Coastal & Port Engineering

23Scott L. Douglass Robert A. Nathan Jeffrey D. Malyszek

ProfessorDepartment of Civil Engineering

University of South AlabamaMobile, Alabama

Moffat & Nichol EngineersTampa, Florida

Moffat & Nichol EngineersTampa, Florida

COASTAL AND PORT

ENGINEERING

Coastal and port engineering encom-passes planning, design, and construc-tion of projects to satisfy society’s needsand concerns in the coastal environ-

ment, such as harbor and marina development,shore protection, beach nourishment, and otherconstructed systems in the coastal wave and tideenvironment.

Over time, the scope of this field of engineeringhas broadened from only navigation improvementand property protection to include recreationalbeaches and environmental considerations. It takesinto account the environmental conditions uniqueto the coastal area, including wind, waves, tides,and sand movement. Thus, coastal engineeringmakes extensive use of the sciences of oceanogra-phy and coastal geomorphology as well as of geo-technical, environmental, structural, and hydraulicengineering principles.

23.1 Risk Level in CoastalProjects

Because of the nature of littoral drift, or longshoresand transport along the coasts, erosion caused bycoastal engineering projects along adjacent shore-lines, sometimes several miles away, has been arecurring problem. Tools for prediction andevaluation of such shoreline dynamics are con-tinually improving but are still limited, in part

because of nature’s unpredictability. Hence, post-construction monitoring of the response of nearbybeaches is often a required component of coastalengineering projects.

The design level of risk in many coastal engi-neering projects may be higher than in other civilengineering disciplines because the price of moreeffective design is often not warranted.

The design environment is very challenging.It varies with time, since design conditions areoften affected by storms that contain much moreenergy and induce very different loadings fromthose normally experienced. Also, because thephysical processes are so complex, often toocomplex for theoretical description, the practice ofcoastal engineering is still much of an art. Con-sequently, practitioners should have a broad baseof practical experience and should exercise soundjudgment.

The practice of coastal engineering has changedrapidly in the last several decades owing to in-creases in natural pressures, such as that created bysea-level rise, and societal pressures, such as thosefrom growing populations along the coast withgreater environmental awareness. The changes arerecorded in the proceedings of specialty confer-ences, such as those of the American Society ofCivil Engineering (ASCE), including CoastalEngineeringPractice;Dredging, Ports, Coastal Sedi-ments, Coastal Zone, International Coastal Engin-eering Conference, and the Florida Shore and

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Source: Standard Handbook for Civil Engineers

Beach Preservation Association’s Beach preser-vation Technology Conference series.

Coastal Hydraulics andSediments

Waves often apply the primary hydraulic forces ofinterest in coastal engineering. Tides and otherwater-level fluctuations control the location ofwave attack on the shoreline. Waves and tidesgenerate currents in the coastal zone. Breakingwaves provide the forces that drive sand transportalong the coast and can cause beach changes,including erosion due to coastal engineeringprojects.

23.2 Characteristics of Waves

Water waves are caused by a disturbance of thewater surface. The original disturbance may becaused by wind, boats or ships, earthquakes, or thegravitational attraction of the moon and sun. Mostof the waves are initially formed by wind. Wavesformed bymoving ships or boats arewakes. Wavesformed by earthquake disturbances are tsunamis.Waves formed by the gravitational attraction of themoon and sun are tides.

After waves are formed, they can propagateacross the surface of the sea for thousands of miles.

The properties of propagating waves have been thesubject of various wave theories for over a century.The most useful wave theory for engineers is thelinear, or small-amplitude, theory.

23.2.1 Linear Wave Theory

Essentially, linear wave theory treats only a train ofwaves of the same length and period in a constantdepth of water. As in optics, this is called amonochromatic wave train. Linear wave theoryrelates the length, period, and depth of waves asindicated by Eq. (23.1).

L ¼ gT2

2ptan h

2pd

L(23:1)

where L ¼ wavelength, ft, the horizontal distancebetween crests

d ¼ vertical distance, ft, between mean orstill water level and the bottom

g ¼ acceleration due to gravity, 32.2 ft/s

T ¼ wave periods, the time required forpropagation of a wave crest over thewavelength (Fig. 23.1)

Wave height H, the fourth value needed to com-pletely define a monochromatic wave train, is anindependent value in linear wave theory, but notfor higher-order wave theories (Art. 23.2.2).

Fig. 23.1 Wave in shallow water. Water particles follow an elliptical path. L indicates length ofwave, crest to crest; H wave height, d depth from still-water level to the bottom. The wave period T is thetime for a wave to move the distance L.

23.2 n Section Twenty-Three



COASTAL AND PORT ENGINEERING

Equation (23.1), implicit in terms of L, requiresan iterative solution except for deep or shallowwater. When the relative depth d/L is greater than1⁄2, the wave is in deepwater and Eq. (23.1) becomes

L ¼ gT2

2p(23:2)

For shallow water, d=L , 1⁄25, eq. (23.1) reduces to

L ¼ Tffiffiffiffiffigd

p(23:3)

Individual water particles follow a closed orbit.They return to the same location with each passingwave. The orbits are circular in deep water andelliptical in shallow water. Linear wave theoryequations for the water-particle trajectories, thefluctuating water-particle velocities and accelera-tions, and pressures under wave trains are given inR. G. Dean and R. A. Dalrymple, “Water WaveMechanics for Scientists and Engineers,” Prentice-Hall, Englewood Cliffs, N. J. (www.prenhall.com);R. M. Sorenson, “Basic Wave Mechanics: ForCoastal and Ocean Engineers,” John Wiley & Sons,Inc., New York (www.wiley.com).)

23.2.2 Higher-Order Wave Theories

The linear wave theory provides adequate approxi-mations of the kinematics and dynamics of wavemotion for many engineering applications. Someareas of concern to civil engineers where the lineartheory is not adequate, however, are very largewaves and shallow water. Higher-order wave

theories, such as Stokes’ second order and cnoidalwave theories, address these important situations.Numerical wave theories, however, have thebroadest range of applicability. Useful tables fromstream-function wave theory, a higher-order, num-erical theory, are given in R. G. Dean, “Evaluationand Development of Water Wave Theories ForEngineering Applications,” Special Report No. 1,U.S. Army Coastal Engineering Research Center,Ft. Belvoir, Va.

Determination of the water surface elevationsfor large waves or waves in shallow water requiresuse of a higher-order wave theory. A typicalwaveform is shown in Fig. 23.2. The crest of thewave is more peaked and the trough of the wave isflatter than for the sinusoidal water surface profilein linear wave theory. For a horizontal bottom, theheight of the wave crest above the still-water levelis a maximum of about 0.8d.

(“Shore Protection Manual,” 4th ed., U.S. ArmyCoastal Engineering Research Center, GovernmentPrinting Office, Washington, D.C. (www.gpo.gov);“Coastal Engineering Manual,” (www.usace.mil/inet/usace-docs/eng-manuals/em-htm).)

23.2.3 Wave Transformations

As waves move toward the coast into varyingwater depths, the wave period remains constant(until breaking). The wavelength and height, how-ever, change because of shoaling, refraction,diffraction, reflection, and wave breaking.

Fig. 23.2 Water surface for a large wave in shallow water.

Coastal and Port Engineering n 23.3




Shoaling n As a wave moves into shallowerwater the wavelength decreases, as indicated byEq. (23.1), and the wave height increases. Theincrease in wave height is given by the shoalingcoefficient Ks.

Ks ¼ H

H0o

(23:4)

where H ¼ wave height in a specific depth of water

H0o ¼ deep-water unrefracted wave height

Ks varies as a function of relative depth d/L asshown in Table 23.1. For an incident wave train ofperiod T, Table 23.1 can be used to estimate thewave height and wavelength in any depth with Eq.(23.2) for Lo.

Refraction n This is a term, borrowed fromoptics, for the bending of waves as they slow down.Aswaves approach a beach at an angle, a portion ofthe wave is in shallower water and moving moreslowly than the rest. Viewed from above, the wavecrest appears to bend.

Refraction changes the height of waves as wellas the direction of propagation. Refraction cancause wave energy to be focused on headlands anddefocused from embayments.

There are two general types of refractionmodels. Wave-ray models trace the path of waverays, lines perpendicular to the wave crests. Theother type of computer refraction model computessolutions to differential equations for the wave-height field. The physics simulated varies slightlyfrom model to model.

Diffraction n Another term borrowed fromoptics, this is the spread of energy along a wavecrest. An engineering example of wave diffractionis the spreading of energy around the tip of abreakwater into the lee of the breakwater. Thewave crest wraps around the tip of a breakwaterand appears to be propagating away from thatpoint. Diffraction also occurs in open water whererefraction occurs. It can reduce the focusing andbending due to refraction.

Reflection n Waves are reflected from obstruc-tions in their path. Reflection of wave energyis greatest at vertical walls, 90% to 100%, and leastfor beaches and rubble structures. Undesirablewave-energy conditions in vertical-walled marinascan often be reduced by placing rubble at thewater line.

Breaking n This happens constantly along abeach, but the mechanics are not well modeled bytheory. Thus, much of our knowledge of breaking isempirical. In shallow water, waves break whenthey reach a limiting depth for the individual wave.This depth-limited breaking is very useful incoastal structure design and surf-zone dynamicsmodels.

For an individual wave, the limiting depth isabout equal to the water depth and lies in the rangegiven by Eq. (23.5.).

0:8 ,H

d

� �max

, 1:2 (23:5)

where (H/d)max ¼ maximum ratio of wave heightto depth below mean water level for a breakingwave. The variation in (H/d)b (the subscript bmeans breaking) is due to beach slope and wavesteepness H/L.

Equation (23.5) is often useful in selecting thedesign wave height for coastal structures in shal-low water. Given an estimate of the design waterdepth at the structure location, the maximumwaveheight Hmax that can exist in that depth of water isabout equal to the depth. Any larger waves wouldhave already broken farther offshore and beenreduced to Hmax.

23.2.4 Irregular Waves

The smooth water surfaces of monochromaticwave theories are not realistic representations of

Table 23.1 Shoaling Coefficient andWavelengthChanges as Waves Move into Shallower Water

d/Lo d/L Ks

0.005 0.028 1.700.010 0.040 1.430.020 0.058 1.230.030 0.071 1.130.040 0.083 1.060.050 0.094 1.020.10 0.140.20 0.220.30 0.310.50 0.50 1.0





the real surf zone. Particularly under an activewind, the water surface will be much moreirregular. Two different sets of tools have beendeveloped by oceanographers to describe realisticsea surfaces. One is a statistical representation andone is a spectral representation.

Statistics of Wave Height n The individualwaves in a typical sea differ in height. The heightsfollow a theoretical Rayleigh distribution in deepwater. In shallow water, the larger individualwaves break sooner, and thus the upper tail of thedistribution is lost.

A commonly used, single wave-height para-meter is the significant wave height H1/3. This isthe average of the highest one-third of the waves.Other wave heights used in design can be related toH1/3 via the Rayleigh distribution as indicated inTable 23.2.

23.2.5 Wave Spectra

Spectral techniques are available that describe theamount of energy at the different frequencies orwave periods in an irregular sea. They providemore information about the irregular wave trainand are used in some of the more advancedcoastal-structure design methods. A wave-heightparameter that is related to the total energy in asea is Hmo

. (Hmois often called significant wave

height also.)Significant wave height Hs is a term that has a

long history of use in coastal engineering andoceanography. As indicated above and in Art.23.2.4, two fundamentally different definitionsfor significant wave height are used in coastalengineering. One is statistically based and the otheris energy- or spectral-based. Since they are

different, the notations, H1/3 and Hmoare recom-

mended to avoid confusion in use of Hs:

H1=3 ¼ statistical significant wave height

Hmo¼ spectral significant wave height

In deep water, Hmois approximately equal to H1/3.

In shallow water, and in particular in the surf zone,the two parameters diverge. (There is little thatis truly significant about either parameter. Fewof the waves in an actual wave train will havethe significant height. It is basically a statisticalartifact.)

Transformations of actual wave seas such asshoaling, refraction, diffraction, and breaking arenot completely understood and not well modeled.Although the monochromatic wave transforma-tions are well modeled, as described in thepreceding, in actuality the individual waves andwave trains interact with each other and changethe wave field. (These wave-wave interactions arethe subject of significant research efforts.) Thus,the more realistic conditions, that is, irregular seas,are the least understood. However, models thataccount for the transformation of wave spectraacross arbitrary bottom contours are available.

23.2.6 Wave Generation by Wind

Waves under the influence of the winds thatgenerated them are called sea. Waves that havepropagated beyond the initial winds that generatedthem are called swell.

Fetch is the distance that a wind blows acrossthe water. For enclosed bays, this is the distanceacross the water body in the direction of the wind.Duration is the time that a wind at a specific speedblows across the water. The waves at any spot maybe fetch-limited or duration-limited. When a wind

Table 23.2 Wave Heights Used in Design

Symbol Description Multiple of H1/3

H1/3 Average height of highest one-third of waves 1.0Hav Average wave height 0.6H10 Average height of highest 10% of waves 1.3H1% Wave height exceeded 1% of the time 1.6Hsin Height of simple sine waves with same energy

as the actual irregular height wave train0.8





starts to blow, wave heights are limited by the shorttime that the wind has blown; in other words, theyare duration-limited. Seas not duration-limited arefully arisen. If the waves are limited by the fetch,they are fetch-limited.

For enclosed bay and lake locations, simpleparametric models can provide useful waveinformation. Table 23.3 gives wave height andwave period estimates for deep water for differentfetch distances and different wind speeds. Thevalues are based on the assumption that the windblows for a sufficient time to generate fully arisenconditions. In shallow water, the wave heights willbe less.

On the open ocean, waves are almost neverfetch-limited. They are free to continue to moveafter thewind ceases or changes. Swellwave energycan propagate across entire oceans. The wavesstriking the beach at any moment in time mayinclude swell from several different locations plus alocal wind sea. Thus, for an open-ocean situation,numerical models that grid the entire ocean arerequired to keep track of wave-energy propagationand local generation.

Wave-generation models can forecast waves formarine construction operations. They can alsohindcast, that is, estimate waves based onmeasured or estimated winds at times in the past,for wave climatology studies, probabilistic design,or historic performance analysis. The U.S. ArmyCorps of Engineers “Wave Information Study

(WIS)” has hindcast 40 years of data, 1956–1995,to generate probabilistic wave statistics for hun-dreds of locations along the coasts of the UnitedStates. The wave statistics are available in tabularform, and the actual time sequence of waveconditions is available in digital form.

(J. B. Herbich, “Handbook of Coastal and OceanEngineering,” Gulf Publishing Company, Houston,Tex (www.gulfpub.com).)

23.2.7 Ship and Boat Wakes

Ship wakes are sometimes the largest waves thatoccur at a location and thus become the designwave. Vessel wakes from large ships can be up to6 ft high and have wave periods less than 3 s. Shipwakes can be estimated with methods presented inJ. R. Weggel and R. M. Sorensen, “Ship WavePrediction for Port and Channel Design,” Proceed-ings, Port Conference, 1986, ASCE. Approaches forestimating the wakes due to recreational boats arepresented in ASCE Manual 50, “Planning andDesign Guidelines for Small-Craft Harbors,” andR. R. Bottin et al., “Maryland Guide Book forMarina Owners and Operators on AlternativesAvailable for the Protection of Small Craft againstVessel Generated Waves,” U.S. Army Corps ofEngineers Coastal Engineering Research Center,Washington, D.C.

