of their use. If uniform guarrystone is used, the individual stones should range from 0.75W to 1.25W with 75 percent of the stones weighing W or more. For graded riprap, W corresponds to W 50 and the recommended gradation is 3.6 W 5.0 to 0 -22 W RlpraVlrhhould be limited to areas where the de!.@_3:gn wave hei'gCn)t' is less than five feet. If a graded stone filter is employed, it may be significantly more fine-grained than the armor layer. This may require the use of an intermediate layer of stone between the armor and the filter. This layer -should consist of units about 1/10 the weight of stone in the armor layer. This intermediate layer is also recommended when a filter cloth is employed because it provides bedding and. resists tearing or puncturing of the cloth under the heavy armor stone. Concrete Wave Height Range: Below five feet. A concrete rubble revetment utilizes. a waste product that is otherwise difficult to dispose of in an environmentally acceptable manner. The concrete should have the durability to resist abrasion by water-borne debris and ice pressure. In addition, all protrud- ing reinforcing bars should be burned off prior to placement. Numerous concrete rubble revetments have failed in the past, but 80 TABLE 13 TABLE 14 TABLE 15 ESTIMATED WEIGHT CORRECTION CORRECTION FOR OF ARMOR STONE FOR SLOPE UNIT WEIGHT WAVE ESTIMATED SLOPE CORRECTION UNIT CORRECTION HEIGHT WEIGHT FACTOR WEIGHT FACTOR H W Wr (f 0 0b) (ft/ft) K I 0b/ft3) K 2 0.5 1 1:2 1.0 120 4.3 1.0 10 1:2@ 0.8 130 2.8 1.5 20 -0.7 135 2.4 0 'eel: 3 mmmelillOw 2.0 50 1: 3@ 0.6 140 2.0 2.5 100 #4 1: 4 0.5 145 1.7 3.0 mmmmENSP-1 60** 1: 4@ 0.4 150 1.5 3.5 260 1: 5 0.4 155mmmogwo-1.3 4.0 390 1: 5@ 0.4 160 1.1 4.5 550 1: 6 0.3 165 1.0 5.0 750 170 0.9 5.5 1000 175 0.8 6.0 1300 180 0.7 6.5 1650 185 0.6 7.0 2100 190 0.6 EXAMPLE GIVEN.' The wave height (H) is 3.0 feet and the structure slope is 1 on 3 (1 Vertical on 3 Horizontal) and one cubic loot of rock weighs 155 lbs (wr) FIND: The required weight of armor stone (W) from the tables (Dashed Line) W = 160 lbs x 0.7 x 1.3 = 145 lbs 81 this has generally been attributable to neglect of f ilter require- ments. Figure 44 shows two cross sections that would probably be more sucessful than random dumping on a slope. The upper section uses three layers of concrete rubble, shaped so that the longest dimension is no greater than three times the shortest, thus in- creasing stability and minimizing uplift on the slabs from wave forces. The revetment shown on Figure 45 is similar, except only one layer of rubble was used. It subsequently suffered damages, but more than one layer of rubble may have improved its perfor- mance. The lower 'section on Figure 44 utilizes shaped-rubble stacked on a slope to create a stepped face. 3 LAYERS OF CONCRETE RUBBLE MHW FILTER CLOTH N\-EXISTING GROUND LINE FILTER. MHW CLOTH EXISTING GROUND LINE Figure 44 Concrete Rubble Revetment Sections Concrete Blocks Concrete blocks for semi-rigid armor layers are designed with various intermeshing or interlocking features, and many of the 82 . . ..... ... . . .... 77 AVI 77 IL Figure 45 Concrete Rubble Revetment units are patented (Figure 46). Blocks have the advantage of a neat, uniform appearance. Many units are light enough to be in- stalled by hand once the slope has been prepared. The disadvantage of concrete blocks is that the interlocking feature between units must be maintained. once one block is lost, other units soon dislodge, and complete failure may result. A stable foundation is required since settlement of the toe or subgrade can cause dis- placement of the units and ultimate failure. Also, some concrete block revetments have smooth faces that can lead to significantly higher wave runup and overtopping. Gobi (Erco) and Jumbo Blocks and Mats Wave Height Range: Below five feet (blocks). Above five feet (mats). Gobi blocks are patented units that weight about 13 pounds each. Erco blocks are similar but they are offered by a different licensed manuf acturer. Jumbo blocks are large-sized Erco blocks that weigh about 105 pounds each. The units are designed for hand-placement on a filter cloth or they are factory-glued to carrier strips of filter cloth. The latter are called Gobimats 83 COBBLETOP 15 2 FILTER FABRIC JUMBO BLOCK GOBI (ERCO) BLOCK SHIPLAP BLOCKS 4 55/e 2.5' 00 MONOSLAB (TURFBLOCK) NAMI RING 161- LOK-GARD BLOCK 8" CONTROL BLOCKS 3.0 16" 8 1.55"R(TYP) 3.3"R(TYP) 4.5"R(TYP) STANDARD CONSTRUCTION BLOCK TERRAFIX BLOCK Figure 46 Revetment Blocks' ic@ R-3 [After U.S. ArMy Corps of Engineers (1981d)] (Etcomats) or Jumbo Ercomats, depending on the size of the units. If the blocks are glued to both sides of the carrier strip, back- to-back, they are called double Gobimats (Ercomats) or double Jumbo Ercomats. Mats are preferred at sites where vandalism or theft is possibile. Both single and double mats require machine placement. Block and mat revetments have generally performed well. A large project on the Gulf of Mexico in Louisiana has weathered several hurricanes and tropical storms with only moderate damage to the block sections and little or no damage to the mat portions. Figure 47 is a photograph of an existing revetment. 41 vll@ 7777," Figure 47 Ercomat Revetment Turfblocks or Monoslabs. Wave Height Range: Below five feet. Turfblocks are designed for hand placement on a f ilter with the long axis parallel to the shoreline (Figure 48). Each block measures 16 x 24 x 4.5 inches and weighs approximately 100 pounds. Field installations have not yielded conclusive results, but their performance should be similar to Jumbo Erco blocks. Their thin, flat shape requires a stable foundation, as any differential set- tlement beneath the blocks makes them susceptible to overturning under wave action. 85 law", lw@ W"M pad 000. AO* AMW 44%, 4A __ I t -., -*__ *"I'- *rft@ @@Zl Pba 0 t n t Figure 48 Turfblock Revetment Nami Rings Wave Height Range: Below five feet. The Nami Ring is a patented concrete block shaped like a short section of concrete pipe, 2.5 feet in diameter by 1-foot high, and weighing 240 pounds. The rings are placed, side-by-side, on a slope over filter cloth. Better performance has been observed when the rings are joined together with tie rods. Sand or gravel caught up in the wave turbulence tends to be deposited inside the rings and in the'voids between adjacent rings, adding to the stability-of the section and protecting the filter cloth. Because of their shape, Nami Rings are susceptible to severe abrasion and damage by water-borne cobbles and, therefore, should be used primarily in sandy environments. 86 Control Blocks Wave Height Range: Above five feet. Control blocks come in various sizes and are similar to stand- ard concrete construction blocks, except that protrusions in the block ends provide a tongue- and-groove interlock between units. Designed to be hand-placed on a filter cloth with the cells ver- tical, the blocks can be alined with their long axes parallel to shore, but optimum performance probably results from placement perpendicular to the water's edge (Figure 49). PIZ Figure 49 Control Block Revetment Awe IV (Note: Perpendicular orienta- tion of blocks with the water- line is preferred over the parallel orientation shown in this photograph.) 4 K Concrete Masonry Blocks Wave Height Range: Above five feet. Standard construction masonry blocks should be hand-placed on a filter cloth with their long axes perpendicular to the shoreline and the hollows vertical. Their general availability is a primary advantage, but they are highly susceptible to theft. They form a deep, tightly fitting section which is stable provided the toe and flanks are adequately protected. Their primary disadvantage is that standard concrete for building construction is not suffi- ciently durable to provide more than a few years service in a marine environment. Special concrete mixes should be used when possible 87 Shiplap Blocks Wave Height Range: Below five feet. Shiplap- blocks are formed by joining standard concrete patio blocks with an epoxy adhesive. At 100 pounds or more per unit, they are designed for hand placement on a filter. The same precau- tions about concrete mixes apply here. These blocks are discussed in Hall and Jachowski (1964). 'A photograph and cross-section of one revetment are shown on Figures 50 and 51. ki E, 4 "74 M' A K N,A Figure 50 Shiplap Block Revetment Wood railing 16 Concrete sidewalk 3'- d' x 6" thick Original ground line, EPOXY Glued Joint ts- C Z- Concrete Block Detoils Woven plastic filter cloth MLW -Z@Stone toe protection--_> 6' Layer to 12 stone 2" x 6" Timber Toe cutoff wall would be required for a sand beach. Figure 51 Shiplap Block Revetment Section [U.S. Army Corps of Engineers (1977c)) 88 Lok-Gard Blocks Wave Height Range: Below five feet. Lok-Gard blocks join together using a tongue-and-groove system (Figure 52). The 80-pound, patented units are designed to be hand-placed on a filter with their long axes perpendicular to the shoreline. Since a Lok-Gard revetment has a smooth surface, in- creased runup heights must be considered in the design. 01 TK> ItT Figure 52 Lok-Gard Block Revetment Terrafix Blocks Wave Height Range: Above five feet. Terrafix blocks are patented units that join together with a mortise and tenon system, and have two cone-shaped projections which fit holes in the bottom of the adjacent block (Figure 46). In addition, holes through the center of each block allow for stainless steel wire connection of many individual blocks. The uniform interlocking of the 50-pound units creates a neat, clean appearance (Figure 53). Stacked Bags or Mats Wave Height Range: Below five feet. Several manufacturers produce bags and mats in various sizes and fabrics that are commonly filled with either sand or a lean 89 Figure 53 Terrafix Block Revetment (Photo Courtesy of Erosion Control Products, Inc.) mixture of concrete for use in revetments. While no special equip- ment is required for sand-filled units, a mixer, and possibly a pump, are needed for concrete-filled units. Bags should be filled and stacked against a prepared slope with their long axes parallel to the shoreline and joints offset as in brick work (Figure 54). Grout-filled bags can be further stabilized by steel rods driven through the bags. The advantage of a bag revetment is its ease of construction and moderate cost. Sand-filled bags are relatively flexible and can be repaired if some of the original bags are dislodged. In addition, stacked bag's are suitable as temporary emergency protec- tion measures. Among their disadvantages, they are limited to low energy areas, have a relatively short service life compared to other revetments, and generally have an unattractive appearance. Since concrete-filled structures are rigid, any movement or dis- tortion from differential settlement of the subgrade can cause a major failure that would be hard'to repair. Sand-filled bags are highly susceptible to damage and possible failure from vandalism, impact by water-borne debris and deterioration of material and seams by sunlight. The smooth, rounded contours of bags also 90 I uclw low* Figule 54 Stacked Bag Revetment Fig ure 55 Grout-Filled Mattress (Fabriform) Revetment (Photo Courtesy of Construction Techniques, Inc.) present an interlocking problem and they should be kept flatter and underfilled for stability. Mattresses are designed to be laid flat on a prepared slope, joined together, and then filled (Figure 55). They form a large mass of pillow-like concrete sections with regularly spaced filter meshes for the passage of water. They should always be installed according to the manufacturer's recommendations. 91 Bags or mattresses should be placed only on a stable slope. While a stacked bag revetment can be placed on a steeper slope than a mattress, it should not exceed 1 vertical on 1.5 horizontal. A stacked bag revetment should be at least two bags thick, preferably with the outside layer concrete-filled and the interior bags sand- filled. When sand is used as filler material, the bag or mat fabric, and its seams, must be resistant to ultraviolet light. Figure 56 shows a nonstabilized bag after six months of exposure. Where vandalism or water-borne debris are likely, only concrete- filled units should be used. Al 7, AF AW Figure 56 Deterioration of Sand Bags Under Ultraviolet Light Some form of toe protection should be provided, or the toe should be buried well below the anticipated scour depth. Also, an adequate filter system, such as a properly installed and sized filter cloth, should be installed. some types of bags and mats which have been used in the past are described below. Burlap Bags. Burlap bags are recommended only when filleT @witn concrete because of rapid deterioration in the shoreline environment and the ease with which they can be torn. Sand Pillows. Sand Pillows are ultraviolet-resistant bags made from a woven acrylic fabric. They weigh approxi- mately 100 pounds when filled. Because of their resistance to sunlight, they are suitable for sand-filling in some areas. 92 Dura BacLs. Dura Bags are large (4 x 12 x 1. 7 feet), and must be filled in place using a pumped sand-slurry or con- crete. Their large size makes them more resistant to movement under wave attack. Fabricated of ultraviolet-resistant mater- ial, they can be used in installations exposed to sunlight. Fabriform Nylon Mat. The mat is designed to be filled with a highly fluid, lean-cement mixture. The exterior cloth envelope serves primarily as a form until the grout hardens. Fabriform is a patented product, available in several fabric styles, including some with filter points (weep holes) to provide slope drainage. Fabriform mats should be installed according to the manufacturer's instructions. Miscellaneous Gabions Wave Height Range: Above five feet. Gabions are rectangular baskets or mattresses made of gal- vanized, and sometimes PVC-coated, steel wire, in a hexagonal mesh (Figure 57). Subdivided into approximately equal sized cells, standard gabion baskets are 3 feet wide, and available in lengths of 6, 9 and 12 feet and heights of 1, * 1. 5 and 3 feet. Mattresses are either 9 or 12 inches thick. At the job site, the baskets are unfolded and assembled by lacing the edges together with steel wire. The individual baskets are then wired together and filled with 4- to 8-inch diameter stone. The lids are finally closed and laced to the baskets, forming a large, heavy mass (Figure 58). & e4 461@* Figure 57 Unassembled Gabions 93 41 -, Va", Figure 58 Gabion Revetment One advantage of a gabion structure is that it can be built without heavy equipment. Gabions are flexible and can maintain their function even if the foundation settles. They can be re- paired by opening the baskets, refilling them, and then wiring them shut again. The disadvantage of a gabion structure is that the baskets may be opened by wave action. Also, since structural performance depends on the continuity of the wire mesh, abrasion and damage to the PVC coating can lead to rapid corrosion of the wire and failure of the baskets. For that reason, the baskets should be tightly packed to minimize movement of the interior stone and subsequent damage to the wire. Rusted 4nd broken wire baskets also pose a safety hazard. Gabion structures require periodic inspections so that repairs are made before serious damage occurs. To insure best performance, use properly sized filler rock. Interior liners or sandbags to contain smaller sized material are not recommended. The baskets should be filled tightly to prevent movement @of the stone and they should be refilled as necessary to maintain tight packing. Gabions should not be used where bombardment by water-borne debris or cobbles is present, or where foot traffic across them is expected.. 