SPRAYDISPOSAL ~T DREDGEDMATERIAl GOASTAI.I.OlllSIANA:

Habitat Impacts and Regulatory PolicyImplications

Donalcf R. Cahoon James H. Cowan, Jr.

LOUISIANA SEA GRANT COLLEGE PROGRAM SPRAY DISPOSAL OF DREDGED MATERIAL IN LOUISIANA

WETLANDS: HABITAT IMPACTS AND REGULATORY

POLICY IMPLICATIONS

Donald R. Cahoon

and

Jatnes H. Cowan, Jr.

Louisiana Sea Grant College Program ACKNOWLEDGMENTS

Thisresearch was funded by theLouisiana Sea Grant College Program, a partof the NationalSea Grant College Program maintained bythe National Oceanic and Atmospheric Administration,U.S. Department of Commerce. The Louisiana program is supportedby thefederal government and the State of Louisiana, Theauthors appreciate theassistance of the following public agencies and private : LouisianaDepartmerIt of Natural Resources, Coastal Division U. S. Fish and Wildlife NationalMarine FisheriesService, Habitat Conservation Division Departmentof the Army, New Orleans District Corps of Engineers SABA Company, Inc. AZTEC Development Company C. F, Bean, Inc.

Thisreport summarizes andevaluates information about spray disposal as usedin dredgingnew access through unaltered marsh in theLouisiana coastal zone. Thereport was designed for use by and regulatory personnel, aswell as wetlandscientists. Consequently, all measurements arereported in Englishunits, the industry standard. Theopinions, findings, and conclusions expressed herein are the authors' and representanappraisal of spray dredging technology, notan endorsement of it.

Published by

I.OUISIANA SEA GRANT COLLEGE PROGRAM Center for Wetland Resources Louisiana StateUniversity BatonRouge, Louisiana 70803-7507 TABLE OF CONTENTS

Page

Introduction.

Dredging and Wetland Loss.

Purpose and History of Spray Technology

Technical Characteristics and Economic Considerations.

Present Management Objectives and Policies

}ualitative Field Assessment of Effectiveness of Spray Technology 12

Management Objectives: Are They Being Realized?. 21

Summary 22

Recommendations... 23

References 25

Addendum. 27 I NT RODU CT ION

Dredgingcanals for navigation,pipelines, and access to sitesis a common activityin theLouisiana coastal zone, Traditionally, the spoil dredged during is bankedalongside the at elevations significantly higher than the surrounding rn;rrsh Cahoonet al. 1986!. In Louisianamarshes, spoil banksaccommodate upland vegetation thatwas not present before the canals were dredged and often provide habitat for birds, waterfowl,and wildlife not found previouslywithin the coastalarea Olson 1975;Bettinger and Hamilton 1985!. It hasbeen suggested that canals and their associated spoil contribute to landloss in theLouisiana coastal zone by ! directly convertingmarsh habitat to openwater and upland spoil ! habitat; and ! alteringthe local hydrologic regime, i.e., sheetflow over the marsh, subsurfaceflow, and saltwater intrusion Turner 1985; Swenson and Turner 1987!, The cumulativeeffects of canalsand their spoil bankson ecosystem hydrologyand wetland loss may also be important Turner 1985; Cowan et al. 1986!. Minimizing the impactsassociated with spoil banksis a majorconcern of stateand federalagencies regulating development in wetlands.Current regulatory practices of' the LouisianaDepartment of NaturalResources' Coastal Management Division LDNR/CMD! requirethat access canals must be plugged and spoil either gapped or backfilledwhen well» are abandoned.The regulatoryrequirements of federalagencies such as the U.S, Fish and Wildlife Service USFWS!, the NationalMarine FisheriesService NMFS!, and the U.S. Army Corpsof Engineers COE! are similarin intent and scope.Therefore, any new technologythat minimizes spoil bank impacts would be of greatinterest to theregulatory agenciesas a resourcemanagement tool. Industry,which must pay for mitigatingthe impactsof currentdredging methods, also would be interestedin any technologythat speedsup thepermitting process and reduces mitigation expenses, provided that it i» not prohibitively expensive.

DREDGING AND WETLAND LOSS Historically,the biological and physical factors that contribute to marshdevelopment or losshave been nearly in balancealong the Louisiana coast, resulting in wetlandgain with someperiodic espisodesof localizedwetland loss Cowanet al. 1986!, Currently, however,the amountof sedimentdeposited by riverine systemsor accunrulatedby biologicalprocesses does not compensatefor thecombined effects of subsidenceand eustatic sea level rise Turner 1985; Cowan et al. 1986!. The land loss rate in the Louisiana coastalzone is about0.8% annually0 mi2! andis increasinggeometrically with time Gaglianoet al. 1981;Turner 1985;Cowan et al, 1986!. Virtually all of the lossoccurs in 'thewetlands and is a complexprocess influenced both directly andindirectly by naturaland man-induced activities. The term wetland loss refers to the conversion of wetland habitat eitherto openwater or to upland spoil bank! habitat Cahoonet al. 1986!. Land loss can resultfrom a varietyof interrelatedcauses; ! naturaland man-induced erosion of the shorelineor the banksof waterwaysand canals; ! the dredgingand filling of marshes, primarily associatedwith the oil andnatural gas extraction industry; and ! submergence of interior marshes.Submergence occurs when natural land or maintenance processes sedimentation and accumulation of plantmatter! lag behindthe geologically mediatedprocesses of subsidence,compaction, and consolidation. Man altersthe natural balancebetween land buildingand land lossindirectly by affectingthe mechanicsof both processes Cahoon et al. 1986!. Erosionand dredging cause wetland loss by thedirect disruption of thesubstrate, resultingin eitheropen water or uplandhabitat Cahoon et al. 1986!.The impact is immediatelyapparent. Dredging activities have directly converted 192,000 acres = 5%!of Louisiana'scoastal wetlands to openwater since 1900 Lindstedtand Nunn 1985!. On the otherhand, canal dredging, spoil banking, and levee building restrict or eliminateregular over-bankflooding Davis1973; Gosselink et al, 1979;Craig et al. 1979;Turner et al. 1982;Turner 1985; Day et al. 1986;Cahoon et al. 1986!,resulting in anindirect, less readilyapparent impact -the submergenceof interior marshes. This indirect impact has been estimated to cause25% to 90% of coastal wetland loss see Turner 1985 for a review!. Coastalsubmergence is influenced by theseactivities because levees spoil banks! affectthe duration and frequency of tidalinundation which, in turn,affects sediment and nutrientsupply, as well asthe availability of oxygenand toxins that may ultimately influenceplant growth and the deposition of organics Cahoon et al. 1986;Swenson and Turner1987!. This is particularlytrue for areasthat inadvertently become partially or totallyimpounded, with no attemptmade to managethe hydrological regime Cahoon et al. 1986;Cowan et al. 1986for review!. High-pressurespray disposal of spoil,a recently developedalternative dredging technique, may ameliorate some of thehydrologic impacts associatedwith spoil bankingin wetlands.

