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The Gila Project, located in southwestern Arizona, is divided into two divisions: the Yuma Mesa Division and the Wellton-Mohawk Division. The Yuma Mesa Division is further subdivided into three units: the Mesa Unit (located south and southeast of Yuma), and the North Gila Valley and South Gila Valley Units, which lie northeast and east of Yuma. The Wellton-Mohawk Division begins about 12 miles east of the city of Yuma and continues upstream on both sides of the Gila River for about 45 miles.
Upon full development, the project could provide irrigation service to 65,000 acres in the Wellton-Mohawk Division (this acreage was reduced from 75,000 acres by the Colorado River Basin Salinity Control Act of 1974) and to 42,131 acres in the Yuma Mesa Division, which includes 17,131 acres in the North and South Gila Valleys. The project currently provides irrigation service to about 98,000 acres of land in the two divisions. The project authorization permits diversion of Colorado River water to satisfy beneficial consumptive use of 300,000 acre-feet of water in each division.
Project features include the Gila desilting works at Imperial Dam, the Gila Gravity Main Canal, the Mesa Unit Canals and distribution system, the lateral system in the North Gila Valley (originally constructed as part of the Yuma Project), the canal and pipeline distribution in the South Gila Valley, and the Wellton-Mohawk Canal distribution and drainage systems and protective works.
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Imperial Dam, which also serves the All-American Canal System of the Boulder Canyon Project, diverts Colorado River water at its east abutment through the desilting basin into the Gila Gravity Main Canal. From turnouts in this canal, irrigation water is diverted to serve the North and South Gila Valleys and the Wellton-Mohawk area. The canal ends at the Yuma Mesa Pumping Plant, where water is lifted 52 feet to the head of the Yuma Mesa distribution system which conveys irrigation water to the Mesa Unit lands and to the Yuma Auxiliary Project.
The Wellton-Mohawk Division of the Gila Project receives Colorado River water from a turnout on the Gila Gravity Main Canal. From this point, water is carried approximately 18.5 miles eastward and parallel to the Gila River through the Wellton-Mohawk Canal, from which it is diverted into the Dome, Wellton, and Mohawk canals. From these three canals, the water is released to distribution laterals for delivery to farms and other water users. The irrigation system layout remains largely the same today as its original construction.
See All American Canal System, Boulder Canyon Project
The Gila headworks of Imperial Dam was constructed with three sets of outlet units, each with three radial gates; water discharges through one gate unit into a settling basin. Original plans contemplated diversions to 585,000 acres, but the area of the Gila Project was reduced by the act of July 30, 1947 (61 Stat. 628), to 117,000 acres. The acreage was reduced again to 107,000 acres by the Colorado River Basin Salinity Control Act. One desilting basin, 1,165 feet long including transitions, is located between the Gila headworks of Imperial Dam and the Gila Gravity Main Canal diversion gates. This single basin has sufficient capacity under normal conditions for one year`s accumulation of sediment. An annual outage of the canal permits draining the basin for inspection, repair, and sluicing the accumulated sediment to the Colorado River below Imperial Dam.
Water is discharged from the desilting basin into the Gila Gravity Main Canal, which has a capacity of 2,200 cubic feet per second and extends from the desilting works 20.5 miles in a southerly direction to the Yuma Mesa Pumping Plant. The canal consists of two tunnels, one 1,740 feet long and the other 4,125 feet long; the 0.39-mile Gila River Siphon; and about 19 miles of open unlined canal. It has 10 turnouts to divert water to the project area.
This unit receives water from two turnouts in the Gila Gravity Main Canal, one 7 and the other 11 miles from Imperial Dam. They have a capacity of 150 and 50 cubic feet per second, respectively. The unit contains 10.2 miles of canals and about 15 miles of laterals. Drainage is provided by open drains and the adjacent Colorado and Gila Rivers.
Water is diverted to the South Gila Valley Unit from a turnout on the Gila Gravity Main Canal, located just upstream from the Yuma Mesa Pumping Plant, to the 7.7-mile-long South Gila Canal. There are seven additional smaller turnouts from the Main Canal, four of which are equipped with pumps. There is a total of 27 miles of underground pipeline laterals in the unit. Total diversion capacity to the unit is 282 cubic feet per second, which is supplemented by three deep wells There are 24 drainage wells to maintain adequate ground-water levels. Two of these wells can be used to supply additional irrigation water.
