Synthesis of Common Management Concerns Associated...

SYNTHESIS OF COMMON MANAGEMENT CONCERNS ASSOCIATED

WITH DAM REMOVAL1

Desiree D Tullos Mathias J Collins J Ryan Bellmore Jennifer A Bountry Patrick J Connolly

Patrick B Shafroth and Andrew C Wilcox2

ABSTRACT Managers make decisions regarding if and how to remove dams in spite of uncertainty surroundingphysical and ecological responses and stakeholders often raise concerns about certain negative effects regardlessof whether these concerns are warranted at a particular site We used a dam-removal science database supple-mented with other information sources to explore seven frequently raised concerns herein Common ManagementConcerns (CMCs) We investigate the occurrence of these concerns and the contributing biophysical controls TheCMCs addressed are the following degree and rate of reservoir sediment erosion excessive channel incisionupstream of reservoirs downstream sediment aggradation elevated downstream turbidity drawdown impacts onlocal water infrastructure colonization of reservoir sediments by nonnative plants and expansion of invasive fishBiophysical controls emerged for some of the concerns providing managers with information to assess whether agiven concern is likely to occur at a site To fully assess CMC risk managers should concurrently evaluate site con-ditions and identify the ecosystem or human uses that will be negatively affected if the biophysical phenomenonproducing the CMC occurs We show how many CMCs have one or more controls in common facilitating the iden-tification of multiple risks at a site and demonstrate why CMC risks should be considered in the context of otherfactors such as natural watershed variability and disturbance history

(KEY TERMS sediment management headcut aggradation reservoir erosion reservoir drawdown wells tur-bidity nonnative plants invasive fish dam removal river restoration)

Tullos Desiree D Mathias J Collins J Ryan Bellmore Jennifer A Bountry Patrick J Connolly Patrick BShafroth and Andrew C Wilcox 2016 Synthesis of Common Management Concerns Associated with DamRemoval Journal of the American Water Resources Association (JAWRA) 1-28 DOI 1011111752-168812450

INTRODUCTION

Background

The heterogeneity of implementation strategiesgeographies and characteristics of dam removals

(OrsquoConnor et al 2015) has resulted in incomplete sci-entific knowledge and predictive models of riverresponses Whereas conceptual models inform someelements of physical responses to dam removal (Doyleet al 2003 Cannatelli and Curran 2012) broadlyapplicable conceptual models to inform predictionsabout biological responses to dam removal and their

1Paper No JAWRA-15-0125-P of the Journal of the American Water Resources Association (JAWRA) Received August 7 2015 acceptedJune 3 2016 copy 2016 American Water Resources Association Discussions are open until six months from issue publication

2Associate Professor (Tullos) Biological and Ecological Engineering Department Oregon State University 116 Gilmore Hall CorvallisOregon 97331 Environmental Scientist (Collins) Restoration Center National Marine Fisheries Service National Oceanic and AtmosphericAdministration Gloucester Massachusetts 01930 Research Fish Biologist (Bellmore) Pacific Northwest Research Station US Forest Ser-vice Juneau Alaska 99801 Hydraulic Engineer (Bountry) Sedimentation and River Hydraulics Group US Bureau of Reclamation DenverColorado 80225 Research Fish Biologist (Connolly) Western Fisheries Research Center US Geological Survey Cook Washington 98605Research Ecologist (Shafroth) Fort Collins Science Center US Geological Survey Fort Collins Colorado 80526 and Associate Professor(Wilcox) Department of Geosciences University of Montana Missoula Montana 59812 (E-MailTullos desireetullosoregonstateedu)

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION JAWRA1

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION

AMERICAN WATER RESOURCES ASSOCIATION

linkages to physical responses are notably absent Asa result resource managers often face uncertaintyabout how quickly and to what extent physical andecological systems will respond to dam removal Inaddition stakeholders and managers often raise con-cerns about potential negative effects with each newproject whether or not a given concern is warrantedThese sentiments illustrate that negative effects canand do occur at some sites but can also reflect incom-plete understanding of the controlling factorsinvolved when overgeneralized to expect negativeeffects at every site Whether or not specific negativeimpacts manifest appears to be strongly influenced bysite conditions such as the hydrogeomorphic settingand the method by which the dam is removed (eginstantaneous or staged removal) (Cannatelli 2013)which offers promise that the occurrence of the man-agement concerns can eventually be predicted

Dam-removal science has increased in scope anddepth but it frequently fails to provide the insightsneeded for managers to know if and when to antici-pate negative effects Based on a recent literaturereview 586 documents related to the science of damremoval were identified but only 179 of these werefound to contain empirical information on measuredresponses (Bellmore et al 2015) This research haslargely emphasized field monitoring (eg Doyle et al2002 Kibler et al 2011 Major et al 2012) ornumerical modeling (Cui et al 2006 Cantelli et al2007 Wells et al 2007 Cui and Wilcox 2008 Downset al 2009 Konrad 2009) to advance understandingof the rates and patterns of erosion and depositionassociated with dam removal-induced sedimentpulses or on the impacts of those sediment pulses onfish (eg Allen et al 2016 plus see Doyle et al 2005for review) and benthic macroinvertebrates (egStanley et al 2002 Reneuroofeuroalt et al 2013 Tulloset al 2014) While these studies increase scientificknowledge they usually do not focus on applied man-agement issues such as identifying when a damremoval is likely to negatively affect ecosystems orinfrastructure or address regulatory engineering orsocioeconomic concerns Furthermore there is a suiteof management concerns not directly related to thestudy of sediment dynamics or biological responsesthat are largely unstudied Dams will continue to beremoved and managers will need to make informeddecisions about potential negative impacts and howto mitigate them to which science should directlycontribute Advancing dam-removal science to helpanswer management questions is therefore impera-tive and as this happens it will be equally importantfor managers to reevaluate applicable regulationsand standards of practice to ensure that they arebased on current science and are appropriate for agiven project

We investigate some of the common concerns man-agers face as they design and implement damremovals in order to (1) explicitly articulate theseconcerns and their potential negative consequences(2) identify where and how commonly these concernswere ultimately valid and (3) evaluate what condi-tions control their occurrence We define these con-cerns henceforth referred to as CommonManagement Concerns (CMCs) as outcomes thatmay require intervention but are broadly assumedsometimes incorrectly to occur at most sites TheCMCs addressed in this review are as follows (1) thedegree and rate of reservoir erosion (2) prolonged orexcessive channel incision upstream of the reservoirpool (3) downstream sediment aggradation (4) ele-vated downstream turbidity (5) impacts of reservoirdrawdown on local water infrastructure (6) nonna-tive plant colonization of former reservoirs and (7)expansion of nonnative fish Figure 1 schematicallydepicts these concerns and their typical geographicoccurrence in a watershed

Identifying CMCs

As part of the US Geological Survey John WesleyPowell Center for Analysis and Synthesis (httppow-ellcenterusgsgov accessed May 2016) dam-removalworking group comprising experts from a broadrange of disciplines (eg geomorphology water qual-ity ecology and engineering) and sectors (eg acade-mia government research institutions governmentmanagement agencies and practitioners) we identi-fied a broad suite of CMCs frequently raised in thedam-removal planning process We narrowed thisbroad set of CMCs to the seven investigated here thatare among the most commonly raised across manygeographies and project types (eg high-head vs low-head dam removals) with others (eg contaminatedsediments) briefly addressed in the Discussion

Case Study Approach

For each identified CMC we evaluated their rele-vance at dam-removal sites with available data ofadequate spatial andor temporal resolution Becausedam removals are often not thoroughly studied andthe results of many dam-removal studies are notwidely disseminated in publicly available literaturethe analysis of each CMC was based on data orinformation from a relatively small number of sitesMoreover because most dam-removal studies onlymonitor a small set of physical or biologicalresponses we were unable to evaluate all sevenCMCs at all of the sites Random sampling or

JAWRA JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION2

TULLOS COLLINS BELLMORE BOUNTRY CONNOLLY SHAFROTH AND WILCOX

FIGURE 1 Illustration of Common Management Concerns across a Catchment


SYNTHESIS OF COMMON MANAGEMENT CONCERNS ASSOCIATED WITH DAM REMOVAL

stratification of sites was not possible given the pau-city and inconsistency of data available to assesseach CMC

We identified candidate sites (Figure 2 SupportingInformation Table A1) henceforth referred to as casestudies for each CMC by querying a recently pub-lished database (Dam-Removal Information Portal)(Bellmore et al 2015) and by searching technicalreports and gray literature The database containsbasic information from 179 scientific studies publishedbetween 1977 and 2014 that measure physical andorecological responses to 130 different dam removalsacross the United States (US) and abroad From eachof these studies the database contains information on(1) the physical water quality and biological responsemetrics measured (2) the type of experimental designemployed as well as the duration and frequency of

sampling and (3) the characteristics of the dam andits removal (eg dam height location and year ofremoval) In addition to the Bellmore et al (2015)database we also identified candidate sites by consult-ing with working group members and informallyquerying networks of practitioners engineers and sci-entists working in the science practice and regulationof dam removals These impoundments referred toherein as reservoirs represent a range of sizesremoval strategies and locations (Supporting Infor-mation Table A1) Despite biases of geography andliterature availability in the data the 65 case studiesthat were selected reasonably represent (SupportingInformation Table A1) the geography of damremovals within the US plus 10 international loca-tions Below we separately present findings for eachof the seven CMCs

TX

CA

MT

AZ

ID

NV

NM

CO

OR

UT IL

WY

KS

IANE

SD

MN

ND

OK

FL

WI

MO

WA

GAAL

MI

AR

IN

LA

PA

NC

NY

MS

TN

VAKY

OH

SC

ME

WV

VT

MD

NH

NJ

MA

CT

DE

RI

0

1 - 25

26 - 50

51 - 75

gt75

Shading Represents Numberof Dams Removed Per State(American Rivers 2014)

Number of Common Management Concerns Evaluated per Dam Removal Site

1 2 3 4 5 6

FIGURE 2 Distribution of Case Studies Analyzed and Numbers of Dams Removed by State In addition to sites shown on mapten international sites were evaluated for a single Common Management Concern (excessive channel incision) including one site in

Australia one site in Taiwan and eight sites in Canada



EVALUATING THE CMCs

Degree and Rate of Reservoir Sediment Erosion

Characterizing the Concern There are twomanagement questions that are central to many damremovals (1) How much of the sediment impoundedwithin a reservoir will erode and (2) How quicklywill the eroded sediment move through the down-stream river corridor (eg Downs et al 2009Sawaske and Freyberg 2012 MacBroom and Schiff2013) From a more practical perspective will reser-voir erosion be slow and incomplete leaving behindexposed impoundment sediment that can be perceivedas a ldquostinking mudflatrdquo from which sediment bleedsout over time or will erosion be rapid and completesuch that fluvial forms and processes are swiftlyreestablished The answer to these questions informsmany other ecological and physical elements of damremoval including several other CMCs that we exam-ine in this article For example the pace and volumeof reservoir erosion influence downstream aggrada-tion and turbidity reservoir incision dynamicsgroundwater impacts revegetation of former reser-voir reaches and responses of downstream biotaQuestions surrounding reservoir erosion also influ-ence public perceptions of project success and informmanagement of reservoir areas including the selecteddam-removal style (gradual vs rapid) and whethersediment excavation or other mitigation measuresare implemented to reduce downstream transportsuch as stabilizing banks in exposed reservoir reaches(eg Downs et al 2009)

Approach Rather than compiling findings fromdam-removal case studies as we do for other CMCsin this article we instead take advantage of and sum-marize recently published syntheses of reservoir ero-sion following dam removal with the intent of layingthe groundwork for discussion of subsequent CMCs

Key Findings Based on their analyses of reser-voir erosion results from 12 predominantly low-head(2-14 m high) dam removals from across the northernUS Sawaske and Freyberg (2012) highlighted theinfluence of reservoir sediment characteristics (grainsize cohesion and spatial variability) and removalmethod on the evolution of reservoir sediment Theyfound that as of one-year post removal the percent ofthe original reservoir sediment volume eroded rangedfrom less than 10 at sites where structures wereconstructed to limit erosion (LaValle Dam BarabooRiver Wisconsin) to approximately 65 where nosediment management was implemented (Merrimack

Village Dam Souhegan River New Hampshire) Inaddition they found that greater fractions of sedi-ment tended to be retained within reservoirs wheredeposits were predominantly fine and consolidated orcohesive Conditions favoring larger (gt15) amountsof retained sediment occur when the ratio of the aver-age width of the reservoir sediment deposit to chan-nel width was gt ~25 or where dam removal wasphased rather than instantaneous Major et al (2016)synthesized post-dam removal reservoir erosion find-ings for 20 cases including some of those assessed bySawaske and Freyberg (2012) along with more recentlarge dam removals Major et al (2016) emphasizedthe role of dam height and removal strategy on reser-voir erosion and found for small and large dams thatthe rate and magnitude of reduction in base levelstrongly influences the rate and magnitude of reser-voir erosion Findings generally indicate that post-breach hydrology is of limited influence at least ini-tially on the rate of reservoir sediment evacuationbecause erosional processes are dominated by thelowering of base level following dam removals (Ran-dle et al 2015 Major et al 2016) though someexceptions exist where event-based erosion dominatedand thus post-removal hydrology drove evacuationrates (eg Peck and Kasper 2013 Harris and Evans2014) Post-removal hydrology is of particular signifi-cance in achieving the final ldquoequilibriumrdquo extent oflateral reservoir erosion and can affect both verticaland lateral progression of reservoir erosion in reser-voir deposits with predominantly cohesive sedimentor ephemeral hydrology

Condit Dam on the White Salmon River Washing-ton which was breached in 2011 by blasting a hole inthe base of the 38-m high dam illustrates how damheight and removal strategy can trump grain size asan influence on reservoir sediment erosion Despite asubstantial fraction of fine sediment in the reservoirdeposit which Sawaske and Freyberg (2012) sug-gested as a key potential factor in inhibiting reservoirerosion erosion by landsliding and mudflows at Con-dit Dam resulted in evacuation of about one-third ofthe reservoir sediment by one week after the breachand about 70 of the total reservoir sediment (ie13 million m3 of the original 18 million m3 of storedsediment) as of one year after dam removal (Wilcoxet al 2014) The removal of Elwha and Glines Can-yon dams on the Elwha River Washington between2011 and 2014 highlights how even for large damsphased removal strategies can initially result in rela-tively slow rates of reservoir sediment release whilethe river erodes and redistributes sediment deltadeposits that had not yet reached the dam at the timereservoir dewatering began (Randle et al 2015)However once the sediment from upstream deltas



reached the dam sites the multi-year phased removalon the Elwha River ultimately released a sedimentquantity many times greater than the averageannual load and exceeded more than 50 of thereservoir-deposit volume Although the implicationsof reservoir erosion may be greatest for dams thatstore large sediment volumes reservoir erosion is aconcern across the spectrum of dam removals (egMacBroom and Schiff 2013) highlighting the needfor ongoing evaluation and improvement of predictivetools to inform dam removal CMCs

Excessive Channel Incision Upstream of Reservoirs

Characterizing the Concern Erosion of reser-voir sediments can occur by a variety of mechanisms(eg Cantelli et al 2007) but typically entails somedegree of channel incision in the former reservoirthat if ldquoexcessiverdquo or prolonged can cause a range ofmanagement problems Here we evaluate CMCsassociated with excessive or prolonged channel inci-sion which we define as follows (1) post-removalincision which may undermine infrastructure suchas bridge piers or increase sediment loads (2) head-ward incision upstream from the former reservoirpool which may result in bank erosion or unintendedimpacts to adjacent habitat or property or (3) pro-longed incision that takes years to occur affectinghow quickly dam-removal goals are achieved andpotentially creating a barrier to aquatic species pas-sage

Approach We examined the magnitudeupstream extent and rate of channel incision withinreservoir sediment deposits after dam removal Weidentified 38 sites via queries of the Bellmore et al(2015) database supplemented with information fromtechnical reports monitoring data and discussionswith project managers andor scientists The monitor-ing methods commonly used to document channelincision in the reviewed studies (Supporting Informa-tion Table A1) were longitudinal profile andor cross-section surveys supplemented with time-lapse cam-eras aerial photography and field inspections Weuse the term ldquoheadcuttingrdquo to describe the process ofupstream progressing channel incision and ldquoheadcutrdquoor ldquoknickpointrdquo to represent the discrete locationwhere there is an abrupt change in slope betweenthe downstream reach that is in the process ofadjusting to the new base-level control and theupstream reach that has not yet incised (Leopoldet al 1964) For cases where data were available wecomputed the dimensionless ratio of the length ofheadcut progression to the length of reservoir sedi-ment deposition

Of the 38 cases evaluated for channel incision 12were phased dam removals 13 were consideredinstantaneous because reservoir drawdown associatedwith dam removal happened within hours to a fewdays and 13 cases involved an unplanned dam fail-ure or breach (ldquoaccidentalrdquo) The height of dams eval-uated (Supporting Information Table A1) range from1 to 64 m reservoir sediment volume ranged from afew tens of cubic meters to tens of millions of cubicmeters and sediment distributions were mostly rep-resented by noncohesive coarse (sands and gravels)sediment A cohesive sediment deposit was present atBrewster Dam (Straub 2007) and within reservoirdeposits behind Elwha and Glines Canyon dams(Randle et al 2015) Relative to reservoir capacitythere was a range of cases from very little stored sed-iment to reservoirs completely full of sediment attime of removal Three sites had ephemeral flow (Din-ner and Maple Creek dams Oregon Wellington DamAustralia) whereas the others had perennial dis-charge One site had tidal influence but the studyarea was located beyond the extent of the tidal back-water (Lake Charles VCU mdash Rice Center Dam Virgi-nia)