94 Steel Fuel Barrels Wave Height Range: Below five feet. This type of revetment is limited to remote areas with an abundance of used fuel barrels of little salvageable value (Fig- ure 59). Due to rapid corrosion of the barrels in warm water, the system is only reliable in arctic regions. The barrels should be completely filled with coarse granular material to preclude damage by floe ice and debris, and the critical seaward barrels should be capped with concrete. Also, partial burial of the barrels in- creases stability. ,low" Figure 59 Steel Fuel Barrel Revetment Concrete Slabs Wave Height Range: Below five feet. Photographs of a typical structure were shown on Figure 20. The structure failed for a number of reasons, including improper filtering, inadequate toe protection, and lack of flank protection. Placed on a flatter slope, and with due regard for proper design considerations, this type of structure can provide low cost protec- tion when large slabs are available. Fabric and Ballast Revetments using a fabric filter cloth as the slope's armor layer, held in place by some form of ballast, have not been suc- cessful and are not recommended. 95 BREAKWATERS Breakwaters are either floating or fixed. Floating break- waters function at or near the water's surface and must be firmly anchored to prevent displacement. Fixed breakwaters are construct- ed on the bottom and may or may not pierce the water's surface. When they do not, they are called sills. Their height and porosity determines how effectively they dissipate wave energy. By trapping sand on their landward side, breakwaters protect the shore while simultaneously enhancing recreational uses. Unlike groins, they are able to trap sand moving both parallel and perpen- dicular 'to shore. Unfortunately, this sand-trapping (accreting) ability can also cause erosion of downdrift beaches. In most cases heavy construction equipment, often barge mounted, is necessary for breakwater construction. Floating Breakwaters Wave Height Range: Below five feet. Floating breakwaters can be constructed of virtually any buoyant material such as rubber tires, logs, timbers, and hollow concrete modules. Floating breakwaters are particularly advan- tageous where offshore slopes are steep and fixed breakwaters would be expensive because of deep water. They can also be used where the tidal range is large and fixed breakwaters would be subjected to widely varying degrees of submergence. Floating breakwaters are also excellent for temporary installations, such as where vegeta- tion requires protection while becoming established. Floating breakwaters have several disadvantages as well. They are effective only against short-period waves (less than five seconds), which are those most commonly present in sheltered loca- tions where low cost protection is most appropriate. Also, they may regarded as eyesores in some areas, they tend to collect float- ing debris, and they may require more maintenance than fixed break- waters. Rubber Tires. Two possible arrangements are shown on Fig- ure 60. The upper configuration, known as a Wave-Maze, is patented and cannot be used without payment of royalties (See Other Help Section). The bottom configuration was developed by the Goodyear Tire and Rubber Company for promotional purposes and may be used without royalties. The use of other configurations is limited only by the imagination of the designer. The basic elements of design for floating tire breakwaters are listed below. Length. The length parallel to shore should be suf- f 'E icie t- to provide the desired protection and will vary with the structure's distance from shore. 96 NCHOR CHAIN WAVE-MAZE + DESIGN BOLTS If Ff It BAY GOODYEAR DESIGN Figure 60 Floating Tire Breakwater Modules [After U.S. Army Corps of Engineers (1978b)] 97 Width. The width should be chosen to yield a satisfac- tory decrease in the transmitted wave height (the wave height behind the structure). No definite criteria would apply, but wave height reductions of 30 percent may be an acceptable starting point for design. This would reduce the energy reaching the protected shoreline to about 49 percent of that of the incident waves (0.7 x 0.7=0.49). if later experience shows this to be an unsatisfactory or excessive level of pro- tection, the breakwater can be made wider or narrower by adding or removing modules, or its distance from shore or length can be changed. The design breakwater width is a function of the wave- length at the site. With a known water depth and wave period, the wavelength can be found using either Figure 26, or Equa- tion (3). Figure 61 gives the wave transmission coefficient, K as a function of the design wave height. The transmitted W@@e height is determined by multiplying the incident wave height by K For instance, if the local wavelength, L, is 80 feet, and V breakwater width, W of 40 feet is proposed, W /L is 0.50, and K is 0 90. I?tLe incident wave height is 5@@ feet, the translitted* wave will be 4.5 feet. This wave will contain 0.9 x 0.9, or 81 percent of the energy of the incident wave. This may not be a satisfactory level of pro- tection in many cases. Draft. Increased depth of penetration in the water column increases the effectiveness of floating breakwaters. In general, the draft should be greater than one-half the design wave height. Two-layer structures or the use of truck or tractor tires will achieve greater draft. Flotation. The air trapped within the top of vertical tires provides sufficient flotation in most cases. In quiet water, the air is eventually dissolved by the surrounding water and the structure sinks. wave action, however, re- plenishes the air supply, but care must be taken not to use tires with puncture holes. More permanent flotation is pos- sible with styrofoam blocks or foam injected into the crowns of the tires. In salt water, marine growth that is not peri- odically removed will eventually sink the structure. Sand also collects in the tires and can sink them, but this can be prevented by drilling holes in the bottoms of the tires. In that case, flotation aids such as styrofoam blocks should be used. Fastening Materials. Stainless and galvanized steel cable; polypropylene, nylon, Poly-D and Kevlar rope; gal- vanized and raw steel chain; and rubber conveyor belt edging have been used for tying tires together. Davis (1977) pre- sented the results of tests using all of these, and found that conveyor belt edging was the most satisfactory. The others failed because of either corrosion, abrasion by the tires, fatigue, or deterioration from other factors. Steel cables sawing through the tires have caused some, devices to fail. 98 1.20 1.00 100 0.80 64 M z M 0 0.60 36 @10 0 0 z E 0.40 16 rn 0 0.20 4 0 0 0.20 OAO 0.60 0.80 1.00 1.20 1.40 Ratio of Breakwater Width to Wavelength'(Wst/L) Figure 61 Transmitted Wave Height Versus structure Width [Giles and Eckert (1979)] Rubber belt edging, a scrap material derived from the manufac- ture of conveyor belts, is available from several rubber companies and comes in a wide range of widths and thicknesses. For tire breakwater construction, the belting should be at least 2 inches wide and 0.375 inches thick. Anchorage. Floating tire breakwaters must be securely ancho:Fe-dto prevent displacement. Mooring loads can be deter- mined from Figure 62. Danforth and other embedment anchors, as well as screw anchors and large concrete blocks, have been used with mixed results. They are probably best suited for seasonal use in a mild wave climate, but they tend to creep over long periods in soft bottoms and are not always desirable for permanent installations. In those cases, driven piles are generally the best means of stable anchorage over long peri- .ods. Giles and Eckert (1979) provide guidance on anchorage systems. Other Materials. other floating materials can be used in place of scrap rubber tires. Bundles of logs can be chained together or other barriers can be fabricated from treated timber. Modules of lightweight concrete filled with flotation foam have also been successful. The proportioning and design factors presented for rubber tire breakwaters would also apply to these. Fixed Breakwaters and Sills An important feature of a fixed breakwater is its height, which determines how much wave energy passes over the structure. In building a fixed breakwater, some settlement should be antici- pated in the structure's design height, the actual amount being a function of the soil type, the weight of the structure, and type of foundation. Longard Tubes Wave Height Range: Below five feet. The advantages and disadvantages of Longard tube bulkheads generally apply to breakwaters. An added disadvantage is that the protective epoxy coating cannot be applied to wet tubes so that damages are more likely. Therefore, they should not be used where the tube may be exposed to vandalism or water-borne debris. Fig- ure 63 contains before and after views of a Longard tube slashed by vandals, eventually causing it to entirely deflate. The tube should be installed over a layer of synthetic filter- cloth with factory-sewn, 10-inch Longard tubes on each edge to reduce the potential for failure due to toe or heel scour. Where a 69-inch tube cannot provide sufficient height, an alternate break- water system should be used. 100 120 100 80 V 60 C 0040 20 [Giles and Eckert (1979)] 0 0 4 5 Incident Wave Height (ft.) Figure 62 Mooring Loads for Floating Tire Breakwaters 8 march 1979 00 7 F15 November 19791 A Figure 63 Before and After Views of a Longard Tube Breakwater Sand-Filled Bags Wave Height Range: Below five feet. Sand-filled bag breakwaters are constructed of stacked bags in a staggered pattern (Figure 64). The integrity of the structure 102 Figure 64 Sand-Filled Bag Breakwater depends on the individual bags remaining in place and intact. The bags and seams must be resistant to ultraviolet light to preclude deterioration from prolonged sunlight exposure. They should not be used where vandalism is expected or where the structure will be exposed to water-borne debris. Lighter bags (100-pound range), like those used for revetments, are displaced when exposed to even moderate waves. Larger units, such as Dura Bags, are recommended even through they are more difficult to handle and require filling in place. A filter cloth should be placed under the bags to reduce settlement in soft bottoms (Figure 65). During construction, bag-to-bag abutment should be insured to minimize wave transmission through gaps between bags. 12-FOOT LONG NYLON SANDBAG 1. 7' _?1HW ANCHOR SANDBAG FILTER CLOTH 10, 201 4 :G Figure 65 Sand-Filled Bag Breakwater Section [After U.S. Army Corps of Engineers (1978c)] 103 Grout-Filled Bags Wave Height Range: Below five feet. The major advantage of grout-filled bags is that the units hold their shape after the fabric deteriorates or is torn. Again, use of larger bags is recommended because the smaller ones are susceptible to displacement. In addition, larger units reduce the number of bag contact points where openings may develop. The recommendations made for sand-filled bags also apply to grout-filled bags, except that vandalism is not a major concern. Gabions Wave Height Range: Below five feet. The same basic design considerations for gabion revetments also hold here. The wire mesh should be PVC-coated, the baskets should be tightly packed, and a filter cloth should be used beneath the structure to help control settlement. A gabion mat should be provided around the structure to protect against scour. Tight packing of the stone is particularly important to avoid large distortion of the baskets under wave action. A typical cross section and photograph of a gabion breakwater are shown on Fig- ures 66 and 67. 18'_O 2'-0 9-0 7'-Ok' wire -0 3'- 0" 2'-d' Mes OFFSHORE SIDE DESIGN WATER Stone LEVEL 0 (.0 Existing Lake Bottom@@J (depth from take bottom to bedrock varies) Figure 66 Typical Gabion Breakwater Section [After U.S. Army Corps of Engineers (1978a)] S 104 At Figure 67 Gabion Breakwater Z-Wall Wave Height Range: Above five feet. A Z-Wall is a patented device constructed with reinforced concrete panels set on edge in a zigzag fashion (Figure 68). The structure is designed for placement close to the shore on the . ...... ... Figure 68 Z-Wall Breakwater 105 existing bottom without the use of a filter. A single bolt acts as a hinge that interconnects adjacent panels and allows for non-uni- form settlement, but with limited tolerance; so that Z-Walls are sensitive to bottom conditions. If the tolerable differential settlement is exceeded, the panels tend to lean against or pull apart from each other, causing the concrete to spall in stressed areas. The nuts on the connecting bolts tend to unwind under wave agitation, and should be inhibited by the use'of double nuts and destruction of the exposed threads behind the nuts. Otherwise, the end units may fall away if the nuts unwind completely. The Z-Wall performs best at a site with a firm bottom. The six-foot panel height limits its use to relatively shallow water. Surgebreaker wave Height Range: Above five feet. A Surgebreaker is a modular device constructed with patented, 3,700-pound, precast, reinforced concrete modules (Figure 69) with vent holes to release wave pressure buildup. The triangular mod- ules are 4 feet high and 7 feet wide - They are designed to be placed side-by-side on the existing bottom with the flatter sloped face of the device toward the waves (Figure 70). V 4A 4.2, Figure 69 Surgebreaker Modules 106 iJ" '@gzl qe R, Figure 70 Surgebreaker Breakwater Sandgrabber Wave Height Range: Below five feet. A patented configuration of interconnected concrete construc- tion blocks (Figure 71), the Sandgrabber is a device that allows 4, Figure 71 Sandgrabber 107 for some differential settlement of the blocks by using U-shaped, galvanized-steel connecting rods. The hollow blocks allow waves to wash sand through, trapping the coarser, water-borne particles behind the structure. The Sandgrabber must be installed by a franchised contractor. The current design does not use any form of toe protection, nor is the structure placed on a filter. As a result, the struc- ture normally settles unevenly and rotates seaward into a scour trench. Because of these movements, the allowable amount of dif- ferential settlement is sometimes exceeded and the resulting stress of the U-ties against the concrete blocks may crack or break them. This can eventually lead to complete collapse of the structure. Weak concrete hastens the process, so compressive strength tests should be performed on each batch of blocks before construction. A precaution when using a Sandgrabber, or any other breakwater, is to avoid downdrift erosion damages. Backfilling with sand should prevent any potential problems. Quarrystone Wave Height Range: Above five feet. A stone breakwater is structurally similar to a stone revet- ment (Figure 72) and stone sizes should also be selected by using Equation (17). However, the stability coefficient, K D should be selected from Table 16, rather than Table 12. %V IrA _'T AT 04 r Figure 72 Quarrystone Breakwater 108 Table 16 KD VALUES FOR STONE BREAKWATERS Structure Structure Trunk Head (End) Slope Armor Layers KD K D cot 0 Quarrystone Smooth rounded 2 2.1 1.7 1.5 to 3.0 Rough angular 2 3.5 2.9 1.5 2.5 2.0 12.0 13.0 Graded riprap Not Recommended A major advantage of a quarrystone breakwater is that the structure does not necessarily fail when differential settlement occurs. Through the years, stone has been used for more breakwater construction than any other material. It is time-tested and can be quite economical if suitable rock is available locally. Timber Piles and Brush Wave Height Range: Below two feet. A brush breakwater is constructed of two parallel rows of posts driven into the offshore bottom, connected across the top with timber crossties, and filled with brush. Brush should be cut longer than the space between the posts and placed parallel to the structure alinement. Not suitable for permanent protection, this breakwater can be used for temporary sheltering of young vegeta- tion. Used Tires and Timber Piles. Wave Height Range: Below two feet. Timber piles can be driven into the bottom, so that every three piles form a triangular pattern, and used automobile tires can then be stacked on the piles. Just above the top tires, the triangularly grouped piles should be interconnected using 2 x 6- inch planks bolted to the piles (Figure 73). The structure, whose stability depends on the depth of pile penetration, has proven effective against mild wave action. 