WSP12636

• File Number: 8282.300
• Description: Colorado River Operations and Accounting - Lower Basin Administrative Procedures
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 8/1/1996
• Author: DOI-BOR
• Title: Description and Assessment of Operations-Maintenance and Sensitive Species of the Lower Colorado River - Volume II - Appendices-Etc - 08-01-96
• Water Supply Pro - Doc Type: Report/Study

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The filling of Lake Powell occurred from 1963 through 1980, during which time all releases
of water in the lower Colorado River system were in response to downstream demands and
other consumptive uses.

Morelos Dam - Morelos Dam is located approximately 9 miles southwest of Yuma, Arizona.
Morelos Dam was constructed by Mexico beginning in late 1948 and was officially
operational on November 8, 1950. Its construction was authorized under Article 12 of the
Mexican Water Treaty of 1944 to provide a diversion for the delivery of Colorado River
water to the Mexicali Valley.

Minute 242 (Minutes are defined as decisions of IBWC and signed by the Mexican and
United States commissioners) of IBWC and the Mexican Water Treaty of 1944 provide
requirements for deliveries at the NIB and SIB near Yuma and San Luis, Arizona,
respectively. Up to 140,000 acre-feet annually of agricultural drainage water can be
delivered to Mexico at the SIB. The remaining 1,360,000 acre-feet of water is to be
delivered to Mexico at the NIB annually and diverted at Morelos Dam to the Mexicali
Valley. For several years after the United States Bypass Drain was completed in 1978, the
Colorado River Channel downstream of Morelos Dam was normally dry. Flows below
Morelos Dam now occur only when water in excess of Mexico's requirements arrive at the
NIB. Recently, however, various wet open areas occur along the channel below Morelos
Dam. Apparently scouring into the ground water table has resulted from flood flows which
were passed below Morelos Dam several times since 1978. The area now supports extensive
stands of riparian woodland vegetation and a number of areas of cattail marsh (Werner pers.
comm. 1996)

Water in excess of Mexico's water order at the NIB is normally passed through
Morelos Dam, through, the Limitrophe Division, and into the original Colorado River
Channel downstream. Water in excess of Mexico's water order occurs when surplus or flood
releases are made from either the Colorado River system or the Gila River system. Excess
water arriving at Mexico may also result from sidewash inflows that occur above or below
Imperial Dam; from a sudden drop in water user demand; or when insufficient storage is
available in Senator Wash, Imperial or Laguna reservoirs.

Flows arriving at Morelos Dam normally range from about 900 cfs to over 3,000 cfs during
the year. During 1983, flows in excess of 40,000 cfs arrived at the NIB due to flood control
releases on the Colorado River, and in 1993 flows in excess of 25,000 cfs arrived at the NIB
due to flooding on the Gila River.

Mexico is responsible for the operation and maintenance of Morelos Dam and associated
expenses. Gaging stations are provided and operated by the United States on the
Colorado River at Yuma, at the NIB, 4 miles downstream of the NIB, and at the SIB. The
United States provides monthly ground-water elevations for lands in the United States above
and below Morelos Dam as well as a silt sampling station at Yuma, Arizona. Mexico is
required to provide river gauges immediately upstream and downstream of Morelos Dam;

Appendix D - 5