Journal of Coastal Research 704-710 Fort Lauderdale. Florida Summer 1997

Responding to Coastal Erosion and Flooding Damages

Joan Pope

U.S. Army Engineer, Wat erways Experiment St ationCoas tal Engineering Resea rch CenterVicksburg. MS 39180, U.S.A.

.tltllllll:.~~.~ 7rf

_A_a... &-

ABSTRACT _

POPE, J., 1997 . Responding to Coastal Erosion and Flooding Damages. Journal of Coastal Research, 13(3 ), 704-710.Fort Lauderdale (Florida), ISSN 0749-0208 .

Throughout recorded history the great seaside centers of culture and commerce have relied upon safe harbors andthe stability of their shores for survival. Today's coastline is of economical, social, cultural, and environmenta l valueto communities and to nations. However, shorelines are dynamic and ephemeral places where erosion trends tend todominate. Development along the shore places the desires of man (to have a safe and stable home) in direct oppositionto the natural trends of nature (to erode, transport , and deposit coasta l lands ).

Human reaction to coastal erosion and flooding problems ran ge from harden ing the shore to continually replacingthe lost material to limiting or stopping future development . Whatever management and engineering steps are takenshould be determined as the result of a well-informed and logical process. Coastal management strategy, includingthe decision to incorporate shore protection works, should be based upon a clear understanding of the problem, siteconditions, and socio-economic expectations. Although the discussion presented here is applicable to all coastal set­tings; the full integration of geologic insights, engineering technology, and human anticipations is particularly criticalin addressing the problems of the rapidly eroding and flood-prone shores of Louisiana.

There are no "silver bullets" for solving coastal flooding and erosion problems. Every human action in the coastalzone has the potenti al to cause both an enhancing and an adverse reaction. However, when properly evaluated andrationally considered, there are effective means for minimizing coasta l flood and erosion damages. This paper exploresthe philosophy and issues associated with developing management and engineering responses to coastal erosion andflooding problems.

ADDITIONAL INDEX WO RDS: Louisia na. shore erosion, shore prot ection. seawalls . coastal armoring , beaches. coastalflooding. coastal management .

INTRODUCTION

Various coastal management strategies and/or shore pro­tection works a re used to control or limit the adverse effectsof coastal ero sion and reduce sto rm flooding da mages. Follow­ing are common types of coastal eros ion a nd flooding prob­lems:

1) long-term chronic land loss associa ted with the erosion ofcohesive sediments , reduced supply of sa ndy sediments ,or subsidence,

2 ) loca lized ero sion impacts caused by a navigation proj ector other coastal construction works,

3) lands and facilities impacted by storm-induced erosion,4 ) flooding by a storm surge with the associated wave attack

damage s,5 ) lost environmenta l resources (i.e., wetlands, oyster reefs,

nest ing a reas, etc ), or6) need for more lands

In many cases a coastal managem ent plan is conceived anddesigned to address a combination of these problems. Th edecision to include en gineering activities within the manage­ment plan should be part of a n overall integrated responsest rategy. Whether or not engineering steps a re taken will de­pend upon the severity of the problem , the siz e of the im-

97032 received and accepted in revis ion 12 March 1997 .

pacted area, economics, and the prognosis for success. Whenengineering ste ps are taken the performance requirementsshould be clearly defined and the expecta t ions of the proj ectarticulated to the customer. The important first step in con­sider ing a solution to a coasta l problem is to dev elop an ac­curate problem statem ent. Th e cha racte r ist ics of the si te andthe needs of the user population have to be incorporated intosuch a statem ent.

The particular eros ion or flooding problem of interestshould be cons idere d with in the context of th e overall coastalsyste m. Prospective engineering approaches have the pot en ­tial to modify or impact this dynamic syst em . A narrowlyfocused solu t ion which "fixes" one problem has the potentialto impact wav e conditions, currents , sedime nt supply, andtransport patterns affecting a broad region .

Lou isia na is s ubject to all the forement ioned erosion a ndflooding problem s summarized in 1) through 6) but to a gr eat­er magnitude th en most other coastal areas. Th e low, hurri­cane -prone, Louisiana shore is subsiding, cohesive , and sa nd­poor; yet ecologica lly rich . Th e cha llenges of man aging thissyste m and address ing the eros ion and flooding problem s inLoui siana require a well-d evelop ed , interdiscip lin ary, region­al approach rather then a ser ies of unrelated, localized "fix­es." Th e Loui siana barrier island s and wetlands a re an in­teracti ve, rapidly evolving system which a re particu larly un­forgi ving to engineer ing mistakes.