109 Figure 73 Used Tire and Timber Pile Breakwater GROINS Important design considerations for groins include their height, length, spacing (if there are more than one) and the lit- toral transport rate. Their height determines how much sand can pass over the structure. Low groins, which essentially follow a foot or two above the natural beach profile, are widely used be- cause they stabilize the beach but do not trap excessive amounts of sand and thereby cause downdrift damages. The groin length should not extend past the breaker zone or else it may force the bypassing sand too far offshore and cause downdrift erosion damages. The groin spacing should generally be two or three times the groin length. Groins can be built as sheet pile structures that depend on ground penetration for support, or as gravity structures that resist movement solely because of their weight. In either case, it is essential to prevent or adequately plan for bottom scour. For sheet pile structures, scour reduces their amount of embedment and makes them vulnerable to tipping. Rigid gravity structures can settle unevenly and be damaged if undermined by scour. 110 Stacked Bags Wave Height Range: Below five feet. A stacked bag groin is similar to a stacked bag breakwater (Figure 74). The bags can either be sand- or grout-filled. As with breakwaters, larger bags are recommended because lighter, smaller bags are too susceptible to displacement. The recommen- dations for bag breakwaters also apply to groins. The bags in the photo were filled between wooden forms to achieve their blocky shape, but this was unnecessary. When installed properly, stacked bag groins have performed well; however, they should only be con- sidered a short-term solution when filled with sand. Oy ZANIMM Figure 74 Stacked Bag Groin Gabions Wave Height Range: Above five feet. The recommendations for gabion revetments generally apply. The groin should be underlain with filter cloth to inhibit settle- ment, and all baskets should be made from PVC-coated wire mesh. Tiers of baskets should be tied together with appropriately sized wire to prevent shifting of upper tiers over lower tiers, and tight packing is needed to minimize distortion of the baskets and damage to the wire. Adequate toe protection is required to prevent set- tlement and basket distortion. Thin gabion mattresses are ideal for this purpose. Figure 75 shows a gabion groin. ill Figure 75 Gabion Groin Steel Fuel Barrels Wave Height Range: Below five feet. The use of steel fuel barrels for construction is only econo- mical in remote arctic areas where used barrels are readily avail- able and they have no other salvage value. Barrel groins have worked well where littoral transport characteristics are suitable for shore stabilization with a low groin. The barrels should be completely filled with gravel to protect them from crushing by ice floes or from damage due to floating debris. They should also be capped with concrete for additional strength, and entrenched to prevent undermining by scour on the downdrift side. Quarrystone Wave Height Range: Above five feet. Quarrystone, a durable and time-tested material for shore protection, should always be considered where locally available. Figure 76 contains a typical crbss section and profile of a quarry- stone groin. The stone should be sized using Equation (17) and values from Table 16. Figure 77 is a photograph of a quarryston% groin. 112 Variable Water Level Datu w., PROFILE NOTE: Dimensions and details to be Vortes determined by particular site conditions. Armor Stone Core Stone (Quarry Run) CROSS-SECTION Figure 76 Quarrystone Groin Section and Profile [U.S. Army COrPs of Engineers (1977c)] a' @ ®r A Figure 77 Quarrystone Groin 113 Longard Tubes Wave Height Range: Below five feet. Longard tubes have performed fairly well when remaining intact (Figure 78). Failure has usually resulted from holes or tears in the fabric and loss of sand fill. Longard tubes are probably best as a short term or emergency measure because of their vulnerability to damage. When used as a groin, the Longard tube should be under- lain by a filter cloth with 10-inch tubes factory-stitched to each side. The filter cloth helps to prevent settlement, and the small tubes hold the cloth in place. . . .. . ...... 14, Figure 78 Longard Tube Groin Sheet Piling Wave Height Range: Above five feet. Sheet pile groins, an old and proven means of shore protec- tion, can be constructed of timber, steel, or aluminum sheeting. Toe protection or adequate embedment is required to insure the structure's stability. The general recommendations given for sheet pile bulkheads also apply to groins. Figure 79 contains a section and profile, and Figure 80 a photograph of a typical sheet pile groin. 114 Riprop Along Updrift Face of Grain Steel Cap Riprop Along Downdriff Face of Groin A L. W. 0. ..Sand Fill wn, Existing Lake Bottom Assumed Clay Line MEMO- -.j A tone Toe Protection _LWD@ -L- Fi 11; i Assumed Clay Line Steel Sheet Pilin SECTION A-A Figure 79 Sheet Pile Groin Section [U.S. Army Corps of Engineers (1977c)] tj, Figure 80 Timber Sheet Pile Groin Steel Sheet PH, 7g 115 Timber and Rock Wave Height Range: Below five feet. Many structural forms are possible for timber and rock groins. Figure 81 shows a timber crib structure that retains a stone f ill. Care must be taken to insure that the rock is larger than the gaps between the timbers. Rock has escaped from the offshore compart- ment of the groin in the figure for that reason. Treated timbers should be used; and to insure structural stability, they should be securely fastened together with long wrought iron or coated steel rods, threaded at the ends to accommodate washers and nuts. Alternate arrangements for timber groins are possible. Two rows of round structural piles can be driven or augered deep into the beach, with timber planking spiked to the piles. The piles can be placed close together with the planking set in the space between (Figure 82), or the piles can be more widely separated to form a crib-type structure (Figure 83). Q_ Figure 81 Timber Crib Groin 116 f fjAp Nio NO Figure 82 Timber Plank Groin -71 Figure 83 Timber Plank Groin f@, Av 117 BEACH FILLS Beach fills are constructed by mechanical means such as dredg- ing and pumping from offshore deposits, or by overland hauling and dumping by trucks. The resulting beach provides some protection to the area behind it, while also serving as a valuable recreational resource. An excess of fill will have to be placed initially because the finer material will be lost from the beach as the waves sort the deposit. The amount of overfill needed to account for these ini- tial losses depends on the textural characteristics of the fill and the in-place material. These are compared by using measures of the mean grain size and sorting of the sand.samples as given by Hobson (1977). Sorting is an indication of the range of particle sizes that are present. A well sorted sample contains particles that are approximately the same 'size. A poorlg sorted sample contains a gradation of particle sizes. Mean grain sizes and sorting are expressed in phi units. These are defined as, -1092 d (mm) (18) where, d the particle diameter in millimeters. Note, (mm) 1092 d(mm) = logio d (mm) /loglo(2). Therefore, -3.32 loglod (mm) (19) Table 17 compares the millimeter and phi size scales. Table 17 PHI VERSUS MILLIMETER PARTICLE SIZES d (mm) 256 -8 64 -6 8 -3 4 -2 2 -1 0 0.5 1 0.25 2 0.125 3 0.0625 4 118 An estimate of the mean particle size is M = 084 + 016 (20) 2 where 084 and 016 are points on the gradation curve that represent the percentage of the sample that is coarser than the particular phi size. Phi sorting can be estimated by S =084 - 016 (21) 2 Figure 84 provides a fill factor that specifies the amount of fill material needed to produce a given volume of in-place materi- al. The axes are defined in terms of the mean particle size of the borrow (fill) and native (in-place) material (Mb and Mn), and the sorting of the borrow and native material (Sb and Sn). For in- stance, if Mb = 3. 0, Sb = 2.0, M = 3.50 and S = 1.00; the fill factor from figure 84 is 1.2. Therefore, if a beach containing Figure 84 Fill Factors for Beach Fills [After Hobson (1977)] 119 1, 000 cubic yards of sand is desired, it will be necessary to initially place about 1, 200 cubic yards of sand from the borrow source. Figure 85 illustrates the important design factors to consider when constructing a beach fill. The berm elevation should be chosen to decrease the likelihood of overtopping by waves during storms. The berm width is determined by geometry to provide for the volume of fill to be placed, or for the shoreline use require- ments. The beach s.lope should be chosen to parallel the existing profiles and slopes. This is based on the assumption that the existing beach is in equilibrium with the wave forces and that the new beach will eventually assume a similar shape. The shaping of the beach fill profile can either be done by equipment at the time it is placed, or it can be reshaped by waves. The final equi- librium slope will depend on the texture of the fill material, coarser-grained sand resulting in a steeper beach slope than pre- viously existed. If fill is placed over a short length of shoreline, it will create a projection that will be subject to increased wave attack. Therefore, it is generally preferable to make the transition to the existing shoreline over a longer distance. This may require a cooperative effort involving a number of landowners. If this is impractical, protective structures such as groins may be required to retain the fill. BERMt EXISTING BOTTOM -DESIGN WATER LEVEL LOW WAT E R INITIAL FILL PLACEMENT ERODED BOTTOM EQUALS DEPOSITED VOLUME -;;-,-DESIGN WATER LEVEL FINAL SLO E -LOW WATER C DEPENDS ON COARSENES OF THE SAND FILL RESPONSE TO STORM WAVES Figure 85 Beach Fill 120 VEGETATION Vegetation has been used for stabilizing shorelines either as a substitute for, or supplement to, structures. Vegetation is an inexpensive, and generally easy, approach to providing erosion control. It is not, however, applicable to all situations. it cannot always prevent erosion, nor can it stop the recession of bluffs caused by groundwater seepage. In order to confront these types of problems, it is necessary to consider a combination solu- tion such as a structural device and vegetation. Vegetation uses are limited by site characteristics such as climate, soil properties, wave exposure, and salinity regimes. The following discussion will focus on species which may be used for marsh, beach, dune and slope plantings. For each species, the applicable geographical region and planting specifications will be described. Further information on these and other species not mentioned in this report can be obtained from county offices of the Soil Conservation Service, state coastal zone management programs, or Corps of Engineers districts. Marsh Plants Coastal marshes are those herbaceous plant communities which are normally inundated or saturated by surface or groundwater. They may be narrow fringes along steep shorelines or they may cover wide areas in shallow, gently sloping shore regions typically found in bays and estuaries (Figure 86). In saltwater marshes, salinity is generally equal to or slightly less than seawater (35 parts per thousand salt). Freshwater marshes experience water level fluc- tuations resulting from groundwater table and seasonal climatic changes. To establish a coastal marsh, the site must be evaluated based on geographic area, tidal elevation and range, salinity, fetch length, and soil properties. The vegetation prevalent in three saltwater marsh regions and the Great Lakes are discussed below. Planting specifications are summarized in Table 18. The suita- bility of a site for marsh plantings can be evaluated using Fig- ure 87. Atlantic Coast Marshes. Common vegetation found in Atlantic coast marshes is describe riefly below. Smooth Cordgrass (Spartina alternaflora). This is the dominant marsh grass from Newfoundland to about central Florida. It is well adapted to soils not exposed to air that range from coarse sands to silty clays. Three distinct height forms are recognized. The tall form is generally found along tidal creeks and drainage channels, the short form grows on flat or gently sloping areas away from channels, and the medium form, when present, is found in transition areas be- tween stands of the short and tall forms. 121 Table 18 PLANTING SPECIFICATIONS FOR MARSH PLANTS Type Planting Time Plant Form Recommended Spacing Tidal Range and Plant Location Atlantic Coast Marshes Smooth cordgrass March-May sprigs 31 apart < 4.51 range-plant MLW to MHW (Spartina alternaflora) 15 week old seedlings 1.51 apart > 4.51 range-plant MTL to MHW 6 month old seedlings 1.5' apart or plugs Saltmeadow cordgrass March-May Sprigs 31 apart MHW to estimated highest tide (Spartina patens) 15 week old seedlings Black needle rush Spring Seedlings As 1-5 percent of cordgrass Ab ove MHW (Juncus roemerianus) plantings Common reed Spring Sprigs 1.5'-3.01 apart Above MHW (Pbragmites communis) Mangroves Late February- Seedlings 1.51 apart Generally MTL and above Black (Avicennia germinans) March Established plants 61-101 apart Red (Rhizophara mangle) White (LaguncUlaria racemosa) Gulf Coast Marshes Gulf cordgrass March-May Sprigs 1.5'-3.01 apart MHW and above (Spartina spartinae) 15 week old seedlings 1.51 apart 6 month old seedlings 1.51 apart Saltgrass spring Seedlings 1.5'-3.01 apart MHW and above (Distichlis spicata) Pacific Coast Marshes Pacific cordgrass April sprigs 1.5'-3.01 apart Below MTL (Spartina foliosa) Pickleweed spring sprigs 0.51-3.01 apart MHW to estimated highest tide (Salicornia spp.) Seeds 5-10 seeds/sq ft. Sedge April-June Seedlings 1.4'-3.01 apart Above MTL (Carex lyngbyei) Tufted hair grass April-May Seedlings 1.5'-3.01 apart Above MLHW (Deschampsia caespitosa) Arrowgrass April-June Seedlings 1.51-3.01 apart Above MTL (Triglochlin maritima) A Figure 86 Marsh Vegetation Smooth cordgrass can be planted with a better chance of success than any other coastal marsh species native to the United States. Its ideal salinity range is 10 to 35 parts per thousand. Two to four weeks after planting, 30 to 45 lb/ac of a fertilizer which contains equal parts of available nitrogen and phosphate should be applied. Saltmeadow Cordgrass (Spartina patens). This species is extensive in the irregularly flooded high marsh zone along the Atlantic coast. It is able to withstand extended periods of both flooding and drought, growing in spots where the surface drainage is poor and water ponds during rainy periods. it cannot, however, tolerate the daily flooding of the intertidal zone. Saltmeadow cordgrass is a valuable stabilizer in the zone between smooth cordgrass and the upland grass species. Two to four weeks after planting, 30 to 45 lb/ac of fertilizer containing equal parts of nitrogen and phosphate should be applied. 