Gravel Removal Studies in Arctic and Subarctic Floodplains in Alaska
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Biological ServicesProgram FWSIOBS-80108 June 1980 Gravel Removal Studies in Arctic And Subarctic Floodplains in Alaska NORTH SLOPE I I SWARD PENINSULA NORTHERN INTERIOR Interagency Energy-EnvironmentResearch and DevelopmentProgram OFFICE OF RESEARCH AND DEVELOPMENT SOUTHERN INTERIOR U.S. ENVIRONMENTAL PROTECTION AGENCY and Fish a.nd Wildlife Service ~~~~~~~~~~~ D@@2968 L""" "" "" U.S. Department of the Interior "" "" -" .. The Biological Sewices Program was establishedwithin the U.S. Fish and Wildlife Service to supply sclentific information and methodologies on key environmental issues that impactfish and wildlife resources and their supporting ecosystems. Projects have been initlated in the following areas: coal extraction and conversion; power plants; mlneral development; water resource analysis, including stream alterations andwestern water allocation; coastal ecosystems and Outer Continental Shelf development; National Wetland Inventory; habltatclassification and evaluation; inventory and data manage- ment systems; and information management. The Blological Services Program consists of the Office of Biological Services in Washington, D.C., which is responsible for overall platming and management; National Teams, which provide the Program's central scien- tific and technical expertise and arrange for development of information and technology by contracting with States, universities, consulting firms, andothers; Regional Teams, which provide local expertise andare an important link betweenthe National Teams and the problems at 'the operating level; and staff at certain Fish and Wildlife Service research facilitles, who conduct in-house research studies. FWSIOBS-80108 June 1980 GRAVEL REMOVAL STUDIES IN ARCTIC AND SUBARCTIC FLOODPLAINS IN ALASKA Technical Report Woodward=ClydeConsultants 4791 Burlness Park Blvd., Suite 1, Anchorage, Alaska99503 Contract Number FWS-14-16-oo08-970 ' Norval Netsch, FWS Project Officer Water Resources Analysis Project Biological Services Program US. Fish and Wildlife Service 1011 E. Tudor Drive Anchorage, AK 99503 This study was funded in part by the Interagency Energy-Environment Research and Development Program Office of Research and Development U.S. Environmental Protection Agency Performed for the Water Resources Analysis Project Office of Biological Services U.S. Department of the Interior Washington, DC 20240 DISCLAIMER The opinions, findings, conclusions, or recommendations expressed in this report are thoseof the authors and do not reflect the views of the Office of Biological Services, Fish and Wild- life Service or the Office of Research and Development, U.S. Environmental Protection Agency. EXECUTIVE SUMMARY A 5-yeargravel removal study was initiatedin mid-1975 toevaluate the effectsof gravel removal from arctic and subarcticfloodplains in Alaska. The primarypurpose of the project was toprovide information that will assistresource managers in minimizing detrimental environmental effects resultingfrom floodplain gravel mining. To achievethis objective 25 ma- terial sites werestudied by a team of scientists andengineers. Two major productsof the project are a TechnicalReport which synthesizes and eval- uatesthe data collected at the sites, and a Guidelines Manual thataids theuser in developing plans and operatingmaterial sites to minimize envi- ronmentaleffects. Datafrom the 25 studysites were collected and analyzedby the follow- ingsix disciplines: RiverHydrology and Hydraulics 0 AquaticBiology TerrestrialEcology Water Qual ity e Aesthetics GeotechnicalEngineering DataAnalysis compared thePhysical Site Characteristics (drainage basin size,channel width, channel configuration, channel slope, and stream ori- gin) and theGravel Removal AreaCharacteristics (type of gravel removal method, locationof gravel removal, andage ofthe gravel removal site) with themeasured effects of mining activities. iii The generalconclusion reached was thatproper site select'ion and projectdesign facilitate gravel mining with minimal effects onthe habi- tats andfauna of floodplains. The keyto the successful mitigation of potentialdetrimental effects is to carefully matchthe material site design and operation (site location, configuration, prof i le,schedule, and rehabi I- itation)with the Physical Site Characteristics of the selected floodplain. VARIABLES INFLUENCING MIN ING EFFECTS PhysicalSite Characteristics Among thePhysical Site Characteristics, channel configuration was themost important. Potential floodplain chahge is least for a braidedriver and greatestfor a straightriver. Size of channel is an importantfactor, withthe least change to beexpected in a largesystem and thegreatest in a smallsystem (assuming equally-sized material