river sediment sources and sediment hazards in colorado

INHERITING OUR PAST:RIVER SEDIMENT SOURCESAND SEDIMENT HAZARDS

IN COLORADO

by

Ellen WohlDepartment of Earth Resources

Colorado State University

with contributions from

Robert McConnellWater Quality Control Division

Department of Public Health and Environ-ment

Jay SkinnerDivision of Wildlife

Department of Natural Resources

Richard StenzelDivision of Water Resources

Department of Natural Resources

No. 7June 1998

“...we must begin by recognizing that wecannot restore the

state’s rivers to pre-19th century

conditions...”

SSWater in the BalanceSS

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AN OPEN LETTER ON RIVER SEDIMENT SOURCESAND SEDIMENT HAZARDS IN COLORADO

Rivers are one of Colorado’s greatest resources. Ecologically-rich river corridors have provided routes oftravel and sustenance for humans for thousands of years. River water has been vital to the State’s agricul-tural, industrial, and municipal growth, and Colorado’s rivers attract recreational users from around theworld. At the same time, river processes may create hazards for human communities and aquatic organ-isms. Many people are aware of the hazards associated with floods such as the 1976 flood in Big Thomp-son Canyon or the 1997 flood in Fort Collins. River hazards may also involve the movement of sedimentalong the river, as when excess sediment accumulating in a reservoir reduces the storage capacity andexpected life of the reservoir, for example.

This report summarizes the hazards associated with river sediment in Colorado. As population in Colo-rado continues to grow, conflicts over the management of rivers will also grow. Satisfactory resolution ofthese conflicts will require that everyone involved understands the basic processes of rivers and sedimentmovement, the history of river and land-use changes in Colorado, and the constraints that currently limitour abilities to mitigate sediment hazards. This report provides an introduction to these issues, and identi-fies actions that can be undertaken to reduce future sediment hazards associated with Colorado’s rivers.

Sincerely,

Ellen WohlAssociate Professor of Earth ResourcesColorado State University

SSColorado Water Resources Research InstituteSS

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PREFACE

Rivers are one of Colorado’s greatestresources. Ecologically-rich river corridorshave provided routes of travel and suste-nance for humans for thousands of years.River water has been vital to the State’sagricultural, industrial, and municipalgrowth, and Colorado’s rivers attractrecreational users from around the world.At the same time, river processes maycreate hazards for human communities andaquatic organisms. Many people are awareof the hazards associated with floods suchas the 1976 flood in Big Thompson Canyonor the 1997 flood in Fort Collins. Riverhazards may also involve the movement ofsediment along the river, as when excesssediment accumulating in a reservoirreduces the storage capacity and expectedlife of the reservoir, for example.

This report summarizes the hazards associ-ated with river sediment in Colorado. Aspopulation in Colorado continues to grow,conflicts over the management of rivers willalso grow. Satisfactory resolution of theseconflicts will require that everyone involvedunderstands the basic processes of rivers andsediment movement, the history of river andland-use changes in Colorado, and theconstraints that currently limit our abilities tomitigate sediment hazards. This reportprovides an introduction to these issues, andidentifies actions that can be undertaken toreduce future sediment hazards associatedwith Colorado’s rivers.


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TABLE OF CONTENTS

page

The Problem ..........................................................................................................................3

Hazards Associated with Sediment .........................................................................................7

T h e R ivers of Colorado

The Plains Rivers ................................................................................................................9

The M ountain Rivers .........................................................................................................11

The Plateau and Canyon Rivers .........................................................................................13

Sedim ent Hazards in Colorado .............................................................................................16

Exam ples of Hazards Associated with Excess Sedim ent.......................................................16

Exam ples of Hazards Associated with Decrease of Sedim ent ...............................................20

Exam ples of Hazards Associated with Contam inated Sedim ents ..........................................21

Our Options for M anaging Sedim ent and W ater ...................................................................23

Societal and legal constraints Hazards associated with sedim ent..........................................23

Environm ental constraints .................................................................................................24

Technical constraints Hazards associated with sedim ent......................................................24

Recom m endations for the Future Hazards Associated with Sedim ent .....................................26

References...........................................................................................................................29


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INHERITING OUR PAST:RIVER SEDIMENT SOURCESAND SEDIMENT HAZARDS

IN COLORADO

THE PROBLEM

River channels are dynamicnatural systems that are continu-ally changing. A channelreflects to some degree all of theprocesses operating within itsdrainage basin. These processesare ultimately controlled bygeology and climate, whichtogether determine regionaltopography, soil development,the growth of vegetation, and theland-use practices of peopleliving within the drainage basin(Figure 1).

Hillslope features such astopography, vegetation, andland-use will influence thecharacteristics of water andsediment yield from thehillslopes to the channel. Themovement of water and sedi-ment along the channel will then

SSSS Figure 1. Schematic diagram of relationships among factorscontrolling sediment movement along rivers. Contaminants may movein association with water and/or sediment.

There are four basic processes by which sedimentmoves down a hillslope. Mass movements involvethe rapid downslope motion of large aggregates ofsediment. These movements include rockfall,landslides, debris flows, and slumps. In each case,the hillslope has become unstable, and the massmovement is a means of quickly redistributingmass.

Causes of mass movements include the additionof mass, as when mining tailings are piled on aslope; a decrease in particle cohesion, as whenprecipitation partially saturates a slope orseismic vibrations jar particles loose; or aremoval of lateral or underlying support, as whenan excavation for a roadway cuts away the toe ofa slope.

depend on channel and valley-bottom geometry,but will also influence that geometry.


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Sediment may also move downslope as individualparticles or small aggregates. Very intense rainfallon a slope of low permeability may create thinsheets of flowing water across the slope, and thiswater may carry sediment with it. The water mayalso concentrate into rills or gullies. The water’serosive force is greatly increased in these smallchannels. Both slopewash and rilling are particu-larly effective on sparsely vegetated slopes or onslopes that have been recently disturbed bysomething such as a forest fire. Finally, sedimentmay move very gradually downslope in cycles tiedto freezing and thawing or wetting and drying.This process of soil creep may be effective even ondensely vegetated slopes.

Once sediment enters a river channel, it mayremain in place, or be transported downstream indissolved, wash, suspended, or bedload. Dis-solved load refers to material carried in solution inthe water column. Dissolved load is high indrainage basins formed on rocks that are readilyweathered and eroded, and in drainage basinswhere water moving slowly through the subsur-face has time to react chemically with its sur-roundings before entering the stream channel.

