DAMS AND RIVERS 

A Primer on the Downstream Effects of Dams 

By MICHAEL COLLIER. ROBERT H. WEBB. and JOHN C. SCHMIDT 

U.S. GEOLOGICAL SURVEY 

Circular 1 1 2 6 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

Charles G. Groat, Director 

For additional information write to: 

Regional Research Hydrologist 

U.S. Geological Survey 

3 4 5 Middlefield Road. MS-4 7 2 

Menlo Park. CA 94025 

First printing: 

1996 

Second. revised printing: 

2000 

Copies of this report are available from: 

U.S. Geological Survey 

Branch of Information Services 

Box 25286 

Denver. CO 80225 
!Forewora 
.!llck._nowfecfgments 

We appreciate the input of Hector Morales. Lester Ray 

Talley. Frank Almendariz. John Taylor. and Doug Milam. 

who live and farm along the Rio Grande and 

Chattahoochee River. The following individuals contributed to this project by discussing with the authors their 

involvement with. and observations about. dams along 

rivers: Curt Kennedy. Salt River Project. Phoenix; Woody 

Fine. Forest Service. Hells Canyon National Recreation 

Area; Dennis Womack. James Miller. Timothy Brewer. and 

Roger Cunn. Idaho Power Company. Boise; James 

Robinson and John Lee. International Boundary and Water 

Commission. El Paso and Presidio. Texas; Benjamin 

Everitt. Utah Department of Natural Resources. Salt Lake 

City; William Couch. Georgia Department of Came and 

Fish. Buford Fish Hatchery; Michael Thomas. Atlanta 

Regional Commission; Mork Winn. Georgia Department 

of Natural Resources. Atlanta; Michael Wilder and Cary 

Rakestraw. Georgia Power Company. Atlanta; Rich Valdez. 

Bio/ West. Logan. Utah; Lloyd Greiner. Dave Sabo. Ron 

Moulton. and Suda Rajamani. Western Area Power Administration. Salt Lake City; Trevor Hughes. Utah State University. Logan; Cary Krapu. Henry Maddox. and Bob Williams. U.S. Fish and Wildlife Service; Cary Hendrix and 

Larry Stevens. National Park Service; Mike McAfee. Doug 

Young. Larry Crist. Bureau of Reclamation; and Edmund 

D. Andrews. Dallas Childers. Richard Marzolf. Jonathan 

Nelson. J. Dungan Smith. David Wangsness. and Carnett P. 

Williams. U.S. Geological Survey. Michael Collier took all 

of the photographs in this report. Mike Yard and Dave 

Wegner. of the Bureau of Reclamation. and Brad Dimock. 

of the Grand Canyon River Guides. critically reviewed 

early drafts ofthe manuscript. George Weiss ofthe U.S. 

Geological Survey helped our thought processes both on 

the river and off. Designed and illustrated by Jeanne 

Sandra DiLeo. Our thanks to you all. 

IV 
'Ia6{e of Contents 

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII 

Conversion factors ........ ...... .. ... .... ... .. .... .... ...... ...... ...... VIII 

Maps and Figures .. ...... ....... ...... .... ..... .... ... .. ...... .. .... .. ... . IX 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I 

Environmental values of rivers downstream from dams ........ 3 

Removing dams ..... ........ .. .. .. .. ..... ... ...... .. ...... .... ... 8 

Upper Salt River .... ... ............. .... .... ... ...... ........... .. ... .... I 0 

The value of streamflow gaging ...... ........ ....... ..... .. .... I 5 

Snake River ..... .... ..... ......... .. 0 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • I 8 

Obstruction offish runs ... .... ........ .. 0 ••••• 0 • •••••• •• • ••••••• 22 

Rio Grande ... ......... ........... .. 0 • • •••• • ••• • ••• • • • • •• 0 • • •• •••• • • • •••• 28 

Chattahoochee River ... .... ....... ...... ..... .... ......... ........ ..... 3 8 

Monitoring water quality ............. ........... ........... 0 ••• 0 4 3 

Platte River .. .... ... ..... ......... ... .... ..... ... 0 • • • •• ••••• • •••••••••••• 46 

Green River ........ .... ..... . 0 • • • • • • • •••••••••••• • •• • ••• ••• • •••••••••••• 54 

Estimating sediment budgets .. .. .. ....... ......... .......... ... 60 

Colorado River .. 0 0 . 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 . 0 0 0 •• 0 0 0 • • 0 . 0 0. 0. 0 0 0. 0 0 0 0 0 0 62 

Repeat photography 0 . 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 . 0 0. 0. 0 0 0. 0 0 0 0 0 0 0 0 68 

Cost of habitat-maintenance flows 0 0 0 0 0 0 0 • 0 0 0 • 0 •• 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 2 

The role of science .......... 0 .... .. .... 0. 0 ............. .... . ...... 0 0 . .. 0 80 

References 0 0 0 0 0 0 0 0 0 0 0 • 0 0 0 0 0 0 0 • 0 0 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 •• • • 0 0 • • • 0 0 0 0 0 • 0 0 • 0 • 0 0 0 8 9 

v 
Maps 

Map of the United States showing the locations of rivers 

discussed in the text and the ratio of reservoir storage to annual 

water supply ... ....... ..... ......... .... ............... ...... ....... 5 

Salt River in central Arizona . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I I 

Snake River in Oregon. Idaho. and Washington .. ........ ..... .... . 19 

Rio Grande between Elephant Butte Dam. New Mexico 

and Presidio. Texas .. .... ........ ........ ...... ...... .... .. .... ... 29 

Chattahoochee River in north-cerytral Georgia ... ......... ......... 39 

Platte River in Wyoming. Colorado. and Nebraska ........ ... .. .... 49 

Green River .. .......... .. ... ..... ... ..... ...... ... .... ..... ...... ... 55 

Colorado River downstream from Glen Canyon Dam ... ... ...... 64 

:figures 

Annual number of closures of large dams .. ...... ...... ....... ....... 4 

Graphs showing flow records for the Salt River . . . . . . . . . . . . . . . . . . . . I 2 

Annual flood series for the Snake River ....... ....... ....... .. .... .. 2 4 

Graph showing beach degradation on the Snake River 

below Hells Canyon Dam .. ........ ...... .. .... .... ... ...... ..... 2 5 

Graph showing the annual flow volume in the Rio Grande 

above the Rio Conchos .. ...... .. ....... ............ ..... ........ . 30 

Graphs showing channel changes in the Rio Grande ............ .. 34 

Graph showing the annual flood series for the Rio Grande .. ... .... 3 5 

Graph showing flow in the Chattahoochee River ........... .... .. . 40 

Graph showing flow in the Platte River .. ...... ..... ......... ...... 50 

Graph showing the annual flood series for the Colorado River .... 6 7 

Repeat photographs showing change in sand bars in 

Grand Canyon ....... .. ...... .... ....... ..... ... .. .......... ...... 69 

Hydrograph for Colorado River near Grand Canyon for 

September 1982 ..... .......... ........ .. ......... .. .. .. . ... .... . 70 

Graph showing a time series of changes in the bed elevation of 

the Colorado River at Lees Ferry. Arizona. 1921-1986 ......... 7 3 

Diagram showing the definition oflsand bars draped around 

an eddy ... .... .. ... .... ....... ... ... ......... .... ................. . 75 

VI 
Conversion ~actors 

For readers who prefer to use metric units. conversion 

factors for the terms in this report are listed below 

Multiply by Toobtain 

inch ........................... (in.) 25.4 ..................... millimeter (mm) 

foot ............................. (ft) 0.3048 ......................... meter (m) 

square foot ................... (ft2) 0.09290 ............... square meter (m2) 

cubicfoot .................... (ft3) 0.02832 ................ cubic meter (m3) 

acre-foot .................... (ac-ft) 1233 .................... cubic meter (m3) 

acre ........................... (ac) 0.404 7 ........................ hectare (ha) 

mile ........................... (mi) 1.609 ...................... kilometer (km) 

square mile ................. (mi2) 2.590 ............. square kilometer (km2) 

cubic foot per second ..... (ft 3 Is) 0.02832 .. cubic meter per second (m3 /s) 

ounce avoirdupois .... (oz avdp) 28.35 ............................. gram (g) 

pound avoirdupois ..... (lb avdp) 0.4536 ...................... kilogram (kg) 

ton. short ............. (2.000 lbs) 0.9072 ................... megagram (Mg) 

gallon ......................... (gal) 3.785 .............................. liter(L) 

degrees Fahrenheit .......... (°F) °F-32 ................ degrees Celsius (°C) 

1.8 

Sea level: In this report. "sea lever refers to the National Geodetic 

Vertical Datum of 1929 (NCYD of 1929)- a geodetic datum derived 

from a general adjustment of the first-order level nets 

of both the United States and Canada formerly 

called "Sea Level Datum of 1929." 

VII 

Introduction 

Dams and river regulation have become an integral part of our 20th century landscape 

and livelihood. Although untamed rivers are part of the cultural heritage of the United 

States. virtually every river in the lower 48 states is now regulated by dams. locks. or 

diversions. These regulated rivers have afforded society many benefits - cheap electricity. 

navigable streams. absence of devastating floods. decreased threat of drought. But regulated rivers are fundamentally different ecological and physical entities from untamed 

rivers. Natural cycles of flooding and sediment transport have been eliminated from many 

of these rivers. Channel shape. riverine vegetation. and instream aquatic communities 

have. in many cases. changed as a result of flow regulation. 

Because of the scale of dam construction that has taken place in the United States. 

society now has before it a set of choices regarding the kind of river characteristics we 

desire. Like it or not. we control the destiny of these streams. Traditionally. river managers 

have focused on issues of engineering efficiency. sometimes to the neglect of in-stream 

environmental values. The engineering matters remain a focus of management, but our 

society must also choose whether or not to manage rivers for their intrinsic environmental 

values. We can consciously choose to manage our rivers for certain anticipated environmental consequences. or we can intentionally choose to accept the environmental 

responses as they haphazardly occur. The purpose of this Circular is to illustrate the 

downstream environmental consequences of dams. and to explain the basis on which 

rivers can be scientifically managed. 

Egyptians were building dams upstream from Cairo 5,000 years ago. Western Europeans constructed dams to power water wheels during the late Middle Ages (Smith.1971). 

Eight hundred years ago. the Anasazi built small check dams on Mesa Verde in Colorado to 

hold storm runoff for later use on their crops (Ortiz. 1979). As early as A.D. 833. the 

Chinese used human and animal power to build a 90-foot-high dam on the Abang Xi River 

(Pens. 1984). Twelve centuries later. this dam is still used for irrigation diversion although 

the reservoir has filled with sediment. 
Imperial Dam on the Colorado River 

upstream from Yuma, Arizona 

But the age of widespread. large-structure dam-building awaited the 

arrival of heavy machinery and the high ambitions of industrialized societies. 

In the United States. the pace of large dam construction hit its quickest stride 

between 1935 and 1965 (Thomas. 1976). 1n the West. Hoover and Grand 

Coulee were completed before World War II; Glen Canyon Dam was finished 

in 1963. ln the East. creation of the 26-dam Tennessee Valley Authority 

system ushered in an era of building dams and managing reservoirs integrated over an entire basin (Cullen. 1962). Currently. there are more than 

75,000 dams higher than 6 feet in the United States; the reservoirs behind 

these dams cover about 3 percent of the Nation's land surface (R.F. Stallard. 

oral commun .. 1994). Worldwide. 193,500 square miles (mi 2) of land is 

inundated by reservoirs. Now in a given year. 60 percent of the United States' 

entire river flow can be stored behind dams (Hirsch and others. 1990). 1n the 

dry American Southwest. dams on the Colorado River can store 4 years of 

typical flow (Andrews. 1991). More dams are being built in developing 

countries. but in the United States. Canada. and Western Europe only a few 

potential sites for large dams remain under realistic consideration. 

Have we benefitted by building these dams? Viewed in one dimension. 

the answer is a resounding "Yes." Hydroelectric powerplants harnessing the 

Columbia River and its tributaries produce 75 percent of the American 

Northwest's electricity (Palmer. 1991). Each year. 8.2 million acre-feet of 

water are diverted from the lower Colorado River to homes and farms in 

California. Arizona. and Mexico through aqueducts that cross hundreds of 

miles of intervening desert. None reaches the Gulf of California. Since dams 

were built across rivers in the Connecticut River Valley. no floods have 

occurred like the ones that killed 108 people and crippled the towns of 

Bolton and Hartford in 1927 and 1936 (Leuchtenburg. 1953). 

In the simplest sense. we build dams for the same reason we wear coats 

in the winter: to exert control over an aspect of an environment that would 

otherwise make living difficult or even impossible. If a valley is subject to 

destructive flooding. we dam its river. If the desert is dry. we build a lake. The 

list of available reasons for building a dam is long and complex- for water 

storage to quench municipal. agricultural. and industrial thirsts; for flood 

control and improved navigation; for sediment trapping; for improvement of 

water quality; for electrical power generation; for recreation. aesthetic. and 

wildlife considerations. 

As dams became bigger and more expensive. a wider array of benefits 

was needed to justify the cost of dam construction. Most dams built after 

1950 had many purposes. and sometimes these purposes were in competition with each other. Glen Canyon Dam in Arizona was initially conceived as 

a tool to balance the water allocations between the upper and lower basin 

states of the Colorado River (Ingram and others. 1991 ). But with an initial 

price tag of $325 million. construction of the dam needed additional justifications. Water conservation. downstream distribution. and hydroelectric power 

were written into the dam's operation considerations. Recreation and flood 

control subsequently were added to the dam's operating criteria. 

2 
t£nvironmenta{ o/a{ues Vownstream from Vatns 

Downstream effects of dams were of little concern during the design and construction of most dams in the United States. Engineers knew that clear water releases 

would erode the channel immediately downstream from spillways and power plants; they 

attempted to calculate the amount of scour to protect the integrity of the dam and its 

structures. Changes in fish populations or riparian vegetation were often unanticipated 

or were not taken seriously: in fact, to build a game-fishing industry, some channels 

downstream from dams and upstream from reservoirs were poisoned to remove native 

fish. It took a little known, and endangered, native fish downstream from the proposed 

Tellico Dam in Tennessee to focus attention in the 1970s on environmental changes 

associated with dam operations. 

Society values its rivers in a more complex manner in the 1990s than it did when 

most dams were originally constructed. More than ever, we count on the traditional 

products of dam operation- water, power, flood control. But we are increasingly aware 

of the environmental values of our rivers. We enjoy whitewater recreation in an increasing fashion; many classic whitewater boating trips are downstream from dams. We flock 

to the blue-ribbon trout fisheries that thrive in the tailwaters of dams. We treasure 

wilderness, and many regulated rivers flow through wild and inspirational landscapes. As 

a society, we have insisted on some protection of our rivers, and the Wild and Scenic 

River designation, enacted by Congress, has been one result. 

Several issues take the forefront in consideration of adverse effects of dam operations. Native fish, protected under the Endangered Species Act, are thought to be 

threatened by the clear, and usually cold, releases from dams. Riparian vegetation can 

either be enhanced or degraded by dam operations. Streamside and channel sedimentary deposits are critical: too much sediment can aggrade channels and cause flooding 

problems, whereas erosion of sediment can degrade habitat and decrease the potential 

for recreational use. These issues are among those that may drive change in the way our 

dams are operated. 

Kayakers on the Chattahoochee River at Duluth, Georgia 
To the uninitiated. a dam might seem little more sophisticated than a plug stuffed into a 

pipe. a few shovelfuls of dirt thrown across a ditch. But a deeper look brings an entire 

world of technological expertise into view. Engineers must identify appropriate sites for a 

dam. locate materials for its construction. conceive the basic shape of the dam. decide 

whether or not to build an associated hydroelectric power plant. and calculate the necessary size of emergency spillways. The design of a dam is directly tied to its fundamental 

purpose. Run-of-the-river designs are usually low in elevation. have small upstream reservoirs. and modify the natural flood and sediment-transport cycle only slightly. Alternatively. 

high dams with large upstream reservoirs can store many months. if not years. of natural 

streamflow and can generate prodigious amounts of hydroelectric energy due to the fall of 

the river at the dam. 

Dams and reservoirs 

differ not only in their 

sizes. but also in operational strategies. Dams 

of the same size may 

hold varying amounts of 

water depending on 

their ultimate purpose. A 

flood-control dam keeps 

its reservoir low at the 

onset of each flood 

season. while a watersupply reservoir tries to 

remain full as long as 

possible. Because the 

actual inflow into a 

reservoir can never be 

precisely anticipated. 

each of these operating 

strategies carries 

inherent risks that the 

reservoir will overflow or 

that the reservoir will go 

dry. The task of the 

E 

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6 

5 

4 

3 

2 

0'----_.....____.__.___.w....o.__._-. 

1910 1920 1930 1940 1950 1960 1970 1980 

Year 

Dates of closure for dams in the continental United States with reservoir 

capacity of I million acre-feet or more (compiled by Graf, 1993). 

water-resource engineer is to develop techniques that will increase the chances of achieving the desired objectives of the dam. while accepting some risk that other situations. less 

relevant to the dam's ultimate purpose. will occur. In other words. a flood-control dam has 

some chance of going dry and a water-supply dam has some chance of spilling. 

But we can't have it all. all of the time. The challenge for today's manager is that yet 

other factors now exist in the dam-management equation - those centered on management of the downstream river corridor and its ecology. Scientifically based management of 

regulated rivers adds a new layer of objectives to the already complex task of the waterresource engineer who designs the strategies of multipurpose reservoir management. 

4 
I ntrotfuction 

The halcyon days of building large dams in the United States have passed. Most of the 

"good sites." based purely on the engineering perspective of high canyon walls. solid 

foundation. and a large basin upstream. have already been used. The price tag on a dam is 

now orders of magnitude greater than for equivalent structures built during the 1930s. But 

more importantly. the American public has grown to expect a full cost/benefit accounting 

of a large project. not just in terms of construction cost versus immediate benefits. but also 

45' 

lO' 

The ratio of reservoir storage to annual water supply in parts of North America 

(modified from Hirsch and others, 1990). The western United States and southwestern Canada have the most extensive reservoir development relative to available water supply. More dams have been constructed in the Columbia River basin 

and in the Tennessee Valley (neither are highlighted), but these basins have higher 

water yields. Many of the largest problems with downstream effects of reservoirs 

are in the basins with the highest ratio of reservoir storage to annual water supply 

because dam operations are constrained more in those basins. 