Table 23.3 Spectral Significant Heights and Periods for Wind-Generated Deep-Water Waves*

Wind speed, knotsFetch length, statute miles

0.5 1 2 10 50

20Hmo

, ft 0.6 0.8 1.1 2.2 4.1Tp, s 1.3 1.6 2.0 3.2 4.7

40Hmo

, ft 1.3 1.8 2.5 5.4 11Tp, s 1.7 2.2 2.7 4.5 7

60Hmo

, ft 2.2 3.1 4.2 9.1 18Tp, s 2.1 2.6 3.2 5.4 8

* Based on method presented in S. L. Douglass et al., “Wave Forecasting for Construction in Mobile Bay,” Proceedings, CoastalEngineering Practice, 1992, pp. 713–727, American Society of Civil Engineers. Hmo

¼ spectral significant wave height and Tp ¼ waveperiod.





23.3 Design Coastal WaterLevels

The design water level depends on the type ofproject. For design of some protective coastalstructures, for example, a water level based on arecurrence interval such as a 10-year or 100-yearreturn period often is selected. The FederalEmergency Management Agency (FEMA) “FloodInsurance Rate Maps (FIRM)” are based on such aconcept. They provide a first estimate of high-waterlevels along the U.S. coastlines. Since the design ofsome coastal structures can be extremely sensitiveto the design water level, more in-depth analysismay be justified. For engineering projects con-cerned with normal water levels, for example,where dock elevations and beachfill elevationsare determined by the water level, an estimate ofthe normal water level and the normal rangearound that mean is needed. All coastal engineer-ing projects should be designed to take intoaccount the full range of potential water levels.

The water level at any time in a specific locationis influenced by the tides, mean sea-level elevation,storm surge, including wind influence, and otherlocal influences, such as fresh-water inflow inestuaries.

Tides n The tide is the periodic rise and fallof ocean waters produced by the attraction ofthe moon and sun. Generally, the average intervalbetween successive high tides is 12 h 25 min, halfthe time between successive passages of the moonacross a given meridian. The moon exerts a greaterinfluence on the tides than the sun. Tides, however,are often affected by meteorological conditions,including propagation of storm tides from the seainto coastal waters.

The highest tides, which occur at intervals ofhalf a lunar month, are called spring tides. Theyoccur at or near the time when the moon is new orfull, i.e., when the sun, moon, and earth fall in line,and the tide-generating forces of the moon and sunare additive. When the lines connecting the earthwith the sun and the moon form a right angle, i.e.,when the moon is in its quarters, then the actions ofthe moon and sun are subtractive, and the lowesttides of the month, the neap tides, occur.

Tidal waves are retarded by frictional forces asthe earth revolves daily around its axis, and the tidetends to follow the direction of the moon. Thus, the

highest tide for each location is not coincident withconjunction and opposition but occurs at someconstant time after new and full moon. Thisinterval, known as the age of the tide, may amountto as much as 21⁄2 days.

Large differences in tidal range occur atdifferent locations along the ocean coast. Theyarise because of secondary tidal waves set up bythe primary tidal wave or mass of water movingaround the earth. These movements are also in-fluenced by the depth of shoaling water and con-figuration of the coast. The highest tides in theworld occur in the Bay of Fundy, where a rise of100 ft has been recorded. Inland and landlockedseas, such as the Mediterranean and the Baltic,have less than 1 ft of tide, and the Great Lakes arenot noticeably influenced.

Tides that occur twice each lunar day are calledsemidiurnal tides. Since the lunar day, or time ittakes the moon to make a complete revolutionaround the earth, is about 50 min longer than thesolar day, the corresponding high tide on succes-sive days is about 50 min later. In some places, suchas Pensacola, Florida, only one high tide a dayoccurs. These tides are called diurnal tides. If oneof the two daily high tides is incomplete, i.e., if itdoes not reach the height of the previous tide, as atSan Francisco, then the tides are referred to asmixed diurnal tides. Table 23.4 gives the springand mean tidal ranges for some major ports.

There are other exceptional tidal phenomena.For instance, at Southampton, England, there arefour daily high waters, occurring in pairs, separa-ted by a short interval. At Portsmouth, there aretwo sets of three tidal peaks per day. Tidal bores, aregular occurrence at certain locations are high-crested waves caused by the rush of flood tide up ariver, as in the Amazon, or by the meeting of tides,as in the Bay of Fundy.

The rise of the tide is referred to some estab-lished datum of the charts, which varies in differentparts of the world. In the United States, it is meanlower low water (MLLW).

Meanhighwater is the average of the highwaterover a 19-year period, and mean low water is theaverage of the low water over a 19-year period.Higher high water is the higher of the two highwaters of any diurnal tidal day, and lower lowwater is the lower of the two low waters of anydiurnal tidal day. Mean higher high water is theaverage height of the higher high water over a 19-year period, and mean lower low water is the





average height of the lower low waters over a19-year period (tidal epoch). Highest high waterand lowest low water are the highest and lowest,respectively, of the spring tides of record. Meanrange is the height of mean high water above meanlow water. The mean of this height is generallyreferred to asmean sea level (MSL).Diurnal rangeis the difference in height between the mean higherhigh water and the mean lower low water.

The National Ocean Service annually publishestide tables that give the time and elevation of thehigh and low tides at thousands of locationsaround the world and that can be used to forecastwater levels at all times. The tide tables forecastthe repeating, astronomical portions of the tide forspecific locations but do not directly account for theday-to-day effects of changes in local winds,pressures, and other factors. Along most coasts,the tide table forecasts are within 1 ft of the actualwater level 90% of the time.

Relative sea-level rise is gradually changing allof the epoch-based datum at any coastal site.Although, the datum that is used for design andconstruction throughout an upland area is notparticularly important, the relation between con-struction and actual water levels in the coastal zonecan be extremely important. The level of the oceansof the world has been gradually increasing forthousands of years. The important change is therelative sea-level change, the combined effect ofwater level and land-mass elevation changes due tosubsidence (typical of the U.S. Atlantic and Gulfcoasts) or rebound or emergence (Pacific coast ofthe U.S.). Measured, long-term tide data for majorU.S. ports show that the relative sea-level risediffers from location to location. For example,

Table 23.4 Mean and Spring Tidal Ranges forSome of the World’s Major Ports*

Meanrange, ft

Springrange, ft

Anchorage, Alaska 26.7 29.6†

Antwerp, Belgium 15.7 17.8Auckland, New Zealand 8.0 9.2Baltimore, Md 1.1 1.3Bilboa, Spain 9.0 11.8Bombay, India 8.7 11.8Boston, Mass. 9.5 11.0Buenos Aires, Argentina 2.2 2.4Burntcoat Head, Nova Scotia(Bay of Fundy)

41.6 47.5

Canal Zone, Atlantic side 0.7 1.1†

Canal Zone, Pacific side 12.6 16.4Capetown,Union of South Africa

3.8 5.2

Cherbourg, France 13.0 18.0Dakar, Africa 3.3 4.4Dover, England 14.5 18.6Galveston, Tex 1.0 1.4†

Genoa, Italy 0.6 0.8Gibraltar, Spain 2.3 3.1Hamburg, Germany 7.6 8.1Havana, Cuba 1.0 1.2Hong Kong, China 3.1 5.3†

Honolulu, Hawaii 1.2 1.9†

Juneau, Alaska 14.0 16.6†

La Guaira, Venezuela 1.0†

Lisbon, Portugal 8.4 10.8Liverpool, England 21.2 27.1Manila, Philippines 3.3†

Marseilles, France 0.4 0.6Melbourne, Australia 1.7 1.9Murmansk, U.S.S.R. 7.9 9.9New York, N.Y. 4.4 5.3Osaka, Japan 2.5 3.3Oslo, Norway 1.0 1.1Quebec, Canada 13.7 15.5Rangoon, Burma 13.4 17.0Reikjavik, Iceland 9.2 12.5Rio de Janeiro, Brazil 2.5 3.5Rotterdam, Netherlands 5.0 5.4San Diego, Calif. 4.2 5.8†

San Francisco, Calif. 4.0 5.7†

San Juan, Puerto Rico 1.1 1.3Seattle, Wash. 7.6 11.3†

Shanghai, China 6.7 8.9Singapore, Malaya 5.6 7.4

Table 23.4 (Continued)

Meanrange, ft

Springrange, ft

Southampton, England 10.0 13.6Sydney, Australia 3.6 4.5Valparaiso, Chile 3.0 3.9Vladivostok, U.S.S.R. 0.6 0.7Yokohama, Japan 3.5 4.7Zanzibar, Africa 8.8 12.4

* “Tide Tables,” National Ocean Service.† Diurnal range.





at Galveston, Tex., there has been about 1 ft ofrelative sea-level rise during the last 50 years. AtAnchorage, Alaska, there has been about 2 ft ofrelative sea-level fall during the last 50 years.

The impact of long-term sea-level rise has rarelybeen taken into account in design, except when ithas already impacted the epoch-based tidal datum,such as MLLW. The National Geodetic VerticalDatum (NGVD) was established at the mean sealevel (MSL) of 1929. Since sea-level rise has con-tinued since then, the NGVD is now below thecurrent day MSL along much of the U.S. Atlanticand Gulf coasts. At many locations, it is betweenthe MSL and the MLLW. For accurate location ofthe NGVD relative to the MSL or MLLW, analysiswith data from a local tide gage is required. Forsome harbor and coastal design, a staff gage isinstalled for recording water levels for a sustainedperiod of time to confirm the relation between thelocal surveyor’s elevation datum, the assumedtidal datum, and the actual water surface elevation.

Storm Surge n This can be defined broadly toinclude all the effects involved in a storm, inclu-ding wind stress across the continental shelf andwithin an estuary or body of water, barometricpressure, and wave-induced setup. The combinedinfluence of these effects can change the water levelby 5 to 20 ft depending on the intensity of the stormand coastal location. Engineers can use return-period analysis curves to estimate the likelihood ofany particular elevation. The Federal EmergencyManagement Agency and the various Corps ofEngineer Districts have developed such curvesbased on historic high-water-mark elevations andnumerical models of the hydrodynamics of thecontinental shelf.

23.4 Coastal SedimentCharacteristics

Most beach sediments are sand. The day-to-daydynamics of the surf zone usually ensure that mostfines, silts, and clays will be washed away to morequiescent locations offshore. Some beaches havelayers of cobbles, rounded gravel, or shingles,flattened gravel.

The size and composition of beach sands variesaround the world and even along adjacent shore-lines. Essentially, the beach at any particular siteconsists of whatever loose material is available.

Quartz is themost commonmineral in beach sands.Other constituents in sands include feldspars andheavyminerals. Some beaches have significant por-tions of seashell fragments and some beaches aredominated by coral carbonate material.

Beach sands are usually described in terms ofgrain-size distribution. The median diameter d50 isa common measure of the central size of thedistribution. The range of the distribution of sandsizes around this median is usually discussed interms of sorting.

The color of the sand depends primarily on thecomposition of the grains. The black sand beachesof Hawaii are derived from volcanic lava. Thewhite sands of the panhandle of Florida are quartzthat has developed a white color owing to mini-ature surface abrasions and bleaching.

23.5 Nearshore Currents andSand Transport

As wave energy enters the surf zone, some of theenergy is transformed to nearshore currents andexpended in sand movement. The nearshore cur-rent field is dominated by the incident wave energyand the local wind field. The largest currents arethe oscillatory currents associated with the waves.However, several forms of mean currents (long-shore currents, rip currents associated withnearshore circulation cells, and downwelling orupwelling associated with winds) can be importantto sand transport.

Longshore current is the mean current along theshore between the breaker line and the beach thatis driven by an oblique angle of wave approach.The waves provide the power for the mean long-shore current and also provide the wave-by-waveagitation to suspend sand in the current. Theresulting movement of sand is littoral drift orlongshore sand transport. This process is referredto as a river of sand moving along the coast.Although the river-of-sand concept is an effective,simple explanation of much of the influence ofengineering on adjacent beaches, the actual sandtransport paths are more complex. This is par-ticularly so near inlets with large ebb-tidal shoalsthat influence the incident wave climate.

Even on an open coast with straight and paralleloffshore bottom contours, the longshore-sand-transport direction changes constantly in responseto changes in the incident wave height, period, and





direction. The so-called CERC equation, or energyflux method, provides a rough estimate of theinstantaneous longshore sand transport rate. Theinstantaneous rate can vary from nil up to severalmillion cubic yards per year in either directionduring storms on some coasts. The variations in theinstantaneous rate are so significant that 90% ofthe sand transport occurs during only 10% of thetime—the storms. Even when averaged over a year,the net sand transport rate can vary significantlyfrom year to year and can even change directions.The daily variability in the longshore-sand-trans-port rate follows a joint, log-normal distribution.This can be used to simulate rates for the design ofsand bypassing systems.

Knowledge of the long-term transfer of sandacross the continental shelf to or from beaches islimited. For short time frames, the cross-shoretransport of sand during storms can be modeled toestimate the beach and dune erosion and theshoreline recession that will occur during somedesign storm.

Harbor andMarina Engineering

A harbor is a bay, cove, inlet, or recess of the seaor a lake, or the mouth of a river in which shipscan enter and be sheltered from wind and waves.A port is a harbor with facilities for the docking ofships, cargo handling and storage, and transfer ofpassengers between land and waterborne trans-portation. A marina is a shallow draft harbor forsmall, predominately recreational craft. Small-craftharbors accommodate commercial operations orwaterborne transportation operations, or both, aswell as recreational boats of various sizes. Harborand marina engineering is concerned with thedesign of navigable waterways in harbors, protec-tive structures, docks, and the facilities for servi-cing boats or ships.

23.6 Types of Ports andHarbors

Harbors may be classified as natural, seminatural,or artificial, and as harbors of refuge, militaryharbors, or commercial harbors. Commercial har-bors may be either municipal or privately owned.

A natural harbor is an inlet or water areaprotected from storms and waves by the natural

configuration of the land. Its entrance is so formedand located as to facilitate navigation whileensuring comparative quiet within the harbor.Natural harbors are located in bays, tidal estuaries,and river mouths. Well-known natural harbors areNew York, San Francisco, and Rio de Janeiro.

A seminatural harbor may be an inlet or a riversheltered on two sides by headlands requiringartificial protection only at the entrance. Next to apurely natural harbor, it forms the most desirableharbor site, other things being equal. Plymouth andCherbourg take advantage of their natural locationto become well-protected harbors by the additionof detached breakwaters at the entrances.

An artificial harbor is one protected from theeffect of waves by breakwaters or one created bydredging. Buffalo, New York; Matarani, Peru;Hamburg, Germany; and Le Havre, France, areexamples of artificial harbors.