Wash load is composed of fine sediments that arecarried in suspension and are deposited along thechannel margins to only a limited extent. Sus-pended load is also carried in suspension, but thesecoarser silt, sand, and gravel particles movesporadically, being carried some distance and thenstored for a time in the channel bed. Bedload iscomposed of the largest particles, which move byrolling, sliding, or bouncing, and always remain incontact with the channel bed.

The grain size distribution and mode of transportof sediment will determine residence time within ariver system: A clay particle that reaches a riverfrom the hillslopes may be transported through theentire system in a few years, whereas a boulderthat moves a short distance as bedload every fewdecades may remain in the river basin for millen-nia.

The relative importance of the different compo-

nents in Figure 1 varies with location in the drain-age basin (Figure 2). The upper portion of adrainage basin is primarily a source for water andsediment. The channels in this source zone tend tobe steep and narrow, with bedrock or bouldersforming the channel boundaries. Sediment intro-duced directly to the channels from the steephillslopes is moved rapidly downstream, withrelatively little sediment storage along the valleybottoms. In Colorado, this source zone is bestrepresented by the Rocky Mountains.

The central portion of a drainage basin is primarilya transport zone for water and sediment. Channelgradient decreases in the transport zone, and thenarrowly confined valleys of the source zone giveway to broader valleys with well-developed flood-plains and larger volumes of stored sediment.Sediment in storage throughout the transport zonehas a longer residence time than sediment in thesource zone, although the downstream sediment isperiodically mobilized. Many of the channels onthe plains of eastern Colorado and the plateaus ofwestern Colorado have the characteristics ofchannels in the transport zone.

The depositional zone at the downstream end of adrainage basin has very low-gradient channelsflowing across very broad valleys. This zone is asediment sink, where the finer sands, silts, andclays that have been transported from the uplandsare stored for long periods of time along the valleybottoms. For many of the rivers originating inColorado, this zone lies beyond the state borders,although some examples can be found in the SanLuis Valley.

Because of the close connection between hillslopesand channels in the source zone, anything thatalters the relationships diagrammed in Figure 1 islikely to affect river channels very quickly. Aforest fire that destabilizes a hillslope may cause anincrease in sediment yield to the channel during thenext rainfall. If the increase in sediment yield issufficiently large, pools along the channel may fillwith sediment, destroying fish habitat, and rifflegravels used for spawning may be become coveredwith silt.


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SSSS Figure 2. Schematic drainage basin illustrating natural sediment sourcesand sinks. This llustration may be applied to any scale of drainage basin.


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Because hillslopes and channels are dynamicsystems, they constantly adjust in response tovarious types of disturbances that affect differentlevels of Figure 1. Examples of disturbancesthat alter water and sediment yield to channelsare forest fires, intense rainstorms or seasonalvariability in precipitation, rockfalls, timberharvest, grazing, the raising of crops, roadconstruction, and urbanization. Each of thesefactors influences how precipitation falling on ahillslope moves down that hillslope into a chan-nel, and how that moving water carries sedimentwith it.

Disturbances that affect in-channel processesinclude floods, debris flows, dams and flowregulation by drop structures or diversionstructures, and placer mining. Different portionsof the drainage basin may respond differently tothese disturbances. A dramatic increase in waterand sediment yield may be necessary to changethe gradient of headwater channels, which areformed in very resistant bedrock and largeboulders. An increase of sediment may causeloss of pool volume in these channels, however,and a change in the size of the sediment formingthe channel bed. In contrast, an increase insediment yield to the lower portions of a drainagebasin may result in a shift from a meanderingchannel to a braided channel with numerous flowpaths between rapidly shifting bars.

Sometimes human structures mitigate the hazard-ous effects of natural processes, as when the damat Strontia Springs stored sediment mobilized bythe 1996 Buffalo Creek fire. The effects ofhuman activities differ from those of naturaldisturbances in that, with the exception ofclimate variability or massive wildfires, human-related disturbances are more likely to affect anentire drainage basin, and to create unforeseenhazards through their cumulative impact. Waterdiversion and flow regulation in the South PlatteRiver drainage basin, for example, are so exten-sive that they affect the ability of many channelsto redistribute sediments contaminated byagricultural runoff. Because of these unforeseenconsequences of human activities, and because ofthe continuing hazards posed by natural distur-bances to sediment movement, it is vital todevelop an integrated approach to hazard mitiga-tion that recognizes hillslope/channel and upper/lower basin linkages.

Sediment hazards in Colorado take three basicforms:

S excess of sediment,S decrease of sediment, andS contamination of sediment.

These hazards may be in reference to pre-human-settlement levels. For example, widespreadurbanization and an increase in paved area withina drainage basin may so decrease sediment yieldto a channel that the channel banks begin to

In contrast, changes in hillslope processes mustbe progressively more widespread, severe, orlong lasting to affect channels in the transportand depositional zones. These channels integrateprocesses operating over a much wider area, andthere is a time lag before changes in water andsediment yield reach these channels. The in-crease in sediment yield following the forest firein the upper basin may not be substantial enoughto affect channels in the transport zone if thesediment is gradually redistributed along theupper-basin channels. A regional shift in cli-mate, however, such as occurred in the centraland western U.S. during the 1930s, may besufficient to cause a change in channel processesthroughout a drainage basin.

Hazards associated with sediment

The movement of sediment from hillslopes andalong channels creates a hazard when it ad-versely impacts humans and their infrastructure,or something which humans value, such as fishhabitat. These hazards may result from pro-cesses that would occur in the absence of humanactivities, or they may result directly from thoseactivities. Timber harvest, for example, mayhave the same effect as a forest fire in that itresults in greatly accelerated movement ofsediment to river channels.


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Excess of sediment generally implies that flow inthe channel is not capable of transporting all ofthe sediment supplied, resulting in a change ofchannel pattern, loss of specific channel featuressuch as pools or spawning sites, filling of thechannel and overbank flooding, or filling of areservoir. Decrease of sediment implies that flowin the channel is capable of transporting moresediment than is being supplied. Consequently,the excess flow energy will be expended on

In order to mitigate these sediment hazards, wehave to first understand the controls on, andprocesses of, sediment movement on hillslopesand channels. Then we must understand howhuman actions alter these controls and processes,because there are today very few places in theState of Colorado where human actions do notplay a role. In addition, it is vital to recognizethat sediment transport, deposition, and erosionare natural processes that will always occuralong rivers. Finally, we must understand thesocietal, legal, environmental, and scientificconstraints on our ability to modify humanactions and to mitigate sediment hazards.

