Title: Colorado Surface-Water Resources
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Title: Colorado Surface-Water Resources
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Abstract: Colorado Surface-Water Resources National Water Summary 1985
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National Water Summary Colorado


COLORADO

Surface-Water Resources


Surface water is sustained largely by snowmelt in the mountainous
western two-thirds of Colorado, and consequently, is not distributed
uniformly really or temporally. In the mountainous western part of the
State where surface water is abundant, ground water is scarce; in the eastern
part of the State where surface water is scarce, ground water is abundant.
Ephemeral streams typify streamflow in most of the eastern one-third of
Colorado-the exceptions generally are streams that head in the mountainous
central part of the State and flow through the eastern part. About 2,210
ft3/s (cubic feet per second) or 1,430 Mgal/d (million gallons per day) of
streamflow enters Colorado from Nebraska, New Mexico, Oklahoma, Utah,
and Wyoming, and about 18,000 ft3/s or 11,600 Mgal/d leaves the State
as streamflow to Kansas, Nebraska, New Mexico, Oklahoma, Utah, and
Wyoming. In 1980, 84 percent of Colorado's population was served by sur-
face water (table I). Total surface-water withdrawals in Colorado in 1980
were 13,000 Mgal/d or 20,100 ft3/s; the largest withdrawals were for ir-
rigation. 11,000 Mgal/d or 17,000 ft'/s. The water quality of 94 percent
of Colorado's stream miles that have been fully assessed supports their
classified uses (Colorado Department of Health, 1984). Waters that have
not been assessed are little affected by human activities and are believed
to have equal or better quality than those that have been assessed.

GENERAL SETTING
Colorado is located in five physiographic provinces (fig. 1).
The Great Plains province in eastern Colorado is characterized by
dissected plains, high plains, rolling hills, and sandhills. Average
annual precipitation in this province ranges from about 12 to 16
inches. The Southern Rocky Mountains province, located to the
west of the Great Plains province, is characterized by steep-sided
valleys that drain very high mountain ranges with scattered high-
elevation mountain parks (broad meadows). Average annual
precipitation ranges from about 7 to 60 inches; maximum precipita-
tion occurs in the mountains in local areas too small to delineate
in figure 1. The Colorado Plateaus province is located along the
western one-fourth of the State (except in the north) and is
characterized by sharply incised valleys that contain numerous
ephemeral streams which drain the lower mountain ranges. Average
annual precipitation ranges from about 8 inches in the lower valleys
1i' 40 inches locally along the mountain crests. The Wyoming Basin
province, located in northwestern Colorado, is characterized by
steep-sided valleys that drain mountain ranges along its eastern and
southern boundaries and by numerous slightly incised ephemeral
streams that originate in dissected plains. Average annual precipita-
tion ranges from about 12 to 40 inches locally (fig. 1). The Middle
Rocky Mountains province in extreme northwestern Colorado has
characteristics of both the Southern Rocky Mountains and the
Wyoming Basin provinces. Average annual precipitation ranges
fro about 12 to 20 inches locally.
Extreme variations in monthly precipitation across the State
result from regional climatic variations and from the orographic
effects of mountains. Monthly precipitation is relatively uniform
i western Colorado but can be extremely variable locally. In con-
trast, monthly precipitation in eastern Colorado is highly variable
but is distributed relatively uniformly really.
Evaporation from water surfaces ranges from less than 35
in./yr (inches per year) to about 65 in./yr (Farnsworth and others,
1982) Less evaporation occurs along the higher mountain ranges,
anti 1ir,1- occurs in the valleys and along the eastern one-third of


Table 1. Surface-water facts for Colorado
[Data may not add to totals because of independent rounding. Mgal/d = million
gallons per day, gal/d = gallons per day. Source: Solley, Chase, and Mann,
1983]

POPULATION SERVED BY SURFACE WATER, 1980
Num ber (thousands) ............................................................ 2,440
Percentage of total population................................ ............. 84
From public water-supply systems:
Num ber (thousands)......................... .......................... 2,220
Percentage of total population............... ......................... 77
From rural self-supplied systems:
Num ber (thousands)....... ... .................. ........................... 220
Percentage of total population .............................. ........... 8