Louisiana Barrier Islands 705

ClASSES OF MANAGEMENT AND ENGINEERINGRESPONSE

Erosion and flood damage response alternatives range fromdoing nothing to various structures for modifying the behav­ior or supply of coastal sediments. All solutions to a coastalerosion/flooding problem fall into the following five functionalclasses. The first three classes involve engineering approach­es, while the last two classes are management approaches.

1) Arrnoring ( "draw the line")2) Moderation ( "slow down the erosion rate")3) Restoration ( "fill the beach up")4) Abstention ("do-nothing")5) Adaptation ( "live with it")

In practice, there is a sixth class which is a concurrent orsequential application of the other five classes. For example,different approaches may be tried together such as modera­tion and restoration ii.e., breakwaters and beach fill). Also,as beach conditions evolve and philosophies change, theremay be different strategies for dealing with the problem (suchas either give up or abstain from further activities) or take amore aggressive approach and commit to protecting (armor­ing) the shore.

Armoring

Coastal armoring includes the use of seawalls, revetments,bulkheads, levees, and dikes in an attempt to harden theshoreline. This is often the approach of last resort. It is mostappropriate where the primary problem is one of storm-in­duced damages, rather than one of chronic erosion. Typically,coastal armoring is used where substantial human invest­ments are at risk and where the purpose of the project is toprotect the upper portion of the beach profile from storm­induced erosion and flooding. Coastal armoring is an attemptto "draw a line along the shore." The lands behind are pro­tected but the area in front of and adjacent to the structurewould continue its natural erosion pattern. A wall at the backof the beach will do nothing to protect the beach or the off­shore. Thus, if coastal armoring is applied in areas of rapidand chronic erosion, particularly in sand-poor, cohesive shoresettings (such as those of Louisiana), the sediment in frontof the structure will continue to erode ii.e., the beach maydisappear), resulting in a steeper profile, deeper water, andbigger waves. Eventually the existing seawall may be under­mined and fail, resulting in the need for further construction;possibly of a more aggressive nature. The continued retreatof adjacent, non-armored shores may flank the armored sec­tion compromising both its stability and protective value.

The use of coastal armoring as a means to mitigate theerosion of the shore is an approach which has realized con­troversy (KRAus, 1988L Some states prohibit the use of coast­al armoring and other hard structures because of a concernthat they may aggravate, rather then reduce, the erosion ofthe beach (PILKEY and WRIGHT, 1988). A good review of thesubject of the effects of coastal armoring on the beach is con­tained in KRAus and PILKEY (1988) and has been updatedby KRAus and McDOUGAL (1996). In addition, the U.S. ArmyCorps of Engineers has sponsored several long-term field

studies which collected data and conducted evaluations to de­termine the impacts of coastal armoring (GHIGnS, TAIT, andCORONA, 1994; BASCO, BELLOMO, and POLLOCK, 1992).Some of mechanisms by which coastal armoring might ac­tively contribute to either real or perceived beach erosion are:

(a) Groin -effect - Jf the armoring structure protrudes fromthe shoreline as a headland it could block the longshoretransport and interrupt the sediment supply. Sand may be­come impounded on the updrift side, while the downdrift sidemay exhibit a localized zone of erosion.

(b) Sediment-pending - The intent of coastal armoring is toprotect the land behind it from erosion. If the structure isfunctioning correctly, the protected area no longer erodes con­tributing sediment to the littoral system. Thus a certain vol­ume of material is withheld and no longer contributes todowndrift beaches. This mechanism is more significant insand-poor areas where the armoring fronts large sections ofthe shore.

(c) Cross-shore reflection - Conceptually, this mechanismmight effect the beach in front of the armored shore, partic­ularly, when a smooth-faced seawall is in the active surf zonefor extended periods. Waves impacting the structure wouldbe reflected off of the structure causing either a localizedscour trench in front of the wall and/or deflection of the near­shore sediment to a location further offshore. However, stud­ies have questioned the validity of this phenomena and havesuggested that any realized impacts are probably temporaryand morphologic rather than a real loss of material (Krausand McDougal, 1996).

(d) End-effects / reflection - Wave reflection off of the ends ofthe structure could aggravate erosion around the structureends if the armored section protrudes from the shoreli ne, issmooth-faced, and transitions abruptly into the adjacentshoreline. Unless frequently exposed to direct wave impact,this is more likely to be a localized, temporary scour effectwithout much implication to the nearshore sediment budget.