This report will summarize these three last issuesspecifically in reference to the State of Colorado.The report provides only a brief, non-technicalintroduction to a highly complex problem.Supplementary references that can assist thereader in gaining further understanding are listedat the end of the report.

erode, endangering structures near the banks. Aconcentration of grazing animals in the riparianzone may lead to loss of riparian vegetation anddecreased bank stability, which in turn results inmore sediment entering the channel, leading toloss of fish habitat. The hazards may also be inreference to what is desired for a specific use ofthe channel, as when an increase in sedimentfollowing a forest fire causes siltation anddamage to irrigation intake structures, or resultsin lost storage capacity behind a dam, thusshortening the expected life of the structure.

The hazards associated with river sediment maybe very local in scale, or they may affect a largeportion of a river’s drainage basin. Grazing alongthe riparian corridor, for example, may affectonly a few miles of river at and immediatelydownstream from the grazed portions of the river.Once the grazing animals are removed, the rivermay recover within a few years. At the oppositeextreme, toxic metals introduced into a river inassociation with mining may be transported tensto hundreds of miles downstream from themining site, and may persist as dangerouscontaminants for centuries after mining hasceased.

channel erosion, resulting in bank collapse,bridge-pier scour, channel downcutting, and otherchanges.

Sediments may be contaminated by materialstoxic to humans and aquatic organisms, such asagricultural and urban pesticides or miningleachates. Sediments may also be contaminatedby excessive levels of nutrients such as urbanand agricultural phosphorus which create algalblooms that reduce dissolved oxygen and harmfish populations, a problem in many of thereservoirs in Colorado used for human recre-ation.


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THE RIVERS OF COLORADO

The State of Colorado includes seven majorwater basins with 105,600 miles of rivers and3,260 lakes, reservoirs, and ponds. The Statecan be divided into three physiographic prov-inces; the eastern plains, the central mountains,

and the western plateaus and canyons (Figure 3).Each of these provinces has distinctive traits ofgeology, climate, soils, vegetation, topography, andland use that in turn produce distinctive types ofriver channels.

SSSS Figure 3. The State of Colorado, with major drainage networks and the threephysiographic provinces. The eastern plains are the white band at the right of thefiture; the mountains are indicated by the shaded band in the center of the figure;and the western plateau and canyon region is the white band at the left of the figure.The triangle at the western edge of the plains represents the City of Denver.

The plains rivers

The larger rivers of Colorado’s eastern plainsoriginate in the Rocky Mountains and are

dominated by the seasonal snowmelt cycle.Smaller tributary channels that originate on the


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plains flow mainly in response to summerrainfall. Prior to European settlement in Colo-rado, the plains rivers had strongly varying flowduring each year, with very little dischargeduring the dry times of the year and large floodsin late spring and summer. The channels werebroad and sandy, with low banks, sparse woodyvegetation, and many smaller channels betweenshifting sand bars. Abundant sediment wascarried along the channels.

The old expressions of the Platte River as “a milewide and an inch deep”, and “too thick to drinkbut too thin to plow” aptly describe the characterof the plains rivers. A warm water fish faunadominated by red shiner, sand shiner, fatheadminnow, longnose dace, white sucker, plainskillifish, and green sunfish lived in these chan-nels. The channels had small clumps of greenash, plains cottonwood, box elder, and willowgrowing along the banks.

The sediment carried by the plains rivers wasultimately derived from weathering and erosionof the Rocky Mountains, and from sedimentcarried into the drainage basin by wind, butmuch of the sediment was locally derived fromthe channel bed and banks, the river’s floodplain,and the nearby hillslopes.

Following the intensive settlement of the plainsthat began with the 1859 gold rush, land-usepractices so altered the water and sediment flowsalong the plains rivers that the channels under-went what scientists call “river metamorphosis”— a thorough change in channel functioning andpattern. The primary influence was flow regula-

tion and diversion, which reduced seasonal floodpeaks and increased dry-season base flow in thechannels. As irrigation water that was divertedand spread across agricultural fields filtered intothe subsurface, regional water tables rose.

These changes in surface and subsurface watermovement facilitated the growth of riparian(stream-side) vegetation. As the vegetation alongthe channel banks grew thicker and erosivefloods decreased, more sediment moving alongthe channel was trapped on the banks, and thechannels gradually became narrower. Channelsthat in the 1800s had been 1400 ft wide andbraided, had by 1980 narrowed to only 300 ftwide, and meandered between densely woodedbanks.

The amount of sediment carried by the plainsrivers decreased as dams built across the riversserved as large settling tanks, and the smallerseasonal high flows had less energy to carrysediment. The water in the deeper, shadedchannels became cooler than it had been histori-cally, and the native fish were displaced byspecies such as common carp, largemouth bass,bluegill, black crappie, and yellow perch thatwere tolerant of the new conditions. Wildlifetraditionally confined to the eastern US spreadwestward along these river corridors, so thatwhite tail deer and eastern bluejays reachedColorado. The exotic riparian species tamarisk,Russian olive and Siberian elm have also invadedthe river corridors, displacing some of the nativespecies and increasing the stability of the riverbanks and islands (Figure 4).


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SSSS Figure 4. The State of Colorado, dotted lines paralleling watercoursesindicate the extent of the exotic riparian tree tamarisk, as of 1988.

The mountain rivers

The rivers of Colorado’s central mountains arelargely driven by snowmelt and have peak flowsin late spring or early summer. Superimposed onthis seasonal cycle are flash floods generated bysummer thunderstorms below approximately7600 ft in elevation. These flash floods can beparticularly destructive, as in the case of the1976 Big Thompson flood. The mountain riverstend to be steep and rocky, closely confined byvalley walls. The water is cold and clear, withvery little sediment transport except duringfloods, and the native aquatic insects and fishhave adapted to these flow conditions.

Greenback cutthroat trout, Colorado Rivercutthroat trout, Rio Grande cutthroat trout,

mountain sucker, and Rocky Mountain whitefishare native to the mountain channels, but theyhave been largely displaced by introducedrainbow, brook, and brown trout. Along thechannels grow narrowleaf cottonwood, riverbirch, alder, red osier dogwood, chokecherry,and willow. Sediment movement along themountain rivers is very closely tied to hillslopeprocesses, because debris flows and rockfallscommonly introduce sediment directly from thesteep canyon walls to the river. Many of theindividual particles of sediment are so large thatthey remain stable in the channel, moving onlyduring very large floods. Relatively little of theriver’s sediment load is derived from the sur-rounding valley bottom.


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Like the plains rivers, the mountain rivers ofColorado have also been significantly affected byhuman activities during the past two centuries.By removing millions of beavers during the1820s-1840s, the fur trappers also removed thesmall dams maintained by the beavers. These logdams, and the ponds behind them, slowed thepassage of floods, trapped some sediment, andcreated a more diverse environment for aquaticand riparian organisms.