80' 70' 

0 300 Miles t---r---.J 

0 300 Kilometers 

5 

D River locations 

Ratio of reservoir storage 

to annual supply 

0.0 ·0.3 
Diversion dam on the Colorado River near Blythe, California 

The Rio Grande above Mesilla Dam near Las Cruces, New Mexico 

6 

in terms of long-range 

environmental and social 

costs. Instead of building new 

dams. we are now spending a 

lot of time. energy. and 

money examining the effects 

of existing ones. The question 

now relevant to dams in the 

United States is not "Should 

we build another one?" but 

"How can we best use the 

ones we have?" 

Historically. our society 

has always found it easier to 

build than destroy a dam. 

Driven by the memory of a 

simpler time and an unfettered river. some people are 

fond of contemplating the 

elimination of certain dams. 

In a few instances. the 

environmental costs of an 

old dam are deemed so 

great that the dam's removal 

is conceivably warranted. 

Examples include the 

Edwards Dam on the 

Kennebec River in Maine. 

the Elwha and Glines 

Canyon Dams in. or just 

outside. Olympic National 

Park. and Hetch Hetchy 

Dam within Yosemite 

National Park in California. 

But by and large. this is 

rarely a realistic option. 

Once a dam has been 

built. we reap its benefits 

and learn to live with the 

environmental effects. The 

real question then becomes: can a dam be 

operated so as to maximize 

its benefits and minimize its 

costs? The exciting answer 

is "maybe." The ground 
Introduction 

rules for answering this question involve taking some long hard looks at costs and benefits. 

What benefits do we value. what costs are we willing to bear? What new values - like 

downstream ecological impact- have been brought to bear in this accounting since the 

dam was designed and built? Arriving at a meaningful answer requires setting aside 

political and personal biases long enough to honestly say what we want from a dam and its 

river. and to accurately evaluate all the dimensions of impact that a dam can have. Society 

must decide what it wants; scientists can help to show what we are likely to get under 

different management strategies. 

Viewed in one carefully chosen dimension. many dams have been worthwhile -this 

dam prevented flooding. that dam generated a lot of electricity. But with time. we have also 

come to realize that the adverse environmental effects of a dam may extend in circles far 

wider than had been appreciated in the past. For decades. people have known and argued 

about the more obvious effects of dams: flooded valleys and displaced farmers; fish 

migrations blocked or disrupted; one state taking water needed by another state downstream; water quality improved or impaired. We did not spend a lot of time thinking about 

the issue of downstream effects when conceiving dams during the first half of the 20th 

century. But in the past 20 years. scientists and the public have begun to appreciate an 

additional effect of dams: changes to the downstream river environment. 

The river emerging from a dam is not the same river that entered its reservoir. That 

new river may be hotter or colder. Its daily discharge may vary wildly. while its seasonal 

pattern of high spring floods and low winter flow may be inhibited beyond recognition. 

Suddenly starved of its sediment load. the clear waters of a river below a dam may scour its 

bed and banks. An entirely new succession of riparian plants and animals may move into 

the river and valley below a dam. Native fishes may die or be severely stressed. 

Oxbow Dam, part of the Hells Canyon Complex, on the Snake River, Idaho 

7 
~moving tJJams 

The Elwha River. which drains part of Olympic National Park in northwest 

Washington. had a significant salmon spawning run before it was impounded in the 

early 1900s. Elwha Dam. 110 feet high. was built in 1913 and forms Aldwell Lake; 

Glines Canyon Dam. 185 feet high. was built in 1926 and forms Lake Mills a short 

distance upstream from Elwha Dam. The dams were built by a logging company to 

supply electrical power to a wood products plant at Port Angeles; the city currently draws its municipal water supply from Lake Mills. Many years after their 

construction, Olympic National Park was established on land drained by the Elwha 

River. 

The National Park Service and other Federal and State agencies are concerned 

that the dams block spawning runs of endangered salmon up the Elwha River. The 

pre-dam salmon runs on the Elwha were large and famous. Because the livelihood 

of these fish and their cultural importance to local tribes are considered more 

important than the economic benefits of the dams and reservoirs. the National 

Park Service is planning to 

dismantle Elwha and Glines 

Canyon Dams and return the 

Elwha River to its original 

condition. One significant 

problem with restoration is 

management of the sediment in the reservoirs; 

extensive deltaic deposits in 

the upper ends of both lakes 

must be redistributed in a 

fashion to minimize downstream effects once the 

dams are completely dismantled. Estimated costs 

for dismantling the dams 

are between $60 and $200 

million; costs would be lower 

if the river is allowed to 

redistribute the sediment 

instead of solutions involving physical removal of the 

sediment. The cost of 

dismantling these dams will 

be borne by U.S. taxpayers. 
I ntrocfuction 

During the past two decades. earth scientists have become increasingly involved in 

the study of downstream effects of dams. The U.S. Geological Survey (USGS) has main· 

rained a nationwide network of stream gaging stations since the late 1800s. Some stations 

have records of the amount of sediment transported downstream. These records provide 

invaluable data concerning the behavior of a river before and after being dammed. 

In this Circular. we explore the downstream effects of dams. First. we look at a freeflowing river- the upper Salt River of Arizona - and its natural cycles of flow and sedimentation. Then we examine six regulated rivers: the Snake. Rio Grande. Chattahoochee. 

Platte. Green and Colorado Rivers. Each of these rivers highlights a particular use of a dam 

or a particular downstream effect. Finally we discuss the role of science in managing dams. 

9 
'Upper Sa[t !Rjver 

5l1{atura[ Stream 
AZ 

Phoenix _.... ~%v / 

.f, · 

(,\111 ~ 

The Salt River in 

Sa[t 2?jver 

.&. Gaging station 

0 10 Miles 

I 1 1 I I 

0 10 Kilometers 

rrhe uppers a[t 2?jver is a boisterous stream tumbling out of the 

White Mountains of eastern Arizona, west towards its confluence with the Gila River near 

Phoenix. The first 125 miles of the Salt. unimpeded by dams. are good examples of an 

unregulated river. The Salt River Canyon is a major east-west trending gash in central 

Arizona. Downstream the river's character changes dramatically. Beginning at Theodore 

Roosevelt Lake reservoir. the Salt becomes a "working" river. A series of four reservoirs that 

supply water for irrigation. industrial. and municipal use in Phoenix marks the end of the 

free-flowing river. 

A natural river has an annual cycle of floods and low-flow periods. depending on 

climate and season. The upper Salt River basin receives moisture from several types of 

storms. The greatest amounts of moisture are delivered to the basin by fall and winter 

storms that roll in from the Pacific Ocean; this moisture is stored as snow pack in the high 

country. If warm rain falls on previously fallen snow, the Salt River can suddenly snap from 

trickle to torrent. On December 17. 1978, a severe winter storm dumped 10 in. ofrain on 

parts of the Salt River drainage (Aldridge and Hales. 1984). Before the storm. the Salt River 

was flowing at 3,460 cubic feet per second (ft3/s); 22 hours later the river surged to 

95 ,000 ft3/ s. Prehistoric floods have reached 160,000 ft3/s (Partridge and Baker. 1987), yet 

flow ofthe Salt is sometimes less than 100 ft3/s in early summer. This river may be an 

extreme example of variability in discharge. but many western rivers rose and fell just as 

quickly before they were dammed. 

Big floods. little floods. Wet years. dry years. So what? Geoscientists must put all these 

numbers into perspective when they try to understand how a river works. They study 

basin and river geometry in order to understand how floods sculpt the river's natural 

channel. Hydrologists try to analyze historical patterns of flow in order to anticipate floods 

that can be expected in the future. Biologists study aquatic organisms and riparian plants in 

relation to these patterns of flow. 

II 
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150.000 

125.000 

100.000 

75.000 

50.000 

25.000 

Near Rj osevelt above 

Steward Mountain Dam 

Below Stewart 

Moumair Dam 

01 5 10 15 

january 199 3 

20 25 30 

140.000 

120.000 

100.000 

80.000 

60,000 

40.000 

20.000 

0 

Hydrograph of the Salt River for January 1993. Peak 

discharge reached 143,000 ft3fs on January 8 above 

Roosevelt Dam. Releases from Stewart Mountain Dam, 

the farthest downstream of four dams on the Salt, are 

dampened and protracted compared to the inrow 

to Roosevelt Lake. 

1915 

Winter 

I Spring 

I Summer 

I Fall 

1925 1935 1945 1955 

AZ 

Stewart 

Mountain '~""' Phoenix Dam ~~ *'\ ·t:.'"' 

Gil~ lli'~' 

1965 1975 1985 

Annual rood series for the Salt River. The large variability in annual roods is an environmental 

stress to which native riparian vegetation and (lshes have adapted. 

Unregulated rivers in the western United States carry prodigious amounts of sediment 

during floods. The Salt River is no exception. The sediment load carried by the Salt can 

vary by orders of magnitude. Much of the year. the river is relatively clear. But in a large 

flood. the Salt can carry extremely large quantities of sediment, scouring material from the 

bottom and sides of its channel that normally is not disturbed by the flow of the river. 

The amount of sediment transported by a river. termed its capacity, increases dramati~ 

cally with discharge, typically in an exponential fashion. That sediment may be suspended 

12 
Sa[t 2?jver 

in the water. or bounced along the bed. The river's competence to pluck larger and larger 

particles from its bed is a direct function of water velocity. as well as the shape of the 

channel where a particular sand grain. cobble. or boulder happens to lie. 

We think of rivers as the cutting edge of erosion. When viewed through the long lens of 

a geologic perspective. it is true: rivers do carve their valleys. But when viewed through 

the shorter focal length of an historical perspective. a river typically is in dynamic equilibrium with its valley. Sometimes the river scours its bed during floods or high flows of long 

The Salt River at Canyon Creek 

duration; sometimes it builds up (aggrades) its bed during lowerflow periods as sidestreams continue to deliver large quantities of 

sediment. For a particular segment of river channel. the instantaneous elements of this equilibrium include discharge. sediment 

load. and channel slope. shape. and roughness (Pickup. 1976). At 

any instant. a river will adjust its channel to these elements. Each 

river system displays a unique response to the inputs of these 

elements (Baker. 1977). Confronted by floods of equal magnitude. a 

segment of river confined to a bedrock channel will behave quite 

differently than another segment flowing across an alluvial plain. 

Riparian vegetation plays an essential role in the evolution of a 

river corridor. Streamside trees and brush take advantage of perennial surface water and fine-grained substrate for growth. The plants 

may be native - willows. cottonwoods. and mesquite - or exotics. 

13 
Tamarisk. a salt-tolerant brushy tree introduced to the West sometime in the late 1800s 

(Robinson. 1965). is the most common nonnative species. Once established. vegetation 

can directly influence the impact of high flows by increasing channel roughness and 

decreasing flow velocities (Graf. 1978). 

The Salt is a tributary of the Gila River. which drains most of central Arizona. Much of 

the Gila's course is lined with tamarisk. Burkham (1972a) did a detailed study of the Gila in 

the 1960s and 1970s. Moderate-sized floods were observed on three occasions. before 

and after dense thickets of tamarisk were intentionally removed from the banks of the river. 

Not surprisingly. when the channel was clogged with tamarisk. it could not efficiently 

handle even moderate flood. As the water sieved through the brush. the river slowed and 

dropped its load of sediment. The floodwaters rose higher above the river banks and 

spread farther out from the banks where the channel was obstructed by tamarisk. Since 

Burkham's work. large floods on the Gila in 1972. 1978 to 1979. 1983. and 1993 have 

ripped most- but not all - of the tamarisk from the flood plains. 

Mesquite thickets. called bosques. are common along the Salt and Gila Rivers 

(Minckley and Brown. 1982). Mesquite uses less water than other species. such as tamarisk. and can grow at higher elevations above the level of the river. Mesquite also can grow 

Kayaker in 

Ledges Rapid 

on the Salt River 

on rocky substrate in addition to sandy flood plains. Periods of small floods. such as the 

middle of the 20th century (Webb and Betancourt.1992). allow bosques to encroach upon 

the flood plain. As with tamarisk thickets. floods wreak havoc on mesquite bosques. In one 

channel bend between the bedrock walls of the canyon. floods on the Gila between 1972 

and 1979 halved the size of one bosque (Minckley and Clark. 1984). Most of the destruction was caused by lateral erosion of the channel banks. as is the case with tamarisk. but 

mesquites can better withstand flooding because of their toehold in the rocky slopes. 

14 
rrlie rrJa{ue of StreamfCow (}aging 

Hydrologists have used streamflow-gaging stations for more than 

a century to assess the water resources in the United States. The first 

gaging station was established on the Rio Grande River near Embudo, 

New Mexico, in January 1889. Currently, the U.S. Geological Survey 

operates about 7,000 gaging stations in the 50 states, Puerto Rico, 

and islands in the Pacific Ocean. Although the early gaging stations 

were read daily by operators who lived nearby, modern gaging stations 

can transmit data instantaneously to satellites and are downloaded to 

ground stations as much as 1.000 miles away. Gaging stations provide 

the necessary data to plan water development and use, to manage 

water resources to meet specific legal requirements, to evaluate the 

effect of climate and land management on water supply, and to quantify 

the relation between flow and environmental quality of a river. 

The amount and variability of streamflow is the single most important feature to monitor in a regulated river. These data are needed to 

quantitatively evaluate the impact of flow regulation on a river. Most 

regulated rivers in the United States were gaged before dams were 

built: comparison of flow before and after regulation provides insight 

into the reasons for changes brought about by dam operations. Even for 

regulated rivers where streamflow was not recorded before regulation, 

establishment of new gaging stations is essential to monitor the ongoing changes brought about by dam releases. 
Native fish evolved under the extreme 

variability of the unregulated river. The Salt 

and Gila Rivers are home to 20 species of 

native fish (Minckley and Brown. 1982). 

most of which are endangered as a result of 

water development and introduction of 

game species elsewhere in the lower 

Colorado River drainage. The temperature 

of the Salt can vary from near freezing in 

winter to 77 degrees Fahrenheit (°F) in 

summer; any fish within the river must be 

prepared to deal with these extremes. The 

fish also must contend with other environmental factors such as extreme changes in 

flow and large variations in sediment 

concentration. 

The largest flood ever recorded 

(143,000 ft3/s) rolled down the Salt River 

into Roosevelt Lake on January 8. 1993. 

Tamarisks and willows were stripped from 

reaches where they had gradually encroached during years of lower flow; 

mesquite bosques were damaged but not 

destroyed. The native fish probably were 

Three views of Hess Creek at the Salt River 

16 
Sa[t 2Uver 

little affected. Certain cobble bars were scoured away. Some banks 

were severely eroded. But this river, like other natural rivers, gives back 

almost as much as it takes away. Where the river is confined by bedrock within the Salt River Canyon, tremendous quantities of new sand 

were deposited within eddies and along the channel margins. Clean 

new beaches remained perched 40 feet above the river after the flood 

receded. Cobble bars and boulder fans within the channel were 

reworked and, in many places, built up. Roosevelt Lake acts as the 

upper Salt's temporary base level, and farmers along the lake's margin 

were pleased to find new topsoil in their fields after the floods receded. In the days prior to construction of Roosevelt Dam. such a 

flood would have inundated a broad swath of the desert where 

Phoenix now exists; terraces of sediment would have been deposited 

throughout that flood plain. 

The upper Salt River has all the characteristics of a healthy unregulated river. Typical of rivers in the Southwest, it displays a wide range of 

flow and sediment transport- it is capable of quickly changing from 

minimal flow to awesome flood. This river is always in the process of 

adjusting its channel to the equilibrium that exists between erosion 

and deposition. The Salt offers a standard against which to compare 

regulated rivers. 

17 

S nak!- tJQ-ver 

Tlie s na/(g.. 2?jver is the most extensively dammed river in the West. Twentyfive dams lie between its headwaters in Yellowstone National Park and its confluence with 

the Columbia River. 1,000 miles downstream. 

The Snake is one of the major tributaries of the 

Columbia River. which drains 259,000 mi2 of 

Canada and the Pacific Northwest. Starting 

with the completion of Grand Coulee Dam. 

the Columbia has effectively been converted 

from 1,210 miles of free-flowing river (Bartlett. 

1984) to a series of dams and reservoirs. each 

backing into the next. capable of generating far 

more electricity than the Northwest was 

initially able to use. The aluminum industry. 

117' 

WASHINGTON 

46' 

The Snake River in Oregon, Idaho, and Washington 

19 

0 20 Miles 

0 30 Kilometers 
with its insatiable appetite for electrical power. was invited to move into the Northwest in 

the 1940s and 1950s after the dams were built. In this case. demand for power followed 

supply. 

The Snake River is many things to many people. Idaho farmers like to think of the 

Snake as a "working river." Halfway between the Snake River's headwaters and the Columbia. diversions at Milner Dam near Burley. Idaho deplete all but a trickle (200 ft3

/s) of the 

river's flow. This water irrigates more than 3 million acres of farm land. an area roughly the 

The Snake River in Hells Canyon 

size of Connecticut (Palmer. 1991). That's a lot of potatoes. Tim Palmer recalls his first 

impression when he visited Shoshone Falls. now usually dry. an impression that stands in 

sharp contrast to the farmers who depend on Snake River water for irrigation: "I wondered where the water had gone. and stood puzzled. feeling that nature had been warped 

in a sinister way. as if I had seen a three-legged deer or a toothless squirrel." 

After passing west through Idaho. the Snake swings north to outline the Idaho/ 

Oregon border. Below Milner Dam. the Snake is recharged by the Thousands Springs 

(whose source is in part the return flow from all those potato fields) and then by the Boise. 