PURPOSE AND HISTORY OF SPRAY TECHNOLOGY High-pressurespray disposal, a techniquethat does not create spoil banks, was developedin response to theneed for minimizingdredging-related impacts on Louisiana's coastalwetlands. The potential of thistechnique for reducingspoil bank impacts was recognizediinmediately by theregulatory agencies, most of whichhave already developed inhousepolicies for usingthis newly emerging resource management tool D. Soileau, USFWS;D. Clark, LDNRJCMD; R. Ruebsamen,NMFS, personalcommunication!. However,the potential impacts of high-pressurespray disposal have not been examined and,hence, its valueas a managementtool neververified. Therefore, the purpose of this studyis to evaluatespray technology as used for dredging new drilling site access canals throughpreviously unaltered marsh in theLouisiana coastal zone. Only new canal sites are evaluated,not sweepout projects of existingwaterways. The evaluation addresses the followingissues: ! thehistory of spraydisposal technology in coastal Louisiana; ! the technicalcharacteristics of spray disposal technology, including economic considerations; ! thepresent management objectives and regulatory policies of stateand federal agencies regardingspray disposal technology; ! theeffectiveness of spray disposal technology in minimizingspoil impacts; and ! therealization of managementobjectives Marshsoils are usually very unstable because of theirhigh water and organic matter contentand thus cannot bear the loadof the heavyequipment normally usedto drill oil and gaswells. In theearly days of petroleumexploration in coastal Louisiana, drilling sites werereached by boardroads constructed from adjacent and more stable upland area", but this methodwas not practicalfor reachingsites miles deepin the marshesand .; is. Theinvention of the submersiblebarge drilling platformin 1934 Davis 1976!ch. ed the petroleumindustry's perspective by makingit possibleto drill wellsin shallowopen-water habitats.All that was neededto reachdistant drilling sitesin wetlandswas a methodof gettingthe submersible through the marsh. By 1938,barge-mounted dredges were beingused to excavatepetroleum drilling site access canals in Louisianamarshes McGhee andHoot 1963!. The combinationof the submersiblebarge platform andbarge-mounted dredgesopened the entire coastal zone of Louisianato explorationand production by the petroleumindustry, The use of canalsto reachdrilling sitesquickly became the industry norm. Early dredgebarges consisted of land-baseddraglines temporarily mounted on the deck McGheeand Hoot 1963!. Thesedredge were not well suitedto working in all regions i,e,, soil types!of the coastbecause of their small size, In someareas, the spoil could not be deposited a sufficient distance away from the water's edge to prevent the tnaterialfroin collapsingthe canal bank and sliding backinto the water Williams 1944!. Consequently,hydraulic dredges, using low-pressurespray disposal, were also usedto dredgedrilling site accesscanals. During the 1930sand 1940s,hydraulic dredges were as corrunonas bucketdredges. In inarshareas where the vegetation was too thick to remove by suctiondredge, both dredgetypes were sometimes used simultaneously. The bucket dredgewould removethe vegetationlayer and then the suctiondredge would reinovethe underlyingsubstrate Williams 1944!. By the mid 1950s,however, conventional bucket dredgingtechnology had improved and the machines enlarged to theextent that they becamemore efficient thanhydraulic dredges and low pressurespray disposal. New machineswith longerreaches, requiring less manpower to operate,became more cost effectiveand by the early 1960shad nearly eliminated low-pressure spray disposal in south Louisiana. Conventionalbucket dredges and their associatedspoil banksremain commonplace to this day. In the late 1960sand early 1970s,however, the researchcommunity began to suggest that the traditionalmethod of bankingspoil in the Louisianacoastal zone might be associatedwith adverseenvironmental and ecological impacts, and the need to minimize theseimpacts became a regulatoryand environmental concern. Hydraulic dredges, equippedwith high-pressurespray disposal technology, were first usedin southLouisiana in 1979and have been used somewhat infrequently since then Figure 1!. High-pressure technologyis viewed favorablyby regulatoryagencies because it doesnot appearto significantlyalter desirable marsh habitats, to drasticallyalter local hydrologicpatterns, or to contributeto wetlandloss to the samedegree as conventional spoil bankinginethods.

TECHNICAL CHARACTERISTICS AND ECONOMIC CONSIDERATIONS

High-pressurespray disposal is an innovativemodification of standardhydraulic dredgingmethodology. The high-pressurehydraulic dredge employs a rotatingcutter head Figure 2! on a swingingladder that breaksup the marshand underlyingsubstrate and sucksit througha pumpwith a cuttingknife wherethe materialis furtherbroken down and thensprayed across the marshas a liquified slurry. The slurry of liquified sedimentand plant materialcan be spreadas much as 250 feet acrossthe marshto a depthof only a few inches Figure 3!. The stemsof the buriedmarsh plants visibly protrudethrough the layer of spoil Figure4!. Also, the high-pressurespray nozzle can be aimedin any direction. Therefore,the spoil neednot be depositedcontinuously around the canal. Suchareas as small naturaldrainage streams or sensitivehabitats can be avoidedcompletely. In saline marsh,the sprayedspoil remainedmostly in place,with little or no run-off into the canal D. Cahoonand J. Cowan,personal observation!. Turbidity levelsin the canalare apparentlykept low, becauseof the useof hydraulicsuction. The dredge'ssmall size,ease of transportation, three-foot draft, and lack of dependenceon fixed-terrain attachments unlike conventionalhydraulic dredges with disposalpipes! make it well suitedto in coastal marsh environments.

Unlike the bucketdredge, which createsa spoilbank of aboutthree feet, or the low- pressurespray hydraulic dredge, which leavesa spoilbank of aboutone foot, high- pressurespray disposal deposits the materialover a widerarea in a depthof only a few inches. This thin-layerspoil depositionpattern is theprimary distinctionbetween high- pressurespray and conventional suction and bucket dredging disposal techniques. Many g O 0 0% 92A CD

P ea h K. g CD gy o ~ c ~ 1 R 4 IIQ O & Li C aR g O Po O 0 OOQ Sl aO, 3 a O

ICI DD g O g g Q ICC 0 gi 'a 9 CD 4 O R' g CA Figure2. High-prcssurehydraulic dredge and rolaung cutler head.