(e) Differential erosion - When one section of the shore isprotected and the adjacent shore is not, the unprotected areacontinues to retreat at a natural rate and the protected shore­line is stable. The result is a displacement of the shorelineand an apparent, but false, interpretation that the seawallhas caused erosion to adjacent shores.

(f) Passive beach erosion - The beaches in front of the coast­al armoring will continue to experience natural erosion andaccretion cycles. If the coastal armoring is placed along aneroding coast, the beach in front of the structure is likely toeventually disappear, not due to an active aggravation of theerosion process, but rather because the backbeach referencehas been stabilized while the shoreline has not.

(g) Subsidence-This process is unusual but is mentionedbecause of its potential to be of concern in Louisiana whereshallow, soft-compressible muds underlie much of the coastalarea. A structure with a substantial cross-section may de­press the local foundation, causing the structure to loseheight and also aggravate local subsidence effects.

Moderation

Beach erosion control techniques are designed to reducethe rate of sediment loss from the project area and thus "mod-

Journal of Coastal Research, Vol. 1:3, No.3, 1997

706

erate" erosion dam ages . Th ese techniques include groins, de­tached breakwater s, artificial headlands, and perched beach­es or nearshore reef/sill sys te ms (U.S. ARMY ENGINEERS,1992; CHASTENet al ., 1993; POPE and DEAN , 1986 ; and POPE,1989). This approach is mor e appropria te for areas where theprobl em is chronic erosion du e to diminish ed sediment sup­ply. Th ese struct ures can be a very useful in a reas where itis too expens ive to maintain a beach by continuing to bringin large quantities of sa nd from an outside source. Groins,breakw aters, a nd headl ands work best in areas where long­shore tran sport is much more dominant than cross-shoretran sport in moving sedime nt out of the project area. Beacherosion control st ructures a lone do not pr otect th e back beachfrom storm-induced flooding a nd eros ion. They provide theirben efit to the shore by trapping and/or holding sa nd in th edesired location a nd a llowing sufficient elevation to be main­tained. Th e beach held by th e stru ctures provides protectionto th e back beach and human developm ent. Th e "trapping"characte ristic of this approac h could mean adverse impactsto adjace nt beach es if sa nd held in th e project area wouldnormally move th rough or accre te on th e neighb oring beach­es . Thus, beach erosion cont rol projects should include th eaddit ion of sufficient sa nd to fill the project beach to equilib­rium relative to th e struc t ures plu s a ny additiona l materi alwh ich th e st ru ctures may cause to be diverted offshore andlost to th e littoral sys te m. Th e pu rp ose of a beach erosioncont rol project should be to slow th e loss of the placed sand,not to trap sa nd from th e littoral sys te m.

Properl y designed beach er osion cont rol projects is one oft he greatest cha llenges of coas tal engineering . Th ese struc­tures are designed , not simply to withstand a critical designwave and water level clima te , but rather , they mu st performthe specific fun ction of inducing a desi red response in th ecoas tal sys te m. The resultant effect to the beach (whether itis to widen the beach at a particular location, redu ce the rateof sediment loss, stabili ze the shoreline, or proh ibit the re­t rea t of th e shore beyond some defined lin e) is very depen­dent upon th e most recent ran ge of wave , water level, andsediment supply conditions. Most beach erosion contro l pro­jects are designed for some "normal" or "average" littoral con­ditions. Th eir successful performan ce may degr ade as localconditions deviate from this anticipated norm. Various em­pirical and numerical simulat ion tools can be very useful indesigning th e configuration of break waters a nd groins to pr o­duce a desired effect. However , th e complex inter action ofth ese structure with the littoral sys te m re quires a good un­derstanding of local beach dynami cs, coas tal processes, a ndacceptable performance toleran ces.

Restoration

Sediment may be brought into an area to mitigate chronicerosion or to provide a buffer which protects th e back beachaga ins t future storm-induced erosion or flooding . A healthybeach may also provide recreational benefits which contrib­ute to th e economic vital ity of a community (NATIONAL RE­SEARCH COUNCIL, 1995 ). This is th e only man agement alter­native which actually adds sa nd back into the littoral system .Restoring th e beach to some previous condition or creating

Pope

an improved beach is usually accomplished by th e placem entof "beach fill" or "beach nourishment." When th e purpose ofthe beach restoration is storm protection , th e project may in­volve cons t ruct ion of a back bea ch dune syste m (U.S. ARMYENGINEERS, 1995). Veget ative planting may be incorpora tedin the project to help sta bilize th e dunes agains t wind ero­sion.