Owyhee. and Payette Rivers. The Snake once again is full-blooded as it rolls into Hells 

Canyon with a yearly discharge of 16 million acre-feet. The river drops into canyons that 

make farming and even ranching progressively more difficult. Hells Canyon is arguably the 

deepest canyon in the United States. Peaks loom 7,900 feet above its waters. 

Deep canyons and a big river were the siren's song that few dam builders could resist. 

20 
S naf&- 2?jver 

In 1906. the Idaho-Oregon Light and Power C ompany tried to take advantage of the 

topography at O xbow by building a dam and then drilling a 1,000-foot tunnel to shortcut a 

2-mile loop of ri ver (C arrey and others. 1979). Despite a significant investment. the 

company managed to generate only 600 kilowatts (kW) at this facility; with debts mounting. the company filed for bankruptcy. Later during the 1940s. the U.S. Army Corps of 

Brownlee Dam on the Snake River 

Engineers and the Bureau of Reclamation were maneuvering for the rights to build a 590-

foot dam in Hells Canyon. But the Idaho Power Company. reorganized from the ashes of 

the Idaho-Oregon Light and Power Company. took advantage of options that it had inherited at the O xbow. and received a license to dam the Snake River upstream at Brownlee. 

Short-circuited by Idaho Power Company. the two Federal agencies would have to be 

content with their eight dams farther downstream on the Snake and the Columbia. In all. 

Idaho Power built three dams. called the Hells Canyon Complex. within a 35-mile stretch 

of the Snake. Brownlee was completed in 1958. a new O xbow Dam in 1961. and Hells Canyon 

Damin1%7. 

When the gates were first closed. combined storage of the Hells Canyon Complex was 1 

million acre-feet of water. with 90 percent held in Brownlee Reservoir. All together. that represents only 7 percent of the river's average annual flow as measured at Hells Canyon. Contrast 

that capacity with storage behind Glen Canyon Dam on the Colorado River. where the single 

reservoir holds 2.3 years of that river's flow. Because the Hells Canyon Complex doesn't have 

much storage capacity. the dams have little value for flood control. and managers are able to 

maximize the potential for the generation of electricity. 

Idaho Power Company is tied into a grid that provides electricity throughout the West. 

The demand for electricity within this grid is not uniform. Daily peak demands occur 

during summer afternoons or earl y winter mornings. The need for power drops off 

markedly on weekends. Weather conditions (and consequently the power needed for 

21 
06struction of :Fish !l{uns 

Salmon once crowded the waters of the Snake River but are increasingly 

rare these days. Summer and fall chinook and sockeye salmon would migrate 

up from the Pacific Ocean through the Columbia and Snake Rivers to spawn on 

the tributary of their origin. Five to fourteen percent of adult salmon are killed 

at each of the eight dams through which they pass on their way up the 

Columbia (Eiey and Watkins, 1991). When spawning is successful. the young 

fish have even lower rates of success in migrating downstream through the 

reservoirs. The chinook are now listed as threatened species, and the sockeye 

salmon is considered endangered (St uebner. 1993). Idaho Power Company 

built fish ladders and other bypass systems into each of its dams of the Hells 

Canyon Complex, but all were unsuccessful. Now no salmon migrate above Hells 

Canyon Dam. 

A few remaining salmon struggle each year to reproduce below Hells 

Canyon Dam. Operations of the Hells Canyon clams (not to mention all the 

dams on the Columi1ia River system) have catastrophically aff8cted 

Uti!2M~rtra !141t. Wilt the fish that the 
Sna~2?jver 

Hells Canyon Dam 

on the Snake River 

heating and cooling) can vary sharply from one part of the grid to another. Instantaneous 

changes can occur if a key transmission line suddenl y drops out of service. Power companies must "wheel'' electricity from one region to another. and the entire grid must be able 

to instantly respond to sudden fluctuations in demand. 

Throughout the West. a large proportion of electricity is generated by coal-fired and 

nuclear plants that efficiently supply constant maximum levels of power. These thermal 

plants become very inefficient. however. when they are run at less than maximum capacity. Once shut down. these plants take hours to come up to full steam. Electrical utilities 

are better off buying additional electrical power from another utility at a premium price to 

cover brief peak demands. rather than covering peak demands by investing in additional 

coal-fired plants or natural gas turbines that will be used for only a few hours a day. 

Hydroelectric power. on the other hand. can be brought on line in a matter of minutes. 

Turbine efficiency remains high throughout a wide range of dam releases. Consequently. 

hydroelectric power has long been viewed as an ideal asset with which to respond to 

perturbations of demand within a power grid. This ability to instantly generate more 

power is valuable. and "peak power" is sold for considerably more than power generated 

during "off-peak" or base-load periods. Idaho Power Company operates coal-fired generating stations that supply base-load energy. but the company obtains all of its peak power 

from dams of the Hells Canyon Complex. The company tries to hold the water of the 

Snake River behind the dams when electrical demand is low. and releases water when 

demand (and the price per kilowatt-hour) is high. 

The Hells Canyon Complex has the capacity to generate 1,400 megawatts (mW) 

when releasing 30,000 ft3/s from all three dams. Larger discharges must flow through 

spillways. bypassing both the dams' generators and the company's revenues. More than 

half of the total generation capacity comes from Brownlee Dam. When possible. the 

company follows the fluctuations of power demand with its Brownlee units. Water 

23 
released from Brownlee quickly passes through the small Oxbow Reservoir into Hells 

Canyon Reservoir. The company attempts to buffer fluctuations from Brownlee Dam by 

releasing water a bit more steadily from Hells Canyon Dam. When possible. a minimum of 

at least 6,530 ft3/s is released from Hells Canyon Dam to meet instream flow requirements for fish and navigation (Dennis Womack, Idaho Power Company. oral commun .. 

1993). 

The dams of the Hells Canyon Complex were not designed specifically for flood 

control. and unexpectedly high flows certainly can occur on the Snake River. The consummate unexpected flow happened 15,000 years ago when Lake Bonneville (ancestor of 

today's Great Salt Lake) suddenly cut a new channel into the upper Snake basin. A peak 

flow of20 to 33 million ft3

/s exploded through Hells Canyon. almost three times greater 

than the largest flood ever measured on the Amazon River (Jarrett and Malde, 1987; 

O 'Connor. 1993 ). Historically. the more typical pre-dam floods would roll through Hells 

Canyon in May and June, reaching peaks of75,000 to 95,000 ft3/s every few years. But 

even with all three dams in place. floods of74,000 ft3

/s or more have passed through the 

Complex on at least five occasions since 1970. Peak flow past the dams in a 1982 flood 

was 87,780 ft3/s. 

The great difference between the pre-dam and post-dam floods lies not in their peak 

flow. but with their sediment content. The three dams of the Hells Canyon Complex act as 

very effective sediment traps. Most suspended sediment reaching Brownlee Reservoir 

drops to the bottom of the lake; what little passes through is trapped behind the two 

reservoirs immediately downstream. Water released by Hells Canyon Dam is usually 

crystal clear. And no significant sediment-bearing rivers join the Snake until the Salmon 

River comes in. 60 miles downstream. 

Annual ffood series for the Snake River at Hells Canyon 

Dam, Idaho. Annual ffoods for 19 2 6 to 19 71 are based 

on correlation with data from the discontinued gagmg "'""~/ stations Snake River at Oxbow, Oregon, and Snake River \ , A> 

below Pine Creek at Oxbow, Oregon. Regulation by \X A ~ ID 

How much sediment are 

we talking about? The Snake 

River below its confluence 

with the Salmon carried as 

Brownlee, Oxbow, and Hells Canyon dams does not significantly l 

affea the size or frequency of ffoods on the Snake River. 

100,000 .... ~ -J 

much as 5 million 

tons downstream 

each year before 

the dams were built 

(Jones and Seitz. 

1980). The current 

status of the 

sediment balance 

80,000 

60,000 

II 

40,000 r 

',( 

20,000 

,, 

: ~ 

II; IIi 

1930 1940 

Flow regulation oegms 

IIi 

1950 1960 1970 1980 

24 

-

-

in the system is 

unknown. One 

approach to 

quantifying sediment on the Snake 

River would be to 

sound the bottoms 

of the three Hells 

Canyon Complex 

reservoirs. especially Brownlee. 
and compare the lake 

bottoms now to the shape 

of the pre-dam canyons. 

Such work has not yet been 

undertaken (Dennis 

Womack. Idaho Power 

Company. oral commun .. 

1993). 

Or one could examine 

beaches along the Snake 

Ri ver below Hells Canyon 

Dam. Paul Crams (1991) 

did just that by comparing 

five sets of aerial photos of 

the canyon taken at intervals between 1955 and 

1982. He found that the 

surface area of beaches in 

Hells Canyon had shrunk 

by 75 percent. Beaches 

between Hells Canyon 

Dam and the confluence of 

the Salmon were most 

heavily degraded; the 

ro ..0 

"0 

c 

"' <./) 

Sna~2ljver 

,--- Location of photographic sites----. 180.000 --......---....... ..--:-. ..... ..__.....--..-_,..........--t..., 

150.000 

120.000 

90,000 

60.000 

30.000 

30 

1964 

1973 

. 1977 

. 1982 

. 1990 

60 90 120 

Snake River in Miles 

Q) 

u 

c 

Q) 

:::> 

= c 

0 

u 

150 180 

Sandbars on the Snake River in Hells Canyon have been shrinking since 

monitoring was begun in 1964; the greatest decrease is documented 

between photographs taken in 1964 and 1973 (modi(ted from Grams, 

1991 ; Schmidt and others, 199 5). 

Salmon appears to be reintroducing enough sediment to stabilize beaches below its 

confluence with the Snake. The greatest losses to beaches within Hells Canyon occurred 

from 1964 through 1973. But Brownlee Dam had been completed in 1958 and Hells 

Canyon Dam in 1967. Why didn't beach degradation begin immediately after closure? 

Crams concluded it had taken that long to flush enough sediment from the bed of the river 

before beach degradation could begin in earnest. As long as some critical amount of 

sediment remained in the system. floods continued to deposit as well as erode beaches. 

But once a river bed is stripped of sand. floods can take what little is left of the beaches and 

give nothing back. 

Crams' study suggested that the beaches of Hells Canyon continue to shrink with 

each passing flood. but at a rate that has been decelerating since 1973. Does it matter? 

River runners think so; with each passing flood. they are more likely to be forced to camp 

in rocky sites amidst the poison ivy off the river. as beach after beach gradually disappears. 

How does one assign a value to the river runners' inconvenience? How does one compare 

the value of landscape relative to society's need for energy. or Idaho Power Company's 

responsibility to its customers and shareholders? Should something be done just for the 

sake of preserving the ecosystem of Hells Canyon? After all. the Snake carries the Wild and 

Scenic River designation and is within a National Recreation Area. But these areas were 

designated in 1975. long after Idaho Power Company was licensed to build the dams. 

The Snake River below Hells Canyon Dam offers a classic example of degradation 

immediately downstream from a dam. Williams and Wolman (1984) documented many 

examples of such degradation below other dams. They concluded that the process begins 

25 
with dam closure. occurs at a fast pace 

for the first few years. then slows with 

time until the bed is "armored" with 

material too coarse to be moved by 

the river. or until a bedrock control is 

exposed. This time-dependent 

process moves downstream as 

progressively more sediment is lost 

from the system. 

Will Hells Canyon ever recover its 

beaches? Probably not in our lifetime. 

Alternative management scenarios for 

minimizing erosion exist. but they all 

have significant drawbacks. The least 

sophisticated alternative would be to 

simply dismantle the three dams. To be 

realistic. the dams in Hells Canyon are 

not among that handful of candidates for 

removal. Alternatively. even though the 

Hells Canyon reservoirs are relatively Sandbar on the Snake River in Hells Canyon 

small. they could be managed primarily 

for flood control rather than for hydroelectric power. The reservoirs would be 

kept as close to empty as possible. and 

floods would be released as slow. steady 

flow into Hells Canyon. The beaches 

might erode more slowly. but riparian 

vegetation would colonize the remaining 

fine-grained substrate. But this would 

cost Idaho Power Company (more 

precisely. Idaho Power Company's 

customers) millions of dollars in lost 

revenues. Such a flow regime could 

engender its own set of downstream 

problems. such as the invasion of 

vegetation along the river banks. 

Another option would be to somehow pass sediment through the dams. 

Idaho Power Company could devise a 

way to transport sediment around its 

turbines. thereby preserving the usefulness of its dams and simultaneously 

reintroducing sand to the sedimentstarved reaches of the Snake River in 

Hells Canyon. This alternative may 

seem attractive. but retrofitting this 

26 
S nak!- 2?jver 

kind of technology would carry a frighteningly large price tag. And even if 

sediment could somehow be introduced to the river channel. that alone 

might not be enough to rescue the beaches. Once scrutinized. none of 

these alternatives offer a balanced solution to the issue of downstream 

effects at Hells Canyon. As much as we might wish to work miracles. 

sometimes the only fruit born of the study of the downstream effects of 

dams is a realistic assessment of relative values and environmental costs. 

27 

~o (jrande 

CJ'fze 2?jo {jrande drains more than 170,000 mi2 of Mexico and the American 

Southwest (Bartlett. 1984). flowing 1,865 miles from the San Juan Mountains of Colorado 

to the Gulf of Mexico at Brownsville. Texas. In northern New Mexico. the Rio Grande is a 

*Denver 

vigorous snow-fed river. with a mean 

annual flow of0.5 million acre-feet. Near 

the Gulf of Mexico. the river has an annual 

flow of 1.8 million acre-feet. But something strange happens in between. From 

Fort Quitman to Presidio. Texas. the river 

can be totally 

co 

dry. At times. 

the Rio 

Grande is like 

one river cut in 

two. both ends 

alive but 

cleaved in the 

middle. 

The story 

of the Rio 

Grande is one 

of withdrawal 

of water for 

agriculture and 

tributary 

streams adding 

it back with 

sediment. 

Most of the 

water that 

flows through 

central New 

Mexico is 

redirected into 

canals in the El 

Paso area. But 

tributaries to 

this stretch of 

the Rio 

Grande are 

mostly unregulated. and 

runoff from 

periodic 

storms can 

108' 

33' 

32' 

3 I 

The Rio Grande 

between Elephant Butte Dam, 

New Mexico, and Presidio, Texas 

NEW MEXICO 

MEXICO 

.a. Gaging station 

0 40 Miles 

I 1 1 I I 

Tamarix bosque an '-11!11!~~­

the Rio Grande 

below Ft Quitman 

0 60 Kilometers 

29 

TEXAS 
sporadically contribute both water and sediment. By the time the Rio Grande passes southcentral Texas. it once again is a full-fledged river; large tributaries have restored much of the 

water diverted in New Mexico. west Texas. and Mexico. What happens in the middle 

illustrates how our attempts 

to control and use the flow of 

a river may backfire in a spiral 

of aggradation. canalization. 

and dredging. 

~ 

The Rio Grande in 

southern New Mexico and 

western Texas has more 

sediment than it can readily 

transport The surrounding 

country is high Chihuahuan 

desert held together by the 

roots of a few creosote bushes. 

When a storm passes through. 

tributaries of the Rio Grande 

don'tjust flow. they flood. For 

instance. Cibolo Creek joins 

v 

~ 

~ u 

<( 

0 

0 

q 

0 

0 

-~ 

Q) 

e.o 

..c: "' 

~ 

i:5 

16 

12 

8 

4 

The annual volume of ffow in the Rio Grande above the Rio Conchas 

(at Presidio, Texas) has decreased dramatically with ffow regulation. 

Gradual increases in irrigation of the Mesilla Valley of New Mexico 

have reduced the annual ffow volume by an order of magnitude. 

Elephant Butte 

Dam 

Caballo 

Dam 

TX 

0 1900 1910 1920 1930 1940 1950 1960 1970 

the Rio Grande at Presidio. It is usually dry. But during a summer storm in 1990. it suddenly 

swelled to 6,000 ft3/s (John Lee. International Boundary and Water Commission. oral commun .. 

1992).1n 1904. a flood on Cibolo Creek washed most of Presidio away. These tributary floods 

transport tremendous quantities of sediment to the channel of the Rio Grande. producing 

alluvial fans that force the river against its opposite bank. 

The Rio Grande's natural channel once maintained an uneasy equilibrium with incoming 

tributary sediment The channel bed would aggrade next to tributary fans; flood plains would 

30 

The Rio Grande 

between Ft Quitman 

and Presidio 
2qo yrande 

grow above the river during moderate overbank floods. Then a larger flood would pass. just 

powerful enough to carry away sediments that had accumulated at the mouths of tributaries. 

The flood would deepen and widen the channel. beveling down the tributaries' alluvial fans. 

Thus the channel form was preserved. But even in its natural state. the middle Rio Grande did 

not have the magnitude of flooding one might expect from a river that drains such an 

Elephant Butte Dam 

on the Rio Grande 

at Truth or Consequences, New Mexico 

immense area. The largest flood on record at El 

Paso was only 24,000 ft3/s. measured on June 12. 

1905 (International Boundary and Water Commission. 1989). 

Stream gaging began at El Paso. Texas in 1889. 

27 years before dams spanned the Rio Grande. 

Before Elephant Butte Dam was completed in 

1916. the Rio Grande at El Paso had an average 

annual flow of 916,430 acre-feet. with most 

arriving during spring runoff in May and June. But 

some years only 100,000 acre-feet flowed by El 

Paso. A decade of predominantly dry years 

through 1904 prompted consideration of Elephant 

Butte Dam midway between Albuquerque. New 

Mexico and El Paso. Texas. Large-scale farming was 

to be possible in the fertile Mesilla and El Paso/ 

Juarez valleys only if the Rio Grande could be 

converted to a dependable year-round source of 

water for irrigation. During that turn-of-the-century 

31 

The Rio Grande below Ft Quitman, Texas 
drought, the Rio Grande had dried up too frequently 

to be trusted. 