A harbor of refuge may be used solely as ahaven for ships in a storm, or it may be part of acommercial harbor. Sometimes an outer harborserves as an anchorage, while a basin within theinner breakwater constitutes a commercial harbor.The essential features are good anchorage and safeand easy access from the sea during any conditionof weather and state of tide. Well-known harbors ofrefuge are the one at Sandy Bay, near Cape Ann,Massachusetts, and that at the mouth of DelawareBay. A fine example of a combined harbor of refugeand commercial harbor exists at Dover, England.

A military harbor or naval base accommodatesnaval vessels and serves as a supply depot.Guantanamo, Cuba; Hampton Roads, Virginia;and Pearl Harbor, Hawaii, are some well-knownnaval bases.

A commercial harbor is one in which docks areprovided with the necessary facilities for loadingand discharging cargo. Drydocks are sometimesprovided for ship repairs. Many commercial har-bors are privately owned and operated by compa-nies representing the steel, aluminum, copper, oil,coal, timber, fertilizer, sugar, fruit, chemical, andother industries. Municipal- or government-con-trolled harbors, often operated by port authorities,exist in many countries and are usually partof extensive port works, such as the harbors inNew York, Los Angeles, and London.

A port is a harbor where marine terminalfacilities are provided. These consist of piers orwharves at which ships berth while loading orunloading passengers and cargo, transit sheds and





other storage areas where ships may dischargeincoming cargo, and warehouses where goodsmay be stored for longer periods while awaitingdistribution or sailing. The terminal must be servedby railroad, highway, or inland-waterway connec-tions. In this respect the area of influence of the portreaches out for a considerable distance beyond theharbor.

A port of entry is a designated location whereforeign goods and foreign citizens may be clearedthrough a custom house.

23.7 Harbor Layout

The number and size of ships using a harbordetermine its size to a large extent, but existing siteconditions are also an important influence. Gener-ally, unless the harbor is a natural one, its size willbe kept as small as feasible for safe and reasonablycomfortable operations to take place. Use of tugs toassist maneuvering of ships in docking may alsoinfluence the size of the harbor.

23.7.1 Turning Basins

A turning basin is a water area inside a harbor or anenlargement of a channel to permit the turning of aship. When space is available, the area should havea radius of at least twice the length of the ship to

permit either free turning or turning with the aid oftugs, if wind and water conditions require. Whenspace is limited, the shipmay be turned bywarpingaround the end of a pier or turning dolphin, eitherwith or without the use of its lines. In those cases,the turning basin will be much smaller and of amore triangular or rectangular shape. The mini-mum diameter should be at least 20% greater thanthe length of the largest ship to be turned.

The usual minimum harbor area is the spacerequired for docks plus a turning basin in front ofthem. In some layouts, where a ship is turned bywarping it around the end of the pier or turningdolphin, the harbor may be even smaller. For in-stance, a minimum harbor with a single pier andturning basin and a long approach channel fromthe open sea (Fig. 23.3) can accommodate two 500-ft ships. This artificial harbor may be formed bydredging a channel through shallow water, pro-tected by offshore reefs and islands, and enlargingthe inshore end to provide the minimum area ofharbor that will meet the shipping requirementsspecified for the project. In leaving its berth, a shipmust warp itself around the end of the pier so asnot to have to back out through the long approachchannel.

Another, less restricted type of harbor is nearlysquare, protected by two breakwater arms, withone opening. The harbor has several docks and aturning basin with an area sufficient to inscribe a

Fig. 23.3 Typical layout for a small artificial harbor.





turning circle with a radius equal to at least twicethe length of the largest ship. This is the smallestradius a ship can comfortably turn on, undercontinuous headway, without the help of a tug.Figure 23.4 shows such a harbor.

23.7.2 Arrangements ofBreakwaters

Breakwaters are required for protection of artifi-cial and seminatural harbors. Their location andextent depend on the direction of maximumwaves,configuration of the shoreline, and minimum sizeof harbor required for the anticipated traffic inthe port. They may consist of two “arms” out fromthe shore, plus a single breakwater, more or lessparallel to the shore, thereby providing twoopenings to the harbor; or the harbor may beprotected with a single arm out from shore. Or the

harbor may be protected by two arms convergingnear their outshore ends and overlapping to form aprotected entrance to the harbor.

Selection of the most suitable arrangement ofbreakwaters depends principally on the directionof the maximum waves. The effectiveness of thechosen arrangement in quieting the harbor may bechecked by model tests. For comfortable berthing,the wave height should not exceed 2 ft and windsshould not exceed 10 to 15 mi/h. But wave heightsup to 4 ft have been allowed where bulk cargois being handled and where the wind directionis such as to hold a docked ship off the dock.In general, winds and current are more bother-some in docking a vessel when it is light than arerelatively small harbor waves and may necessitateuse of a tug.

Rarely will a location be found where the wavesare from one direction only. Generally, it is better

Fig. 23.4 Medium-sized artificial harbor with full-sized turning basin.





in a harbor having two openings for ships to enterfrom the direction of the minimum wind andwaves and to leave toward the direction of themaximum wind and waves. On leaving the harbor,the ships usually have open water in which tomaneuver, whereas on entering the harbor, theyare immediately in a restricted area and mustapproach the docks at reduced speed and at acertain inclination to its face.

A single breakwater armmay be used where thewaves predominate from one direction only. It alsomay serve where the configuration of the shorelinereduces the fetch in the opposite direction to suchan extent that the wave-generating area is not suf-ficient to permit formation of bothersome waveswithin the harbor.

23.7.3 Use of Moorings andAnchorages

An offshore mooring is provided usually where itis not feasible or economical to construct a dock orprovide a protected harbor. Such an anchorageconsists of a number of anchorage units, each con-sisting of one or more anchors, chains, sinkers, andbuoys to which the ship will attach its mooringlines. These anchorages are supplemented in mostcases by the ship’s bow anchors. Bulk cargo isusually transported to or from the ship by pipelineor trestle conveyor; other cargo may be transferredby lighter.

An anchorage area is a placewhere shipsmay beheld for quarantine inspection, to await dockingspace, sometimes while removing ballast in prep-aration for taking on cargo, or to await favorableweather conditions. Special anchorages are some-times provided for ships carrying explosives ordangerous cargo and are usually so designated onharbor maps by name and depth of water.

23.7.4 Harbor Entrances

To reduce wave height within a harbor, entrancesshould be no wider than necessary for safe nav-igation and for preventing dangerous currentswhen the tide is coming in and going out. Theentrance width should be in proportion to the sizeof the harbor and the ships using it. In general, thefollowing widths will be satisfactory: small har-bors, 300 ft; medium harbors, 400 to 500 ft; andlarge harbors, 500 to 1000 ft. When the entrance isbetween breakwaters with sloping faces, the width

is measured at the required harbor or channeldepth below low water. Thus, the entrances will beappreciably wider than the recommended widthsat low-water level. In such cases, it is advisable tomark the full harbor depth of the entrance withbuoys, placing one or more on each side of theentrance channel.

The entrance should be on the lee side of theharbor, where possible. If the entrance must belocated at the windward end of the harbor,breakwaters should overlap so vessels may passthrough the restricted entrance and be free to turnwith the wind before being hit broadside by thewaves. Also, the interior of the harbor will beprotected from the waves.

When the entrance to a harbor is unobstructed,storm waves from the sea pass through the openinginto the harbor. Unless they are reflected by a ver-tical surface, they will gradually decrease in heightas they progress away from the entrance and as theharbor widens relative to the entrance width. Modeltests will give an indication of wave conditions andare essential for studying various arrangements ofbreakwaters for important harbors.

In tidal harbors where there are strong currents,the entrance width should be sufficient to preventthe velocity of the current through the opening atebb tide from exceeding 4 ft/s; otherwise, it mayaffect navigation of ships and create scour at thebase of adjacent breakwaters.

If waves pass through an entrance and strike avertical face on the opposite side of the harbor, theyreflect. The result is an increase in wave heightwithin the harbor. This condition can be correctedby building wave-absorbing beaches, flat slopes ofrock or granular material, in front of the verticalsurface. However, when the vertical surface is awharf or bulkhead used for berthing of ships, it isimpossible to use a beach. Where conditions willpermit use of a hollow structure, the outsidevertical wall may be perforated or slotted and theenergy of the waves absorbed in the chamber inback of the wall. Other means may be resorted to,suchas installationof shortwave-deflectingwalls orwave traps along the approach channel to the dock.

23.7.5 Channel Depth

The harbor and approach channel for idealoperating conditions should be of sufficient depthto permit navigation at lowest low water whenships are fully loaded. This depth must include an





allowance for the surge of the ship, which is aboutone-half the wave height, the out-of-trim or squatwhen in motion, and from 2- to 4-ft clearance underthe keel, the larger figure being used when thebottom is of hardmaterial such as rock. When thereis a very soft mud bottom, a keel may at timestouch bottom because of surge and squat withoutdamaging the ship, but it would be disastrous tohave its fully loaded weight bump a hard rockbottom. Therefore, greater allowances must bemade in computing the depth when the bottom ishard. Also, the harbor and approach channel orapproach sea lanes must be carefully swept tomake sure there are no obstructions, such as reefsor rocky pinnacles, boulders, or sunken ships,above the required depth for safe navigation.

In some harbors, some ships arrive or departon the rising tide. But the advent of supertankerswith deadweight tonnage over 300,000 tons anda draft exceeding 80 ft creates a need for deeperharbors. Otherwise, the cargo has to be transferredto smaller tankers or piped ashore through sub-marine lines from offshore anchorages.

Tides significantly influence harbor depth. Table23.4 (p. 23.8) gives the tidal ranges in feet atprincipal ports throughout the world. Note that thetidal range along the coasts of the United Statesseldom exceeds 10 ft, and therefore the harborsare dredged to provide the required depth fornavigation at lowest low water. The condition isentirely different in the British Isles and on thewestern coast of Europe, where the port ofLiverpool, England, has a spring tidal range of27 ft; London, England, 20 ft; Calais, France, 20 ft;and others have even greater variations. In mostcases, this fluctuation in sea level has resulted inthe use of wet docks in all stages of the tide. Thesedock systems require entrance locks with massivegates, heavy swing or bascule bridges and themachinery for working them, pumping equipment,and other accessories. Since all this results ingreat cost, as well as continuing operational andmaintenance expense, the question arises as to thelimiting range for the natural tidal working of portswithout recourse to enclosed docks. Generally,about 10 to 15 ft is considered the dividing point.

23.7.6 Channel Width

Width of a channel may be measured between thetoes of the bordering side slopes or at the designdepth.

Minimum nominal width required for a channeldepends on many factors. The following are themost important:

1. Maximum beam of traversing ships

2. Length and maneuverability of the longestvessels

3. Accuracy and reliability of navigational aids

4. Speed, volume, and nature of traffic

5. Nature, intensity, and variation of currentsalong the channel

6. Ability and experience of mates and pilots

7. Channel depth and curvature

8. Whether ships are to pass each other

Because of insufficient knowledge of the influ-ence of these factors when determining a minimumdesign width, standard channel widths have notbeen established. The Permanent InternationalAssociation of Navigation Congress, however,recommended in 1978 that the nominal width of aone-way channel under ideal conditions should beat least five times the beam of the largest shipexpected to use the channel. On a curve, this widthshould be increased by L2/8R, to account for theeffect on the width of the ship’s path because of thelength L of the vessel and the radius R of the curve.The width on a curve should be additionallyincreased to take into account maneuvering dif-ficulties. If ships are to pass in a one-way channel,the nominal width of the channel should be at least12 times the largest beam (ship width). For a two-way channel, the width should be adequate toprovide a distance between passing ships of at leasttwo times the beam of the larger vessel. The pre-ceding recommended minimum widths should beincreased, if necessary, to allow for the effects ofcrosswinds and crosscurrents.

23.7.7 Channel Alignment

Basically, a channel should provide a path for aship through the harbor entrance directly to a berthwithout requiring difficult maneuvering or sub-jecting the ship to strong crosscurrents or highwaves. If the channel must be curved, the radius ofthe curves should be at least five times the length ofthe longest ship expected to use the channel.

Straight tangents should be used betweensuccessive curves. (S curves should be avoided.)





The tangents should have a length of at least 10times that of the longest vessel.

In a sea strait, the channel preferably shouldcoincide with the deepest troughs of the strait andhave as few curves as possible. Sight distanceshould be at least 0.5 mi.

23.7.8 Port Structures

A marine terminal is that part of a port or harborthat provides docking, cargo-handling, and storagefacilities. When only passengers embark anddisembark along with their baggage and miscella-neous small cargo, generally from ships devotedmainly to the carrying of passengers, it is called apassenger terminal. When the traffic is mainly cargocarried by freighters, although many of these shipsmay carry also a few passengers, the terminal iscommonly referred to as freight or cargo terminal. Inmany cases, it is known as a bulk cargo terminal,where such products as petroleum, cement, andgrain are stored and handled.

Docking facilities may consist of a single pier oras many as 1000 piers. The number of berthsdepends on the anticipated number of ships thatwill use the port and the time it will take todischarge and take on cargo or passengers. Thiswill vary for different kinds of cargo, but usually avessel will not be in port more than 48 h. Manybulk cargo ships are loaded in 24 h or less.

Wharves and piers should be located in themost sheltered part of the harbor or along the leeside of the breakwaters. Where possible, piersshould be so oriented as to have ships alongsideheaded as nearly into the wind and waves as pos-sible. This is particularly important if the harbor isnot well-protected.

Onshore marine-terminal facilities may consistof one or more of the following, depending on thesize of the port and the service it renders:

Transit sheds are located immediately in back ofthe apron on a pier or wharf. Their function is tostore for a short period of time cargo awaitingloading or distribution after being unloaded fromships.

Warehouses may replace transit sheds at somemarine terminals. But when used to supplementsheds, warehouses are usually located inland andnot on the pier structure.

Bulk storagemay be in open piles over conveyortunnels, which may be covered with shedswhen protection from the elements is required;

in bins and silos or elevators (for grain storage);or in storage tanks (for liquids). These shouldbe located as near the waterfront as possible,and sometimes directly alongside the wharf orpier, to enable direct loading into the hold ofthe ship.

A terminal building houses port-adminis-tration personnel and custom officials if a sepa-rate custom house is not provided. The terminalbuilding should be located in a prominent andconvenient location with respect to the docks.

Guardhouses are located at strategic points inthe port area, such as the entrance gates of high-ways and railways, entrances to piers or terminalareas, bonded storage, and so on.

Stevedores’ warehouses house cargo-handlinggear, wash and locker rooms, and other facilities forstevedores.

Miscellaneous buildings and structures in-clude a fire house and fire-fighting equipment,power plant, garages, repair shops, drydocks,marine railways, fishing piers, or yacht basins.

(P. Bruun, “Port Engineering,” 4th ed., GulfPublishing Company, Houston, Tex (www.gulfpub.com).)

23.8 Hydrographic andTopographic Surveys

After preliminary layouts of a port have beencompleted and before the final design is started, itis necessary in most instances to obtain additionalsite information.

A hydrographic survey, if not already available,should be made to determine the elevations of thebottom of the body of water and should extendover an area somewhat larger than the proposedchannel and harbor. In addition, the surveyshould locate the shoreline at low and high waterand all structures or obstructions in the water andalong the shore, such as sunken ships, reefs, orlarge rocks.