OFFSTREAM USE, 1980
FRESHWATER WITHDRAWALS
Surface water and ground water, total (Mgal/d)...................... 16,000
Surface water only (M gal/d)..................... ......................... 13,000
Percentage of total .. ........... .............. .............. 81
Percentage of total excluding withdrawals for
thermoelectric power....................... ......... ........... 81
Category of Use
Public-supply withdrawals:
Surface water (M gal/d).................................................... 540
Percentage of total surface water................. ..................... 4
Percentage of total public supply............................... ....... 92
Per capital (gal/d)................... ..... ... ... ... ..... ..... 243
Rural-supply withdrawals:
Domestic
Surface water (Mgal/d)..................... ...... .......... 62
Percentage of total surface water.................................. 0.5
Percentage of total rural domestic.............................. 63
Per capital (gal/d)................................ ....... ........... 281
Livestock:
Surface w after (M gal/d .................................................... 86
Percentage of total surface water....................................... 0.7
Percentage of total livestock................. .............. ......... 78
Industrial self-supplied withdrawals:
Surface water (Mgal/d) ............................... 890
Percentage of total surface water....................................... 7
Percentage of total industrial self-supplied:
Including withdrawals for thermoelectric power................... 98
Excluding withdrawals for thermoelectric power................... 99
Irrigation withdrawals:
Surface water (Mgal/d)...................................................... 11,000
Percentage of total surface water.................................. 85
Percentage of total irrigation.......................... ............ 79

INSTREAM USE, 1980
Hydroelectric power (Mgal/d)................................... ............ 5,500



the State. The highest rates of evaporation occur in the extreme
southeastern corner of the State.
Runoff in Colorado, like precipitation, is extremely variable
seasonally, annually, and really. Average annual runoff ranges
from 0.1 inch or less over much of the eastern quarter of the State
to 40 inches at the headwaters of the Conejos River (maximum not
shown in fig. 1). A large percentage of runoff from the western
mountains is a result of snowmelt in the spring and early summer;
most runoff from eastern Colorado is from rainfall in spring and
summer.


PRINCIPAL RIVER BASINS
Colorado occupies parts of four major regions (Seaber
and others, 1984). These regions, and the principal river in each
region, are the Missouri Region (the North and the South Platte
Rivers); the Arkansas-White-Red Region (the Arkansas River);
the Rio Grande Region (the Rio Grande); and the Upper Colorado


F


167 ,







168 National Water Summary Surface-Water Resources

Region (the Colorado River main stem, the Green River, the Gun-
nison River, and the San Juan River). These river basins are de-
scribed below; their locations, and long-term variations in
streamflow at representative gaging stations, are shown in figure
2. Selected streamflow characteristics and other pertinent informa-
tion are given in table 2.

MISSOURI REGION
North and South Platte Subregions
These subregions are the drainage basins of the North and
the South Platte Rivers. The North Platte River basin occupies about
2 percent of the State's 104,247-mi2 (square mile) area, and the
South Platte River basin occupies about 18 percent. The North Platte
River originates in the north-central mountains; it drains a high
mountain park and flows about 45 miles north into Wyoming. There
are no significant concerns about surface-water quality in the North
Platte River basin. Principal use of surface water is for irrigation
of hay meadows.
The South Platte River originates in the center of the State
and flows generally northeastward about 270 miles into Nebraska.
Water quality in this basin is suitable for most uses, except along
the South Platte River (and the lower reaches of tributaries) from
a few miles above Denver to a few miles below the mouth of the
Cache la Poudre River, where the classified uses are impaired by
fecal coliform bacteria, un-ionized ammonia (toxic to aquatic life),
and metals (Colorado Department of Health, 1984). The classified
uses along the upper reaches of Clear Creek are impaired by con-
centrations of trace metals. Principal use of water is for irrigation
of croplands and for municipal supply. About 65 percent of the
population of Colorado is concentrated in a 30-mile-wide area along
the South Platte River from the point where it enters the plains (18
miles southeast of Denver) to a point about 80 miles northward along
the eastern foothills (62 miles north of Denver). About 341 Mgal/d
or 528 ft'/s of water is imported annually from the Colorado River
basin (Harold Petsch, U.S. Geological Survey, written commun.,
1985), about 10 Mgal/d or 15.4 ft'/s from the Arkansas River basin,
and about 19 Mgal/d or 29.4 ft3/s from the North Platte River basin,
to supplement irrigation and municipal supplies. Because of water
imports, an increasing streamflow trend is indicated by the curve
of average discharge by water year in figure 2 for the South Platte
River (site 3). About 77 percent of the imported water also is used
to produce hydroelectric power. The South Platte River and its
tributaries in the Great Plains province are a major cause of severe
spring and summer flooding from thunderstorm activity in that part
of the drainage basin. Three large flood-control structures in the
drainage basin provide flood protection to much of the Denver
metropolitan area: Chatfield Lake (completed in 1975 with 235,000
acre-ft (acre-feet) or 76,600 Mgal (million gallons) of storage capa-
city) on the South Platte River; Cherry Creek Lake (completed in
1950 with 92,800 acre- ft or 30,200 Mgal of storage capacity) on
Cherry Creek; and Bear Creek Lake (completed in 1979 with 58,400
acre-ft or 19,000 Mgal of storage capacity) on Bear Creek. Recrea-
tional development has occurred at almost all storage and flood-
control reservoirs in the basin.
Surface-water issues in the South Platte River basin relate
to use of water rights granted in the South Platte River Compact
of 1926; effects of increased urbanization and industrialization on
water quality; effects of former mining and processing of metal ores,
radium, and coal on water quality; effects of hazardous waste sites
Son ground-water quality (and probable resultant effects on surface-
water quality); catastrophic flash floods on streams flowing through