Starting in 1859, placer and lode mining had amuch more substantial effect on the channels.Miners commonly stripped the channel sedimentsto bedrock in productive mining regions, in theprocess greatly increasing sediment mobility andconsequently reducing water quality and killingmany aquatic organisms. The increase insediment transport was so severe that irrigatorson the plains portion of these rivers complainedthat their intake structures were being buried bysediment. The miners introduced heavy metalsthat have persisted in the stream sediments longafter mining ceased, creating toxic contaminationof these sediments.

The need to transport people and goods betweenthe mountains and other regions lead to wide-spread road and railroad construction, and thedisruption of hillslope vegetation and soilsassociated with these activities caused a furtherincrease in sediment to the mountain rivers.Many of the ties used in construction of localrailroads and transcontinental lines such as theUnion Pacific came from trees cut in the FrontRange. The timbers were stacked beside therivers during the winter, and then rafted down-stream to towns such as Ft. Collins or Greeleyduring the spring flood. The rafting of hundredsof thousands of logs down a mountain river actedlike a mammoth scouring brush on the river;channel width increased, pool volume decreased,the channel bed was disrupted and sedimentmobilized, and the riparian vegetation wasdamaged or destroyed.

Simultaneous with these changes, the growinghuman communities at the foot of the mountains

were storing and diverting water from higher andhigher in the drainage basins, causing changes inflow magnitude, timing, and duration. The resultof all of these impacts has been a shift towardmore uniform rivers. The abundant woodydebris and beaver dams that used to create deeppools have given way to channels with smallerpools and greater lengths of runs or riffles. Thechanges in flow regime and channel form, alongwith competition from introduced species, haslead to endangered status for the native green-back cutthroat trout, and has caused a generaldecline in the abundance and diversity of bothriparian and aquatic species.

The rivers of Colorado’s western plateaus andcanyons are similar to those of the eastern plainsin that flow in the larger rivers is dominated bysnowmelt from the mountains, whereas thesmaller, ephemeral channels may be driven byrainfall from summer thunderstorms. The riversof western Colorado are commonly confined bybedrock canyons that may be very steep andnarrow, or may have a broad valley bottomcovered by a thick veneer of sediment. Many ofthese canyon rivers have alternating pools andrapids, with the coarse sediment that forms therapid coming from rockfall or from debris flowsand floods down the tributary canyons. Thewater of the western rivers was historically warmand turbid with sediment, supporting awarmwater fauna of Colorado squawfish,bonytail chub, razorback sucker, humpbacksucker, roundtail chub, speckled dace,flannelmouth sucker, bluehead sucker, andmountain sucker. These rivers also supportedlarge stands of Fremont cottonwood, sandbarwillow, peachleaf willow, and hackberry alongthe valley bottoms.

During the past 100 years, and particularly sincethe 1930s, flow along the western rivers has beenextensively regulated by a series of large damsand diversions, such as Williams Fork Reservoiron the Williams Fork River, Green Mountain

The plateau and canyon rivers


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Reservoir on the Blue River, Flaming GorgeDam on the Green River, or Blue Mesa Reservoiron the Gunnison River. Contemporaneous withthese changes were the accidental and deliberateintroduction of non-native fish species includingred shiner, northern pike, fathead minnow,channel catfish, longnose sucker, white sucker,common carp, smallmouth bass, green sunfish,black crappie, and sand shiner. The fourteennative Colorado River fish now have to competewith more than forty non-native species.

Also introduced was the non-native riparian planttamarisk. Tamarisk is a particularly tenaciousand successful plant that quickly colonizes newriver-bank deposits and grows in dense standsthat effectively trap sediment. Combined withthe decrease in flood peaks following flowregulation, the spread of tamarisk has causeddramatic channel narrowing and a decrease insediment load along some western Coloradorivers. Between 1870 and 1970 the Green Riverin Dinosaur National Monument, for example,narrowed by up to 55% of its former width.The water released by the large dams is cold,

clear, and poor in nutrients. This change inwater quality, combined with changes in themagnitude, timing, and duration of flow, theintroduction of non-native species, and the loss offloodplain habitat, has caused the Coloradosquawfish, the humpback chub, and the razor-back sucker to decline to the point that they mustbe listed as endangered. The native cottonwoodgroves are also threatened along many of thewestern rivers because of the competition fromtamarisks and the change in channel dynamicsassociated with flow regulation.

Many of Colorado’s rivers have undergonesubstantial changes since 1800 as a result ofhuman activities (Figure 5). In some instances,the effects of these activities completely dominatethe natural controls on sediment movement intoand along the rivers. However, there remainsediment issues that are unique to each of thethree physiographic provinces because of thegeologic and climatic characteristics of thoseprovinces. The next section of this reporthighlights a series of examples of sedimenthazards in Colorado.

SSSS Figure 5. The State of Colorado. Black dots indicate dams and reservoirs inthe state, including very minor reservoirs.


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SEDIMENT HAZARDS IN COLORADO

Most of the case studies of sediment hazardshighlighted in this section somehow involve humanimpacts on sediment processes. Human activitiesmay indirectly affect river channels if the move-ment of water and sediment from hillslopes tochannels is altered. Examples of such activitiesinclude timber harvest, crops, grazing, roadconstruction, and urbanization. Human activitiesmay also directly affect river channels by alteringthe flow of water and sediment along the channel,as results from dams, flow diversions,channelization, beaver trapping, or placer mining.These types of effects have occurred on riverchannels throughout Colorado.

Examples of hazards associated with excess sediment

(1) North Fork Poudre River, Larimer County:The draining of Halligan Reservoir in lateSeptember 1996 was accompanied by the releaseof approximately 7,000 cubic yards of clay togravel sized sediment that had accumulated in thereservoir. Flow from the drained reservoir wasshut down immediately after the sediment wasreleased, allowing the sediment to settle alongmore than 10 miles of river downstream from thereservoir. The sediment covered riffles with athin veneer and filled pools up to 14 feet deep(Figure 6). The immediate effect of the sediment

Figure 6. Looking upstream along the North Fork Poudre River in October 1996,following the sediment release from Halligan Reservoir (approximately 500 yardsupstream from this view). The portion of channel in the foreground is a pool thatwas up to 14 feet deep prior to the sediment release.


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release was a massive kill of aquatic organisms;the Colorado Division of Wildlife (CDOW)estimated 4,000 dead fish along the ten miles ofchannel immediately downstream from the reser-voir. Over the longer term, the continuing pres-ence of excess fine sediment along the channel hasinhibited re-colonization by aquatic insects andfish. CDOW is now proposing to re-stock fishalong a river that had supported a self-sustainingpopulation prior to the sediment release.

