International Commission on Irrigation & Drainage Commission Interationale des Irrigation et du Drainage



World Heritage Irrigation Structures

Alamo Irrigation System


The project consisted of the construction of a controlled, gravity-fed irrigation system within the Colorado River basin.  The River is a principal river (2,330 km in length) of the Southwestern United States and northern Mexico.  The project constructed a new water channel and control structures: the Alamo Canal (1900), the Hanlon Heading (1906), and the Rockwood Gates (1918). The canal project and temporary gates were constructed by the California Development Company (CDC) to divert water from the Colorado River to irrigate the Imperial Valley in a controlled and reliable manner, while the existing structures were constructed by the Imperial Irrigation District.  The project construction encompassed two countries- the US and Mexico.

Water was channelled via gravity flow, from a site in the US at Pilot Knob, in Southern California, and through a newly constructed 23-kilometer Alamo Canal that crossed south of the border into Mexico, and ran parallel to the Colorado River for approximately 6 km before connecting westerly to the Mexican Arroyo Alamo (a dry river bed).  The Arroyo Alamo bed was cleared out, enlarged, for connection by the new Alamo Canal.  At a point about 67.5 km west of the Colorado River, the canal moved northward, across the US/Mexico boundary line again, and into California.   

The channel worked fine for the first couple of years, but the lack of a solid structural heading and reliance on an 18 meter-wide, 1005 m-long cut through the alluvial fill in Mexico (without a control gate), proved catastrophic. There had also been a little experience in the handling of the heavily silt-laden waters of the Colorado River which posed numerous challenges. The Colorado River has one of the greatest percentages of silt contents of any river in the world. Silt build-up, coupled with flood seasons caused major damage to early farm operations. Following the flood season, the increased elevation of the bed of the intake channel (due to this heavy silt deposit), made it difficult during low stages of river flow to divert sufficient water to meet irrigation demands, resulting in water shortages during the winters of 1902-03 and 1903-04.

In the winter of 1905, there were five floods, prompting attempts by the CDC's engineers to close the cut and construct a control gate. Attempts to build dams were washed away, and the cut widened to 46 meters. The Colorado River began to eat away at the banks of the cut to a point in which it had grown to 823 meters wide and resulted in major flooding.  The Hanlon Heading was built at Pilot Knob to channel and control water from the Colorado River to combat these impacts.  The heading also incorporated a built-on railway used to haul rock south into Mexico to seal the breach at the Lower Mexican intake that had failed. The Hanlon Heading gates had powerful lifting apparatus that made it possible to be operated by hand.  Water was first admitted through the Hanlon gate and into the Alamo Canal after the closing of the [Lower Mexican] intake in November of 1905.

Although the Hanlon Heading alleviated some of the silt challenges, the ultimate design and incorporation of the Rockwood Gate completed in 1918 became inevitable. Rockwood Heading was constructed in the bank of the River, 2 km upstream from Hanlon Heading. The structure was designed as a long overpour weir, over 213 m in length, and constructed parallel to the flow of the River to assist with diversion during extremely low flows in the River by drawing from the surface flow and reducing the amount of silt entering the Alamo Canal.  The project was operational and effective through 1942 at which time it was replaced with an “all-American” route. The reroute was necessary to avoid conflicts resulting from the Mexican Revolution, which made canal operations difficult in Mexico.  By then, the irrigation system in the Imperial Valley was well established with over 128 km of main canals and over 1,127 km of distribution canals.  

Structure Description and Salient Features

The Alamo Irrigation System consisted of the construction of the Alamo Canal (1900), the Hanlon Heading (1906), and the Rockwood Gates (1918), by the California Development Company and the Imperial Irrigation District.  The purpose of the project was to provide irrigation to the Imperial Valley in the US from the Colorado River.  The River is a principal river (2,330 km in length) of the Southwestern United States and northern Mexico.  The irrigation project channelled water from a site in the US (at Pilot Knob), through a newly constructed 23-kilometer Alamo Canal that crossed south of the border into Mexico and ran parallel to the Colorado River, for approximately 6 km, before connecting westerly to the Mexican Arroyo Alamo.  The Arroyo Alamo was a dry river bed which drained northerly, ultimately reaching the Imperial Valley via gravity-fed flow. 

