BOARD00345

• Board Meeting Date: 11/19/2001
• Description: ISF Section - Proposed ISF Recommendations for 2002
• Board Meetings - Doc Type: Memo

Pitt et aI, August 2001. Replacing the Bypass Flow On '1'11(: Colorado River

Commission in 1972, and the subsequent passage of the Colorado River Basin Salinity Control
Act of 19745 (CRBSCA) were intended to address Mexico's concerns over rising salinity levels
in the Colorado.

Mexico's complaints about salinity in the Colorado' River started when extraordinarily high
volumes of salt were introduced to the river by agriculture in the Wellton-Mohawk Irrigation and
Drainage District. The Wellton-Mohawk Irrigation and Drainage District (WMIDD) is located
in Yuma County, Arizona along the Gila River valley. A division of the Gila Project, Wellton-
Mohawk is located 12 miles east of the city of Yuma and extends 45 miles into the Gila River
valley. Groundwater irrigation of the area began in 1906 and by 1934 many Wellton-Mohawk
wells were exhibiting excessive levels of salt and the water table had declined dramatically.
Many farms were abandoned until 1952 when the Bureau of Reclamation brought Colorado
River water to the area with the Gila project.6 Unfortunately, poor drainage throughout WMIDD
resulted in the mixing of irrigation wastewater with highly saline aquifer water. The brackish
groundwater eventually rose to the surface of the agri~ultural fields, killing thousands of acres of
crops and flooding basements. In order to mitigate these problems, the BOR installed an
elaborate tile drain system in the early 1960's, at a cost of$14 million.?

The saline drainwater (6300 ppm as compared to 700 ppm before WMIDD irrigated with
Colorado River water) was pumped into the Gila River near its confluence with the Colorado
River. Delivery of the drainwater to the Colorado Riyer resulted in overall increased salinity in
the River and extensive damage to agricultural fields downstream in the Mexicali Valley. In
1965, the US and Mexico adopted Minute 218 of the International Boundary and Water
Commission (IBWC) to reroute the saline Wellton-Mohawk drain water away from the Colorado
River mainstem, and into Mexico's Gulf of California via a newly constructed canal.s However,
an extension to this new canal, known as the Main Outlet Drain Extension (MODE),9 was built
with its terminus in a below sea-level depression in what formerly was the delta of the Colorado
River. Now that Wellton-Mohawk drainwater, known as the bypass flow, has flowed there for
several decades it has revived some of the delta's former ecosystem, and presently sustains the
Cienega de Santa Clara. At present the MODE delivers an annual average of 110,000 acre-feet
of water to the Cienega de Santa Clara.tO

The Clenega de Santa Clara
The introduction of Wellton-Mohawk's saline drainwater into the Cienega, de Santa Clara
reclaimed some of the Colorado River's delta. Before development upstream diminished the
Colorado River's flows in its southernmost reaches, the Colorado River delta was a vast,

s 43 U.S,C, ~ 1571 et sea,
6 U,S, Bureau of Reclamation, Gila Project webpage: < htto://dataweb,usbr.aov/htmllaila,html>. Colorado River
water was first delivered to Wellton-Mohawk fields in 1952 wit~ completion of the Gila Project in 1957,
7 U.S. Bureau of Reclamation, (1977), Colorado River Basin Salinity Control Project, Title I Division, Desalting
Complex Unit, Arizona, Status Report, p, 146.
s Full Text of Minute 218 can be found in U.s. Bureau of Reclamation, (1985), Colorado River Basin Salinity
Control Act Handbook, A-II-A-13.
9 The MODE is in facta sequence of canals known (from upstream down) as the Main Outlet Drain, the Main
Outlet Drain Extension, and the Bypass Extenstion,
10 International Boundary and Water Commission (1991-1998).'Westem Water Bulletin: Flow of the Colorado and
other Western Boundary Streams and Related Data. Department of State, USA. [published annually],

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