Figure 3. High-pressurehydraulic dredge in operalionshowing spoil disposal plume nearDog Lake, Louisiana. Figure4. Recentlydeposited high-pressure-sprayed spoil showing characteris- tic patternof depositionover marshplants SparrinaaI erniflora!. of theecological impacts associated with thick-layerspoil depositionare presumedto be relatedto the way it changesover-marsh and subsurfacewater-flow patterns,Therefore, importantcharacteristics to be consideredin evaluatinghigh-pressure spray and conventionaldisposal methods are thedimensions of the spoil area,the depositionpattern, and economics.

Dimensions of the Spoil Area Thin-layereddisposal methodology deposits spoil over an areaup to 250 feet wide, usuallyonly a fewinches thick, while thick-layereddisposal techniques deposit spoil over an areaup to 75 feet wide, usuallyone foot to six feet thick, dependingon soil type and on whetherlow-pressure spray or bucketmethodology is used. Thesespoil thicknessesare for newly deposited spoil and decreaseas the spoil dewaters and subsides.

Deposition Pattern Thin-layereddisposal methodology can deposit spoil discontinuouslyaround canal and marsh surfacefeatures so that sensitive habitats are avoided. The spoil is deposited as a liquified, completelyunsegregated slurry. Low-pressurespray disposal can depositspoil discontinuouslyaround the canalbut the depositionpattern depends on fixed-terrain disposal pipes that must be moved frequently to prevent high spoil accumulation. The spoil is maceratedand liquified, but not slurried. Consequently,heavier material is deposited closestto thedischarge point . A bucketdredge can deposit spoil discontinuouslyaround the canal but is limited by the reach of the boom in avoiding sensitive habitats and the thicknesswith which the spoil is deposited.Therefore, the unseparatedand unmacerated spoil is usually deposited continuously around the canal.

Economic Considerations

High- andlow-pressure spray disposal technology is two to 14 times more expensive than conventional bucket technology under current market conditions Table 1!. Bucket dredgingis cost effectivebecause it is rapid, not laborintensive, and requires less complicatedequipment. The elevatedcosts of low-pressurehydraulic dredging are due, in part,to the additionalman-power needed to handleand place the fixed-terraindisposal pipesnecessary for spoil deposition a crew of 17 versusfive for a bucketdredge!. High- pressure spray disposal technology is not labor intensive utilizes a crew of 2-3!, but, unlike the bucketdredging industry, it is not widely establishedin coastalLouisiana. If equipment must be brought in from out of state,the cost of high-pressure spray disposal may be even higher. Today,high-pressure spray disposal costs about $1. X!per cubic yard, while bucketdredging costs between $0.35 and $0.50 per cubic yard. It is important to note,however, that the priceof bucketdredging was approximately $L00/cubic yard in the early 1980s, before the current recessionin the oil industry. It is not clear how much of a price difference there would be between the two in a boom economy.

There are other costs that must be consideredwhen determining the total cost of reaching a drill site. After dredging is completed, a 7 x 16-foot wooden platform called a keyway must be constructedin the slip to provide a stableplatform for the drilling barge, A bucket dredge can be used to construct this by replacing the bucket with a hydraulic hammer. The hammer drives neededto construct the keyway into the canal bottom. A high-pressure spray dredge cannot be used to construct the keyway becauseit has no boom. For the samereason, suction dredgescannot be used to excavate pits in the spoil Table 1. Costof low- andhigh-pressure spray dredging expressed as a multipleof bucket dredgingcost for five recentdrilling siteaccess projects.

Federai/State Cubic Yards Low-Pressure High-Pressure Permit Number of Dredging Spray Dredge Cost Spray Dredge Cost

Lake Coquille 9/ P8S12S8 329,789 no bid +5,71 to +14.29" open water/ marsh

Bay Dosgris 1/ P860092 75,101 no bid +6.21 open water/ marsh

BayouDupont 55/ P860117 184,600 no bid +4.34 to +5,54* open water/ marsh

Lafourche PWL 606/ P 860428 45,000 no bid +2.66 to +3.14 open water; marsh

Raphael Pass 8, Plaquemines 39,000 PWL 456 marsh only +2.52 to +6,59 +1.98

RANGE +2.52 to +6.59 +1,98 to +14.29

~ Thebucket dredging bid calledfor propwashingthe majority of therequired cubic yards of spoilwhile thc high-prcssurespray bids werc based on dredging thc entire amoun L Hence,the cost di fference appears larger thanit reallywas because thc bucket dredging bid wasbased on dredging fewer cubic yards. bank. Thus, an additional trip must be made to the drill site by a construction barge, further increasingthe oil company'scost of site access,These additional costs would accrue regardlessof market influences on the cost per cubic yard. Therefore, present spray disposaltechnology is not pricedcompetitively with bucketdredging in today'smarket. Even thoughthe cost of spraydisposal may be more thanthat of bucketdredging, the environmental impacts may be far less. High-pressure spray disposal technology holds muchpotential for thepreservation of desirablemarsh habitats if a! theoriginal marsh vegetationis capableof survivingthin-layer spoil deposition, b! not all of the surrounding marsh is sprayed with spoil, and c! erosion of the canal banks does not occur. In addition,local hydrologicpatterns will not be alteredif a! the original marshvegetation survives, b! the depth of the dewatered spoil is minimal a few inches or less!, and c! naturaldrainage streams and ponds are not filled. It is this potentialthat hasexcited the interestof the regulatoryagencies charged with managingand preserving our coastal resources.

PRESENT MANAGEMENT OBJECTIVES AND POLICIES

The differences between spray and conventional bucket dredging technology and their methods of banking spoil are obvious even to an untrained eye. Becauseconventional methods of banking spoil in wetlands have been associatedwith wetland loss Turner 1985! and local hydrological impacts Swenson and Turner 1987!, it is easy to presume that any alternative technology with a lessapparent impact is actually less damaging environmentally. The impacts associatedwith spray disposal inay in fact be less damaging, but at the moment this is a presumptionnot basedupon scientific evaluation. This presumption, however, is the basis for current regulatory policy on dredging in coastal Louisiana. A primary managementobjective of the regulatory agenciesis to minimize dredging-related impacts through the use of feasible alternatives Clark et al. 1983; Moore et al. 1984!. Becauseof its perceived advantages,spray disposal has become the primary technological alternative to conventional disposal methodology recommendedby the agencies,even though the premise that spray disposal prevents or reducesdestruction of coastal resourcesremains untestedand unproved.

Policy Objectives

Current regulatory policy of the permit ting LDNR and COE! and commenting USFWS and NMFS! agencieson spoil disposal in wetlands associatedwith accesscanal dredging has two objectives: ! to minimize conversion of wetlands to nonwetland habitat types; and ! to maintain wetland habitat quality. The agenciesdeclare that the purported impactsreduced or avoidedand benefits realized by useof spraytechnology presentedin Table 2! fulfill theseobjectives. The avoidanceof the creationof spoil banksand upland shrub/scrub habitat plus reduction in wetland loss fulfill objective one; the re-establishment and nourishment of marsh, the survival of existing vegetation, the maintenanceof marsh elevation,the lack of hydrologicalterations, and the feasibility for open-watermarsh creation fulfill objective two.