Determination of the relief of the bottom of thebody of water is made by soundings or by the useof a fathometer designed for hydrographic sur-veys. The latter method is being used by theNational Ocean Survey and has superseded lead-line soundings to a large extent. A fathometer ordepth-recording instrument is usually mountedin a motorboat, which is kept on course onestablished range lines or its location is followed





by use of an electronic positioning system as therecording chart registers a natural profile of thebottom. The fathometer, when operated by experi-enced personnel and properly adjusted and cali-brated daily, is superior to lead-line soundings inboth accuracy and speed with which a survey canbe made.

The depths of soundings are referred to waterlevel at the time made and later corrected to thedatum water level with tide gages or tide tables.Therefore, it is important to keep a record of thetime and day the soundings aremade and to have aconcurrent tide- or water-level gage operating inthe immediate vicinity.

Soundings should be made at about 25-ft inter-vals along lines from 50 to 100 ft apart, dependingon the irregularity of the bottom. Closer spacingmay be needed where greater detail is required todetermine sharp changes in the profile of the bot-tom or to outline obstructions.

Soundings are plotted, usually relative tolow-water datum, on a drawing (hydrographicmap), which should show the datum, high- andlow-water lines, contour lines of equal depthinterpolated from the soundings, and principalland and water features. Contour depths may bein either feet, meters, or fathoms, although the lastis not used generally for making harbor andmarine-terminal studies and layouts. Since the seabottom is usually less precipitous and the slopesmore gentle and uniform than those on land, thescale of the hydrographic map may be somewhatsmaller than would normally be used for plottingland topography. Unless the harbor area is verylarge, a scale of 1 in ¼ 200 ft or 1 :2000 in aproportional scale is satisfactory. It is desirable tohave all the hydrography on one sheet becausethis gives a better overall picture of the harbor. Ingeneral, the scale should be large enough so thatnot more than 10 contour lines, in 2-ft intervals,occur within 1 in.

If dredging of a harbor or channel is required,the material is usually measured in place todetermine the quantity for payment. To determinethis quantity, soundings on fixed sections are takenbefore and after dredging, and the changes incross sections are determined by computation orplanimeter. It is usually specified that payment willbe made for material removed to a maximum of 2 ftbelow the required dredged bottom, but allmaterial must be removed to at least the minimumdepth specified.

A topographic survey of the marine-terminalarea should be made, to obtain ground contours at2- to 5-ft intervals. The larger figure is used whereterrain is rough and in areas where there is to belittle or no construction of importance. In buildingareas, elevations on 25-ft centers in two directions,with additional elevations at abrupt changes inground, provide satisfactory information. Wherethere is dense ground cover, the cross-profilemethod is most suitable. The profiles may bemade with level and tape or stadia, on about 100-ftcenters, by clearing paths to permit an unob-structed line of sight. The ground between the 100-ft profiles should be examined, as far as possible,and any prominent irregularities in ground levelestimated and noted, so that contours, which areinterpolated from elevations along the profiles, canbe estimated for the areas in between.

Topographic maps, besides showing the con-tours of the ground, should locate all borings andtest pits, buildings, utilities, and any prominentlandmarks. Contours generally are referred tohigh-water datum. The map scale should be suchthat the contour lines are not spaced closer than 30to the inch. Where considerable detail is involvedthe scale should be 1 in ¼ 100 ft or 1 :1000 or less,but for small-scale maps 1 in ¼ 1000 ft or 1 :10,000or more may be used.

(H. Agerschou et al., “Planning and Design ofPorts and Marine Terminals,” John Wiley & Sons,Inc., New York (www.wiley.com); J.B. Gerbich,“Handbook of Coastal and Ocean Engineering,”Gulf Publishing Company, Houston, Tex. (www.gulfpub.com); A. D. F. Quinn, “Design andConstruction of Ports and Marine Structures,”McGraw-Hill Publishing Company, New York(books.mcgraw-hill.com).)

23.9 Ship Characteristics

The length, beam (breadth), and draft of ships thatwill use a port have a direct bearing on the designof the approach channel, harbor, and marine-terminal facilities. The last is affected also by thetype of vessel, its wind area, and its capacity ortonnage. The draft of a ship, expressed in relationto its displacement of water as either loaded orlight draft, is the depth of the keel of the ship belowwater level for the particular condition of loading.

Displacement tonnage is the actual weightof the vessel, or the weight of water displaced





when afloat, and may be either “loaded” or “light.”Displacement loaded is the weight, in metric tons,of the ship and its contents when fully loaded withcargo to the Plimsoll mark, or load line, painted onthe hull of the ship (1 ton ¼ 2205 lb). The Plimsollmark, used on British ships, and the load line,commonly used on American vessels, designatethe depth under the maritime laws to which a shipmay be loaded in different bodies of water duringvarious seasons of the year. Displacement light isthe weight, in metric tons, of the ship withoutcargo, fuel, and stores.

Deadweight tonnage is the carrying capacity ofa ship in metric tons and the difference betweendisplacement light and displacement loaded to thePlimsoll mark or load line. It is the weight of cargo,fuel, and stores a ship carries when loaded to theload line, as distinguished from loaded to spacecapacity. This tonnage varies with latitude andseason. It also depends on salinity of the waterbecause of the effect of temperature and salinity onthe specific gravity and buoyancy of the water inwhich the vessel is operating. Unless otherwiseindicated, deadweight tonnage is the mean oftropical, summer, and winter deadweight. Dead-weight tonnage is indicated by weight, and grosstonnage by volume measurement; both indicatecarrying capacity.

Ships are registered with gross or net tonnageexpressed in units of 100 ft3. Gross tonnage isthe entire internal cubic capacity of a ship, andnet tonnage is the gross tonnage less the spaceprovided for the crew, machinery, engine room,and fuel.

Cargo or freight tonnage, a commercial expre-ssion, is the basis of the freight charge. This tonnagemay be measured by either weight or volume.

An ordinary seagoing vessel that can carry anominal deadweight of 8000 tons of cargo, fuel,and stores will have a displacement of about11,500 tons, a gross of about 5200 tons, and a net ofabout 3200 tons.

Ballast is the weight added in the hold or ballastcompartments of a ship to increase its draft after ithas discharged its cargo and to improve itsstability. It usually consists of water and isexpressed in long tons. In an oceangoing tanker,saltwater ballast replaces a certain amount ofpetroleum when the ship is unloaded, whereas adry-cargo or passenger vessel has separate com-partments for ballast.

23.10 Types of Ship MooringStructures

Facilities for mooring of ships aremajor elements ofports and harbors. Such facilities include docks,wharves, bulkheads, piers, dolphins, fixed moor-ing berths, and ground tackle in fixed positions forattachment of a ship’s mooring lines. Appurte-nances for these facilities include fenders forabsorption of ship impact during mooring ordeparture, trestles, catwalks, bitts, bollards, cleats,chocks, hooks, and capstans.

A dock, in general, is a marine structure formooring or tying up of vessels, loading andunloading cargo, or embarking and disembarkingpassengers. Often, piers, wharves, bulkheads, and,in Europe, jetties, quays, or quay walls, are calleddocks. In Europe also, where there are largevariations in tide level, a dock is commonlyconsidered an artificial basin for vessels and iscalled a wet dock. When the basin is pumped out,it is termed a dry dock.

A wharf or quay is a dock that parallels theshore. It is generally contiguous with the shore butmay not necessarily be so. On the other hand, abulkhead or quay wall, although similar to awharf and often referred to as such, is backed up byground; the name is derived from the very natureof holding or supporting ground in back of it.

In many locations where industrial plants are tobe built adjacent to water transportation, theground is low and marshy; it is therefore necessaryto fill it in. The fill is often obtained by dredging theadjacent waterway, creating a navigable channel orharbor along the property. To retain the madeground, which will now be at a much higherelevation along the waterway, a bulkhead isusually installed. This, or a part of its length, maybe used as a wharf for docking vessels if mooringappurtenances, paving, and facilities for handlingand storing cargo are added. It is then called abulkhead wharf.

A pier or jetty is a dock that projects into thewater. Sometimes it is referred to as a mole. Whenbuilt in combination with a breakwater, it is termeda breakwater pier. In contrast with a wharf, whichcan be used for docking on one side only, ships mayuse a pier on both sides. But there are instanceswhere only one side is used, owing to either thephysical conditions of the site or the lack of needfor additional berthing space.





A pier may be more or less parallel to the shoreand connected to it by a mole or trestle, generally atright angles to the pier. In this case, the pier iscommonly referred to as a T-head pier or L-shapedpier, depending on whether the approach is at thecenter or at the end.

Dolphins are marine structures for mooringvessels. They are commonly used in combinationwith piers and wharves to shorten the length ofthese structures. Dolphins are a principal part ofthe fixed-mooring-berth type of installation usedextensively in bulk-cargo loading and unloadinginstallations. Also, they are used for tying up shipsand for transferring cargo between ships mooredalong both sides of the dolphins. There are twotypes of dolphins: breasting and mooring.

Breasting dolphins, usually the larger of the twotypes, are designed to take the impact of a shipwhen docking and to hold the ship against abroadside wind. Therefore, they are provided withfenders to absorb the impact of the ship and to pro-tect the dolphin and ship from damage. Breastingdolphins usually have bollards or mooring posts totake the ship’s lines, particularly springing lines formoving a ship along the dock or holding it againstthe current. These lines are not very effective in adirection normal to the dock, particularly when aship is light.

To hold a ship against a broadsidewind blowingin a direction away from the dock, additionaldolphins must be provided off the bow and stern,some distance in back of the face of the dock. Theseare called mooring dolphins. They are not designedfor the impact of the ship since they are away fromthe face of the dock, where they will not be hit. Iftwo mooring dolphins are to be used, they shouldbe located about 458 off the bow and stern andpermit mooring lines not less than 200 ft or morethan 400 ft long. The largest ships may require twoadditional dolphins, off the bow and stern. Thesedolphins are usually located so that the mooringlines will be normal to the dock, which makes themmost effective for holding the ship against anoffshore wind. Mooring dolphins are providedwith bollards or mooring posts and with capstanswhen heavy lines are to be handled. The maximumpull usually should not exceed 50 tons on asingle line, or 100 tons on a single bollard if twolines are used.

A fixed mooring berth is a marine structureconsisting of dolphins for tying up a ship anda platform for supporting the cargo-handling

equipment. The platform is usually set back 5 to10 ft from the face of the dolphins so that the shipwill not come in contact with it. Therefore, theplatform does not have to be designed to take theimpact of the ship when docking.

Offshore moorings for ships consist of groundtackle placed in fixedpositions for attaching a ship’slines. Each unit of ground tackle consists of one ormore anchors with chain, sinker, and buoy to whichthe ship’s line is attached. These mooring units areusually located so as to take the bow and stern linesand, if the ship is large, one or more breasting lines.For some moorings, where the wind is in onedirection, the shipmay use its own bow anchor andthe fixed tackle off the bow may be omitted.

(P. Bruun, “Port Engineering,” Gulf PublishingCompany, Houston, Tex. (www.gulfpub.com).)

23.11 Dock andAppurtenance Designfor Ship Mooring

Wharves, piers, bulkheads, and fixed mooringberths fall generally into two broad classifications:docks of open construction with their decks sup-ported by piles or cylinders; and docks of closed orsolid construction, such as sheetpile cells, bulk-heads, cribs, caissons, and gravity (quay) walls.

The following codes, references, and standardsare recommended as a basis for analysis and designof a wharf structure, fill containment structure,mooring and fender devices, and associatedequipment.

Primary Codes for Design

l American Concrete Institute (ACI) “BuildingCode Requirements for Reinforced Concrete”

l American Institute of Steel Construction (AISC)“Manual of Steel Construction”

l Uniform Building Code (UBC)

l American Society of Civil Engineers (ASCE)“Minimum Design Loads for Buildings andOther Structures”

Information and Reference

l American Association of State Highway andTransportation Officials (AASHTO) “StandardSpecification for Highway Bridges” (ReferenceDocument)





l Military Handbook “Piers and Wharves” (MIL-HDBK-1025/1) (Reference Document)

l Naval Facilities Engineering Command (NAV-FAC) Design Manual “Fixed Moorings” (DM26.4) (Reference Document)

l Naval Facilities Engineering Command (NAV-FAC) Design Manual “Seawalls, Bulkheads, andQuaywalls” (DM 25.04) (Reference Document)

l U.S. Army Corps of Engineers (USACE) “ShoreProtection Manual”

l U.S. Army Corps of Engineers (USACE) “Coas-tal Engineering Manual”

Two structure classifications are considered forwharf design:

l Open-Type Marginal Wharf

l Solid-Type Marginal Wharf

These options and their methods of constructionare discussed below.

23.11.1 Open-Type MarginalWharf

A marginal wharf is a wharf structure that isconnected to the upland shore area along its fulllength. Such an arrangement is adaptable to theland transfer of containers, luggage, and passen-gers for cruise and/or cargo transport. The alter-natives that lend themselves to this arrangementare the open-type marginal wharf with revetedslope, and the solid-type marginal wharf.

For an open-type marginal wharf with revetedslope, the wharf geometry is dictated by therelatively deep-water conditions at the face of theberth.

The following five pile supported structureconfigurations for use as open-type marginal wharfstructures with reveted slope.

l Precast Box Beam

l Cast-in-Place Flat Plate

l Composite Panel Flat Plate

l Cast-in-Place Slab and Bent

l Ballasted Flat Plate

A summary of advantages and disadvantages ofthe open type marginal wharf alternatives areprovided in Table 23.5.

Precast Box Beam Wharf n The firstmarginal open wharf alternative presented consistsof a composite concrete deck surface supported byprecast box beams which in turn are supported byconcrete bent caps and prestressed concrete piles.A schematic drawing of the precast box beamalternative can be found in Fig. 23.5.

The main working surface is a concrete com-posite deck composed of precast panels and a cast-in-place concrete topping slab. The deck would besupported by standard AASHTO precast pre-stressed concrete box beams which would bespaced to optimize structure costs.

The advantages of this alternative includeminimization of the total number of piles support-ing the wharf structure and maximization of theuse of precast construction, which will reduce thefield labor and construction time required. Precastdeck panels would serve as a bottom form for thecast-in-place concrete deck thus reducing costlyformwork placement and removal. The slab designis such that the cast-in-place deck slab will becomposite with the precast bottom form.

The disadvantages of this alternative are relatedto the use of precast elements. The size of theprecast box beams will require specialized materialhandling equipment to place the box beams. Theuse of precast elements results in the need fortighter construction tolerances. Unlike with cast-in-place construction where adjustments are easilymade to accommodate misalignments or elevationvariations, precast construction requires veryaccurate construction and constant monitoring ofprecast element placement. Finally, precast con-struction inherently has two problems—specialdetailing required for continuity of connectionsbetween individual precast elements, and high costof specialty elements. Continuity is required be-cause vertical and lateral loads must have acontinuous, structural pathway between precastelements to allow transfer of these loads to the pilesand subsequently to the soils.

Cast-in-Place Flat Plate Wharf n Thesecond marginal, open wharf type is a pilesupported cast-in-place concrete flat plate slab.The cast-in-place concrete deck provides two-wayslab action to resist vertical and lateral loading.This type of construction is relatively new in theheavy waterfront construction industry but hasbeen gaining in popularity due to the initialconstruction cost savings that can be achieved.