Construction of Elephant Butte Dam began in 

1912. This was to be the centerpiece of the Rio 

Grande Project. an early offspring of the 1902 Reclamation Act that fathered the Bureau of Reclamation 

(U.S. Department of the Interior. 1981 ). Elephant Butte 

Dam's initial reservoir capacity was 2.6 million acrefeet, enough to store almost 3 average years of the 

river's flow. With the dam's completion in 1916, 

irrigation waters could be guaranteed to farms on 

200,000 acres (U.S. Department of the Interior. 1981) 

that lay downstream in southern New Mexico and 

western Texas. 

One consequence of this dependable water was 

that peak spring runoff averaging 4,400 ft3

/s in predam years was suddenly slashed to 1,300 ft3

/s 

(Mueller. 1975). The Rio Grande below Elephant Butte 

was transformed into a very different river: a river 

stripped of its floods. Below Elephant Butte Dam. the 

Rio Grande became a clear-water stream. Starved of 

sediment, the ri ver scoured approximately 2 feet from 

the bed of its channel from Elephant Butte to Las 

Cruces during the first 15 years of the dam's operation (Lagasse. 1980). This sediment made its way 

downstream toward El Paso. where the river gradient 

Riverside Dam on the Rio Grande flattened and the sediment dropped out of transport. 

downstream from El Paso, Texas With Elephant Butte Dam in place, New Mexico 

and Texas farmers were able to reliabl y divert millions 

of cubic feet of water every year. The 1906 Water 

Allocation Treaty assured Mexico that the United 

States would deliver 60,000 acre-feet of irrigation 

water annually at the International Dam between El 

Paso and Juarez (Mueller. 1975). Drainage ditches 

from both countries returned water from their irrigated fields back to the river - water that then carried 

high concentrations of salt out to the river and on 

downstream. The price of dependable water can be 

higher for some people than others. higher than some 

people wish to pay. 

Further change came to the Rio Grande with a 

program of channel rectification undertaken by the 

International Boundary and Water Commission 

(IBWC). The IBWC had grown out of an 1884 treaty 

between the United States and Mexico. stipulating that 

the international boundary from El Paso to 

32 
2?jo (jrande 

Brownsville would be the deepest channel of the Rio Grande. Despite the treaty. the river 

refused to hold still. The deepest channel migrated back and forth across the flood plain, acting 

more like an out-of-control fire hose than a well demarcated line of significant political importance. The IBWC's answer to this erratic river behavior was to stabilize the channel with 

unnaturally straight levees on both the United States and Mexican sides of the river. Between El 

Paso and Fort Quitman. meanders were bypassed and the channel was tidied into a 65-foot slot 

between levees. The old river distance of 155 miles was shortened to 88 miles (Mueller, 197 5 ). 

Similarly. the Bureau of Reclamation straightened and deepened the river's channel from 

Elephant Butte to El Paso. 

Tributary floods continued, of course. and sediment was frequently delivered to the 

channel. This tributary sediment, combined with sediment stripped from the river's banks 

and bed closer to Elephant Butte Dam. began to accumulate downstream. The Rio 

Grande's bed through El Paso rose almost 13 feet between 1907 and 1933 (Reinhardt. 

1937). TheEl Nino years of 1941 and 1942 were anomalously wet throughout the Rio 

Grande's upper drainage. Two million. eight hundred thousand acre-feet of water flowed 

into Elephant Butte Reservoir in 1941 (U.S. Department of the Interior. 1981). and for the 

first time. water not earmarked for irrigation had to be released from the dam. The smaller 

Caballo Dam. built 22 miles downstream in 1938. could not dampen the flood. The river 

crested in El Paso on May 18. 1942. with a measured discharge of 7,000 ft3

/s. lf the river's 

natural channel had not been clogged with sediment. this flood might have passed El Paso 

without problems. But on May 18. 1942, the lower reaches of town were afloat. 

Despite efforts by the Bureau and IBWC. sediment still piles up in the Rio Grande 

faster than man or nature can remove it. Since 1951. the annual flow just upstream from 

Presidio is only 30,000 acre-feet (Everitt. 1993), one-tenth of the pre-dam average. The 

tributaries continued to add sediment. and the channel continued to aggrade. ln 1987. a 

flood of less than 6,000 ft3

/s again wreaked havoc in El Paso. 

The relatively small flood of 1987 carried tremendous amounts of sediment downstream. When the sand-choked flood reached the end of the channelized section below 

33 

The Rio Grande 

between Ft 

Quitman and 

Presidio, Texas 
Fort Quitman. it encountered a river without a defined channel. Water fanned over the old 

flood plain. and sediment settled out. In places. fields were awash for 2 years before drying 

enough to support the IBWC's dredging equipment. 

Lester Ray Talley moved to the country below El Paso with his family in 1934. He was 5 

years old and the Great Depression was in full swing. To get started at farming. his father 

sharecropped land just above Fort Quitman. Lester guesses that 100 families once farmed 

along both banks of the Rio Grande from Fort Quitman to Ojos Calientes in the 1950s. but 

most have left now. Lester looks downstream as he says. 'The river's all choked up; ain't 

good for nothing." 

The IBWC calls the 155 miles of the Rio Grande between Fort Quitman and Presidio 

its Boundary Preservation Project. 

defined entirely by what has not 

been done there: no canalization. 

no rectification. no sand-and-gravel 

mining. no bridges (Everitt. 1993). 

There is little but tamarisk stretching down the flood plain as far as 

the eye can see. Tamarisk was first 

reported along the Rio Grande near 

Las Cruces in 1910 (Robinson. 

1965). Once-dominant galleries of 

2595 ....----.-----r---,.---

2590 

~ Q) 

L.L.. 

.£ 

c 2585 0 

·~ 

> 

Q) 

w:; 

2580 

2575 

0 

] 2845 .£ 

c 

0 

-~ 

~ 2840 w:; 

30 60 

Distance, in Feet 

U.S. 

abandoned field 

2+00 

Centerline Channel Stationing. in Feet 

34 

Mexican 

levee 

Time series of channel aggradation 

at Presidio, Texas, between 1933 

and 1974. Because ofthe addition 

of sediment from tributaries, and the 

decreased ffow in the Rio Grande, 

sediment is deposited in the channel. 

In response, the channel's bed 

elevation rises and its width narrows. 

(Modi(led from Everitt, 1993) 

A cross section of the Rio Grande 

2 km downstream from Candelaria, 

Texas. When measured in 1974, 

the channel bed was higher than 

its ffood plain. (From Everitt, 1993) 
cottonwood and willow along the Rio Grande have been overrun 

by this introduced species (Howe and Knopf.1991). Tamarisk 

bosques in the Preservation Project do provide some understory 

for animal nesting. but when compared to the displaced native 

cottonwood/willow habitat. they offer little opportunity for 

feeding by birds and mammals accustomed to the area (EngelWilson and Ohman. 1978). 

Midway through the Preservation Project. Mayfield Canyon 

joins the Rio Grande in Box Canyon. Flash floods down this 

tributary have dumped sand. gravel. cobbles. and boulders onto 

the bed of the Rio Grande. Once floods on the larger river would 

have been able to clean out this debris. But regulation at Elephant 

25.000 

a 

20.000 

-o 15.000 c 

0 

u 

<l> 10,000 <./) 

Qj 

0.. 

Q) 5000 <l> 

'"-

u 

:.0 

:::J 0 

u 

~ 

o) 80.000 00 

ro b .c 

~ 

0 60.000 -"" "' <l> 

c... 

(ij 40.000 ~ 

~ 

20.000 

0 1890 

R1oCrande 

at El Paso. Texas 

Elephant Butte Dam 

1162.000 

I 

Rio Conchos near Ojinaga Chihuahua 

1910 1930 1950 1970 1990 

Butte. water withdrawals for irrigation and municipal use. and the 

dampening effect of tamarisk bosques have all worked to reduce the 

discharge and power of any flood coming down the Rio Grande. 

Sand and some of the gravel are moved downstream. but the 

cobbles and boulders remain in place. The river is no longer able to 

supply downstream force at the magnitude required to move these 

larger obstacles. A steep rapid has formed at the mouth of Mayfield 

Canyon. Confined by the canyon walls. the river is not free to 

migrate away from the tributary's debris. Waters backing up on the 

Rio Grande behind this debris fan had deposited 10 feet of floodplain sediment between 1945 and 1979 (Everitt. 1993). 

35 

!Rjo (jrande 

The ffood history 

of the Rio Grande 

and Rio Conchas 

are dramatically 

different, even 

though both rivers 

are heavily regulated. 

Dams on the Rio 

Conchas are not 

operated primarily 

for ffood control. 
This scenario of aggradation continues downstream to Presidio, Texas. A dramatic 

change occurs there as the Rio Conchos enters from Mexico. The Conchos is not a trivial 

tributary; a flood in 1904 is estimated to have peaked at 162,000 ft3

/s. lts total annual flow 

averaged 737,000 acre-feet through the 1980s. more than five times the flow of the Rio 

Grande measured just above its confluence with the Conchos (IBWC. 1989 ). And unlike 

the Rio Grande, the Rio Conchos has an ongoing history of intermittent high flows: 71 ,300 

ft3/s in 1978,45,900 ft3/s in 1991. The effects ofthese high flows are immediately obvious 

to anyone looking at the Rio Grande channel below its confluence with the Conchos. That 

channel is wide and well-defined. The tamarisks have been beaten back by the flood 

waters. Below the Conchos. in Big Bend National Park. the Rio Grande starts looking less 

like a swamp and more like a river again. 

As Lester Ray Talley said, the Rio Grande from Fort Quitman to Presidio is just all 

choked up. By and large, people have abandoned the river here. Could the situation be 

different? The IBWC could spend a lot of money to extend its rectification down through 

the Preservation Project. Rectification would certainly make the IBWC's job of maintaining 

this section of the international border easier. at least for a while. Lester Ray Talley thinks it 

would eventually allow farming along the river valley again. 

Flood control has been a long-standing reason for dams. In the days before dams and 

tamarisk and artificial channels. occasional floods rumbled down the Rio Grande and 

maintained a channel where sediment and seasonal flows were in equilibrium. Could 

Elephant Butte and Caballo dams be operated in a different manner that would minimize 

the aggravation of aggradation? It is conceivable that intermittent flushing flows released 

from Elephant Butte Dam could minimize the damage caused by uncontrolled flooding. 

But Las Cruces, El Paso, and Juarez have grown a great deal since the last unrestrained 

flood passed through in 1905. Who would want to pick up the tab for the damages from 

even a small intentional flood sent down the Rio Grande? 

The Rio Grande from Elephant Butte Dam to Presidio is a fine example of a river now 

caught in a web spun with good intentions. Dams reduce peak flows. Irrigation canals 

36 
!Rjo (jrantfe 

siphon off annual discharge. Canalization temporarily helps 

handle floods. but tributary sedimentation cripples the 

effectiveness of the canals. We cross our fingers as we build 

levees. watch the river bed fill with sediment. and raise the 

levees a little higher. We build flood and sediment retention 

dams across tributaries and dredge out the river's channel. 

All the while. the growing populations of local cities push 

onto flood plains that ultimately cannot be made floodproof. 

Any one action will cause a reaction somewhere else. 

Does the complexity of this water system preclude any 

effective measures for dealing with its problems? No. Do we 

need to come up with more than temporary solutions? 

Obviously. We need to be aware of all the tools available to 

us in addressing problems of water delivery. flooding. and 

sedimentation. it is conceivable that intentional larger-thannormal flow releases will one day be used as such a tool. 

37 

Chattahoochee 2?jver 

.9l.jter tfie Civi[ War, John Taylor's great-grandfather 

settled along the Chattahoochee River 40 miles upstream from Atlanta to 

farm and raise a family. John grew up farming along the Chattahoochee. 

and remembers the big floods of winter and early spring before Buford 

Dam was finished in 1956. He would row across the swollen river. up into 

the trees where his neighbor Doug Milam now lives. The flood waters 

CA 

The Chattahoochee River 

in north-central Georgia. 84° 

.& Gaging station 

0 !Omiles 

0 I 5 kilometers 

The U.S. Army Corps of Engineers started 

construction of Buford Dam in 1952; 4 years and 

$45 million later. the dam was completed and Lake 

Sidney Lanier began to fill. Buford Dam was intended to provide flood control. improved navigation. hydroelectric power. and a reliable supply of 

instream water as the river passed Atlanta. More 

dams have been built downstream on the 

Chattahoochee. and navigation is no longer considered feasible on this stretch of the river. The dam 

has admirabl y performed the tasks of flood control 

and instream water suppl y. Since completion, no 

destructive floods have occurred on the 

Chattahoochee below Buford. And the river is far 

and away the most important (and usually reliable) 

source of drinking water for millions of people 

downstream. 

39 

were thick with mud and 

sand. receding after a few 

days to reveal a new layer of 

organic-rich silt that lined the 

riverbank and spread across 

his fields. On January 8. 1946. 

53,000 ft3/s flowed through 

here (Stokes and others. 

1991). These days. the river is 

dammed and discharge is 

rarely a fifth that of the old 

floods. John doesn't miss 

those floods. but he feels that 

the daily fluctuating releases 

from Buford Dam are ultimately more detrimental to 

his land. The new regime of 

clear water and daily fluctuation steadily erode a little 

more soil from the river's 

banks each year. but gives 

back nothing. 

Fisherman on Lake Sidney Lanier 

above Buford Dam in Georgia 
'0 

c 

Flow records for the Chattahoochee River 

at Norcross, Georgia. Buford Dam has been 

successful in controlling ffoods, but the total 

annual ffow has remained unchanged. 

60.000 r----,--.-----r---r---.-..-... ! 

8 50.000 GA 

Greater metropolitan Atlanta is an 

energetic growth 

center for the New 

South: 2,500,000 

people lived here in 

1991 (Atlanta 

Regional Commission. 1992). with 

more than another 

million expected to 

arrive in the next 2 

decades. By the year 

2010. the Atlanta 

Regional CommisQ) 

V'J 

Q; 

~ 40.000 

~ 

:5 30.000 ::> 

u 

.£ 

~ 20,000 Buford Dam Closed 

..c: "' 

~ 

i:5 

10,000 

O '----:-1-:!9:-::1 0:--:-1 ::':92:-::0~19::'::3-::-0-:-:19J..,-40-=--I:-:::9':c50=-" 1960 1970 1980 1990 

sion forecasts that the metropolitan area will require 200 acre-feet of water on an average 

day. and 310 acre-feet on a hot day (Atlanta Regional Commission. 1991). Virtually all of 

this water will come from the Chattahoochee River. The Corps is required to release 

enough water from Buford Dam to insure a minimum instream flow of750 ftl/s (1,490 

acre-feet per day) as the Chattahoochee passes Atlanta. The city would like to see the flow 

increased. giving it more leeway in taking out water for its own uses (Atlanta Regional 

Commission. 1991). 

A large and growing population consumes considerable electrical power. The Corps 

of Engineers has continued to abide by its mandate to generate electrical power at Buford 

Dam. The dam's three generators have a combined capacity of 86,000 kW Typically. offpeak flow out of Buford is reduced to 1,300 ft3

/s on weekdays. and 600 ft3/s on weekends. 

thus saving water for peak-time release (Benton Odom. U.S. Army Corps of Engineers. oral 

Canoeing on the Chattahoochee River in Atlanta, Georgia 

40 
commun., 1992). A consortium of electric 

utility companies. along with the water 

users represented by the Atlanta Regional 

Commission. examine the Corps' weekly 

water allocation and assign an hour-byhour schedule of releases for the upcoming week (Atlanta Regional Commission. 

1991). 

Flow releases in the Chattahoochee 

are timed to augment the Southeastern 

power grid's peak demands, when 

electrical power is most valuable. Eightthousand. eight hundred ft3

/s are released 

during maximum power generation at 

Buford Dam; any flow higher would 

necessarily be sent through the spillway 

and wasted for power generation. As long 

as too much water isn't sent downstream 

over the course of the week, and as long 

as the river always measures at least 750 

ft3/s in Atlanta. the electrical companies 

are basically free to shape the release 

from Buford Dam any way they please 

(Michael Wilder. Georgia Power Company. oral commun .. 1992). 

A curious development has occurred 

along the Chattahoochee. however. The 

people of northern Georgia have fallen in 

The Chattahoochee River 

below Buford Dam 

41 

Cftattafwocfzee 2?jver 

Eroded banks 2 miles 

below Buford Dam 
Warning on the 

Chattahoochee 

River immediately 

below Buford Dam 

love with their reservoir and its water. The Corps of Engineers has recognized recreation 

as a priority by which to operate Buford Dam. In 1990. 19 million people came to visit 

Lake Sidney Lanier. more than any other federally managed reservoir in the country. 

Twelve thousand homes surround this 38,000-acre reservoir. Twenty thousand boats are 

parked at 6,700 docks on the lake. The docks can tolerate some fluctuation of lake level. 

but not much. All those people spent $422 million recreating here in 1990 (Montgomery. 

1991). By contrast. hydropower generation of electricity at Buford earned $1.3 million 

during the year ending September 30, 1992. 

In 1978. Congress established the Chattahoochee National Recreation Area. It 

comprises 14 units scattered along the river between Buford Dam and Atlanta. As land 

and funding become available for future purchases. the recreation area will expand to its 

authorized total of6,800 acres. Predictably. the recreation area is heavily used by the 

millions of people who live within just a few minutes' drive. There they all are. furiously 

fishing. canoeing. bicycling. bird-watching. picnicking. jogging. and swimming. The National Park Service. charged with administration of the recreation area. worries about 

visitor safety (John Hendrix. Chattahoochee River National Recreation Area. oral 

commun .. 1992). Does the river's water quality meet standards safe for swimming? Will 

canoeists be caught in the tangle of fallen trees that litter the channel? Will fishermen be 

surprised by the sudden dai ly rise of river level? 

Signs warning about fluctuating dam releases have been erected every few hundred 

feet along the Chattahoochee's banks for many miles below Buford Dam. A series of earsplitting sirens go off every time the river is about to rise. There are even low-powered AM 

radio stations broadcasting the changes ofriver level. Nonetheless. fishermen are swept 

downstream every year. Recreational safety is a major issue along this regulated river. 