Ther e are severa l ways sand can be brou ght into the projecta rea. Th e material may be min ed from offshore or land-basedborrow sites, a lthough "borrowed" sa nd is rarely returned .Alternatively, the sedime nt could be the by-product of a har­bor ma inten an ce pr oject or oth er coastal excavation activi­tie s. In thi s case "dredged ma teri al" becomes a "dredged re­source." Another source of sediment may be by-passin g,where sa nd is mechanically removed from one side of an inletand deposi ted on th e other side to ret ain th e natural long­shore tra ns port sys te m (U.S. ARMY, 1991J.

Beach restoration typically involves placing material on th eupp er pa rt of the beach profile where it is visible and whereth e benefits are imm ed iate. However , in some cases, th erema y be economic, environmental, and engineering ad vantag­es to placing the material on th e under water portion of th eprofile (BRUUN, 1988; HANDS and ALLISON, 1991J. In thi scase, th e active beach is still nourished, but th e benefit s arenot as obvious . Imm ediately afte r placement th e materialma y provide some wave protection ben efit s as th e shallowedprofile shoa ls incoming waves a nd reduces th e amount of en­ergy th at reach es th e beach. Depending upon local littoralpr ocesses, depth of placement, a nd gra in-size of th e materi al ,sediment placed on th e underwater portion of th e beach couldreali ze different long-term fates. Sediment tha t is too fine­grained or pla ced at the wrong tim e of th e year might bequickly mobilized a nd dis sipated to th e offshore and lost tothe sys te m. Materi al placed on th e very outer portions of th eprofile could remain as a discernable feature for severa lyears. When prop erl y enginee red, th e mater ial may effective ­ly nourish the profile eithe r by flattening th e underw ater pro­file, feeding th e nearsh ore bar sys te m or eventually migrat­ing onsh ore and weld ing onto the subaeria l beach (BODGE,1994 ; FOSTER, HEALY, and DELANGE, 1994; HANDS 1991J.Cobbles have even been shown to move onto th e upp er beachfrom properl y design ed feeder berms (ZENKOVITCII andSCHWARTZ, 1987 ). UDA, NAITO, and KAN DA(1991) monitoredonsh ore movement of a n experi me ntal feeder berm th roughgap s between a segme nte d br eakwater . Nearshore berm smay thus have applicat ion as a method to restore chronicallyeroding beaches and increase sediment supply. Thi s is par­ticul arl y true where th e availabl e sediment contai ns toomu ch silty mater ial to be accepta ble for direct beach place­ment, wher e it is much chea per to place th e sa nd in th e near­shore , or where on-beac h placement may disturb a sensit iveor enda ngered habitat.

Abstention

In some situa t ions no action is tak en to protect human de­velopments along th e sh ore. Mankind abstai ns from any pro­tective or compen satory acti vity and simply let s th e beachbeh ave as it will regardl ess of th e cau se of th e erosion or th e

Jou rn al of Coastal Resea rch. Vol. ia, No. a, 1997

Louisiana Barrier Islands 707

Table 1. Example philosophies of coastal construction.impacts. This is sometimes called the "do-nothing" alterna­tive. Erosion, whether natural or man-induced, continues.This may be the appropriate response in areas where shoreerosion or flooding problems are so severe that there are noeconomically viable solutions (where the cost of the protectionwould exceed the value of the investment). This also may bethe preferred approach in areas where the natural erosionand accretion cycle is an important part of the character andattractiveness of the system. Examples are highly dynamicand migrating barrier islands such as the Chandeleur Islandsof the Louisiana Coast.

Classes ofResponse StablelHard

Armoring Traditional:SeawallsBulkheadsRevetments

Moderation Rock groinsSillsBreakwaters

Dynamic/Soft

Gravel revetments

VegetationDune fixents

"Removable"

Hay balesGeotextile bagsGeotextile mats

Floating BWBeach drainsDune fencingGeotextile bags

Adaptation

Policies and restrictions which are implemented to forcethe human occupant to adapt to the coastal system are oftenincorporated into coastal zone management strategies . Theexisting erosion-accretion cycle is allowed to continue withoutmodification but other actions are taken to protect the humaninvestment. Adaptation includes identifying those areas("hazard zones") where the human user must accept the con­sequences of developing along the shore ii.e.. learn to "livewith it") without modifying the existing system. Approachesinclude implementing set-back restrictions, development lim­itations, relocation, flood-proofing, etc.