steep canyons in the eastern foothills; and flooding from
thunderstorms in the eastern plains.

ARKANSAS-WHITE-RED REGION
Upper Arkansas Subregion
The Arkansas River drains about 27 percent of the State's
area. The Arkansas River originates in the central part of the State:
it flows to the south for about 75 miles, then flows gene. *,
eastward for about 160 miles into Kansas. Water quality is suitable
for most uses, except for short reaches of the Arkansas River at
the headwaters and below Fourmile Creek, where the classified uses
are impaired by concentrations of trace metals; in short reaches
near the center of Fountain Creek and the Huerfano River, where
fecal coliform bacteria and metals impair classified uses; and along
the Arkansas River from Pueblo to the Colorado-Kansas State line,
where elevated fecal-coliform-bacteria counts have been found
(Colorado Department of Health, 1984). Principal water use is '
irrigation of croplands. About 114 Mgal/d or 176 ft'/s of wat,:i
is imported annually from the Colorado River Basin to supplement
irrigation and municipal supplies. About 10 Mgal/d or 15 ft3/s of
the imported water is exported to the South Platte River basin for
municipal use, and about 64 Mgal/d or 99 ft3/s of the imported water
is used to generate hydroelectric power. The Arkansas River and
its tributaries in the Great Plains physiographic province are a ma-
jor cause of severe spring and summer flooding from thunderstorm
activity in that part of the basin. The unusually high periodic average
discharge by water year shown in figure 2 for the Arkansas Rivc;
(site 6) are the result of these severe thunderstorms. The basin con-
tains three major flood-control structures: John Martin Reservoir
(completed in 1943 with 616,000 acre-ft or 201,000 Mgal of storage
capacity) on the Arkansas River, Pueblo Reservoir (completed in
1974 with 358,000 acre-ft or 117,000 Mgal of storage capacity)
on the Arkansas River, and Trinidad Lake (completed in 1977 with
92,000 acre-ft or 30,000 Mgal of storage capacity) on the Purgatoire
River. These reservoirs also are storage reservoirs for irrigation
supply. Most storage-and flood-control structures in the basin arc
used for recreation.
Surface-water issues in the Arkansas River basin relate to
whether Kansas is receiving the authorized amount of water under
the Arkansas River Compact of 1948; the effects of increased ur-
banization and industrialization on water quality; the effects of
mining and processing (former and current) of metal ores, uranium,
and coal on surface-water and ground-water quality; and flooding
from thunderstorms in the Great Plains province.

Rio GRANDE REGION
Rio Grande Headwaters Subregion
The Rio Grande drains about 7 percent of the State's area.
The Rio Grande originates in the southern Colorado mountains and
flows about 130 miles to the east and south into New Mexico. The
State's smallest average annual precipitation (7 inches) occurs near
the center of the Rio Grande drainage basin. Water quality is suitable
for most uses, except for short reaches along the Rio Grande near
the headwaters; in a short reach of the Conejos River near its mouth.
where concentrations of trace metals impair the classified use; and
in a short reach of the Rio Grande below Alamosa, where fecal-
coliform bacteria are present (Colorado Department of Health,
1984). Principal uses of water are for irrigation of hay meadows
and other croplands. About 3.2 Mgal/d or 5 ft3/s is imported an-
nually from the Colorado River Basin to supplement irrigation sup-
plies. Most reservoirs in the basin were built to provide storage