Key Findings The case studies generally con-formed with conceptual stages of channel incisiondescribed in the literature for the vertical response todam removal in the upstream impoundment (Doyleet al 2002 Cannatelli and Curran 2012) The mag-nitude of incision within the reservoir sedimentdeposit was generally equivalent to the thickness ofthe deposit above the pre-dam river bed for any givenlocation The post-removal channel stopped incisingwhen the pre-dam gradient was achieved This gradi-ent typically coincided with the pre-dam river bedlocation composed of an armored river bottom withrelatively coarser sediment than the reservoir sedi-ment deposit Exceptions were documented on theElwha River where within a matter of weeks theriver incision in Lake Aldwell formed a new channelacross the valley from the pre-dam channel Duringinitial drawdown at Lake Aldwell the river was flow-ing on the opposite side of the valley from the pre-dam channel location As a result during reservoirdrawdown the river incised into a former terrace witha dense network of large tree stumps During post-removal floods the river laterally migrated backtoward the pre-dam alignment in most locations Fur-ther the delta was composed of cohesive sedimentthat initially limited lateral erosion duringeight months of phased drawdown Two years postremoval when the first large floods (5- to 20-year fre-quency) occurred the river began to laterally migrateinto the cohesive delta sediment back toward the pre-dam alignment In total the river incised 56 km



upstream of the Elwha Dam which was 20 fartherthan the estimated upstream reservoir extent Uponremoval of Dinner Creek Dam and Maple Gulch Damin Oregon the initially rapid headcuts (several mh)stalled when they encountered a former bedrock val-ley wall that confined the pre-dam channels (Stewart2006) At Dinner Creek Dam the second flood fourmonths post removal resulted in channel erosionthrough an adjacent floodplain forest However atMaple Gulch Dam the discharge was intermittentand the channel remained perched above the originalriver bed at the conclusion of the study

Few studies provide evidence of incision progress-ing below the pre-dam river bed However this didoccur at Union City Dam Connecticut (Wildman andMacBroom 2005) where deep incision occurred dueto an exposed sanitary sewer pipe with rock riprapthat caused local downstream scour Once the pipefeature failed (five years post removal) the headcutprogressed upstream about 05 m below the originalriver bed This resulted in a total incision length of04 km extending slightly farther upstream of thereservoir sedimentation effects

Research from 10 of the 38 sites documented thatincision progressed upstream beyond initial expecta-tions while another 10 studies documented that theextent of incision was within the identified reservoirbackwater or sedimentation effects Two of the studieshad minimal sediment deposits that did not extend tothe upstream end of the reservoir so determining theheadcut location was not applicable At Condit Damproject managers noted the knickpoint migrated a con-siderable distance upstream of the established projectboundary but the expected upstream extent of inci-sion was not estimated before removal (PacificCorpApril 2015 personal communication) The extent andspeed of downcutting of the riverbed in the upperreaches of the reservoir following the breach of ConditDam (Wilcox et al 2014) exceeded expectations andcaused a loss of salmon redds (ie nests) during theyear of dam removal (Engle et al 2013) At ElwhaDam incision exposed the pier foundation of an activehighway bridge originally expected to have net aggra-dation from large sediment loads being released fromupstream removal of Glines Canyon Dam (Randleet al 2015) Eight sites were associated with histori-cal dam failures in Canada where knickpoints contin-ued up to three times beyond the boundary ofestimated reservoir impoundments The knickpointswere approximately 05 m in height and similar in sizeto nearby riffle features (Amos 2008) There were noidentified consequences of the headcut migratingbeyond the reservoir impoundment at these sites overa period of years to decades

Five studies stopped monitoring before the incisionprogressed to the upstream end of the reservoir and

12 studies did not include monitoring in theupstream-most portion of the reservoir Possibleexplanations are lack of safe access limited monitor-ing budgets or lack of perceived consequences Addi-tionally it can be technically difficult to determinethe upstream extent of reservoir sediment Further-more it can be challenging to determine the exactlocation of a migrating headcut as it decreases inmagnitude and in some cases looks similar to natu-rally occurring steep cascades or riffles Increasedsedimentation and vegetation in the delta can alsoextend the distance of upstream sedimentation overtime (Morris and Fan 1998) Using complementarymethods may help technical staff provide or refinesedimentation extent estimates to managers for deci-sion making These methods may include pre-damtopography (rare for small dams or sites constructedpre-1900) photos and maps projecting estimated pre-dam slopes from the dam site upstream looking atdepositional features that appear finer than adjacentsediment features in upstream and downstream allu-vial reaches and sediment probing or drilling investi-gations

The case studies illustrate that managers canexpect rapid (hours to weeks) initial incision inresponse to base-level lowering This is followed byslower (weeks to years) subsequent event-driven inci-sion when high flows are capable of eroding coarsersediments or sediments more distal from the newlyformed channel (Pearson et al 2011 Major et al2016) The subsequent incision from event-drivenperiods occurs during higher flow seasons of the yearas proposed by Cannatelli and Curran (2012) withlimited incision between events Interestingly thedocumentation available did not indicate that delayedor prolonged incision in itself caused any adverse con-sequences in achieving dam-removal goals Oneexplanation may be that slower rates of sedimentevacuation into the downstream channel are desiredand considered a benefit For example at BrewsterDam the knickpoint took approximately a decade toprogress upstream Straub (2007) noted that it can bebeneficial to remove a dam in phases for some set-tings where phased removal can reduce possible envi-ronmental effects by allowing the impoundedsediment to slowly move downstream and a stablestream and re-vegetated floodplain to form upstream

The rate of upstream progression of channel inci-sion varies with degree of reservoir sedimentationrate of reservoir drawn down (phased vs instanta-neous) and erodibility of reservoir sediment Thefastest progression of channel incision occurred whenremovals were instantaneous and reservoir sedimentswere noncohesive (Pearson et al 2011 Major et al2012 Bountry et al 2013 Tullos and Wang 2014)Channel incision temporarily stalled or slowed when



the river encountered newly exposed infrastructureincised down to resistant pre-dam terraces or inter-cepted coarser delta sediment at the upstream end ofthe reservoir These instances required managementaction to remove or modify the infrastructure a largeflood capable of eroding more resistant delta sedimentand bed layers or a channel-widening phase thatallowed the river to migrate off the terrace to theoriginal stream bed location The slowest rates ofheadcut progression (months to years) occurred atWellington Dam and Maple Gulch Dam due toephemeral hydrology at Brewster Creek and BoulderCreek ldquoupper damrdquo due to cohesive reservoir sedi-ment and at five sites where dam removal wasphased over a period of months to years (Orr et al2006 Stewart 2006 Straub 2007 Burroughs et al2009 Neave et al 2009 Randle et al 2015) On theElwha River tributaries within the reservoir experi-enced lagged channel incision due to less streamflowrelative to the main channel or becoming abandonedabove the main channel during the incision phase

Thirty cases documented the upstream extent ofincision which ranged from 02 to 56 km and wasassociated with dam heights ranging from 1 to 64 mFifteen sites recorded incision extent to be less than1 km 9 sites had incision that extended 1 to 3 kmwhile the remaining 12 sites had incision thatextended between 3 and 56 km upstream of the damFour sites had dams greater than 30 m in heightand as would be expected these dams (Condit Bar-lin Elwha and Glines Canyon dams) were associatedwith larger incision extents ranging from 27 to56 km However the extent of incision for damsbetween 0 and 10 m was variable with 13 damsextending 0-1 km upstream 6 extending 1-3 km and5 sites extending 3-5 km upstream The pre-damslope divided by the dam height was found to be agood way to estimate the extent of upstream incisionat some sites including those that lacked channelobstructions such as bedrock outcrops but not at allsites Potential explanations for sites with poor corre-lations include incorrect assumptions of pre-damslope or complex pre-dam profiles with slope breaksor bedrock outcrops

In some cases post-removal sediment managementwas performed to slow or stop channel widening orgrade control was placed at the dam site to limit ero-sion In the cases reviewed unanticipated storageand fining of new sediment occurred once the damwas removed because of the replacement of the base-level control which in one case impacted the pro-jectrsquos ability to meet restoration goals (Greene et al2013) Use of a grade control may only be warrantedwhen excessive downstream channel incision hasoccurred that could propagate upstream or conse-quences of additional sediment release are not

tolerable Additionally use of bank stabilization maybe warranted to prevent lateral migration where crit-ical infrastructure or property is at risk Howeverany such implementation of bank protection soonafter dam removal should proceed with cautionbecause if the river has not had enough time toadjust its slope and width during post-removal highflows the bank protection may be undercut or out-flanked

Downstream Sediment Aggradation

Characterizing the Concern While the restora-tion of sediment continuity is a benefit of some damremovals the deposition of sediment (ie aggrada-tion) downstream of dam removals can produce man-agement concerns for aquatic ecosystems and humanuses (eg infrastructure) Aggradation can influenceecosystems by directly burying organisms (egspawning redds) and altering aquatic and riparianhabitats (eg habitat homogenization by reducingthe variability of bed elevations) Potential effects ofaggradation on human uses include increases in themagnitude and frequency of overbank flow (ie flood-ing) as well as adverse impacts to water supply (egif groundwater-surface water exchange is altered or ifdiversion structures are affected) and recreationaluse (eg if river access points are impacted) From amanagement perspective it would be helpful to knowhow much of the sediment eroded from the reservoirwill be transported downstream where depositionwill occur how much will be delivered to the nextwater body downstream and for how long depositionwill persist However quantifying patterns of deposi-tion is complicated by the spatially and temporallydynamic nature of deposition processes Conse-quently understanding physical vs ecological man-agement concerns associated with sedimentdeposition may require alternative monitoringapproaches For example cross-section-averaged val-ues of channel aggradation may be relevant to inves-tigating potential changes in stage-dischargerelationships and effects on overbank flooding yetsuch values may obscure patterns of aggradation atscales relevant to aquatic organisms (eg betweenbars and pools Zunka et al 2015)

Approach Post-removal changes in downstreambed elevation based on comparisons of pre- and post-removal topography collected using a range of surveymethods have been documented in numerous dam-removal studies The distances downstream ofremoved dams for which aggradation results havebeen reported are not standard due to differences instudy designs varying distances to downstream



confluences and variations in downstream morphol-ogy and deposition potential Duration of data collec-tion is also inconsistent although most data arelimited to within one-year post-dam removal Wetherefore report findings on downstream aggradationas of one-year post-dam removal for six case studiesall except one of which are in the Pacific Northwest(Supporting Information Table A1) recognizing thatimpacts frequently diminish over time and thus long-term responses will likely vary from those reportedbelow

Key Findings For some of the dam removalsevaluated the magnitude and duration of down-stream sediment deposition following dam removaltended to be most influenced by proximity to thedam ie aggradation was greatest near the damFollowing removal of Savage Rapids Dam from theRogue River Oregon filling of pools immediatelydownstream of the dam was detected in the yearafter removal (Bountry et al 2013 Tullos et al2014) Aggradation of downstream riffles was limitedalthough sediment did accumulate immediatelydownstream along the intakes of the pumping stationconstructed to replace the diversion dam Clogging ofthe intakes required small volumes (~1500-4500 m3)of sand and gravel to be excavated in the first twosprings following dam removal before irrigation sea-son but no action was needed in subsequent years(Bob Hamilton USBR personal communication)

Likewise following removal of Marmot Dam on theSandy River Oregon downstream aggradation pat-terns were strongly influenced by proximity to thedam and by the coarse grain size of the reservoirdeposit Immediately downstream of the dam the bedaggraded in a sediment wedge that tapered from amaximum thickness of 4 m to zero thickness (ieback to the pre-removal channel bed) 13 km down-stream of the dam site during the first year afterremoval This sediment wedge represented about one-third of the sediment eroded from the reservoir in thefirst year following removal (Major et al 2012) Theremainder of the eroded reservoir sediment traveleddownstream of this initial wedge where the rivertransitions into a steep and confined reach in whichsediment aggradation was generally limited andrestricted to pools Downstream of the gorge (9 kmfrom the dam) in a reach where managers had ini-tially been concerned about potential aggradationimpacts on salmon redds minimal aggradation wasobserved (Major et al 2012)

A riverrsquos transport capacity which depends onchannel slope discharge grain size and confinementis also a primary control on the magnitude and dura-tion of downstream sediment deposition and in somecases can trump the effects of proximity to the dam

Removal of Condit Dam exposed a 53-km reachbetween the dam and the Columbia River to sedimentdeposition and channel aggradation In a steep andconfined reach downstream of the dam rifflesreturned to near pre-removal elevation within15 days of breaching (Wilcox et al 2014) a conditionthat persisted as of one year post removal Down-stream in a less-confined reach influenced by thebackwater effect of the Columbia River large-magni-tude (3-6 m) and persistent (as of nine months post-breach and likely beyond) bed-elevation increasesoccurred following dam removal (Colaiacomo 2014)From a management perspective the primary issueraised by aggradation of the lowermost White SalmonRiver was temporary loss of access to a tribal fishingsite associated with filling of a deep pool

After removal of Milltown Dam on the Clark ForkRiver Montana downstream aggradation showedsubstantial spatial variability that reflected transportcapacity rather than proximity to the dam Repeatcross-section surveys in a high transport-capacityreach extending from 2 to 6 km downstream of thedam indicated minimal topographic change as of oneyear after dam removal Sixteen km downstream inan unconfined reach with lower transport capacityaggradation on the order of 1 m was estimated onbars within the first year following dam removalAnecdotally this aggradation led to filling of irriga-tion ditches and modified aquatic habitat

Other dam removals show a mix of controls ondownstream aggradation Removal of Merrimack Vil-lage Dam released sediment into a short (~05 km)reach of the Souhegan River in New Hampshirebefore it enters the Merrimack River The MerrimackRiver influences hydraulics and deposition in thislowest portion of the Souhegan River (Pearson et al2011) analogous to the White Salmon Riverrsquos conflu-ence with the Columbia River In the first severalweeks after dam removal bed aggradation averaging21 m and as much as 32 m occurred in the Souhe-gan River downstream of the former dam This aggra-dation resulted in a steeper river gradient whichincreased transport capacity that subsequentlyincised through the new deposits As of one-year postremoval average net aggradation in the ~05 kmdownstream of the dam was 024 m (maximum15 m) although in some locations the channel hadincised to a lower elevation than the pre-removal bed(Pearson et al 2011) Bed-elevation changes on theSouhegan River following dam removal reflected ahybrid of sediment transport associated with high-flow events and inter-event sand transport and depo-sition associated with backwatering of the MerrimackRiver (Pearson et al 2011)

On the Elwha River where the largest-ever dam-removal volume of reservoir sediment is being released



into a downstream river system downstream of theformer Elwha Dam and Lake Aldwell in the ~7-kmldquolower reachrdquo one-year post-removal aggradation wasgenerally on the order of 01-05 m in the channel and039 m (043 m) in floodplain channels (East et al2015) Greater aggradation was observed in the secondyear of dam removal on the Elwha River when a largesediment pulse from the upper reservoir Lake Mills(mobilized by removal of Glines Canyon Dam) moveddownstream The resulting aggradation included wide-spread bed-elevation increase of ~1 m in the lowerreach accompanied by new bar formation andincreased braiding and greater sediment thicknessesaccumulating in former pools (East et al 2015) Thisaggradation (and continued bed load transport) in thelower Elwha River temporarily impaired a water sup-ply intake for the city of Port Angeles which was miti-gated by mechanical sediment removal in the vicinityof the intake and construction of additional pumpsOverall effects on water supply infrastructure how-ever were limited as a result of pre-removal mitigationefforts (Bountry et al 2015) Once substantial erosionout of Lake Mills (ie past Glines Canyon Dam) beganaggradation levels in the ~14-km ldquomiddle reachrdquobetween Glines Canyon Dam and Lake Aldwell weresimilar to those seen in the lower reach despite a stee-per (07-08) gradient in the middle reach Manage-ment implications of this aggradation includedflooding of campgrounds and bank erosion whichwould be expected in a sediment starved fluvial reachafter re-introducing bed load (Bountry et al 2015) Asthe sediment wave (largely originating from the upperreservoir Lake Mills) passed the middle and lowerElwha River reaches began to undergo incisionthrough the new sediment deposits Downstream inci-sion was already apparent as of two years into theremoval of the Elwha dams (East et al 2015)

As the cases above suggest (see also Major et al2016) downstream sediment deposition followingdam removal tends to be influenced by proximity tothe dam the riverrsquos transport capacity and thedownstream distance to the next larger river orwater body the overall effect can be transient (lessthan one year) persistent (greater than one year)or longer term (gtfive years) The ratio of the volumeof stored reservoir sediment to the riverrsquos averageannual sediment load denoted here as V can bepredictive of downstream aggradation where loweror higher V values are associated with smaller orgreater downstream impacts respectively (USBR2006) However the data needed to estimate Vmay be unavailable in many rivers potentiallyrestricting its use for predicting aggradationpotential