The Yuma Mesa Pumping Plant lifts water about 52 feet from the Gila Gravity Main Canal into the main canal of the Yuma Mesa distribution system, which carries water to about 25,000 acres in the Mesa Unit and to about 3,400 acres in the Yuma Auxiliary Project. The main canal of the distribution system divides into the A and B Canals, which have a total length of 23 miles. There are 43 miles of laterals within the system. The present capacity of the pumping plant is 700 cubic feet per second.
The 18.5-mile Wellton-Mohawk Canal diverts from the Gila Gravity Main Canal about 15 miles below Imperial Dam and has a capacity of 1,300 cubic feet per second. Its branches, the Wellton Canal and the Mohawk Canal, are 19.9 and 46.8 miles long respectively. The Wellton Canal has a diversion capacity of 300 cubic feet per second and the Mohawk Canal has a diversion capacity of 900 cubic feet per second. Three large pumping plants along the Wellton-Mohawk Canal lift the water a total of 170 feet. Thirteen small pumping plants are scattered throughout the Wellton-Mohawk Division on 227 laterals. The Texas Hill Canal takes water from the Mohawk Canal north of the Mohawk Mountains and extends 9.8 miles to the east to irrigate lands in the Texas Hill area. It has an initial capacity of 125 cubic feet per second.
The 13-mile Dome Canal branches off the Wellton-Mohawk Canal about 10 miles from its beginning and serves the western end of the division. Its diversion capacity is about 220 cubic feet per second. It has 7.5 miles of laterals.
Power for pumping is furnished through the Department of Energy`s Parker-Davis transmission system.
The Imperial Irrigation District currently operates and maintains Imperial Dam, the All American Canal and the Gila Diversion works. Operation and maintenance of the Gila Gravity Main Canal has been transferred to the districts obtaining water from this canal -- the North Gila Valley Irrigation and Drainage District, Wellton-Mohawk Irrigation and Drainage District, Yuma Irrigation District, Yuma Mesa Irrigation and Drainage District, and Unit B Irrigation and Drainage District. The distribution system in the North Gila Valley Unit is owned and operated by the North Gila Valley Irrigation District. The Yuma Mesa Irrigation and Drainage District operates the Yuma Mesa Pumping Plant and the distribution system downstream from the pumping plant. The Wellton-Mohawk Irrigation and Drainage District operates the irrigation facilities in the Wellton-Mohawk Division.
Spain dominated the Arizona desert for nearly 300 years after its discovery. The United States acquired the territory north of the Gila River in 1848 and, in 1856, took formal possession of the lands south of the Gila.
Early history of agricultural development in the Wellton-Mohawk area dates back to 1538 when the Pima Indians irrigated some of the bottom land adjacent to the Gila River. Early pioneer settlement started with the establishment of the Butterfield Stage Line in 1857. The Southern Pacific Railroad began serving the area on February 1, 1879. In the late 1800's, the Mohawk Canal was constructed with diversion headworks on the Gila River at Texas Hill, and the Antelope Canal was constructed to serve the Wellton area. However, calamitous floods that washed out crops and destroyed diversion works, alternating with long periods of drought, continuously plagued the early settlers. These conditions resulted in the settlers turning to the use of the abundant groundwater in the area for irrigation and other purposes.
In 1906, the Antelope Irrigation District was formed and a wood-burning steam generating plant was built near Wellton to provide energy for pumping. In 1921, the Gila Valley Power District was organized to develop and supply electric power for pumping irrigation water and for municipal and industrial uses. The settlers continued to drill wells but, by 1934, Wellton-Mohawk farms were facing another hazard. Excessive salt appeared in many wells and the water table had declined alarmingly.
One after another, farms were abandoned as water and soil became too saline for successful farming. So the Bureau of Reclamation initiated construction in the Yuma Mesa Division during the late 1930's, which included construction of the Gila Gravity Main Canal between 1936 and 1939. But permanent relief would come only with the importation of Colorado River water. Congress passed the Gila Project Reauthorization Act in 1947, to provide funding for the Wellton-Mohawk Division of the project. In 1952, water deliveries via the newly constructed Wellton-Mohawk Canal arrived in the area. The remaining features of the Wellton-Mohawk canal system were completed by Reclamation by 1957.
Irrigation with water from the Colorado River caused the water table to rise and threatened crops with drowning. Drainage wells were constructed to remove the excess groundwater. But the drainage water was highly saline, initially averaging about 6,000 parts per million, so this drainage water was discharged into the Gila River.