123 I* SHORE 2., DESCRIPTIVE CATEGORIES 3* VARIABLES (SCORE AS INDICATIRM ) FETCH -AVERAGE Score: 0 Score: 2 Score: 4 Score: 6 Score: 8 Score: 10 AVERAOI MIANU LIEU 3.1 6.1 9.1 12.1 awmat * UMFTM (MILES) 11.91 13.81 13.71 (7.6) * OPEN WATER SEAMED THAN to to to to KOMCM TO 30 1S.0 ME NMI Of 4S 11.81 6.0 9.0 12.0 IS.0 (9-41 EITKISOWM?EBKKAI ____NZE7 13.71 IS.6) (7.51 19.4) b.FETCH-LONGEST SCOW 0 ScoEs: 2 Score: 4 1 Score: 6 Score: 8 Score: 10 MUST DISTANCE LESS 4.1 8.1 12.1 16.1 mmAnn IS UNETERS (MILES) THAN 12.6) IS.11 (7.61 110.11 OF OPEN RAT" ND"u THAN KWMUW Is .4.0 to to to to 20.0 (2.5) ME UWE IM as 112.6) .0 12.0 16.0 20.0 PER DIM SIDE If PENDICULAN. (5.0) 17.51 (10.01 (12.61 c. SHORELINE Score: 0 Score: 2 - Score: 4 GEOMETRY COVE NWWU1T HUD"ND sixwom OR ST"mm SENERAL SRAPE Of ME SNOOELINI S1101miNE AT ME PONT OF INTEREST PLUS 211 METERS (no FT ON EITNIER SIDE . . . . . . . . . . . . . . . . ZN Score 0 d. SHORE SLOPE I Score: 4 SLIM OF ME PLANTM6 AREA, GRADUAL I VERTICAL To NORinmik ) LESS STEEP 5;;;;;;w 1 to IS ON MORE THAN 1 to is a. SEDIMENT Score: 0 Score: 2 1 Score: 4 1 Score: 6 1 Score: 8 61ARE SITE of S[glMENIS SILT a FINE MIEDIUM COASISE CLAY SAND I SAND SAND I GRAVEL f. BOAT TRAFFIC Score : 0 Score : 8 Score: 16 PROXIMITY Of SITE TO 1AVIUIIOj CMAMNELS NO NAVIGATION NAVIGATION CHANNEL NAVIGATION CHANNEL CHANNEL WITHIN FIR LAASE VESULS I KILOMETER WITHIN I KILOMETER WITHIN 100 METERS It SOUL RECREATIONAL CUR 10.6 MILES 1 10.6 MILES I 133OPF) g. WIND Score: 0 Score : 4 Score: 8 SHIELTIENIIED DOES NOT FACIE FACES 0 ME ORIENTATION Of ME gf[ IN THE DIKCTION OF THE DIIIIECTION OF 10 RELAIIIIII 11 LOCAL WINDS FROM PWEVAIUNG WINDS MVAIUNG WINDS WIND on on FIIIEQUENT STORM WINDS LFREQUENT STORE WINDS 4, CUMULATIVE WAVE CLIMATE SCORE SCORE 1 TO 10: USE SPRIGS AT 3-FOOT SPACINGS IN 10-FOOT (MINIMUM) ZONES. 11 TO 20: USE SPRIGS*OR 15-WEEK SEEDLINGS AT D2-FOOT SPACINGS IN 10-FOOT (MINIMUM) ZONES. 21 To 30: USE 5-7 MONTH SEEDLINGS OR PLUGS AT D2--FOOT SPACINGS IN 20-FOOT (MINIMUM) ZONES. ABOVE 30: DO NOT PLANT Figure 87 site Evaluation Form for Marsh Plants [After U.S. Army Corps of Engineers (1980)] 124 Black Needle Rush (juncus roemerianus). This species is extensive along the Ttlantic coast south of New England. It is found in high marshes where it is f looded only by wind- driven tides or in areas near the edge of uplands where fresh- water seepage regularly occurs. It is a good stabilizer, although difficult to propagate, yet under favorable condi- tions it will invade areas already populated by cordgrasses. Common Reed (Phragmites communis). The common reed grows 4.5 to 12 feet tall and is widely distributed in brackish (salinity range 1 to 35 ppt) to freshwater areas above the mean high water level. It is easy to transplant and provides good stability; however, it does tend to compete with other plants and may become a nuisance by crowding out more desir- able species. Mangroves. Three species of mangrove--black (Avicennia germinans), red (Rhizophora mangle), and white (Laguncularia racemosa) --occur along the south Atlantic coast, primarily in Florida. Mangroves are good stabilizers, but they require considerably more- time (2 or 3 years) than grasses to become established. During this time, - the plants are susceptible to possible damage from tides, traffic, and browsing animals. Mangrove seeds, seedlings, or plants are best planted in established cordgrass stands, which provide stability until the mangroves are established. Slow-release (e.g., Osmocote) or a magnesium-ammonium- phosphate fertilizer can be placed in the planting hole if needed, especially for the larger transplants. Daily watering may be required if flooding does not occur. Gulf Coast Marshes. The vegetation found in gulf coast mar- shes does not substantially differ from south Atlantic coast mar- shes. Grasses, primarily saltgrass and gulf cordgrass, are preva- lent, while smooth cordgrass, saltmeadow cordgrass, and black needle rush are also common. Gulf Cordgrass (Spartina spartinae). Gulf cordgrass is found al-ong the gulf coast from southwest Louisiana to Texas. It performs well above the mean high water level. It is propagated like saltmeadow, cordgrass, using the same pro- cedure. Saltgrass (Distichlis spicata). Saltgrass is generally limited to the more saline, high marshes along the gulf coast. The plant is usually found in a mixture with saltmeadow cord- grass or black needle rush, and is rarely the dominant species except in poorly drained areas or in narrow bands. Saltgrass is more difficult to establish than the cordgrasses and usu- ally is allowed to volunteer into cordgrass plantings. Pacific Coast Marshes. Vegetation in marshes along the 'T'_ the Atlantic coast. Pacific coast is more diverse than along 125 Pacific cordgrass is found along the central and southern Cali- fornia coasts. Pickleweed! sedges, arrowgrass, and tufted hair grass are common along the northern Pacific coast. Pacific Cordgrass (Spartina follosa). It is similar to smooth cordgrass, hilt, it takes longer to establish. It domi- nates below the mean tide level of intertidal marshes. Plants and sprigs should be inserted by hand in holes made in soft, fine-textured soils. Fertilizers should contain equal quanti- ties of available nitrogen and phosphate. Pickleweed (Sallcornia spp. ). From mean high water to extrei'ehigh tide, various species of pickleweed can be used upslope of Pacific cordgrass. It will spread both by seeds and vegetatively (by rhizomes and tillers), but because it is shallow-rooted, it is probably not as useful for stabilization as Pacific cordgrass. Pickleweed may be easily established by seeding or by transplanted peat-pot seedlings, and in fact, it often invades disturbed surfaces during the first growing season. Sedge (Carex 1Vngbgei). Sedge marshes are usually found in areas such as river deltas where silty soils exist. They grow above the mean tide level and are not especially salt tolerant. The plant may respond to nitrogen and phosphorous under deficient conditions. It appears to be one of the best marsh plants available in the Pacific Northwest. Tufted Hair Grass (Deschampsia caespitosa). This plant predominates in high marshes subject to flooding' only by higher high tides. It is a good sediment accumulator and stabilizer once established. It is generally easy to trans- plant and quick to establish. Fertilizers should be applied where nutrient deficiencies are suspected. Arrowgrass (Triglochlin maritima). This plant will frequently invade and colonize disturbed marshes, trapping sediments and debris and helping to create a substrate for other plants. Planting should follow the method described for sedges. Great Lakes Marshes. Marshes of the Great Lakes are generally limited in extent, and confined primarily to the protected shores of bays and inlets of Lakes Huron and Michigan. Establishing fresh water marshes may not provide as satisfactory a level of erosion prevention as saltwater marshes. ' The landowner interested in establishing fresh water marshes should consider the common reed, rushes (Scirpus spp. ) 'such as spike rush, bulrush, and great bul- rush, and, in some instances, upland grasses such as reed canary grass (Phalaris arundinacea). More specific information may be obtained from those sources suggested at the beginning of this section. 126 Beach and Dune Plants The protection of the upland portions of sandy shorelines can be accomplished through the creation of barrier dunes and the sta- bilization of present dunes. Vegetation used to initiate the building of barrier dunes is specially adapted to the more severe environment of the beach area (Figure 88). Barrier dune formation can occur naturally, but it is usually slow and in some areas does not happen. Utilization and proper management of the natural processes can accelerate the development. f AV ;YI NO IZ 7, Figure 88 Dune Vegetation The beach provides a generally harsh environment for plant growth. Plants must tolerate rapid sand accumulation, flooding, salt spray, sandblasts, wind and water erosion, wide temperature fluctuations, drought, and low nutrient levels. Plants capable of stabilizing coastal dunes do, however, occur in most coastal regions where there is sufficient rainfall to support plant growth. These regions and several of the most successful species are dis- cussed below. 127 Planting specifications for several selected beach grass species are summarized in Table 19. Table 19 SELECTED BEACH AND DUNE GRASS PLANTING SPECIFICATIONS Species Beach Grass Element American Panic European Sea Oats Planting Season Late fall to early winter Yes+ Yes Yes No Midwinter Yes+ Optimum Yes Optimum Late winter to early spring Optimum+ Optimum Optimum Yes Early spring to mid-spring Yes Yes Yes No Available Source Transplants Commercial Yes Yes Yes Yes Wild harvest Yes Yes Yes Yes Seed Commercial No No No No Wild harvest Yes Yes Yes Yes Planting Density Eroding site 18-inch centers 18-incb centers 18-inch centers 18-inch centers Noneroding site 24-inch centers 24-inch centers 24-inch centers 24-inch centers Stems per transplant 3 1 3 1 Fertilization, Fi st Growing Season o Composition NPK6 3-1-0 2-1-1 7-0-0 2-1-1 Rate lbs/acre (annual) 200 24 40 240 Application periods March April April April (equal applications in May June Julie months indicated) July August August September Illegal to harvest in some states. +Season not recommended for Great Lakes. "NPK--Nitrogen-Phosphorous-Potassim. o 3-1-1 in Great Lakes. [After U.S. Army Corps of Engineers (1977c)ll North Atlantic Region. Extending from the Canadian border to the Virginia capes, American beachgrass is the dominant dune sta- bilizing plant in this region; bitter panicum offers promise as a companion plant. American Beachgrass (Ammophila breviligulata). This species is probably the most widely used for the initial stabilization of blowing sand because it grows rapidly and can effectively trap sand by the middle of the first growing season. Once established, it multiplies quickly. It prefers cool weather and plants start growing in early spring and continue through fall under the most favorable conditions. The grass can be transplanted over a long planting season with a good chance of survival. American beachgrass is available commercially or may also be harvested from wild stands. Seedlings are the preferred method of planting. Starting from seed is usually uneconomical because seed supplies are un- reliable and weeds are difficult to control. American beachgrass should be planted 8 to 10 inches deep in loose, dry sand. Shallow planting is the most common cause 128 of failure, therefore it is better to place the plant too deep than too shallow. Transplants may be made from October through May with the optimum period being February through April. The seedlings should be one or more healthy, vigorous stems (culms), with one to three seedlings per hill. First year growth is related to the size of the seedlings (number of stems) planted. Spacing varies with the characteristics of the site, but a strip of beachgrass 24 to 40 feet wide, planted 18 inches apart, will generally be effective by t 'he last half of the first growing season. A more practical (and less expensive) method for planting would be 4 rows of 18-inch spacings at the approximate center of the proposed dune. This plot should be flanked on both sides, by four rows each of plants spaced 24, 36, and 48 inches. Newly planted stands of American beachgrass will often respond to the application of 90 to 135 pounds of nitrogen and 30 to 45 pounds of phosphorous per acre. These fertilizations should be divided into three applications. The first should be applied as new growth emerges, with subsequent applications at 4- to 6-week intervals. Bitter Panicum (Panicum amarum). This grass is indige- nous along the Atlantic coast from Connecticut southward. It is best used as a companion to American beachgrass, especially in those areas where the beachgrass is subject to severe attack by the disease soft scale. Bitter panicum should generally be planted at the same time and with the same methods as American beachgrass. since it prefers warm weather, it may be wise to wait until April to plant. Bitter panicum can be transplanted as mature primary stems or as tillers. Primary stems must be used during late winter and spring until tillers become available. Young tillers, with some roots and rhizomes attached, grow with very little delay and are the preferred method of planting when available. Plants should be placed 8 to 10 inches deep in the soil. Bitter panicum should be planted as a percentage (10- 20%) of the total beachgrass planting and in the same pattern. Pure stands of bitter panicum are not usually successful except in very small spots, such as those where beachgrass has been reduced by insects or disease. Fertilizer applications are similar to those recommended for beachgrass. South Atlantic Region. This region extends from the Virginia capes to Key West. Sea oats is the dominant plant. However, both American beachgrass and bitter panicum, when planted in combination with sea oats, will successfully establish dunes, especially in the northern part of the region. Sea Oats (Uniola paniculata). More persistent than other stabilizing pecies, sea oats does not provide much initial protection. It grows slowly, is difficult to propagate, and is not widely available commercially. However, sea oats 129 provide excellent protection when established. To provide initial protection, sea oats should be planted in mixes with American beachgrass and bitter panicum to the Carolinas and with bitter panicum farther south. As the other grasses thin out, sea oats will spread and dominate the dune. Planting is similar to bath American beachgrass and bitter panicum. Plants should be placed 8 to 10 inches deep, because they are slow starters and the depth is required to prevent dessication and blowouts. Transplanting can be suc- cessful at any time given proper moisture conditions and healthy transplants. -Optimum planting months are January and February, although in more severe climates, February to April are better. Single stem transplants perform as well as mul- tiple , stem plantings under most conditions. Two-year-old, nursery-grown plants appear to be the best stock for trans- plants. Since sea oats is generally planted as part of a mixture, it is recommended that one or two rows of sea oats (or every 10th to 20th row in extremely large plots) be planted no closer than 24 inches. A moderate application of nitrogen and phosphate similar to that recommended for American beachgrass can be used to speed establishment of new plantings and to maintain growth and vigor in sand-starved areas. Saltmeadow Cordgrass (Spartina patens). This plant is more commonly used in marsh plantings (see prior d iiscussion), but it will frequently invade a beach area and create small dunes which will support other vegetation. It is particularly well suited for this use on low, moist sites where periodic saltbuildup occurs. Plants should be set 6 to 8 inches deep to stay in the moist zone. For dune stabilizing plantings, 'the optimum time is late winter and spring; however, saltmeadow cordgrass can be transplanted in the early summer providing sufficient moisture is available. Vigorous, multi-stemmed transplants from uncrowded nursery stands are recommended. With vigorous plants, adequate nutrients, and favorable moisture, saltmeadow cordgrass can be planted 16 to 24 inches apart in a single species planting. The transplants will usually benefit from a total of 90 to 135 pounds of nitrogen per acre applied over two to three applications during the first year. Subsequent fertilization should deliver similar amounts of nitrogen in single applications over the following two or three years. Bermuda Grass (Cynodon dactglon). Although this is not a prominent dune species, it can be used very effectively in special situations. The coastal hybrid is deep rooting and rapidly establishing and can be used to revegetate areas where American beachgrass has been killed by insects or disease. Turf hybrids will, when properly managed, perform well on the dune environment, where they form a more traffic resistant stand than other types of vegetation. 