All shore damage reduction or response alternatives can bedescribed in terms of the preceding five classes. Most projectsor communities end up applying a combination of several, oreven all, of these functional classes to address their shoredamage problems. This is particularly the case where the phi­losophy of dealing with erosion and flooding problems hasevolved over time. An example is the barrier island of GrandIsle, Louisiana where placed beach fill, constructed dunes,groins, and breakwaters front a community where the firstfloor of many of the dwellings are constructed above a specificelevation, and public lands at the east end are devoid of de­velopment.

DESIGN CONSIDERATIONS

All five classes of shore damage responses and many indi­vidual construction techniques have been used throughoutthe world and in the United States along the Atlantic, Gulf,Pacific, and Great Lakes shores and waterways. Selecting thestyle of construction and expected life are almost as impor­tant as selecting the intended function of the solution. How"permanent" versus how "temporary" will the selected ap­proach be? Considering the project needs, is a static "hard"structure (such as armoring) or a dynamic "soft" structure(such as beach fill) better? What will be the trade-off betweenhigh initial construction costs and life cycle maintenancecosts? All shore protection projects are built with the intentto be either removable, soft, or hard. Table 1 illustrates someexamples of the various construction philosophies which maycontrol the effective life of the project. The grouping used inthis table is certainly subject to debate, particularly whencomparing "soft" versus "removable" approaches. Based onthe specific project setting and the designer's goals; the lifecycle of a particular approach could be quite different thansuggested by this table.

Restoration Fixed bypassing Dredgingplant Beach fill

Dune buildingNearshore berms

Abstention N/A N/A N/A

Adaptation N/A N/A N/A

Issues to be addressed during the design process include,but are not limited to, questions regarding the expected du­rability (how long will it last), the expectations of the user/public, future land-use scenarios, environmental impacts andimpacts to the sand transport system. The functional classand the construction approach that are best for a specificproblem and location would be determined based upon thefollowing design considerations:

(a) Hydrodynamic site characteristics (understanding thewave climate, wave transformation, current patterns, fair­weather vs storm conditions, water level fluctuations, waterdepths);

(b) Geological site characteristics (present sediment supplyrates and transport dominance, recent littoral evolutionarytrends, inherited geologic features representing non-littoralprocesses, foundation conditions, sediment characteristics,profile variability, availability and quality of constructionmaterials);

(c) Project Economics ( benefit-cost ratio, performance re­quirements, future land-use and partner funding expecta­tions, constructability, the ability to perform future mainte­nance, acceptable levels of risk);

(d) Environmental (land use, biological communityrequirements, environmental policy, potential for physicaland biologic impacts, endangered species, cultural resources);and

(e) Social-Political (customer and partner expectations, fu­ture development trends, user community requirements, pub­lic safety and accessibility, local legal or zoning restrictions,national and state regulatory and funding policies).

A review of evolutionary trends due to historical variationsin the littoral processes, an analysis of storm histories andwave climate, and field measurement including site mappingand sediment transport analyses are just a few examples ofthe information needed to characterize the project site con­ditions. Engineering a response to a shore erosion or floodingproblem should follow a logical process that starts with theproblem statement and continues with development of abaseline of design considerations and development of a rangeof alternatives (Figure 1). The result of this process should

Journal of Coastal Research, Vol. 13, No.3, 1997

708

Develop Probl em Statement l(Defin e Project Intent)

__.~ J

Docum ent Site Characteristics

Hydrod ynamicGeolog icEconom icEnvironment alSocial -Political

_. . I _ _ _

I D~"opM"M"" "," ~Preliminary Design 01Configuration

I __~minary_~~~ ig ~~ ~~:tu: (~r:_:.~~~tiOn) _

Evaluate Each Alternative

Determine Perform ance Expectations

Determine Cost (i.e. Const ruction & Life Cycle)

Determ ine Benefit s

Analyze Environmental Impacts

Assess Acceptability to User/Customer

Select Recommended Alternat iv-; - J------ _ ._-----_._--

I1---,,-=--- -- -------- -- -~- -l

~ailed~~s~~~~~Hl ected Pla:....J

Figure 1. Engin eeri ng process for desig ning a coasta l erosion or flooddam age reduction project.

be a solutio n whi ch corrects the problem for the minimumcost, pro vid in g the most ben efit s , wit h the least amount ofadverse impacts , and the most acce ptable to th e users of thisa rea.