(2) Sheep Creek (northern Poudre River drainagebasin), Larimer County: Segments of the SheepCreek banks have been fenced as grazingexclosures since 1956 so that the impact ofdifferent intensities of grazing can be evaluated.Comparison of grazed and ungrazed segments

immediately adjacent to one another along thechannel indicates that grazing cows trample thestream banks and destroy riparian vegetation,causing an increase of fine sediment in thechannel. This excess fine sediment preferentiallyaccumulates in pools, reducing fish habitat. Thefine sediment also infiltrates the riffle gravelsused by fish for spawning, with the result that theflow of water and oxygen past the fish eggs isreduced, and the embryos die. The removal ofover-hanging vegetation and the trampling of thebanks creates a wide, shallow channel with warmwater, whereas most of the aquatic organismsliving in channels such as Sheep Creek areadapted to cold, clear water with overhead coverthat protects them from predators (Figures 7 and8).

Figure 7. Looking downstream along a portion of Sheep Creek that is excludedfrom grazing. The channel is densely shaded by willows, and is approximately12 feet wide.


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(3) Buffalo Creek, Jefferson County: Following aforest fire that burned 2,000 acres of the BuffaloCreek drainage in May 1996, massive sedimentyields came from the burned hillslopes during aseries of rainstorms in June and July 1996 and1997 (Figure 9). The highly weathered graniteunderlying the hillslopes provided a source ofabundant sediment once the vegetation wasremoved during the fire. The summer rainstormscaused 9 floods that were greater than the 100-year flood (pre-fire conditions), as well asnumerous smaller floods (R. Jarrett, U.S. Geo-logical Survey, unpub. report). Sediment associ-ated with the floods and debris flows filledchannels and culverts, buried houses and otherstructures along the channel banks, and caused

several million dollars in public and privateproperty damage. Two lives were lost during the12 July 1997 flood. The combination of exces-sive sediment and large woody debris thataccumulated downstream from the burned area,in Strontia Springs Reservoir, reduced waterquality in the reservoir and threatened reservoiroperations to the point that the City of Denverflushed sediment from the reservoir three timesbetween September 1996 and September 1997.Nutrients contained within this sediment intro-duced thousands of tons of nitrogen and phos-phorus into Chatfield Reservoir, downstreamfrom Strontia Springs, and affected water qualityin Chatfield.

Figure 8. Looking across the channel of Sheep Creek immediately upstream fromthe view in Figure 7. This portion of the channel is open to cattle grazing. Thechannel here is approximately 30 feet wide.


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(4) Green River, Moffat County, DinosaurNational Monument: With the completion ofFlaming Gorge Reservoir in 1962, flow along theGreen River downstream from the dam changeddramatically. Prior to the dam, the spring floodwould last for approximately a month, with anaverage discharge of 32,000 ft3/s. The springflood since the dam has averaged 4,000-4,700ft3/s. This reduction in peak discharge decreasedthe river’s ability to transport the silt and sandabundantly supplied to the main channel bytributaries such as the Yampa River. Thedecrease in scouring of the channel bed andbanks by floods also facilitated the invasion ofthe non-native riparian tree tamarisk, whichgrows in dense thickets that effectively trap

(5) Arkansas River, Pueblo County: Water storagein Pueblo Reservoir has reduced the volume andvelocity of flow along the Arkansas River down-stream from the reservoir to the point that thechannel is accumulating sediment. Citizens andcity officials in La Junta believe that this accumu-lation of sediment in the channel, in combination

Figure 9. Views of Buffalo Creek during the summer of 1996, following the forestfire and subsequent floods. The upper photograph is looking upstream along asmall tributary channel. In the foreground of the photograph, sediment is beingalternately stired and then eroded and transported downstream from a former pool.Note the eroded banks at the rear of the photograph. The lower photograph is of anarea of extensive sediment deposition, and damage to structures, along BuffaloCreek. The creek is at the far right in this photograph.

sediment. As a result, portions of the GreenRiver narrowed by 55% between 1871 and 1976.Fine sediment accumulation on spawning bars,along with the loss of floodplain nursery habitatand competition from introduced fish, hasendangered the native species Colorado squaw-fish, razorback sucker, and humpback chub inthe Green River.


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(2) Elkhead River, Moffat County: Elkhead Reservoirwas constructed along the Elkhead River outside ofCraig, Colorado in 1974. Landowners along theriver have subsequently alleged that excessiveerosion has occurred along this sand-bed meander-ing channel as a result of sediment retention in thereservoir. Approximately 4 miles of channel belowthe reservoir are affected, and in some areas thechannel has migrated 70 feet laterally during thepast 30 years.

Examples of hazards associated with contaminated sediments

(1) California Gulch, Arkansas River basin, LakeCounty: The former mining area of CaliforniaGulch has been designated as a Superfund site bythe U.S. Environmental Protection Agency. Con-centrations of heavy metals (Mn, Fe, Cu, Zn, Pb,

(2) South Platte River, Adams, Weld, Morgan,Logan, Sedgwick Counties: The lower portion ofthe South Platte River basin in Colorado hasbeen impacted by various human activities sincethe 1850s. Agricultural and urban land use inparticular have produced contaminants carriedinto stream channels by surface runoff andsubsurface flow. These contaminants are storedin river sediments for varying lengths of time, aswell as being transported by stream flow andaccumulating in the bodies of aquatic organisms.

The U.S. Geological Survey has made the lowerSouth Platte River one of the target basins for theNational Water Quality Assessment (NAWQA)Program. As of early 1998, NAWQA scientistshad identified agricultural herbicides (atrazine,metolachlor, EPTC, cyanazine, DCPA, alachlor)and urban herbicides (prometon, simazine) andhousehold insecticides (diazinon, carbaryl) in theSouth Platte River, as detailed on the NAWQASouth Platte River home page on the Internet.Concentrations of these contaminants increase insummer and during stormwater runoff, butpersist year-round.