To evaluate if ecologically significant aggradationhas occurred after dam removal measuring bed

adjustments in terms of bed relief defined as the dif-ference in elevation along a cross section between thebottom of a pool and the top of a bar (Zunka et al2015) can provide an assessment of habitat variabil-ity and homogenization Bed relief can be normalizedby the 90th percentile of observed pre-dam-removalrelief values within a reach providing a dimension-less metric for assessing aggradation This type ofanalysis could be categorized by channel units toillustrate if only low-energy pools and backwaterareas have filled with sediment or additionally higherenergy hydraulic controls have also aggraded thatcould increase flood stage

Elevated Turbidity

Characterizing the Concern Suspended sedi-ment is a naturally occurring and necessary compo-nent of many biophysical processes yet unnaturallyelevated concentrations can have deleterious ecologi-cal effects and consequences for human uses (USEPA2006) For example fish can suffer a range of directand indirect effects on both behavioral (eg inabilityto see prey) and physiological (eg impaired gills)systems (Kemp et al 2011) Human use impactsfrom elevated turbidity include recreation estheticsand safety as well as increased drinking-water treat-ment costs (USEPA 2006) In addition 30 of the 32states that have numeric criteria for regulating sedi-ment in surface waters prescribe criteria for turbidity(USEPA 2006) and thus dam-removal practitionersand regulators are concerned about exceeding stateturbidity regulatory standards and the impacts thosestandards are designed to avoid At most damremovals with stored sediment some proportion ofthe released sediment is fine-grained and willincrease the suspended-sediment load downstreamat least temporarily (eg Major et al 2012 Bountryet al 2013)

Approach There are a limited number of pub-lished dam-removal studies that have quantitativeanalyses of turbidity data (lt20) and some of thesepresent data from the same sites (Bellmore et al2015) We restricted our analysis to projects withhigh temporal resolution turbidity data (le1 h)upstream and downstream of the removal for at leastone month before and after project implementationFour sites from the Pacific Northwest US one fromNew England and two from the Mid-Atlantic USmet these criteria (Table 1) At each site the pairedturbidity data were collected by the US GeologicalSurvey using comparable instruments methods andsampling frequencies (Chaplin et al 2005 Majoret al 2012 Magirl et al 2015 C Anderson and W



TABLE

1TurbidityDataState

CriteriaandOccurren

ceCharacteristics

forSev

enDam-R

emov

alSitesFormazinNep

helom

etricUnits(FNUs)

are

similarto

Nep

helom

etric

TurbidityUnits(N

TUs)

totheex

tentthatbothmea

sure

scattered

lightat90degfrom

theinciden

tlightbea

mHow

everthey

are

mea

suredusingdifferentwavelen

gthsof

light

tocomply

withdifferentregulatory

standard

s(ISO

7027andEPA

method

1801resp

ectively)For

moreinform

ation

seehttporwaterusgsgov

grapherfnuhtm

l

Dam(s)

RiverSta

te

USGS

Gage

Number

Turbid

ity

Data

Sta

teThresh

old

(ST)

Tmax1(

)Tdur2(

)

Above

Below

Unit

Freq3

Criteria

4ST56

Above

Below

Above

Below

Pre

Post

Pre

Post

Pre

Post

Pre

Post

Vea

zieGreatWorks

Pen

obscotME

01036390

FNU

60

Non

e25

1160

1240

97

102

Sim

kins

Patapsco

MD

01589000

01589025

NTU

15

150NTU

150

15

1047

51

1247

012

017

SavageRapids

Rog

ue

OR

14361050

14361180

FNU

15

nat+10

64

188

1724

1207

3292

03

123

109

145

Marm

otSandyOR

14136500

14137002

FNU

1530

nat+10

143

4336

7483

3497

7483

473

82

315

119

Chiloq

uinSprague

OR7

11501000

11502500

FNU

15

nat+10

176

477

341

295

290

227

44

59

14

Goo

dHop

eMillCon

odog

uinetPA

01570064

01570078

NTU

15

Non

e29

879

1272

3793

4828

78

106

941

692

Elw

haG

lines

Canyon

Elw

haWA8

12044900

12046260

FNU

15

nat+5NTU

922

205

gt6091

532

gt7545

68

74

143

966

1Tmax=(m

axim

um

pea

kvalueST)100

2Tdur=(duration

ofSTex

ceed

ancem

onitoringduration

)100

3Samplingfreq

uen

cyin

minutes

TheMarm

otsite

haddifferentsa

mplingfreq

uen

cies

forthesensors

abov

eandbelow

thedam

4See

httpw

aterep

agov

scitech

swguidancestandard

swqslibraryindex

cfm

accessedJuly

302014

5Basedon

upstream

record

forallsitesex

ceptPen

obscotwhichon

lyhasadow

nstream

record

withalongpre-rem

ovalmon

itoringperiod

6ldquoN

aturalrdquo

conditionsare

estimatedbythe90th

percentile

value

ifnostate-w

idecriteria90th

percentile

isused

7Dow

nstream

gageis

onWilliamsonRiver

below

Spragueconfluen

ce

8Turbidityinstru

men

tsherehaveop

eration

alranges

upto

1500FNU

(Figure

3c)values

abov

e1200FNU

are

considered

unreliable

(Curranet

al2014)

9When

naturalis

50NTU

orless

(USGSreports

FNU

atElw

haproject

gages)



Banks personal communications) Only three of theseven sites had pre- or post-removal data collected formore than one year so our analyses evaluate rela-tively short-term acute and likely maximum turbid-ity impacts from dam removal

We compared observed turbidities at the sevensites to applicable state turbidity standards evaluat-ing the occurrence and degree of elevated turbiditypre- and post-removal by measuring estimated statethreshold (ST) exceedance magnitude and durationrespectively as follows

TmaxethTHORN frac14 ethmaximum peak value=STTHORN100

TdurethTHORN frac14 ethduration of ST exceedance

monitoring durationTHORN100

Of the five states where the sites are located onehas absolute numeric criteria and two have numericcriteria indexed to ldquonaturalrdquo conditions for the stream(Table 1) Neither of the state standards that areindexed to natural conditions prescribe methods fordetermining them so we estimated natural condi-tions as the range of values below and including the90th percentile value in the upstream turbidity timeseries (ODEQ 2014) This approach may be less com-mon than using contemporaneous readings as a con-trol instrument above the project site as the ldquonaturalrdquocomparison (eg Major et al 2012 Bountry et al2013) but our approach facilitates comparisonsbetween observations at the downstream impact loca-tion and the full record of natural variability at theupstream control

Two sites are in states with no turbidity standardsConodoguinet Creek (Pennsylvania) and the Penob-scot River (Maine) For the Conodoguinet site wecompared observed turbidities to natural conditionsdefined as above the 90th percentile value of theupstream turbidity record At the Penobscot Riverdam removals where there is no turbidity recordupstream we estimated natural conditions as the90th percentile value of the downstream record bene-fitting from an extended pre-removal monitoring per-iod Our estimate may therefore be affected byparticle settling in the two upstream reservoirs beforethe Penobscot dams were removed However webelieve this effect is negligible because the reservoirstrapped very little suspended sediment as a resultof basin physiography impoundments furtherupstream local hydraulics and reservoir operations(Collins et al 2012)

Key Findings Not surprisingly contemporane-ous turbidity measurements upstream and down-stream of dam-removal sites frequently show larger

downstream turbidities in the days and months fol-lowing dam removal (Figure 3) Indeed the data weexamined show that the largest turbidity valuesdownstream of dam removals are commonly at leastan order of magnitude higher than the estimated ST(ie Tmax gt 1000) Yet this is also true during highflows at the gages upstream of these sites andor atthe downstream gage during high flows in the pre-removal period indicating that turbidity peaks asso-ciated with dam removals are generally within therange observed during storm events (Table 1 Fig-ures 3a and 3b) In addition the relative magnitudesof Tmax for upstream and downstream sites duringstorm events are similar for their respective pre- andpost-removal periods and the directions of changefrom pre- to post-removal are the same (Table 1)Tmax values computed for the Elwha River removalsare artificially low because the nephelometer instru-ments used to measure turbidity there have an opera-tional range up to 1500 FNU (Figure 3c) and valuesabove 1200 FNU are considered unreliable (Curranet al 2014) Turbidity durations above estimated ST(Tdur) also suggest storm events are a more importantinfluence on river turbidity than dam removals Formost sites Tdur values in respective pre- and post-removal periods for upstream and downstreamrecords correspond as do directions of change frompre- to post-removal (Table 1) Data from sites we didnot quantitatively analyze broadly support our obser-vations that dam removal-induced turbidity eventsare analogous to events produced naturally by stormsin their magnitude and duration (Stewart 2006Granata et al 2008 Gibson et al 2011 Marion2014)

There are two important exceptions among theseven sites we analyzed The downstream gage at theElwha River shows a clear post-dam-removal shift toprolonged elevated turbidity that is not manifest inthe upstream turbidity record and reflects site-speci-fic conditions and a phased dam-removal strategy asdiscussed below (Table 1 and Figure 3c Magirl et al2015) The other exception is the Conodoguinet Creekin Pennsylvania where the downstream gage hasprolonged elevated turbidity pre- and post-removalrelative to the estimated ST (Figure 3d) and theupstream record (Table 1) Chaplin et al (2005) sug-gest that elevated turbidity here may reflect unmea-sured inputs from an urbanized tributary andordisturbance by waterfowl recreational boaters andfisherman

Considering a large proportion of the annual sedi-ment load of many rivers is transported during just afew days of the year when flows are high (Wolmanand Miller 1960) and that many impoundmentshave low volumes of stored reservoir sediment rela-tive to the riverrsquos average annual sediment load (V)



it is reasonable that turbidities caused by damremoval would infrequently exceed those producednaturally by event flows Moreover the finer sedi-ment fractions that compose suspended load are often

not trapped effectively in the many shallow riverineimpoundments in the US (Brune 1953) Thus evenimpoundments storing multiple years of bed loadmay be storing considerably less suspended load and

FIGURE 3 Paired Upstream and Downstream Turbidity Time Series for Four Dam-Removal Sites The vertical line in each panel showsthe dam-removal start date Only overlapping periods of record for site stations are plotted Units and ordinate scales vary across sitesResults are from (a) Savage Rapids Dam (b) Simkins Dam (c) Elwha River Dams and (d) Good Hope Mill Dam The downstream recordpre- and post-removal at (d) may be affected by tributary inputs bioturbation and human uses (Chaplin et al 2005) Formazin Nephelomet-ric Units (FNU) are similar to Nephelometric Turbidity Units (NTU) to the extent that both measure scattered light at 90deg from the incidentlight beam But they are measured using different wavelengths of light to comply with different regulatory standards (ISO 7027 and EPAmethod 1801 respectively) For more information see httporwaterusgsgovgrapherfnuhtml



those materials may not be accessed en masse afterdam removal (Bountry et al 2013)

Cases where dam removal-induced turbidityexceeds storm-induced turbidity either in magnitudeor duration appear to be associated with exceptionalsituations where large impoundments storing decadesof annual sediment load are removed andor withspecific dam-removal methods For example the twoElwha River reservoirs together stored approximately100 years of annual sediment load nearly half ofwhich was fine material (lt0063 mm Warrick et al2012 Magirl et al 2015 Randle et al 2015) Largequantities of fine sediments combined with a multi-year phased removal resulted in elevated turbidityfor durations much longer than observed at othersites we examined (Figure 3c and Table 1) Anotherexample is the Condit Dam removal where the damstored approximately 100 years of annual sedimentload with a large proportion of fine sediment (35 byvolume lt0063 mm) (Wilcox et al 2014) Estimatedturbidity magnitudes downstream in the days andweeks following dam removal were at least an orderof magnitude higher than any values documentedduring storms at an upstream turbidity station overthe six months preceding and the year followingremoval (Kleinfelder et al 2012 Riverbend Engi-neering and JR Merit 2012) This occurred becauseof the large quantity of stored fines and an unusualdam-removal method an explosion at the base of thedam that facilitated rapid water and sediment drai-nage from the impoundment and ultimately resultedin hyperconcentrated flow (Wilcox et al 2014) Theseresults highlight how reservoirs with a high V andfine-grained sediment can lead to large post-removalturbidity pulses which may be mitigated by phaseddrawdown and revegetation (to stabilize reservoirsediment) or dam removal during low-flow conditionsin order to minimize sediment suspension

Drawdown Impacts on Local Water Infrastructure

Characterizing the Concern Reservoir draw-downs associated with dam removal not only causeerosion of impounded sediments but also lowering ofwater tables that may have been elevated because ofthe dam As a result communities that developedaround reservoirs and came to rely upon infrastruc-ture around the elevated water-table upstream ofdams or the associated groundwater pressure gradi-ent downstream of dams may be impacted by reser-voir drawdown Reservoir drawdown may haveadditional effects on septic systems well-water sup-ply (USBR 1997) and groundwater-dependent habi-tats (HDR 2010) We focus our review on the impactson wells in near proximity to the reservoir or those

located along the depositional zone in the down-stream river because stranded wells appear to be themost common concern around local groundwaterchanges with dam removal

Approach At each site we attempted to identifythe number of pumps and wells impacted if thoseimpacts were anticipated and investigated inadvance the costs of modifications to and replace-ments of impacted wells and pumps the distance ofthe pumps and wells to the dam site and otherpotentially relevant factors associated with theimpact of the reservoir dewatering on local waterinfrastructure However peer-reviewed literature onlocal water infrastructure is scarce which led us toseek information from engineering memos Environ-mental Impact Statements (EIS) an unpublished dis-sertation and Federal Energy RegulatoryCommission (FERC) documents associated with thecase studies In addition we contacted dam-removalproject managers to discuss their knowledge ofimpacts to wells and pumps at dam-removal sitesThe result is a review of five case studies from thePacific Northwest Intermountain West and North-east of the US

Key Findings We identified three primary sce-narios associated with impacts to local water infras-tructure The first and most common scenario waswhen the aquifer was hydraulically connected to thereservoir and managers anticipated that wells con-structed after the dam was built needed to be deep-ened or moved in advance of the dam removal Thisoccurred at Milltown Gold Ray and the Elwha andGlines Canyon dam removals (Supporting Informa-tion Table A1) The drawdown of the reservoirbehind the 128 m tall Milltown Dam Montanaimpacted groundwater elevations within the reservoirarea as well as 6 km downstream and 2-3 kmupstream of the dam with the degree of loweringvarying with distance to the reservoir and the direc-tion of groundwater flow (Berthelote 2013) Ananalysis of groundwater elevations pre- (2006) andpost- (2010) dam removal indicates that the watertable dropped by up to 24 m though most locationswere in the range of 15-18 m (USEPA 2011a) Mon-itoring of groundwater wells also indicated that damremoval modified the direction of groundwater flownear the dam (USEPA 2011a) The impacts to thegroundwater table were mitigated through the con-struction of 82 new wells lowering of 20 pumps andreconfiguration of an unspecified number of addi-tional wells (USEPA 2011a) At Gold Ray Dam Ore-gon it was anticipated that some of the wells within04 km of the reservoir would be affected by the low-ering of the reservoir (NMFS 2010) though no



quantitative analysis was conducted Following damremoval two nearby private potable water wells(Jackson Co personal communication)mdashboth shallowwells that were hydrologically connected to the artifi-cially elevated sloughmdashwent dry interrupting watersupply At Elwha and Glines Canyon dams pre-removal projections indicated that wells upstream ofthe reservoirs would be impacted by the reservoirdrawdowns and surface-water intakes downstream ofthe dams would be impacted by the changes in waterstage and clogging from increased suspended sedi-ment (USBR 1997 URS 2001) Analyses were basedon field exploration of the surficial and subsurfacegeology and aquifer testing as well as groundwatermodeling ranging from Darcy flow calculations andgroundwater budgeting to two-dimensional ground-water modeling (URS 2001) Anticipated impactswere concentrated on water infrastructure down-stream of each former dam and recommendations formitigation measures included the replacement ofdomestic and municipal supply wells (USBR 1997)though not all of the recommendations were imple-mented While formal groundwater monitoring post-removal was not funded landowners anecdotallyreported decreased yields from their wells Key fac-tors controlling impacts to downstream water usersappear to be the location of the channel and sedimentaccumulation in side channels (East et al 2015)

The second scenario for drawdown impacts onwater infrastructure is a hydraulically connectedreservoir where managers failed to anticipate thatwells needed to be deepened or moved in advance ofthe dam removal Impacts on local wells from thedrawdown of the reservoir behind Condit Dam werenot anticipated in the pre-removal EIS analysis (San-dison 2010) though the FERC surrender order hadprovided some indication before dam removal thatwell impacts were anticipated (FERC 2010) Afterthe removal at least eight wells were impacted bythe lowering of the groundwater table (Learn 2011)Whether PacifiCorp the dam owner was legally obli-gated to replace or modify the wells was debatedgiven the seniority of their water rights and becausethe wells drilled after dam construction in 1913accessed groundwater that was artificially elevatedby the reservoir PacifiCorp offered to pay propertyowners up to $5500 to drill deeper wells thoughlocal landowners argued that the compensation wasnot adequate (Learn 2011) Another unanticipatedconsequence of groundwater response to dam removaloccurred on the Elwha River where some groundwa-ter-fed side channels within the floodplain of thelower reaches dewatered (with a water-table decreaseof approximately 1 m) within a year after the start ofdam removal after the lower reservoir had beendrained of water Prior to reservoir dewatering the

water-surface elevation in those same side channelshad been constant throughout the previous six yearsof pre-dam-removal monitoring (Draut and Ritchie2015) The reduced groundwater contribution to flood-plain side channels had ecological consequencesbecause these channels constitute important rearinghabitat for young fish in gravel-bed rivers of the Paci-fic Northwest (Morley et al 2005) though the impactis not likely to be persistent