130 Sprigs of Bermuda grass, spaced 18 to 24 inches ap .art, should adequately stabilize the dune once they are estab- lished. For turf development, a spacing of 12 inches should be used. Sprigs may be planted from early spring to the beginning of summer where adequate moisture is available. Sprinkling the sprigs during dry spells will help to assure the survival of the plants. Bermuda grass requires more nutrients than other dune grasses. As soon as new growth begins in the spring, 30 to 45 pounds of nitrogen per acre should be applied every 4 weeks until the end of summer. Traffic resistant turf can be developed by applying 450 to 900 lb/ac of 10-10-10 formula fertilizer in the early spring and supplementing that with 45 to 70 pounds of nitrogen per acre every 4 weeks through the summer. Gulf Region. The region extends from the gulf coast of Florida to the Mexican border. sea oats and bitter panicum are the dominant dune stabilizing species. other species include railroad vine and saltmeadow cordgrass. Establishment of sea oats, bitter panicum, and saltmeadow cordgrass should follow prior recommenda- tions. Local variations exist, and the landowner should consult local agricultural extension agents and others about differences in technique and management of plantings of these species. Railroad Vine (Ipomea pes-caprae). This plant is one of the more prominent pioneer species in this region. It is not generally planted because it is somewhat less effective in trapping sand than dune grasses. It is, however, capable of rapidly spreading over foredunes, and transplants of the vine may be included as part of a grass establishment planting. North Pacific Region. This region extends from the Canadian border to Monterey, California. European beachgrass and American dunegrass are the dominant sand stabilizing plants of the region. American beachgrass may also be applicable in the area. European Beachgrass (An2mophila arenarla). This plant is inexpensive and uspX-widely in this region. Although it effectively traps sand, it forms dense stands with little outward spread, causing the resulting dunes to have steep windward slopes. Another disadvantage is that it will often exclude native species, making it difficult to establish mixed plantings. Planting should not be done when the temperature exceeds 600 F or is below freezing. Moist sand should be within 3 to 4 inches of the surface and the minimum planting depth is 12 inches. The optimum conditions of moisture and temperature for planting usually occur during the late fall, winter, and early spring months in this region. Three to five stems per hill are recommended for transplanting since establishment of dense stands is imperative with the wind conditions in this area. Spacing and planting patterns should be adapted to the site, but generally, an 18- x 18-inch planting with three to five stems per hill is sufficient. A pattern of several rows 131 with plants spaced 12 x 12 inches, bordered by several rows each of plants spaced 18 x 18, 24 x 24, and 36 x 36 inches, will build a stable foredune at less expense than a uniformly spaced planting. When rapid growth begins (early April), 35 to 55 pounds of nitrogen per acre should be applied. American Dunegrass (ElVmus mollis). Although this grass is naEl-veto the northwest, it is more difficult and expensive to propagate than either European or American beachgrass. The grass tends to produce low, gently sloping dunes, often pre- ferable to those dunes built by European beachgrass. American dunegrass should be set 12 inches or more deep in moist sand. satisfactory planting occurs primarily in the months when the grass is dormant; late November through Febru- ary in the northern portion of the region, and not at all in the southern extent. Planting should be limited to tempera- tures below 550 F. Planting several stems per hill would be desired; however, due to the expense, a close spacing of 12 inches with one viable stem makes better use of scarce plant- ing stock. An application of 35 pounds of nitrogen per acre from a soluble source is recommended as new growth starts. South Pacific Region. This region extends from Monterey, California, to the Mexican border. While some of the beach grasses discussed above (e.g., European beachgrass) are applicable in the .northern portions of this region, the dominant plants are forbs such.as the sea fig. Sea Fig (Carpobrotus edulis and C. aequilaterus). Sea fig is effective as a sand stabilizer but not good as a dune builder. It is quite easy to establish; cuttings 4 to 6 inches long should be placed about 18 to 24 inches apart in moist sand. An occasional application of nitrogen at a rate of 30 to 35 pounds per acre is recommended to maintain the plants once established. Great Lakes Region. Dune development is mostly confined to the Michigan and Indiana shores of Lake Michigan; however, the discussion which follows is applicable to all the shores of the Great Lakes. American beachgrass is the dominant species-.- Native species, especially prairie sandreed, will often invade naturally. Once the dunes have been stabilized'. volunteer or planted species of upland vegetation can be established. Species of grasses sug- gested would include reed canary grass, big bluestem, little blue- stem, and switchgrass, all native to the area. These grasses may be planted from early May to the middle of June at a rate of about 0.5 pounds of seed per 1,000 square feet. All require full sun and may be mowed occasionally. Reed canary grass is especially useful in wet spots. Various ground covers may also be planted. The species which may be utilized are best suggested by local agricultural experts. 132 The same holds true for shrubs and trees. When planting grasses and ground covers, application of 12 pounds of 12-18-12 fertilizer per 1,000 square feet is recommended. An additional problem which landowners in the Great Lakes region have is the stabilization of bluffs. Often, structural corrections are required in concert with vegetation. Once the structural stabilization is accomplished, vegetative cover will aid in preventing erosion, reducing seepage, and slowing runoff. The type of vegetation which can be established on bluff slopes is dependent upon the slope angle. Slopes steeper than 1 on 1 generally preclude successful vegetation, 'but slopes flatter than 1 on 3 can be planted as a lawn and maintained in the usual manner. Slopes between 1 on 3 and 1 on 1 can be planted with grasses which will not be mowed, ground covers, trees and shrubs, or combinations of these three. As mentioned before, local exper- tise (e.g., agricultural extension agents) can aid the landowner in selecting suitable species and in describing the most practical methods of establishment and maintenance. PERCHED BEACHES Perched beaches are constructed by placing sand fill behind a low breakwater or sill. Sills can be constructed of virtually any material described earlier for fixed breakwaters. Beach material should be chosen in accordance with guidelines previously given for beach fills. Proper filtering should be provided beneath and behind the sill to prevent settlement and loss of retained fill. In some cases, navigation markers may be required. Sheet Piling Sheet pile sills are similar to bulkheads. Timber sheet piling will generally require filter cloth backing of the shoreward face to prevent loss of backfill through joints in the sheeting. This is not generally a problem with steel or aluminum sheet pil- ing. Sheet pile sills also form an abrupt step to deeper water which may be hazardous to bathers, particularly children. The same precautions about adequate embedment and toe protec- tion -for bulkheads also apply to sills. 133 Concrete Boxes Precast, open concrete boxes (for use in drainage structures) can be placed side-by-side and filled with sand to form a sill (Figure 89). During placement, the. gaps between adjacent boxes must be minimized to prevent excessive wave transmission through the structure and to help retain the perched beach. Filter cloth backing is required and toe protection should be provided on the offshore side. air Figure 89 Concrete Box Sill 134 PROPRIETARY DEVICES AND SPECIALTY MATERIALS The devices and many of the materials discussed in this report are not generally available or familiar to local suppliers. Table 20 covers principal manufacturers that are active nationwide. Inclusion of manufacturers in this directory does not necessarily represent an endorsement or recommendation of their products by the government. In fact, some items listed herein were not recommened for specific applications in this report. Table 20 PROPRIETARY DEVICES AND SPECIALTY MATERIALS Device or Material Manufacturer Erco Blocks Erosion Control Systems, Inc. Ercomat 3349 Ridgelake Drive Suite 101-B Metairie, Louisiana 70002 504/834-5650 Fabric Bags Advance Construction Specialities, Inc. Advance P. 0. Box 17212 Memphis, Tennessee 38117 901/362-0980 Acrylic Sand Pillows Monsanto Textiles Company Customer Service Center P. 0. Box 5564, Station B Greenville, South Carolina 29606 803/242-6700 Dura Bags Erosion Control, Inc. 205 Datura Street Suite 319 West Palm Beach, Florida 33401 305/655-3651 Fabriform Construction Techniques, Inc. 11900 Shaker Boulevard Cleveland, Ohio 44120 216/623-0679 Filter Cloth Advance Construction Specialities, Inc. P. 0. Box 17212 Memphis, Tennessee 38117 901-362-0980 (Woven and Nonwoven) darthaqe Mills 124 West 66th Street Cincinnati, Ohio 45216 513/242-2740 (Woven) 135 Table 20 (continued) Device or Material Manufacturer Celanese Fibers Marketing,Company Department CE0504 1211 Avenue of the Americas New York, New York 10036 800/223-9811 (exc. New York, Alaska, Hawaii) 212/764-8224 (Nonwoven) DuPont Company Room 38095 Wilmington, Delaware 19898 (Nonwoven) Menardi-Southern Division of United States Filter Soil and Erosion Control Department Headquarters 3908 Colgate Houston, Texas 77017 713/643-6513 -(Woven and Nonwoven) Nicolon Corporation Erosion Control Products Suite 1990 Peachtree Corners Plaza Norcross (Atlanta), Georgia 30071 404/447-6272 800/241-9691 (Woven) Erosion Control Products, Inc. Route 5 Box 406 Daphne, Alabama 36526 205/626-3510 (Woven and Nonwoven) Gabions Maccaferri Gabions, Inc. P. 0. Box 43A Williamsport, Maryland 21795 301/223-8700 Terra Aqua Corporation Division of Bekaert Steel Wire Corporation P. 0. Box 7546 Reno, Nevada 89510 702/329-6262 136 Table 20 (continued) Device or Material Manufacturer Gobi Blocks Nicolon Corporation Gobimat Erosion Control Products Suite 1990 Peachtree Corner Plaza Norcross (Atlanta), Georgia 30071 404/447-6272 800/241-9691 Jumbo Blocks Erosion Control Systems, Inc. Jumbo Ercomat 3349 Ridgelake Drive Suite 101-B Metairie, Louisiana 70002 504/834-5650 Lok-Gard Blocks Coastal Research Corporation 1100 Crain Highway, S.W. Glen Burnie, Maryland 21061 301/761-0584 Longard Tube Edward E. Gillen Company 218 West Becher Street Milwaukee, Wisconsin 53207 414/744-9824 Nami Ring Robert Q. Palmer 5027 Justin Drive, N.W. Albuquerque, New Mexico 87114 Sandgrabber Sandgrabber, Inc. 3105 Old Kawkawlin Road Bay City, Michigan 48706 517/686-6601 Surgebreaker Great Lakes Environmental Marine, Ltd. 39 South LaSalle Street Chicago, Illinois 60603 312/332-3377 Terrafix Blocks Erosion Control Products, Inc. 9151 Fairgrounds Road West Palm Beach, Florida 33411 305/793-5650 Turfblock (Monoslab) Anchor Block Company P. 0. Box 3360 St. Paul, Minnesota 55165 612/777-8321 137 Table 20 (continued) Device or Material Manufacturer Wave-Maze Robert L. Stitt 10732 E. Freer Street Temple City, California Z-Wall The Fanwall Corporation 670 Old Connecticut Road Farmingham, Massachusetts 01701 617/879-3350 138 OVERVIEW OF THE DESIGN PROBLEM CHARACTERIZATION OF THE SITE The site to be considered is a sheltered location within an estuary. The shoreline is a low bluff about nine feet high. At mean low water (MLW), it is fronted by a 15-foot-wide beach. The stillwater level is at the toe of the bluff at mean high water (MHW). The bluff slope is approximately 1:1, and the soil is fine-grained, mostly sand and silt, with a heavy overgrowth of brush and other plants (Figure 90). The number of trees standing in the water and lying on the beach is evidence of a long-term and chronic erosion problem. The beach itself consists of fine- to coarse-grained material, mostly sand, but with a significant frac- tion of gravel and cobbles. The offshore bottom slope is approxi- mately 1 on 33. Figure 90 Design Problem Site WATER LEVELS The spring tide range and mean tide level were determined by reference to Tide Tables [U.S. Department of Commerce (1976)]. Local experience indicated that two feet of storm setup was ap- propriate. The site profile and water levels are summarized on Figure 91. 139 ,-EXISTING BLUFF + 3.60' M LW DESIGN SWL -4 MLW SPRING TIDE LE +0.5' LW_ - - - - - - 0.00' MLW LOW TIDE LEVE 1. EXISTING OFFSHORE SLOPE-) 5d FROM LOCAL EXPERIENCE FROM TIDE TABLES STORM SURGE z 2,0 FT. SPRING TIDE RANGE= 1.70 FT. (1) BLUFF HEIGHT=9' MEAN TIDE LEVEL= + 0. 75 FT MLW (2) BLUFF SLOPE - I on I rho sprinalide ronae is centerdon the meon tide 1"elot 40.75'ML (3) OFFSHORE SLOPE - Ion 33 (4) MEASURED DEPTH 50' OFFSHORE= 1.5'at MLW DESIGN (5) DEPTH AT SPRING TIDE - 3. C STILLWATER LEVEL + 3.60 MLW (6) STORM SURGE= 2.0' (7) DESIGN WATER DEPTH -(5)+(6)z3.I',2.O'-5.1' (8) DESIGN WAVE HE)GHTzDESIGN DEPTH xO.8z5.IxO.8z4.O` @2.0 SPRING TIDE LEVEL .1.60 M_LW MEAN TIDE LEVEL 0.85, -0.75 MLVJ MEAN LOW WATER (MLW) 0.00 Figure 91 Profile and Physical Conditions at the Site WAVE CONDITIONS The fastest-mile windspeed for the site is: 10-year: 65 mph Fetch lengths at the site were displayed earlier on Figure 17. This is reprodu as Figure 92 for the convenience of the reader. Fetch Line t Length: 2.80 nm x 1.15 = 3.22 mi 2.80 nm x 6080 = 17,025 ft Average Depth: 7.2 ft at MLW 10.8 ft at design stillwater level Fetch Line Lenqth: 2.10 nm x 1.15 = 2.41 mi 2.10 nm x 6080 = 12,770 ft Average Depth: 11.6 ft at MLW 15.2 ft at design stillwater level Using Tables 5 to 9, or Equations (5) and (6), find the design ,ING "TU@EVE@L@O' T6@L @EC_20 V +0 M L W - wave height and period (10-year return period). 140 V FETCH LINE .4 2 DEPTHS DEPTHS 6 5 5 6 3 10 12 36 7", :8 .:Mkri 1 12 10 @0,04 2 T, :9 ............. 6 1 18 6 2.: 9 18 PAS 10 R SCA 3 11 PA 6 12 sg )W:, 10 12 2 4 27 10 14 IF I - 24'Mk, 12 5 13 .12 12 ".2 5T ma,ke, Avg: 7.2' MLW Avg: 11.6' MLW 13'' ".4 NAUTICA Piles 4. Fetch Length: Fetch Length: -'.14 .3 2.80 nm 2.10 nm 2' 10 10 P,te PA Files PA 3.20 mi 2.40 mi 12i 3 14 3: 4 2 F, .13 .13@ ',2 1.5 hV'- 12 pil 2 2 1A .3 4 4 F-j 10 ;2 5 2 lr-j .7: .......... 3 brd -@o@ S* G 14 IL 4 8 6" 0 990 '7 i e 12"10 35 2 12 2 2 10 2 2 ... . .......... 4 33 9 Ms,kv 2 2 22 4 12 'c' q"11.4 7i :17"."- SA4"4,,2 12 2 2 20.: IS.. 7 4 2' 2 Z WINDMILL 16 :7: 5 4 :31Pi- 3 1 15 jkl * ."' 1' 1, 15 Dot 7,@ 2 14 9 5 fs" to 4 ........... 3 7 -4- 2 17 16 3 7 S)* a Aft' "17" . ............ 4 5 4 M6 R 7 R NO 0 '2' PA .......... 