Trout do not naturally thrive in the typically warms waters of Georgia. But water from 

deep within Lake Sidney Lanier is cold and clear. ideal for trout. The State's Buford Hatchery releases hundreds of thousands of 10- to 12-inch trout every year to the waiting lures of 

42 
Monitoring Water Quauty in 2{egufated !Rjvers 

A river's health can be assessed by many measures: the volume of water 

carried, the size of the channel, and the amount of sand on its banks. But rivers 

transport more than water. Organic and inorganic substances, either dissolved 

or attached to sediments or organic debris, are all integral components of 

flowing water. Dams can dramatically increase or decrease transport of these 

substances. For example, salinity frequently increases downstream from dams 

on most western 

rivers because of 

the combination of 

reservoir evaporation and the 

addition of runoff 

from salt-rich 

strata. In the east, 

algae and nutrients can increase 

below dams, or 

dissolved oxygen 

can decrease. 

Decreased sediment load increasesthe 

amount of light 

passing through 

the water, further 

altering the biotic 

system. 

Measurement of water quality in rivers requires more than simply filling 

a bottle and "testing" it. Water samples from two nearby points in a river may 

yield significantly different results. Hydrologists quantify sediment and 

nutrient loads, typically expressed in units of weight per day. Calculation of 

loads requires measurement of discharge at a stream-gaging station and 

periodic collection of samples that are discharge-weighted, or representative 

of the total flow through a cross section. Water quality can also be assessed 

by analyzing the biota; for example, fish concentrate metals and other contaminants in their body tissue. The types and density of organisms is another 

measure of water quality. Sampling of water quality is very expensive but is 

what is necessary to answer basic questions about the integrity of our 

Nation's rivers. 
folks lining the banks downstream (William 

Couch, Buford Rsh Hatchery. oral commun., 

1992). The Came and Fish Department 

monitors water temperatures as well as the 

amount of iron. manganese, and dissolved 

oxygen in the Chattahoochee below Buford 

Dam. When water is drawn from near the 

bottom ofthe lake, oxygen concentrations 

can drop as low as one-half part per million 

(ppm), well below the 5-10 ppm level 

considered desirable for trout Recreation 

has become a driving force on the 

Chattahoochee. So have water quality. 

and fish and wildlife concerns. All of these 

priorities have taken their place alongside 

the four authorizations by which Buford 

Dam was originally operated. 

In 1975, the U.S. Geological Survey 

undertook a 3-year study of the hydrology 

and water quality of the upper 

Chattahoochee basin. The study looked 

in detail at the river's biochemical oxygen 

demand. dissolved oxygen. phosphates. 

thermal pollution. and other measures of 

water quality (Cherry and others. 1980). 

Engineers modeled the flow of water in 

order to predict its movement downstream from Buford (Jobson and Keefer. 

1979 ). Strategies of dam operation were 

suggested that could most economically 

deal with problems of dissolved oxygen 

(Schefter and Hirsch, 1980). Geologists 

investigated the rate at which sediment 

was being swept into the river from 

nearby farms and logging operations (Faye 

and others. 1980). The State of Georgia 

made good use of the data that arose from 

the project; they legislated formation of 

the Atlanta Regional Commission, 

charged with design and implementation 

of a Chattahoochee Corridor Plan. This 

plan has been the vehicle by which a 

good deal of scientific thinking was 

converted into the nuts and bolts of 

municipal planning and zoning. 

44 
Lake Sidney Lanier 

Chattahoochee 'Rjver 

Two-hundred and nineteen thousand 

tons of sediment are annually carried into 

the upper reaches of Lake Sidney Lanier 

(Montgomery, 1991). But at the other end 

of the lake, waters emerging from Buford 

Dam are clear and devoid of sediment. 

Below the dam. the Chattahoochee River 

is vigorously eroding its banks. John Taylor 

will tell you all about that; he feels that the 

river's daily fluctuations are hastening the 

erosion of his farm. If he had his way. the 

river would flow without fluctuation. If the 

thirsty city of Atlanta had its way. the river 

would have a higher minimum flow, thus 

necessitating lower peak flows. If fishermen had their way. releases from Buford 

would be cold water with adequate 

oxygen for their introduced trout. If 

boaters on Lake Sidney Lanier had their 

way. the lake would vary not an inch from 

its normal pool level of 1,070 feet above 

sealevel. 

So many demands but just one river. 

Dam releases could be designed to 

minimize downstream erosion. but power 

generation would suffer. Likewise. reduction of extreme fluctuations in flow would 

increase recreational safety but diminish 

the capability of load-following power 

generation. The operation of Buford Dam 

has been subject to a lot of tinkering since 

the dam's original authorization and 

construction in the 1950s. More changes 

are likely to come in the future. The 

inexorable growth of cities along the river 

will put water supply. water quality. and 

recreational interests at an even greater 

premium. The Army Corps of Engineers is 

likely to hold sway as far as flood control is 

concerned. but water allocations for 

generation of peak power could become 

an historical curiosity when that value is 

eclipsed by environmental and recreational needs that may. in time. become 

higher priorities. 

45 
' -

- P(atte '!l~i'Yit 

Cftan { fJta ro'U{.irtg 
P[atte !Rjver 

'])us!(_ settfes over tfie P{atte :t(jver as the sky fills with lesser sandhill 

cranes gliding in to roost. Their 3-foot wings are extended but not beating. bony legs 

already pointing toward earth. The sprawling flock of birds looks like thousands of gray 

umbrellas. all open. all drifting down to earth. The air is thick with the cranes' chattering 

cry. In February and March every year. almost a half million sandhill cranes return to roost 

along the Platte River in a scene that has been repeated annually since the Ice Age (Krapu 

and others. 1982). The river has always offered habitat that the cranes need: shallow water 

spread across a wide channel. broken up by numerous sand spits and islands. But during 

this centur y. that riparian habitat has been drastically altered. largely by the placement of 

dams upstream. 

Each morning in March before daybreak. the air above the river is filled with a rising 

chorus of cranes: a dry crackling cacophony that swells as the sun rises. An occasional bird 

lifts from the islands. and then everywhere flights of cranes launch skyward. Initially their 

movements are labored. uncertain. But after a few seconds the long ungainly legs are 

stowed aft and the great wingbeats become synchronous. almost stylized. The cranes are 

off for another day of foraging. The birds might fly a few miles before descending onto 

nearby cornfields that have been dormant since the previous fall's harvest. During its 6 or 

47 

8 weeks along the 

Platte. each crane 

will add 15 percent 

or more to its 

wintertime body 

weight of7 pounds. 

Corn pecked from 

the farms offers 

more than 90 

percent of this 

nutrition; the 

balance is gathered 

among meadows 

along the river 

where the birds 

find earthworms. 

snails. grasshoppers. and other 

delectables 

(Reinecke and 

Krapu. 1986). At 

day's end. the 

flocks once again 

return to their 

favored sandbars 

along the Platte. 
The Platte is a quintessential river of the Great Plains: flat, wide. and shallow. Its banks 

were a major thoroughfare for the westward migration of the mid-1800s. Travelers consistently commented upon the river's sand-choked waters; they warned each other that no 

trees were available along its course for fuelwood. The river's main tributaries. the North 

and South Platte. reach like two great pincers around the Rocky Mountains of Colorado 

and Wyoming. Coming down out of the mountains. these tributaries encounter the 

relatively dry country of southeastern Wyoming. northeastern Colorado. and then western 

Nebraska. Rainfall along the North Platte as it flows from Wyoming into Nebraska is only 13 

in/ yr (Eschner and others. 1983 ). Beyond the shadow of the Rockies. precipitation increases to 25 in/yr at Grand Island, Nebraska (Williams. 1978) and even more as the river 

flows farther to the east. The upper Platte and its tributaries depend on springtime snowmelt from the Rockies to provide the greatest part of its annual flow. 

The confluence of the North and South Platte Rivers lies just west of the 1 OOth meridian. John Wesley Powell. a famous western explorer and one of the founders of the U.S. 

Geological Survey. had observed the dramatic decline of rainfall across the Great Plains 

(Powell. 1879). Crowing up on a Midwest farm. he knew how difficult the life of a farmer 

could be. And without reliable water. farming that might have just been difficult becomes 

Platte, Nebraska 

impossible. All through the 1870s. Powell championed 

the importance of irrigation as the prerequisite for 

organizing and settling agricultural lands west of the 

1 OOth meridian. 

Primitive irrigation was practiced in the upper South 

Platte drainage as early as 1838, when Antoine Janis 

diverted water from the Cache Ia Poudre River onto his 

48 
P[atte 2?jver 

fields within the river's flood plain. Twenty years later. spurred by the demands of the 1858 

gold rush in the mountains west of Denver. the pace of water diversion to irrigated farmland began to increase. Canals proliferated out from the river onto bench lands above the 

flood plain like cracks radiating through shattered glass. By 1885. more water had been 

appropriated by canal builders and farmers than actually flowed in the South Platte during 

the summer irrigating season (Eschner and others. 1983).1n contrast. the North Platte was 

never the focus of a mining frenz y and developed more slowly. Cattlemen in Wyoming 

gradually embraced the benefits of irrigating fields to provide feed for their stock. It would 

be 1917 before the entire North Platte River was over-appropriated during summer. 

In 1890. the Platte River Valley was well on its way to becoming the embodiment of 

Powell's ideal of irrigation and reclamation when the Western Frontier was officially closed. By 

109' 

42' 

WYOMING 

COLORADO 

Farmland near Overton, Nebraska 

101 ' 

I 

Cheyenne 1 

I 

WY 

A. Gaging station 

0 100 Miles 

0 !50 Kilometers co 

The Platte River in Wyoming, Colorado and Nebraska. 

1894 canals were irrigating 365,000 acres within the 

valley (Krapu and others. 1982). But by the turn of the 

century, canal construction began to decline as 

progressively less water could be wrung from the 

Platte at times when the water was most needed for 

irrigation. Private companies had built a few dams 

across small tributaries before the turn ofthe century. 

hoping to impound a bit of spring runoff for summertime use. But these were small structures and most of 

the Platte's springtime water still went downstream. 

slipping through the farmers' fingers. Who could afford 

49 
Diversion strudure for the Tri-County Supply Canal below the confluence of 

the North and South Platte Rivers at North Platte, Nebraska. 

to build the larger 

dams desired by the 

farmers? The question was unequivocally answered by 

passage of the Federal 

Reclamation Act of 

1902. which ushered 

in an era of big dams 

on the North Platte. 

Flush with Federal 

money and armed 

with the best of 

intentions. dam 

builders descended 

upon the North Platte. 

Beginning with 

Pathfinder Dam in 

1909. six major dams were built across this river in Wyoming and Nebraska. Seminoe. 

Pathfinder. Alcova. Glendo. and Guernsey reservoirs in Wyoming have a total storage 

capacity of 3 million acre-feet. Kingsley Dam was built in 1941. forming 1.9 million acrefoot McConaughy Reservoir just upstream from the river's confluence with the South 

Platte in central Nebraska (Williams. 1978). The South Platte. with fewer reservoir sites. 

was bridled with dams that could hold back only 1.3 million acre-feet (Krapu and others. 

1982). Now water could be gathered year-round and delivered when it was needed for 

irrigation in summer. 

And delivered it was. With the reservoirs in place. demand for irrigation water expanded to meet the supply. Another wave of canal building swept down the North Platte. 

4 

3 

2 

Annual flow volumes for the Platte River at Overton, 

Nebraska. Five dams built since 1909 provide flow 

regulation for irrigation of farmland in Wyoming and 

Nebraska. 

SeminoeDam 

Alcova I . Dam K1ngsley 

~ r·m 

• 

Glendo 

Dam 

• 

QL--L~L-~~L_~~--J_~--J_~--~~--~_L __ L_~ 

19 15 1925 1935 1945 1955 1965 1975 1985 1995 

50 
lasting until the 1930s. Even more water was sucked from the 

river. and farmers turned to ground water for additional irrigation. 

By 1979. only two other states had more land under irrigation 

than Nebraska. Annual flow of the Platte at Overton. Nebraska 

once averaged 2.9 million acre-feet per year; by 1984. less than 

one-third as much water would pass Overton during a typical 

year (Krapu and Eldridge. 1984). Peak springtime flows that had 

once rolled past the town of North Platte steadily dropped from 

a pre-dam average of 18,000 ft3

/s to 2,500 ft3/s for the period 

1957-1970 (Williams. 1978). Spring flooding had become a thing 

of the past. 

P[atte 2?jver 

Canada and Snow Geese near the Platte River at Kearney, Nebraska 

Still. the sandhill cranes keep returning. They congregate in 

greatest numbers from Overton to Grand Island along the Platte 

River. A smaller group is found on the North Platte River just 

above its confluence with the South Platte. The cranes roost on 

sandbars where the channel is at least 500-feet wide. and are 

rarely found in areas where the channel is less than 150-feet wide 

(Krapu and others. 1984). These preferences were not a problem 

100 years ago; a railroad survey in 1866 reported that the islandstudded channel was 4,000- to 6,500-feet wide from North Platte 

down to Kearney. But the steady reduction of both peak springtime flows and total annual flows have taken their toll. In the 

absence of floods. cottonwood. elm. and willow have successfully 

51 
Sandhill cranes dancing near Kearney, Nebraska 

52 

invaded the bare sandbars. Islands 

that once isolated the cranes from 

their predators are now connected to 

the river's banks; sediments fill the 

intervening channels, and spring 

ftoods are no longer available to ftush 

these minor channels clear (Eschner 

and others. 1983). 

Each spring. the cranes returning 

to the Platte find many stretches of 

the river a little bit narrower. In its 60-

mile stretch above Overton, the 

channel by 1965 was only 10 to 20 

percent of the width measured in 

1865 (Williams. 1978). The cranes 

have abandoned a bit more river 

every year; by 1956. they had retreated from the 50-mile stretch from 

North Platte to Cozad. Each spring. 

the birds are packed a little bit tighter 

against each other. Crowding increases the likelihood of infectious 

disease. An avian cholera outbreak 

decimated tens of thousands of 

waterfowl in the Rainwater Basin, just 

a few miles from the cranes' roosting 

areas along the Platte (Krapu and 

others. 1982). 

Unlike whooping cranes. sandhill 

cranes are not endangered. Despite 

the habitat reduction along the Platte. 

their numbers may actually be 

increasing. It is refreshing, for a 

change. to contemplate measures to 

insure the persistence of a species. 

not when it is tipped beyond the brink 

of extinction, but while it is still in its 

prime. Botanists have suggested that 

moderate releases of water in late 

spring could submerge sandbars that 

would otherwise host the germination of new cottonwoods and willows. 

And hydrologists now contemplate 

dam releases capable of opening and 

maintaining a channel adequate for 
P[atte !Rjver 

use by the cranes. There is no cookbook method for determining the amount of water 

required to produce both of these results. A feedback loop of altered dam releases and 

subsequent downstream observation (known as Adaptive Management) would be required to determine how much water would have to be released for how long. 

Part of the equation is cost: reduced irrigation water for farmers living upstream. The 

potential trade of farm productivity for crane habitat is not as simple as it might seem. The 

timing of releases might coincide with periods when farmers do not require water. Or 

crops could be converted to ones that require less irrigation. Although scientists can offer 

answers to many of these questions. the central question -the relative value of cranes 

versus farm productivity -can be answered only by our society. 

... , J 1 ... 

53 

Landscapes within tfie 

drainage of tfie (jreen 2?jver are 

reminiscent of more western movies than you 

might ever want to watch. The 45 ,000 mi2 

area of Wyoming. Colorado. and Utah that 

contributes runoff to this river is a spectacular 

mix of mountains and high desert. The ri ver's 

source in Wyoming's Wind River Range is 730 

miles upstream from its confluence with the 

Colorado River in Utah's Canyonlands 

National Park. Along the way. the Green 

passes through Dinosaur National Monument 

UTAH '-----~~~~~----

Glen Canyon 

;ational 

Recreation 

Area 

Canyonlands 

adona! Par, 

& Gaging station 

0 30Miles 

0 30 Kilometer~ -

The Green River from Flaming Gorge Dam 

to its connuence with the Colorado River 

in Utah 

55 

WY 

co 

(jreen 2?jver 

as well as several 

national recreation 

areas and wildlife 

refuges. It gathers the 

flow of the Yampa and 

White Rivers. which 

drain the Rocky 

Mountains of northwestern Colorado. as 

well as the Duchesne. 

Price. and San Rafael 

Rivers. which drain 

the Uinta Mountains. 

Wasatch Plateau. and 

the lower deserts of 

Utah. The high 

mountains and 

plateaus that form the 

rim of the Green River 

basin contribute most 

of the river's annual 

flow. even though they 

are only a small part of 

the entire drainage 

basin (lorns and 

others. 1965). 
Before construction of dams in the basin. the Green would begin to rise in March. 

swollen with snowmelt from its headwaters. The spring flood would peak in early June and 

not recede until July. The average peak flood at the most downstream gaging station -

Green River at Green River. Utah- was 32,000 ft3

/s for the period from 1895 to 1962; and 

the highest peak ever measured at this station was 68,100 ft3

/s in 1917. Torrential spring 

floods would carry great loads of sand and silt. but only small amounts of sediment were 

derived from the water-producing headwater stretches of the river. 

The Green River has a split personality: its water originates in the mountainous 

highlands. but its sediment is derived from the low-lying deserts. The forested headwaters 

yield little sediment during the spring 

snowmelt. The desert areas are 

subject to brief. violent summer 

thunderstorms. which strip sediment 

from the sparsely vegetated slopes. 

Prior to construction of Flaming 

Gorge Dam. most of this sediment 

was deposited on the channel bottom 

until spring floods could transport it 

downstream. 

The Green River. like most other 

large rivers on the Colorado Plateau. 

once displayed a wide range of 

hydrologic behaviors. The water was 

nearly clear during low-flow periods. 

Cold spring floodwaters were thickened with enough sediment to "stand 

up a spoon in a coffee cup." Sluggish 

summer flows were occasionally 

stirred into a muddy frenzy by the 

input of a local thunderstorm. Winter 

flows became cold enough above 

Jensen that the top 2 or 3 feet of the 

river would freeze solid. 

