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Imperial DamLocated about 20 miles northeast of Yuma, Arizona, Imperial Dam is the diversion point for water flowing from the Colorado River to the All-American Canal, which serves Imperial and Coachella Valleys. Imperial Dam was a first for the world of irrigation, where river water would be held and then diverted into a giant desilting plant before being released into the All-American Canal.


Background

Construction of Imperial Dam and its desilting works began in 1935 and was completed in 1938 under the authorization of the Boulder Canyon Project Act of 1928. Imperial Dam's main function is diversion of Colorado River water to the All-American Canal, the Coachella Canal, the Yuma Project and the Gila Gravity Canal.

The need for Imperial Dam as a diversion point dates back to the mid-1850s when settlers began searching for the means and the location to divert Colorado River water to the Imperial Valley.

Colorado River water was first delivered to the Imperial Valley through the Imperial (Alamo) Canal in June 1901. George Chaffey, president of the California Development Company, constructed headworks and a canal to take water from the Colorado River at a point in California immediately above the international boundary. The river headgate, known as the Chaffey Gate, was constructed as a temporary wooden gate on the intake canal about 500 feet north of the international boundary to control inflow of water into the canal.

A more permanent headgate, known as Hanlon Heading, was constructed in 1906 to replace Chaffey Gate. The following year, Southern Pacific Company assumed ownership of the bankrupt California Development Company. The Imperial Irrigation District was formed in 1911 and by 1916 had acquired all California Development assets.

There was a growing realization that an all American canal, located entirely within the United States, was needed. The first field survey for the canal was conducted in 1913. However, the Bureau of Reclamation reported that such a canal would be impractical without a dam to control flooding. In the meantime, the IID found it increasingly difficult to control the amount of bedload silt brought into the canal system from the Alamo River. So, in 1918 the Rockwood Heading was built one and one-fourth miles upstream from Hanlon Heading to serve as a diversion point and a desilting works.

As part of a 1918 contract with the federal government, IID received the right to use Laguna Dam (completed in 1909 under the Federal Reclamation Act) as a diversion for the All-American Canal. But that right was never exercised. In 1919, the bureau issued its recommendation for an All-American canal and the government construction of a storage reservoir on the Colorado River.

The final result of the negotiations with the Bureau of Reclamation was the Boulder Canyon Project Act in 1928, which authorized construction of Boulder (Hoover) Dam, Imperial Dam and the All-American Canal.

Today, the storage capacity of the reservoir above Imperial Dam is minor. Due to its shallow depth, the original storage space was soon filled with silt and sand. The reservoir area now consists of a shallow lake with well-defined channels to the All-American Canal and Gila Headworks.

Structures

Imperial Dam straddles the California-Arizona border. The All-American Canal trashrack and headgates are located adjacent to the California abutment of the dam. Three desilting basins (design capacity 4,000 cubic feet per second each) remove the sand and silt from the river water before it passes to the All-American Canal. The sand and silt removed are continuously returned to the river through the California Sluiceway Channel.

The Gila Canal Headgates are located adjacent to the Arizona abutment of the dam. One desilting basin removes the sand from the water before it enters the Gila Gravity Main Canal, which serves the Yuma area. The sediment removed is returned to the river when necessary by opening the sluiceway gates located on the bottom and downstream end of the basin. The basin will handle a flow of 2,200 cfs.

Operation

The Imperial Dam, Gila Headworks, All-American Canal Works and the All-American Canal are operated and maintained by the IID with costs shared by the Bureau of Reclamation, Coachella Valley Water District, Yuma County Water Users and other water users.

Facts about Imperial Dam

Imperial Dam

Dimensions:

 

Overall length
(Including a 490-foot dike at the Arizona end)

3,485 feet

Overflow Weir Section:

 

Length

1,197 feet

 

Height
(From base to crest at 181 feet elevation)

31 feet

Operating Bridges over Non-Overflow Section:

 

Elevation

197 feet

 

Freeboard above crest of maximum calculated flood

6 feet

 

Maximum calculated flood over weir

10 feet

Maximum Diversion Capacities:

 

All-American Canal

15,155 c.f.s

 

Gila Canal

2,200 c.f.s

Type Construction:

Reinforced concrete slab and buttress type

Desilting

Three desilting basins:

 

Length

770 feet

 

Width

540 feet

 

72 scrapers

125 feet in diameter

 

Flow Capacity

4,000 c.f.s each

 

Sediment Removal Capacity

70,000 tons/day

Costs:

 

Imperial Dam
(Includes Arizona and California abutments, California sluiceway and overflow weir.)

(approx.) $3,000,000

 

All-American Canal Headworks

$1,300,000

 

All-American Canal Desilting Basins

$4,000,000

Gila Headworks and Desilting Basins

$2,000,000

Total cost of works

$10 to $11,000

Last updated: 9/17/2010 11:27:56 AM