19 4 Bridge Creek privatel :17 is marked R _NFI 4sec 15ft 4 M 1 J& A4 I tained channel Piles PA 13 beacons I thru 19. Ard Figure 92 Fetch Lengths at the Site Fetch Line(Dwith F 3.2 mi and WS = 65 mph: Table 6: d = 10 ft; H = 3.0 ft;,T = 4.0 sec, Table 7: d = 15 ft; H = 4.0 ft; T = 4.0 sec Therefore, by interpolating for d 10.8 ft; H = 3.2 ft; and T 4.0 sec. Fetch Line Q with F = 2.4 mi and WS 65 mph: Table 7: d 15 ft; H = 3.5 ft; T = 4.0 sec, Table 8: d 20 ft; H = 4.0 ft; T = 4.0 sec Therefore, by interpolating for d 15.2 ft; H 3.5 ft; and T = 4.0 sec. Fetch Line(D is more critical for design, therefore, use H = 3.5 feet, and T = 4.0 seconds. This value should be checked against the maximum bre@aking wave at the site or just offshore. (Recall that Fetch Line U1. crosses a shoal area near Cedar' Point where the depth is ap roximately 3 feet under the design stillwater level. Fetch Line )i@l however, . UZ I was more critical for design purposes). With the design stillwater condition, the depth at the bluff toe, d s = 3.1 feet (Figure 90). From Figure 18 with, ds /gT2= (3.1)/32.2 (4.0)2 0.0060, and m = 0.03 Hb/ds = 0.98 therefore, Hb = 3.1 x 0.98 = 3.0 ft Therefore, for shoreline protection, use a design wave height of 3.0 feet, because that is the maximum that can occur at the site under design water level conditions. For any offshore structures, such as breakwaters or perched beach sills, the maximum breaker height should be checked based on the design depth at the toe of the structure. 142 SELECTION OF DEVICES Landowner's Criteria 1. No recreational use of the beach for bathing or fishing is anticipated. 2. The owner eventually hopes to extend an existing dock to deeper water for berthing a pleasure boat. 3. No structures are planned at the top of the bluf f that would interfere with any shore protection devices. 4. The shore protection plan should provide about ten years of protection with minimal maintenance requirements. Alternatives No Action Inappropriate. Unacceptable to the landowner. Current erosion rates represent a considerable financial loss at prevailing real estate prices. Relocate Inappropriate. The land is now undeveloped. The owner will build a retirement home with a large setback from the shore. He desires to stop erosion now. Bulkhead Appropriate. Equipment access to the job site presents no problems. Steps can be added later for access to the dock. Recreational use of the beach is not a high priority. Revetment Appropriate. There is sufficient room for a regraded slope. Breakwaters Inappropriate. Scour at the bluf f toe would not be positively prevented. Groins Inappropriate. There is little sand-sized material in alongshore transport at the site. Beach Fill Inappropriate. Fill provides no positive protection against toe scour. No recreational beach is desired. The plan must have minimal maintenance requirements. Vegetation Inappropriate. Plantings provide no positive protection to the bluff toe. Coarse soils are not suitable for plantings. 143 Infiltration and Inappropriate. Drainage and infiltration are Drainage Controls not problems at this site. Slope Flattening Inappropriate. Suitable only in combination with a revetment. Slope stability is not a basic problem. Perched Beach Inappropriate. Could be used in combination with a toe protection structure for the bluff (revetment or bulkhead) and vegetation to help retain the beach fill, but this would conflict with owner's desire to extend the existing dock for berthing a pleasure boat. Also, a recrea- tional beach is not desired. 144 PERMIT REQUIREMENTS Federal, state, and possibly local permits are required for construction in, across, under, or on the banks of navigable waters of the United States. Federal permits are coordinated by the applicant and the states through division and district offices of the U. S. Army Corps of Engineers, and they are issued as a result of two laws, Section 10 of the Rivers and Harbors Act of 1899, and Section 404 of the Clean Water Act of 1977, as amended. Section 10 of the 1899 act requires permits for structures and dredging in navigable waters of the United States, which are those coastal waters subject to tidal action and inland waters used for inter- state or foreign commerce. In tidal areas, this includes all land below the mean high water line. On the Great Lakes, permits are required under this section for construction lakeward of the highwater mark, the definition of which varies from state to state, and may differ from the federal definition. Where doubt exists, an appropriate state agency or Corps district office can provide assistance. Section 404 of the Clean Water Act mandates a federal permit for discharges of dredged or fill material in waters of the United States, which include'navigable waters as under Section 10 permits, as well as tributaries and wetlands adjacent to navigable waters of the United States. Jurisdiction extends inland to the headwaters of streams at a point where the average flow is five cubic feet per second. Wetlands are defined as "those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal conditions do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas" [U. S. Army Corps of Engineers (1977b)]. A standard application form (ENG Form 4345) must be obtained from the local Corps district office. The application must include a description of the proposed construction, "including necessary drawings, sketches or plans; the location, purpose, and intended use of the proposed activity; scheduling of the activity; the names and addresses of adjoining property owners; the location and dimen- sions of adjacent structures; and the approvals required by other federal, interstate, state or local agencies for the work, includ- ing all approvals received or denials already made" (U. S. Army Corps of Engineers (1977b)). Upon receipt of the application, a public notice inviting comments on the application is normally issued. The comment period is generally 30 days, although it may be longer or shorter, depend- ing on the circumstances. Applications are generally coordinated with the appropriate federal, state, and local agencies as well as adjacent property owners, sometimes leading to comments that re- quire modification of the original proposal. Beyond these possible modifications, if the comments received and study conducted by the 145 Corps reveal no overriding public interest or environmental prob- lems, the application is approved and a permit issued. Although variations exist, the process normally requires 75 to 90 days for routine applications. Controversial applications can take con- siderably longer. The Corps has adopted a number of conditional general permits on a regional and nationwide basis to reduce red tape and paper- work. No separate application is required for activities where general permits have been issued. Applicants should check with the local District Engineer to determine if the proposed work is cov- ered by a general permit and what conditions may apply. Additional information pertinent to local areas is available through Corps of Engineers' district offices, or certain state and local agencies. Permit applications should be initiated early to avoid unnecessary delays later. 146 OTHER HELP CORPS OF ENGINEERS OFFICES It is imperative to contact the Corps early to preclude un- necessary delays later in the permit application processing. Corps offices are also possible sources of information on water levels, wave action, and other physical conditions at a site. Mail addres- ses, office locations, and phone numbers for Corps personnel fa- miliar with coastal processes are given in Table 21. Table 21 CORPS OF ENGINEERS OFFICES Address Phone Jurisdiction U. S. Army Engineering Division, New England 617/894-2400 X-554 Atlantic coast from Maine to the Connecticut- 424 Trapelo Road New York Line Waltham, Massachusetts 02154 U. S. Army Engineering District, New York 212/264-5174 Atlantic coast of New York and the New 26 Federal Plaza Jersey coast north of Manasquan Inlet New York, New York 10007 U. S. Army Engineering District, Philadelphia 215/597-4714 Atlantic coast of New Jersey and Delaware U. S. Custon House from Manasquan Inlet, south to the Delaware- 2nd,:dnd Che:tnut Street Maryland Line, including Delaware Bay and Phi elphi , Pennsylvania 19106 the C&D Canal U. S. Army Engineering District, Baltimore 301/962-2545 Atlantic and Chesapeake Bay shorelines of P. 0. Box 1715 Maryland Baltimore, Maryland 21203 Office Location: 31 Hopkins Plaza Baltimore, Maryland 21201 U. S. Army Engineering District, Norfolk 804/441-3764 Atlantic and Chesapeake Bay shorelines of 803 Front Street Virginia Norfolk, Virginia 23510 U. S. Army Engineering District, Wilmington 919/343-4778 Atlantic coast and interior bays and sounds P. 0. Box 1980 of North Carolina Wilmington, North Carolina 28402 Office Location: 308 Federal Building Wilmington, North Carolina U. S. Army Engineering District, Charleston 803/724-4248 Atlantic Coast of South Carolina P. 0. Box 919 Charleston, South Carolina 29402 Office Location: Federal Building 334 Meeting Street Charleston, South Carolina 29402 U. S Army Engineering District, Savannah 912/944-5502 Atlantic coast of Georgia P* 0. Box 889 Savannah, Georgia 31402 Office Location: 200 E Saint Julian Street Savannah, Georgia 31402 U. S. Army Engineer District, Jacksonville 904/791-2204 Atlantic coast of Florida and Gulf coast of P. 0. Box 4970 Florida to the St. Marks River Jacksonville, Florida 32201 Office Location: 400 West Bay Street Jacksonville, Florida 32202 U. S. Army Engineering District, Mobile 205/690-3482 Gulf Coast of Florida from the St. Marks P. 0. Box 2288 River west Louisiana-Mississippi line Mobile, Alabama 36628 Office Location: 109 St. Joseph Street Mobile, Alabama 36602 U. S. Amy Engineering District, New Orleans 504/838-2480 Gulf coast of Louisiana P. 0. Box 60267 New Orleans, Louisiana 70160 Office Location: Foot of Prytania Street New Orleans, Louisiana 70160 147 Table 21 (Continued) Address Phone Jurisdiction U. S. Army Engineering District, Galveston 713/764-1211 X -314 Gulf coast of Texas P. 0. Box 1229 Galveston, Texas 77553 Office Location: 110 Essayons Boulevard 400 Barracuda Avenue Galveston, Texas 77550 U. S. Army Engineering District, Los Angeles 213/688-5400 Pacific coast of California from the Mexican P. 0. Box 2711 border north to Cape San Martin Los Angeles, California 90053 Office Location: 300 North Los Angeles Street Los Angeles, California 90012 U. S. Army Engineering District, San Francisco 415/556-5370 Pacific coast of California from Cape San 211 Main Street Martin north to the California-Oregon line San Francisco, California 94105 including San Francisco Bay U. S. Army Engineering District, Portland 503/221-6477 Pacific coast of Oregon P. 0. Box 2946 Portland, Oregon 97208 Office Location: Mulnomah Building 319 S.W. Pine Portland, Oregon 97204 U. S. Army Engineering District, Seattle 206/764-3555 Pacific coast of Washington and Puget P. 0. Box C-3755 Sound Seattle, Washington 98124 Office Location: 4735 East Marginal Way South Seattle, Washington U. S Army Engineering District, Alaska 907/752-3925 Coast of Alaska P. 0. Box 7002 Anchorage, Alaska 99510 Office Location: Building 21-700 Elmendorf Air Force Base, Alaska U. S. Army Engineering Division, Pacific Ocean 808/438-2837 Hawaii and the Pacific Trust Territories Building 230 Ft. Shafter, Hawaii 96858 U. S. Army Engineering District, Detroit 313/226-6791 U. S. shorelines of Lakes Superior, Huron P. 0. Box 1027 and St. Clair; the Lake Michigan shoreline Detroit, Michigan 48231 except in Illinois and Indiana; Lake Erie Office Location: Patrick V. McNamara Building shoreline of Michigan 477 Michigan Avenue Detroit, Michigan 48226 U. S. Army Engineering District, Chicago 312/353-0789 Lake Michigan shoreline of Illinois and 219 S. Dearborn Street Indiana Chicago, Illinois 60604 U. S. Army Engineering District, Buffalo 716/876-5454 X-2230 U. S. shorelines of Lakes Ontario and Erie 1776 Niagara Street except in Michigan Buffalo, New York 14207 STATE COASTAL ZONE MANAGEMENT OFFICES State coastal zone management of f ices can also be sources of information and assistance. Table 22 contains addresses and phone numbers of offices for states that operate coastal zone management programs. 148 Table 22 STATE COASTAL ZONE MANAGEMENT PROGRAM OFFICES State Office Address and Phone Number Alabama Coastal Area Board P. 0. Box 755 Daphne, Alabama 36526 205/626-1880 Alaska Division of Policy Development and Planning office of the Governor Pouch AP Juneau, Alaska 99801 907/465-3541 California California Coastal Commission 631 Howard Street, Fourth Floor San Francisco, California 94105 415/543-8555 Connecticut Director, Coastal Area Management Program Department of Environmental Protection 71 Capitol Avenue Hartford, Connecticut 06115 203/566-7404 Delaware Coastal Management Program office of Management, Budget, and Planning James Townsend Building Dover, Delaware 19901 302/736-4271 Florida office of Coastal Zone Management Department of Environmental Regulation Twin Towers Office Building 2600 Blair Stone Road Tallahassee, Florida 32301 904/488-8614 Georgia Coastal Resources Division Department of Natural Resources 1200 Glynn Avenue Brunswick, Georgia 31520 912/264-4771 Hawaii Department of Planning and Economic Development P. 0. Box 2359 Honolulu, Hawaii 96804 808/548-4609 149 Table 22 (Continued) State Office Address and Phone Illinois Illinois Coastal Zone Management Program 300 North State Street, Room 1010 Chicago, Illinois 60610 312/793-3126 Indiana State Planning Services Agency 143 West Market Street Indianapolis,-Indiana 46204 317/2@2-1482 Louisiana Coastal Management Section Department of Natural Resources P. 0. Box 44396 Baton Rouge, Louisiana 70804 504/342-7898 Maine State Planning Office Resource Planning Division 189 State Street Augusta, Maine 04333 207/289-3155 Maryland Department of Natural Resources Tidewater Administration Tawes State Office Building Annapolis, Maryland 21401 301/269-2784 Massachusetts Executive Office of Environmental Affairs 100 Cambridge Street Boston, Massachusetts 02202 617/727-9530 Michigan Department of Natural Resources Division of Land Use Programs Stephens T. Mason Building Lansing, Michigan 48926 517/373-1950 Minnesota State Planning Agency 550 Cedar Street, Room 100 St. Paul, Minnesota 55155 612/296-2633 150 Table 22 (continued) State office Address and Phone Mississippi Bureau of Marine Resources Department of Wildlife conservation P. 0. Box Drawer 959 Long Beach, Mississippi 39560 601/864-4602 New Hampshire office of State Planning 2-1/2 Beacon Street Concord, New Hampshire 03301 603/271-2155 New Jersey Bureau of Coastal Planning and Development Department of Environmental Protection P. 0. Box 1889 Trenton, New Jersey 08625 609/292-9762 New York Coastal Management Unit Department of State 162 Washington Street Albany, New York 12231 518/474-8834 North Carolina Department of Natural Resources and Community Development Box 27687 Raleigh, North Carolina 27611 919/733-2293 Ohio Department of Natural Resources Division of Water 1930 Belcher Drive, Fountain Square Columbus, Ohio 43224 614/466-6557 Oregon Land Conservation and Development commission 1175 Court Street, NE Salem, Oregon 97310 @503/378-4097 Pennsylvania Department of Environmental Resources Third and Reily Streets P. 0. Box 1467 Harrisburg, Pennsylvania 17120 717/783-9500 151 Table 22 (continued) State office Address and Phone Rhode Island Coastal Resources Management Program Washington County Government Center Tower Hill Road South Kingstown, Rhode Island 02879 401/789-3048 South Carolina South Carolina Coastal Council wildlife and Marine Resources Department 1116 Bankers Trust Tower Columbia, South Carolina 29201 803/758-8442 Texas Natural Resources Division Texas Energy and Natural Resources Advisory Council E.R.S. Building 200 East 18th Street Austin, Texas 78701 512/475-0773 Virginia Council on the Environment Ninth Floor, Ninth Street Office Building Richmond, Virginia 23219 804/786-4500 Washington Department of Ecology PV-11 State of Washington Olympia, Washington 98504 206/753-4348 Wisconsin Office of Coastal Management Department of Administration General Executive Facility 2 101 South Webster Street Madison, Wisconsin 53702 608/266-3687 152 OTHER SOURCES OF INFORMATION Hydrographic Charts Hydrographic charts are available for a small fee for all U. S. coastal waters. These provide information on water depths and fetch lengths to determine the exposure of a site to wave action. Identification of the specific chart and important infor- mation about the available chart series are contained in the Nau- tical Catalogs given below. , Catalog No. 1 - Atlantic and Gulf coasts, Catalog No. 2 - Pacific coast and Hawaii, Catalog No. 3 - Alaska, Catalog No. 4 - Great Lakes. For information or mail orders write to: Distribution Division, C44 National Ocean Survey Riverdale, Maryland 20840 301/436-6990 Counter sales are also available at that location as well as regional offices of the National Ocean Survey at: 439 West York Street .Norfolk, Virginia 23510 and 1801 Fairview Avenue East Seattle, Washington 90102 Charts can also be obtained from the U. S. Coast Guard at the locations given below. 