Policy Developtnent

During 1985and 1986,the regulatoryagencies recommended spray disposal for 11 proposedprojects involving the dredgingof new canalsand slips in marsh Table 2!. Of these11 applications,10 projectswere permitted and one applicationwithdrawn. Five of Table2. Reasonsgiven inlettersofrecommendation,permitjustifications,orfindingsof fact! byregulatory agencies forconsidering spraydredging asan alternative tobucket dredging in11 perrzutapplications requesting drilling site access viacanal through unaltered marshin 1985-1986. COE= CorpsofEngineers; LDNR= LouisianaDepartment ofNatural Resources; NMFS= Na- tionalMarine Fisheries Service; USFWS = Fish and Wildlife Service!.

Was Spray Dredg- Federal / State ing Required by Permit Number Rationale Behind Recommendation Permit? ~

BayouLaLoutre 75/ applicationwithdrawn F851257 "...to avoid creatingspoil bankson the adjacentmarshes..." NMFS

"...wouldguarantee a maximum2-inch spoiloverlay..." USFWS

Lake Coquille9/ Yes P851258 "...wouldguarantee a maximum2-inch spoil overlay..."USFWS

BayouDupont 53/ P851565 "...wetlandloss would be further reducedand thesubsiding marsh enhanced...; ...to pro- motegrowth of emergentvegetation without killing theexisting marsh..." NMFS

"...marsh loss...minimized..."USFWS

Lafourche PWL 626/ No; recommendation P 860113 "...enablingre-establishment of marsh vege- tation...;...minimize spoil-associated withdrawn impactson existing marsh..." USFWS

BayouDupont 55/ No P860117 "...enablingre-establishment of marsh vegetation..."USFWS

"....to nourish marsh...; ...would not smothermarsh vegetation..." NMFS

Terrebonne PWL 798/ P860163 "...toestablish marsh elevation surfaces in Yes openwaters and slightly increase the elevation of existinglow subsided!marsh...by one or two inches..." NMFS

"...initialelevation of spoildeposits shall not exceed1 footabove the elevationof theadjacent marsh..." USFWS

10 Table 2. continued

BayouSauveur 7/ P860203 "...sprayedout over marsharea to nourish Yes; however appli- it..." LDNR cant moved drilling lo- cation to open water Io "...enablingre-establishment of marsh avoid dredging vegetation..." USFWS Lafourche PWL 606/ P860428 "...initial elevation of spoil deposits shall No; applicant avoided not exceed 1 foot above the elevation of the dredging by reaching adjacentmarsh..." USFWS site on high tide Bayou Juanita 1/ P860557 "...to evenly disperse the spoil over the marsh.; ...placed in open water areasto an elevation conducive to the establishment and growth of marshvegetation..." NMFS PlaqueminesPWL 456 "...eliminate.spoil banks..; Although the Yes area of impact would be greater due to the need to spreadthe dredgedmaterial over a largerarea, the degreeand duration of impactwould be reduced; ...elevation after subsidence would still be suitablefor supportingmarsh vegetation, and hydrologicdisruptions would be minimal."; "...no long term lossof wetlanddue to spoil deposition.; ...provide valuable sediment to the deterioratingmarsh.; ...water...wouldbe allowed to flow out over the marsh, replenishing the rapidly subsidingand eroding substrate." COE

"...initial elevation of spoil deposits not exceeding 1 foot above the elevation of the adjacent marsh..." NMFS Raphael Pass8 "...eliminate...spoilbanks...; Although the area Yes of impactwould be greaterdue to the needto spread the dredgedmaterial over a largerarea, the degreeand durationof impactwould be reduced;...elevation after subsidencewould still be suitable for supporting marsh vegetation, and hydrologic disruptions would be minimal....no long term loss of wetland due to spoil deposition.; ...providevaluable sediment to the deteriorating marsh....water...would be allowed to flow out over the marsh,replenishing the rapidly subsiding and eroding substrate." COE "...initial elevation of spoil deposits not exceeding 1 foot above the elevation of the adjacent marsh..." NMFS "...enablingre-establishment of marshvegetation...; ...the initial elevation of spoil deposits shall not exceed 1 foot above the elevation of the adjacent marsh..." USFWS

' A yesindicates that spray dredging was required by the COE or LDNR, or both agencies. thepermits approved theuse of bucket disposal oneof the recommendations forspray disposalwaswithdrawn, andthe other four were issued over the objection ofthe commentingagency!, while the other five required spray disposal. Ofthese final five, one wasdrilled from open water toavoid the necessity ofdredging andthe other four were dredgedwith spray disposal methodology Table 2!. Theinterest ofthe agencies inapplying spray technology tothe construction ofnew canalsand slips has apparently grown during the past two years. High-pressure spray technologydeveloped themeans todredge through marsh in1983 T. Deal, personal communication!.A review ofpermit records from 1983 to the present reveals that spray disposal,although often recornrnended forsweeping projects during this time, was not recommendedatall in 1983and 1984, only once in 1985,and ten times in 1986for dredgingnewcanals. For example, theNMFS and USFWS have taken anactive interest inspray disposal asan alternative tobucket dredging during the past two years R. Ruebsarnenand D. Soileau,personal communication!. Spraydisposal policy isdifficult toimplement andevaluate because every dredging locationisenvironmentally different, and spray disposal technology really isa rangeof technologies,A critical management issueisthe threshold i.e.,height orthickness of spoil!atwhich a spoil impact takes effect. Isfour inches toothick, orcan impacts be avoidedatgreater depths? If depth ofspoil iscritical, then failing todistinguish between high-and low-pressure spraytechnology, whichspreads spoilin different patterns, canbe ascritical a mistakeasnot recommending spraydisposal where it may be well suited. NMFShas recognized thispolicy issue and distinguishes between high- and low-pressure spraymethods byreferring tothem asspray and spread technologies, respectively. In ordertoensure that site-specific disposal dimensions areachieved without recommending specificdredging companies aconflict ofinterest forany public agency!, mostregulatory agencieshaveadopted a policy ofrecommending specificconstruction dimensions, suchas "...initialelevation ofspoil deposits shall not exceed [aspecified dimension - usually one- footbut sometimes twoinches] above the elevation ofthe adjacent marsh..." Table 2!, Whathas not been established through scientific investigation iswhere this threshold shouldbeset and whether thethresholds currently adopted bythe agencies areappropriate to meettheir policy objectives. QUALITATIVEFIELD ASSESSMENT OFEFFECTIVENESS OF SPRAYTECHNOLOGY IN MINIMIZINGSPOIL IMPACTS

Project Descriptions Twocanals were dredged with high-pressure spraytechnology through saline marsh in St.Bernard and Terrebonne parishes Lake Coquille 9,dredged February, 1986, and TerrebonneParish Wetlands 798, dredged August, 1986, respectively! and twc dredgedwithlow-pressure technology infresh fiotant marsh atDelta National W..ie Refuge Raphael Pass8 and Plaquemines ParishWetlands 456,dredged April, 1987!. See Figure 1 for locations. LakeCoquille 9.This project involved dredging a 500-foot canalthrough saline inarsh inorder toreach anopen-water drilling location inLake Coquille Figure 5!. The permit allowedforspray disposal ontomarsh oneither side of the canal but material wassprayed onlyon the southern sidebecause ofstrong winds. The well was a dryhole, so plugs cappedwith shell were placed ateither end of the canal asrequired bythe permit.

