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
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Statewide Water Supply Initiafive
3.1 Statewide Overview
Evaluations conducted under SWSI followed CWCB's
delineations of Colorado's eight major river basins, as
shown in Figure 3-1. The basins include the Arkansas,
Colorado, Dolores/San Juan/San Miguel, Gunnison,
North Platte, Rio Grande, South Platte, and Yampa/
White/Green Basins. Basin descriptions were completed
to gather information on the current physical, institutional,
regulatory, demographic, economic, and social settings
as they relate to water use in each of these basins. The
purpose of this section is to provide an overview of these
factors for reference in the SWSI process. These
descriptions are broken down into the following major
sections for each basin:
^ Geography
^ Climate
^ Topography
^ Land Use
^ Surface Geology
^ Surface Water
^ Groundwater
^ Water Quality
^ Areas of Environmental Concern, Special Attention
Areas, and Threatened and Endangered Species
^ Energy and Mineral Resources
Virtually all of these topics are interconnected or affect
the state's water supplies and water quality - either
through natural or man-made/induced factors. The
topography of the Continental Divide, the backbone of
Colorado's Rocky Mountains, dictates the direction of
water flow either to the west or to the east for each of the
river systems in the state. The Divide is also home to the
headwaters of several major rivers and their tributaries
that run throughout Colorado. The Colorado River begins
in Rocky Mountain National Park in eastern Grand
County and flows to the west toward the Pacific Ocean.
The Colorado River system comprises an area that
covers approximately one-third of the state, including the
major tributary systems of the Yampa, White, and
Dolores Rivers. Nearly 70 percent of the water that
leaves Colorado flows through the Colorado River and its
tributaries. However, only a small fraction of the state's
population lives within this corridor.
In contrast, over half of Colorado's land area and
85 percent of the state's population lies in the South
Platte and Arkansas Basins, which contribute only about
5 percent of the flows leaving the state. These two river
systems travel from the east side of the Continental
Divide to the Mississippi River and ultimately the Gulf of
Mexico. The Rio Grande, accounting for 3 percent of the
water exiting Colorado, flows south into New Mexico,
then east to the southern border of Texas, and into the
Gulf of Mexico. The Animas, Florida, and San Juan
Rivers and their tributaries also flow south into New
Mexico, and make up almost 20 percent of the water
leaving the state. The North Platte and Laramie Rivers
flow north into Wyoming and make up about 4 percent of
the water leaving the state (Colorado SEO 2003). Other
surface water resources, which cover about
164,000 acres throughout the state, include lakes and
reservoirs (CDPHE 2000).
Groundwater resources also play a pivotal role in
meeting Colorado's water needs. In 1995, groundwater
withdrawals in Colorado were slightly more than
2.5 million AF, with agricultural users comprising about
90 percent of this amount. Overall, groundwater
withdrawals by agricultural and M&I users in 1995
represented slightly more than 20 percent of the state's
total for these uses, with the remainder coming from
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Figure 3-1
Co/orada's Eight Major River Basins