National Water Summary Colorado


%r GREAT PLAINS








PHYSIOGRAPHIC DIVISIONS

CLIMAX DENVER


2







', MoJJA5 ONDJFMONTA.
MONTH


MONTH

AVERAGE MONTHLY
PRECIPITATION


ANIMALS RIVER
AT DURANGO









ON0 J FMAM J J A S


PRECIPITATION

EXPLANATION

-30- Line of equal average annual precipitation
Interval, in inches, is variable

Line of equal average annual runoff
Interval, in inches, is variable

S National Weather Service precipitation
gage-Monthly data shown in bar
graphs

A USGS stream-gaging station-Monthly
data shown in bar graphs


EXPLANATION

Average annual discharge
In cubic feet per
second




RELATIVE DISCHARGE


ND MAM J JAS ONDJFM A J JAS
MONTH MONTH


SCALE 1:6,000,000
R0 50 100 MILES


AVERAGE MONTHLY DISCHARGE 0 II KIL
0 50 100 KILOMETERS
Figure 1. Average annual precipitation and runoff in Colorado and average monthly data for selected sites, 1951-80.
(Sources: Preciptation annual data from Colorado State University, 1984; monthly data from National Oceanic and Atmospheric Administration, 1982. Runoff-
annual data from Gebert, Graczyk, and Krug, 1985 Discharge-monthly-and relative-discharge data from U.S. Geological Survey files Physiographic diagram
from Rais? 19M, divisions from Fenneman, 1946.)


3000


uO
V)
700
0
ti-





7500


U0


uo


i- 1O
C3








170 National Water Summary Surface-Water Resources


Table 2. Selected streamflow characteristics of principal river basins in Colorado
[Gaging station: Period of analysis is for the water years used to compute average discharge and may differ from that used to compute other streamflow characteristics.
Streamflow characteristics: The 7-day, 10-year low flow is a discharge statistic; the lowest mean discharge during 7 consecutive days of a year will be equal
to or less than this value, on the average, once every 10 years. The average discharge is the arithmetic average of annual average discharges during the period
of analysis. The 100-year flood is that flow that has a 1-percent chance of being equaled or exceeded in a given year. Abbreviations: Do. = ditto; mi'= square
miles; ft'/s=cubic feet per second; .. =insufficient data or not applicable. Sources: Reports of the U.S. Geological Surveyl

Site Gaging station Streamflow characteristics
no. 7-day,
see Orainage Period 10-year Average 100-year egree
fi Name and area of low flow discharge flood of
USGS no. Imip analysis Ift'/sl ft'Isl Ift'/s regulation Remarks

MISSOURI REGION
NORTH AND SOUTH PLATE SUBREGIONS

1. North Plane River 1,431 1915-84 35 440 7,870 Negligible Irrigation development (hay
near Northgate meadows) upstream.
1066200001.
2. South Platte River 880 1933-84 3.3 79.1 2,410 Moderate Irrigation development Ihay
above Elevenmile meadows and storage
Canyon Reservoir, upstream.
near Hansel
1066950001.
3. South Platte River 9,598 1901-84 51 834 40,400 Appreciable Affected by upstream
near Kersey regulation, irrigation
1067540001. diversion, bypass diversion,
and imported water.The
7-day. 10-year low flow and
100-year flood analyses
include effects of
regulation in diversion
period.
4. South Platte River 23.138 1902-84 7.6 524 62,300 do Affected by upstream
at Julesburg regulation, irrigation
1067640001. diversion, bypass diversion,
and imported water. The
7-day, 10-year low flow and
100-year flood analyses
include effects of
regulation in diversion
period.