Table 23.5 Open Type Marginal Wharf Alternatives

PrecastBox Beam

Cast-in-PlaceFlat Plate

CompositePanel

Cast-in-PlaceSlab and Bent

Ballasted Cast-in-Place Flat Plate

ADVANTAGES

Minimizesnumber of pilesrequired

Affordseconomy ofmaterials

Maximizes use ofprecastelements

Constructiontolerances arenot as critical

Affords economyof materials

Maximizes use ofprecastelements

Minimizes fieldlabor

Reducedconstructiontime

Reduces need forformwork

Provides highestdegree ofstructuralcontinuity

Minimizesformwork costs

Less specializedequipmentrequired forconstruction

Minimizes fieldlabor

Precast elementsare relativelysmall

Requires nospecialequipment forconstruction

Reducedconstructiontime

Conventionaltype ofconstruction

Easy to formrecessed utilitypits, trenches,and other items

No specialequipmentrequired forconstruction

Provides highestdegree ofstructuralcontinuity

Minimizesformwork costs

Less specializedequipmentrequired forconstruction

Flexibility foradding rail andutilities

DISADVANTAGES

Requires specialmaterialshandlingequipment

Requires tighterconstructiontolerances

Requires deeperpileembedment

Requires specialdetailing forcontinuity ofconnections

Difficult toexpand for rail

Requires highlyqualified labor

Labor intensiveconstruction

Increasedconstructiontime

Requires specialdetailing forductility

Requires specialconcretecastingsequence


Requires tighterconstructiontolerances

Requires specialdetailing forcontinuity ofconnections

Requires a largemember ofpiles


Highlydependent onqualified labor



Requires specialconcrete castingsequence

Formworkrelatively costly


Requires highlyqualified labor



Requires specialdetailing forductility

Requires specialconcretecastingsequence

Note: All open-type wharves require excavation and complete demolition of existing structures.





The flat plate design consists of a cast-in-placeconcrete deck, which provides two-way slab actionto resist vertical and lateral loading. A drop-panelfascia on the waterside face of the wharf accom-modates the dock fender system and the mooringdevices, as well as providing a transition area thatwould accommodate any required utility or servicepits.

The flat plate slab would be supported byprecast prestressed concrete piles. Piles are spacedtomatch slab and pile capacities. The advantages ofthe flat plate alternatives include minimization offorming costs for cast-in-place concrete construc-tion and economy of materials. The driven piles actas supports for the bottom form, which is level.Because the structure is principally cast-in-placeconstruction, less specialized equipment is re-quired during construction. Most general contrac-tors can perform the necessary forming andconcrete placement required. Finally, since thestructure consists only of cast-in-place concrete andprecast piles, there are fewer structural compo-nents to integrate together, and thus, this designprovides a high degree of structural continuity.

The disadvantages associated with this designare related to the extensive use of cast-in-place

concrete. The techniques employed for construc-tion are labor intensive. This includes the place-ment of formwork and the need to strip theformwork and move it to the next slab unit beingplaced. To minimize the time on the site and toaccount for shrinkage effects, a special concretecasting sequence must be used. A large pool ofrelatively skilled workmen will be required. Inaddition, this type of construction requires moretime in the field than a precast alternative as thecontractor must wait for adequate strength devel-opment of the concrete slab before form strippingcan begin. Also, with this type of wharf futureexpansion for rail is very difficult and costly.

Note that the pile spacing for this type ofstructure is controlled primarily by span limi-tations of the cast-in-place concrete deck slab undervertical loading. Therefore, pile spacing is selectedindependent of lateral resistance requirements ofthe substructure. Lateral resistance is incorporatedinto the substructure by selecting a pile sizecapable of resisting the lateral design loads.

Composite Panel Wharf n The thirdmarginal open wharf design consists of a compo-site concrete deck surface supported by either a

Fig. 23.5 Precast box beam open wharf.





cast-in-place or precast pile cap which in turn issupported by a precast prestressed concrete pile. Aschematic drawing of the composite panel alterna-tive can be found in Fig. 23.6.

The main working surface of this design is aconcrete composite deck composed of precastconcrete panels and cast-in-place concrete toppingslab. Precast reinforced or precast prestressedconcrete deck panels would be placed uponmasonite bearing pads, which in turn would besupported by precast or reinforced cast-in-placeconcrete pile caps. Each pile cap would in turnbe supported by a square precast prestressedconcrete pile. A cast-in-place concrete drop-panelfascia on the waterside face of the wharfaccommodates the dock fender system and themooring devices, as well as providing a transitionarea that would accommodate any required utilityor service pits.

One of the main advantages of composite panelconstruction is the minimization of labor intensiveconcrete formwork over water, resulting in reducedfield labor costs and generally a reduction in theconstruction time. Additionally, precast items theo-retically afford a greater degree of quality control.Modular type construction is also inherently lesstime consuming than more labor intensivemethods such as the cast-in-place concrete alterna-

tives. Most of the precast elements for thisalternative are of the size and configuration thatwould facilitate casting on site.

The disadvantages of the composite panelalternative include the relative discontinuity ofadjacent structural members. This results in theneed for tighter construction tolerances and specialconnection details. This alternative requires a largevolume of material and special connection detailsto make up for the relatively flexible nature of thistype of structure and to effectively transfer lateralloads from the deck elevation into the supportingpile system. Also, with this type of wharf futureexpansion for rail is very difficult and costly.

Cast-in-Place Slabwith Bent Wharf n Thefourth, marginal open wharf design considered is acast-in-place slab and bent system. This is a moreconventional means of construction that utilizespile supported cast-in-place concrete bent caps anddeck slab. A schematic drawing of the cast-in-placeslab with bent design can be found in Fig. 23.7.

This alternative consists of a cast-in-place con-crete deck that provides one-way slab action toresist vertical and lateral loading. The slab is castintegrally with a series of pile supported concretebent caps. A drop-panel fascia on the watersideface of the wharf accommodates the dock fender

Fig. 23.6 Composite panel open wharf.





system and the mooring devices, as well asproviding a transition area that would accommo-date any required utility or service pits. Thetransverse beams would be supported by pre-stressed concrete piles.

The advantage of this cast-in-place slab and bentconfiguration is that construction tolerances aregenerally not as critical as that of precast ormodular systems. While cast-in-place constructionis usually more time consuming and labor inten-sive than precast methods, it may be feasible alter-native where there is an available supply of lowcost labor. In addition, this type of construction canbe completed by most general contractors andrequires no special construction equipment orhandling techniques.

The disadvantages of this type of constructionprincipally involve the use of cast-in-place con-struction. This type of work is extremely laborintensive, so a dependable supply of low cost labormust be available. In addition, this type of con-struction requires more time in the field than aprecast alternative as the contractor must wait foradequate strength development of the concrete slabbefore form stripping can begin. Finally, to mini-mize the time on the site and to account forshrinkage effects, a special concrete castingsequence must be used.

Ballasted, Cast-in-Place Flat PlateWharf n The fifth, marginal open wharf designconsidered is a ballasted open marginal wharf,which can be constructedwith orwithout a toewall.This structure is identical to the cast-in-place flatplatewharf described, but the deck is constructed ata lower elevation, then covered with a granular fillmaterial, which can then be paved with asphalt.A schematic drawing of the ballasted flat platealternative can be found in Fig. 23.8.

This consists of an 18-inch thick, cast-in-placeconcrete deck, which provides two-way slab actionto resist vertical and lateral loading. An upset fasciasystem on the waterside face of the wharf retainsthe fill and accommodates the dock fender systemand the mooring devices. Utility trenches can beconstructed in the fill material between the deckand the asphalt.

The main advantages of the ballasted construc-tion are the flexibility provided by asphalt pavingand the lower deck elevation saves a row of piles.The advantages of the flat plate deck constructioninclude minimization of forming costs for cast-in-place concrete construction and economy ofmaterials. Because the structure is principally cast-in-place construction, less specialized equipment isrequired during construction. Most general con-tractors can perform the necessary finishing and

Fig. 23.7 Cast-in-place slab with bent.





concrete placement required. Finally, since thestructure consists only of cast-in-place concrete andprecast piles, there are fewer structural componentsto integrate together, and thus, this alternativeprovides a high degree of structural continuity.

The disadvantages associated with this alterna-tive are related to the extensive use of cast-in-placeconcrete. To minimize the time on the site and toaccount for shrinkage effects, a special concretecasting sequence must be used. A large pool ofrelatively skilled workmen will be required.

Note that the pile spacing for this alternative iscontrolled primarily by span limitations of the cast-in-place concrete deck slab under vertical loading.Lateral resistance is incorporated into the sub-structure by selecting a pile size capable of resistingthe lateral design loads.

23.11.2 Solid-Type Marginal Wharf

The term solid-type marginal wharf refers to awharf that has a continuous vertical face at or nearthe pierhead line. Such structures would includecellular cofferdams, either steel or concrete sheetpiles walls, or some other type of structure that cancontain backfill while providing a safety factoragainst sliding and overturning.

The six solid-type wharf alternatives consideredhere as follows:

l Cellular Cofferdam

l Open Cell Cofferdam

l Steel King Pile Bulkhead

l Steel Sheet Pile Bulkhead with Relieving Plat-form

l Precast Concrete Caisson

l Precast Concrete Gravity Wall

Each of these alternatives is best located so thatthe vertical load bearing elements of the structuresare used. With slid-type marginal wharf structures,the width of the wharf is not constrained by geo-metry as with the open, pile-supported wharveswhere the minimum width is controlled by thereveted slope and cut-off wall. Solid-type wharvesare only limited by the width of the cap.

A summary of advantages and disadvantages ofthe solid type marginal wharf alternatives areprovided in Table 23.6. A description of eachalternative follows thereafter.

Cellular Cofferdam n A cellular cofferdamalternative can be considered a solid-type marginal

Fig. 23.8 Ballasted cast-in-place slab open wharf.





Table 23.6 Solid Type Marginal Wharf Alternatives

Cellular

Cofferdam

Open Cell

Cofferdam

Steel King

Pile

Bulkhead

Steel

Pile with

Relieving

Platform

Precast

Concrete

Caisson

Precast

Concrete

Gravity

Quaywall

ADVANTAGES

Facilitates

backfilling and

vibro-

compaction

Reduces width

of wharf

Stable in

seismic event

Reduced

settlements

Constructed

from land

Facilitates

backfilling and

vibro-

compaction

Reduces width

of wharf

Stable in

seismic event

Reduced

settlements

Constructed

from land

Combines

vertical and

horizontal

load bearing

elements

Reduces initial

dredging

Minimizes

structure

requirements—

fewer driven

piles

Combines

vertical and

horizontal

load bearing

elements

Reduces initial

dredging

Minimizes

structure

requirements—

fewer driven

piles

Precast

Elements

Afford Better

Quality

Control

Minimizes

Field Labor

Combines

Vertical and

Horizontal

Load Bearing

Elements

Reduced

Settlements

Precast

Elements

Afford Better

Quality

Control

Combines

Vertical and

Horizontal

Load Bearing

Elements

Reduces

Width of

Wharf

Reduced

Settlements

DISADVANTAGES

Sheet piling

requires

corrosion

protection

Requires

complicated

concrete

closure pours

for fascia

Increased

time for

construction

Highly

dependent

on quality

of soils

Requires

partial

demolition

of existing

structure

Sheet piling

requires

corrosion

protection

Requires

complicated

concrete

closure pours

for fascia

Dependent on

quality of soils

Requires

partial

demolition

of existing

structure

Highly

dependent on

quality of

backfill

material

Requires

geosynthetics

for materials

segregation

Increased

settlement

potential

Highly

dependent on

quality of

backfill

material

Requires

geosynthetics

for materials

segregation

Special

equipment

required

Requires use

of dry-type

casting yard

Complicated

construction

sequence

Requires

demolition

prior to

construction

Construction

from barge

Large

excavation

and backfill

quantities

Special

equipment

required

Requires use

of dry-type

casting yard

Requires

geosynthetics

for materials

segregation

Requires

removal of

existing

structure

prior to

construction

Requires

construction

from barge

Requires large

quantities

from

excavation

and backfill

Note: All solid-type wharves require less excavation and demolition than open-type wharves.





wharf containment structure. Although normallyassociated with providing a dry work area inwaterfront construction, the inherent mass andstability of a cofferdam structure lends itself to fillcontainment for construction staging. Cofferdamsmay also be integrated with landside and water-side structures to provide a working platform forport operations.

Cellular cofferdams are generally constructedusing straight web, steel sheet piling with con-trolled fill materials placed within the cells. Severalgeometric configurations of cellular cofferdamsare available, including circular, diaphragm, andparallel wall configurations with open anchor cells.Circular cells are generally preferred for offshoreconstruction and their circular shape favors singleunit stability, east of forming templates for con-struction, and economy of material.

Cellular cofferdams depend on the interactionof the steel sheet piling and the material used to

fill the cell to provide stability. Quality of thefill material has a direct effect on the size and,therefore, the expense of the sheet pile cofferdam.An ideal fill material would be a dense, granular,free-draining material with a high angle of internalfriction and a low percentage of silt and claymaterials. Fill materials that do not meet all of theserequirements may be improved somewhat byvibratory compaction after placement within thecell. Unsuitable soils can be removed and replacedwith suitable soils.

A schematic drawing of a cellular cofferdamalternative, intended for use as a solid-type mar-ginal wharf, and combined with dock fenderingdevices is provided as Fig. 23.9.

A cellular cofferdam structure is generally mostfeasible when the underlying materials are densegravel, rock, or other similar dense and hardmaterials. Founding the coffer structure in thistype of material allows the structure to develop

Fig. 23.9 Cellular cofferdam.





sufficient strength to resist the overturning andsliding forces that act on such a gravity structure.The drawback is that pre-drilling is required whenshallow rock layers are encountered.

Transfer of the anticipated horizontal loads frommooring and berthing would be accomplishedthrough special details which connect the facingstructure to the cofferdam. These details couldconsist of a continuous reinforced concrete closurepour and additional horizontal restraining featuressuch as longitudinal and transverse reinforcedconcrete shear keys.

Open Cell Cofferdam n An open-cell coffer-dam is a variation of the cellular cofferdam andpresented as a solid type marginal wharf. For asketch of the configuration of an open-cell coffer-dam, see Fig. 23.10.

The tail walls anchor the system and extendlandward from the curved segments of sheet pilewall. The driving tolerances and template require-ments are not as tight as those for the cellularcofferdam structures. Embedment depths on this

type of structure are shallower than for the otherstructures discussed, reducing material costs. Thetail walls can be manipulated to avoid obstructionsillustrating the exceptional tolerances inherent inthe system.

Open cell cofferdams depend on the interactionof the steel sheet piling and the material used tofill the cell to provide stability. Quality of the fillmaterial has a direct effect on the size and, there-fore, the expense of the sheet pile cofferdam. Anideal fill material would be a dense, granular, freedraining material with a high angle of internalfriction and a low percentage of silt and claymaterials. Fill materials that do not meet all ofthese requirements may be improved somewhat byvibratory compaction after placement within thecell. Unsuitable soils can be removed and replacedwith suitable soils.

