S3_11-15-04

• Basin: Statewide
• Title: SWSI Phase 1 Report - Section 3 Physical Environment of the Major River Basins
• Date: 11/15/2004
• Author: CWCB
• SWSI - Doc Type: Final Report

Section 3
Physical Environment of the Major River Basins
surface water supplies. The median value for
groundwater use as a percentage of total use for all
counties in the state is 9 percent, with agricultural areas
in the eastern plains and in the San Luis Valley in south
central Colorado relying more substantially on
groundwater over surface water sources (Colorado
Geological Survey [CGS] 2003).
The state's unique topography and climate are clearly
intertwined with its water resources. Topography is an
important component of water resources planning, in that
it dictates the direction of natural flows within a
watershed. Much of the state's precipitation is
concentrated on its mountainous and western slope
areas. Snowpack in the state's alpine headwaters areas
provides the vast majority of water supplies, with spring
runoff causing significant flow peaking in virtually all of
the state's river systems. Groundwater storage and its
recharge are also largely affected by the topography and
climatological patterns that characterize the state.
Water quality can be affected by geography and various
land uses including runoff from point and non-point
discharge sources. For example, mining in the
mountainous regions, urbanization along the Front
Range, and agriculture in the eastern plains and
elsewhere can impact the quality of the state's waters
and aquatic habitats. Habitat degradation, nutrient
loading, soil erosion, and increased stormwater runoff
are only a few examples of the concerns associated with
rapid urbanization, particularly in the mountain
recreational areas (CDPHE 2000).
Improving water quality and restoration and protection of
water bodies in Colorado is occurring through programs
such as the TMDL process, Gold Medal fisheries
establishment, instream flow programs, and federal and
state listed threatened, endangered, and species of
special concern. These programs were presented in
Section 2, and key flow issues are also discussed by
basin in Section 6. More specific information on these
protection measures are presented below for each basin,
along with the topics described above.
Each section that follows describes one of Colorado's
eight major river basins. Figures associated with the
descriptions of each basin are compiled at the end of
each basin's write-up.
3.2 Arkansas Basin
3.2.1 Arkansas Basin Geography
The Arkansas Basin is spatially the largest river basin in
Colorado covering an area of 28,268 square miles, or
27 percent of the surface area of the state (Wolfe 2003,
CDPHE 2000). It comprises the southeast portion of the
state, as shown in Figure 3-2. The largest cities in the
basin are Colorado Springs (population 373,328) and
Pueblo (population 103,846) (DOLA 2003).
3.2.2 Arkansas Basin Climate
The climate in the Arkansas Basin is characterized by a
high degree of variability with average daily temperatures
ranging from 46 degrees Fahrenheit (°F) in the upper
river valley to 55°F in the lower valley (Smith and Hill
2000). Temperature extremes in the lower valley can
range from 0°F in the winter to 100°F in the summer
(Abbott 1985). Precipitation also varies greatly within the
basin. Figure 3-3 shows a contour plot of the average
annual precipitation throughout the basin. Basinwide
average annual precipitation ranges from less than
10 inches per year in the plains to over 30 inches per
year in the high mountain regions.
3.2.3 Arkansas Basin Topography
Steep slopes characterize the western part of the
Arkansas Basin, while relatively flat plains characterize
the eastern portion. The headwaters of the Arkansas
River begin near Leadville at an elevation of more than
14,000 feet and drop to 3,340 feet at the Colorado and
Kansas state line, representing a more than 10,000-foot
change (CGS 2003).
3.2.4 Arkansas Basin Land Use
Land use in the Arkansas Basin (USGS 1992) is shown
in Figure 3-4 and summarized in Table 3-1. Grassland
and forest are the predominant land use types in the
basin covering approximately 67 percent and 13 percent
of the basin, respectively. The grassland areas are
concentrated in the central portion of the basin whereas
the forested land is located on the western portions of
the basin.
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