ColoradoBasinWaterSupplyandNeedsReport

• Basin Roundtable: Colorado
• Title: Water Supply & Needs Report for the Colorado Basin
• Date: 5/1/2006
• Basin Roundtables - Doc Type: Needs Assessment Documents

Section 3
Physical Environment of the Colorado Basin
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subdivisions, commercial centers, roads, ski area
expansions, and naturally erosive soils (CDPHE 2002).

Salinity has long been recognized as one of the major
issues on the Colorado River. The salt loads in the river
system originate primarily from easily eroded saline-rich
sedimentary rocks that are extensive in the lower basin.
The Colorado River Basin Salinity Control Program is
designed to prevent a portion of this salt supply from
moving into the river system (Colorado River Basin
Salinity Control Forum 2002).

Nearly half of the salinity in the Colorado River System is
from natural sources. Saline springs, erosion of saline
geologic formations, and runoff all contribute to this
background salinity. Irrigation, reservoir evaporation, out-
of-basin exports, and M&I sources make up the balance
of the salinity loading in the Colorado Basin. Estimated
salt sources and percentages for the mainstem and
waters tributary to the Colorado River at Hoover Dam
have been estimated as follows (U.S. Environmental
Protection Agency [EPA] 1971):

. Natural - 47 percent
. M&I and out-of-basin exports - 4 percent
. Reservoir evaporation - 12 percent
. Irrigated agriculture - 37 percent

Another water quality issue that has historically been the
center of attention is metals pollution attributed to a
Superfund site and inactive mining areas. The Eagle
River is impacted by metals pollution from the Eagle
Mine Superfund site near Gilman, although remediation
has significantly decreased metal loads to the Eagle
River and Cross Creek over the last several years. Peru
Creek, the upper Snake River, and French Gulch in
Summit County are all heavily impacted by acid mine
drainage from abandoned or inactive mines (CDPHE
2002) .

Agricultural activities also affect water quality in the
Colorado Basin. Nutrients derived from fertilizers can
indirectly cause detrimental effects on aquatic fauna by
overstimulating the growth of various algal species.
Pesticides are commonly used in agricultural areas in the
Upper Colorado Basin and its major tributaries, which
can cause damaging effects on the biota because of
acute or chronic toxic exposure. Studies conducted on
the water quality of irrigation return flows in the Upper
Colorado Basin have indicated adverse effects on biota

CDIVI

3-4

from pesticides and selenium, a naturally occurring
element in the soil (Apodaca et al. 1996).

Figure 3-7 identifies the locations of surface waters in the
Colorado Basin that have been listed for impairment for
one or more parameters on Colorado's 2002 303( d) list.
Stream segments proposed for listing via the 2004
303( d) list and the accompanying Monitoring and
Evaluation list are described in Colorado Water Quality
Control Commission (WQCC) Regulations 93 and 94.
The state's 2004 proposed 303( d) list incorporates
several additions from the 2002 list. It includes significant
numbers of mainstem and tributary stream segments as
being impaired for selenium, largely in the lower portions
of the basin. The 2004 proposed listings for impairment
in the upper part of the basin are primarily associated
with metals such as copper, cadmium, lead, and zinc.

The water quality of streams can also be affected when
interbasin water transfers decrease the dilution capability
of the streams by removing water from the system.
Interbasin water transfers generally occur near the
stream headwaters, and the amount of streamflow
diverted can be a substantial part of the streamflow near
these sources. The numerous reservoirs, water
diversions, and municipal discharges in the basin alter
the natural streamflow, which can affect the aquatic
habitat and water quality of the streams (Apodaca et al.
1996) .

3.2.9 Areas of Environmental Concern,

Special Attention Areas, and

Threatened and Endangered

Species

The 15-Mile Reach, the stretch of the Colorado River
from the Grand Valley Diversion Dam near Palisade to
the Gunnison River, is an area of environmental concern
in the Colorado Basin. The 15-Mile Reach is of concern
for the following reasons:

. The 15-Mile Reach provides valuable spawning
habitat for the endangered Colorado pikeminnow and
razorback sucker fish species.

. The 15-Mile Reach provides an optimum balance
between temperature and food availability for adult
Colorado pike minnow in the Colorado River.

. The 15-Mile Reach provides an important refuge for
endangered fishes should a catastrophic event cause

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