In evaluating an open cell cofferdam as a solid-type marginal wharf structure, considerationshould be given to construction sequencing, andvertical and horizontal load carrying capability ofthe structure.

Fig. 23.10 Open cell cofferdam.





An open cell cofferdam structure is generallymost feasible when the underlying materials aredense gravel, rock, or other similar dense andhard materials. Founding the coffer structure onthis type of material allows the structure to developsufficient strength to resist the overturning andsliding forces, which act on such a gravity struc-ture. The drawback is that pre-drilling is requiredwhen shallow rock is encountered, which drives upthe cost of construction.

Transfer of the anticipated horizontal loads frommooring and berthing would be accomplishedthrough special details that connect the facingstructure to the cofferdam. These details couldconsist of a continuous, reinforced concrete closurepour and additional horizontal restraining featuressuch as longitudinal and transverse reinforcedconcrete shear keys.

Steel King Pile Bulkhead n A steel king pilebulkhead is another form of a solid-type marginalwharf. For this type of structure, the bulkhead faceis located as close as practical to the pierheadline. For a sketch of a steel king pile bulkhead, seeFig. 23.11.

The sheet pile bulkhead can consist of a high-modulus, H-piles interlocked with “Z” sheeting.

This will develop a significant vertical capacity,accomplished by driving the H-piles into anyunderlying hardrock layer. The “Z” sheeting can bedriven to considerably less depth than the verticalload bearing elements (H-piles). This form of sheetpiling is widely used, especially in Europe, with agreat deal of success. Its main drawback is the needto provide an effective corrosion protection systemfor the steel. With proper corrosion protectionmeasures, the steel sheet piling will provide aservice life that meets or exceeds the service designlife requirements of the port facility. Depending onthe depth of intermediate sheet piles, this config-uration can be susceptible to scour. In order toprovide lateral capacity to resist the loads gener-ated from retained fills and moored ships, the useof a conventional tieback system of tie rods anddeadmen is typically incorporated.

Sheet Pile Bulkhead with RelievingPlatform n A sheet pile bulkhead with relievingplatform is another solid-type marginal wharf con-tainment structure. In order to reduce the size of thebulkhead structure required, a relieving platformwould be incorporated into the system. Therelieving platform transfers the vertical live loads

Fig. 23.11 King pile bulkhead with tie-rod and deadman.





from the deck directly into the underlying soils.Thus, the bulkhead is not required to resist thelateral surcharge, which would be generated fromthe live loads. To minimize the material require-ments, the bulkhead has been developed to supportsome of the vertical loads from the wharf deck tosupplement to relieving platform load bearingelements. A schematic of this is shown in Fig. 23.12.This design uses “Z” configuration steel sheet piles.

The relieving platform portion of this designis a cast-in-place concrete structure supported onprestressed concrete piles. The bottom of therelieving platform deck would be constructed ator near the mean high water elevation. At theoutboard face of the relieving platform a gravity-type retaining wall would serve to contain thepavement supporting fill material.

In order to provide lateral capacity to resist theloads generated from retained fills and mooredships, it would be possible to incorporate a series ofbattered piles into the relieving platform structure.Another alternative for lateral restraint involvesthe use of a conventional tieback system of tie rodsand deadmen.

Precast Concrete Caisson n The mostcommon of the available configurations of precastconcrete caissons is that of a multicell box-typedesign. Structures of this type are usually con-structed in drydocks, cofferdams, or other similardry-type basins. Upon completion, the caissons arethen floated into position, where they are floodedand lowered onto a prepared leveling course. Theconstruction sequence is completed by the fillingof the cells with a suitable ballast material. Theinherent mass and stability of a large caissonstructure lends itself to fill containment duringconstruction staging. Caissons may also be inte-grated with landside and waterside structures toprovide a working platform for port operations.For a sketch of a proposed configuration of aprecast concrete caisson, see Fig. 23.13.

One of the most important aspects in the utili-zation of a caisson structure is that of preparation ofa proper foundation course. It is also important todesign into the structure tolerances that allow fordifferential settlement between adjacent caissonunits. Joint design also merits careful considerationso that the structure is soil-tight.

Fig. 23.12 Sheet pile bulkhead with relieving platform.





The anticipated sequence of construction for aprecast concrete caisson solid-type wharf structureis as follows:

n Perform the initial dredging of existing river siltmaterial in the entire area of the caissonstructure. Dredge a keyway within the limits ofthe caisson.

n Construct the compartmentalized precast con-crete caisson. The length of caisson will bedependent on the configuration of the proposedcasting facility.

n Provide a gravel base leveling course in thesocketing trench and graded to suit the dimen-sions of caisson selected.

n Transfer the caisson unit(s) from the casting yardto the site using tugs. Maneuver the precastconcrete caisson into place, and begin loweringthe unit by filling with water.

n Align and adjust the structure while it isbuoyant. When alignment is achieved, beginplacement of the rock ballast fill. Adjust theleveling and placing process by controlled place-ment of ballast.

n Provide a base protection material of graded rip-rap. At this point, the terminal side fill materialmay be placed.

In order to accomplish the transfer of the anti-cipated horizontal loads from mooring and berth-ing, special details would need to be developed toconnect the facing structure to the caisson. Thesedetails could consist of a continuous reinforcedconcrete closure pour and additional horizontalrestraining features such as reinforced concreteshear keys.

Precast Concrete Gravity Quaywall n

A precast concrete gravity quaywall design ispresented as a solid-type marginal wharf structure.Components of these structures are usually cast inwork yards and then transported to the site onbarges, where they are lowered onto a preparedleveling course. The inherent mass and stability ofa large gravity wall structure lends itself to fillcontainment during construction staging. In orderto achieve a properly interlocked structure, theseparate concrete elements are usually match-castand marked before transport to the field for

Fig. 23.13 Precast concrete caisson.





placement. For a sketch of a configuration of aprecast concrete gravity quaywall, see Fig. 23.14.

One of the most important aspects in the util-ization of a precast concrete gravity structure is thatof providing a properly prepared foundationcourse. It is also important to design into thestructure tolerances that allow for differentialsettlement between adjacent structure units. Jointdesign and soil key interlock design also meritcareful consideration so that the structure is stableand soil-tight.

The anticipated sequence of construction for aprecast concrete gravity containment structurewould be as follows:

n Perform the initial dredging of existing mat-erials in the entire area of the wall structure.Dredge a keyway within the limits of thegravity wall.

n Construct the precast concrete wall sections. Thesize of the blocks will be dependent on thecapabilities of materials handling equipment,cost for transport, and other similar factors.

n Provide a gravel base leveling course in asocketed trench graded to suit the dimensions ofthe precast concrete gravity wall.

n Transport the concrete blocks to the site, andlower the blocks onto the prepared bed. Backfillthe area behind the wall with select materials sothat the resultant active earth pressures on thewall are minimized.

n Provide a base protection material of gradedrip-rap.

Transfer of the anticipated horizontal loads fromthe wharf structure to the gravity quaywall wouldbe required. This load transfer would be accom-plished through the use of a continuous concretecap block that links the wharf to the wall.Additional horizontal restraining features mayalso include transverse reinforced concrete shearkeys. An additional advantage of this type ofsystem is that the wall structure may serve as avertical load bearing element for a waterside cranebeam, thereby reducing some of the structure costsassociated with the crane beam support.

Fig. 23.14 Precast concrete gravity quaywall.





23.11.3 Loads on Docks

When the type of dock and its general constructionfeatures have been determined, it is necessary toestablish the lateral and vertical loads for whichthe dock is to be designed. These consist of thefollowing:

Wind Forces n Mooring lines, which pull theship into or along the dock or hold it against theforce of the wind or current, exert lateral forces on adock. Themaximumwind force equals the exposedarea, ft2, of the broadside of the ship in a lightcondition, multiplied by the wind pressure, psf,to which a shape factor 1.3 is applied. This is acombined factor that takes into consideration areduction due to height and an increase for suctionon the leeward side of the ship. The wind forcevaries with the location and local building codes.

Current Forces n The force of the current, psf,equals wn2/2g, where w is weight, lb/ft3, of water,n is the velocity of the current, ft/s, and g is 32.2ft/s2. For salt water this results in a pressure, psf,equal to n2. The velocity of current usually variesbetween 1 and 4 ft/s, which results in pressures of1 to 16 psf, respectively. Current pressure isapplied to the area of a ship below the water linewhen the ship is fully loaded. Since ships aregenerally berthed parallel to the current, this forceis seldom a controlling factor in design of thestructure. However, currents are important infender system design.

Impact n Docking impact is caused by a shipstriking the dock when berthing. The assumptionis usually made that the maximum impact to beconsidered is that produced by a ship fully loaded(displacement tonnage) striking the dock at anangle of 108 with the face of the dock, with avelocity normal to the dock of 0.25 to 0.5 ft/s(Fig. 23.15). A few installations have been designedfor as much as 1.0 ft/s, but this may be excessive;it corresponds to a velocity of approach of about31⁄2 knots at an angle of 108 to the face of the dock,and such an impact could damage a ship.

Fender systems are designed to absorb thedocking energy of impact. The resulting force to beresisted by a dock depends on the type and con-struction of the fender and the deflection of thedock if it is designed as a flexible structure.

Earthquake Forces n These have to be con-sidered if a dock is in an area where seismic distur-bances may occur. The horizontal force, applied atthe dock’s center of gravity, may vary between0.025 and 0.15 of the acceleration of gravity g timesthe mass. The force also can be expressed as 0.025to 0.15 of the weight, respectively. The weight to beused is the total dead load plus one-half the liveload. Unless the dock is of massive or gravity-typeconstruction, seismic effect on the design willusually be small since the allowable stress, whencombined with dead- and live-load stresses, maybe increased by 331⁄3%.

Gravity Loads n These consist of the deadweight of the structure, or dead load, and the liveload, which usually consists of a uniform load and

Fig. 23.15 Ship is assumed to strike pier at 108 angle for design against impact.





wheel loads from trucks, railroad cars or locomo-tives, cargo-handling cranes, and equipment. Theuniform live load may vary from 250 to 1000 psfon the deck area. The smaller figure is used for oildocks and similar structures that handle bulkmaterials by conveyor or pipeline and wheregeneral cargo is of secondary importance. Gen-eral-cargo piers usually are designed for heavierlive loads, ranging from 600 to 800 psf. Piershandling heavy metals, such as copper ingots,may be designed for 1000 psf or more. The uni-form live load controls design of the piles and pilecaps, whereas the concentrated wheel loads,including impact, usually control the design ofthe deck slab and beams. A reduction of 331⁄3% issometimes made in the uniform live load in fig-uring the pile loads and designing the pile caps orgirders, based on the assumption that the entiredeck area of adjoining bays will not be fullyloaded at one time.

23.11.4 Dock Fenders

Fenders act as the interface between the vesseland structure. They serve to protect both the struc-ture and the vessel from damage while the vessel ismoored. There are several categories of commer-cially available fenders including buckling fenderswith low friction panels, foam filled and pneumaticfloating fenders, cylindrical side loaded fenders,and molded arch type fenders with low frictionpanels. Low friction panels are coated with an ultrahigh molecular weight polyethylene (UHMW-PE).

Buckling fenders include cell fenders and P-shaped fenders. A small length to height ratio ispreferred for P-shaped fenders. The panels dis-tribute the reaction force over a large area therebyexerting a low hull pressure while absorbing a highquantity of energy. These fender systems are oftenused for cruise ships and container vessels. Theyare moderately priced.

Foam filled and pneumatic floating fenders aremost widely used for ship-to-ship operations andin areas where tidal variations are extreme. Theyare easily moved, absorb a high quantity of energy,and exert very low hull pressures. Due to theirbuoyancy, they move vertically with the vesselwhen the water level changes and allow berthingof several types of surface vessels. The fender re-quires a backing system to distribute the load.

Cylindrical side loaded fenders are used pre-dominately for berthing small ships and pleasure

craft. They are usually constructed of rubber andattached to the structure with chains. Cylindricalfenders absorb less energy than other fendersystems and are often not used alone. They exerta moderately high hull pressure on the vessel anddo not allow the ship to slide as well as low friction(UHMW-PE) panels. They are moderately priced.

Molded arch type fenders with low frictionpanels are similar to buckling rubber elementfenders, but they are smaller and do not absorb asmuch energy due to their increased length toheight ratio. The rubber fender is attached to theberthing structure and steel panels topped withUHMW-PE provide the contact surface for thevessels.

References for the design and selection of fendersystems are the Military Handbook “Piers andWharves” MIL-HDBK-1025/1 and PIANC 1984Report of the International Commission for Impro-ving the Design of Fender Systems.

23.11.5 Dolphins

Dolphins are designed principally for horizontalloads of impact, wind, and current forces from aship when docking or moored. These forces aredetermined in the same manner as for design ofdocks.

Dolphins may be of the flexible or rigid type.Wood-pile clusters are examples of the formertype. These are driven in clusters of 3, 7, 19, etc.,piles, which are wrapped with galvanized cable(Fig. 23.16). The center pile of each cluster is usuallypermitted to extend about 3 ft above the other pilesto provide a means of attaching a ship’s mooringlines. A modification of this type of dolphin arran-ges the piles symmetrically and on a slight batter.They are bolted to wood cross members locatedjust above low-water level, with wood framing atthe top. Large steel cylinders and groups of steel-pipe piles have also been used to provide flexibledolphins.

In general, dolphins of the flexible type havebeen used for mooring small vessels, not exceed-ing 5000 DWT (deadweight tonnage), as an outerdefense for protection of docks, or for breasting offsomewhat larger vessels from loading platformsand structures not designed to take the impact ofships. Bottom soil conditions must be suitable for aflexible-type installation. If the soil is too soft, thedolphins or pile clusters will not rebound to theiroriginal positions after being struck by a vessel,





and their energy-absorbing ability, which dependson deflection, will be gradually dissipated.

For larger cargo ships and tankers of 9000 to17,000 DWT, a wood-platform type of rigid dolphin,utilizing wood batter piles, may be used for moor-ing and breasting. Since the wood platform is rela-tively lightweight, its lateral stability depends to alarge extent on the pullout value of the wood piles.In general, a lateral force of about 40 to 50 tons isabout the most that a dolphin of this type can resistwithout becoming too large and unwieldy.

If bottom soil conditions are suitable, sheetpilecells make excellent dolphins. They can be de-signed to withstand the forces from the largestships, if provided with adequate fenders. Cells,because of their circular shape, are well suited forturning dolphins, for warping or turning a shiparound at the end of a dock. Cellular dolphins areusually capped with a heavy concrete slab, towhich the mooring post or bollard is anchored.When large ships are to be handled, a poweredcapstan should be provided to draw in the heavywire-rope mooring lines.

