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Imperial Dam

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Imperial DamImperial Dam, located about 20 miles north of Yuma, Arizona, is a diversion structure for the river, All-American Canal and Gila Canal water deliveries, serving southeastern California, Arizona and Mexico. The operations of IID's River Division Office at Imperial Dam, as well as system wide water distribution, all fall under the direction of the United States Bureau of Reclamation. Water diverted at Imperial Dam for use in the Imperial Valley first passes through one of three desilting basins, used to remove silt and clarify the water. Each desilting basin is 540 feet wide by 770 feet long and is equipped with 72 scrapers designed to remove 70,000 tons of silt per day. The silt is returned to the river by means of six sludge return pipes that deposit the silt into the California Sluiceway. From the desilting basins, water is then delivered to the Imperial Valley through the All-American Canal.


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 Imperial Irrigation District 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.


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 at 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.


The Imperial Dam, Gila Headworks, All-American Canal Works and the All-American Canal are operated and maintained by IID with costs shared by the Bureau of Reclamation and the California and Arizona water agencies served.

Facts about Imperial Dam

Imperial Dam



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

3,485 feet

Overflow Weir Section:



1,197 feet


(From base to crest at 181 feet elevation)

31 feet

Operating Bridges over Non-Overflow Section:



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


Three desilting basins:



770 feet



540 feet


72 scrapers

125 feet in diameter


Flow Capacity

4,000 c.f.s each


Design Sediment Removal Capacity

70,000 tons/day

Costs (at time of construction):


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

(approx.) $3,000,000


All-American Canal Headworks



All-American Canal Desilting Basins


Gila Headworks and Desilting Basins


Total cost of works

$10,000,000 to $11,000,000