3rd District Governors Island New York, New York 10004 9th District 1240 East 9th Street Cleveland, Ohio 44199 Water Levels Tide Tables are available for all coastal areas of the United States. These contain predictions of high and low tide elevations and their time of occurrence for one calendar year at primary tide stations. Values of time and elevation differences from the pri- mary station are also given for numerous secondary stations, as are the mean, spring or diurnal tidal ranges for all stations. Tide Tables are available from the Distribution Division, National Ocean §urvey, at the address above. 153 Lake levels are also available in summary form through the Monthly Bulletin of Lake Levels for the Great Lakes. This contains the current level for each of the lakes, a s Iix-month projection of future lake levels, and the historic high and low lake levels. The Monthly Bulletin is available, free, from the: Department of the Army Detroit District, Corps of Engineers P. 0. Box 1027 Detroit, Michigan 48231 SUGGESTED READING Numerous booklets, brochures, and reports, many of them free, are available for further study in selected topics and subjects presented in this report. Most government reports include either their NTIS or GPO accession numbers. Use the NTIS number to order documents from: National Technical Information Service (NTIS) Attention: Operations Division 5285 Port Royal Road Springfield, Virginia 22161 703/557-4650 Use the GPO number to order documents from: Superintendent of Documents U. S. Government Printing office (GPO) North Capitol and H Streets, N.W. Washington, D.C. 20401 202/783-3238 154 Shore and Lake Processes Beach Processes and Sedimentation, Komar, P., Prentice-Hall, Engle- wood Cliffs, New Jersey, 1976, 464 pp. Coastal Processes and Beach Erosion, Caldwell, J. M., R 1-67, U. S. Army Coastal Engineering Research Center, January 1967, (NTIS #652 025). Ebb and Flow: The Tides of Earth, Air and Water, Defant, A., Ann Arbor Science Library Series, University of Michigan Press, Ann Arbor, Michigan, 1958. 1 Land Against the Sea, Rayner, A. C., editor, MP 4-64, U. S. Army Coastal Engineering Research Center, May 1964, (NTIS # 453 227). Landslides: Analysis and Control, Special Report 176, Transpor- tation Research Board, National Academy of Sciences, Washington, D.C., 1978, 234 pp. Mechanics of Coastal Landslides and the Influence of Slope Para- meters, Edil, T. B. and Vallejo, L. E., Engineering Geology, Vol. 16, 1980, pp. 83-96. New Distributions of Extreme Winds in the United States, Thom, H.C.S., Journal, Structural Division, ASCE, ST 7, July 1968, pp. 1787-1801. Our New Beach: How It Works, Dade County Beach Erosion Control and Hurricane Protection Project, U. S. Army Engineer District, Jack- sonville, Jacksonville, Florida, 20 pp. (free). A Primer of Basic Concepts of Lakeshore Processes, Duane, D. B., et. al., MP 1-75, U. S. Army Coastal Engineering Research Center, January 1975, (NTIS# A008 010). Proposed Criteria for Interpreting Stability of Lakeshore Bluffs, Edil, T. B. and Haas, B. J., Engineering Geology, Vol. 16, 1980, pp. 97-110. Shoreline Erosion and Landslides in the Great Lakes, Edil, T. B. and Vallejo, L. E., Proceedings of the 9th International Conference on Soil Mechanics and Foundation Engineering, 1977, Vol. 2, pp. 51-58. Shore Processes and Shoreline Development, Johnson, D. W., Wiley- .London, 1919, 584 pp. Shore Protection Manual (Vols. I, II, and III), U. S. Army Coastal Engineering Research Center, 1977, (GPO Stock # 008-022-00113-1). Waves and Beaches: The Dynamics of the Ocean Surface, Bascom, W., Anchor Books, Garden City, New York, 1964. 155 Shore Protection (General) Consumer Investment in Shoreline Protection, Braden, P., Michigan Sea Grant Program, 2200 Bonisteel Boulevard, Ann Arbor, Michigan 48109. Harmony With the Lake: Guide to Bluff Stabilization, Division of Water Resources, Illinois Department of Transportation, Room 1010, Marina City Office Building, 300 North State Street, Chicago, Illinois 60610, (free). Help Yourself, North Central Division, U. S. Army Corps of Engi- neers, 536 South Clark Street, Chicago, Illinois 60605, (free). Low Cost Shore Protection: Final Report on the Shoreline Erosion Control Demonstration Program, Office, Chief of Engineers, U. S. Army Corps of Engineers, Washington, D. C., 20314, (1981). The Michigan Demonstration Erosion Control Program in 1976, Brater, E. F., et al., University of Michigan Coastal Zone Laboratory, Michigan Sea Grant Technical Report No. 55, February 1977. A Pictorial History of Selected Structures Along the New Jersey Coast, Vesper, W. H. and Essick, M. G., MP 5-64, U. S. Army Coastal Engineering Research Center, October 1964, (NTIS # 612 764). Shore and Beach, American Shore and Beach Preservation Association, P. 0. Drawer 2087, Wilmington, North Carolina 28401, (published quarterly: $20 annually). Shore Ero, sion Control: A Guide for Waterfront Property Owners in the Chesapeake Bay Area, Baltimore District, U.S. Army Corps of Engineers, P.O. Box 1715, Baltimore, Maryland 21203, 62 pp., (free). Shoreline Erosion Control, Philadelphia District, U. S. Army Corps of Engineers, Attention: -NAPEN-P (SECDP), Custom House, Second and Chestnut Street, Philadelphia, Pennsylvania 19106 (free). Shore Protection Guidelines: National Shoreline Study, Office, Chief of Engineers, U. S. Army Corps of Engineers, Washington, D. C., August 1971, 59 pp. Waves Against the Shore: An Erosion Manual for the Great Lakes Region, Lake Michigan Federation, 53 West Jackson Boulevard, Suite 1710, Chicago, Illinois 60604, January 1978. What You May Need to Know About Owning Shore Property, Great Lakes Communicator, Volume II, No. 5, February 1981. 156 Shore Protection Design AWPI Technical Guidelines for Pressure-Treated Wood (1970). S2 Bulkheads: Design and Construction - Part I S3 Bulkheads: Design and Construction - Part II S4 Bulkheads: Design and Construction - Part III S5 Bulkheads: Hardware and Fasteners Pl Timber Piling American Wood Preservers Institute, 1651 Old Meadow Road, McLean, Virginia 22101. Building Salt Marshes Along the Coast of the Continental United States, Woodhouse, W. W., SR 4, U. S. Army Coastal Engineering Research Center, May 1979, (GPO #008-022-00133-6). Concrete Shore Protection, Portland Cement Association, 33 West Grand Avenue, Chicago, Illinois, 1955. Designing for Bank Erosion Control with Vegetation, Knuston, P. L., R 78-2, U. S. Army Coastal Engineering Research Center, February 1978, (NTIS #A051 571). Designing Retaining Walls, Bulkheads and Seawalls of Treated Timber, American Wood Preservers Institute (address given above). Determination of Mooring Load and Transmitted Wave Height for a Floating Tire Breakwater, Giles, M. L., and Eckert, J. W., U. S. Army Coastal Engineering Research Center, CETA 79-4, September 1977, (NTIS # A077 905). Dune Building and Stabilization With Vegetation, Woodhouse, W.W., Jr., SR-3, U.S. Army Coastal Engineering Research Center, September 1978, (GPO #008-022-00124-7). Evaluation of Potential Use of Vegetation for Erosion Abatement Along the Great Lakes, Hall, V. L., and Ludwig, J. D., U. S. Army Coastal Engineering Research Center, MP 7-75, June 1975, (NITS A014 137). Evaluation of Tying Materials for Floating Tire Breakwaters, Davis, Albert P. J., University of Rhode Island, Marine Technical Re- port 54, April 1977. Factors Affecting the Durability of Concrete in Coastal Structures, Mather, B., TM 96, U. S. Army, Beach Erosion Board, June 1957, (NTIS #158 634). Floating Tire Breakwaters, Gifford, C. A., et. al, Marine Advisory Program, 6022 McCarthy Hall, University of Florida, Gainesville, Florida, September 1977, (SUSF-SG-77-002). How to Build a Floating Scrap Tire Breakwater, Kowalski, T.and Ross, N., Marine Advisory Service, University of Rhode Island, Narragansett Bay Campus, Narragansett, Rhode Island 02882. 157 Planting Guidelines for Marsh Development and Bank Stabilization, Knuston, P. L., CETA 77-3, U. S. Army Coastal Engineering Research Center, August 1977, (NTIS #A046 547). A Practical Design Method for Flexible Marine Retaining Walls, Kaiser Aluminum and Chemical Sales, Inc., 300 Lakeside Drive, Oakland, California 94643. Review of Design Elements for Beach'Fill Evaluation, Hobson, R. D., U. S. Army Coastal Engineering Research Center, TP 77-6, June 1977, (NTIS # A042 748). Revised Wave Runup Curves for Smooth Slopes, Stoa, P. N., U. S. Army Coastal Engineering Research Center, CETA 78-2, July 1978, (NTIS # A058 407). The Role of Vegetation in Shoreline Management, Great Lakes Basin Commission, P. 0. Box 999, Ann Arbor, Michigan 48106, .(single cop- ies, free). Salt Marsh Establishment and Development, Garbisch, E. W., Jr., et al., U. S. Army Coastal Engineering Research Center, TM 52, June 1975, (NTIS # A014 136). Simplified Design Methods of Treated Timber Structures for Shore, Beach and Marina Construction, Ayers, J. and Stokes, R., U. S. Army Coastal Engineering Research Center, MR 76-4, March 1976, (NTIS A022 337). Steel Sheet Piling Design Manual, U. S. Steel Corporation, 1975, (ADUSS 25-3848-05). SurveV of Coastal Revetment TVpes, McCartney, B. L., U.- S. Army Coastal Engineering Research Center, MR 76-7, May 1976, (NTIS # A026 255). Vse of Plastic Filters in Coastal Structures, Barrett, R. J., Pro- ceedings of the 10th International Conference on Coastal Engineer- ing, Tokyo, September 1966. Variations in Groin Design, Berg, D. W. and Watts, G. M., U. S. Army Coastal Engineering Research Center, R 4-67, September 1967, (NTIS # 659 172). Wave Runup on Rough Slopes, Stoa, P. N., U. S. Army Coastal Engi- neering Research Center, CETA 79-1, July 1979, (NTIS # A073 354). Woven Plastic Cloth Filters for Stone Seawalls, Dunham, J. W. and Barrett, R. J., Journal, Waterways, Harbors and Coastal Engineering Division, ASCE, Vol. WWI, February 1974, pp. 13-22. 158 Permits and Regulations Permi t Program: A Guide for Applicants, EP 1145-2-1, U. S. Army Corps of Engineers, Washington, D. C. Regulations to Reduce Coastal Erosion, Wisconsin Coastal Zone Management Program, State Office of Planning and Energy, GEF I1, 101 South Webster Street, Madison, Wisconsin 53702, (free). RegulatorV Program of the Corps of Engineers, Federal Register, Tuesday, 19 June 1977. Shore Management Guidelines: National Shoreline Studg, Office, Chief of Engineers, U.S. Army Corps of Engineers, Washington, D.C., August 1971. 159 GLOSSARY Accretion - Accumulation of sand or other beach material at a point due to natural action of waves, currents and wind. A build-up of the beach. Alongshore - Parallel to and near the shoreline; same as LONGSHORE. Apogean Tides - Decreased tidal ranges that occur each month when the moon is farthest from the earth (apogee). Backhoe - Excavator similar to a power shovel except that the bucket faces the operator and is pulled toward him. Bar - Fully or partly submerged mound of sand, gravel, or other unconsolidated material built on the bottom in shallow water by waves and currents. Beach - Zond of sand or gravel extending from the low water line to a point landward where either the topography abruptly changes or permanent vegetation first appears. Beach Fill - Sand or gravel placed on a beach by mechanical meth- ods. Beach, Perched - See PERCHED BEACH. Bluff - High, steep bank at the water's edge. In common usage, a bank composed primarily of soil. See CLIFF. Boulders Large stones with diameters over 10 inches. Larger than COBBLES. Breaker A wave as it spills, plunges, or collapses on a shore, iia-tural obstruction, or man-made structure. Breaker Zone - Area offshore where waves break. Breaking Depth - Stillwater depth where waves break. Breakwater - Structure alined parallel to shore, sometimes shore- connected, that provides protection from waves. Bulkhead - Structure that retains or prevents sliding of land or protects the land from wave damage. Clav - Extremely fine-grained soil with individual particles less tRzat 0.00015 inch in diameter. Cliff - High steep bank at the water's edge. In common usage, a bank composed primarily of rock. See BLUFF. 161 Cobbles - Rounded stones with diameters ranging from approximately 3 to 10 inches. Cobbles are intermediate between GRAVEL and BOULDERS. Crest Upper edge or limit of a shore protection structure. Culm Single stem of grass. Current - Flow of water in a given direction. Current, Longshore - Current in the breaker zone moving essentially parallel to shore and usually caused by waves breaking at an angle to shore. Also called alongshore current. Deep Water - Area where surface waves are not influenced by the bottom. Generally, a point where the depth is greater than one- half the surface wavelength. Diffraction- Progressive reduction in wave height when a wave spreads into the shadow zone behind a barrier after the wave has passed its end. Diurnal - Period or cycle lasting approximately one day. A diurnal tide has one high and one low in each cycle. Downdrift Direction of alongshore movement of littoral materials. Dune - Hill, bank, bluff, ridge, or mound of loose, wind-blown i-aterial, usually sand. Duration - The length of time the wind blows in nearly the same directi'on across a FETCH (generating area). Ebb Tide - Part of the tidal cycle between high water and the next low. The falling tide. Equatorial Tides - Tides that occur semimonthly as the result of the moon beinTover the equator. At these times the tendency of the moon to cause an inequality in mixed tides is minimized. Equilibrium - State of balance or equality of opposing forces. Erosion - Wearing away of land by action of natural forces. Fetch - Area where waves are generated by wind which has steady a@irection and speed. Sometimes called FETCH LENGTH. Fetch Length - Horizontal direction (in the wind direction) over which a wind generates waves. In sheltered waters, often the maximum distance that wind can blow across water. Filter Cloth - Synthetic textile with openings for water to escape, but which prevents passage of soil particles. 