For big ships, dolphins may be designed withheavy concrete platform slabs supported by ver-tical and batter piles, usually of steel or precastconcrete. This type of dolphin with low-reaction-

force, high-energy-absorption rubber fenders cantake the docking and mooring forces from thelargest supertankers. For this purpose, a largenumber of batter piles are required. The uplift fromthese piles, in turn, makes it necessary to have aconsiderable amount of deadweight since thevertical piles will in general resist only a relativelysmall portion of the uplift. This deadweight issupplied by the concrete slab, which may be 5to 6 ft thick. A sufficient number of vertical pilesmust be provided to support this deadweight. Inaddition, the vertical piles must not be spaced toofar apart; otherwise, it will be difficult and expen-sive to provide forms for the concrete. When thedepth of slab exceeds 4 ft 6 in, it is usually eco-nomical to cast the slab in two lifts, with horizontalshear keys at the construction joint. This greatlyreduces the cost of the forms.

23.12 Marina Layout andDesign

The layout of marinas varies according to localmarkets, customs, and site geometry. Marinas pro-vide berthing space in calmwater, access to utilitiesfor boats, parking, fueling and sometimes repair

Fig. 23.16 Typical wood-pile dolphins in clusters of 3, 7, and 19 piles.





service, boat ramps, stores, launch hoists, andstorage sheds or areas. Marinas should be designedto meet the needs of the physically impaired asrequired by the Americans with Disabilities Act.

Selection of slip length is based on economicsand the local boating community’s typical lengths.Fairway aisles widths are 1.5 to 2 times the sliplength (Fig. 23.17), depending on whether or notover-length boats are allowed in the slips. Thewidth of single slips is about 4 ft wider than theboat beam or about half the slip length for slips lessthan 30 ft long. Piers can be either fixed or floatingwith ramps down from the surrounding gradelevel. Fixed-elevation piers are typically used inareas with a tide range of less than 3 ft. The widthof piers gives at least 5 or 6 ft of clearance (inside ofboat and utility boxes). Finger-pier widths are less.Wider piers are used for long piers that have moretraffic.

Channel-depth requirements are often dictatedby local physical conditions and boat fleet require-ments. Dredging of marinas to provide adequatedepth is a planning challenge because of the permitrequirements related to the dredging and disposalof dredged material. (See J. B. Herbich, “Handbook

of Coastal and Ocean Engineering,” Gulf Publish-ing Company, Houston, Tex (www.gulfpub.com).)

23.12.1 Design Considerations forMegayachts

Recreational vessels typically 80 feet in length orgreater are referred to as megayachts. Require-ments for berthing facilities for these larger vesselsdiffer from the requirements for berthing the smal-ler recreational boats in the 25 to 50 foot length.

Dock systems can be either fixed or floating, butrequire higher freeboard than normal to allowaccess from the vessel. The dock width should alsobe wider since most megayachts have their owngangway or steps that extend onto the dock. Thefendering system along the dock to protect theexpensive finishes on the vessels is more sub-stantial than a typical marina dock. The wind loadsexerted on the dock from a megayacht are alsohigher.

Utility requirements for megayachts are sub-stantial. Electrical requirements may range fromsingle phase, 50-amp to three phase, 400-amp. The

Fig. 23.17 Layout of marina with single and double slips.





larger water holding tanks on the yachts mayrequire 1- to 3-inch water mains to fill the tankswithin a reasonable time.

23.12.2 Breakwaters for Marinas

Some form of breakwater may be required to re-duce wave heights to an acceptable level, usuallyless than 1 ft. (Although they may be necessary,breakwaters usually do not directly produce in-come for the marina.) Breakwater layout shouldprovide adequate protection as well as allow safemovement into and out of the marina. The width ofthe entrance channel is often dictated by the localboat fleet. Enough room should be provided forsafe passage in two-way traffic. This leads to use oftypical entrance widths of 75 to 125 ft of navigabledepth. Alternative breakwater types include rub-ble-mound, caissons, floating breakwaters, verticalwalls, or wave fences. (See R. R. Bottin et al.,“Maryland Guidebook for Marina Owners andOperators on Alternatives Available for the Pro-tection of Small Craft against Vessel GeneratedWaves,” U.S. Army Engineers Coastal EngineeringResearch Center, Washington, D.C.)

Wave protection of a breakwater is expressed interms of the wave transmission coefficient kt:

kt ¼ Ht

Hi(23:6)

where Hi ¼ incident wave height

Ht ¼ transmitted wave height in the lee ofthe breakwater

Transmission through breakwaters is caused bywater moving through the interstices of the rocksand by splash over the top. The wave energy thatrounds the edges of breakwaters is diffractionenergy. The wave heights in the lee of a structurewill be the result of a combination of transmissionand diffraction. The “Shore Protection Manual,”U.S. Army Coastal Engineering Research Center,Government Printing Office, Washington, D.C.,provides design guidance for rubble-mound struc-tures used primarily for protection against largewaves.

Floating breakwaters are an attractive alterna-tive for use in deep water and sites with shortfetches for wind that allow only short-period seas.Transmission coefficients kt for floating break-waters depend on the ratio of the width of thefloat to the incident wavelength; the ratio of the

depth of penetration below water level to the waterdepth; and the stiffness of the mooring system. Forrelatively deepwater, kt ranges from 0.2 to 0.4 whenthe ratio of float width to wavelength is greaterthan 0.5. For example, for a float width of 15 ft, thisratio gives a wavelength L ¼ 30 ft. This L corres-ponds to a wave period T of about 2.4 s [Eq. (23.2)].For a windspeed of 40 knots, this corresponds to afetch distance of about 1 to 2 miles (Table 23.3).Thus, for fetches of about 1.5 miles and designwind conditions of 40 knots, the incident waveheight of 2.2 ft would be reduced to less than 1 ftby a 15-ft-wide floating breakwater. Transmissioncoefficients can be much higher for narrowerwidths or longer waves. (See J. W. Gaythwaite,“Design of Marine Facilities for the Berthing,Mooring, and Repair of Vessels,” Van NostrandReinhold, New York, and “Planning and DesignGuidelines for Small-Craft Harbors,” Manual 50,American Society of Civil Engineers.

Transmission at complete, impermeable, verti-cal walls is zero. However, diffraction and wavereflection allow energy to penetrate breakwatergaps into lee areas.

Wave fencelike structures are built to allowsome water flow through them. These structuresalso are most effective with short-period wind-generated seas from limited fetches. For significantreduction of wave energy, the gap spacing betweenfence boards should be such that the total gap areais less than 10% of the total area. These small gaps,however, may close because of biofouling anddefeat the original purpose.

23.12.3 Design of Docks for Marinas

Dock design includes design of the dock structureand the related, desired utilities, such as electrical,water (domestic and fire protection), telephone,cable television, and sanitary sewer hookups orpumpouts.

Fixed piers may be constructed of timber, steel,concrete, aluminum, or plastic. Manufactured floa-ting dockage systems are available. Flotation isprovided by either an airtight compartment, foam,or wood. Reliable anchorage is essential; manyfailures of floating dockage systems have beenattributed to inadequate anchorage.

Horizontal live loads are the sum of current andwave loads and wind loads due to the exposedcross section of the dock and boats.





Wood decking on piers is often 2 � 6-in pres-sure-treated lumber with galvanized screws. Boltingof cleats to the structural frame of the deck isrecommended (ASCE Manual 50 (www.asce.org).)

23.12.4 Boat Ramps

Boat ramps are an inclined paved surface thatextends into the water that allows trailerable boatsto be launched and retrieved. The top elevation ofthe ramp should be a least 2 feet above the highestexpected water level the ramp is designed tooperate and at least 4 feet below the lowestexpected water level that the ramp is designed tooperate. The number of lanes is dependent uponthe use and demand. The lane width should be12 feet minimum; 15 feet is preferred. Studies haveindicated that a single lane can handle up to50 launches and 50 retrievals per day under aver-age conditions. The grade of the ramp should beuniform and between 12.5% and 15%. A smoothtransition with a vertical curve should be madebetween the top of the ramp and the approach tothe ramp.

Ramps are typically constructed of reinforcedconcrete or precast reinforced concrete slabs placedover an aggregate base. It is important to provide anon-skid surface to allow for maximum traction forvehicles launching and retrieving boats. Concreteramps should be finished with a V-groove surfacewith the grooves placed at an angle of 60 degreesfrom the axis of the ramp.

Boarding docks, fixed or floating, are providedfor access to the boats after launching and beforeretrieving.

(B. O. Tobiasson and R. C. Kollmeyer, “Marinasand Small-Craft Harbors,” Van Nostrand Reinhold,New York; “Planning and Design Guide for Small-Craft Harbors,” ASCE Manual 50 (www.asce.org).)

23.12.5 Ice in Marinas

Ice is a significant marina engineering concern,including horizontal and vertical ice loadings onstructures and boats. The most common adverseeffect is the vertical jacking of piles as ice grips themand then rises with the tide. The severity of thecondition depends on site location and seasonal useof the marina. (See C. A. Wortley, “Ice EngineeringManual for Design of Small-Craft Harbors and

Structures,” University of Wisconsin Sea GrantInstitute; ASCE Manual 50 (www.asce.org).)

23.12.6 Marina Flushing Analysis

Marina facilities may pose a threat to the health ofaquatic systems if they are poorly planned or man-aged. The water in a marina must meet applicablewater quality standards. Thus, water qualityconsiderations are a part of the planning andpermit application process for marina constructionand modification. Pollutants at marinas includeboat grease, oil, and gas, head discharges, bilgedischarges, and land runoff. Runoff can introduceto the marine water typical nonpoint-source runoffpollutants, such as automobile oil and grease fromparking lots and fertilizers, pesticides, and herbi-cides from adjacent grass areas. Proper runoffmanagement practices can be critical to protectionof marina water quality.

A simple tidal-prism analysis tool for estima-ting the flushing of a proposed marina is describedin “Coastal Marinas Assessment Handbook,” Envi-ronmental Protection Agency (EPA). The funda-mental concept is the same as that for estuary orbay flushing: A pollutant concentration in a mar-ina will decrease with each tidal dilution but willnever completely flush. A typical analysis goal is toestimate the time needed to reduce the concentra-tion of a pollutant to 10% of its initial concentration.The tidal-prism analysis can be extended to adissolved oxygen or nutrient balance to address thequestion of whether or not a significant reductionwill occur in dissolved oxygen or nutrient level overa tidal cycle.

The EPA methodology assumes that tidal ex-change is the dominant flushing mechanism. It canbe used with fresh-water inflow. It does not,however, specifically account for other water ex-changes, such as wind- and current-generatedcirculation. A more limiting assumption is thatthe water is well mixed inside the marina.

There are several commercially available num-erical modeling software systems capable ofmarina flushing analysis. Examples of such pro-grams are the RMA2/RMA4 programs in theSurface-Water Modeling Systems (SMS) created byBrigham Young University or the Water Qualityor Spill Analysis modules in MIKE21 developedby DHI. Typical input parameter for numericalmodels include bathymetry and hydrodynamicdata, boundary conditions and extents, pollutant





concentrations and type, and simulation length.There are also many input variables available foreach model to customize simulations to specificcriteria.

23.13 Beach Nourishment

Also called beachfill, this refers to mechanically orhydraulically placed sand on a beach. The argu-ments for beach nourishment are threefold:

1. Enhanced recreation and increased propertyvalue. A sandy beach is a desirable recreationarea. This is a very important consideration fordevelopments along many coastlines and isprobably the primary reason for most beachfills.The strand, the sand (andmaybe also the dunes)between the water and hard structures such ashouses, has economic and aesthetic value,although it may not be easily documented.

2. Increased property protection. Beach nourish-ment can provide a volume of sand that protectsproperties behind the beach from the sea. Thisprotection may be in the form of long, high sanddunes that are designed to erode somewhatduring storms without breaching or low, widebeaches, which reduce wave heights, or both.

3. Beneficial disposal of dredged material. Beach-fills can serve as disposal sites for sedimentdredged from nearby coastal construction pro-jects. Sometimes, the purpose of the placementof dredged material on adjacent beaches is tocontinue the natural littoral drift or river of sandby keeping dredged inlet sands in the littoralsystem. Sometimes, the beachfill is for conveni-ence in obtaining construction permits or toavoid more expensive disposal options.

With respect to the first two contentions, beachnourishment is justified if the annualized economicbenefits exceed the annualized cost of the beachfill.Note that beach nourishment should be perceivedas an ongoing or maintenance requirement. Peri-odic renourishment is a requirement of manynourishment projects.

Many very large beachfills (several million cubicyards each) have been placed on open ocean beachesas well as in more sheltered locations, such as bayshorelines. The purposes of some of these beachfillshave been wetlands habitat protection and creationas well as recreation and property protection.

Beachfill Behavior n One of the fundamen-tal design criteria for beachfills is estimated projectlife. There is not at present a consensus on whatthis value should be.

One of the best ways to estimate the behavior ofa planned beachfill is to evaluate the behavior ofthe last beachfill at that site. This, however, is notalways possible, but it is justification for implemen-tation of a monitoring system. If a beach is nowbeing nourished, it probably will need nourishingin the near future. If a beachfill was previouslyplaced at that site, the result with more beachfill,however, will not be the same, even if the beachfilldesign is exactly the same as before. Fill responsedepends on time variations in waves and long-shore transport. Alterations in the volume, length,width, configuration, or size of the sand will alsochange the backfill behavior. However, qualitativeand quantitative estimates based on previous fillbehavior are valuable if the designs are similarenough.

The behavior of beachfills follows some generalpatterns. These can be viewed as the constructedbeach moving into dynamic equilibrium withthe wave and water-level climate. The volume ofsand per unit length of beach is the sum of thefollowing:

1. Volume of sand required to create an equilibratedbeach of the desired width (profile equilibration)

2. Volume expected to move out of the projectlimits in the longshore direction (planform equi-libration) during the design life

This sum should be multiplied by an overfill factorfor winnowing due to source-native sand-size dif-ference (size equilibration).

Cross-shore or profile equilibration is the mostrapid adjustment of a beachfill. Beaches changeshape constantly in response to changes in incidentwaves and water levels. Natural beach slopes aremild, from 1:10 to 1 :100. Often, the constructedbeach has a much steeper beach face than thatwhich occurs naturally (Fig. 23.18).

Sand is pulled offshore from the dry beach ontothe portions of the beach that are below the watersurface. Since the dry beach area rapidly decreases,this change is often incorrectly perceived as a lossof the beachfill. Although the public may beunimpressed by the unseen, underwater portionsof a beachfill, they are no less important than the





underground foundation of a building. The fullvolume of sand required to widen the dry beachsome distance must account for the underwaterportion of the profile. Given that the dry beach isoften a primary reason for benefits, however, theredoes not seem to be much reason for attempting toconstruct a more natural, milder beach slope. Thiswould be difficult anyway. Public education,including construction-site signs and public meet-ings, are often used to inform the public that theinitially constructed beach width is much greaterthan the intended design beach width.

A common technique for estimating the re-quired volume of sand to build a desired beachwidth is based on the assumption that the post-construction beach slopes will match the nativebeach slopes but will be offset seaward by thedesign beach width (Fig. 23.18). There is oftensome ideal or healthy composite beach profile thatrepresents the features, primarily slopes, of thebeaches along a coast. This is essentially an esti-mated profile based on site-specific data on theequilibrium beach profile. The data include theactual wave climate and grain-size distribution.Often, a number of profiles estimated for several

locations along the beach and based on a commonpoint (HWL, MWL, toe of dunes) can be overlain todevelop the composite profile. Care should betaken to account for overstarved profiles that havebeen previously armored and are not representa-tive of healthy profiles.