The Pilot Knob site was selected for the headings and gates due to the availability of solid rock foundation and to avoid the Algodones Dunes.  Hanlon Heading is a massive steel and cement gate structure built on the solid rock foundation, of reinforced concrete, having 11 culverts (3.05 m high and 3.66 m wide), being separated by 45.7 cm thick walls. The floor is 29 m above sea level and 1.5 m below the bed of the River. The gates are of "Taintor" type, having radial arms of steel. Instead of sliding in vertical grooves, they revolved for a portion of a circle about a horizontal shaft placed behind them with 4.3 m radius.  The pressure of the water against the gate was transmitted to the turning point on the shaft, thus the lifting apparatus was powerful and operated by hand. The structure has a height of 3.66 meters above the culverts that held back high water and provided room for the gates when they were raised with a flow capacity in excess of 10,000 cubic feet per second. A railroad spur was also constructed across the heading structure by the Southern Pacific Railroad to haul rock into Mexico.

A second heading, Rockwood Heading, was constructed in the bank of the River, 2 km upstream from Hanlon Heading to assist with diversion during extremely low flows in the River and the increased bed elevation from the excessive silt deposits of the River (the River has one of the highest silt content percentages of any river in the world). The structure was designed as a long overpour weir, over 213 m in length and constructed parallel to the flow of the River with 75 openings, each about 2 m wide, through which water entered the Alamo Canal.  Water was controlled by flashboards placed in grooves in the gates. The sills of the upstream 27 gates were 2.4 m lower than the remainder, to assist diversion during extremely low flows by continuing to draw from surface flow, reducing the amount of silt entering the Canal. The project transmitted River water to the Imperial Valley connecting to over 128 km of main canals and over 1,127 km of distribution canals.

Project System and Heritage Composition

The Alamo Irrigation System diverted water from the Colorado River (a principal river, spanning 2,330 km in length, of the Southwestern United States and northern Mexico) into two barren valleys within each respective country.  The US-based California Development Company (CDC) constructed the project to channel water for irrigation to southern California, Imperial Valley and by convenience also benefitted the Mexicali Valley in Mexico. The project physically extended into and benefited both nations.  Both the Imperial and Mexicali Valleys were perceived as untameable, flood-prone desert deltas before the project. The project-initiated settlement increased food production to exceptional levels and created thriving agricultural economies in both valleys.  Originally designed on geographic conditions, it was ultimately constructed with special attention to the environmental aspects of the time.   

In the late 18th Century, the project area remained almost completely unpopulated, mostly due to its harsh climate.  The Imperial Valley is one of the most arid sections of the US, with annual rainfall averaging approximately 75 mm, and in some years amounting to less than 12.5 mm.  The intense summer heat has maximum temperatures in excess of 37.8 °C for more than 110 days out of the year.  The nearest water source was the Colorado River located approximately 60 km east, beyond the Algodones Dunes.  The Dunes constituted a challenge in channelling water from the River due to the broad erg between the two.  The Dunes are approximately 72 km long by 9.7 km wide, covered with wind-swept sand with little or no vegetation.  Thus, an alternate route was pursued by the CDC to build a canal from a point in the US, travelling south, into Mexico, and connecting westerly to the dry Arroyo Alamo that drained at a northwest orientation (in the direction of the Imperial Valley/Salton Sink).  The strategy to route the channel into Mexico and back to the US, by making use of an existing natural drain route, was perceived as the fastest, least expensive and most practical option, given the existing terrain. 

In 1900, the CDC constructed the Alamo Canal from Pilot Knob, on the US side, and with the authorization of the Mexican government-connected it to the Arroyo Alamo in Mexico.  The CDC was able to clear the Arroyo Alamo bed, enlarge it, and at a point about 67.5 km west of the Colorado River, they carried their canal northward, across the US/Mexico boundary line again, into California.  The CDC utilized most of the Alamo River (US Territory) as a part of their initial irrigation system and the first waters were brought into the Imperial Valley in 1901.  The channel worked fine for the first couple of years but due to siltation issues required the construction of the Hanlon Heading and Rockwood Gates which served as a long overpour weir.  The Imperial Valley prospered at unprecedented rates.   Irrigated acreage in the Valley had increased from 1,500 acres in 1901 to 80,000 acres by 1905. Over 128 km of main canals had been constructed in the Imperial and Mexicali Valleys belonging to the CDC and the Mexican Company (a Mexican corporation that had been formed by the CDC in 1898).  An additional 1,127 km of distribution canals in Imperial Valley were also in place by 1905.  Irrigated acreage in the Imperial Valley had increased to 220,000 acres by 1911.   It is believed that this record constitutes the most rapid development of any reclamation project in the western United States.

The 1911/1912 Mexican Revolution made normal canal operations impossible and so the planning and eventual construction of a re-route for an “all-American” canal were initiated by the Imperial Irrigation District which had bought out the CDC.  The Alamo Canal and all of its structures were sold in 1961 after the 1942 construction of the All-American Canal that ran parallel to the US/Mexico border on US property.  An environmental cost is that south of the All-American Canal, the Colorado River no longer flows above ground at all for much of the year into Mexico. Under a 1944 Water Treaty, however, Mexicali is "...guaranteed [an] annual quantity of 1,500,000 acre-feet (1.9 km) [of water] to be delivered..." from the Colorado River.