ARKANSAS-WHITE-RED REGION
UPPER ARKANSAS SUBREGION

5. Arkansas River at 3,117 1888-1981 129 715 14,300 Moderate Affected by upstream
Canon City regulation and imported
1070960001. water.
6. Arkansas River at 12.210 1912-73 4.8 244 96,300 Appreciable Affected by upstream
La Junta 1974-84 3.8 233 19.300 do .regulation, irrigation
(071230001. diversion, bypass diversion,
and imported water Flow
further affected by Pueblo
Reservoir 70 miles upstream,
since January 1974. The
7 day, 10 year low flow and
100-year flood analyses
include effects of
regulation in diversion
period.
7. Purgatoire River 795 1895-1976 2.7 83.3 34,400 Negligible Virtually natural flow prior to
at Trinidad 1977-81 . 64.3 . Appreciable regulation by Trinidad Lake,
107124500. (August 19177.
8. Purgatoire River 3,503 1922-31, 0.34 116 94.000 Moderate Irrigation development upstream.
near Las Animas 1948-76 For 1922-31, 1948-16. the
1071285001. 1977-84 . 81.0 . .. do -day, 10 year low flow and
100-year flood analyses in
dude effects of regulation
in diversion period.
9. Arkansas River at 19,780 1913-42 1.1 301 131,000 Appreciable Sizable irrigation development
Lamar 1071330001. 1948-84 0.63 93.6 35.500 do upstream. For 1913-42, the
7 day, 10 year low flow and
100-year flood analyses include
effects of regulation in diver-
sion period. For 1948-84,
analysis based on period
since regulation began

RIO GRANDE REGION
Rio GRANDE HEADWATERs SUBREGION

10. Rio Grande near Del 1.320 1889-1984 107 901 13,400 Moderate Affected by irrigation storage
None 1082200001. reservoirs upstream
11. Rio Grande near 7,700 1899-1984 7.1 575 19,900 Appreciable Affected by irrigation
Lobatos diversion and storage
1082515001. upstream. Drainage area
includes 2,940 mi' in
closed basin in Colorado





-U I


National Water Summary Colorado


Table 2. Selected streamflow characteristics of principal river basins in Colorado-Continued
(Gaging station: Period of analysis is for the water years used to compute average discharge and may differ from that used to compute other streamflow characteristics.
Streamflow characteristics- The 7-day, 10-year low flow is a discharge statistic; the lowest mean discharge during 7 consecutive days of a year will be equal
to or less than this value, on the average, once every 10 years. The average discharge is the arithmetic average of annual average discharges during the period
of analysis. The 100-year flood is that flow that has a 1-percent chance of being equaled or exceeded in a given year. Abbreviations: Do. ditto, mi'= square
miles; ft3/s=cubic feet per second; . =insufficient data or not applicable. Sources: Reports of the U.S. Geological Survey]

Site Gaging station Streemflow characteristics
no. 7-day.
(see Drainage Period 10-year Average 100-year Degree
fig. Name and area of low flow discharge flood of
USGS no Imi'l analysis ltt'lsl Ift'lsl IhftlI regulation Remarks

UPPER COLORADO REGION
COLORADO HEADWATERS SUBREGION

12. Colorado Rier near 4,394 1940-84 536 2.136 23,800 Appreciable Affected by storage reservoirs.
near Doisero exports of water, and hydro.
1090705001 power generation.
13. Colorado Rier 8.050 1933-84 997 3.900 41,900 do Affected by storage reservoirs,
near Cameo sports of water and hydro-
1090955001 power generation.
GUNNISON SUBREGION
14. Gunnison River 1,012 1910-28 148 888 11.500 Negligible Virtualy natural flow prior to
near Gunnron 1944-84 115 709 9,000 Moderate regulation by Taylor Park
1091145001 Reservoir 119371. For
1944-84. the 7-day. 10-year
low flow and 100-year flood
analyses based on period
since regulation began
15. Gunnison River near 7,928 1896-1965 265 2,611 38,100 Negligible Virtually natural flow prior to
Grand Junction 1968-84 495 2,659 30.500 Moderate 1966. For 1968-84. the
1091525001. 7-day. 10-year low flow and
100- year flood analyses
based on period since
regulation began
WHITE-YAMPA SUBREGION
16. Yampa Rier near 3,410 1916-84 39 1,573 19,900 Negligible Virtually natural flow.
P Maybell
1092510001
17. White River near 755 1901-84 179 626 6,570 .. .do Do.
Meeker
1093045001.
SAN JUAN SUBREGION
18. Animas River at 692 1912-84 128 819 15,500 Negligible Virtually natural flow.
Durango
1093615001.


for irrigation but now also are used for recreation. The decreasing
trend in average discharge by water year streamflow shown in figure
2 for the Rio Grande (site 11) is probably caused by withdrawals
of water for irrigation.
Deficiencies in delivery of water to New Mexico under
the Rio Grande Compact of 1938, and ways to ameliorate these
deficiencies, are the major surface-water issues in the basin.