Finally the third scenario was no hydraulic con-nection between aquifer reservoir and local infras-tructure In the one case we identified representingthis scenario analysis was conducted in advance toevaluate the need for mitigation Pre-removal investi-gations of the potential impacts of Great Works andVeazie dams Maine on local wells indicated that allexamined wells were drawing water at elevationsbelow the expected post-removal water-surface eleva-tion in many cases much below and thus were unli-kely to be impacted (PRRT 2009) Many of the wellswere drilled into bedrock and the water source wasnot hydraulically connected to the reservoir there-fore the likelihood of negative effects on the wellswas low (PRRT 2009) This prediction was validatedwhen no wells were affected by the project

The case studies examined herein appear to havecertain commonalities around shallow groundwaterand primarily drinking-water uses Anticipating ifpump and well impacts will occur and require mitiga-tion is an important element of the dam-removalplanning process requiring knowledge of the localhydrogeology The relevant hydrogeologic processesthat control if reservoir drawdown will impact localinfrastructure are consistent with processes associ-ated with rising local water tables following dam con-struction (Leopold and Maddock 1954 Rains et al2004 Heilweil et al 2005) driven primarily by val-ley confinement and water-table depth (Berthelote2013) that impact groundwater recharge and dis-charge The hydrogeologic conditions associated withlarge groundwater table responses to dam removalthat can impact water infrastructure appear to be (1)a large drop in reservoir elevation relative toimpacted infrastructure (2) a high degree of connec-tivity and groundwater flow directions that providehigh rates of exchange between the reservoir riverand groundwater and (3) wells drawing from an allu-vial and artificially elevated aquifer as opposed to aconfined aquifer

The available tools for evaluating if these condi-tions exist at a site range from simple to complex Toassess potential impacts on local water infrastruc-ture project scientists and engineers might (1) ana-lyze surficial geology information and depth togroundwater well records (where available) and pro-jected dam-removal hydraulics (2) develop



mathematical statistical andor water budget modelsof groundwater flows (eg URS 2001 Berthelote2013) andor (3) apply numerical groundwater mod-els to simulate water-table elevations (eg Berth-elote 2013) Post-removal monitoring of wellsdischarge from springs and water levels in nearbylakes wetlands and alluvial floodplain channels(Shuman 1995 Draut and Ritchie 2015) will provideevidence to validate models and advance generalunderstanding of groundwater responses to damremoval

Nonnative Plant Colonization of Reservoirs

The introduction and spread of nonnative speciesincluding both fish and plants is considered to be oneof the largest threats to ecosystems around the globe(Simberloff et al 2013) When removed from ecologi-cal constraints found in their native environmentnonnatives can become ldquoinvasiverdquo which then havethe potential to out-compete and hybridize withnative species (McLaughlin et al 2013) restructurefood webs (Cross et al 2013) and undermine ecosys-tem diversity and productivity (Rahel 2007)

Characterizing the Concern Colonization andspread of nonnative plants on former reservoir sedi-ments is a common concern of resource managersThis CMC applies across various land managementobjectives including protection and maintenance ofnatural ecosystems and species diversity (Chenowethand Acker 2009 Woodward et al 2011) or munici-pal-park management (Orr and Stanley 2006) How-ever the acceptable range of nonnative plantcolonization or expansion varies with each dam-removal case and management entity though it islikely that most resource managers would find itunacceptable if one or a few nonnative species cameto dominate a former reservoir site Also control andcontainment of noxious weeds or particularly invasivespecies may be legally required in some cases

Approach We assessed the severity of nonnativeplant richness (ie the number of nonnative speciespresent at a site) or abundance (ie percent cover orfrequency) by comparing values in recently exposedsediments at former reservoirs to values reported forriparian corridors Studies in South Africa Franceand North America suggest that nonnative plantscommonly comprise 20-30 of the species present inriparian floras (Planty-Tabacchi et al 1996 Hoodand Naiman 2000) To assess the extent to whichnonnative plant species colonize and spread on for-mer reservoir sediments we compiled datasets frompublished or gray literature or unpublished data that

contained a high-quality list of species present at asite andor a quantitative estimate of the abundanceof each species present Further we excluded sitesthat were known to have had significant manage-ment such as weed control or active revegetationThis resulted in 25 sites with acceptable species rich-ness data and 18 sites with acceptable abundancedata (Figure 4) Because data collection methodswere not consistent across sites (ie sample plot dis-tribution and size abundance metrics) we were only

Relative richness of non-native vascular plant species

Years since dam removal

0 10 20 30 40 50 60

evitan-nonnoitc arF

00

01

02

03

04

05

06

07

08

Relative abundance of non-native vascular plants


0 10 20 30 40 50

evitan-nonnoi tcarF

00

01

02

03

04

05

06

07

08

a)

b)

FIGURE 4 (a) Relative Species Richness of Nonnative VascularPlants in 25 Former Reservoir Areas Following Dam RemovalValues are the fraction of total species richness (b) Relative abun-dance of nonnative vascular plants in 18 former reservoir areas fol-lowing dam removal Relative abundance values are theproportional contribution to frequency of occurrence or percentcover depending on the study Symbol sizes reflect dam heightslarge symbols = dams gt10 m tall medium symbols = dams 4-10 msmall symbols = dams lt4 m



able to calculate the relative contribution of nonna-tive species to species richness and vegetation abun-dance estimated as the proportion of nonnativespecies in the observed flora for each dam-removalsite (richness) or the relative abundance of nonnativevascular plants Typical abundance measures beforerelativizing were percent cover or frequency

Further we explored relationships between vari-ables known or hypothesized to influence patterns ofplant colonization and succession in former reservoirsor similar environments including two available forall sites (time since dam removal dam size) and sev-eral others which we discuss based on a relativelysmall number of case studies (landform or topo-graphic position sediment grain size and chemistryweed control active revegetation efforts nonnativepropagule pressure)

Key Findings The proportion of nonnative spe-cies averaged 031 and ranged from 013 to 068 atthe 25 study sites for which data were available (Fig-ure 4a) The proportion of nonnative taxa at themajority of the sites (15 of 25) was 03 or less similarto many riparian floras around the world (see above)The proportion at five sites was between 031 and 04and was gt04 at five sites Most sites were sampledfrom 2 to 10 years following dam removal and therewas not a significant quadratic or linear relationshipbetween time since dam removal and the proportionof nonnative species Height of the former dam aproxy for reservoir area also does not appear to havea clear influence on the contribution of nonnativetaxa to species richness (Figure 4a)

The relative abundance of nonnative plants wasvery similar to relative species richness averaging032 and ranging from 007 to 071 (Figure 4b) Orrand Stanley (2006) noted a high frequency of occur-rence of nonnative species in their study plots buttheir metric was quite different than ours and doesnot reflect the relative frequency of occurrence whichwe calculated from their data (C Orr personal com-munication) and which is much lower Though highlyvariable across the full range of sites there weresome instances where nonnative species were highlyabundant including some of the small dam-removalexamples in Wisconsin (Lenhart 2000 Orr and Stan-ley 2006) The most commonly cited nonnative inva-sive plant in these studies was reed canary grass(Phalaris arundinacea) which occurred at 100 ofthe Wisconsin study sites P arundinacea is also acommon invasive plant in other parts of the USincluding the Pacific Northwest where it occurred inpost-dam-removal vegetation surveys on the Rogueand Sprague Rivers in Oregon (Tullos unpublisheddata) and the Elwha River (Schuster 2015) Acrossall sites examined for this synthesis only 2 (Parfrey

Glen Dam on the Pine River Wisconsin and Wone-woc Dam on the Baraboo River Wisconsin) of 18exceeded 50 relative abundance of nonnative plantsAs with relative species richness neither the heightof the former dam nor the time since dam removalappears to have a clear relationship to relative abun-dance of nonnative plants

A number of variables likely influence nonnativespecies richness and relative abundance in formerreservoirs and are relevant to managing reservoirplant colonization These variables include landformtype sediment texture and chemistry revegetationand weed control and propagule pressure (eg localseed source) of nonnative plants Time since damremoval was expected to influence the relative rich-ness or abundance of nonnative species as sites withhigh dominance of P arundinacea or Urtica dioicamay have the potential to arrest successional change(Lenhart 2000 Orr and Stanley 2006) Howeverconsistent with Orr and Stanley (2006) and Aubleet al (2007) we found no clear evidence (Figure 4) ofnonnative species richness and abundance increasingwith time since removal

Formerly inundated landforms typically includeslopes that were uplands or valley walls prior to damremoval and various surfaces composed of alluvialsediments (Shafroth et al 2002) The height of thedam and distribution of trapped sediment influencethe types and relative abundance of different land-forms including high terraces in some cases Withrespect to nonnative species sites closer to the sur-rounding uplands could receive seeds of nonnativetaxa that are growing nearby which can varydepending on adjacent land uses The initially bareopen nature of all surfaces in former reservoirswould be expected to support weedy pioneer speciessome of which are likely to be nonnative Schuster(2015) examined native and nonnative species rich-ness and cover on three landforms (valley wall ter-race riparian) in two former reservoirs His resultssuggest that there may have been slightly higher rel-ative nonnative species richness on terraces than val-ley walls and riparian areas but little difference inrelative cover of nonnative species between land-forms

The texture and chemistry (eg nutrient status) ofsediments can influence the composition and abun-dance of colonizing vegetation Some nonnative inva-sive plants perform better in high nutrient soils invarious ecosystems (Dukes and Mooney 1999) andsediments in former reservoirs can have relativelyhigh nutrient levels (Stanley and Doyle 2002) Thereis some evidence that exotic species richness andcover may be related to concentrations of differentnutrients (eg N P K) in former reservoirs on theElwha River (Werner 2014 Schuster 2015)



However native species richness and cover are alsoinfluenced by nutrient status and teasing apart therelative differences is challenging Lenhart (2000)suggested that high nutrient levels in fine sedimentsof small dam removals in Wisconsin may have con-tributed to success of invasive species Finer sedi-ments in the former Elwha reservoirs tend to havehigher nutrient levels and water-holding capacitythan fluvial sediments outside of the reservoir andthey are associated with greater plant cover growthrates and species richness (Calimpong 2013Schuster 2015)

Resource managers frequently implement actionssuch as controlling nonnative plants andor plantingnative species immediately following decommission-ing and at regular intervals afterward in efforts toreduce nonnative plant dominance sometimes as arequirement of the dam removal permit or plan (egUS Army Corps of Engineers 2012) The extent towhich these activities have occurred is clear in some(eg Lenhart 2000 Orr and Koenig 2006 Cheno-weth 2013) but not all of the studies we examinedA few studies report findings of revegetation effortsthat allow some inference into the effects on nonna-tive species richness and abundance Orr and Koenig(2006) reported findings from two small dam-removalsites where significant planting of native taxaoccurred and where monitoring occurred one and fouryears following removal Although planting initiallyappeared to be having the desired effects of increas-ing the ratio of native to nonnative species andexcluding some particularly aggressive nonnativetaxa after four years the proportion of nonnativetaxa increased at both sites and the authors con-cluded that the planting efforts were largely unsuc-cessful (Orr and Koenig 2006) In the two formerreservoirs on the Elwha River the frequency of non-native plants was slightly lower (by 39-5) inplanted areas than in unplanted areas except on val-ley walls in one of the former reservoirs where thefrequency of nonnative plants was only 04 higherin planted vs unplanted areas (J Chenoweth per-sonal communication) At the former Milltown Damsite on the Clark Fork River in Montana seeded andplanted species comprised approximately 25 of totalcover and about 15 of total species richness (Sacryet al 2013) In most of these studies it is difficult todirectly assess the extent to which planting nativevegetation inhibits nonnative species richness how-ever it is reasonable to infer that the space occupiedby these plants is not available for nonnatives andtherefore plantings likely limit abundance

Finally the abundance and proximity of propag-ules (eg seeds or existing stands of spreadingplants) is a key factor influencing the extent of non-native plant colonization and spread These

propagule sources may vary depending on surround-ing land use and interact with time since removallandform and the direct management actions dis-cussed above Through surveys of nonnative plantpopulations in areas upstream and surrounding adam-removal site managers can evaluate potentialnonnative plant propagule pressure prior to damremoval to help assess the likelihood of significantinvasion (Woodward et al 2011)

Expansion of Nonnative Fish

Characterizing the Concern By modifyingriverine conditions the construction of dams canfacilitate the introduction and spread of invasive fishMany of these introductions have been the result ofdeliberate management decisions aimed at creatingproductive fisheries either in the reservoir itself (Bed-narek 2001 Havel et al 2005 Johnson et al 2008Rahel and Olden 2008) or in the tailwaters below thedam (Pejchar and Warner 2001) For example atGlen Canyon Dam on the Colorado River Arizonawarm water sport fish have been introduced in thereservoir above the dam and rainbow trout have beenintroduced to the cold tailwater below (Schmidt et al1998) Fish introductions that were not planned byfisheries managers have also occurred for exampleas a result of fish releases by self-motivated individu-als (Lintermans 2004) To succeed however theseintroduced fish populations must be predisposed forsurvival and reproduction in the newly created habi-tats and conditions afforded by the dams and theiroperations

Whereas some dams may facilitate the introduc-tion of nonnative species other dams are servingpurposely or incidentally to block access of undesiredfish species to upstream waters (McLaughlin et al2013) Consequently this raises the concern that theremoval of some dams may unintentionally extendthe range of invasive species and increase theireffects on native species and ecosystems (Hart et al2002 Jackson and Pringle 2010) In some cases bar-riers have been built specifically to protect native spe-cies and ecosystems from potentially harmfulinvaders such as those to prevent encroachment bynonnative trout species that represent threats for dis-placement introgression or hybridization (Novingerand Rahel 2003 Fausch et al 2009) In the GreatLakes region of the US numerous small dams werein place before introduction of the sea lamprey(Petromyzon marinus) and serve to suppress theirspread (Lavis et al 2003) Here we ask based onavailable case studies what evidence exists that damremovals have facilitated the spread of invasive fishspecies and have these new invasions had



undesirable impacts on aquatic communities andecosystems

Approach We queried the Bellmore et al (2015)database to identify dam-removal case studies thatexplicitly stated a concern for introduced or undesiredfish species andor for those studies that indicated anattempt to document the spread of nonnatives andtheir impacts on native fish communities Wesearched the database using the following keywordsldquoinvasiverdquo ldquononnativerdquo ldquoexoticrdquo ldquointroducedrdquo and ldquoin-troductionrdquo While there were many published worksthat expressed concern that undesirable introducedfish species would invade the newly opened habitatbecause of dam removal few studies actually trackedand documented this response after a dam wasremoved Four case studies published in the literature(a total of six dam removals in four watersheds inWisconsin South Carolina and Ohio) (Table 2) werecombined with three unpublished dam-removal casestudies in the Pacific Northwest (Supporting Informa-tion Table A1) where concerns about the spread ofinvasive fish exist but are not yet expressed in pub-lished literature We do not attempt a quantitativeanalysis with the limited number of case studies butinstead review the responses observed across thesecase studies and broadly discuss the potential controlson the spread and impact of invasive fishes followingdam removal

Key Findings Of the four case studies found inthe published literature three of these confirmed thatinvasive fish spread upstream of the former dam site(Gottgens 2009 Kornis et al 2014 Marion 2014)but the fourth did not observe an upstream invasion(Stanley et al 2007) Marion (2014) found nonnativeAlabama spotted bass (Micropterus henshalli) whichcan hybridize and compete with native redeye bass(M coosae) upstream of the removed Woodside damson Twelvemile Creek in South Carolina Howeverthe magnitude of impact if any of the spotted bassinvasion was not known In the case of the removalof Big Spring Dam from Big Spring Creek in Wiscon-sin nonnative white sucker (Catostomus commer-sonii) and Yellow Perch (Perca flavescens) quicklyinvaded upstream and became a major portion of thefish population while the native Mottled Sculpin(Cottus bairdii) population decreased by more thanhalf (Kornis et al 2014) In the Ottawa River inOhio the removal of Secor Dam coincided with thespread of invasive round goby (Neogobius melanosto-mus) a potentially harmful and difficult-to-containinvasive fish (Corkum et al 2004) Within two yearsafter this dam removal round goby composed 9 ofthe fish population at sites upstream of the formerdam though the dam may not have been an effective

barrier because the bulkhead ports were opened (JimEvans personal communication)