DEVELOPING SHORE PROTECTIONALTERNATIVES

The process of planning a nd design ing a sho re protectionproject should include development of sound performancegoals and objectives (i .e., what do you expect th e proj ect to doa nd how should it fun cti on under cert ai n conditionsi' l. Met­r ics for defin ing and measuring project success ba sed on pro­ject objecti ves should be developed . Develop ing a se lectedplan includes establish ing design crite ria and design ing th eva r ious alternatives to a stage where it is possibl e to deter­mine how mu ch eac h alternat ive will cost and wh at sort ofben efit s and impa cts will result.

Pope

Selecting t he a ppropria te cons t ruction a pproach should in­volve addre ssi ng th e following qu estions:

(1) What is t he project' s expected performanc e? (What do youexpect th e proj ect to do? What ben efit s are desired v)

(2) Is th e st ru cture stable und er th e ant icipated range of con­di tions?

(:3 ) What is th e st ruct ure's desired durability? (How long doyou expect it to last? )

(4 ) What a re th e socia l-politica l expectations? (Wha t does thecustom er/user wantf )

(5) What types of env ironmen ta l impacts are anticipated andwhat impacts are tolerable?

(6) Ca n we reasonabl y predi ct th e res ponse of th e sand trans-port system, under a range of conditi ons?

(7) What design crite ria should we use?(8) How mu ch will th e project cost over its life cycle?(9 ) What is an acceptable level of risk and un certainty rela­

tive to st ru cture stability and project performance?

For every action (na tural or man-mad e) in th e coastal envi­ronme nt , a wide range of physical imp acts might be reali zed .Som e of these impacts are ben eficial and desired. However ,others may be deem ed adv erse. Mechanisms for identifyinga nd eva luating th ese poten tial impacts need to be devel opedand, where needed , mitigative plans impl emented . Knowl­edge of coastal proces ses combined with inform ation on howprevious projects have performed can be used to assess thecoastal response to an event or a propos ed shore protectionapproach . Various a na lyt ica l procedures and numerical sim­ula tion tools a re ava ilable to help in th is process.

PROJECT PERFORMANCE MONITORING

No solution for addressing coasta l erosion and floodin gdamages is ever final a nd no such coas t a l project is eve r com­plete. Both th e coas tal environment and land use trends con­t inue to evolve. Whether a st ruc t ura l or a managerial ap­proach is ta ke n, continued tracking of the physical condit ionand th e degree of the ha zard is warranted. Erosion a nd floodcontrol responses need continual re-evaluation, main tenance,management, a nd possibl y modification . Thi s is particularlyt rue where the engineer ing works (such as armori ng , break ­waters, groins, or beach fill ) induce a temporary condit ion ofdisequilibr ium. Eve ntua lly th e coastal env ironme nt adj uststo the presence of th e modifying , a rmoring, or restoringworks. In ord er to track th is evolving sit ua t ion , a monitoringprogram will require esta blishing a base line conditio n (eitherpre -project or for adjacent , bu t un altered shores) for compar­ison . An ideal monitoring program starts be fore any construc­t ion is undertaken and conti nues over a period of seve ra lyears . Both th e processes (wa ves , water level s , sto rms, cur­rents ) and th e response (topogra phy , ba th ymetry, sediments)should be measured . In many cases, t he biological environ­men t a nd economic benefits shou ld a lso be documented. TheNATIONA L RES~;A RCH COUNCIL (1995 ) an d U.S. ARMY EN­GINEERS (199:ll hav e provid ed re views of performance mon ­itoring philosophy, a pproac hes , and techniques .

•Journ al or Coastal Resear ch, Vol. 1:3, No. :l, 1997

Louisiana Barrier Islands 709

ISSUES WITH NON-TRADITIONAL SHOREPROTECTION

Non-traditional shore protection alternatives are frequent­ly marketed as patented solutions to beach erosion problems.There are non-traditional ways to armor, stabilize, or restorethe coast. These approaches are usually "removable" (tem­porary), "soft" (flexible and dynamic or adjustable), or "hard"(static, fixed, structures constructed out of traditional mate­rials) (Table 1),

