skip to the content of this page
AZ.gov Arizona's Official Website Arizona Department of Water Resources
Arizona Department of Water Resources AZ.gov Arizona's Official Web Site
Securing Arizona's Water Future

Lower Colorado River Hydrology - Surface Water

Click to view Figure 7.0-5

Figure 7.0-5  USGS Watersheds in the Lower Colorado River Basin

The U.S. Geological Survey (USGS) divides and subdivides the United States into successively smaller hydrologic units based on hydrologic features.  These units are classified into four levels. From largest to smallest these are: regions, subregions, accounting units and cataloging units.  A hydrologic unit code (HUC) consisting of two digits for each level in the system is used to identify any hydrologic area (Seaber et al., 1987).  A 6-digit code corresponds to accounting units, which are used by the USGS for designing and managing the National Water Data Network.  There are all or portions of four watersheds in the planning area at the accounting unit level: Lower Colorado River below Lake Mead; Lower Gila River below Painted Rock Dam; Agua Fria River-Lower Gila River; and the Rio Sonoyta (Figure 7.0-5).  More detailed information on stream flow, springs, reservoirs and general surface water characteristics are found in the individual basin sections.

Lower Colorado Below Lake Mead Watershed

This watershed extends north to Hoover Dam and includes all or parts of three basins in the Upper Colorado River Planning Area (see Volume 4, Figure 4.0-5).  Within the Lower Colorado River Planning Area, all or parts of Butler Valley, Ranegras Plain, Parker, Harquahala, Lower Gila and Yuma basins are included in the watershed.  The Colorado River is the only perennial surface water in the entire watershed.  Within the planning area, the river flows for about 200 miles south of Parker Dam to Mexico at the Southerly International Boundary.  There are many diversions and several dams along the Colorado River.  Dams include Imperial, Laguna and Morelos. There are major diversions from Imperial Dam to the All-American Canal, which delivers agricultural water to California and to the Gila Gravity Canal for use in Arizona.  Drainages to the Colorado River in the planning area are ephemeral and contribute little to river flow with the exception of the Gila River during flood events.

Dam construction and diversions have fundamentally altered flow in the Colorado River, including the portion in the planning area.  Historically, the Colorado was a broad, meandering, unpredictable, sediment-laden watercourse, with annual flooding and frequent changes in the configuration of the channel.  It sometimes overtopped its banks and flowed west to the Salton Sink, forming intermittent lakes.  In the early 1900s water began to be diverted from the Colorado River via the Imperial Canal to irrigate California’s Imperial Valley.  When the canal filled with silt, a cut was made in the west bank of the river to temporarily allow water to flow into the valley.  In 1905, massive flooding on the Colorado overtopped this diversion canal and diverted the river toward the Salton Sink (Salton Sea Authority, 2000).  This flow flooded the valley, destroying farms and towns and began filling the Salton Sink, creating the modern Salton Sea.  Flow continued for 18 months and for a time the Colorado ceased flowing into Mexico (Tellman and others, 1997).  There were concerns that if the cutback erosion in the flow channel reached the Colorado River, it would be permanently diverted to the Salton Sink.  In 1907 the Southern Pacific Railroad, which had substantial business interests in the region, repaired the gap in the diversion canal and the river resumed its natural course toward the Gulf of California.

Colorado River in the Parker Basin

Colorado River in the Parker Basin

Prior to dam construction on the Colorado River, the river flowed to the Gulf of California, forming a delta with a maze of lagoons and dense riparian habitat.  Today only about 420,000 acres of the original two million acre delta survives and the river reached the sea only about half of the years between 1981 and 2002.  Since 1979, an average of about 100,000 acre-feet of salty drainage water from the Wellton-Mohawk Irrigation District is delivered annually to the eastern side of the delta, creating the Cienega de Santa Clara. (Glenn and others, 2004)

There are streamflow records for eight Colorado River streamgages in the watershed. Of these, five are currently in operation and four are real-time gages.  There are two active gages in the Parker Basin, one in the Lower Gila Basin and two in the Yuma Basin. The active gages in the Parker Basin portion of the watershed report similar median and mean flows (Table 7.6-2). Median flow at the gage below Parker Dam is 7.2 maf and the mean is 8.9 maf.  The highest maximum annual flow (20.4 maf) in the watershed was reported at this gage in 1984. The three operating downstream gages (located below the major California diversion structures) report mean flows substantially greater than median flows. For example, the gage on the Colorado River below Laguna Dam reports a median flow of 0.39 maf and a mean flow of 1.8 maf. The highest maximum annual flow among the three downstream gages was 15.4 maf at the Colorado River at the NIB above Morelos Dam gage (Table 7.11-2)

There are no major (>10gpm) or minor (1-10 gpm) springs in the entire watershed, and only 15 to 16 smaller springs, primarily in the Parker Basin.

A 28-mile reach of the Gila River (from Coyote Wash to Fortuna Wash) is designated as “impaired” due to elevated concentrations of boron and selenium that exceed the designated use standard for aquatic and wildlife uses (Tables 7.4-7 and 7.11-6)

Colorado River, Lower Gila Basin

Colorado River in the Lower Gila Basin

Lower Gila River Below Painted Rock Dam Watershed

This watershed includes almost all of the Lower Gila Basin and part of the Yuma Basin.  Major surface water drainages are the Gila River, Tenmile Wash and San Cristobal Wash (see Figure 7.0-5).

The Gila River drains the eastern and central parts of the planning area and extends 150 miles from Gillespie Dam (located where the Gila River enters the planning area in the Gila Bend Basin) to its confluence with the Colorado River in the Yuma Basin.  The river originates in New Mexico and flows 600 miles from east to west across Arizona.  The entire Gila River Watershed drains about 57,900 square miles and is the largest watershed in Arizona, covering over half of the state’s total land area (Tellman and others, 1997).