12 TerrebonneParish Wetlands798. An existingoil andgas canal was sweptto a depth of eight feet anda new499-foot canal and slip dredgedthrough marsh and the natural waterwaysat its tip, nearDog Lake in southernTerrebonne Parish. Spoil from the sweepingoperation was sprayedon existing spoil banks,while spoil from the canalwas sprayedon adjoiningmarsh and waterways. However, material from the canal dredging wasdeliberately not sprayedon certainmarsh-waterway areas at the discretionof the dredge operator Figure 6!. RaphaelPass 8 and PlaqueminesParish Wetlands456. Two canals,one 470-feetand the other600-feet, were dredged through floating roseau cane Phragmitesaustralis! marsh. The spoil was sprayedonto marshalong the adjoiningwaterway Figure 7!. The sprayedmaterial did not accumulatesubaerially because the spoil sankinto the soft, highly organicflotant substrateor becameresuspended in the watercolumn and floated off-site. Theonly evidencethat spoil had been sprayed at thesite was the crushed vegetation Figures7 and 8!.

Field Assessment

An assessmentof the impactsand benefitsof spraydisposal was made through ground and aerialsurveys of the four sitesdescribed above during April, 1987. Measurementsand visual inspectionswere made to determinethe distance and average depth to which spoil was sprayed,degree of vegetativerecolonization, species composition, and impact on local hydrologicpatterns e.g.,filling in of naturalstreams!. The resultswere usedto evaluate the purportedenvironmental advantages of sprayover conventionaldisposal technology as opined by the regulatory agencies. The impactsof spraydisposal in theflotant marshwere negligible because the dredged materialsank or floatedaway. However, it is ouropinion that the disposal impacts of any dredgingtechnique would be negligiblewith sucha highlyorganic substrate. Therefore, our evaluationof impactswill berestricted to the two marshsites dredged by high- pressuretechnology. The authorswish to note,however, that spraytechnology is well suitedto dredginghighly organicsubstrates because it sucksthe materialup ratherthan grabbing it. We havedivided the purportedenvironmental advantages of high-pressurespray over conventionaldisposal into two major categories:! impactsavoided or reduced, and! benefitsaccrued Table 3!. Oneimpact is apparentlynot avoided,and a few benefitsare imrriediatelyrealized, but mostpurported environmental impacts can not be appraised because of insufficient data.

ImpactsAvoided or Reduced.The only observedimpact common to conventional disposaland spraydisposal was the smotheringof vegetation.At both Lake Coquille and Dog Lake, most of the existingvegetation was smotheredand killed Figures9 and 10!, althoughsome vegetation did survivearound the edgesof thedisposal areas and in areas wherespraying was light Figure 11!. However,the creationof a spoilbank, two to three feet high and70 feet wide, was avoided, The materialwas sprayedfour to six inchesdeep and230 feet into the marshat Dog Lake andseven to 15 inchesdeep and 260 feet inland at Lake Coquille. The differencein dimensionsbetween the two sitesis presumablycaused by the sprayingof all thematerial on oneside of thecanal at Lake Coquille.

No upland shrub/scrub habitat was createdat either site becausespoil elevation was comparativelylow. The limited vegetativerecolonization that took placeeight to 14 months after sprayingwas by intertidalmarsh species, Spartina alterniflora, Distichli s spicata,and

13 Figure 5. Aerial view of 5 O-foot canalthrough saline marsh at Lake Coquillc, St. Bernard Parish. All spoil was sprayed onto the south side of thc canal. Note the irreg- ularly shapedopen water areas within the disposalarea from which materialwas bor- rowed from below the original marshelevation for constructingthe plugs at either cnd of the canal. Photographtaken 14 monthsafter spoil deposition.

Figure 6. Aerial view of canal/slipdredged through saline marsh near Dog Lake, Ter- rebonneParish. Note the wellheadand spoil bankof the old canal,and naturalwater- ways intersectedby the new canal/slip. Photographtaken eight monthsafter spoil depostllon.

14 Figure7. Aerialview of slipdredged through roseau cane Phragmi res australis! marsh at Delta National Wildlife Refuge. Note that the spoil is depositedin the adjoining waterwaysrather than along the edgeof the new canaVslip.Photograph taken two weeks after spoil deposition.

Figure $. Aerial view of vegetationcrushed during spoil depositionat Delta National Wildlife Refuge. Comparethe -shapedpattern of overlappingdischarge points to the fan-like patternof high-pressurespray disposal in Figures5 and6. Photograph taken two weeks after spoil deposition.

15 Figure 9. Ground view of sprayedspoil at Lake Coquillc site 14 monthsafter deposi- tion. Borrow pit createdduring plug constructionis visible at right,

Figure 10. Groundview of sprayedspoil at Dog LAe siteeight months after deposition.

16 Figure11. Viewof marshsurface on fringeof disposalarea at DogLake site eight monthsafter deposition. Note original vegetation with underlyinglayer of dredged material.

17 Table 3, Purported environmental benefits of spray dredging methodology as expressedby state and federal regulatory agenciesin their letters of recomtnendationand permit authorizations! and results of qualitative field evaluation of high-pressurespray techniques.