Most patented shore protection approaches involve the useof pre-cast concrete or geotextile mats or units to either ar­mor the beach or to reduce sediment losses by protecting anarea from wave attack. Geotextile curtains ii.e; a network ofgeotextile sheets or floats which dampen the wave field) ormodular concrete units may be designed to function as abreakwater or sill with the purpose of stabilizing the beachthrough attenuating the wave energy. Drains and pumpsburied in the beach as a dewatering system are designed withthe intention of stabilizing the beach by reducing the wavebackwash which carries sand off of the beach face. Precastconcrete mats and geotextile bags may be used to armor theback beach. In some cases the installation may be built withthe intent of being removed, or with proper maintenance en­visioned as a fairly long-term structure. The success of thesealternatives, relative to more traditional methods and con­struction materials, is usually a function of the stability ofthe units during storm conditions and their durability overan economic life.

The ability of a non-traditional approach to perform itspromised function, survive for predictable life, its environ­mental acceptability, and its economy should be examinedcarefully. There are a number of questions which should beasked whenever considering a non-traditional approach:

Is it heavy enough, particularly considering storm waves?Will it be properly anchored so that it doesn't fall apart?If the structure does fail, could the loose components be-

come an environmental or public safety hazard?Will the installation be tolerant of erosion or scour effects

around its base?Will the material from which it is being constructed last?What are the design criteria in terms of events or longev­

ity?How will it perform and will it do what we want it to do?If it does do what we want it to do, could there be adverse

impacts to adjacent areas?How much will constructing the non-traditional system

cost compared to more traditional methods?What will it cost to maintain and can it be repaired when

damaged?What is its effective life?What will it cost to remove the system if necessary?

SUMMARY

This discussion regarding coastal damages and the processof developing shore protection alternatives includes severalphilosophical concepts. These concepts may be thought of asa general context within which the development of a shore

protection activity could be considered. Actions undertakento protect the shore or to respond to a shore damage problemare neither globally good nor bad. An informed approach willrequire an understanding of the system and must includesome rational expectations and a measure of success. Thereare no absolutes along the coast; only compromise and ad­aptations. Ten summary statements are presented here asproposed truisms regarding the philosophy of shore protec­tion:

(1) There is no such thing as "permanent" shore protection.Nothing we build in the dynamic coastal environmentwill last forever.

(2) Noone type of shore protection is best for all locations.What works well in one place will not necessarily workwell somewhere else.

(3) No shore protection approach will work equally well inall conditions. Every shore protection approach is de­signed for a certain range of conditions. If those condi­tions are exceeded or not realized, the project may failto function as intended.

(4) There is no such thing as "low cost" shore protection.There are no shore protection bargains.

(5) There are approaches which can protect a project areafor an effective economic life.

(6) There are engineering practices which can work withcoastal processes in a predictable way.

(7) There are areas where the degree of human commit­ment precludes doing nothing.

(8) There are areas where hard structures are appropriate.(9) There are areas where soft structures are appropriate.

(10) There are areas where no shore protection should be un­dertaken.

ACKNOWLEDGEMENTS

The philosophy and general knowledge of shore protectionproject performance and the engineering process presentedhere are based on lecture notes prepared by the author insupport of a US Army Corps of Engineers (USACE) CoastalEngineering Course. This information is being further devel­oped for incorporation into the USACE Coastal EngineeringManual under the sponsorship of the USACE Research andDevelopment, Coastal Structure Evaluation and Design Pro­gram. The reviews provided during the development of thispaper by Mr. John H. Lockhart (Headquarters, USACE) andDr. Yen-hsi Chu (USACE, Waterways Experiment Station)are gratefully acknowledged. Particular recognition and ap­preciation are extended to Mr. Thomas W. Richardson (USA­CE, Waterways Experiment Station), the two "peer" JCR re­viewers of an earlier draft, and Dr. Gregory W. Stone (editorof this special publication) for their perceptive reviews andinsightful comments. Permission to publish this paper wasgranted by the Chief of Engineers.

LITERATURE CITED

BASCO, D.R.; BELLOMO, D.A., and POLLO(~K, C. 1992. Statisticallysignificant beach profile change with and without the presence ofseawalls. Coastal Engineering 1992 Proceedings (American Societyof Civil Engineers), pp. 1924-1937.

-Iournal of Coastal Research, Vol. 13, No.3, 1997

710

BOOGE, K.R., 1994. Perform ance of 1992/93 nearshore berm disposalat Port Ca na veral, Florida. Proceedings, Beach Preservation Tech­nology 1994. Tall ahassee, Florida: TAIT, L.S . (ed.), Flor ida Shore& Beach Preser vation Association, pp. 285-301.