sites). Combining these two var-iables(channel configuration and sire),gravel removal operations can be expectedto have the least effect on large braided rivers and thegreatest effect on smallstraight rivers. Otherinfluencing Physical Site Characteristics, which are related to configuration and size,are the availability and sizeof unvegetated gravel bars,floodplain width, and the distance that can be maintainedbetween the miningsite and theactive channel. For example, in a smallstraight river systemthe floodplain is narrowand gravel bars are neither plentiful nor large. Thus, toextract gravel, either a significantlength of active flood- plain or theadjacent inactive floodplain and terrace mustbe disturbed.In thelatter case thenarrowness of the floodplain forces the operation to closelyencroach upon theactive channel. In large river systems these problems can beless significant because gravel bars are larger and, if the inactivefloodplain or terraceare used,the wider floodplain allows mainten- ance of a broaderundisturbed buffer zonebetween the material site and activefloodplain. Gravel Removal AreaCharacteristics All ofthe Gravel Removal AreaCharacteristics were found to signifi- cantlyinfluence the effects of gravel mining. The location of thematerial siterelative to the active channel is considered to bethe most important factor. Whethera materialsite is scraped or pit-excavated is important, butoften pits are located away from an activechannel, avoiding the types ofchanges that can beassociated with scraping in active floodplains. The majoreffects of pit sites located in inactive floodplains and terracesare the loss ofvegetated habitat, the possibility for the occur- renceof fish entrapment, a change inthe appearanceof the floodplain, and long-termdelay in the re-establishment of predisturbanceconditions. Where pitsites are situated close to active channels, particularly on the inside bends in meanderingsystems, the possibility exists for diversion of the channelthrough the pit, eventually forming a channelcutoff in the meander. Thishighlights the importance of providing a bufferbetween the material site and theactive channel. Where pitsites are of suitable size, of suffi- cientdepth, and havecontoured perimeters, they can increase local habitat diversity and provideconditions suitable for fish and variousspecies of terrestrial fauna. Scrapedmaterial sites in active floodplains have minimal effects onthe floodplain environment when onlyexposed gravel bars are excavated abovethe water level, and when slope and contoursare maintained (resew blingthose of natural bars). Removal ofvegetated areas or banks, which resultsin decreasedlateral stability of active channels or allows waterto spreadover a largearea, isnot desirable. Decreased water depth'and veloc- ityincreases sedimentation rates, alters water temperature, and alters dissolvedoxygen levels. These changes in aquatic habitat usually affect the localdistribution andcomnunity structure of benthos and fish, The effectsof scraping in vegetated areas of inactivefloodplains and terracescan be similar to those described for pits. However, long-term closedsite will facilitatere-establishment of pre-mining vegetation con- dit ions. Ifmaterial sites are located andoperated toprevent or greatly mini- mizeeffects onchannel hydraulics, and to utilize only exposedgravel bars,the probability of major localized changes to a floodplaingenerally is greatly reduced. Where exposedgravel bars are not available or are inadequate, a tradeoffdecision between sites must be made thatweighs the potentialeffects of aquatic disturbances against terrestrial disturbances. Inthese cases, minimization of hydraulic change to active channels should beimportant in the decision -- majorhydraulic changes can have a greater long-termeffect on terrestrialsystems than the controlled disturbances associatedwith a sitelocated in a vegetatedinactive floodplain or ter- race RECOMMENDEDFUTURE S;FUD IES Duringthe present study a number ofsubject areas were identified thatshould be investigated. I. Evaluationof gravel mining from coastal and uplandsources; and, preparationof guidelines for users of these sources. These alternatives to sourceshave not been studied. 2. Evaluationof the effects of multiple sites onone river system. Such an investigationshould be aimed at determining the critical, spatial, andtemporal relationshipsof multiple sites. Gravel replenlshment rate predictionsshould be an integralpart of this investigation. 3, Severalfloodplain gravel removal sites should be investigated before,during, and after mining to assess the adequacy ofthe Guidelines Manua I . 4. Severaltopics of the Guidelines Manual shouldbe studied in detail to assesstheir adequacy, (i.e., buffers, pit design, and active channel dredg i ng 1 . vi Thisreport was submittedin fulfillment