In addition, approximately 7,000 tons of nitro-gen and 860 tons of phosphorus enter streams inthe basin each year, and phosphorus concentra-

Examples of hazards associated with the decrease of sediment

(1) Bessemer Ditch, Pueblo County: This irrigationditch takes water out of Pueblo Reservoir on theArkansas River. Prior to construction of thereservoir, the ditch had a 15-18% water loss toinfiltration. This increased to 45% water lossfollowing construction of the reservoir. The changein infiltration rate has been attributed to theabsence of fine sediment in the flow along theditch; previously, this fine sediment accumulated inthe cracks that form periodically along the ditch,filling the cracks and reducing water loss. Ap-proximately 10 miles of the 35-mile long ditch havebeen lined with cement, following a $1 millionlawsuit that forced the government to line the ditch.

with the invasion of phreatophytic vegetation inthe channel, has reduced flow conveyance,enhanced overbank flooding, and increasedinfiltration of water along the channel. As aresult, the local water table has risen to the levelthat there are problems with saturation and salin-ization of agricultural fields, and flooding inresidential basements.

tailings piles to the river, and are now carrieddownstream in suspension during high dis-charges. Much of the historic mining activitywithin the Arkansas River basin occurred alongtributary streams. Today, the diversity and totalabundance of aquatic insects are lower down-stream from the junction of contaminated tribu-tary streams, and higher below the junction ofclean tributaries. The fish population is reducedor absent below the contaminated tributaries.Both insects and fish at polluted sites have higherconcentrations of Zn, Cd, and Cu than thoseupstream.

Mb, Cd) in the Arkansas River downstream fromCalifornia Gulch are highly dependent on flowand tend to increase during high spring runoff.This suggests that these metals are abundant inthe fine sediments that have traveled from the


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(4) Terrace Reservoir, Alamosa River, ConejosCounty: Terrace Reservoir is 15 miles down-stream from the Summitville Mine site, whichhas a history of underground and surface mining.The site has had increased surface mining sincethe early 1980s, which has resulted in increasedsediment yield to the river and the reservoir.Sediments in the reservoir have levels of zinc,cadmium, lead, arsenic, copper, antimony,aluminum and iron that are elevated relative tobackground levels of these metals (elevated up toone thousand times background levels, in thecase of copper). Fish kills have occurred in thereservoir, which is no longer fishable. Thereservoir owners have also released sedimentsdownstream into the Alamosa River.

(3) Upper Colorado River, Summit, Eagle,Garfield, Mesa, Delta, Montrose, and OurayCounties: The upper Colorado River basin isanother NAWQA study site. Bed sedimentsalong several channels (e.g. French Gulch, PeruCreek, Cross Creek, Oh-be-joyful Creek, SnakeRiver, Uncompahgre River) contain high levelsof trace metals downstream from mining sites.Although the United States has not set standards

numbers of fish near urban areas. Organochlo-rine compounds not used since 1972-1988 arestill present, and at some sites these compoundsoccur at concentrations above levels of concern.The National Academy of Sciences guidelines forconsumption of fish by wildlife are exceeded forDDT, PCB, and chlordane at some sites alongthe South Platte River. Further details of con-tamination along the South Platte River may beaccessed at http://webserver.cr.usgs.gov/ nawqa/splt/splt_home.html/.

for bed sediment contamination, the concentra-tions of zinc, cadmium, lead, copper, and arsenicin these sediments are at levels judged by Cana-dian standards to have adverse affects on aquaticbiota. Fish at these contaminated sites arereduced in number or absent, and the fish haveelevated levels of metals in their bodies. Al-though the metal concentrations in bed sedimentsdrop quickly proceeding downstream from themining sites, suspended sediments carry thecontaminants much farther downstream.

tions exceed the U.S. Environmental ProtectionAgency recommended limit for avoiding acceler-ated algae growth in lakes and reservoirs.Nutrient loads are highest downstream fromGreeley, which has extensive feedlots.

The South Platte River has fewer species and


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OUR OPTIONS FOR MANAGING SEDIMENT AND WATER

Our abilities to mitigate the types of sedimenthazards outlined in the preceding sections of thisreport are constrained by societal and legal consid-erations, environmental considerations, and techni-cal considerations. Ultimately, mitigating sedimenthazards will mean (1) keeping sediment out of siteswhere it creates a hazard, or removing the sedimentonce it reaches those sites; (2) supplying sedimentto sites where its absence creates a hazard; or (3)containing contaminated sediment, or removing thatsediment from sites where it creates a hazard.Water is critical to each of these mitigation methodsbecause water is the most common agent of sedi-ment transport, and the ratio of water/sediment willgovern whether there is an excess or absence ofsediment.

Societal and Legal Constraints

Both past and future trends in Colorado willconstrain our ability to devise solutions that utilizewater to mitigate sediment hazards. Colorado hasan extremely complex history of water-law prece-dents, as well as the largest number of waterlawyers per capita of any state. Because the systemof prior appropriation, which serves as the ultimatebasis for water allocation in Colorado, the ability touse water to supply or remove sediment from a sitewill be governed in many cases by the ratio ofwater costs to sediment-hazard costs. For over-appropriated rivers, the water necessary to reducesediment hazards simply may not be available on aregular basis. At present, we do not have well-defined legal connections between water qualityand water quantity.

Continuing trends of population growth in Coloradowill also constrain our uses of water. The FrontRange urban corridor of Ft. Collins to Pueblopresently has 3 million people; demographicprojections predict 3.8 million people by the year2020. However, the rapid growth of cities such as

The expectations of Colorado residents with respectto rivers are also changing. A predominantly urbanpopulation tends to place a high value on water-based recreation such as trout fishing, whitewaterrafting, and reservoir fishing and boating. Indi-vidual groups of recreational users may preferdifferent patterns of water use (e.g. reservoirboating vs. whitewater rafting). Urban dwellers arealso likely to have certain expectations with respectto rivers flowing through their communities; thesechannels should have clean, flowing water yearround, but should not be subject to extreme floodsor to lateral movement such as meander migration.In addition to the expectations of their constituents,local government agencies are subject to city,county, state, and federal regulations on floodcontrol and urban drainage when designing watermovement in urban environments.

A final legal constraint on water use is the State’slegal obligations to other groups of water users. Asone of the Upper Basin states in the 1922 ColoradoRiver compact, the State of Colorado’s use of thatriver’s water is strictly confined. We also haveother obligations to surrounding states such asNebraska that are downstream along the SouthPlatte River. Native American groups are arguingfor water rights, as in the case of the Ute MountainUte Indian Tribe and the Animas-La Plata project,and federal land-management agencies are alsolegally requesting water rights related to the landsunder their jurisdiction.

Sediment removal that is not water-based will besubject to legal constraints in the form of state andfederal permitting procedures for dredging andfilling operations.

Durango and Steamboat Springs suggests that otherregions of the state will also have increasing waterdemands. As demographic balance in the statecontinues to shift from agriculture toward urbanand industrial consumption, both the pattern ofwater use and the cost of water will change.