Impacts purportedly avoided or reduced Results of Field Evaluation ~ smothering /killing of existing vegetation not completely avoided creation of spoil banks 2 to 3 feet high avoided ~ creation of upland shrub / scrub habitat avoided; recolonized by marsh species ~ spoil-associatedimpacts compaction insufficient data ~ blockage of tidal exchange sheet flow insufficient data - tidal streams reduced

wetland loss at disposal site reduced; recolonized by marsh species - in vicinity of disposal site insufficient data

Benefits purportedly accrued ~ elevation after dewatering suitable to yes; recolonized support marsh vegetation by marsh species ~ nourishment of marsh at disposal site vegetation mostly smothered adjacent to disposal site insufficient data maintain subsiding marsh through insufficient data restoration of elevation initial depth of spoil deposit < l foot not always maximum of 2-inch dewateredspoil depth dewatered spoil depth= 4 to 15 inches

option for creating marsh in shallow yes open water habitat Salicorniaspp. The presence of thebrackish and salt pan species, D, spicataand Salicornia spp,represent new colonizing episodes because the original marsh was dominated by the Iowmarsh species, S. alterniflora. It is notclear whether the recolonization effort by S. alterniflorarepresents the regrowth of plantsexisting at thesite prior to sprayingor the invasionof new individualsfrom the surroundingpopulation Figure 12!. Recolonization bymarsh animals was evidenced by thepresence of crab burrows at theDog Lake site. Thereis insufficientinformation to analyzethe impactsof sprayedspoil on substrate compaction.A detailed analysis of thegeotechnical features of thespoil and niarsh substrateis required,Therefore, we do notknow if sprayedspoil will havethe same impactson substrate compaction and subsidence asNichols 959! documentedfor conventionallevee construction. One could hypothesizethat the wide, shallowdimensions of sprayedmaterial would have less impact, but this remains to beproved. Theblockage of tidalexchange by spoildeposition can occur in two ways:! the interruptionof sheet surface! flow acrossthe marsh, and ! thefilling in of tidalstreams. Sheetflow is very sitespecific, depending on localtides, winds, drainage patterns, and elevation.We do notknow how sprayed spoil will affectsheet flow. A detailedstudy of theseconditions at each site is necessaryto determineif a dewateredspoil elevation of four to 15inches provides a significantbarrier to dailytidal floodingof themarsh. As for the filling in of tidalstreams, both conventional and spray disposal methods can be selective in spoilplacement. However, bucket dredges are restricted by thelength of theboom and havea limitedability to "throw"spoil to a locationor in a thinlayer. In contrast,high pressurespray can easily control the amount of materialit laysdown in anygiven area. At theDog Lake site, material was sprayed over the large and small tidal streams shown in Figure6 withoutfilling in or restrictingwater flow. Figure13 shows the small tidal stream locatedat the tip of the slip eight monthsafter spraying. Conventionalspoil disposal causes wetland loss through the conversion of marsh habitatto uplandshrub/scrub spoil habitat. It hasalso been implicated in thedeterioration of interiormarshes Scaife et al. 1983;Turner 1985! through its influenceon surfaceand subsurfacehydrology. Our preliminary results indicate that spray disposal does not directlyconvert marsh to uplandhabitat because, to date,all recolonizationhas been by intertidalmarsh species. On theother hand, there is noway of analyzingthe influence of spraydisposal on deteriorationof interiormarshes because we do notfully understand spraydisposal's impact on hydrology. BenefitsAccrued. Benefits are defined as those characteristics or consequencesof spraydisposal that the regulatory agencies believe help minimize dredging-related impacts on wetlandfunctions, particularly habitat quality. Spraydisposal minimizes disposal impacts on wetland loss because the elevation of the spoilafter dewatering is suitableto supportmarsh vegetation. On theother hand, the ability of sprayedmaterial to nourishthe marshis limited, at best. High-pressurespray disposaldeposits spoil in a finerain-like mist in a comparativelythin layer,much like the actof sprayingfertilizer on cropsor a lawn Figure4!. Hence,there is a presumptionthat spraydisposal has a nourishingeffect on themarsh. Our results do not supportthis contention,at leastfor the site of deposition,because most of the vegetationis buriedand killed, The materialmay providenourishment for recolonizingspecies but it hasno nourishingeffect for the smotheredvegetation. Rain and tidesmay washthe deposited materialacross the adjoining marsh and hence provide nourishment to marshesin the vicinity, but this remainsto be testedand proved.

19 Figure 12. Groundview of Spanina alrerniflora recolonizingspray disposal site at Dog Lake eight monthsafter deposition. Note deadremains of original vegetation.

Figure13. Groundview of tidalstream located at thetip of theslip at DogLake with waterflowing through it eightmonths after deposition. Note sprayedspoil present alongits banks.

20 Spraydisposal appears tohave great potential asa toolfor maintaining subsiding marsh throughthe restoration ofelevation bydeposition, because thespray operator can exercise fargreater control over the thickness ofthe material than can a bucketoperator. However, thispotential has never been tested or proved. Themaximum initial and dewatered depths of sprayedspoil observed or calculatedfor LakeCoquille and Dog Lake exceed the construction dimensions recommended bythe regulatoryagencies inmost cases. At Lake Coquille, the measured dewatered depth was sevento 15inches. Therefore, the initial depthof spoildeposit could not have been less thanone foot throughout theentire disposal area. The recommended dimension couldprobably have been achieved if the material had been sprayed on both sides of the canal.The initial depth of spoildeposited atDog Lake was observed bythe authors during dredgingand was less than one foot. However, the dewatered depth of spoilexceeded two inches at both sites. Theflexibility exhibited by spray disposal in spoil placement makes it a suitableoption forbanking spoil in shallow-waterhabitats for the purpose ofcreating marsh, The material canbe sprayed down in thinlayers 200 to 300 feet from the point of dredging, asopposed todeposited bythe bucketful less than 200 feet away. Also, the shallower draft of the spraydredge allows it tooperate in shallow water sites with less disturbance tothe water- bottom.

MANAGEMENT OB JECTIVES: ARK THEY BEING REALIZED? Thepolicy objectives of theregulatory agencies can be realized through the irnplernentationof spray disposal only if thedeclared advantages of spray disposal are realized.The potential of eachdeclared advantage forrealizing the agencies' stated managementobjectives is summarized below. Also evaluated below are two advantages notexplicitly declared bythe agencies and two related management issues which should be addressedby the agencies.

Declared Advantages Spraydisposal ofdredged material partially fulfills objective one minimizingthe conversionof wetlandto nonwetlandhabitat. A highspoil bank with uplandshrub/scrub vegetationisnot created and wetland loss is reduced, atleast at the disposal site, because recolonizationis by intertidalmarsh vegetation. It should be noted, however, that recolonizationis gradual and, at present, the disposal areas are mostly unvegetated. In addition,the indirect impact of sprayedspoil on the deterioration of interior wetlands, throughinfluences on surface and subsurface hydrology, is notknown. Theinfluence of spraydisposal on the maintenance of habitat quality nourishing existingvegetation, restoring surface elevation, creating marsh in openwater, and maintaininghydrologic exchange! is less clear. There is noinformation available to determineif spray disposal nourishes themarsh or helps to maintain surface elevation in a subsidingenvironment. It is probablywell suited to creatingmarsh in openwater, althoughthis has not been quantified. However, like conventional methods, spray disposal clearlystnothers and kills existing vegetation atthe disposal site, though it doesso over a largerarea. The initial depth of sprayedspoil deposits can be less than one foot, depending onthe quality of theequipment and skill of the dredge operator, though the declared advantageof two inches maximum dewatered depth was not realized ateither Lake Coquille

21 or Dog Lake. What influencethese spoil depthshave on sheetflow hasnot been investigated,but spraydisposal does not block local tidal streams.