UPPER COLORADO REGION
The Upper Colorado Region encompasses 37 percent of
the State's area. About 448 Mgal/d or 693 ftl/s of water is exported
annually to the Arkansas, the Platte, and the Rio Grande basins
to the east, and about 95 Mgal/d or 147 ftl/s of water is exported
annually to the Rio Grande basin in New Mexico. Severe flooding
is rare. Even during the 1984 runoff season (April through July),
which was much higher than normal (U.S. Geological Survey,
1985b), peak flows caused only minor flooding in Colorado. Most
reservoirs in the basin were built to provide storage for irrigation,
but they also provide recreation and flood control. Surface-water
issues common to all of the Upper Colorado Region in Colorado
are the use of water rights granted in the Colorado River Compact
of 1922 and in the Upper Colorado River Basin Compact of 1948,


the control of salinity in the Colorado River Basin (U.S. Geological
Survey, 1984), and the transfer of water to the eastern side of the
Continental Divide.

Colorado Headwaters Subregion
The Colorado River originates in the central mountains of
the State and flows about 230 miles westward into Utah. Water
quality in this subregion is suitable for most uses except for short
reaches of tributaries in the Blue and the Roaring Fork River basins,
in a short reach of the Colorado River above the Colorado-Utah
State line, and along the Eagle River (except at its headwaters) where
classified uses are impaired by concentrations of trace metals (Colo-
rado Department of Health, 1984). Principal uses of water are for
irrigation of hay meadows, croplands, and orchards. Surface-water
issues are the same as those discussed for the Upper Colorado
Region above, as well as potential hydrologic effects of oil-shale
development.

Gunnison Subregion
The Gunnison Subregion encompasses about 8 percent of the
State's area. The Gunnison River originates in the south-central
mountains of Colorado; it flows generally westward for about 170








172 National Water Summary Surface-Water Resources


miles, then to the northwest for 30 miles to the city of Grand Junc-
tion, where it flows into the Colorado River. Water quality is suitable
for most uses, except that classified uses are impaired by the oc-
* currency of metals in short reaches in the Gunnison River head-
waters and by the fecal- coliform bacteria in the Uncompahgre River
below Montrose (Colorado Department of Health, 1984). Principal
water use is irrigation of hay meadows, croplands, and orchards.
Less than 3.2 Mgal/d or 5 ft3/s is exported annually from the Gun-
nison River. The Curecanti unit of the U.S. Bureau of Reclama-
tion Colorado River storage project is located on the Gunnison
River. The Curecanti unit is comprised of Blue Mesa Reservoir
(completed in 1965 with 830,000 acre-ft or 270,000 Mgal of storage
capacity), Morrow Point Reservoir (completed in 1968 with 117,000
acre-ft or 38,100 Mgal of storage capacity), and Crystal Reservoir
(completed in 1977 with 25,200 acre-ft or 8,200 Mgal of storage
capacity).
White-Yampa Subregion
This subregion encompasses about 8 percent of the State's
area. The Yampa and the White Rivers are the principal Colorado
tributaries of the Green River. Water quality in this subregion is
suitable for most uses except for a short reach of the Yampa River
near its headwaters, where the classified use is impaired by trace
metals (Colorado Department of Health, 1984).
The Yampa River originates in the northwestern central
mountains of Colorado and flows generally westward for about 165
miles to its mouth at the Green River. Principal water use is irriga-
tion of hay meadows. The major surface-water issues in the Yam-
pa River basin are the effects of surface and underground coal
mining on salinity, and trace-element concentrations.
The White River originates to the west of the Yampa River
headwaters and flows westward for about 120 miles into Utah. Prin-
cipal water use is irrigation of hay meadows. Major surface-water
issues in the White River basin, other than those common to the
Upper Colorado River Basin, are the potential hydrologic effects
of oil-shale development.

San Juan Subregion
This subregion encompasses about 6 percent of the State's
area. The rivers in this basin that originate in Colorado generally
flow to the south into New Mexico or to the west into Utah (fig.
2). Streams in the western part of the basin are mostly perennial,
have their origin in low mountains, and have tributaries that are
mostly ephemeral. Streams in the eastern part of the basin are peren-
nial, have their origin in the southwestern mountains (mostly along
the Continental Divide), and have tributaries that are mostly peren-
nial. Water quality in this subregion is suitable for most uses ex-
cept for a short reach of the Animas River headwaters, where the
classified uses are impaired by trace metals (Colorado Department
of Health, 1984). In the western part of the basin, principal water
use is irrigation of croplands; about 106 Mgal/d or 164 ft3/s is im-
ported annually from the Dolores River basin to supplement irriga-
tion supplies. In the eastern part of the basin, principal water uses
are irrigation of croplands and hay meadows, and limited
hydroelectric-power generation (on the Animas River). A small


