Spray Disposal of Dredged Material in Louisiana
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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 organizations: LouisianaDepartmerIt of Natural Resources, Coastal Management Division U. S. Fish and Wildlife Service NationalMarine FisheriesService, Habitat Conservation Division Departmentof the Army, New Orleans District Corps of Engineers SABA Dredging Company, Inc. AZTEC Development Company C. F, Bean, Inc. Thisreport summarizes andevaluates information about spray disposal technology as usedin dredgingnew access canals through unaltered marsh in theLouisiana coastal zone. Thereport was designed for use by industry 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 drilling sitesis a common activityin theLouisiana coastal zone, Traditionally, the spoil dredged during construction is bankedalongside the canal 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 banks contribute to landloss in theLouisiana coastal zone by ! directly convertingmarsh habitat to openwater and upland spoil bank! 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 building 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 barge 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