Of the three unpublished case studies in the Paci-fic Northwest all are located in the Columbia Riverbasin Condit and Powerdale dams were removedfrom downstream reaches near their junctions withthe Columbia River (5 and 7 rkm upstream from theColumbia respectively) Nonnative fish thrive in theColumbia River (Sanderson et al 2009) includingsmallmouth bass (M dolomieu) and walleye (Sandervitreus) which prey on native salmon and steelhead(anadromous form of rainbow trout Oncorhynchusmykiss) and the introduced American shad (Alosasapidissima) (Petersen et al 2003) So far howevernone of these introduced species have been observedby moderate to intensive monitoring efforts above theformer Condit (Allen and Connolly 2011) or Pow-erdale (Rob Regan Oregon Department of Fish andWildlife personal communication) dam sites Thethird Pacific Northwest case study involves a removalsite well upstream (19 rkm) of the main stem Colum-bia River (Hemlock Dam on Trout Creek) where it isconsidered unlikely that smallmouth bass walleye orAmerican shad could reach because of various fallsand cascades Without a barrier however TroutCreek is now vulnerable to settlement by nonnativespring Chinook salmon (O tshawytscha) severalthousand of which pass the mouth of Trout Creekannually as they home toward their natal fish hatch-ery 11 rkm upstream The concern is that these non-native Chinook salmon may establish a population inTrout Creek and compete with native steelheadwhich are the subject of a long-term and expensiverestoration effort (Jezorek and Connolly 2015) Todate spring Chinook salmon have not established apopulation in Trout Creek as evident from rigorousannual smolt trapping (Buehrens et al 2014) andelectrofishing (Jezorek and Connolly 2014) Howevera few individual adult Chinook are likely to swim upand beyond the old dam site as suggested by the occa-sional adult Chinook that were caught in the trapwithin the former fish ladder of the old dam

There are two potential explanations for the lackof observed invasions by fish in the case studies wereviewed First the duration of post-removal monitor-ing where it has occurred at all may be too shortBiological communities may require several years tostabilize following dam removal (Kornis et al 2014but see Tullos et al 2014) with the response timefor fish being longer than that of other biota such asmacroinvertebrates (Maloney et al 2008) Whileshort-term shifts in fish assemblages may be evidentlong-term shifts may continue to develop over time(Poulos et al 2014) Second the newly opened habi-tat may be poorly suited to invasive fish Environ-mental and biological factors interact in unique



TABLE

2Rev

iew

ofStudieson

FishIn

vasion

withDam

Rem

oval

RiverSta

teNonnativeFish

of

ConcernDownstream

NonnativeFish

ofConcernUpstream

DesiredSpecies

ofConcerns

Post-R

emovalResp

onse

Degreeof

Monitorin

gSource

Bou

lder

CrWisconsin

Browntrou

tBrook

trou

tLim

ited

tonoeffect

browntrou

tnot

observed

toinvade

twoyea

rsafter

remov

al

High

Stanleyet

al(2007)

Twelvem

ileCr

Sou

thCarolina

Alabamasp

ottedbass

flathea

dcatfish

Flathea

dcatfish

Red

eyebass

Alabamasp

ottedbass

foundupstream

unknow

nifhybridized

withredey

ebass

flathea

dcatfish

increa

sed

High

Marion

(2014)

Big

SpringCrWisconsin

Largem

outh

bass

yellow

perch

blueg

ill

whitesu

cker

Mottled

sculpin

andother

nativesp

ecies

Yellow

perch

and

whitesu

cker

invaded

andestablish

edpop

ulation

supstream

Dow

nstream

dam

stillin

place

provided

sourcefornon

nativefish

High

Kornis

etal(2014)

OttawaROhio

Rou

ndgob

yNativefish

assem

blagein

gen

eral

Rou

ndgob

yfirstob

served

inmid-2008madeup

9

oftotalcatch

upstream

and21

dow

nstream

byen

dof

2009

High

Gottgen

s(2009)

WhiteSalm

onR

Wash

ington

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

k

steelhea

d

bulltrou

tothers

Noinvadersob

served

Low

Allen

andCon

nolly

(2011)BAllen

USGSpersonal

communication

TroutCrWash

ington

Chinooksa

lmon

Steelhea

dJuven

ileChinooksa

lmon

havenot

beenob

served

High

Jezorek

andCon

nolly

(2014)TBueh

rens

Wash

ington

Dep

artmen

tof

Fish

andWildlife

personal

communication

Hoo

dROregon

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

kstee

lhea

d

bullTroutothers

Noinvadersob

served

High

RRea

gan

Oregon

Dep

artmen

tof

FishandWildlife

personal

communication



combinations across the geographical extremes of spe-cies distribution which create various strengths ofresistance to fish invasion (Fausch 2008) Frequencyof disturbance (Leprieur et al 2006) water tempera-ture and habitat structure (Jones et al 2003) canconstrain the ability of fish to establish a populationin the new habitat This resistance however is sub-ject to change as the environmental (eg climatechange) (Rahel and Olden 2008) and biological (egfood web changes) (Jackson et al 2001) conditionsthemselves change through time These observationssuggest that the mere presence or proximity of anintroduced fish species does not predispose its spreadand establishment in newly available habitat Assess-ments of dam-removal risks will need to examine theenvironmental (eg temperature and flow regimes)and ecological (eg food resources fish assemblage)characteristics of habitats in relation to the biologyand life history of potential invaders to evaluate thepotential for invasive species to spread Moreoverthese risks will have to be weighed against the poten-tial for the reestablishment of desired native species

DISCUSSION

The CMCs addressed in this study directly impactthe practice of dam removal These concerns fre-quently affect project advancement because conversa-tions among dam owners project managers and thepublic are often colored by past case studies that mayhave been outliers with unique conditions misinfor-mation andor incomplete analyses Our investiga-tion represents a first attempt to systematicallyreview the available information for these CMCsThis information highlights the issues and misconcep-tions associated with each CMC which can be usedto guide more focused and transparent pre-removalevaluations Our review shows that there is substan-tial knowledge derived from individual dam removalsbut also illustrates how it is difficult to identifydefinitive generalizable findings for a given CMC

CMCs What Do We Know

A common thread among CMCs is an incompleteunderstanding of the physical andor biological pro-cess controls that influence their occurrence at a siteAs a result managers and particularly the publictend to assume that the negative consequences ofCMCs will occur at all sites even when their occur-rence is unlikely In our experience incompleteunderstanding operates at two levels First there are

cases where the highly specialized expertise neces-sary to correctly assess a given CMC is simply notrepresented on a project team though a generalunderstanding of the relevant processes does existamong specialists Second even where relevantexpertise is available scientific understanding of con-trolling processes may be incomplete Dam-removalscience is frequently not readily available to projectteams and studies are not typically framed in refer-ence to management concerns Despite the manychallenges to analyzing CMCs as discussed belowour review allows us to improve understanding atboth levels by identifying the specific biophysical phe-nomena associated with each of the CMCs We alsoattempt to identify site conditions that suggest therewill be a management implication if a phenomenonassociated with the CMC occurs This is importantbecause there will be no basis for management con-cern at a site if there are no impacts people or regula-tors care or know about

Challenges to Analyzing CMCs A number ofchallenges prevent generalizing about the occurrenceof CMCs First study designs and methods are ofteninconsistent across sites and monitoring durationsare insufficient to answer questions of interest Sec-ond projects are often focused on very specific objec-tives (eg FERC requirements) and thus may notgenerate enough data to say something comprehen-sive about physical and biological processes relevantto CMCs Third access to information about priordam removals is often limited or hard to find Forexample studies reported in National EnvironmentalPolicy Act documents consultant reports and othergray literature are difficult to discover and accessOther issues like confidentiality can also impact datadiscovery such as finding information about privatewells for evaluating impacts to water infrastructureFor some of the more contentious dam removalsmanagers and dam owners may not be permitted todiscuss details of project impacts due to pending liti-gation Finally despite working with the best avail-able information there may be biases in ourinformation sources toward particular dam sizesgeographies and management scenarios (Bellmoreet al 2015) Thus future monitoring that focuses onhypotheses about biophysical processes relevant todam removal CMCs (eg Table 3) conducted withproper designs monitoring durations and broad pub-lic dissemination would improve understanding ofCMC occurrence and drivers

Eliminating Surprises Conditions ControllingCMC Occurrence The oft-stated claim that ldquoeverydam is differentrdquo (Poff and Hart 2002) reflects the localvariability and nuances between sites that contribute



to uncertainty about whether a CMC will occur duringdam removal Even if the physical andor biologicalphenomena underlying a given CMC are ubiquitous(eg reservoir drawdown increased connectivity) it isthe local infrastructure politics social values and reg-ulatory thresholds that dictate if those phenomenagenerate unacceptable impacts that require manage-ment Indeed the human dimensions of dam-removaldecision making are frequently more complex than thebiophysical dimensions (Heinz Center 2002 Johnsonand Graber 2002 Provencher et al 2008) To facili-tate an evaluation of the interacting human and bio-physical dimensions for the CMCs we analyzed weoutline the biophysical processes that control occur-rence of each CMC and provide examples of site condi-tions that suggest management implications (Table 3)With this information managers can assess whether a

CMC should be investigated further at their projectsite or else proceed with confidence that the CMC isunlikely to be problematic

We suggest a process through which managers candetermine both the likelihood of the biophysical phe-nomena occurring and its intersection with a man-agement implication This evaluation can be based ona series of decision points based on linking the bio-physical phenomena to management outcomes andmanagement implicationsmdashie there must be ecologi-cal or human uses at stake that people care aboutFirst project managers can ask if the biophysical pro-cess controls for their CMC of interest (Table 3) arelikely to be operative at their particular site Forexample if the groundwater table is regionally nearthe surface and not substantially elevated by thereservoir managers may proceed with confidence

TABLE 3 Conditions Controlling CMC Occurrence ldquoNArdquo for the degree and rate of reservoir erosion reflects the different approach takenfor this CMC where we summarized a number of synthesis papers rather than directly evaluated individual case studies V is the ratio ofthe volume of stored reservoir sediment to the riverrsquos annual sediment load with lower or higher V values associated with smaller orgreater downstream impacts from aggradation respectively

CMC Case Studies Biophysical Process Controls

Example Site ConditionsSuggesting Management

Implications

Degree and rate ofreservoir erosion

NA bull High of stored fine-grained sediments1

bull Average sediment depositwidthchannel width gt~25

bull Phased removal2

Stakeholder values fish passageneeds or sensitive habitats

Excessive channelincision upstream of reservoir

38 bull Reach-scale incision downstream

bull High of stored fine-grained sediments1


bull Coarse delta

bull Ephemeral flow

In-stream infrastructure withinreservoir deposit infrastructureor property along reservoirmargins at risk for bank erosionfish passage needs or sensitivehabitats

Downstream aggradation 6 bull Proximal to dam

bull Antecedent channel has low slopeunconfined

bull High V2

Low-lying properties transportationinfrastructure pump intakes fishpassage needs or sensitive habitats

Elevated turbidity 7 bull High of stored fine-grained sediments1

bull High V2

bull Rapid reservoir drawdown

Sensitive aquatic organisms humanrecreational uses drinking-watertreatment intakes

Drawdown impacts onlocal water infrastructure

5 bull Large drop in water-surface elevation

bull High degree of connectivity betweenthe reservoir river and the groundwater

bull Regionally deep groundwater table

Wells or intakes in the reservoirvicinity

Nonnative plantcolonization of reservoirs

25 bull Proximity to nonnative seed sources


(with high nutrient content)

bull No planting or weed control

Legal requirements for noxious weedandor invasive species controlstakeholder values

Nonnative fish 7 bull Abundance and proximity of nonnative fish

bull Availability of suitable habitat andtemperatures for nonnative species

State fisheries regulations ormanagement plans stakeholdervalues

1This process is common across four CMCs2This process is common across two CMCs



that wells will not be impacted by the reservoir draw-down Second project managers should investigate ifthere is an intersection of the biophysical phenomenawith a human use of relevance to stakeholders Forexample is there water infrastructure proximal tothe impoundment that will be affected by reservoirdrawdown Third because CMCs can co-occur wesuggest that managers identify CMCs that have bio-physical process controls in common that might indi-cate co-occurrence For example the grain size ofstored sediment appears to be an important controlon the degree and rate of reservoir erosion excessivechannel incision (headcut migration rate through thereservoir) elevated turbidity and nonnative plantcolonization of the reservoirs Broadly evaluating thebiophysical controls shown in Table 3 to identifythose that are operative at a site may lead to discov-ery of unanticipated CMCs These three separate butrelated evaluations will help managers facilitatescience-based discussion among stakeholders avoidsurprises and inform stakeholders of likely outcomesand allow managers to develop plans for addressingCMCs in a timely manner

Other Relevant Management Concerns

We attempted to select the most frequent anduncertain dam-removal CMCs but we acknowledgethat our analyses are incomplete There are othermanagement issues that may occur some of whichcan be anticipated

For example contaminated sediments are animportant management concern at some sites (Evans2015) most famously at Fort Edward Dam in 1973(Stanley and Doyle 2003) and more recently at Mill-town Dam (USEPA 2011b) Reservoir sediment con-tamination is most likely to occur in reservoirs withhigh proportions of fine sediment and watershed landuse histories that suggest contaminant releases werepossible which is why the likelihood of contaminatedsediments and degree of contamination are muchhigher in some areas (eg Major and Warner 2008)than others Managers need to identify if sedimentsare clean and they face additional challenges includ-ing (1) a lack of consistency regarding biologicallyand legally acceptable limits of concentration andduration of contaminants in the sediment releasedduring dam removal (2) limited knowledge of theeffectiveness of various management strategies forcontaminated sediments (capping phased drawdownisolation) and (3) a need for better characterizationof contaminant risks based on the bioavailability ofthe contaminant (Evans 2015)

Disruption of aquatic communities downstream ofdam removals is another potentially important

management concern In locations where nativefreshwater mussels occur there is typically a concernthat increased sediment loads will bury and suffocatemussel beds (Stanley and Doyle 2003) This concernmay apply to other aquatic invertebrates (but seeTullos et al 2014) but the concern is high for mus-sels because they are long-lived species with longgeneration times and limited mobility such that itmay take decades for populations to reestablish aftera mass mortality event (Box and Mossa 1999Strayer et al 2004) Other example managementconcerns include stranding of biota in the reservoiras drawdown occurs destruction of tribal and cul-tural resources as the reservoir is dewatered followedby a sediment pulse moving downstream (NMFS2010 USBR amp CDFG 2012a) and impacts to waterrights (USBR amp CDFG 2012b)

CONCLUSIONS

Data for the seven CMCs we investigated are notsufficient to support broadly applicable conclusionsabout the probability of their occurrence at dam-removal sites Most CMCs have few case studies thatare limited to the geography of where dams have beenremoved and the study durations are typically shortNonetheless the CMC occurrence data we have com-bined with established knowledge of relevant pro-cesses reveal important biophysical phenomena thatact as controls for the occurrence of CMCs We proposethat managers evaluate CMCs in the context of riskwhereby both the likelihood of the biophysical phe-nomena contributing to a concern occurring at a siteand its intersection with a management implicationare evaluated Knowledge of the biophysical phenom-ena controlling CMCs enables managers to betterdetermine if further analyses are warranted to assessCMC risk and provide science-based information tostakeholders Increased knowledge of these biophysi-cal controls will be gained with ongoing and likelyexpanded scientific dam-removal studies

In addition to assessing CMC risk it is importantto acknowledge and communicate that long-term ben-efits of dam removal may be accompanied by trade-offs inherent to dam removal and to unrelated basin-scale activities (Stanley and Doyle 2003) In mostcases studies indicate that negative impacts associ-ated with dam removal are transient (eg Tulloset al 2014) In addition even if managers determinethat their site is at risk those potential negativeimpacts should be weighed against the potential ben-efits of dam removal By articulating project goalsdeveloping metrics for evaluating project success and



identifying and monitoring triggers for adaptivelymanaging to minimize negative impacts (Peters et al2014) the tradeoffs with dam removal can be effec-tively managed and communicated Furthermoreecosystem disturbances caused by dam removal suchas elevated turbidity should be contextualized bycomparison to natural variability andor other humandisturbances

Dam-removal practitioners thus have the chal-lenge of estimating CMC occurrence at their sitesevaluating the potential risks in light of tradeoffsand other project context and communicating thisinformation to project stakeholders in a manner thatallows communities to make informed decisions Sci-entists also have a challenge to advance practice-relevant dam-removal science to further supportpractitioner efforts Our analysis and findings pro-vide a means for managers to assess some of thecommon management concerns of dam removal andhighlight the need for additional dam-removalscience to inform practice

SUPPORTING INFORMATION

Additional supporting information may be foundonline under the Supporting Information tab for thisarticle A table providing the names locations andsome characteristics of the case studies analyzed foreach CMC

ACKNOWLEDGMENTS

This article is derived from discussions and analysis efforts con-ducted by the working group on Dam removal Synthesis of ecologicaland physical responses of the US Geological Surveyrsquos John WesleyPowell Center for Analysis and Synthesis In addition we very grate-fully acknowledge Jeff Duda Amy East Laura Craig Melissa FoleyJim Evans and Chris Magirl for their reviews of an earlier versionof this manuscript We appreciate assistance with graphics fromCindy Gray and Joel Murray at the Bureau of Reclamation

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Allen MB RO Engle JS Zendt FC Shrier JT Wilson andPJ Connolly 2016 Salmon and Steelhead in the White SalmonRiver after the Removal of Condit DammdashPlanning Efforts andRecolonization Results Fisheries 41(4)190-203

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Amos RA 2008 Upstream River Responses to Low Head DamRemoval Masterrsquos Thesis University of Waterloo WaterlooCanada

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Berthelote AR 2013 Forecasting Groundwater Responses toDam Removal PhD Dissertation University of Montana Mis-soula Montana

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Bountry JA YG Lai and TJ Randle 2013 Sediment Impactsfrom the Savage Rapids Dam Removal Rogue River OregonIn The Challenges of Dam Removal and River Restoration JVDe Graff and JE Evans (Editors) Geological Society of Amer-ica Reviews in Engineering Geology 2193-104 DOI 10113020134121(08)