amount of water (less than 2 Mgal/d or 3.1 ft'/s) is exported an-
nually from the eastern part of the basin to streams in the Rio Grande
headwaters, but about 95 Mgal/d or 147 ft'/s is exported annually
to the Rio Grande basin in New Mexico. The Animas River-the
largest San Juan River tributary in Colorado-originates in the
State's southwestern mountains. The Animas River flows to the
south for about 70 miles into New Mexico.
Principal uses of water in the Animas River are irrigation
and hydroelectric-power generation. Major surface-water-related
issues in the San Juan River basin are those common to the Upper
Colorado Region, discussed earlier, as well as concerns of the Ute
Indians regarding their water rights.

SURFACE-WATER MANAGEMENT
The water law of Colorado is solidly based on the doctrine
of prior appropriation. According to sections 5 and 6 of Article
XVI of the State Constitution, the water of every natural stream
in the State of Colorado, not previously appropriated, is public pro-
perty and is dedicated to the use of the people of Colorado. The
right to divert unappropriated water for beneficial use cannot be
denied. Water for domestic use has preference over all other uses,
and water for agricultural use has preference over water for
manufacturing use.
The State Engineer (Colorado Department of Natural Re-
sources, Division of Water Resources) has general supervisory con-
trol over measurement, recordkeeping, and distribution of the public
waters of the State. The State Engineer also is charged with the
administration of the Interstate River Compacts and administers the
decisions of the Supreme Court of the United States that affect Colo-
rado's interstate water relations. Title 37, Article 90, Sections
101-141, of the 1973 Colorado Revised Statutes established the
Colorado Ground Water Management Act and places the administra-
tion of ground water partly under the authority of the State Engineer
and partly under the authority of the Colorado Ground Water
Commission.
Many Federal, State. and local agencies are involved with
the management of surface water in Colorado. Federal agencies
with the largest management responsibilities are the U.S. Bureau
of Reclamation and the U.S. Army Corps of Engineers. The North-
ern Colorado Water Conservation District and the Southeastern
Water Conservancy District are the two largest recipients of water
from U.S. Bureau of Reclamation projects in Colorado; these
districts, in turn, are responsible for managing that water. The Board
of Water Commissioners, City and County of Denver, are managers
of the largest municipal supply in the State. Most Colorado cities
and some counties also manage municipal supplies. Several irriga-
tion districts, conservancy districts, and other State and Federal
agencies play a role in managing water.
The U.S. Geological Survey, in cooperation with Federal,
State, and local cooperators, maintains a network of 350 streamflow-
gaging stations in Colorado, most of which provide data that sup-
port cooperator's water-management objectives. Hydrologic studies
conducted by the U.S. Geological Survey also provide significant
information needed by cooperators to manage Colorado water
resources.








National Water Summary Colorado 173

NORTH PLATE SUBREGION
41 1109 108 107* 106' 1050 104 103

I ampa basin .irth fSSO,

o o ITE-YA P ^IUt\' ^'c,. J-

jUS(BREGOIO 1 -7

White basin i
40"

Dot"ieroz AO basi





UNISON UPPFR ARKANSA

( %r s .R IO NB""i Po 1. C

SSUBRElIN GRANDEl Arns 4 A
SrSUBRE ON,
R"O" GRANDE I "RAN
SA,1S'1i 6 UUBRE!OrNGAND ARKANI SAS ITE. 14, Ci,
370 Gbrio *San. ,r rda'
37. a E Dns G




EXPLANATION
I Water-resources region Dam- Reservoir formed A3 USGS stream-gaging
boundary by dam has storage station-Number
Water-resources sub- capacity of at least refers to accompany-
region boundary 5,000 acre-feet ing bar graph and to S
Principal river basin Powerplant-Generating 0 50 100 MILES
boundary capacity of at least I I I
25,000 kilowatts 0 so 100 KILOMETERS
4000 1500 3000
SOUTH PLATTE RIVER NEAR KERSEY 3 ARKANSAS RIVER AT LA JUNTA 6 RIO GRANDE NEAR LOBATOS 11

82000 o O-
iz


ooo oo 00oo


0 0 0
a15 1 5 1935 10S s5 I 17S 5 1905 W915 I 392 5 145 955 S05 l185 105 15 10 1(9 1935 1S 13 1SS5 W15 1
WATER YEAR WATER YEAR WATER YEAR
8000 4000 1500
COLORADO RIVER NEAR CAMEO 13 YAMPA RIVER NEAR MAYBELL 16 ANIMALS RIVER AT DURANGO 18