162 Flood Tide - Part of the tidal cycle between low water and the next high. rising tide. Glacial Till - Unstratified glacial drift consisting of unsorted clay, sand, gravel, and boulders intermingled. Gravel Small, rounded granules of rock with individual diameters ranging from 3.0 to 0.18 inches. Gravels are intermediate between SAND and COBBLES. Groin - Shore protection structure built perpendicular to shore to trap sediment and retard shore erosion. Groin Field - Series of groins acting together to protect a section of beacS_.Also called a groin system. Grout - Mixture of portland cement, fine aggregates (usually sand), and water. Usually used to seal openings or fill bags or other containers.' H-Pile- Straight length of structural steel with an H-shaped cross ie`ction designed for driving into the earth. High Tide Maximum elevation reached by each rising tide. see also TIDE. High Water See HIGH TIDE. High Water Line - Intersection of the level of MEAN HIGH WATER with the shore. Shorelines on navigation charts are approximations of the high water line. Hogwire - Short, smooth-wire fencing of the kind normally used to enclose a pig sty. Impermeable - Not having openings large enough to permit water to freely pass. International Great Lakes Datum (IGLD) - Common reference datum for the Great Lakes area based on mean water level in the St. Lawrence River at Father Point, Quebec, and established in 1955. Intertidal Zone Land area alternately inundated and uncovered by tides. Usually considered to extend from MEAN LOW WATER to MEAN HIGH WATER. Lee - Sheltered; part or side facing away from wind or waves. Leeward - Direction toward which wind is blowing or waves are travelling. Littoral Material - Sediments moved in the LITTORAL ZONE by waves and currents. Also called littoral drift. 163 Littoral Transport Movement of LITTORAL MATERIAL by waves and currents. Littoral Zone - Indefinite zone extending from the shoreline to just beyond the breaker zone. Longshore - Parallel to and near the shoreline: same as ALONG- SHORE. Longshore Transport Rate - Rate of transport of littoral material parallel to shore. Usually expressed in cubic yards per year. Low Tide - Minimum elevation reached by each falling tide. Low Water Datum (LWD) - The elevation of each of the Great Lakes to which are referenced the depths shown on navigation charts and the authorized depths of navigation projects. Low Water Line - Intersection of the low tide level with shore. Marsh - Area of soft, wet, or periodically inundated land, gener- ally treeless, and usually characterized by grasses and other low growth. Mean Higher High Water (MHHW) Average height of the daily higher high water over a 19-year period. Only the higher high water of each of the high waters of a tidal day is included in the mean. Mean High Water (MHW) - Average height of the daily high waters over a 19-year period. For semidiurnal or mixed tides, the two high waters of each tidal day are included in the mean. For diurnal tides, the single daily high water is used to compute the mean. Mean Lower Low Water (ML@@ - Average height of the daily lower low waters of a 19-year period. Only the lower low water of each pair of low waters of a tidal day is included in the mean. Long used as the datum for Pacific coast navigation charts, it is now gradually being adopted for use across the United States. Mean Low Water (MLW) - Average height of the low waters over a 19-year period. For semidiurnal and mixed tides, the two low waters of each tidal day are included in the mean. For a diurnal tide, the one low water of each tidal day is used in the mean. Mean Low Water has been used as datum for many navigation charts published by the National Ocean Survey, but it is being phased out in favor of Mean Lower Low Water for all areas of the United States. Mean Sea Level - Average height of the sea surface over a 19-year period. Not necessarily equal to MEAN TIDE LEVEL. 164 Mean Tide Level - Plane midway between MEAN HIGH WATER and MEAN LOW WATER. Not necessarily equal to MEAN SEA LEVEL. Also called half-tide level. Mixed Tide - A tide in which there is a distinct difference in height een successive high and successive low waters. For mixed tides there are generally two high and two low waters each tidal day. Mixed tides may be described as intermediate between semidiurnal and diurnal tides. Module - A structural component, a number of which are joined to make a whole. National Geodetic Vertical Datum (NGVD) - Datum of the United States geodetic level net. Mean Sea Level varies slightly from this datum from place to place along the shores of the nation. Neap Tides - Tides with decreased ranges that occur when the moon is at first or last quarter, and the pull of the. sun and moon are in opposition to each other. The neap range is smaller than the mean range for semidiurnal and mixed tides. Nearshore - In beach terminology, an indefinite zone extending seaward from the shoreline well beyond the breaker zone. Nourishment - Process of replenishing a beach either naturally by longshore transport, or artificially by delivery of materials dredged or excavated elsewhere. offshore - (1) (Noun) In beach terminology, comparatively flat zone of variable width extending from the breaker zone to the seaward edge of the Continental Shelf. (2) (Adjective) Direction seaward from the shore. OvertopRinq - Passing of water over a structure from wave runup or surge actlon. Peat - Residual product produced by partial decomposition of or- ganic matter in marshes and bogs. Peat Pot (vegetation) - Pot formed from compressed peat and filled @i_i@ther with soil or peat moss in which a plant or plants, grown from seed, are transplanted without being removed from the pot. Perched Beach - Beach or fillet of sand retained above the other- wise normal profile level by a submerged dike or sill. Perigean Tides Increased tidal ranges that occur each month when the moon is closest to the earth (perigee). Permeable - Having openings large enough to permit free passage of appreciable quantities of sand or water. 165 Pile - Long, heavy section of timber, concrete or metal driven or Te-tted into the earth or seabed as support or protection. Pile, Sheet - Pile with a generally slender, flat cross section driven into the ground or seabed and meshed or interlocked with like members to form a diaphragm, wall, or bulkhead. Piping - Fluidizing of backfill or an embankment to the extent that large quantities of material are pumped by wave action through holes under or through a bulkhead or revetment. Plasticity - As applied mainly to clay, the relative ease with which the material yields or deforms under pressure. Plug - core containing both plants and underlying soil, usually cut with a cylindrical coring device and transplanted to a hole cut by the same device. Polyvinyl Chloride (PVC) - Plastic material (usually black) that forms a resilient coating suitable for protecting metal from corro- sion. Profile, Beach - Intersection of the ground surface with a vertical plane that may extend from the top of the dune line to the seaward limit of sand movement. PVC - (see POLYVINYL CHLORIDE). Ravelling - Progressive deterioration of a revetment under wave iiE`tion. Refraction (of water waves) - (1) Process by which direction of a wave moving in shallow water at an angle to the contours is changed. Part of the wave advancing in shallower water moves more slowly than the part still advancing in deeper water, causing the wave crest to bend toward alinement with the underwater contours. (2) Bending of wave crests by currents. Revetment - Facing of stone, concrete, etc., to protect a scarp embankment, or shore structure against erosion by waves or cur- rents. Rhizome - Underground stem or root stock. New shoots are usually produced from the tip of the rhizome. Riprap - Layer, facing, or protective mound of stones randomly placed to prevent erosion, scour, or sloughing of a structure or embankment; also, the stone so used. Rubble - (1) Loose, angular, waterworn stones along a beach. (2) Rough, irregular fragments of broken rock or concrete. 166 Runup - The rush of water up a structure or beach on breaking of a wave. Amount of runup is the vertical height above stillwater level that the rush of water reaches. Sand - Generally, coarse-grained soils having particle diameters between 0.18 and approximately 0.003 inches. Sands are inter- mediate between SILT AND GRAVELS. Sandbag - Cloth bag f illed with sand or grout and used as a module in a shore protection device. Sand Fillet- Accretion trapped by a groin or other protrusion in the lit 1 zone. Scour - Removal of underwater material by waves or currents, espe- a=ally at the base or toe of a shore structure. Screw Anchor - Type of metal anchor screwed into the bottom for holding power. Seawall - Structure separating land and water areas primarily to prevent erosion and other damage by wave action. See also BULK- HEAD. Semidiurnal Tide - Tide with two high and two low waters in a tidal day, each high and each low approximately equal in stage. Setup, Wind - Vertical rise in the stillwater level on a body of water caused by piling up of water on the shore due to wind action. Synonymous with wind tide and STORM SURGE. STORM SURGE usually pertains to the ocean and large bodies of water. Wind setup usu- ally pertains to reservoirs and smaller bodies of water. Shallow Water - Commonly, water of such a depth that surface waves are noticeab y affected by bottom topography. It is customary to consider water of depths less than one-twentieth the surf ace wave- length as shallow water. Sheet Pile - see PILE, SHEET. Shoal - (noun) Rise of the sea bottom from an accumulation of sand or other sediments. (verb) - (1) to become shallow gradually. (2) To cause to become shallow. (3) to proceed from a greater to a lesser U-epth of water. Shoot - Collective term applied to the STEM and leaves or any growing branch or twig. Shore - Narrow strip of land in immediate contact with the sea, including the zone between high and low water lines. A shore of unconsolidated material is usually called a beach. 167 Shoreline - Intersection of a specified plane of water with the shore or beach (e.g., the high water shoreline would be the inter- section of the plane of mean high water with the shore or beach). The line delineating the shoreline on National Ocean Survey nauti- cal charts and surveys approximates the mean high water line. Sill - Low offshore barrier structure whose crest is usually sub- merged, designed to retain sand on its landward side. Silt - Generally refers to fine-grained soils having particle r__ Uiameters between 0.003 and 0.00015 inches. Imtermediate between CLAY and SAND. Slope - Degree of inclination to the horizontal. Usually expressed as a ratio, such as 1:25 or 1 on 25, indicating 1 unit vertical rise in 25 units of horizontal distance; or in degrees from hori- zontal. Sloughing - Process where a weakened mass of soil fails and moves downslope. Sprig - Single plant with its relatively bare roots, as pulled apart from a clump and used for transplanting. Spring Tides - Increased tidal ranges that occur semimonthly when the moon is new or full and the pull of the sun and moon are nearly in phase. The spring range is larger than the mean range for semi- diurnal or mixed tides. Stem - Main axis of a plant, leaf-bearing and flower-bearing, as air-s-tinguished from the root-bearing axis. Stillwater Level - Elevation that the surface of the water would assume if all wave action were absent. Storm Surqe - Rise above normal water level on the open coast due Eo -action of wind on the water surface. Storm surge resulting from a hurricane also includes the rise in level due to atmospheric- pressure reduction as well as that due to wind stress. See SETUP, WIND. Suspended Load - Material moving in suspension in a turbulent field. Swell - Wind-generated waves travelling out of their generating area. Swell characteristically exhibits a more regular and longer period and has flatter crests than waves within their fetch. Tidal Period - Interval between two consecutive like phases of the tide. Tidal IRanqe - Difference in height between consecutive high and low (or higher high and lower low) waters. The mean range is the dif- 168 ference in height between mean high water and mean low water. The diurnal range is the difference in height between mean higher high water and mean lower low water. For diurnal tides, the mean and diurnal range are identical. For semidiurnal and mixed tides, the spring range is the difference in height between the high and low waters during the time of spring tides. Tide - Periodic rising and falling of water resulting from gravi- Ta-T-lonal attraction of the moon, sun and other astronomical bodies acting upon the rotating earth. Although the accompanying hori- zontal movement of the water resulting from the same cause is also sometimes called tide, it is preferable to designate the latter as tidal current, reserving the name TIDE for vertical movement. Tide, Ebb - See EBB TIDE. Tide Station - Place at which tide observations are being taken. A primary tide station is a location where continuous observations are taken over a number of years to obtain basic tidal data for the locality. A secondary tide station is operated over a short period of time to obE-ain data for a specific purpose. Tiller - A plant shoot which springs from the root or bottom of the original plant stalk. Topography - Configuration of a surface, including relief, position of streams, roads, buildings, etc. Transplant - SHOOT or CULM removed from one location and replanted in another. Trough of Wave - Lowest part of a waveform between successive crests. Also, that part of a wave below stillwater level. Tropical Tides - Tides that occur .semimonthly when the declination of the moon is maximized. During these times, the diurnal range tends to be greatest. Updrift - Direction opposite the predominant movement of littoral materials in longshore transport. Wake (boat) - Waves generated by the motion of a vessel through water. Wale - Horizontal beam on a bulkhead used to transfer horizontal loads against the structure laterally along it and hold it in a straight alinement. Waterline - Juncture of land and sea. This line migrates, changing with the tide or other fluctuation in water level. Where waves are present on the beach, this line is also known as the limit of backrush. (Approximately, the intersection of land with the still- water level.) 169 Wave - Ridge, deformation, or undulation of the surface of a liquid. Wave Climate - Normal seasonal wave regimen along a shoreline. Wave Crest - Highest part of a wave or that part above the still- water level. Wave Diffraction - See DIFFRACTION. Wave Direction - Direction from which a wave approaches. Wave Height Vertical distance between a crest and the preceding trough. Wavelength Horizontal distance between similar points on two successive waves measured perpendicular to the crest. Wave Period - Time in which a wave crest traverses a distance equal to one wavelength. Time for two successive wave crests to pass a fixed point. Wave Refraction See REFRACTION (of water waves). Wave Steepness Ratio of wave height to wavelength. Wave Train Series of waves from the same direction. Wave Trough Lowest part of a wave form between successive crests. Also, that part of a wave below stillwater level. Weep Hole - Hole through a solid revetment, bulkhead, or seawall for relieving pore pressure. Wind Setu2 - See SETUP, WIND. Windward Direction from which wind is blowing. Wind Waves - (1) Waves being formed and built up by wind. (2) Loosely, any waves generated by wind. 170 LITERATURE CITED American Wood Preservers' Association, "Standard C18-77: Standard for Pressure Treated Material in Marine Construction", 1977. American Wood Preservers Institute, 11AWPI Technical Guidelines for Pressure Treated Wood - S2 Bulkheads: Design and Construction - Part 1", 1970. Bertram, G. E., "An Experimental Investigation of Protective Filters", Harvard University Publication 267, January 1940. Davis, A. P., Jr., "Evaluation of Tying Materials for Floating Tire Breakwaters", Marine Technical Report 54, University of Rhode Island, April 1977. Giles, M. L. and Eckert, J. W., "Determination of Mooring Load and Transmitted Wave Height for a Floating Tire Breakwater", CETA 79-4, U. S. 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