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Calimpong C 2013 Elwha River Revegetation 2013 A Plant Per-formance Study Masterrsquos Thesis University of WashingtonSeattle Washington

Cannatelli K 2013 Rethinking Dredging A Quantitative Analysisof Dam Removal Techniques httplibravirginiaeducatalogli-bra-oa3417 accessed February 2016

Cannatelli K and J Curran 2012 Importance of Hydrology onChannel Evolution Following Dam Removal Case Study andConceptual Model Journal of Hydraulic Engineering 138(5)377-390

Cantelli A M Wong G Parker and C Paola 2007 Numerical ModelLinking Bed and Bank Evolution of Incisional Channel Created byDam Removal Water Resources Research 431-16

Chaplin JJ RA Brightbill and MD Bilger 2005 Effects ofRemoving Good Hope Mill Dam on Selected Physical Chemicaland Biological Characteristics of Conodoguinet Creek Cumber-land County Pennsylvania with a Section on Response of theFish Assemblage by Paola Ferreri US Geological Survey Sci-entific Investigations Report 2005-5226 37 pp

Chenoweth J 2013 2013 Elwha Revegetation Annual SummaryReport National Park Service Olympic National Park Draft

Chenoweth J and SA Acker 2009 Lake Mills and Lake AldwellReservoir Revegetation and Restoration Plan National ParkService Olympic National Park 83 pp

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Collins MJ G Aponte Clarke C Baeder D McCaw J Royte RSaunders and T Sheehan 2012 Large-Scale Dam Removal inthe Northeast United States Documenting Ecological Responsesto the Penobscot River Restoration Project Abstract EP54C-06Presented at 2012 Fall Meeting AGU San Francisco Califor-nia December 3-7

Corkum LD MR Sapota and KE Skora 2004 The RoundGoby Neogobius melanostomus a Fish Invader on Both Sides ofthe Atlantic Ocean Biological Invasions 6173-181

Cross WF CV Baxter MJ Rosi-Marshall RO Hall TA Ken-nedy KC Donner HA Wellard Kelly SEZ Seegert KEBehn and MD Yard 2013 Food-Web Dynamics in a LargeRiver Discontinuum Ecological Monographs 83311-337

Cui Y G Parker C Braudrick WE Dietrich and B Cluer2006 Dam Removal Express Assessment Models (DREAM)Part 1 Model Development and Validation Journal of Hydrau-lic Research 44(3)291-307

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HDR 2010 Jackson County Gold Ray Dam Removal Project Wet-land Determination HDR Portland Oregon

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Heinz Center 2002 Dam Removal Science and Decision MakingHeinz Center for Science Economics and the EnvironmentWashington DC p 236

Hood GW and RJ Naiman 2000 Vulnerability of RiparianZones to Invasion by Exotic Vascular Plants Plant Ecology148105-114

Jackson CR and CM Pringle 2010 Ecological Benefits ofReduced Hydrologic Connectivity in Intensively DevelopedLandscapes BioScience 6037-46

Jackson DA PR Peres-Neto and JD Olden 2001 What Con-trols Who Is Where in Freshwater Fish CommunitiesmdashTheRoles of Biotic Abiotic and Spatial Factors Canadian Journalof Fisheries and Aquatic Sciences 58157-170

Jezorek IG and PJ Connolly 2014 Wind River SubbasinRestoration US Geological Survey Annual Report November2012 through December 2013 Bonneville Power AdministrationPortland Oregon Document ID P138064

Jezorek IG and PJ Connolly 2015 Biotic and Abiotic Influenceson Abundance and Distribution of Non-Native Chinook Salmonand Native ESA-Listed Steelhead in the Wind River Washing-ton Northwest Science 8958-74



Johnson SE and BE Graber 2002 Enlisting the Social Sciencesin Decisions about Dam Removal BioScience 52731-738

Johnson TJ JD Olden and MJV Zanden 2008 Dam InvadersImpoundments Facilitate Biological Invasions into FreshwatersFrontiers in Ecology and the Environment 6(7)357-363

Jones ML JK Netto JD Stockwell and JB Mion 2003 Doesthe Value of Newly Accessible Spawning Habitat for Walleye(Stizostedion vitreum) Depend on Its Location Relative to Nurs-ery Habitats Canadian Journal of Fisheries and AquaticSciences 601527-1538 DOI 101139f03-130

Kemp P D Sear A Collins P Naden and I Jones 2011 TheImpacts of Fine Sediment on Riverine Fish Hydrological Pro-cesses 25(11)1800-1821 DOI 101002hyp7940

Kibler K D Tullos and M Kondolf 2011 Evolving Expectationsof Dam Removal Outcomes Downstream Geomorphic EffectsFollowing Removal of a Small Gravel-Filled Dam Journal ofthe American Water Resources Association 47408-423 DOI101111j1752-1688201100523x

Kleinfelder Ellis Ecological Services and J R Merit 2012 WaterQuality Monitoring Annual Report Year Ending September 302012 Condit Hydroelectric Project Decommissioning FERCProject No 2342 Prepared for PacifiCorp Energy San DiegoCalifornia

Konrad CP 2009 Simulating the Recovery of Suspended Sedi-ment Transport and River-Bed Stability in Response to DamRemoval on the Elwha River Washington Ecological Engineer-ing 35(7)1104-1115

Kornis MS BC Weidel SM Powers MW Diebel TJ ClineJM Fox and JF Kitchell 2014 Fish Community DynamicsFollowing Dam Removal in a Fragmented Agricultural StreamAquatic Sciences 77465-480

Lavis DL A Hallett EM Koon and TC McAuley 2003 His-tory of and Advances in Barriers as an Alternative Method toSuppress Sea Lampreys in the Great Lakes Journal of GreatLakes Research 29(1)362-372

Learn S 2011 Well Owners Want PacifiCorp to Pay More forDamage Done by Removal of Condit Dam The Oregonian Port-land Oregon

Lenhart C 2000 The Vegetation and Hydrology of Impoundmentsafter Dam Removal in Southern Wisconsin MS Thesis Univer-sity of Wisconsin Madison Wisconsin

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Leopold LB MG Wolman and JP Miller 1964 Fluvial Process inGeomorphology WH Freeman Company San Francisco California

Leprieur F MA Hickey CJ Arbuckle GP Closs S Brosse andCR Townsend 2006 Hydrological Disturbance Benefits aNative Fish at the Expense of an Exotic Fish Journal ofApplied Ecology 43930-939

Lintermans M 2004 Human-Assisted Dispersal of Alien Freshwa-ter Fish in Australia New Zealand Journal of Marine andFreshwater Research 38(3)481-501

MacBroom J and R Schiff 2013 Sediment Management at SmallDam Removal Sites Reviews in Engineering Geology 2167-79

Magirl CS RC Hilldale CA Curran JJ Duda TD StraubM Domanski and JR Foreman 2015 Large-Scale DamRemoval on the Elwha River Washington USA Fluvial Sedi-ment Load Geomorphology 246669-686 DOI 101016jgeo-morph201412032

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In D Tsutsumi and J LaRonne (Editors) Gravel-Bed Riversand Disasters Wiley and Sons pp

Major JJ JE OrsquoConnor CJ Podolak MK Keith GE GrantKR Spicer S Pittman HM Bragg JR Wallick DQ TannerA Rhode and PR Wilcock 2012 Geomorphic Response of theSandy River Oregon to Removal of Marmot Dam USGS Pro-fessional Paper 1792 64 pp

Maloney KO HR Dodd SE Butler and DH Wahl 2008Changes in Macroinvertebrate and Fish Assemblages in a Med-ium-Sized River Following a Breach of a Low-Head Dam Fresh-water Biology 531055-1068 DOI 101111j1365-2427200801956x

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Morley SA PS Garcia TR Bennett and P Roni 2005 JuvenileSalmonid (Oncorhynchus spp) Use of Constructed and NaturalSide Channels in Pacific Northwest Rivers Canadian Journal ofFisheries and Aquatic Sciences 622811-2821

Morris G and J Fan 1998 Reservoir Sedimentation HandbookMcGraw-Hill Book Co New York City New York

Neave M S Rayburg and A Swan 2009 River Channel ChangeFollowing Dam Removal in an Ephemeral Stream AustralianGeographer 40235-246

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Novinger DC and FJ Rahel 2003 Isolation Management withArtificial Barriers as a Conservation Strategy for CutthroatTrout in Headwater Streams Conservation Biology 17772-781

OrsquoConnor J J Duda and G Grant 2015 1000 Dams and Count-ing Science 348496-497

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Orr CH and S Koenig 2006 Planting and Vegetation Recoveryon Exposed Mud Flats Following Two Dam Removals in Wiscon-sin Ecological Restoration 2479-86

Orr CH KL Rogers and EH Stanley 2006 Channel Morphol-ogy and P Uptake Following Removal of a Small Dam Journalof the North American Benthological Society 25(3)556-568

Orr CH and EH Stanley 2006 Vegetation Development andRestoration Potential of Drained Reservoirs Following DamRemoval in Wisconsin River Research and Applications 22281-295

Pearson AJ NP Snyder and MJ Collins 2011 Rates and Pro-cesses of Channel Response to Dam Removal with a Sand-FilledImpoundment Water Resources Research 47(11)15 DOI1010292010WR009733

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Pejchar L and K Warner 2001 A River Might Run through It AgainCriteria for Consideration of Dam Removal and Interim Lessonsfrom California Environmental Management 28(5)561-575

Peters RJ JJ Duda GR Pess M Zimmerman P Crain ZHughes A Wilson MC Liermann SA Morley JR McMillanK Denton D Morrill and K Warheit 2014 Guidelines for Moni-toring and Adaptively Managing Restoration of Chinook Salmon(Oncorhynchus tshawytscha) and Steelhead (O mykiss) on theElwha River httpwwwfwsgovwafwopdfPeters20et20al20201420Elwha20Mon20Adapt20Mng20Finalpdf

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Planty-Tabacchi A E Tabacchi RJ Naiman C DeFerrari andH Decamps 1996 Invasibility of Species-Rich Communities inRiparian Zones Conservation Biology 10598-607

Poff NL and DD Hart 2002 How Dams Vary and Why It Mat-ters for the Emerging Science of Dam Removal BioScience 52(8)659-668

Poulos HM KE Miller ML Kraczkowski AW Welchel RHeineman and B Chernoff 2014 Fish Assemblage Responseto a Small Dam Removal in the Eightmile River System Con-necticut USA Environmental Management 541090-1101

Provencher B H Sarakinos and T Meyer 2008 Does SmallDam Removal Affect Local Property Values An Empirical Anal-ysis Contemporary Economic Policy 26(2)187-197

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Rahel FJ and JD Olden 2008 Assessing the Effects of ClimateChange on Aquatic Invasive Species Conservation Biology 22(3)521-533

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Randle TJ JA Bountry A Ritchie and K Wille 2015 Large-Scale Dam Removal on the Elwha River Washington USAErosion of Reservoir Sediment Geomorphology 246709-728DOI 101016jgeomorph201412045

Reneuroofeuroalt BM A Lejon M Jonsson and C Nilsson 2013 Long-Term Taxon-Specific Responses of Macroinvertebrates to DamRemoval in a Mid-Sized Swedish Stream River Research andApplications 291082-1089 DOI 101002rra2592

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Sanderson BL KA Barnas and AMW Rub 2009 Nonindige-nous Species of the Pacific Northwest An Overlooked Risk toEndangered Salmon BioScience 59(3)245-256

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Simberloff D JL Martin P Genovesi V Maris DA Wardle JAronson F Courchamp B Galil E Garcia-Berthou M PascalR Sousa E Tabacchi and M Vila 2013 Impacts of BiologicalInvasions Whatrsquos What and the Way Forward Trends in Ecol-ogy amp Evolution 28(1)58-66

Stanley EH MJ Catalano N Mercado-Silva and CH Orr2007 Effects of Dam Removal on Brook Trout in a WisconsinStream River Research and Applications 23792-798

Stanley EH and MW Doyle 2002 A Geomorphic Perspective onNutrient Retention Following Dam Removal BioScience 52(8)693-701

Stanley EH and MW Doyle 2003 Trading Off The EcologicalEffects of Dam Removal Frontiers in Ecology and the Environ-ment 115-22 DOI 1018901540-9295(2003) 001[0015TOTEEO]20CO2

Stanley EH MA Luebke MW Doyle and DW Marshall 2002Short-Term Changes in Channel Form and MacroinvertebrateCommunities Following Low-Head Dam Removal Journal of theNorth American Benthological Society 21172-187

Stewart G 2006 Patterns and Processes of Sediment TransportFollowing Sediment-Filled Dam Removal in Gravel Bed Riv-ers PhD Dissertation Oregon State University CorvallisOregon

Straub TD 2007 Erosion Dynamics of a Stepwise Small DamRemoval Brewster Creek Dam Near St Charles Illinois The-sis Colorado State University

Strayer DL JA Downing WR Haag TL King JB LayzerTJ Newton and JS Nichols 2004 Changing Perspectives onPearly Mussels North Americarsquos Most Imperiled Animals Bio-Science 54(5)429-439

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Werner C 2014 Early Succession in Plant CommunitiesRegrowth and Invasion in the Drained Elwha River ReservoirsUndergraduate Thesis Princeton University Princeton NewJersey

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linkages to physical responses are notably absent Asa result resource managers often face uncertaintyabout how quickly and to what extent physical andecological systems will respond to dam removal Inaddition stakeholders and managers often raise con-cerns about potential negative effects with each newproject whether or not a given concern is warrantedThese sentiments illustrate that negative effects canand do occur at some sites but can also reflect incom-plete understanding of the controlling factorsinvolved when overgeneralized to expect negativeeffects at every site Whether or not specific negativeimpacts manifest appears to be strongly influenced bysite conditions such as the hydrogeomorphic settingand the method by which the dam is removed (eginstantaneous or staged removal) (Cannatelli 2013)which offers promise that the occurrence of the man-agement concerns can eventually be predicted

Dam-removal science has increased in scope anddepth but it frequently fails to provide the insightsneeded for managers to know if and when to antici-pate negative effects Based on a recent literaturereview 586 documents related to the science of damremoval were identified but only 179 of these werefound to contain empirical information on measuredresponses (Bellmore et al 2015) This research haslargely emphasized field monitoring (eg Doyle et al2002 Kibler et al 2011 Major et al 2012) ornumerical modeling (Cui et al 2006 Cantelli et al2007 Wells et al 2007 Cui and Wilcox 2008 Downset al 2009 Konrad 2009) to advance understandingof the rates and patterns of erosion and depositionassociated with dam removal-induced sedimentpulses or on the impacts of those sediment pulses onfish (eg Allen et al 2016 plus see Doyle et al 2005for review) and benthic macroinvertebrates (egStanley et al 2002 Reneuroofeuroalt et al 2013 Tulloset al 2014) While these studies increase scientificknowledge they usually do not focus on applied man-agement issues such as identifying when a damremoval is likely to negatively affect ecosystems orinfrastructure or address regulatory engineering orsocioeconomic concerns Furthermore there is a suiteof management concerns not directly related to thestudy of sediment dynamics or biological responsesthat are largely unstudied Dams will continue to beremoved and managers will need to make informeddecisions about potential negative impacts and howto mitigate them to which science should directlycontribute Advancing dam-removal science to helpanswer management questions is therefore impera-tive and as this happens it will be equally importantfor managers to reevaluate applicable regulationsand standards of practice to ensure that they arebased on current science and are appropriate for agiven project

We investigate some of the common concerns man-agers face as they design and implement damremovals in order to (1) explicitly articulate theseconcerns and their potential negative consequences(2) identify where and how commonly these concernswere ultimately valid and (3) evaluate what condi-tions control their occurrence We define these con-cerns henceforth referred to as CommonManagement Concerns (CMCs) as outcomes thatmay require intervention but are broadly assumedsometimes incorrectly to occur at most sites TheCMCs addressed in this review are as follows (1) thedegree and rate of reservoir erosion (2) prolonged orexcessive channel incision upstream of the reservoirpool (3) downstream sediment aggradation (4) ele-vated downstream turbidity (5) impacts of reservoirdrawdown on local water infrastructure (6) nonna-tive plant colonization of former reservoirs and (7)expansion of nonnative fish Figure 1 schematicallydepicts these concerns and their typical geographicoccurrence in a watershed

Identifying CMCs

As part of the US Geological Survey John WesleyPowell Center for Analysis and Synthesis (httppow-ellcenterusgsgov accessed May 2016) dam-removalworking group comprising experts from a broadrange of disciplines (eg geomorphology water qual-ity ecology and engineering) and sectors (eg acade-mia government research institutions governmentmanagement agencies and practitioners) we identi-fied a broad suite of CMCs frequently raised in thedam-removal planning process We narrowed thisbroad set of CMCs to the seven investigated here thatare among the most commonly raised across manygeographies and project types (eg high-head vs low-head dam removals) with others (eg contaminatedsediments) briefly addressed in the Discussion

Case Study Approach

For each identified CMC we evaluated their rele-vance at dam-removal sites with available data ofadequate spatial andor temporal resolution Becausedam removals are often not thoroughly studied andthe results of many dam-removal studies are notwidely disseminated in publicly available literaturethe analysis of each CMC was based on data orinformation from a relatively small number of sitesMoreover because most dam-removal studies onlymonitor a small set of physical or biologicalresponses we were unable to evaluate all sevenCMCs at all of the sites Random sampling or