The Green River near Sand Wash, Utah 

The extreme variability in flow. sediment concentration. 

and temperature of the Green River gave rise to an array of fish 

species found nowhere else in the world. The river was home 

to at least 13 endemic species in the minnow. sucker. trout. 

Humpback Chub 

and sculpin groups. This combination evolved into an interlocked community. balanced delicately amongst themselves 

and attuned to the demands of the river (Tyus and Karp. 1991 ). 

Seventy-four percent of fish first found in the Green and 

Colorado Rivers lived only in these rivers (Miller. 1959). Among 

these species are the razorback sucker (Xyrauchen texanus). 

bonytail chub (Gila elegans). humpback chub (Gila cypha). 

56 
(jreen 2?jver 

and Colorado pikeminnow (Ptychocheilus lucius). But today the bonytail chub may 

already be extinct, and the razorback sucker is only occasionally found. Each species 

developed unique adaptations to the rigors of life in the Green River and its own preference for different reaches of the river. The suckers. chubs, pikeminnow. and dace are now 

threatened by changes that have swept down the river since the 1960s. 

For 2 million years the humpback chub has been coping with these vagaries. preferentially seeking the reaches in desert canyons with rapids. The chub is an odd-looking fish, 

with a pointy head and fins that seem disproportionately large compared to the rest of its 

body. The hump on its back is an adaptation that provides stabilization in swift currents. 

The humpback chub is not a particularly strong swimmer; instead it uses its oversize fins 

to hydrodynamically "soar" underwater. Its lateral stripe is so sensitive that the chub can 

feel tiny vibrations caused by nearby insects - an ability well suited to life in muddy water 

with low visibility (Valdez. 1993). The humpback chub commands respect because it is a 

unique survivor. It demands concern because it is now endangered. 

Native fishes can be threatened by many environmental factors. only some of which 

are directly related to dam construction. Many new species have been introduced to the 

Green River. among them channel catfish (lctalurus punctatus), red shiners (Notropis 

lutrensis), and carp (Cyprinus carpio). Collectively these species now greatly outnumber 

The Green River entering Split Mountain 

in Dinosaur National Monument, Utah 

57 

the native species. Some of these nonnatives compete for the same food and 

habitats as the natives. and sometimes the 

natives (especially when young) are eaten 

by the nonnatives. 

Some dam-related stresses to the 

native fishes were inevitable, while others 

did not have to happen. Just before the 

gates of Flaming Gorge Dam closed in 

September 1962, a triumvirate of Federal 

and State agencies dumped 21,500 gallons 

of 5-percent rotenone into the Green River 

at various stations in Wyoming. The intent 

was to kill the "rough" fish that might 

interfere with stocked trout. Potassium 

permanganate was added to the brew 29 

miles below the dam, in hopes of neutralizing the rotenone before it reached Dinosaur National Monument. The effect of this 

experiment was to kill significant numbers 

of the native fish that we now labor to save 

under the Endangered Species Act. 
Flaming Gorge Dam has also been responsible for other direct and less avoidable 

effects on the native fish community. Because water is released from deep within the 

reservoir. water temperatures plummeted from a pre-dam average of66° F to 42° F 

(Vanicek and Kramer. 1969). Although native fish can live in such cold waters. as they did 

each winter in the northern parts of the watershed. the low temperatures inhibit their 

spawning. For example. the Colorado pikeminnow is reluctant to spawn in water colder 

than 59°F; its optimum spawning conditions are closer to 71-77°F (Tyus. 1990). The cold 

water forced the pikeminnow (as well as most other native fish) to abandon the Green River 

from the dam down to the mouth of the warmer Yampa River (Vanicek and others. 1970). 

The clear. cold water of the regulated Green River became the home of introduced 

trout; the fishery has an international reputation that attracts millions of dollars in sport 

fishing each year. However. the water released from the dam was initially even too cold for 

trout- the low temperature inhibited their growth. In 1978. the Bureau of Reclamation 

spent $20 million to retrofit multilevel intake structures at Flaming Gorge Dam to allow for 

seasonal warming of the downstream waters to increase the growth rate of trout. This 

engineering solution enabled the Bureau to release waters from different levels and 

different temperatures. The trout grew fatter. 

t 

Flaming Gorge Reservoir filled for the first time in 1966; since then, the annual total 

amount of water released downstream has not significantly differed from the annual total 

prior to dam closure. However. the timing of water flow has been radically altered. With the 

dam in place. winter flows have increased and the spring flood has almost entirely disappeared. Flow almost never exceeds powerplant capacity. 

The dam's powerplant is designed to generate 36,000 kW when 4,700 ft3/s is released through the turbines at maximum reservoir capacity. Because peak electrical 

power demands occur during summer and winter, these are now the times of maximum 

river flow. Since the peak demands only exist for a few hours each day, the river would 

fluctuate so as to produce maximum power during the few hours each day when the 

needs are greatest. Immediately downstream from the dam, vertical fluctuations in daily 

river levels could be measured in yards. River levels 107 miles downstream at Jensen. Utah 

rise and fall as much as 1.5 feet each day (Valdez. 1989 ). These fluctuations can break up 

the ice cover. which is now thinner; the fish are forced to scatter as the ice grinds against 

the shore. Fluctuations in flow affect aquatic habitat and can compromise the ability offish 

to survive through the winter. 

Flaming Gorge Reservoir effectively intercepts all sediment that enters its headwaters. 

Water released from the dam is devoid of any sand or silt. Between.the dam and its 

confluence with the Yampa, the clear water of the Green River is carrying away sediment 

from its banks and bed. and tributaries only replace some of it. This reach of the channel 

has been actively scoured in response to the dam. The situation changes when the Yampa 

River joins the Green 68 miles downstream from the dam. The Yampa has no dams along 

its entire course and is essentially unregulated. It plays a pivotal role in the viability of the 

Green River below Flaming Gorge Dam. With its high spring flows, sediment load, and 

warm summer waters. the Yampa is a sanctuary for the pikeminnow, chubs, and razorback 

suckers that continue to spawn in its waters. 

The Yampa delivers most of the annual load of 3.2 million tons of sediment that the 

Green carries past Jensen, Utah since Flaming Gorge Dam was completed (Andrews, 

58 
1986). Throughout the 98 miles below Jensen. the 

Green's sediment budget is balanced- aggrading and 

degrading in approximately equal volumes since 

construction of the dam. Farther downstream, desert 

sidestreams contribute relatively high sediment-laden 

water to the Green. Now deprived of the large spring 

floods that once could move this sediment, the 

channel of the Green has aggraded and narrowed 

below Jensen, Utah. This aggradation has caused 

narrowing of the channel, infilling of secondary 

channels. and attachment of mid-channel bars to the 

river banks (Andrews, 1986). 

Three and a half million acre-feet of water flow 

down the Green River every year. And every year. 

withdrawals totalling 1.3 million acre-feet are allotted 

for agriculture, mining, power plants, and consumptive 

(jreen 2?jver 

use. In the late 1970s, the Central Utah Project began The Green River below Ouray, Utah 

to take an additional143 ,000 acre-feet from the 

Duchesne River through its Strawberry Aqueduct. But 

on February 27, 1980, the U.S. Fish and Wildlife Service invoked the Endangered Species 

Act. and issued a Biological Opinion in defense of the Green River's native fish population. 

The Service said that if more water was to be withdrawn at the Strawberry Aqueduct, then 

a reasonable and prudent alternative must be formulated to protect the fish elsewhere. 

The alternative all parties finally agreed upon was to modify the operation of Flaming 

Gorge Dam. No longer would dam releases be dictated solely by the timetables of irrigation. flood control, and peak-power demands. Instead. the dam would be operated in a 

manner that would protect the habitat and livelihood of the endangered chubs, suckers. 

and pikeminnow. 

Biologists suddenly wielded a new and 

unusual tool with which to protect native fish: 

a 502-foot-high dam. Interim flows were 

instituted at Flaming Gorge Dam in 1985. 

Studies offish carried out during the 1980s 

prompted refinements of the Biological 

Opinion. Dam releases are now seasonally 

adjusted to roughly mimic the river's pre-dam 

hydrograph. A steady 4,000 to 4,700 ft 3

/s is 

released for 1 to 4 weeks in May to match the 

peak of the Yampa's spring flood. Flows are 

gradually reduced after this peak, until summer 

flows of 1,100 to 1,800 ft 3

/s (measured below 

the confluence with the Yampa) are reached 

and then maintained throughout the summer. 

Small daily fluctuations are allowed during the 

summer, but are discouraged during wintertime. 

The Green River through Canyonlands National Park 

59 
Tstimating Sediment 'Budgets 

Assessing the sediment budget downstream from a dam is a technique 

usefutfor developing a management plan for a regulated river. Calculating a 

sediment budget is similar to balancing a check book: one attempts to account 

for all sediment entering, leaving, and stored in a reach of river. The budget can 

be formulated asS; + S t -So= 8S r' where So= the rate of sediment leaving the 

reach, S; =the rate of sediment entering the reach, St =the rate of tributary 

additions, and 8Sr =the rate of change in storage along the river's banks and 

bed. For most rivers downstream from dams, S :::::: 0 because the reservoir I 

traps most of the sediment that previously was transported downstream. So 

is measured at the gaging station at the downstream end of the reach and can 

be manipulated by changing the pattern of flow releases from the dam. 8S r' 

which also can be altered by flow releases, is measured using bed-monitoring 

techniques or remote sensing. St, which is delivered by small tributaries, can be 

measured or estimated. Tributary additions of sediment, which are affected by 

local geology, land use, and climate, are less easily altered to affect a regulated 

river. 

A sediment budget can help explain the consequences of historical dam 

releases and flow regulation. Because the Salt River is unregulated, and S; is 

much greater than zero, 8Sr is approximately zero over periods of decades. On 

rivers such as the Green below Flaming Gorge Dam, the Chattahoochee, and the 

Snake in Hells Canyon, where tributaries are small, St is much less than S0

• As a 

result, 8Sr is negative and the rivers are scouring their beds and banks. For the 

Rio Grande and the Platte, St is much larger than S0

, resulting in a large, positive 

8Srand aggradation of the channels. Tributary additions are a recognized 

problem along the Rio Grande, and sediment-retention structures span some 

tributaries in an attempt to reduceS t' The Colorado River in Grand Canyon is a 

mixture of both types: large tributaries supply some sediment forSt, and the 

pattern of flow releases from Glen Canyon Dam has reduced S0

• Because of this 

flexibility, releases from the 

dam can be modified to 

manipulate 8Srand redistribute sediment along the 

channel. In all cases, the 

sediment-budget approach 

is used to suggest the 

source of the problem and 

point to potential management solutions. 
{jreen !lljver 

The redistribution of Flaming Gorge Dam water releases revolved around the survival of 

endangered native fish. Spring peaks are meant to facilitate spawning and protect young fish 

in backwaters. These high flows scour the channel bed and expose gravel that is necessary 

for egg attachment. Gradually declining peak flows are thought to help prepare backwater 

nursery habitats as well as stimulate specific biologic responses in native fish. During summertime. water of a temperature desirable to native fishes is released by using the dam's 

multilevel intake structures that were initially designed to aid introduced trout. By minimizing winter fluctuating flows. fish may be protected from unnecessary jostlings of the ice pack 

beneath which they live. In short. dam releases throughout the year are used to promote 

native fish habitat as much as possible. 

The operation of Flaming Gorge Dam has been shaped by engineers and scientists who 

wished to provide the benefits of power as well as an intact downstream ecosystem. 

Scientists from the Bureau of Reclamation were able to correlate discharge with backwaterhabitat availability (Pucherelli and others. 1990). Fisheries scientists determined the life 

history. spawning cycle. and nursery habitats of native fish (Grabowski and Hiebert. 1989; 

Tyus and Karp. 1991; Valdez. 1993). USGS hydrologist Ned Andrews computed sediment 

budgets for successive segments of the river (Andrews. 1986) and. in cooperation with 

USGS hydrologist Jon Nelson. developed a model of how the Green River adjusts its shape 

to high discharges (Andrews and Nelson. 1989). Ongoing research by the Bureau of Reclamation. Fish and Wildlife Service. States of Colorado and Utah. and Utah State University's 

College of Natural Resources is refining the interactive relations among reservoir releases. 

channel morphology. aquatic habitat formation and availability. and survival of endangered 

fish. 

Time will tell if native fish can make a comeback on the Green River. Dam operations 

have been modified in ways thought to be beneficial to the habitat of native fish. But other 

factors. such as the presence of introduced species. also affect the fishes' chances for 

survival. The work done collaboratively by geologists. hydrologists. engineers. biologists. and 

economists on operations of Flaming Gorge Dam sets a precedent for a cooperative approach to minimizing the problems that exist below dams. Their methods and mathematical 

modeling can be applied to many rivers beyond the Green. 

+ 

61 

The Green River 

in Desolation 

Canyon, Utah 

Coforacfo 2?jve:r 

9vfu[tipfe Mandates, 9vfu[tipfe 'Use 
J?Lbout five mi{fion peopfe peer over tlie rims of (jrand Canyon 

every year. and if they find themselves at the right spot. they may even see the Colorado 

River. almost a mile below. Some visitors will amble down the canyon's trails in the morning 

and struggle back to the rim later in the day. A few will stay overnight or longer. collectively 

spending a total of 80,000 nights a year camping in the canyon. Another 22,000 people 

annually spend 6 to as many as 28 days each. rafting down the 

Colorado River. camping on its beaches. By any measure. Grand 

Canyon is one of the Nation's most popular national parks. 

The Colorado River downstream from 

Glen Canyon Dam in Grand Canyon, Arizona. 

Ironically. the river experience. although found within the deepest part of the canyon. 

is a trip through that part of the Grand Canyon environment most directly affected by 

human activity. That activity- the construction and daily operation of Glen Canyon Dam 

- is located 15 miles upstream from Lees Ferry. the launch point for all boating trips 

through Grand Canyon. 

The Colorado River is the very heart of Grand Canyon. John Wesley Powell was first to 

float through the canyon in 1869. Every few miles. a major rapid punctuates the river's 

otherwise quiet course. These legendary rapids have colored the vision that we have of 

ourselves in the Great Outdoors: tiny heroic figures clinging to wooden boats. tossed and 

tipped by 15 waves. But the rapids constitute only a small portion of the river's overall 

length. The Colorado River has a great deal more to offer than simple amusement-park 

potential. 

For the most part. the Colorado glides silent as a snake through the Canyon. Bits of 

river-litter - leaves and twigs. an occasional piece of tree root- dance along the squiggly 

line that separates the main current from an eddy flowing back upstream. Like once64 
Coforacfo 2Q,ver 

forgotten memories. vortices suddenly swirl to the surface without warning. created 

where the current encounters unseen obstructions that lie along the channel bed. Late in 

the day. sunstruck cliffs 3,000 feet above the river cast their glow on the water's quiet 

surface: golden ripples. liquid reflections. The river seems at peace with the walls that 

confine its course. 

Historically (i.e. , before 1963). an average of 12 million acre-feet of water rolled 

through Grand Canyon each year. The Colorado's flow followed a distinct seasonal 

pattern. The floods of May and june typically peaked at greater than 86,000 ft3

/s. When 

spring passed. the river dropped. Thunderstorms later in the summer would intermittently 

Surveyor on the Colorado 

River in the Grand Canyon 

The Colorado River at 

Lees Ferry, Arizona 

swell the river to perhaps 30,000 ft3/s. By winter the 

river was usually reduced to little more than a small 

clear stream; january mean flows were only 5,260 

ft3/s before the dam was built. 

A remarkable flood passed Lees Ferry on July 18. 

1884. Warren johnson was the ferryman; jerry 

johnson was his observant son. The flood was high 

enough to drive jerry's rabbit well up into an apple 

tree. Johnson's recollection of that rabbit 37 years 

later led E.C. LaRue to back-calculate the discharge 

of the 1884 flood at 300,000 ft3/s (Howard and 

Dolan. 1981). 1t is likely that even larger floods have 

come through Grand Canyon within the last couple 

millennia. Flood deposits are perched well above 

normal river stage just downstream from Lees Ferry; 

they offer tantalizing evidence of a flood larger than 

500,000 ft3/s within the last 1,600 years (O'Connor 

and others. 1994). 

In contrast to Flaming Gorge Dam. which is 

located upstream from the major sediment-producing tributaries of the Green River. Glen Canyon Dam 

65 
traps the vast quantity of sediment (66 million tons per year) that once flowed through 

Grand Canyon. The drainage area upstream from Lees Ferry is 111 ,800 mi2

. The water 

running off that area flows into Lake Powell from the high country of Wyoming, Colorado. 

and Utah. but the sediment has largely come from the desert country of southern Utah. 

southwest Colorado. and northwestern New Mexico. Desert tributaries in this region bear 

only 15 percent of the Colorado River's flow. but contribute 69 percent of its sediment. 

Thus. the release of clear water into a canyon that once carried extremely high 

sediment loads is a recipe for substantial environmental change. Grand Canyon's sediment balance would be even more skewed if it were not for two downstream tributaries. 

Before construction of Glen Canyon Dam. the small Pari a River entering the Colorado at 

Lees Ferry contributed only 0.16 percent of the river's volume but added almost 5 percent 

of the river's sediment load (lorns and others. 1965; Andrews. 1991). The Pari a still carries 

an average of about 3 million tons of sand. silt. and clay a year into the Colorado. The Little 

Colorado River. joining the Colorado 62 miles farther downstream. brings in three times 

more sediment. 