BRUUN, P., 1988 . Profi le nourishment : It s ba ckground and economicadva ntages. Journ al of Coastal Research, 4 (2), 219- 288 .

DELANGE, W. and HEALY, T., 1994. Assessing the stability of innershe lf dr edge spoil mound s using spreadshee t applicati ons on per­sona l computers . Journal of Coastal Research, 10 (4), 946- 958 .

FOSTER, G.A.; H ~;ALY , T.R., and DELANm :, W.P. , 1994. Sedimen tbudget and equ ilibrium beach profiles applied to renourishmen tof an ebb tid al delta adjacent beach , Mt-Ma unganui, New Zeal and.Journ al of Coastal Research. 10 (3), 564-575.

GRIGGS, G.B. ; TAIT, J .F ., a nd CORONA, W. 1994. The inter acti on ofseawalls and beaches: Seven years of monitoring, Monter ey Bay,California . Sh ore and Beach, 62(3), 21-28.

HANOS, E.B., 1991. Unprecedented migration of a submerged moundoff th e Alabam a coast. Proceedin gs of the 12th Confofthe WesternDredging Association and the 24th Annual Texas A&M DredgingSeminar. College St ation, Texas: Cente r for Dredging Studies, pp.245-2 69.

I-lANlJs , E.B. and ALLISON, M.C., 1991. Mound migration in deeperwater and methods of categorizing act ive and stable depths. Pro­ceedings of a Specialty Conference on Quantitative Approa ches toCoastal Sed iment Processes, Coastal Sediments '91 (Seatt le, Wash ­ington ), (American Society of Civil Engi neers, New York ), Vol 2,pp 1985-1 999.

KRAUS, N.C. and PH,KEY, a .H. (eds ), 1988 . Th e effects of sea wallson the beach. Journ al of Coastal Research, Special Issue No.4,146p .

KRAUS, N.C., 1988. Th e effects of sea walls on the beach: An extended

Pope

liter ature review . Journ al of Coastal Research. Special Issue No.4, pp 1-29.

KRAUS, N.C. and McDO UGAL, W.G., 1996. Th e effects of seawalls onth e beach: Part I, an upd ated lit erature review, Journal ofCoastalResearch, 12(3), 691-701.

MULI)~:R, J .P .M.; VAN DEKREEKE, J ., and VAN VESSEM , P., 1995.Experimental Sh oreface Nourishment , Terschell ing (NLl. Proceed­ings 24th Coastal Engin eering Conference. (ASCEJ. pp. 2886-2899.

NATIONAL RESEARCH COUNCIL, 1995. Beach Nourishment and Pro­tection. Washington, D. C.: National Acad emy Press, 334p.

PILKEY, a.H . and WHIGHT, H.L., 1988. Seawall s verses beaches.Journal of Coastal Research, Special Issu e No.4, 41-64.

Por-te , J ., 1989 . Role of br eakwater s in beach erosion cont rol. BeachPreservation Technology '89: Strategies and Alt ernati ve In ErosionControl. American Sho re and Beach Pr eser vation Associat ion, pp.167-176.

Po t-s, J . and DEAN, J.L. , 1986. Development of design criteria forsegme nted breakwater s. Coastal Engineering 1986 Proceeding s(ASCE), pp . 2144-2158.

UIJA. T.; NAITO, K., and KANDA, Y., 1991. Field experiment on sandbypass off th e Iioka coast. Coastal Engin eering in Jap an , 34 2,205-221.

U.S. AI{MYENG I N E ~;HS , 1991. Sand by-passin g system select ion. En­gineering Manual 1110-2-1616 , 31 J anuar y 1991.

U.S. AHMY ENGI N~;~:RS , 1992. Coasta l groins and nearsh ore bre ak­waters . Engineering Manual 1110-2-1617, 20 August 1992.

U.S. ARM Y ENGINEERS, 1993. Coasta l project monitoring. Engin eer­ing Manual 1110-2-1004. 30 November 1993.

U.S. ARMY ENGI NEEHS, 1995. Design of beach fills . Engin eeringManu al 1110-2-3301, 31 May 1995.

ZENKOVICH, V.P. and SCHWAHTZ, M.L., 1987. Pr otect ing th e BlackSea-Georgian SSR gr avel coast. Journal of Coastal Research. 3(2 ),201-209.

Journal of Coastal Research, Vol. 13. No.3 . 1997