The unsurpassed, progressive impact of the project to the agricultural economies of the two countries is noteworthy. Today, the Imperial Irrigation District manages over 2,575 km of canals and laterals which deliver water to approximately 4,700 delivery gates serving the 479,000 acres of farmland within the Imperial Valley. The mild winter season and year-round water supply means that the area is always in production, with most fields being double or triple-cropped. The total irrigated crop acreage as of 2017 was 455,461 acres and the area (including an additional 22,401 acres just outside the valley) had gross agricultural production of $2,065,600,000 for the same calendar year.  Imperial Valley produces over 100 different types of crops.  

According to the California Department of Food and Agriculture, Imperial County was the sole producer of sugar beets; #1 producer of alfalfa hay, onions, wheat, sweet corn, alfalfa seed, and Sudan hay; and among the top five producers of cattle/calves, lettuce, broccoli, carrots, celery, cauliflower, spinach, potatoes, cantaloupes, watermelon, sheep/lambs, salad greens, grapefruit, dates and honeydew melons. Today, the Imperial Valley produces 80% of the country’s winter vegetables and agriculture is the largest industry in the Valley accounting for 48% of all employment.

The Mexicali Valley also prospered significantly, becoming one of the largest fertile valleys in Mexico with a current population reaching one million (over five times the size of the Imperial Valley).   There are over fifty different crops produced in the Mexicali Valley.  Although mostly producing wheat, cotton and vegetables, Mexicali is one of Mexico's most important exporter of asparagus, broccoli, carrots, green onions, lettuce, peas, peppers, radishes and tomatoes to the world.

Benefits

ENUMERATED BENEFITS

1900

1910

1925

1950

2000

 

Prior to Project

10 Yrs After Project

25 Yrs After Project

50 Yrs After Project

100 Yrs After Project

Crop Varieties Harvested

0

5

25

41

93

Livestock Industries

0

0

6

6

3

Irrigated Acres

0

200,000 Acres

515,000 Acres

612,658 Acres

521,359 Acres

Domestic Population Served (Imperial Valley) ²

0

12,591

50,000

61,175

143,361

   

 

 

 

 

Agricultural Gross Value¹

$0

 

 

 $ 105,936,224

 $ 919,610,000

Agricultural Sales¹

$0

 

 

 

 $ 1,410,748,000

           

¹Imperial County Board of Trade (Imperial County Agricultural Commissioner)

     

²US Decennial Census (1925 is an estimate)

     

 

Present State of Conservation

In the late 1800’s a Canadian Engineer became associated with the California Development Company to build a canal from Pilot Knot in the southwestern United States into and out of Mexico, and eventually channel water into the Imperial Valley of Southern California.    There are several factors that affected the Alamo Canal Irrigation System throughout the years, inclusive of multiple incidents of severe flooding and the unpredictability of the Mexican government resulting in adverse impacts on system operations.  Listed below are some of the enumerated factors that have affected the Alamo Canal Irrigation System: 

1900       California Development Company builds the Alamo Canal from Pilot Knob, USA, into and out of Mexico and into the Imperial Valley. The 23-kilometer canal was built to connect to a dry riverbed that drained northerly and naturally flowed during pre-historic times to the Salton Sink, a geographic sink in the Imperial Valley within the Salton Trough in southeastern California. 

1901       An intake channel, slightly less than a kilometer in length on the US side, diverted water from the Colorado River to the newly constructed Alamo Canal and the first waters flow into the Imperial Valley via the Alamo Canal irrigation system in 1901.  A control gate was not constructed at that time because plan approvals by Mexican engineers would not be approved and instead a 1,005-meter cut through alluvial fill was used to divert water from the Colorado River and into the Alamo Canal.

1902       Intake siltation between 1902 and 1904 created considerable quantities of “bedload” that made it difficult during low river flow to divert sufficient water to meet irrigation demands in the Imperial Valley. In percentage of silt, the Colorado River has one of the greatest silt contents of any river in the world.  For two winters water shortages occurred due to the built-up siltation and a second intake was excavated.

1903       A by-pass was cut around the wood gate structure to increase diversions to meet the irrigation demands.

1904       A third intake was temporarily opened immediately south of the international border, the Lower Mexican Intake, but siltation levels had substantially raised the canal bottom.  Another channel 18 meters wide and also 1,005 meters in length was temporarily constructed.