In Grand Canyon. the Colorado is a major 

desert river that once wielded two powerful 

tools to shape its environment: intermittent 

high flows and a tremendous supply of sediment. Great volumes of sand were stored along 

the main channel under conditions of lower 

flow. During floods. sand would be mobilized 

from the. bottom and draped along higher 

terraces not normally inundated. As a result. the 

river deposited beautiful sand beaches throughout the Canyon. Despite shrinkage since the 

completion of Glen Canyon Dam. these 

beaches remain an integral aspect of the 

Canyon -about one-third of a million people 

have used them for camping sites. In the predam landscape. these river deposits were also 

the substrate for the mesquite. catclaw. and 

hackberry trees that comprised the flood-level 

plant community and on which various smaller 

plants and animals relied. 

t Confluence of the Little Colorado River at 

the Colorado River in the Grand Canyon 

At 2:00 p.m. on March 13. 1963, the gates of Glen Canyon Dam swung shut. The 

Colorado River and Grand Canyon would never be the same. Glen Canyon Dam was to 

be the cornerstone of the Colorado River Storage Project. a series of six dams on the 

Colorado. Green. San Juan. and Gunnison Rivers (Martin. 1989). Coupled with Hoover 

Dam. 355 miles downstream. Glen Canyon would help provide flood control. irrigation. 

and municipal water supply for Arizona. California and Nevada. Lake Powell, a 26.7-

million-acre-foot reservoir created by the dam. would provide recreation for millions of 

people each year. Sediment retention within Lake Powell would prolong the life of Hoover 

Dam and its Lake Mead reservoir. The 1956 Federal legislation authorizing Glen Canyon 

66 
Coforado 'Rjver 

stipulated that electricity would be generated by the dam so as to most efficiently recoup 

construction costs not only for Glen Canyon but other projects within the Colorado River 

Storage Project. 

The most compelling early impetus for the dam's construction was the fact that each 

of the states through which the Colorado. San Juan. and Green Rivers flowed were anxious 

to reserve as much water as possible for their own use. The Colorado River Compact of 

300.000 

"0 250.000 c: 

0 

v 

Q) 

V) 

a; 200,000 c.. 

0:> 

.1: 

v 150,000 :.0 

:::l 

u 

.5 

~ 100.000 

"' .L: 

~ 

C5 50.000 

0 1920 

Annual flood series for the Colorado 

River near Grand Canyon, Arizona 

1930 1940 1950 1960 

Glen Canyon 

Dam closed 

1970 1980 1990 

1922 had divided the river among the upper (Wyoming·Colorado·Utah-New Mexico) and 

lower (Arizona-Nevada-California) basin states. Today. Glen Canyon Dam is operated as 

the main spigot separating these upper and lower basin states. Its mandate is to release 

8.23 million acre-feet a year and not a drop more unless Lake Powell is threatening to spill 

over (Ingram and others. 1991). 

The Colorado River Compact and five subsequent congressional acts are the basis for 

year-by-year management of water released by Glen Canyon Dam. Th.e U.S. Bureau of 

Reclamation adjusts the dam's releases on a month-to-month basis according to its 

projections of how much water is likely to flow into Lake Powell and how much room is left 

in the lake. The hour-by-hour release of each month's total is. in turn. controlled by the 

Western Area Power Administration (WAPA). a Federal power broker whose mandate is to 

sell power to utility companies at the best price WAPA can arrange. 

Embedded within Glen Canyon Dam are eight penstocks. each leading to a turbine. 

The Bureau of Reclamation was originally allowed to send up to 33,200 ft3/s through these 

eight penstocks for power generation. Operations are currently restricted by law to a 

release no greater than 25,000 ft3/s. resulting in a peak generation capacity of approximately 1,050 mW (U.S. Department of the Interior. 1995). When emergencies arise that 

require excess water to be released. anything above turbine capacity must be directed 

through bypass tubes and the spillways. and therefore does not generate electricity. From 

the perspective of power generation. that water is wasted. 

During the 18 years between dam closure and 1980 when Lake Powell was filling. the 

Bureau of Reclamation released an average of8.2 million acre-feet per year 

67 
Photographers in the Grand Canyon 

reproducing photographs taken by 

Stanton a century before 

~peat Pfwtography 

Robert Brewster Stanton was an unlikely visionary. He was an engineer 

who, in 1889, set out to establish a railroad route that followed the Colorado 

River, intending to deliver Colorado coal to California markets. In the course of 

two river trips. he made 445 high-quality, large-format photographs of the 

river and its banks through Grand Canyon. One hundred years later, Robert 

Webb of the U.S. Geological Survey followed Stanton's footsteps, precisely 

relocating the camera position of the original photographs. Webb has analyzed 

the matched photographs to document changes that occurred during the 

intervening century (Webb, 1996). In some cases, side canyon floods have 

carried tremendous quantities of new material down to the river's edge. At 

other places, even the most precariously balanced small pebbles are resting 

exactly as they did when Stanton came through. The photographs document 

the changing nature of the rapids on the Colorado. And they hold significant 

information about vegetation. Webb has found individuals of 41 plant species 

still growing exactly where Stanton photographed them in 1890. The photographs document changes in beaches that can be related to the construction 

of Glen Canyon Dam. Many beaches are deflated, but some have persisted in 

much the same condition as in 1890. The most severe erosion is closest to 

Glen Canyon Dam; the effects diminish with distance downstream (Schmidt 

and others, 1995). 
Steve Tharnstrom 

replicated this 

upstream view on 

February 22, 199 2, 

at 9:00 a.m. (Webb, 

1996). Because of 

considerable erosion, 

the sandbar could 

be used only with 

considerable 

difficulty by modern 

river runners. The 

sandbars near 

water level have 

steadily decreased in size, but the high 

sandbar on the far 

right side of the 

view aggraded as a 

result of the 1983 

ffood. 

In the winter of 1889-

90, Robert Brewster 

Stanton led the second 

successful expedition 

through Grand Canyon. 

On the morning of 

February 20, 1890, 

after camping on a 

small beach at mile 

115, Stanton 

photographed this view (number 542, National 

Archives, Washington, D.C.) at 8:00a.m. 

while the crew loaded 

the last of the 

equipment and 

supplies onto the 22-

foot wooden boats. 
Sockdolager Rapids on the Colorado River in the Grand Canyon 

Colorado River \ 

near Grand Canyon 

30.000 

" c: 

0 25.000 u 

Q) 

V> 

v 

0.. 20.000 

a:; 

~ 

u 

:.0 15.000 :::l 

u 

~ 

Q) 10.000 

eo 

.c "' 

u 

"' 5000 0 

0 5 

AZ 

" "'-

10 

through Glen Canyon Dam - the 

allocation earmarked for the lower basin 

states and Mexico. WAPA managed the 

hour·by·hour release of water by reduc· 

ing flow through the dam's penstocks at 

night and increasing flow during the day. 

It was not unusual to see daily fluctuations during early summer from 8,000 to 

as much as 28,000 ft3/s. Minimum flows 

during the weekends were even lower. 

Hydrograph for the Colorado River near Grand Canyon, Arizona. 

Instantaneous discharges for September 1982. Fluauating ffows 

such as these have been used to generate load-following power 

from the power plant at Glen Canyon Dam. 

15 20 25 

September 1982 

Lake Powell filled for the first time in June 1980. and the Bureau of Reclamation subsequently endeavored to keep the lake as full as possible (Carothers and Brown, 1991). High 

flows were released during winter and summer peak demands. and the reservoir was 

intentionally lowered during the winter to accommodate the anticipated inflow of May and 

June floods. The story of flow regulation at Glen Canyon Dam took a sudden and dramatic 

turn in 1983. By late June. Lake Powell was again full. and an unexpectedly large runoff 

roared into Lake Powell. The Bureau and WAPA were releasing maximum penstock flows 

through Glen Canyon, but the lake still rose at a rate of 6 inches a day. Plywood 

splash boards were placed along the top of the spillway gates to hold the water back. Finally. 

the inevitable happened: the reservoir could no longer hold the inflowing water and the 

dam's jet tubes and spillways had to be opened. On June 29. 1983. the Colorado River at 

Lees Ferry was flowing 97,300 ft3

/s for the first time since Glen Canyon Dam was completed. This unprecedented discharge was so powerful that cavitation plucked great blocks 

of concrete and sandstone from the spillway walls (Carothers and Brown. 1991). The dam's 

structural integrity was threatened but the only failures were inside the spillways. 

70 
Co[orado !lljver 

When it rains. it pours. 1984 was another record-breaking year for runoff in the 

Colorado River drainage. greater even than 1983. However. due to better planning. the 

spillways were not needed. The period 1983 to 1986 turned out to be the wettest consecutive 4-year period on record. During each of these years. Glen Canyon Dam released 

an average of 18.5 million acre-feet. far in excess of its target of 8.23 million acre-feet. 

Instantaneous discharges from Glen Canyon never again reached the high levels of June 

1983. but were commonly in the 45,000 to 50,000 ft3

/s range during the late spring and 

early summers. 

One certainly wonders what effect all this hydraulic energy had on Grand Canyon. 

River runners and scientists in the mid-1970s had noticed that some beaches were disappearing and that plant and animal life along the river was changing. The Glen Canyon 

Environmental Studies (CCES) program had been started in 1982 by the Bureau of 

Reclamation to investigate the dam's effects on downstream environmental and recreational resources (Wegner. 1991).1n 1989 the Secretary of the Interior announced that a 

Glen Canyon Dam Environmental Impact Statement (EIS) would be required for continued operation of the dam. Congress passed the Grand Canyon Protection Act in 1992. 

stipulating that Glen Canyon Dam is to be operated in a manner that protects resources 

within Grand Canyon and that long-term scientific studies be conducted to monitor the 

downstream effects of the dam. 

Guided by these multiple mandates. CCES joined forces with the National Park 

Service. U.S. Fish and Wildlife Service. U.S. Geological Survey. and the Arizona Came and 

Fish Department to study the Colorado River through Grand Canyon. Together. this 

alliance of agencies has investigated the regulated river's impact upon fish. birds. insects. 

and mammals including river runners (U.S. Department of the Interior. 1989). The alliance 

examined archaeologic sites that lay within the river's potential grasp (Hereford and 

others. 1993). studied all manner of plants along the riparian corridor (Stevens and Ayers. 

71 

1993). and surveyed 

many types of sediment 

within Grand Canyon 

(Webb and others. 1989; 

Schmidt and Craf. 1990; 

Beus and Avery. 1992). 1t 

is this final impact upon 

sediment that will 

receive a closer look 

here. 
Cost of Jia6itat Maintenance :Jfows 

Many variables contribute to the cost of a beach-building flow. A 

simplified accounting model can show how to estimate the cost of a 

habitat-maintenance flow. Assuming a full Lake Powell, 40.78 kW are 

generated for each cubic foot per second released by the dam under 

33,200 ft3/s; any water in excess of this discharge cannot be used to 

generate power. If 50,000 ft3/s was released for one week, 20.08 billion 

ft3 would have passed through the dam's turbines and 10.16 billion ft3 

would have bypassed the turbines. 

In 1994 dollars, power produced during peak demand (7 a.m.-11 p.m., 

Monday through Saturday) has a value of $0.05 per kilowatt-hour (kW-hr), 

and $0.0137/kW-hr during off-peak periods [Ron Moulton, Western Area 

Power Administration (WAPA), oral commun., 1993]. During a beach-building 

flow, WAPA would produce $7,834,000 worth of power. We now assume 

that the alternative is "typical" fluctuating flow; for our model, flow will 

either be 20,000 or 8 ,000 ft3/s for peak and off-peak hours respectively. 

WAPA would have produced $4,237,000 worth of power during this hypothetical week -and still have had 13.3 billion ft3 left in Lake Powell to be 

released later. If it was possible to release the entire 13.3 billion ft3 at peakdemand times, that water would produce power worth $7,503,000. 

During a beach-building flood, WAPA would have received $7,834,000. 

Alternatively, WAPA would have received $4,236,683 if the dam had been 

operated during that same week according to a typical fluctuating-flow 

regime. But water worth as much as $7,503,000 would still be stockpiled in 

Lake Powell. All together, the beach-building flow would have cost WAPA 

$3,905,196. But Glen Canyon Dam produces $140,000,000 in revenues 

per year. If a habitat-maintenance flow occurred once every 5 years, it would 

represent about one-half of 1 percent of the gross receipts from operations 

ofthedam. 

WAPA, GCES, and other interested parties have created more sophisticated models that integrate variables such as flow duration, water 

availability, pricing structure, and alternative generation costs for a beachbuilding flow. These more sophisticated estimates place the cost of a 

beach-building flood between $500,000 and $1,500,000 (David Wegner. 

GCES, oral commun., 1993). Such a price tag must be weighed against the 

flood's possible benefits to both the multimillion dollar rafting industry and 

the environmental quality of Grand Canyon National Park as mandated by 

the Grand Canyon Protection Act. 
Q) 

~ 0 -~ 

.J 

c: 

·c; 

~ 

~ ·10 ....J 

ro 

~ 

~ -20 Q) 

cc 

Palisades Creek in Grand Canyon 

Time series of changes in the bed elevation of the Colorado River 

at Lees Ferry, Arizona, 1921-1986 (modified from Burkham, 1986). 

Before construction of Glen Canyon Dam, the bed was occasionally 

scoured 20-30 feet during spring noods. After June 1965, in the 

absence of river-borne sediment, bed elevation fell and did not 

recover its previous elevation. Now releases from Glen Canyon 

Dam have little effect on the armored bed. 

1960 

Year 

Coforado !f<jver 

Water released by Glen 

Canyon Dam carries almost 

no sediment Any sediment 

along the Colorado River 

below the dam was either 

already present when the dam 

was built or has since been 

brought in by tributaries. 

Tributaries deliver sediment to 

the river in one of two basic 

patterns: slow. steady additions of silt and sand. or 

sporadic floods containing 

everything from huge boulders 

to fine silt Both processes are 

important to the evolution. 

homeostasis. and general wellbeing of Grand Canyon. 

Within Grand Canyon. the Paria and Little Colorado Rivers provide the lion's share of the 

total volume of sand brought to the mainstream river in the post-dam era. Debris flows are 

another important source of materials deposited in the Colorado River. A debris flow consists of 

cobbles and boulders within a matrix of sand and silt that has been transformed into a fluid with 

as little as 10 percent (but no more than 40 percent) water by volume. Hydrologists with the 

U.S. Geological Survey have examined debris flows that sweep down steep tributary canyons 

within Grand Canyon (Webb and others. 1989 ). These slurries usually start as rain-induced 

slope failures of clay-rich shales or talus. part way up the walls of Grand Canyon. The falling 

detritus hits the bottom of a tributary canyon. entraining cobbles and boulders en route. and then 

surges on down to the river with velocities estimated at 10 to 30 ft/s (Melis and others. 1994 ). 

73 
An unusually heavy rainstorm inundated the upper drainage of Crystal Creek in December 

1966. The resulting debris flow had a discharge of about 10,000 ft3 /s of water. mud. and 

boulders. The slurry surged well out into the Colorado River. severely constricting the river's 

channel against the opposite wall. Boulders deposited in the main channel instantly transformed 

Crystal from a benign riffle to one of the Canyon's most difficult rapids. Indeed. virtually all the 

rapids in Grand Canyon have been created by debris flows hurling a fan of boulders into the 

river. Such events recur at intervals of as little as one every 20 years to less than one per century 

for individual tributary canyons (Melis and others. 1994). 

Debris flows beget rapids because the boulders they transport are too large to be 

quickly removed by typical discharges of the Colorado River (Craf. 1980). The high river 

flows of 1983 did partially rework the Crystal Creek debris fan. moving boulders and 

changing some aspects of the 

rapid. USGS geologist Susan Kieffer 

estimated that a flood of 400,000 

ft 3 /s would be required to remove 

that debris fan (Kieffer. 1985). 

Certainly a 300,000 ft 3 /s flood. 

like the one that drove Jerry 

Johnson's rabbit up a tree in 1884. 

would significantly alter or even 

smooth out many of Grand 

Canyon's rapids. But smaller floods 

may also help maintain the river's 

Island at the mouth of the Little Colorado River channel; the deposits of a larger 

debris flow at Lava Falls Rapid were 

removed by a 120,000 ft3 /s flood 

in 1941 and dam releases augmented with small floods from the Little Colorado River 

have eroded several debris fans (Melis and others. 1994). A question relevant to today's 

flood-control policy at Glen Canyon Dam is how many debris flows will occur before the 

next large boulder-rolling flood sweeps down the mainstem Colorado River. 

Debris fans constrict the Colorado River. setting up the conditions that create sandbars. Water flow accelerates within the constriction created by the debris fan. Downstream from the fan. the river expands and decelerates. This variation of both channel 

shape and velocity spawns an eddy. with its water flowing upstream. opposite the direction of the main channel. Water within an eddy tends to have a velocity well below that of 

the rest of the river. As water (with whatever sand it happens to be carrying) moves from 

the main channel into the eddy. it decelerates and consequently drops some of its suspended sediment. Sand begins to fill the eddy. 

Schmidt and Craf (1990) built upon the work of Howard and Dolan (1981) to develop 

a descriptive model of sand that is deposited in eddies. They noticed that some sand is 

deposited just below the point where the river's main current separates from the channel 

walls. forming a separation bar. More sand is deposited downstream where the current 

reattaches to the channel walls. forming a reattachment bar. As sand is deposited or 

removed. and as the river level rises or falls. the two bars may shift slightly up or downstream. but they do not migrate out of the eddy in which they form. Schmidt and Craf also 

mentioned channel margin bars. which generally do not occur in association with eddies. 

but along the riverban ks where flow is slower than in mid-channel. 

74 
Co[orado ~ver 

Sand within the Colorado River is cached in one of four locations that can be compared 

to bank accounts: on the main channel bed. underwater within an eddy. perched above the 

present water line in the form of beaches. or in transport by the moving river water. We can 

measure beaches and measure suspended load. but at this point we can only guess the 

relative sizes of underwater eddy deposits and channel-bed deposits. Experience suggests 

that eddies can trap tremendous quantities of sand. People camping along the Colorado 

River are most likely to use beaches that formed as separation bars when the river flowed at 

greater than 30,000 ft3 Is. 

The river can rise and overtop a debris fan. and if this occurs. the flow is likely to erode 

rather than deposit a beach. Now sand is being shuffled from one account to the other at a 

furious pace. The Colorado River or any canyon river is always in a state of dynamic equilibrium. At a given discharge. it will be creating with one hand and destroying with the other. 

Change the discharge. change the suspended sediment. change the channel shape and the 

equilibrium will shift all along the river. 