Historically, the Gila River flowed in the planning area in the spring due to winter rain and snowmelt and in the summer following monsoon storms.  Construction of dams resulted in loss of flows and water supplies downstream. 

Construction of Gillespie Dam in 1921 and Painted Rock Dam in 1959, impounded Gila River flow in the planning area for diversion to agricultural areas and to prevent flooding downstream.  Prior to construction of the Painted Rock Dam, an average of approximately 6 AFA of groundwater was forced to the surface by the volcanic rocks of the Painted Rock Mountains and rock outcrops in the river channel at Painted Rock Narrows (Rascona, 1996).  Gillespie Dam was breached during January 1993 when a 135-foot section of the dam collapsed during flooding. The same flood event filled Painted Rock Dam to full capacity of 2.5 maf, making it the largest lake in Arizona, and high volumes of spillwater caused extensive downstream damage.  The reservoir is normally dry.

In the planning area, the Gila River now flows only in response to precipitation events, irrigation return flow or releases from upstream dams.  Recent sources list the river as either intermittent (AZGF, 1997) or ephemeral (ADWR, 1994a).  The Gila River is a flashy stream, showing wide variations in annual flow in the planning area.  There are four operating streamflow gages on the Gila River.  Two gages are above Painted Rock Dam in the Agua Fria River-Lower Gila River Watershed in the Gila Bend Basin, one is in the Lower Gila Basin and one is in the Yuma Basin.  All four gages have years with no flow (see Tables 7.2-2, 7.4-2 and 7.11-2).  By contrast, total annual flow at the gage below Gillespie Dam and the gage below Painted Rock Dam were over 5 maf in 1993.  Further downstream near the confluence with the Colorado, the gage at the Gila River near Dome recorded a maximum annual flow of over 4.7 maf in 1993, but an has recorded annual median flow of less than 4,800 acre-feet.

There are no major (>10gpm) or minor (1-10 gpm) springs in the Lower Gila River Watershed below Painted Rock Dam, and only six to eight smaller springs.

Agua Fria River-Lower Gila River Watershed

The Agua Fria River - Lower Gila River Watershed includes the drainage areas of the Agua Fria River and the Gila River from below its confluence with the Salt River to Painted Rock Dam.  Within the Lower Colorado River Planning Area, Gila Bend, Harquahala, McMullen Valley and Tiger Wash basins are included in the watershed. 

The Gila River is the only major watercourse.  Centennial Wash is the major tributary and is an ephemeral stream with no streamgage data within the planning area.  The only streamgage data for the watershed, other than those on the Gila River (mentioned above), is a discontinued gage at Sauceda Wash near Gila Bend with a maximum annual flow of about 1,100 acre-feet (see Tables 7.2-2).  

Centennial Wash

Centennial Wash is the major tributary to the Gila River and is an ephemeral stream with no streamgage data within the planning area.

There are no major (>10gpm) or minor (1-10 gpm) springs in the Agua Fria River-Lower Gila River Watershed, and only five to seven smaller springs, three of which are located in the Tiger Wash Basin.

The waters of the Gila are designated as “impaired” due to elevated concentrations of organic compounds that exceed the designated use standard for fish consumption from it’s point of entry into the planning area to Painted Rock Dam. Below Painted Rock Dam the Gila is impaired due to dissolved oxygen, organics, selenium and boron concentrations that exceed fish consumption or aquatic and wildlife uses (see Tables 7.2-7 and 7.4-7).

Rio Sonoyta Watershed

The Rio Sonoyta Watershed in Arizona includes the San Simon Wash and Western Mexican Drainage basins and the south central portion of the Lower Gila Basin. Major drainages in the San Simon Wash Basin, all ephemeral, are Hickiwan Wash, San Simon Wash and Vamori Wash (Figure 7.8-4).  Vamori Wash flows northwest to San Simon Wash, which in turn flows south to the Rio Sonoyta in Mexico.  There are two active streamgages in the watershed in the San Simon Wash Basin, one on Vamori Wash at Kom Vo and one on San Simon Wash near Pisinimo.  These ephemeral streams flow primarily in the summer as a result of monsoon precipitation.  Annual mean flow at the Vamori Wash gage is over 6,600 acre-feet and almost 2,400 acre-feet at the San Simon gage (see Table 7.8-2).  The largest ephemeral tributary to the Rio Sonoyta in the Western Mexican Drainage Basin is Aguajita Wash (Figure 7.10-4).

The only major (>10gpm) and minor (1-10 gpm) springs in the entire planning area are found in this watershed in the Western Mexican Drainage Basin. Quitobaquito Springs are the only major spring with a combined discharge of 28 gpm.  Located adjacent to the international boundary in Organ Pipe Cactus National Monument, the springs flow from fractured granite that forms the Quitobaquito Hills.  Groundwater moves through the fractured granite and discharges in a line of springs on the southwest side of Quitobaquito Hills (Carruth, 1996). Two of the largest springs have been developed and diverted into a man-made stream channel that flows to a half-acre pond that provides habitat for the endangered Quitobaquito pupfish (Knowles, 2003).  The springs are relatively warm, (a near about 74°F), and slightly brackish.  The two minor springs in the planning area are located nearby.  In total there are about 20 total springs in the watershed, with most located in the San Simon Wash Basin.

 

 

water drop  Continue to Section 7.0.3 Climate

 

Arizona Water Atlas Home

Lower Colorado River Planning Area Home

Download pdf of Lower Colorado River Planning Area Overview

Colorado River
Lower Colorado River Planning Area

Volume 7

Parker Dam
Agriculture in Yuma Basin