TX

CA

MT

AZ

ID

NV

NM

CO

OR

UT IL

WY

KS

IANE

SD

MN

ND

OK

FL

WI

MO

WA

GAAL

MI

AR

IN

LA

PA

NC

NY

MS

TN

VAKY

OH

SC

ME

WV

VT

MD

NH

NJ

MA

CT

DE

RI

0

1 - 25

26 - 50

51 - 75

gt75



1 2 3 4 5 6





EVALUATING THE CMCs

















































Elevated Turbidity





TABLE

1TurbidityDataState

CriteriaandOccurren

ceCharacteristics

forSev

enDam-R

emov

alSitesFormazinNep

helom

etricUnits(FNUs)

are

similarto

Nep

helom

etric

TurbidityUnits(N

TUs)

totheex

tentthatbothmea

sure

scattered

lightat90degfrom

theinciden

tlightbea

mHow

everthey

are

mea


gthsof

light

tocomply


standard

s(ISO

7027andEPA

method

1801resp

ectively)For

moreinform

ation


grapherfnuhtm

l

Dam(s)

RiverSta

te

USGS

Gage

Number

Turbid

ity

Data

Sta

teThresh

old

(ST)

Tmax1(

)Tdur2(

)

Above

Below

Unit

Freq3

Criteria

4ST56

Above

Below

Above

Below

Pre

Post

Pre

Post

Pre

Post

Pre

Post

Vea

zieGreatWorks

Pen

obscotME

01036390

FNU

60

Non

e25

1160

1240

97

102

Sim

kins

Patapsco

MD

01589000

01589025

NTU

15

150NTU

150

15

1047

51

1247

012

017

SavageRapids

Rog

ue

OR

14361050

14361180

FNU

15

nat+10

64

188

1724

1207

3292

03

123

109

145

Marm

otSandyOR

14136500

14137002

FNU

1530

nat+10

143

4336

7483

3497

7483

473

82

315

119

Chiloq

uinSprague

OR7

11501000

11502500

FNU

15

nat+10

176

477

341

295

290

227

44

59

14

Goo

dHop

eMillCon

odog

uinetPA

01570064

01570078

NTU

15

Non

e29

879

1272

3793

4828

78

106

941

692

Elw

haG

lines

Canyon

Elw

haWA8

12044900

12046260

FNU

15

nat+5NTU

922

205

gt6091

532

gt7545

68

74

143

966

1Tmax=(m

axim

um

pea

kvalueST)100

2Tdur=(duration

ofSTex

ceed

ancem

onitoringduration

)100

3Samplingfreq

uen

cyin

minutes

TheMarm

otsite

haddifferentsa

mplingfreq

uen

cies

forthesensors

abov

eandbelow

thedam

4See

httpw

aterep

agov

scitech

swguidancestandard

swqslibraryindex

cfm

accessedJuly

302014

5Basedon

upstream

record

forallsitesex

ceptPen

obscotwhichon

lyhasadow

nstream

record

withalongpre-rem

ovalmon

itoringperiod

6ldquoN

aturalrdquo

conditionsare

estimatedbythe90th

percentile

value

ifnostate-w

idecriteria90th

percentile

isused

7Dow

nstream

gageis

onWilliamsonRiver

below

Spragueconfluen

ce

8Turbidityinstru

men

tsherehaveop

eration

alranges

upto

1500FNU

(Figure

3c)values

abov

e1200FNU

are

considered

unreliable

(Curranet

al2014)

9When

naturalis

50NTU

orless

(USGSreports

FNU

atElw

haproject

gages)














































0 10 20 30 40 50 60

evitan-nonnoitc arF

00

01

02

03

04

05

06

07

08



0 10 20 30 40 50

evitan-nonnoi tcarF

00

01

02

03

04

05

06

07

08

a)

b)































TABLE

2Rev

iew

ofStudieson

FishIn

vasion

withDam

Rem

oval

RiverSta

teNonnativeFish

of

ConcernDownstream

NonnativeFish

ofConcernUpstream

DesiredSpecies

ofConcerns

Post-R

emovalResp

onse

Degreeof

Monitorin

gSource

Bou

lder

CrWisconsin

Browntrou

tBrook

trou

tLim

ited

tonoeffect

browntrou

tnot

observed

toinvade

twoyea

rsafter

remov

al

High

Stanleyet

al(2007)

Twelvem

ileCr

Sou

thCarolina

Alabamasp

ottedbass

flathea

dcatfish

Flathea

dcatfish

Red

eyebass

Alabamasp

ottedbass

foundupstream

unknow

nifhybridized

withredey

ebass

flathea

dcatfish

increa

sed

High

Marion

(2014)

Big

SpringCrWisconsin

Largem

outh

bass

yellow

perch

blueg

ill

whitesu

cker

Mottled

sculpin

andother

nativesp

ecies

Yellow

perch

and

whitesu

cker

invaded

andestablish

edpop

ulation

supstream

Dow

nstream

dam

stillin

place

provided

sourcefornon

nativefish

High

Kornis

etal(2014)

OttawaROhio

Rou

ndgob

yNativefish

assem

blagein

gen

eral

Rou

ndgob

yfirstob

served

inmid-2008madeup

9

oftotalcatch

upstream

and21

dow

nstream

byen

dof

2009

High

Gottgen

s(2009)

WhiteSalm

onR

Wash

ington

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

k

steelhea

d

bulltrou

tothers

Noinvadersob

served

Low

Allen

andCon

nolly

(2011)BAllen

USGSpersonal

communication

TroutCrWash

ington

Chinooksa

lmon

Steelhea

dJuven

ileChinooksa

lmon

havenot

beenob

served

High

Jezorek

andCon

nolly

(2014)TBueh

rens

Wash

ington

Dep

artmen

tof

Fish

andWildlife

personal

communication

Hoo

dROregon

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

kstee

lhea

d

bullTroutothers

Noinvadersob

served

High

RRea

gan

Oregon

Dep

artmen

tof

FishandWildlife

personal

communication




DISCUSSION















Implications










bull Coarse delta

bull Ephemeral flow




bull High V2



bull High V2


























CONCLUSIONS









ACKNOWLEDGMENTS


LITERATURE CITED





























































































































































TX

CA

MT

AZ

ID

NV

NM

CO

OR

UT IL

WY

KS

IANE

SD

MN

ND

OK

FL

WI

MO

WA

GAAL

MI

AR

IN

LA

PA

NC

NY

MS

TN

VAKY

OH

SC

ME

WV

VT

MD

NH

NJ

MA

CT

DE

RI

0

1 - 25

26 - 50

51 - 75

gt75



1 2 3 4 5 6





EVALUATING THE CMCs

















































Elevated Turbidity





TABLE

1TurbidityDataState

CriteriaandOccurren

ceCharacteristics

forSev

enDam-R

emov

alSitesFormazinNep

helom

etricUnits(FNUs)

are

similarto

Nep

helom

etric

TurbidityUnits(N

TUs)

totheex

tentthatbothmea

sure

scattered

lightat90degfrom

theinciden

tlightbea

mHow

everthey

are

mea


gthsof

light

tocomply


standard

s(ISO

7027andEPA

method

1801resp

ectively)For

moreinform

ation


grapherfnuhtm

l

Dam(s)

RiverSta

te

USGS

Gage

Number

Turbid

ity

Data

Sta

teThresh

old

(ST)

Tmax1(

)Tdur2(

)

Above

Below

Unit

Freq3

Criteria

4ST56

Above

Below

Above

Below

Pre

Post

Pre

Post

Pre

Post

Pre

Post

Vea

zieGreatWorks

Pen

obscotME

01036390

FNU

60

Non

e25

1160

1240

97

102

Sim

kins

Patapsco

MD

01589000

01589025

NTU

15

150NTU

150

15

1047

51

1247

012

017

SavageRapids

Rog

ue

OR

14361050

14361180

FNU

15

nat+10

64

188

1724

1207

3292

03

123

109

145

Marm

otSandyOR

14136500

14137002

FNU

1530

nat+10

143

4336

7483

3497

7483

473

82

315

119

Chiloq

uinSprague

OR7

11501000

11502500

FNU

15

nat+10

176

477

341

295

290

227

44

59

14

Goo

dHop

eMillCon

odog

uinetPA

01570064

01570078

NTU

15

Non

e29

879

1272

3793

4828

78

106

941

692

Elw

haG

lines

Canyon

Elw

haWA8

12044900

12046260

FNU

15

nat+5NTU

922

205

gt6091

532

gt7545

68

74

143

966

1Tmax=(m

axim

um

pea

kvalueST)100

2Tdur=(duration

ofSTex

ceed

ancem

onitoringduration

)100

3Samplingfreq

uen

cyin

minutes

TheMarm

otsite

haddifferentsa

mplingfreq

uen

cies

forthesensors

abov

eandbelow

thedam

4See

httpw

aterep

agov

scitech

swguidancestandard

swqslibraryindex

cfm

accessedJuly

302014

5Basedon

upstream

record

forallsitesex

ceptPen

obscotwhichon

lyhasadow

nstream

record

withalongpre-rem

ovalmon

itoringperiod

6ldquoN

aturalrdquo

conditionsare

estimatedbythe90th

percentile

value

ifnostate-w

idecriteria90th

percentile

isused

7Dow

nstream

gageis

onWilliamsonRiver

below

Spragueconfluen

ce

8Turbidityinstru

men

tsherehaveop

eration

alranges

upto

1500FNU

(Figure

3c)values

abov

e1200FNU

are

considered

unreliable

(Curranet

al2014)

9When

naturalis

50NTU

orless

(USGSreports

FNU

atElw

haproject

gages)














































0 10 20 30 40 50 60

evitan-nonnoitc arF

00

01

02

03

04

05

06

07

08



0 10 20 30 40 50

evitan-nonnoi tcarF

00

01

02

03

04

05

06

07

08

a)

b)































TABLE

2Rev

iew

ofStudieson

FishIn

vasion

withDam

Rem

oval

RiverSta

teNonnativeFish

of

ConcernDownstream

NonnativeFish

ofConcernUpstream

DesiredSpecies

ofConcerns

Post-R

emovalResp

onse

Degreeof

Monitorin

gSource

Bou

lder

CrWisconsin

Browntrou

tBrook

trou

tLim

ited

tonoeffect

browntrou

tnot

observed

toinvade

twoyea

rsafter

remov

al

High

Stanleyet

al(2007)

Twelvem

ileCr

Sou

thCarolina

Alabamasp

ottedbass

flathea

dcatfish

Flathea

dcatfish

Red

eyebass

Alabamasp

ottedbass

foundupstream

unknow

nifhybridized

withredey

ebass

flathea

dcatfish

increa

sed

High

Marion

(2014)

Big

SpringCrWisconsin

Largem

outh

bass

yellow

perch

blueg

ill

whitesu

cker

Mottled

sculpin

andother

nativesp

ecies

Yellow

perch

and

whitesu

cker

invaded

andestablish

edpop

ulation

supstream

Dow

nstream

dam

stillin

place

provided

sourcefornon

nativefish

High

Kornis

etal(2014)

OttawaROhio

Rou

ndgob

yNativefish

assem

blagein

gen

eral

Rou

ndgob

yfirstob

served

inmid-2008madeup

9

oftotalcatch

upstream

and21

dow

nstream

byen

dof

2009

High

Gottgen

s(2009)

WhiteSalm

onR

Wash

ington

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

k

steelhea

d

bulltrou

tothers

Noinvadersob

served

Low

Allen

andCon

nolly

(2011)BAllen

USGSpersonal

communication

TroutCrWash

ington

Chinooksa

lmon

Steelhea

dJuven

ileChinooksa

lmon

havenot

beenob

served

High

Jezorek

andCon

nolly

(2014)TBueh

rens

Wash

ington

Dep

artmen

tof

Fish

andWildlife

personal

communication

Hoo

dROregon

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

kstee

lhea

d

bullTroutothers

Noinvadersob

served

High

RRea

gan

Oregon

Dep

artmen

tof

FishandWildlife

personal

communication




DISCUSSION















Implications










bull Coarse delta

bull Ephemeral flow




bull High V2



bull High V2


























CONCLUSIONS









ACKNOWLEDGMENTS


LITERATURE CITED























































































































































EVALUATING THE CMCs

















































Elevated Turbidity





TABLE

1TurbidityDataState

CriteriaandOccurren

ceCharacteristics

forSev

enDam-R

emov

alSitesFormazinNep

helom

etricUnits(FNUs)

are

similarto

Nep

helom

etric

TurbidityUnits(N

TUs)

totheex

tentthatbothmea

sure

scattered

lightat90degfrom

theinciden

tlightbea

mHow

everthey

are

mea


gthsof

light

tocomply


standard

s(ISO

7027andEPA

method

1801resp

ectively)For

moreinform

ation


grapherfnuhtm

l

Dam(s)

RiverSta

te

USGS

Gage

Number

Turbid

ity

Data

Sta

teThresh

old

(ST)

Tmax1(

)Tdur2(

)

Above

Below

Unit

Freq3

Criteria

4ST56

Above

Below

Above

Below

Pre

Post

Pre

Post

Pre

Post

Pre

Post

Vea

zieGreatWorks

Pen

obscotME

01036390

FNU

60

Non

e25

1160

1240

97

102

Sim

kins

Patapsco

MD

01589000

01589025

NTU

15

150NTU

150

15

1047

51

1247

012

017

SavageRapids

Rog

ue

OR

14361050

14361180

FNU

15

nat+10

64

188

1724

1207

3292

03

123

109

145

Marm

otSandyOR

14136500

14137002

FNU

1530

nat+10

143

4336

7483

3497

7483

473

82

315

119

Chiloq

uinSprague

OR7

11501000

11502500

FNU

15

nat+10

176

477

341

295

290

227

44

59

14

Goo

dHop

eMillCon

odog

uinetPA

01570064

01570078

NTU

15

Non

e29

879

1272

3793

4828

78

106

941

692

Elw

haG

lines

Canyon

Elw

haWA8

12044900

12046260

FNU

15

nat+5NTU

922

205

gt6091

532

gt7545

68

74

143

966

1Tmax=(m

axim

um

pea

kvalueST)100

2Tdur=(duration

ofSTex

ceed

ancem

onitoringduration

)100

3Samplingfreq

uen

cyin

minutes

TheMarm

otsite

haddifferentsa

mplingfreq

uen

cies

forthesensors

abov

eandbelow

thedam

4See

httpw

aterep

agov

scitech

swguidancestandard

swqslibraryindex

cfm

accessedJuly

302014

5Basedon

upstream

record

forallsitesex

ceptPen

obscotwhichon

lyhasadow

nstream

record

withalongpre-rem

ovalmon

itoringperiod

6ldquoN

aturalrdquo

conditionsare

estimatedbythe90th

percentile

value

ifnostate-w

idecriteria90th

percentile

isused

7Dow

nstream

gageis

onWilliamsonRiver

below

Spragueconfluen

ce

8Turbidityinstru

men

tsherehaveop

eration

alranges

upto

1500FNU

(Figure

3c)values

abov

e1200FNU

are

considered

unreliable

(Curranet

al2014)

9When

naturalis

50NTU

orless

(USGSreports

FNU

atElw

haproject

gages)














































0 10 20 30 40 50 60

evitan-nonnoitc arF

00

01

02

03

04

05

06

07

08



0 10 20 30 40 50

evitan-nonnoi tcarF

00

01

02

03

04

05

06

07

08

a)

b)































TABLE

2Rev

iew

ofStudieson

FishIn

vasion

withDam

Rem

oval

RiverSta

teNonnativeFish

of

ConcernDownstream

NonnativeFish

ofConcernUpstream

DesiredSpecies

ofConcerns

Post-R

emovalResp

onse

Degreeof

Monitorin

gSource

Bou

lder

CrWisconsin

Browntrou

tBrook

trou

tLim

ited

tonoeffect

browntrou

tnot

observed

toinvade

twoyea

rsafter

remov

al

High

Stanleyet

al(2007)

Twelvem

ileCr

Sou

thCarolina

Alabamasp

ottedbass

flathea

dcatfish

Flathea

dcatfish

Red

eyebass

Alabamasp

ottedbass

foundupstream

unknow

nifhybridized

withredey

ebass

flathea

dcatfish

increa

sed

High

Marion

(2014)

Big

SpringCrWisconsin

Largem

outh

bass

yellow

perch

blueg

ill

whitesu

cker

Mottled

sculpin

andother

nativesp

ecies

Yellow

perch

and

whitesu

cker

invaded

andestablish

edpop

ulation

supstream

Dow

nstream

dam

stillin

place

provided

sourcefornon

nativefish

High

Kornis

etal(2014)

OttawaROhio

Rou

ndgob

yNativefish

assem

blagein

gen

eral

Rou

ndgob

yfirstob

served

inmid-2008madeup

9

oftotalcatch

upstream

and21

dow

nstream

byen

dof

2009

High

Gottgen

s(2009)