Late in 1961, the Wellton-Mohawk Main Conveyance Channel was constructed for the entire length of the Wellton-Mohawk Division to carry drainage water from about 67 wells. Additional wells were installed in 1963 to allow for selective pumping to reduce the salinity of the effluent during the winter months and to provide drainage to other areas with high groundwater.
In 1934, the Bureau of Reclamation submitted a favorable report based on an investigation of Gila Project potentialities. The investigations were authorized by the Boulder Canyon Project Act of 1928.
The project was originally authorized for construction under a finding of feasibility approved by the President on June 21, 1937, pursuant to section 4 of the act of June 25, 1910 (36 Stat. 836), and subsection B of section 4 of the act of December 5, 1924 (43 Stat. 701). It was reauthorized and reduced in area to 117,000 acres by the act of July 30, 1947 (61 Stat. 628). Further reduction in irrigable acreage of the Wellton-Mohawk Division was authorized by the Colorado River Basin Salinity Control Act of June 24, 1974 (88 Stat. 266).
Project construction was begun in 1936, and the first water was available for irrigation from the Gila Gravity Main Canal on November 4, 1943. Construction was postponed during World War II. Canal and lateral construction resumed as soon as hostilities ended.
Construction of the Wellton-Mohawk Division features began in August 1949. On May 1, 1952, water from the Colorado River was turned onto the Wellton-Mohawk fields for the first time. The project was essentially complete by June 30, 1957.
In 2004-2005, the Gila Gravity Main Canal was rehabilitated to help reduce water losses from seepage and increase control of water usage and overall operational efficiency of the canal. Activities included sediment removal; installation of equipment to provide real-time data to better gauge water requirements and remote control of canal gates to improve deliveries; and sealing the canal to help prevent water losses through seepage.
Reclamation is presently negotiating the transfer of title to Wellton-Mohawk Division facilities to the Wellton-Mohawk Irrigation and Drainage District. The federal facilities owned by Reclamation within the 130,000 acre service area include irrigation and drainage systems that serve 62,875 acres of irrigable land, various administrative buildings, and flood control facilities. The flood control facilities consist of the Gila River Flood Channel, which protects district lands from river floods, and numerous dikes and floodway channels that protect against overland runoff during rainstorms.
The primary project beneficiaries include North Gila Valley Irrigation and Drainage District, Wellton-Mohawk Irrigation and Drainage District, Yuma Irrigation District and Yuma Mesa Irrigation and Drainage District. Other beneficiaries of the system include the City of Yuma, Marine Corps Air Station, Unit B Irrigation and Drainage District and the Gila Monster Ranch.
The Gila Gravity Main Canal delivers Colorado River water for irrigation and domestic purposes to approximately 100,000 acres in an area located east of the City of Yuma extending to the Mohawk Pass. Principal crops grown are lettuce and other produce crops in the fall and winter months and wheat, cotton, hay and melons in the spring and summer months. Together with the crops in the Yuma Valley, agriculture in the Gila Project is responsible for more than half of Arizona’s total agricultural production.
Domestic, Municipal and Industrial Water
Domestic water users receiving water through the Gila Gravity Main Canal include Far West Water Company serving the area known as the “Foothills” east of Yuma and the City of Yuma. Eventually, the City of Yuma will rely on the Gila Gravity Main Canal for delivery of a substantial portion of the City’s domestic water supply as the City constructs a new water treatment plant east of Yuma.
The Bureau of Reclamation did not provide a return flow system as part of the original construction of the Wellton-Mohawk Division of the Gila Project. But, the rapid rate at which land was put into production in the early years of the District, the magnitude of the need to leach (“flush”) the naturally salty soils, the water application requirements made necessary by high temperatures and light soils, and the nature of the underlying aquifer itself made the return flow system essential in less than ten years after Colorado River water was first applied to the land.
Today, the Wellton-Mohawk Irrigation and Drainage District has control over the local groundwater table through a network of approximately 90 wells. The wells, at an average depth of about 100 feet, are equipped with 40 to 75 HP motors. After being removed from beneath crops, highly saline agricultural return flows are prevented from re-entering the aquifer by discharge into the concrete-lined Wellton-Mohawk Main Conveyance Channel that extends beyond the western limit of the District, to the Colorado River main channel, near Yuma.