Undeclared Advantages A readilyapparent benefit not explicitly stated in anyletters of recommendationis the flexibilityof spoilplacement. Waterways and small tidal streamscan have a thinlayer of spoil depositedon themwithout alterationto flow, or can be avoidedentirely during spraying.This makes spray disposal well suitedto dredgingin sensitivehabitats where selectiveplacement of spoilis required.Another undeclared advantage is thatall avoidedor reducedimpacts listed in Table3 arerealized immediately, not just after thewell is abandoned.This is not a trivial benefitbecause oil and gaswells may producefor decades. For example,with conventionalspoil disposal,the presenceof a continuousspoil bank is unavoidableuntil the canalis backfilledor gapsare made in the spoil manyyears after the canal was dredged.

Related Management Issues Two environmentalissues have not beenaddressed by the agencies,but warrantfurther consideration. One is land loss that occurs when the banks of man-made canals erode; this hasbecome a seriousproblem in somecoastal areas of Louisiana Johnsonand Gosselink 1982!. The widths of spray-dredgedcanals should be monitoredfor severalyears to determinethe degreeof bankerosion, and the wideningrate of spray-dredgedand bucket dredged canals should be compared. Thedredging of materia1to constructa plugat themouth of a canalwhen i tis abandonedis anotherissue in needof investigation.Since the early 1980s,all permitsfor dredgingoil andgas access canals in wetlandsroutinely require that the canalbe plugged uponabandonment. The dredge operator often borrows material from the spoil bank to constructthe plug, particularly if thematerial frotn nearby water bottoms is poorlysuited. If thereis no spoil bank,from wherewill the materialcome? The marsh? In Figure5, the borrowditches created during plug construcuonare evidence of the attemptto borrow from thethinly sprayedlayer of material,resulting in open-waterhabitat that haslittle chanceof naturallybecoming marsh again. In this respect,spray disposal does not help achieve policy objectiveone--minimizing wetland loss.

SUMMARY

High-pressurespray disposal of spoil in salinemarshes has great potential to minimize dredging-relatedimpacts on Louisiana'scoastal resources. Salt marsh at thedisposal site is not convertedto uplandshrub/scrub habitat because a spoilbank two to six feet high is not createdon the marshsurface. Vegetation at thedisposal site is crushed,as it is with conventionalbucket dredging, but the sprayedmarsh is recolonizedby intertidalmarsh plants, High-pressurespray disposal is capableof depositingspoil in a thinlayer approximatelyfour inches!,giving it greatpotential for minimizing hydrologicimpacts and maintainingmarsh eIevations. Further research is needed,however, to determineif this potential is actually being realized.

22 RECOMMENDATIONS Spraydisposal of dredged material has potential for minimizing impacts on wetland resourcesassociated with canaldredging, but this potential has not been quantitatively evaluatedand hence is mostlyunproven. As a resultof ourqualitative evaluation, we recommendthat current policy be refined, quantitative investigations performed, and long- term monitoringof spraydisposal sites commenced.

Refinements of Policy Currentpolicy needs to recognizeand distinguish between actual verifiable! and potentialadvantages of spray technology. The first step in thisprocess isto recognize that thereis a rangeof spraytechnologies, both low and high pressure, with varying modificationsand refinements. The ability of eachtechnique to achieverecommended constructiondimensions varies, The most refined technique is high-pressurespray and it appearsthat the policies are written to suit this method. This is evidenced bythe generic useof thephrase Jet-Spray by agencypersonnel todescribe all spraytechnology. If an agencywishes the high pressure method to beused, the construction dimensions in the letterof recommendationwill haveto matchhigh-pressure capabilities closely to ensurethat anothertechnique is not used. But a maximumdewatered spoil depth of twoinches over anentire disposal area does not appear feasible for anytechnique in saltmarsh environments.It may not be realistic to assumethat the advantages of spray technology are thesame in all soilor marshtypes. The impacts of spoildisposal are strikingly different amongfiotant, fresh, and saline marshes. The suitability of spraytechnology in marsh typesother than saline should be investigated, More importantly, however, even if spray technologycan achieve the recommended construction dimensions, we still do not know if thiswill reduceor avoidspoil bank impacts. We need to determinethe thresholds atwhich impactsoccur in orderto developmeaningful regulatory policies. Anotherissue, not addressed by theagencies in theirletters of recommendation, concernsthe source of materialfor plugconstruction, The needs for eachproject must be evaluatedand addressed in thepermit conditions. Otherwise, the marsh may end up being a commonsource of materialfor plug construction at spray disposal sites, thus negating anyadvantage of thin-layereddisposal.

Quantitative Investigations Theability of sprayedspoil to maintainmarsh elevation, nourish the marsh, and not alterlocal hydrologic conditions is yet to bequantified for any marsh, Maintenance of elevationand nourishing effect should be evaluated in all soiland marsh types. The influenceof sprayedspoil deposits on soil compaction and subsurface flow needs investigatingalong with the barrier effect of sprayedspoil on surface flow. At whatheight doesspoil block surface water flow? Proper construction dimensions and design cannot be recommendeduntil this influence is quantified.

Long-Term Monitoring A multiyeardata base is neededto evaluatethe influence of spraydisposal on conversionof wetlandto nonwetlandhabitat types, Aerial and ground surveys should be conductedregularly to evaluaterevegetation patterns, wetland loss rates in thevicinity, and canalwidening rates, Vegetational recolonization should be monitored for severalyears to

23 determineif the disposalareas become dominated by marshor uplandspecies, or remain mostlybarren mud flats. Waterfowland wildlife populations normally associated with spoil bankhabitats should be monitoredfor long-termchanges caused by habitatloss. The deteriorationof interior marshesin thevicinity shouldbe monitoredfrom aerial photographsand canal widening rates verified with groundmeasurements.