1905       The winter of 1904-1905 experienced five major flooding events for three years that broke through the channel, widening from 18 meters to 46 meters, and devastated settlements in the Imperial Valley including some farm operations and caused what is known today as the Salton Sea.  Although the Sea naturally existed for millions of years as a result of natural flows from the Colorado River, it was a dry sink at the time. The Salton Sea is a shallow, saline, endorheic rift lake in California’s Imperial and Coachella valleys.  

1906       The permanent concrete headgates at Hanlon Heading were completed in 1906. The original gate which controlled the flow from the Colorado River into the canal had 11 gate openings each 3.6 meters wide and 3 meters high.  Whether by poor design or heavy silt deposits, the gate ended up being 1.5 meters above the Colorado River much of the time. A weir (a floating mass of brush creating an artificial sandbar) was built just beyond the gate that elevated the river level enough to cause its flow into the irrigation canal. This was only a temporary solution, however. Meanwhile, silt was building up in the canal.

1906       A series of attempts to control the Colorado River were made. Dams were built, but the river flooded over them. Plans were made to install gates, so the cut could be fixed during a low water period, but the low water period did not come. The cut in the river had grown to 823 meters wide. A series of three dams built in October and November of 1906 brought the river back to its old pattern, away from the Salton Sea, but these were also washed away in December 1906 as the Gila River overflowed into Colorado near Yuma, sending its water flooding into the Imperial Valley again.

1907       Rock dams hauled in by the Southern Pacific (Railroad) Company were used for the second and successful closure.  February 11, 1907, was the date the Colorado River began flowing back towards the Gulf of Mexico.

Damages from the break:

  • Erosion of the New River and Alamo Rivers destroyed an estimated 13,000 acres of irrigable land in the Imperial Valley.
  • The Salton Sea, which had been practically dry had gone from 83 meters below sea level to 59 meters below sea level and a surface area of about 805 square kilometers by the time the break was closed.
  • Destruction of two flumes over the New River resulted in over 12,000 acres under cultivation no longer able to receive water services.
  • Southern Pacific (Railroad) Company lost several rail lines.

Benefits from the break:

  • The New River and the Alamo River channels became the main drainage outlets to the Salton Sea for the extensive drainage system that was later to be constructed.
  • While the 1905 break was a bitter and costly experience, the knowledge gained from it and the realization of the need for a levee system, perhaps saved Imperial Valley from a far worse disaster at a later time through the River diverting itself into the Valley.

1910       A rock weir was constructed in 1910 with a railroad placed on top of a trestle from which the rock was dumped until the Colorado River level was raised about .75 meters.

1910       The Mexican Revolution during 1910/1911 caused operational challenges in the irrigation system.

1911       The Imperial Valley farmers formed the Imperial Irrigation District and provided directive on a new “All-American Route” to replace the Alamo Canal.

1914       Improvements to the canal system were made on US side via the construction of the East Highline Canal for a length of approximately 80 kilometers from the Alamo Canal in Mexico and northward providing service to some 110,000 acres on the easterly side of the Imperial Valley.

1915       There were over 400,000 acres of land being Irrigated in the Imperial Valley by 1915. The Imperial Irrigations’ total district boundaries reached 584,068 acres.

1916       The Imperial Irrigation District purchased all the ex-California Development
Company assets
from Southern Pacific and assumed operation of the Alamo Canal, and Hanlon Heading on the US and through the formation of a Mexican company also purchased assets in Mexico.

1918       Rockwood Gates were constructed on the US Pilot Knob area, 2 kilometers north of Hanlon Heading, to assist with the diversion during extremely low flows from the Colorado River and the increased bed elevation from the excessive silt deposits.  The structure was over 213 meters in length and parallel to the flow of the Colorado River.

1930       By 1930 the Imperial Irrigation System had constructed over 119 kilometers of a protective levee system in the District of Mexico having used over 611,643 cubic meters of rock.

1935       The Colorado Hoover Dam was put into operation on the United States Side providing greater control of water flows. Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Nevada and Arizona.

1941       The All-American Canal construction was completed in 1941 by the IID.  The All-American Canal runs parallel to the US/Mexico border, entirely on US property.

1961       The Alamo Canal and all of its structures on Mexico territory were sold in 1961, however, the Hanlon Heading and Rockwood gates remain is US control, albeit not in an operational status.

HIGHLIGHTS

Country: USA

Province: California

Latitude : 32.72 Longitude : -114.72

Built: 1900

River: Colorado River

Basin: Colorado River Basin

Irrigated Area: 479000 acres (193844.423 Ha)

RECOGNIZED AT:

70th IEC Meeting, Bali, Indonesia, 2019

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