Sandbars are draped around an eddy in a prediaable pattern in most bedrock-controlled rivers. The debris fan, which 

is formed from periodic debris flows from the tributary canyon, constricts the river. The expansion zone downstream 

allows flow separation in an eddy. Separation bars form on the downstream side of the debris fan, beginning at the 

point of flow separation. Reattachment bars form at the stagnation point on the downstream side of the eddy. 

Channel margin bars are deposits that form along the channel margin in the lee of boulders and other obstruaions 

(from Schmidt and Graf, 1990). 

Many Grand Canyon beaches are smaller now than they were before Glen Canyon 

Dam was built (Kearsley and others. 1994). River-runner suspicions and GCES studies 

have long focused on fluctuating flows as the prime culprit responsible for the disappearance of beach sand. GCES scientists have taken great pains to examine the rate at which 

daily fluctuations occur. studying the effects of the range of daily fluctuations as more and 

then less water is released from the dam for peak-power generation. The scientists have 

75 
The Colorado River in Grand Canyon 

also studied the possibility that when Glen Canyon Dam rapidly decreases its release of 

water (a fast "downramping" rate). beaches downstream would erode more quickly (Beus 

and Avery, 1992). 

Fluctuations in flow do cause erosion of beaches. and beaches will continue to disappear in Grand Canyon in the absence of sediment-laden flood flows. Gravity will eventually pull beach sand back underwater. and the river will carry the sand downstream. At 

best. some dam operation regimes might be more successful than others at minimizing 

beach erosion. But the moderate daily high flows associated with the generation of 

hydroelectric power at Glen Canyon Dam are not likely to rebuild the high beaches that 

once existed in the canyon. 

Should river runners despair? 

Perhaps not. Although scientists 

now understand that beach erosion 

is an inevitable process. and despite 

the fact that most sediment once 

carried by the Colorado River is 

now stored behind Glen Canyon 

Dam. there may still be sufficient 

sediment supplied by the tributaries 

to replenish Grand Canyon's 

beaches at the rate of once every 

few years. The secret to this 

replenishment lies primarily with 

the sand supplied by the Paria and 

Little Colorado Rivers. Imperial Dam north of Yuma, Arizona 

76 
Beach at Badger Rapid in Grand Canyon 

Coforado 2?jver 

As early as 1981. 

University of Virginia 

researchers Alan Howard 

and Robert Dolan estimated that the bed of the 

Colorado River was accumulating sediment despite 

the observed erosion of 

camping beaches. because 

the rate of sediment 

contribution from the Paria 

and Little Colorado exceeds the transport capacity of the flood-regulated 

Colorado. Under the 

auspices of the GCES. 

Wilson (1986) made a riverlength side scan sonar image of the river bottom and found that substantial parts of the 

channel bed were covered with sand. Randle and others (1993) estimated that more than 

25 million tons of sand accumulated along the river bed in the first 90 miles of Grand 

Canyon between 1965 and 1982. 

Beaches disappearing on the channel margins but sand accumulating on the channel 

bed. This is not a contradiction. Two processes were operating at the same time: beaches 

slumping into the river. and tributaries like the Paria simultaneously conveying new sediment to the river. Until1983. the sediment-carrying capacity of water released from Glen 

Canyon Dam was insufficient to mobilize sediment accumulating on the riverbed throughout Grand Canyon. Other than one brief burst of high water in 1965. the canyon had not 

experienced a truly big flood since dam closure. But during the highwater years between 

1983 and 1986. the floods came and the river's sediment account was shuffled in some 

places. squandered in others. Some sand was transferred to higher elevations in eddies. 

but most sand was stripped from the river bed and carried downstream. 

This loss of sediment occurred in two stages. When the first high releases of June 1983 

rolled through the canyon. the 97,300 ft3

/s discharge stirred up sand from the main 

channel bed. from eddies and from beaches that had normally been above high waterline. 

This frothy brown mixture rushed downstream and in places was redeposited as beach 

sediment that remained after that first flood abated. Brian and Thomas (1984) concluded 

that. on average. beaches in the first 180 miles of Grand Canyon suffered net erosion in 

1983. but beaches farther down gained sediment. Overall during this first stage. the canyon 

lost a lot of sediment. After the flood receded. however. a small but significant percentage 

of available sand remained perched where it had been deposited by the high waters of the 

flood. This sand formed new beaches or added to preexisting ones. 

The second stage of sediment loss began in 1984 when 45,000 ft3/s flows were 

released three summers in a row. With each release. the riverbed had significantly less 

sediment to mix into the water. With each release. more sediment was stripped from the 

canyon and less was returned to beaches after the flooding ceased. By 1986. the beaches 

of Grand Canyon were scoured. and the riverbed had little material with which to rebuild 

them. 

77 
Grand Canyon National Park,Arizona 

It's all too easy to second-guess 

the engineers at the Bureau of 

Reclamation. saying that they 

should have operated Glen Canyon 

Dam some other way. But the 

period between 1983 and 1986 

were anomalously wet years. The 

Bureau of Reclamation has since 

unofficially designated the uppermost one-half-million acre-feet of 

storage in Lake Powell as a buffer 

against floods. in an attempt to 

avoid the reservoir spills of the mid1980s. 

Smillie and others (1992) 

developed a sand budget that 

suggests that if daily fluctuating flow 

is kept between 5,000 and 20,000 

ft3/s. only 484,000 tons of sand will 

be transported out of the canyon in 

a given year. Contrast that figure 

with the 1.2 million-ton annual 

sand input of the Paria River alone. 

Thus. sand can be stored on the 

channel bed and. when a sufficient 

amount has accumulated. could be 

remobilized by intentional high 

floods to rebuild beaches farther 

downstream. The EIS for the 

operation of Glen Canyon Dam 

(U.S. Department of the Interior. 

1995) called for flows to be held between 5,000 and 25,000 ft3/s. Presumably. sediment 

will accumulate on the riverbed under those conditions. 

With increasing frequency. scientists have called for "beach-building flows" (Schmidt 

1992) or "habitat-maintenance flows" (U.S. Department of Interior. 1995). Beginning on 

March 26. 1996. Glen Canyon Dam spilled 45,000 ft3

/s for 8 days- the first intentional 

flood ever released for environmental purposes. The Grand Canyon crawled with scores 

of scientists. measuring the flood's effects on beaches and backwaters. photographing 

eddy patterns. and sampling sediment loads. When the flood receded. a great deal of clean 

new sand had been perched well above the normal high-water line. The long. beautiful 

beaches were reminiscent of the pre-dam Grand Canyon. 

The Bureau of Reclamation picked up the tab for the 1996 flood. estimated to be as 

much as $4.25 million dollars (Dave Saba. personal commun .. 1996). This covered the 

cost of lost revenues and scientists' salaries. Was it worth it? Time will tell. The beaches 

quickly began to readjust when the water dropped back to normal flows. Studies of the 

flood's biologic impacts will take months to complete. But a tremendous precedent had 

been set: never before had a flood been used as a management tool. 

78 
Coforado 2?jver 

The Grand Canyon experienced larger floods during the 1980s but those 

occurred in quick succession and in response to unusually large inflow into 

Lake Powell. Beach-building flows must be released only after adequate 

amounts of sand have built up on the river bed. Then high flows are most 

likely to be beneficial. Intentional floods might be timed to coincide with 

natural floods down the Paria and Little Colorado Rivers. which would carry a 

wider array of sediment sizes into eddies. Or the Bureau of Reclamation 

might be given the flexibility to time such releases to coincide with predicted 

high levels in Lake Powell. reducing the threat of an uncontrolled spill. 

Periodic beach-building flows are an exciting new tool in dam management because they are an outgrowth of scientific investigations into the 

downstream effects of dams. At this point. no hydrologist or geologist pretends to know the ideal parameters for such a flow: how big, how long. how 

often. What we do know is that a beach-building flow may benefit some 

resources within the canyon while simultaneously degrading others. Some 

beaches would be enlarged, others would shrink. What would the effects be 

on native fish. on archaeologic sites. or on riparian vegetation? How much 

revenue would be lost because of bypassed electrical generation? Could the 

benefits of such a flow be used to balance the environmental cost of fluctuating flows? Ultimately dam management must aspire to a balance between 

environmental benefits and societal costs. In Grand Canyon. much hangs in 

the balance: the environmental quality of one of the Nation's premier national 

parks on one side, and the power-generation capability of one of the West's 

largest hydroelectric power plants on the other. 

Rapid in Grand Canyon National Park, Arizona 

79 
2(ofe of Science 
2(_p[e of Science 

:Few [arge dams wi[[ ever again 6e 6ui[t in the 1lnitec£ States. 

It is certainly reasonable to expect that the downstream impacts of any future dam would 

be closely scrutinized before construction. The real task facing scientists (and society) is to 

examine the effects of dams already in place. Although some dams such as Glen Canyon 

have already received considerable attention for their downstream impacts. the effects of 

most dams have not been studied at all. 

This Circular has surveyed a few rivers to illustrate some of the adverse effects that 

dams can create downstream. The undammed upper Salt River determines its own 

capacity for transporting sediment. and continues to shape a unique environment that 

supports natural vegetation and native .birds and fish. In contrast to the Salt. dams on the 

Elephant Butte Dam near Truth or Consequences, New Mexico 

Sandbar on the Salt River 

81 
Snake River are operated for peak power production, and the river downstream has lost a 

significant amount of its sediment and may lose its native salmon population. The Rio 

Grande is little more than an inconvenient afterthought below Elephant Butte Dam; the 

limited flows below the dam are incapable of transporting sediment that now builds up in 

the channel. Buford Dam has significantly changed the character of the Chattahoochee 

River; the river's flow represents a compromise between the needs for hydropower and 

water delivery, and Atlanta's needs for recreation. The Platte River has steadily shrunk in 

flow and channel width over the past century and a half; persistence of the sandhill crane 

may require that the original variability and viabi lity of the system be restored. Natural 

Flaming Gorge Dam on the Green River in Utah 

82 

environments of the 

Green and Colorado 

Rivers developed in a 

closed system defined 

by seasonal variability; 

today dams control 

these rivers. and several 

native fish have become 

endangered or extinct 

as a result. 

The application of 

science to the study of 

downstream effects is 

new and growing. The 

questions that society is 

The Rio Grande ab< 

Mesilla Dam near L 

Cruces, New MexiCt 
2\pfe of Science 

now asking can be complex in some cases, simple in others. For some rivers where 

impacts have not been studied. it may be possible to efficiently address questions about 

downstream problems by applying information and insights gathered on similar rivers. In 

other cases. it may be necessary to undertake new research. Some questions may be 

sufficiently complex that answers will require sophisticated and costly new research and 

development of predictive tools. In other cases. we will be able to rely on already-existing 

data collected before and after construction of a dam. 

Dams have profound but varied impacts on the rivers that they harness. A pattern of 

seasonal high water is usually replaced by flow that resembles a daily tidal flood. Sediment 

typically is trapped in the reservoir 

above a dam. Downstream, sediment 

Dredging operation on 

the Chattahoochee River 

in Duluth, Georgia 

may either diminish or accumulate, 

depending on distance from the dam. 

input from tributaries. and the difference between pre-dam flows and dam 

releases. The channel downstream 

from a dam may narrow in some 

reaches or widen in others. Riparian 

plants may increase or decrease in 

response to flood control and the 

altered amount of flow. Water temperature, suspended sediment and flow 

patterns may change sufficiently that 

fish - particularly native fish - face an 

entirely different set of challenges to 

which they must adapt. 

All other things being equal, dams 

of different design and operation will 

produce dissimilar effects downstream. The hydrograph created by a 

Dike reinforcement on the Rio Grande at Redford, Texas 

83 
dam that produces load-following power will look totally different than one from a dam 

whose reservoir provides base-load power. Flood-control operations have different impacts than run-of-the-river releases. Dams operated for water-supply or irrigation purposes 

have different effects than hydropower dams. 

We cannot responsibly expect dams of one design to be operated according to the 

demands of quite another design. For example. the small reservoirs and high flows associated with the Hells Canyon Complex dams do not allow these dams to be efficiently 

operated as primary storage facilities or for flood control. Retrofitting is always a possibility. 

but the cost of structural changes can be astronomical. 

Scientists are increasingly being called upon to suggest dam operation regimes that will 

minimize a particular negative impact to the downstream environment Geoscientists have a 

large role to play because many ofthe adverse impacts relate to changes in sediment transport 

The Colorado River below Westwater Canyon, Utah 

84 

and physical aspects of the 

river's channel. Scientific 

insights gained from 

geomorphic research may 

be useful. but these 

suggestions must be 

integrated with recommenWash near Ganado, Arizona 
dations from the fields of biology. economics. and engineering. Any scientific 

recommendation that alters a dam's 

operation must be evaluated in the 

contextofthe people whose lives will be 

most directly affected - people whose 

interests may be as disparate as the river 

runner who wants steady in stream flow, 

and the farmer trying to irrigate his crops 

with low-salinity water. 

t 

Floods are a key element in the 

future management of dams. Without 

periodic high flows. some channels 

downstream from dams will aggrade 

with sediment or narrow with overgrown vegetation. Two or three floodfree decades may have been traded for 

more devastating floods in the future. 

As exemplified by the Hells Canyon 

Complex. not all dams are designed to 

prevent floods. The unpredicted 1983 

high releases in Grand Canyon show 

!l?JJ{e of Science 

The North Platte River below Keystone 

Dam near North Platte, Nebraska 

that a fickle climate can defeat the best efforts at flood control. Dredging, channelization. 

and mowing riparian vegetation are temporary measures that can forestall problems 

caused by reduced floods; but in some cases, like the Rio Grande below Elephant Butte 

Dam, our interventions have not always been timely or effective. 

Smokey the Bear has fallen out of favor in the last few years. Decades of fire suppression have radically changed the makeup of American forests, and now scientists and the 

public are questioning the wisdom of long-term fire suppression. Analogously, we are just 

beginning to realize that flood suppression has created situations along some rivers that 

may be responsible for future problems or disasters. For most rivers. floods are an integral 

element of their natural equilibrium, necessary for maintaining channels, and replenishing 

bankside sediment and nutrients. 

The benefits of dams are tightly woven into our daily lives. Despite the problems that 

they can create. most dams will not, and should not, simply be dismantled. Part of learning 

to live with them is to realize the extent of adverse effects, and to appreciate that those 

effects can be manipulated to some degree. Any number of tinkerings in dam operations 

can be proposed to minimize downstream changes - low fluctuating releases. seasonally 

adjusted flows, periodic high floods. sediment augmentation, multilevel intake structures. 

But the fact is, with a dam in place, we forever forego an entirely natural environment 

below the dam. As we try to maximize one quality within a downstream riparian system, 

we will inevitably alter and possibly degrade other qualities. There can be only one river 

and one flow regime below a dam. To pretend otherwise, to promise more than can be 

delivered. is naive at best, irresponsible at worst. 

85 
Any regulated river can respond to its dam with a dizzying array of changes. Future 

management of dams and rivers must take this dynamic nature into account. Adaptive 

management attempts to track these changes through time. As dam operations are 

modified, the resultant downstream effects are tracked and integrated back into the 

dam's management plan. With this approach, the very uncertainty ofriver response is 

used as an advantage in the development of monitoring programs and dam management 

alternatives. 

Scientists have already spent a great deal of time and money studying rivers below 

dams. $90 million alone at Grand Canyon since 1982. Have we accomplished anything? 

Was the money well spent? Not surprisingly. most work on the downstream effects of 

dams has been retrospective: scientists examining changes after they happen. The 

knowledge gained from this sort of science is valuable. but payoffs are typically discussed 

in the future tense. Times are changing. Flaming Gorge Dam is being run according to the 

Fish and Wildlife Service's Biological Opinion. and Glen Canyon Dam operations have 

been altered by the scientific findings of the Glen Canyon Environmental Studies program. The world's first intentional flood roared through Grand Canyon in 1996. Scientists 

must soon assume the uncomfortable responsibility of looking back over their shoulders 

to see if the changes they induced actually saved an endangered species. reconstructed a 

beach. or improved a habitat. 

We should not confuse the roles of scientists with those of engineers or politicians. 

Nevertheless. no one works in a vacuum. Our ideas and observations will be put to test, 

not just in the rarified atmosphere of academic science. but integrated into the very real 

world that runs according to cost per kilowatt-hour. water rights. and mandated protection 

of the natural environment. Scientists dealing with the downstream effects of dams - at 

levels ranging from basic research to applied engineering- must formulate questions 

whose answers can ultimately make a difference. To strive for anything less is to be just 

another bureaucrat. 

Luna Leopold. one ofthe Nation's leaders of water research and resource issues. 

concluded a symposium on Colorado River ecology and dam management by stating: 

The interpretation of scientific understanding. however limited or conditional. must 

be translated by the scientists into concrete recommendations designed for the 

manager. We must make small changes initially. But it should be understood very 

clearly by the people who are supporting the investigation that more changes will be 

needed. The need for long-term measurement is the unassailable conclusion of the 

studies made to date. The data-collection program should be designed with great 

care. it should consider a wide variety of data needs. and each part should be installed and operated as soon as practicable even though not all parts ... begin at one 

time (Leopold. 1990). 

Leopold's comments go beyond issues restricted to the Colorado River in Grand 

Canyon. As we have seen, scientists have already addressed various aspects of the 

downstream effects of dams on many rivers. The U.S. Geological Survey has a long 

history of monitoring and research concerning the Nation's streams. Scientists within the 

Geological Survey and other Federal agencies are building upon long-term datasets of 

gaging trends to develop sophisticated explanations of the movement of water and 

sediment below dams. 

Rivers and riparian habitats are critical elements of our environment. As a society. we 

have gradually refined our vision of how we would like our rivers to look. We have tried to 

86 
2\pfe of Science 

achieve a balance between extractable resources and environmental values. We need a 

concerted effort to understand the changes that dams can cause and learn to predict the 

changes that are most likely to occur. Some useful management tools have been proposed: 

intermittent high releases from dams may have beneficial downstream effects. Science can 

offer options for better dam management; it's up to society to choose. 

87 
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94