WhiteSalm

onR

Wash

ington

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

k

steelhea

d

bulltrou

tothers

Noinvadersob

served

Low

Allen

andCon

nolly

(2011)BAllen

USGSpersonal

communication

TroutCrWash

ington

Chinooksa

lmon

Steelhea

dJuven

ileChinooksa

lmon

havenot

beenob

served

High

Jezorek

andCon

nolly

(2014)TBueh

rens

Wash

ington

Dep

artmen

tof

Fish

andWildlife

personal

communication

Hoo

dROregon

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

kstee

lhea

d

bullTroutothers

Noinvadersob

served

High

RRea

gan

Oregon

Dep

artmen

tof

FishandWildlife

personal

communication




DISCUSSION















Implications










bull Coarse delta

bull Ephemeral flow




bull High V2



bull High V2


























CONCLUSIONS









ACKNOWLEDGMENTS


LITERATURE CITED































































































































































































Elevated Turbidity





TABLE

1TurbidityDataState

CriteriaandOccurren

ceCharacteristics

forSev

enDam-R

emov

alSitesFormazinNep

helom

etricUnits(FNUs)

are

similarto

Nep

helom

etric

TurbidityUnits(N

TUs)

totheex

tentthatbothmea

sure

scattered

lightat90degfrom

theinciden

tlightbea

mHow

everthey

are

mea


gthsof

light

tocomply


standard

s(ISO

7027andEPA

method

1801resp

ectively)For

moreinform

ation


grapherfnuhtm

l

Dam(s)

RiverSta

te

USGS

Gage

Number

Turbid

ity

Data

Sta

teThresh

old

(ST)

Tmax1(

)Tdur2(

)

Above

Below

Unit

Freq3

Criteria

4ST56

Above

Below

Above

Below

Pre

Post

Pre

Post

Pre

Post

Pre

Post

Vea

zieGreatWorks

Pen

obscotME

01036390

FNU

60

Non

e25

1160

1240

97

102

Sim

kins

Patapsco

MD

01589000

01589025

NTU

15

150NTU

150

15

1047

51

1247

012

017

SavageRapids

Rog

ue

OR

14361050

14361180

FNU

15

nat+10

64

188

1724

1207

3292

03

123

109

145

Marm

otSandyOR

14136500

14137002

FNU

1530

nat+10

143

4336

7483

3497

7483

473

82

315

119

Chiloq

uinSprague

OR7

11501000

11502500

FNU

15

nat+10

176

477

341

295

290

227

44

59

14

Goo

dHop

eMillCon

odog

uinetPA

01570064

01570078

NTU

15

Non

e29

879

1272

3793

4828

78

106

941

692

Elw

haG

lines

Canyon

Elw

haWA8

12044900

12046260

FNU

15

nat+5NTU

922

205

gt6091

532

gt7545

68

74

143

966

1Tmax=(m

axim

um

pea

kvalueST)100

2Tdur=(duration

ofSTex

ceed

ancem

onitoringduration

)100

3Samplingfreq

uen

cyin

minutes

TheMarm

otsite

haddifferentsa

mplingfreq

uen

cies

forthesensors

abov

eandbelow

thedam

4See

httpw

aterep

agov

scitech

swguidancestandard

swqslibraryindex

cfm

accessedJuly

302014

5Basedon

upstream

record

forallsitesex

ceptPen

obscotwhichon

lyhasadow

nstream

record

withalongpre-rem

ovalmon

itoringperiod

6ldquoN

aturalrdquo

conditionsare

estimatedbythe90th

percentile

value

ifnostate-w

idecriteria90th

percentile

isused

7Dow

nstream

gageis

onWilliamsonRiver

below

Spragueconfluen

ce

8Turbidityinstru

men

tsherehaveop

eration

alranges

upto

1500FNU

(Figure

3c)values

abov

e1200FNU

are

considered

unreliable

(Curranet

al2014)

9When

naturalis

50NTU

orless

(USGSreports

FNU

atElw

haproject

gages)














































0 10 20 30 40 50 60

evitan-nonnoitc arF

00

01

02

03

04

05

06

07

08



0 10 20 30 40 50

evitan-nonnoi tcarF

00

01

02

03

04

05

06

07

08

a)

b)































TABLE

2Rev

iew

ofStudieson

FishIn

vasion

withDam

Rem

oval

RiverSta

teNonnativeFish

of

ConcernDownstream

NonnativeFish

ofConcernUpstream

DesiredSpecies

ofConcerns

Post-R

emovalResp

onse

Degreeof

Monitorin

gSource

Bou

lder

CrWisconsin

Browntrou

tBrook

trou

tLim

ited

tonoeffect

browntrou

tnot

observed

toinvade

twoyea

rsafter

remov

al

High

Stanleyet

al(2007)

Twelvem

ileCr

Sou

thCarolina

Alabamasp

ottedbass

flathea

dcatfish

Flathea

dcatfish

Red

eyebass

Alabamasp

ottedbass

foundupstream

unknow

nifhybridized

withredey

ebass

flathea

dcatfish

increa

sed

High

Marion

(2014)

Big

SpringCrWisconsin

Largem

outh

bass

yellow

perch

blueg

ill

whitesu

cker

Mottled

sculpin

andother

nativesp

ecies

Yellow

perch

and

whitesu

cker

invaded

andestablish

edpop

ulation

supstream

Dow

nstream

dam

stillin

place

provided

sourcefornon

nativefish

High

Kornis

etal(2014)

OttawaROhio

Rou

ndgob

yNativefish

assem

blagein

gen

eral

Rou

ndgob

yfirstob

served

inmid-2008madeup

9

oftotalcatch

upstream

and21

dow

nstream

byen

dof

2009

High

Gottgen

s(2009)

WhiteSalm

onR

Wash

ington

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

k

steelhea

d

bulltrou

tothers

Noinvadersob

served

Low

Allen

andCon

nolly

(2011)BAllen

USGSpersonal

communication

TroutCrWash

ington

Chinooksa

lmon

Steelhea

dJuven

ileChinooksa

lmon

havenot

beenob

served

High

Jezorek

andCon

nolly

(2014)TBueh

rens

Wash

ington

Dep

artmen

tof

Fish

andWildlife

personal

communication

Hoo

dROregon

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

kstee

lhea

d

bullTroutothers

Noinvadersob

served

High

RRea

gan

Oregon

Dep

artmen

tof

FishandWildlife

personal

communication




DISCUSSION















Implications










bull Coarse delta

bull Ephemeral flow




bull High V2



bull High V2


























CONCLUSIONS









ACKNOWLEDGMENTS


LITERATURE CITED























































































































































TABLE

1TurbidityDataState

CriteriaandOccurren

ceCharacteristics

forSev

enDam-R

emov

alSitesFormazinNep

helom

etricUnits(FNUs)

are

similarto

Nep

helom

etric

TurbidityUnits(N

TUs)

totheex

tentthatbothmea

sure

scattered

lightat90degfrom

theinciden

tlightbea

mHow

everthey

are

mea


gthsof

light

tocomply


standard

s(ISO

7027andEPA

method

1801resp

ectively)For

moreinform

ation


grapherfnuhtm

l

Dam(s)

RiverSta

te

USGS

Gage

Number

Turbid

ity

Data

Sta

teThresh

old

(ST)

Tmax1(

)Tdur2(

)

Above

Below

Unit

Freq3

Criteria

4ST56

Above

Below

Above

Below

Pre

Post

Pre

Post

Pre

Post

Pre

Post

Vea

zieGreatWorks

Pen

obscotME

01036390

FNU

60

Non

e25

1160

1240

97

102

Sim

kins

Patapsco

MD

01589000

01589025

NTU

15

150NTU

150

15

1047

51

1247

012

017

SavageRapids

Rog

ue

OR

14361050

14361180

FNU

15

nat+10

64

188

1724

1207

3292

03

123

109

145

Marm

otSandyOR

14136500

14137002

FNU

1530

nat+10

143

4336

7483

3497

7483

473

82

315

119

Chiloq

uinSprague

OR7

11501000

11502500

FNU

15

nat+10

176

477

341

295

290

227

44

59

14

Goo

dHop

eMillCon

odog

uinetPA

01570064

01570078

NTU

15

Non

e29

879

1272

3793

4828

78

106

941

692

Elw

haG

lines

Canyon

Elw

haWA8

12044900

12046260

FNU

15

nat+5NTU

922

205

gt6091

532

gt7545

68

74

143

966

1Tmax=(m

axim

um

pea

kvalueST)100

2Tdur=(duration

ofSTex

ceed

ancem

onitoringduration

)100

3Samplingfreq

uen

cyin

minutes

TheMarm

otsite

haddifferentsa

mplingfreq

uen

cies

forthesensors

abov

eandbelow

thedam

4See

httpw

aterep

agov

scitech

swguidancestandard

swqslibraryindex

cfm

accessedJuly

302014

5Basedon

upstream

record

forallsitesex

ceptPen

obscotwhichon

lyhasadow

nstream

record

withalongpre-rem

ovalmon

itoringperiod

6ldquoN

aturalrdquo

conditionsare

estimatedbythe90th

percentile

value

ifnostate-w

idecriteria90th

percentile

isused

7Dow

nstream

gageis

onWilliamsonRiver

below

Spragueconfluen

ce

8Turbidityinstru

men

tsherehaveop

eration

alranges

upto

1500FNU

(Figure

3c)values

abov

e1200FNU

are

considered

unreliable

(Curranet

al2014)

9When

naturalis

50NTU

orless

(USGSreports

FNU

atElw

haproject

gages)














































0 10 20 30 40 50 60

evitan-nonnoitc arF

00

01

02

03

04

05

06

07

08



0 10 20 30 40 50

evitan-nonnoi tcarF

00

01

02

03

04

05

06

07

08

a)

b)































TABLE

2Rev

iew

ofStudieson

FishIn

vasion

withDam

Rem

oval

RiverSta

teNonnativeFish

of

ConcernDownstream

NonnativeFish

ofConcernUpstream

DesiredSpecies

ofConcerns

Post-R

emovalResp

onse

Degreeof

Monitorin

gSource

Bou

lder

CrWisconsin

Browntrou

tBrook

trou

tLim

ited

tonoeffect

browntrou

tnot

observed

toinvade

twoyea

rsafter

remov

al

High

Stanleyet

al(2007)

Twelvem

ileCr

Sou

thCarolina

Alabamasp

ottedbass

flathea

dcatfish

Flathea

dcatfish

Red

eyebass

Alabamasp

ottedbass

foundupstream

unknow

nifhybridized

withredey

ebass

flathea

dcatfish

increa

sed

High

Marion

(2014)

Big

SpringCrWisconsin

Largem

outh

bass

yellow

perch

blueg

ill

whitesu

cker

Mottled

sculpin

andother

nativesp

ecies

Yellow

perch

and

whitesu

cker

invaded

andestablish

edpop

ulation

supstream

Dow

nstream

dam

stillin

place

provided

sourcefornon

nativefish

High

Kornis

etal(2014)

OttawaROhio

Rou

ndgob

yNativefish

assem

blagein

gen

eral

Rou

ndgob

yfirstob

served

inmid-2008madeup

9

oftotalcatch

upstream

and21

dow

nstream

byen

dof

2009

High

Gottgen

s(2009)

WhiteSalm

onR

Wash

ington

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

k

steelhea

d

bulltrou

tothers

Noinvadersob

served

Low

Allen

andCon

nolly

(2011)BAllen

USGSpersonal

communication

TroutCrWash

ington

Chinooksa

lmon

Steelhea

dJuven

ileChinooksa

lmon

havenot

beenob

served

High

Jezorek

andCon

nolly

(2014)TBueh

rens

Wash

ington

Dep

artmen

tof

Fish

andWildlife

personal

communication

Hoo

dROregon

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

kstee

lhea

d

bullTroutothers

Noinvadersob

served

High

RRea

gan

Oregon

Dep

artmen

tof

FishandWildlife

personal

communication




DISCUSSION















Implications










bull Coarse delta

bull Ephemeral flow




bull High V2



bull High V2


























CONCLUSIONS









ACKNOWLEDGMENTS


LITERATURE CITED


































































































































































































0 10 20 30 40 50 60

evitan-nonnoitc arF

00

01

02

03

04

05

06

07

08



0 10 20 30 40 50

evitan-nonnoi tcarF

00

01

02

03

04

05

06

07

08

a)

b)































TABLE

2Rev

iew

ofStudieson

FishIn

vasion

withDam

Rem

oval

RiverSta

teNonnativeFish

of

ConcernDownstream

NonnativeFish

ofConcernUpstream

DesiredSpecies

ofConcerns

Post-R

emovalResp

onse

Degreeof

Monitorin

gSource

Bou

lder

CrWisconsin

Browntrou

tBrook

trou

tLim

ited

tonoeffect

browntrou

tnot

observed

toinvade

twoyea

rsafter

remov

al

High

Stanleyet

al(2007)

Twelvem

ileCr

Sou

thCarolina

Alabamasp

ottedbass

flathea

dcatfish

Flathea

dcatfish

Red

eyebass

Alabamasp

ottedbass

foundupstream

unknow

nifhybridized

withredey

ebass

flathea

dcatfish

increa

sed

High

Marion

(2014)

Big

SpringCrWisconsin

Largem

outh

bass

yellow

perch

blueg

ill

whitesu

cker

Mottled

sculpin

andother

nativesp

ecies

Yellow

perch

and

whitesu

cker

invaded

andestablish

edpop

ulation

supstream

Dow

nstream

dam

stillin

place

provided

sourcefornon

nativefish

High

Kornis

etal(2014)

OttawaROhio

Rou

ndgob

yNativefish

assem

blagein

gen

eral

Rou

ndgob

yfirstob

served

inmid-2008madeup

9

oftotalcatch

upstream

and21

dow

nstream

byen

dof

2009

High

Gottgen

s(2009)

WhiteSalm

onR

Wash

ington

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

k

steelhea

d

bulltrou

tothers

Noinvadersob

served

Low

Allen

andCon

nolly

(2011)BAllen

USGSpersonal

communication

TroutCrWash

ington

Chinooksa

lmon

Steelhea

dJuven

ileChinooksa

lmon

havenot

beenob

served

High

Jezorek

andCon

nolly

(2014)TBueh

rens

Wash

ington

Dep

artmen

tof

Fish

andWildlife

personal

communication

Hoo

dROregon

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

kstee

lhea

d

bullTroutothers

Noinvadersob

served

High

RRea

gan

Oregon

Dep

artmen

tof

FishandWildlife

personal

communication




DISCUSSION















Implications










bull Coarse delta

bull Ephemeral flow




bull High V2



bull High V2


























CONCLUSIONS









ACKNOWLEDGMENTS


LITERATURE CITED


















































































































































































TABLE

2Rev

iew

ofStudieson

FishIn

vasion

withDam

Rem

oval

RiverSta

teNonnativeFish

of

ConcernDownstream

NonnativeFish

ofConcernUpstream

DesiredSpecies

ofConcerns

Post-R

emovalResp

onse

Degreeof

Monitorin

gSource

Bou

lder

CrWisconsin

Browntrou

tBrook

trou

tLim

ited

tonoeffect

browntrou

tnot

observed

toinvade

twoyea

rsafter

remov

al

High

Stanleyet

al(2007)

Twelvem

ileCr

Sou

thCarolina

Alabamasp

ottedbass

flathea

dcatfish

Flathea

dcatfish

Red

eyebass

Alabamasp

ottedbass

foundupstream

unknow

nifhybridized

withredey

ebass

flathea

dcatfish

increa

sed

High

Marion

(2014)

Big

SpringCrWisconsin

Largem

outh

bass

yellow

perch

blueg

ill

whitesu

cker

Mottled

sculpin

andother

nativesp

ecies

Yellow

perch

and

whitesu

cker

invaded

andestablish

edpop

ulation

supstream

Dow

nstream

dam

stillin

place

provided

sourcefornon

nativefish

High

Kornis

etal(2014)

OttawaROhio

Rou

ndgob

yNativefish

assem

blagein

gen

eral

Rou

ndgob

yfirstob

served

inmid-2008madeup

9

oftotalcatch

upstream

and21

dow

nstream

byen

dof

2009

High

Gottgen

s(2009)

WhiteSalm

onR

Wash

ington

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

k

steelhea

d

bulltrou

tothers

Noinvadersob

served

Low

Allen

andCon

nolly

(2011)BAllen

USGSpersonal

communication

TroutCrWash

ington

Chinooksa

lmon

Steelhea

dJuven

ileChinooksa

lmon

havenot

beenob

served

High

Jezorek

andCon

nolly

(2014)TBueh

rens

Wash

ington

Dep

artmen

tof

Fish

andWildlife

personal

communication

Hoo

dROregon

Walley

esm

allmou

thbassAmericansh

ad

Chinoo

kstee

lhea

d

bullTroutothers

Noinvadersob

served

High

RRea

gan

Oregon

Dep

artmen

tof

FishandWildlife

personal

communication




DISCUSSION















Implications










bull Coarse delta

bull Ephemeral flow




bull High V2



bull High V2


























CONCLUSIONS









ACKNOWLEDGMENTS


LITERATURE CITED
























































































































































DISCUSSION















Implications










bull Coarse delta

bull Ephemeral flow




bull High V2



bull High V2


























CONCLUSIONS









ACKNOWLEDGMENTS


LITERATURE CITED





























































































































































Implications










bull Coarse delta

bull Ephemeral flow




bull High V2



bull High V2


























CONCLUSIONS









ACKNOWLEDGMENTS


LITERATURE CITED





























































































































































CONCLUSIONS









ACKNOWLEDGMENTS


LITERATURE CITED























































































































































Synthesis of Common Management Concerns Associated...

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