24 REFERENCES Bettinger,K.M. and R. B. Hamilton. 1985. Avian use of levee habitat types, Rockefeller WildlifeRefuge, Louisiana. In: Bryan,C. F., P. J. Ewank and R. H. Chabreck eds.!.Fourth Coastal Marsh and Estuary Management Symp., Baton Rouge, Louisiana: 165-186. Cahoon,D. RJ. Donley,S. Hamilton and R. E. Turner. 1986. Prototype handbook for evaluatingdrilling site access in wetlands via canals. Final Rep. Lee Wilson and Assoc.,Inc. for U. S,Environ. Protection Agency. P. O. Box931, Santa Fe, New Mexico. 87504-0931 Clark,D. R.,D. R. Cahoon, J.L. Lindsey,and T. R.Osborn. 1983. A reviewof the Louisianacoastal resources permitting program from 1980-1983. Pages 171-191. In: Vamell,R. ed.! Proceedingsof theWater Quality and Wetland Management Conference,August 4-5, 1983,New Orleans. Louisiana. 460 pp. Cowan,J. H,, Jr.,R. E. Turnerand D. R. Cahoon.1986, A preliminaryanalysis of marshmanagement plans in coastalLouisiana for useby theEnvironmental Protection Agency,Final Rep. to Lee Wilson and Assoc., Inc. for U. S.Environ, Proctection Agency.P. O. Box931, Santa Fe, New Mexico, 87504-0931. Craig,N. J., R. E. Turner, and J. W, Day, Jr, 1979,Land loss in coastalLouisiana U.S.A.!.Environmental Management 3!:133-144. Day,J. W., Jr., R, Costanza, K. Teague, N, Taylor, G. Paul Kemp, R. H. Day and R. E. Brecker,1986. Wetland Impoundment: A Global Survey for Comparisonwith the LouisianaCoastal Zone. Final Rep. Geological Survey Div., Louisiana Dept. Natural Res. 140 pp. Davis,D. W. 1973.Louisiana canals and their influence on wetland development. Ph.D. Dissertation. Louisiana State Univ., Baton Rouge. 199 pp. Davis,D. W. 1976.Changes in marsh environments through canalization. In: Time- stressedcoastal environments: assessment and future action, proceedings of thesecond annualconference. Arlington, Virginia. TheCoastal Society: 224-232. Gagliano,S.M., K. J.Meyer-Arendt, andK. M.Wicker. 1981. Land loss in the MississippiRiver deltaic plain. Trans, Gulf Coast Assoc. Geol. Soc. 31: 295-300, Gosselink,J.G., C. L. Cordesand J. W. Parsons. 1979. An ecologicalcharacterization of theChenier Plain coastal ecosystem in Louisiana and , Vol. l, U. S.Fish Wildl. Serv. Biol. Serv.Program FWS/OBS-78/9. 302 pp. Johnson,W. B. andJ. G. Gosselink.1982. Wetland loss directly associated with canal dredgingin theLouisiana coastal zone. Pages 60-72. In: Boesch,D. ed.!. Proceedingsof the Conference onCoastal Erosion and Wetland Modification in Louisiana:Causes, Consequences, and Options. U. S. FishWildl. Serv.,Biol. Serv. Prog., FWS/OBS-82/59. 256 pp. Lindstedt,D. andL. Nunn, 1985. development in Louisiana'scoastal zone, Pages1410-1416. ! nMagoon, 0, T.,D. Miner, D, Clark,and L. T, Tobin eds.!, CoastalZone 85, volume 2, Proceedingsof theFourth Symposium on Coastaland OceanManagement, July, 1985,Baltimore, Maryland,

25 McGhee, E. and C. Hoot. 1963. Mighty dredgers, little-known work horses of coastal drilling, producing, pipelining, now 25 years old. Oil and Gas Journal 61:150-152,5.

Moore, D., P. Keney, R. Ruebsamen,and J. Lyons. 1985. National Marine Fisheries Service activities to reduce adversedredging impacts in Louisiana coastal marshes. Pages 27-48. In: Bryan, C. F., P. Zwank, R. Chabreck eds.!, Proceedings of the Fourth Coastal Marsh and Estuary Management Symposium, June 6-8, 1984, Baton Rouge, Louisiana: 27-48.

Nichols, L. G. 1959. Rockfeller Refuge Levee Study. Tech. Rep. Louisiana Wildl. Fish. Comm., New Orleans.

Olson, R. B. 1975. Bird usageof spoil banks in the intermediate marshesof southwestern Louisiana. MS Thesis, Louisiana State Univ., Baton Rouge. 155 pp,

Scaife, W., R. E. Turner and K. Costanza. 1983. Coastal Louisiana recent land loss and canalimpacts. Environ. Manage.7:433-422.

Swenson, E. M. and R. E. Turner. 1987. Spoil banks: effects on a coastal marsh water level regime. Estuarine and Coastal Shelf Sci. 24: 599-609.

Turner, R. E., R. Costanza, and W. Scaife. 1982. Canals and wetland erosion rates in coastal Louisiana. Pages 73-84 In: D. F. Boesch. Proceedings of the conference on coastal erosion and wetland modification in Louisiana: causes,consequences, and options. U. S. Fish Wildl. Serv. Biol. Serv. Program FWS/OBS-82/59. 259 pp.

Turner, R. E. 1985. Coastal landloss, canals and canal levee relations in Louisiana. U.S. Fish Wildl. Serv. Biol. Prog. Rep. 854!. 58 pp.

Williams, N. 1944. Dredging canals for servicing fields in marsh and swamp districts of Louisiana. Oil and Gas Journal 43: 95-96.

Addresses of Individuals Cited irt Text

Mr. David Soileau: United States Fish and Wildlife Service P.O. Box 4305, Lafayette, Louisiana 70502

Mr. Darryl Clark: Louisiana Department of Natural Resources,Coastal Management Division, P. O. Box 94124, Baton Rouge, Louisiana 70804-9124,

Mr. Ricky Ruebsamen: National Marine Fisheries Service, Habitat Conservation Division, Center for Wetland Resources,Louisiana State , Baton Rouge, Louisiana 70803-7503.

Mr. Troy Deal: President, AZTEC Development Company, 1331 W. Central Blvd., P. O. Box 3348, Orlando, Florida 32802.

26 ADDENDUM

Anotheraerial survey of theLake Coquille and Dog Lake sites was conducted onJuly 31,1987, three months after the April aerial survey. The qualitative results of theJuly surveyare presented in this addendum because the final version of thereport was completedand submitted tothe Louisiana Sea Grant College Program in May, 1987. Inthe three months from April to July, both spray disposal sites underwent continued recolonizationbynative intertidal marsh species. After nearly two complete summer growingseasons, themajority ofthe Lake Coquille disposal site was revegetated. At the DogLake site, the fringes and more lightly sprayed areas of thedisposal site became revegetatedinless than one year. Therefore, recolonization bynative intertidal marsh vegetationdoes not appear tobe as limited or gradual assuggested inthe report, but it appearsthat if completerevegetation does occur it willtake at least three years.

27 ioutsw~ 1~ SEA QRAIYT .,PAR COLLEGE PROGRAN LSU Center for Wetland Resources