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Enforcement of measures such as the EndangeredSpecies Act, for example, may involved specify-ing the instream flow necessary to maintain anendangered species. Federal regulations alsogovern activities in specially-designated publiclands including the national parks, nationalforests, and wilderness lands administered by theForest Service or the Bureau of Land Manage-ment. State regulations such as those governingColorado’s Clean Water Act, which includesnarrative sediment regulations administered bythe State Water Quality Control Commissionwith oversight by the U.S. EPA, pose additionalpotential constraints.

The enforcement of these various Acts byregulatory agencies may be limited by other legalconstraints, such as prior appropriation orprivate property rights, because water quality isoften related to water quantity. (The legalconnection of water quantity and quality remainsvague, however.) With increasing public demandfor habitat preservation and outdoor recreation, itis no longer considered acceptable to mitigatesediment hazards to human structures at theexpense of river ecosystems, as indicated by thepublic indignation following the deliberaterelease of sediment from Halligan Reservoir in1996.

Our ability to mitigate sediment hazards is alsoconstrained by our limited knowledge of thephysical and chemical processes by which

Our ability to mitigate sediment hazards mayalso be constrained by difficulties in identifyingthe source of the hazard. We know relativelylittle of the “natural” or background levels ofsediment present along some rivers in Coloradoprior to 19th century human occupation of theriver basins. This knowledge is particularlylacking for the eastern plains rivers. There isgeological evidence of decades-long cycles ofsediment accumulation and subsequent erosionalong these rivers, independent of human land-use, and these cycles seem to be inherent to riversin arid and semiarid regions of the westernUnited States. Because of this inherent variabil-ity in sediment yield, it may be difficult todetermine the specific cause of an increase ordecrease in sediment along a river.

adsorbed onto particles of silt and clay and moveonly when the sediment moves. It is possible to testthe effects of individual contaminants on a variety

Environmental Constraints

Legislation designed to protect environmentalqualities, as well as public demands for environ-mental protection, will constrain some optionsfor mitigating sediment hazards. Environmentallegislation includes specific federal measuressuch as the Endangered Species Act, the CleanWater Act, and the Wild and Scenic Rivers Act.These Acts may regulate water, and hencesediment distribution.

Technical Constraints

because if the sediment grain is sheltered by otherlarger particles the current will have to be muchfaster to move it than if the sediment grain isexposed on a flat channel bed. The uncertaintyassociated with this range of velocities maytranslate into a substantial uncertainty in thedischarge necessary to flush sediment from achannel reach of concern.

sediments and contaminants move through a riverdrainage basin. Both sediment yield fromhillslopes and sediment movement in riverchannels are stochastic and unpredictable in thatthey are controlled by site-specific conditions thatare difficult to characterize adequately enough forquantitative modeling and prediction. Numerousstudies have demonstrated that timber harvest oragriculture within a drainage basin will increasesediment movement into river channels. But theexisting sediment-routing models are not yet able tospecify precisely that a 3% increase in cattlegrazing within the basin, for example, will cause a2% increase in sediment yield each year, which willin turn result in a 50% decrease in the useful life ofa reservoir downstream.

Similarly, we can predict the average flowvelocity at which a given size grain of sedimentwill begin to move in a stream, but that averagevalue may have a high standard deviation


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We also know far too little about the behavior ofcontaminants in natural environments. Somesubstances move downstream in solution, othersare of organisms in a lab setting, but it has beendifficult to adequately reproduce the variouscombinations of contaminants to which anorganism may be exposed in the real world. Andit has proven difficult to predict chemicalchanges in contaminants once they enter theenvironment, such as the breakdown of DDT toDDE.

Legal, societal, environmental, and technicalconstraints pose numerous and complicatedchallenges for mitigating sediment hazards inColorado as we enter the 21st century. Popula-tion growth in Colorado is unlikely to decrease inthe immediate future, and individuals and groupsof people are unlikely to stop pressing for theforms of natural resources management that theybelieve to be most appropriate. Within theseconstraints, there are some basic steps that maybe taken toward mitigating present and futurehazards resulting from sediments.


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RECOMMENDATIONS FOR THE FUTURE

When addressing water and sediment issues inColorado, we must begin by recognizing that wecannot restore the State’s rivers to pre-19thcentury conditions, but we also cannot linearlyextrapolate present patterns of water use withouta serious degradation of the environment and ourquality of life. The magnitude of the problemfacing Colorado is suggested by the list ofreservoirs within the State which are associatedwith some type of sediment hazard (Table 1).Americans have always struggled to find abalance between individual freedom and propertyrights versus the duty of the government to

protect the rights and quality of life for the publicas a whole. This is exemplified by past treatmentof sediment issues in Colorado, where flowregulation or land use by private individuals orsmall companies may clash with governmentalprotection of clean water. Too often, decisionsbetween these competing interests have beendecided on a case-by-case basis, with legalprecedents given equal or greater weight thanscientific understanding of the physical processesinvolved. We begin, therefore, with twobroadscale recommendations:

(1) Sediment hazard issues must be considered at the scale of the entire drainagebasin, rather than on a very site-specific basis.

The loss of reservoir storage capacity may be adirect result of poor land-use and lang-manage-ment practices upstream from the reservoir, andthe sediment release designed in an attempt torestore reservoir capacity may damage aquatichabitat downstream. The point is that thereservoir is not an isolated entity; it is closelyconnected to processes upstream and down-stream. Therefore, any long-term plan to miti-gate sediment hazards at the reservoir must alsoconsider upstream and downstream controls. Inaddition, sediment generated at one point along ariver may be carried miles downstream before itis deposited.

In practice, such an approach to hazard mitiga-tion will probably require government oversightrather than piecemeal individual control. Al-though state government agencies have anabundance of work with existing regulations, itseems apparent that unless a knowledgeable,interdisciplinary oversight body is charged withthe task of drainage-basin-scale management,problems will continue to be addressed within aninappropriately confined scope.

(2) The process of effective mitigation of sediment hazards would be facilitated by adecision-making process resting on scientific understanding of sediment dynamicsrather than on legal precedents or court mandates.

For example, following the 1996 sediment releasefrom Halligan Reservoir, a group of state govern-ment employees, private water users, environ-mental activists, and research scientists wasformed to develop protocols for reservoir sedi-ment release that would avoid the environmentaldegradation associated with the Halligan release.

This is a less divisive and costly approach than alawsuit to compensate parties adversely impactedby the sediment release. If analogous groupscould develop protocols for minimizing the typesof sediment hazards outlined in this report,everyone in Colorado would benefit greatly. Thedevelopment of such protocols depends closely


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RESERVOIRS

Cherry CreekChatfieldBear CreekBarrJackson LakeMiltonPrewitt

TellerMaryLadoraDerbyMcPheeNavajoNarraguiunepSanchezTerracePueblo

HalliganDeWeeseStrontia SpringsPaoniaKenney

HAZARD

Contaminants - phosphorus

Contaminants - toxics/metals

Excess sediment (perceived as aproblem because of loss ofstorage within reservoir, orbecause reservoir releases toomuch sediment to river downstream)

At the more specific level, there remain several issuesthat must be addressed before we can effectively

manage sediment. Each of these requires basicand applied research into sediment movement.