000 ooo 3
Z 0O


D 5 0 0 O
1925 1935 145 155 165 1975 1085 1915 1925 135 145 1955 1965 1i 1985 125 1035 155 1w 5 1975 185
WATER YEAR WATER YEAR WATER YEAR
Figure 2. Principal river basins and related surface-water resources development in Colorado and average discharges for selected sites.
Bar graphs show average discharge by water year at selected stream-gaging sites, the curve is a 15-year weighted moving average of the annual values. (Sources:
Water-resources regions and subregions from Seaber and others, 1984, surface-water-resources development modified from Hitt, 1985; discharge data from U.S.
Geological Survey files.)


1








174 National Water Summary Surface-Water Resources

SELECTED REFERENCES

Bartlett, R. A., ed., 1984, Rolling rivers: New York, McGraw-Hill, 398 p.
Colorado Department of Health, 1984, Status of water quality in Colorado,
1984: Denver, 1 v.
Colorado State University, Department of Atmospheric Science, Colorado
Climate Center, compiler, 1984, Colorado average annual precipita-
tion 1951-80: Denver, Colo., U.S. Geological Survey map, scale
1:500,000.
Farnsworth, R. K., Thompson, E. S., and Peck, E. L., 1982, Evaporation
atlas for the contiguous 48 United States: National Oceanic and At-
mospheric Administration Technical Report NWS 33, 26 p.
Fenneman, N. M., 1931, Physiography of the Western United States: New
York, McGraw-Hill, 534 p.
1946, Physical divisions of the United States: Washington, D. C.,
U.S. Geological Survey special map.
Gebert, W. A., Graczyk, D. J., and Krug, W. R., 1985, Average annual
runoff in the United States, 1951-80: U.S. Geological Survey Open-
File Report 85-627, scale 1:2,000,000.
Hitt, K. J., compiler, 1985, Surface-water and related-land resources
development in the United States and Puerto Rico: U.S. Geological
Survey special map, scale 1:3,168,000.
National Oceanic and Atmospheric Administration, 1982, Monthly normals
of temperature, precipitation, and heating and cooling degree days
1951-80, Colorado: Climatography of the United States no. 81.
Raisz, Erwin, 1954, Physiographic diagram, p. 59, in U.S. Geological


7


Survey, 1970, National atlas of the United States of America:
Washington, D.C., U.S. Geological Survey, 417 p.
Seaber, P. R., Kapinos, F. P., and Knapp, G. L., 1984, State hydrologic
unit maps: U.S. Geological Survey Open-File Report 84-708, 198 p.
Solley, W. B., Chase, E. B., and Mann, W. B., IV, 1983, Estimated use
of water in the United States in 1980: U.S. Geological Survey Cir-
cular 1001, 56 p.
U.S. Environmental Protection Agency, 1982a, Maximum contaminant
levels subpartt B of part 141, National interim primary drinking-water
regulations): U.S. Code of Federal Regulations, Title 40, Parts
100-149, revised as of July 1, 1982, p. 315-318.
S1982b, Secondary maximum contaminant levels (section 143.3
of part 143, National secondary drinking-water regulations): U.S. Code
of Federal Regulations, Title 40, Parts 100-149, revised as of
July 1, 1982, p. 374.
U.S. Geological Survey, 1974, Hydrologic unit map of Colorado: U.S.
Geological Survey Hydrologic Unit Map, scale 1:500,000.
_ 1982, Water resources data for Colorado: U.S. Geological Survey
Water Data Report CO-81-1, 415 p.
_ 1984, National water summary 1983-Hydrologic events and
issues: U.S. Geological Survey Water-Supply Paper 2250, 243 p.
_ 1985a, National water summary 1984-Hydrologic events, selected
water-quality trends, and ground-water resources: U.S. Geological
Survey Water-Supply Paper 2275, 467 p.
_ 1985b, Water resources data for Colorado: U.S. Geological
Survey Water Data Report CO-84 [In press].


FOR ADDITIONAL INFORMATION
District Chief, U.S. Geological Survey, Building 53, Denver Federal Center, Mail Stop 415, Box 25046, Lakewood, CO 80225.


Prepared by Harold E. Petsch, Jr.


U.S. Geological Survey Water-Supply Paper 2300




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