Southeast basins supply water for compact
Utah is divided by the United State Geological Survey (USGS) and the state division of water resources into 11 drainage basins.
With the exception of one basin, the drainages in northern and western Utah flow into a terminal lake system.
In the southern and eastern portions of the state, two of the basins feed a terminal lake system while the rest eventually flow into the Colorado River drainage.
One of the basins with terminal drainage is the Sevier River.
The Sevier River basin is shaped similar to a horseshoe, bounded on the north by Utah County, on the west by the Great Salt Lake Desert drainage, on the east by the Wasatch Plateau and on the south by Kane and Washinton counties.
The main surface water source in the area is the Sevier River. In the days before dams and irrigation, the river flowed somewhat seasonal, into Sevier Lake. Sevier is the second largest lake in the state when it is full. Currently, Sevier is termed a dry lake, usually receiving flows only during seasons when floods and high water occur.
The main river, the Sevier, is more than 220 miles long from its beginnings in the Markagunt and Paunsaugunt plateaus of southern Utah.
Other major tributaries feeding the system are the East Fork Sevier and San Pitch rivers as well as Otter Creek.
Major communities that fall into the Sevier basin include Richfield, Filmore and Delta.
The mean precipitation throughout the basin is 13 inches, with the actual runoff being two inches per year.
The other terminal drainage is the Cedar-Beaver basin. The basin is located in the middle of the horseshoe of the Sevier drainage. The basin drains primarily north into the Sevier system.
The major river in the basin is the Beaver River. The drainage once flowed into ancient Lake Bonneville and later into Sevier Lake. But the Bear River drainage currently ends near Clear Lake in Millard County.
The basin is boarded on the west by the Nevada state line and on the south by the Dixie National Forest. Major cities include Beaver, Milford and Cedar.
The mean precipitation in the Bear River basin is 13 inches, but actual runoff is less than one inch annually. The Bear dainage is one of the driest basins in the state.
In the northeastern section of Utah lies the Uintah hydrologic unit. In effect, the entire basin drains into the Colorado River via the Green. The Green is the major river in the area.
The Green River flows through the area and picks up moisture, but its headwaters are located in Wyoming. The drainage is bordered on the east by the Colorado line, on the north by the Wyoming line, on the south by the Bookcliffs and on the west by the Uinta Basin.
Major tributaries within the drainage are the Duchesne, the Uintah and the White rivers along with Nine Mile Creek. Cities located within the boundaries of the drainage include Vernal, Roosevelt and Duchsene.
The mean annual precipitation in the Uintah unit is about 16.5 inches, with about three and one-half inches of actual runoff.
Much of the heavy snowfall on the north slope of the Unitah Mountains drains into the Bear River basin. In addition, the mountains east of the Green are drained by the Yampa River drainage that flows into Colorado.
The next basin is the southeast Colorado drainage. It lies south of the eastern part of the Uintah drainage, bordered by the Book Cliffs on the west and the Colorado line on the east into San Juan County. The basin swings west in an L shape to nearly to the edge of Kane County.
The basin lies in the middle of the Colorado River drainage. The major river is the Colorado.
Major tributaries include the Green River, San Juan River and the Paria River drainage which flows into the Colorado River near Lee's Ferry, Ariz. The Delores River also flows into Utah from Colorado and then joins the river near Cisco.
The major cities in the area include Moab, Monticello, Kanab and Blanding.
This is an area of sandstone, salt domes and high desert plateaus. Water runs off the plateaus almost as soon as it falls.
The mountain ranges within the drainage system include the LaSal and Blue Mountains.
Snowfall in these mountains can be heavy at times, with accumulations of many feet of snow during a normal winter.
The mean annual precipitation is almost 12 inches, but only about one inch of that is runoff.
Another drainage that exists in the far southwest corner of the state is the Virgin River/Kanab creek drainage. This is a small drainage, but an important one to the Colorado River system.
It's southern border is the Arizona state line, the western boarder is the Nevada state line, to the north it boarders Iron County and to the east it stretches into the western end of Kane County.
Major cities include St. George and Hurricane. According to studies, the population in this area is expanding at a rapid rate with the population growing in the last 25 years from 30,000 to over 100,000 people. This has impacted the water use and storage immensely.
The principal stream in the area is the Virgin River. This river, along with its tributaries, the Santa Clara River and LaVerkin Creek draw their water from the Pine Valley Mountains and the highlands along Zion National Park.
Most of the runoff from this area comes in mid-spring as the highlands give up their accumulated moisture from snow melting.
However, the Virgin River itself does keep a continual flow during some of the winter and summer months due to storms that range over the area. Flash flooding is common in nearby streams and washes.
The mean annual precipitation is a little under 16 inches per year, with actual runoff only averaging 7.5 percent or 1.2 inches annually.
The final drainage basin in the state is a vast one that encompasses everything south and west of the bookcliffs to the Wasatch Plateau in the west.
To the south it borders the southeast drainage, just north of Lake Powell.
This drainage is called the west Colorado drainage and major cities include Price, Helper, Castle Dale and Green River.
There are many rivers in the area, all of which flow out of the western mountains toward the Green or Colorado Rivers. Tributaries include the Price, San Rafael, Dirty Devil and Escalante Rivers.
This area has very irregular topography with deep canyons, steep sided washes and high mountains.
The annual precipitation is a little over 11 inches per year, but only 1.2 inches is actually off flow. The rest is contained within the watershed.
Stream flow in the area varies with the Price River providing 92,740 acre annually which is measured near Woodside.
The San Rafael River has the largest annual flow, with 113,700 acre feet annually which is measured near Green River.
With the exception of the Sevier River and Cedar-Beaver drainage systems, all of the drainages previously mentioned affect the Colorado River drainage and ultimately the water delivered by Utah under the provisions of the Colorado River compact.
That delivery, amongst others on down the line, has been a point of controversy for years and years, thus requiring steam flow gages and statistics on water flow for legal and practical reasons.