When the source material has a different size orsize distribution from that of the native sand, atheoretical equilibrium approach based on anequilibrium-beach-slope concept can be used. Thetime required to reach cross-shore equilibrium of abeachfill can be roughly estimated with some formof a cross-shore transport model.

Longshore transport or planform equilibrationmoves sand from the constructed project limits inthe alongshore direction. Natural longshore sandtransport processes will move sand from theconstructed location to adjacent beaches or inlets.Although the sand is not lost from the littoralsystem, it is lost from the project. There are threegeneral ways to estimate the rate of planformequilibration:

1. Use of some historical or background erosionrate. Historical profile and shoreline change

Fig. 23.18 Vertical cross section through a beach showing the existing beach profile, beachfillconstruction profile, and the effects of the cross-shore equilibration process.





data can be used to estimate volumetric erosionrates. Vital to this estimate is a clear under-standing of the local coastal processes, particu-larly the cause of erosion at the site. Thisapproach assumes that the beachfill sand willleave the project area at the same rate as sandhas been leaving the existing beach. However,constructed beaches may change faster than theexisting beach has been, because the constructedbeaches are not in equilibrium with adjacentbeaches and shoals and the wave climate.

2. Use of a diffusion-typemodel for planform equili-bration. The spread of sand away from a locationmay be computed from the same differentialequation as that for the spread of heat in a bar,the classic heat or diffusion equation. One theo-retical result of this approach is that if the lengthof a beachfill is doubled, the beachfill longevitywill be quadrupled. This type of approach ismost appropriate for long, straight coastlinesaway from the influence of inlets. It suffers fromthe constraint that it is based on some single,representative-wave-height parameter and doesnot directly account for the time variability oflongshore sand transport.

3. Use of a time-dependent shoreline changemodelcould be applied to estimate the fate of the fillunder assumed incident-wave conditions.

Winnowing of fines or sand-size equilibrationis the wave-induced sorting and winnowing ofany fines that may be in the fill material. Manydredging projects include large portions of finematerial that will not remain in the active beachenvironment. The type of dredging used influen-ces this process. In general, hydraulic dredgingremoves much of the fines during the washinginvolved in the construction process itself. This cancreate a suspended sediment plume from the pipeoutfall area. The alternative, mechanical place-ment, probably reduces the construction plumeand leaves more room for fill deflation due towinnowing. Alternative sources of beachfill sandare nearby inlets, offshore shoals, upland quarries,back-bay dredging, and sand hauled from a distantsource. The amount of fine-sand winnowing canbe estimated with the overfill ratio method descri-bed in the “Shore Protection Manual,” 4th ed., U.S.Army Coastal Engineering Research Center,Washington, D.C.

The duration of each portion of the equilibrationprocess can range frommonths to years, depending

on the size of the beachfill. Larger beachfills inmilder wave climates take longer to respond fully.

Because of the public nature of most beachfillsand the confusion concerning the success or fail-ures of beachfills, postconstruction monitoringshould be a prearranged, funded component ofthe project. A well-designed monitoring programwill allow a more complete and rational evaluationof beachfill behavior. Also, monitoring results willbe valuable for design of future beachfills at thesite.

On some coastlines, structures can be built toextend the life of beachfill projects. Offshoresegmented breakwaters with a beach nourishmentor marsh construction project in the lee are onealternative for constraining beach erosion that canprovide environmental habitat benefits. Rosati andWeggel provide design guidance for offshore seg-mented breakwaters. Bender outlines a headlandbreakwater concept that may be used to constructpocket beaches with beachfill.

[T. Bender, “An Overview of Segmented Off-shore/Headland Breakwater Projects Constructedby the Buffalo District,” in “Coastal EngineeringPractice ’92,” Proceedings of a Specialty Con-ference on the Planning, Design, Construction,and Performance of Coastal Engineering Projects,American Society of Civil Engineers (ASCE). J. D.Rosati, “Functional Design of Breakwaters forShore Protection: Empirical Methods,” TechnicalReport CERC-90-15, U.S. Army Engineer Water-ways Experiment Station, Vicksburg, Miss.; D. K.Stauble and N. C. Kraus, “Beach NourishmentEngineering and Management Considerations,”ASCE. L. S. Tait, Proceedings of the AnnualNational Conference on Beach Preservation Tech-nology, The Florida Shore & Beach PreservationAssociation, Tallahassee, Fla. Shore ProtectionManual, 4th ed., U.S. Army Coastal EngineeringResearch Center, Government Printing Office,Washington, D.C.; J. R. Weggel, “Coastal Groinsand Nearshore Breakwaters,” Engineer ManualEM 1110-2-1617, U.S. Army Corps of Engineers,Washington, DC 20314-1000.]

23.14 Monitoring Programsfor Coastal EngineeringProjects

Postconstruction monitoring of coastal engineer-ing projects should be standard coastal engineer-





ing practice. In addition to engineering benefitsfrom such practice, there are public relations andscientific reasons for monitoring.

A formal monitoring program consists ofresponse measurements, such as surveys, andforcing-function monitoring, such as wave clima-tology. If well designed, the program facilitates averifiable, fact-based evaluation of project func-tioning.

Monitoring is especially important for projectsthat have a potentional for adverse impact onnearby beaches, waterways, coastal structures, ordredging. Beachfill projects also should be moni-tored to obtain information on how fast the sand isleaving project boundaries.

The primary purpose of monitoring programsis to obtain data for future management deci-sions relating to the project site. Though presentability to model quantitatively the complex naturalprocesses of the coastal zone are limited, project-specific monitoring is a proven method for devel-opment of cost-effective engineering solutions.Monitoring provides the data for an improvedunderstanding of how a beach responds to engin-eering and also why it responds that way. Amonitoring program is often funded with projectconstruction.

Coastal Structures

23.15 Effects of CoastalStructures on Beaches

One of the recurring problems with engineeredstructure on beaches is evaluation of their impacton adjacent beaches. Because the littoral system isinterconnected, what is done on one stretch ofbeach can have significant impacts on nearbybeaches. The impact is related to the coastal pro-cesses of the area, in particular the longshore sand-transport rate. Longshore sand transport alongbeaches can extend for many miles. Inlet shoals arepart of the same littoral system as the adjacentbeaches if sand can move from the beaches to theshoals and vice versa.

Coastal structures by themselves can onlyfunction to redistribute the sand that is in thelittoral systems. They do not create sand.

Structures such as groins that are perpendicu-lar to the shore cause a buildup of sand on theupdrift side by reducing the sand supply to the

downdrift side. A field of groins will essentiallyrealign the shoreline toward the dominant waveclimate. Information on groin fields is limited butthere is some indication that they are probablybeneficial in stabilizing some stretches of coast.They probably provide wave protection and slowthe local longshore transport rate because of thelocal realignment in shoreline angle. Groins, how-ever, reduce the sand movement to the downdriftside. Also, they can induce nearshore circulationcells with rip currents capable of removing sandfrom the beach face into the sand-bar system. Thenet result is probably a beach system with a morestable shoreline. The beach neither comes nor goesas much as it would without the groins.

Inlet jetties can have impacts on adjacentbeaches as do groins because of trapping of sandon the updrift side. They also can realign andchange the volume of sand that is stored in thetidal shoal system.

Mechanical bypassing of sand is used to main-tain the littoral drift system at some engineeredinlets. The bypassing can consist of either periodicdredging with disposal on downdrift beaches orconstruction of a fixed bypassing plant. Design ofa bypassing scheme is based on estimates of boththe rate and variability of longshore sand transportat the site.

Dredging of navigation channels, even withoutinlet jetties, can contribute to beach erosion throughtwo mechanisms:

1. The sand dredged from the ebb-tidal shoal isoften disposed offshore in deeper water andthus removed from the littoral system.

2. The dredging can realign the main ebb-tidalchannel, which results in realignment of the ebb-tidal shoals and thus affects the sheltering of theadjacent beaches provided by those shoals.

Seawalls, bulkheads, and revetments protect theland behind the wall, not the beach in front ofthe wall. There is little clear evidence that seawallsactually cause erosion, except for the impact ofthe reduction in sediment available for the littoralsystem if the shoreline erodes to the seawall.However, a seawall constructed on a beach that isreceding for other reasons, the usual site for aseawall, will contribute to loss of beach. (“ShoreProtection Manual,” 4th ed., U.S. Army CoastalEngineering Research Center, Government Print-ing Office, Washington, D.C., “Coastal Engineering





Manual,” (www.USACE.mil/net/asce-docs/eng-manuals/em-htm).)

23.16 Revetment andSeawall Design

A revetment, or seawall, is built to protect propertyfrom erosion. Many revetments are constructed asa rubble mound, because the technique has provedto be effective in the harsh and dynamic waveenvironment. One particularly attractive feature ofrubble-mound structures is that, when designedcorrectly, they continue to function even afterdamage due to storms larger than the design storm.

There are four typical failure mechanismsfor revetments: inadequate armoring, flanking, toescour, and splash. All are related to inadequateprotection of the underlying soil on the down-stream side of the structure. Armor, or front-face,design includes selection of the armor unit size andlayer thickness plus any underlayers required. Forrubble-mound structures (Fig. 23.19), the armor-unit rock size can be calculated from Hudson’sequation:

W ¼ wrH3

KD(Sr � 1)3 cot u(23:7)

where W ¼ median weight of armor units

H ¼ design wave height

Sr ¼ specific weight of armor unit material

wr ¼ unit weight of armor unit

u ¼ slope of structure face

KD ¼ empirical coefficient that includesshape, roughness, and interlockingability of the armor units

Hudson’s equation is based on a 5% damage levelobserved in laboratory tests with monochromaticwaves. There is no factor of safety inherent inHudson’s equation.

For rough, angular, randomly placed quarry-stone placed in at least two layers, Kd varies from1.5 to 4, depending on the structure slope, whetherthe stones are exposed to breaking or nonbreakingwaves, and whether the stone is at the head of apointed structure or in the main body of a longrevetment. For breaking waves on the main bodyof a revetment of 1 :3 slope, KD ¼ 2.0 when the gra-dation of the individual units is within the fairlynarrow range 0.75W , W , 1.25W. For smalldesign wave heights (H , 5 ft), a wider range ofstone size, riprap with a weight range of0.25W50 , W , 4W50, can be used with a stabilitycoefficient of 2.2 to 2.5. W50 is the median stoneweight. The stability coefficient can be higher forconcrete armor units, such as tetrapods, dolosse,or quadrapods.

The design wave height H used in Eq. (23.7)should be the average of the heights of the highest10% H10 or 5% H5 of the waves. The wave heightis often depth-limited.

Slopes of 1 :2 (vertical to horizontal) or 1 :3, forheavy wave action, are recommended. Although

Fig. 23.19 Rubble-mound revetment with armor layer stones, underlain by a stone filter layer andpermeable geosynthetic membrane.





slopes as high as 1:1.5 have been tested withHudson’s equation and much steeper slopes can bebuilt by careful crane operators, more failures haveoccurred on these steeper slopes. Alternatives forsteeper slopes include vertical sheetpile bulkheadsor gabions. Gabions, galvanized wire basketswith rocks, are used in very mild (H , 1 ft) waveenvironments.

Underlayers should be sized so that the stonesdo not get pulled through the gaps in the overlay-ing layer. To meet this requirement, underlayerstones should have a minimum median weight of10% of the overlying median weight. Permeablegeotextiles may be installed between the revetmentlayers and the underlying soil. The toe designshown in Fig. 23.19 allows armor units to roll downinto any scour hole that may form.

An alternative to the type of design in Fig. 23.19with its layers and large armor units is a dynamicrevetment with a larger volume of stones of asmaller size and wider gradation. The objective ofthe dynamic revetment is to allow the revetment tomove in response to stormwaves, much as a cobblebeach responds.

The splash of storm waves over a revetment cancause failure by removing underlying soils. Thelevel of wave runup above the design still-waterlevel can exceed the equivalent of one to two fullwave heights, depending on the structure slopeand roughness and the incident wave period. Run-up elevations of irregular waves vary following aform of a Rayleigh distribution, much as waveheights do. Revetments are commonly designedfor a certain level of runup and are provided witha splash apron of stones or grass, or both, forprotection against the waves that overtop thestructures. Estimating the amount of water wash-ing over a seawall or bulkhead is difficult becauseof limited test data and the extreme sensitivity ofovertopping to still-water level.

Flanking due to shoreline recession at the endsof a revetment can be avoided by either tying itinto another adjacent seawall or revetment or con-structing return walls perpendicular to the shore.Return walls should be long enough to protectagainst long-term shoreline recession, any stormrecession, and excess storm erosion due to thepresence of the seawall. Since a structurally soundseawall protects the underlying sediment fromerosion during a storm, excess erosion may occuradjacent to walls during storms. This excess ero-sion is roughly 20% of the length of the wall.

Bulkhead Design n Design of vertical bulk-heads is controlled primarily by geotechnicalconsiderations. Two coastal engineering consider-ations are the potential for scour at the wall base(due to wave action) and wave-induced pumpingaction at improperly joined seams. Scour at the toeof a vertical wall can approach 1 to 1.5 times thewave height. Inasmuch as waves are often depthlimited and, on a horizontal bottom, the maximumwave height is about equal to the water depth, thescour elevation below the mudline is about 1 to 1.5times the depth of the water above the originalmudline. Scour can be accounted for by designingthe wall for a lowered mudline.

Another alternative is to design a rubble-moundtoe. The size of the armor units at the base of therubble mound can be determined from Eq. (23.7)for toes that will be exposed to breaking waves. Forsubmerged toes, the design median weight of therocks should be

W ¼ wrH3

(Sr � 1)3N3s

(23:8)

where Ns, the stability number, varies from 1.8 ,Ns , 5.H is depth limited orH10 orH5. Other termsare defined as given for Eq. (23.7).

(Y. Goda, “Random Seas and Design of Mari-time Structures,” University of Tokyo Press, Tokyo.J. B. Herbich, “Handbook of Coastal and OceanEngineering,” Gulf Publishing Company, Houston,Tex (www.gulfpub.com). “Seawall, Bulkheads, andRevetment Design,” Engineer Manual EM-1110-2-1614, U.S. Army Corps of Engineers, Washington,DC 20314-1000 (www.USACE.army.mil/inet/USA-CE-docs/eng-manuals/em-htm).)

23.17 Use of Physical andNumerical Models inDesign

Physical and numerical models are used in coastalengineering for a variety of reasons. The traditionalphysical model is used to account for turbu-lent processes that limit the ability of equationsto predict phenomena. With small-scale physicalmodels, engineers have the ability to addressproblems with site-specific and design-specificgeometry, but the models have some scaling





constraints that limit their usefulness. Numericalmodels, or systems of equations, have been de-veloped to address a wide variety of coastalengineering related problems. Use of any modelshould consist of two distinct phases, calibrationand verification, before the application.

(M. V. Cialone, “The Coastal Modeling System(CMS): A Coastal Processes Software Package,”Journal of Coastal Research, vol. 10, no. 3, pp. 576–587; S. A. Hughes, “Physical Models and Labora-tory Techniques in Coastal Engineering,” WorldScientific Publishing Co., River Edge, Nev.)





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