(3) Sediment accumulation in reservoirs

This is one of the most widespread sedimenthazards in Colorado. We must improve our

on widespread recognition and understanding ofsediment issues. It seems unlikely, for example,that reservoir operators would deliberately

Table 1. A partial list of reservoirs in Colorado associated with some type of sediment hazard (Source:State Dept. Of Public Health and Environment, Water Quality Division, 305B Report, 1994). In additionto the reservoir problems listed here, the Colorado Department of Public Health and Environment’s 1998303(d) report (Water Quality Limited Segments Still Requiring TMDLs) lists 85 river segments withsediment problems, 12 river segments with metal-contaminated sediments, and 6 river segments withnutrient contamination.

destroy fish habitat or water quality if they wereaware of other, less hazardous methods ofmanaging sediment.

understanding of how to limit sediment move-ment into, and accumulation in, reservoirs.


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(4) Sediment transport along channels

Whether the excess sediment comes from basin-wide land use, reservoir release, or flow diminu-tion, sediment accumulation and consequent loss ofwater quality and habitat remain a problem alongmany rivers. We need to develop models thatdescribe how various types and quantities of

(5) Contaminant dispersion and disposal

We are desperately in need of basic research onhow individual contaminants combine with eachother and with sediment along a stream channel;where they are stored and when they are mobilized;how they affect aquatic organisms and humans;and how long they remain biologically dangerous.We also need to develop basic protocols on how toremove contaminated sediments; how removal isaccomplished; who pays for removal; and wherethe contaminated material is to be stored.

The hazards posed by sediment along rivers inColorado are complex. Mitigation of these hazardsrequires a carefully planned and integrated ap-proach which must include people with variousbackgrounds and areas of expertise. However,

Technologies exist for sediment dredging,bypassing, and flushing, but most of these arelimited in application by cost or by downstream

consequences such as possible water qualityreduction from contaminants in the reservoirsediment.

sediment are transported along different types ofchannels. Such models could specify, for ex-ample, the minimum flushing flow necessary toprevent downstream pool sedimentation during areservoir sediment release.

recognition of a problem is the first step towardsolving that problem. We can continue to dealwith each sediment hazard as it develops at aspecific site. This approach is reactive andcostly in that the situation is allowed to reach ahazardous level before action is taken, and thataction is very limited in scope. Or, we candevelop a proactive means of mitigating sedimenthazards by designing basin-scale protocols foranticipating and preventing sediment-relatedhazards such as sediment releases from reser-voirs or the downstream transport of contami-nated sediments. As increasing populationintensifies land use in Colorado, the potential forsediment-related hazards also increases. Now isthe time to act.


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References

M. Collier, R.H. Webb, and J.C. Schmidt. 1996. Dams and rivers: primer on the downstream effects ofdams. U.S. Geological Survey, Circular 1126, 94 pp.

K.D. Fausch and K.R. Bestgen. 1997. Ecology of fishes indigenous to the central and southwestern GreatPlains. In, F.L. Knopf and F.B. Samson, eds., Ecology and conservation of Great Plains vertebrates.Springer-Verlag, New York, p. 131-166.

W.L. Graf. 1978. Fluvial adjustments to the spread of tamarisk in the Colorado Plateau region. GeologicalSociety of America Bulletin, v. 89, p. 1491-1501.

W.L. Graf. 1979. Mining and channel response. Annals of the Association of American Geographers, v.69, p. 262-275.

L.J. Gray and J.V. Ward. 1982. Effects of releases of sediment from reservoirs on stream biota. ColoradoWater Resources Research Institute, Completion Report No. 116, 82 pp.

M.M. Hilmes and E.E. Wohl. 1995. Changes in channel morphology associated with placer mining.Physical Geography, v. 16, p. 223-242.

D. Knighton. 1984. Fluvial forms and processes. Edward Arnold, London,

C.T. Nadler and S.A. Schumm. 1981. Metamorphosis of South Platte and Arkansas Rivers, easternColorado. Physical Geography, v. 2, p. 95-115.

R.J. Naiman, C.A. Johnston, and J.C. Kelley. 1988. Alteration of North American streams by beaver.BioScience, v. 38, p. 753-762.

R. Olson and W.A. Hubert. 1994. Beaver: water resources and riparian habitat manager. University ofWyoming, Laramie, 48 pp.

A.D. Richmond and K.D. Fausch. 1995. Characteristics and function of large woody debris in subalpineRocky Mountain streams in northern Colorado. Canadian Journal of Fisheries and Aquatic Sciences, v. 52,p. 1789-1802.

R. Schmal and T. Wesche. 1989. Historical implications of the railroad crosstie industry on current ripar-ian and stream habitat management in the central Rocky Mountains. In, R.E. Gresswell, B.A. Barton, andJ.L. Kershner, eds., Practical approaches to riparian resource management: an educational workshop. May8-11, 1989, Billings, Montana, p. 189.


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About the Colorado Water Resources Research Instituteand WATER IN THE BALANCE

The Colorado Water Resources Research Institute(CWRRI exists for the express purpose of focusingthe water expertise of higher education on theevolving water concerns and problems faced byColorado citizens. CWRRI strives to constantlybring the most current and scientifically soundknowledge to Colorado’s water users and manag-ers.

For more information about CWRRI and/or thewater expertise available in the higher eductioninstitutions in Colorado, please contact CWRRI atthe address below or by phone, fax, or email asfollows:

Phone: 970/491-6308

FAX: 970/491-2293

E-mail: [email protected]

CWRRI went on-line with its web page inDecember of 1994. The CWRRI home page islocated at the following URL:

http://www.colostate.edu/Depts/CWRRI

WATER IN THE BALANCE was created in thespirit of informing the public about complexwater management issues.

The activities on which this report is based werefinanced in part by the Department of the Inte-rior, U.S. Geological Survey, through the Colo-rado Water Resources Research Institute underAward Number 1434-HQ-96-GR-02660. Thecontents of this publication do not necessarilyreflect the views and policies of the Departmentof the Interior, nor does the mention of tradenames or commercial products constitute en-dorsement by the United States Government.

Colorado Water Resources Research Institute410 N University Services CenterFort Collins, CO 80523

river sediment sources and sediment hazards in colorado

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