Bulletin 1.pdf - California Department of Water Resources - State of ...

WATER RESOURCES OF CALIFORXIA 645
acre-feet guaranteed by the treaty. This quantity, which may be made
up of any waters of the Colorado from any and all sources, whether
direct river flow, return flow, or seepage, will be delivered by the United
States in the boundary portion of the river, except that until 1980
Mexico may receive 500,000 acre-feet annually, and after that year
375,000 ·acre-feet annually, through the All-American Canal as part of
the guaranteed quantity. Davis Dam has been built by the United States
to provide regulation of flow required to meet commitments of the Mexican
treaty. The treaty provides that Mexico shall construct, at its expense,
a main diversion structure below the point where the northernmost part
of the international land boundary line intersects Colorado River. In
complying with this provision, the Mexican Government has constructed
Morelos Dam on Colorado River about five miles southwest of Yuma.
Since February, 1942, all water delivered to the Alamo Canal through
the Pilot K.nob Wasteway of the All-American Canal, plus water diverted
from the Colorado into the Alamo Canal, has been used in Mexico.
For the major part of its length between Hoover Dam and Havasu
Lake created by Parker Dam, the Colorado flows in well confined canyon
sections where there is little opportunity for meandering. There is, however,
an exception to this general topography immediately upstream from
Topock, where the river flows through an alluvial valley about 33 miles
long and from two to five miles wide. In years past the river has meandered
through this valley, with general aggradation of the valley floor.
.As a result, the river now spreads over almost the full width of the lower
half of this valley, forming a swamp through which water flows in a
number of small channels, with resulting heavy water losses. The United
States Bureau of Reclamation has a channel rectification project under
construction in this reach.
Natural Flow of Colorado River Above Gila River
Katural flow of Colorado River above Gila River was determined
by deducting recorded flow of Gila River at Dome from that of Colorado
River at Yuma, and correcting the resulting record for effects of upstream
regulation, diversion, and irrigation consumptive uses on the main Colorado
River and upstream tributaries. Records of flow of Colorado River
at Yuma and of Gila River at Dome are available for the entire period
from 1904-05 to 1947-48 used in the current study.
Regulation, diversions, and irrigation consumptive uses in the Upper
Basin of the Colorado were estimated as set forth in the discussion of the
natural flow at Lee Ferry. Similarly, impairments to natural flow of the
river in the Lower Basin were estimated by reaches above and below
Hoover Dam.
Irrigation diversions above Hoover Dam include those from the Virgin
and Little Colorado Rivers, and Kanab Creek. Available records from
the Bureau of Censns were used to estimate annual irrigated acreage
segregated by stream systems. These acreages were then multiplied by
estimated unit values of seasonal consumptive use, which were computed
separately for each stream system.
Diversions from the Colorado below Hoover Dam are mainly for
irrigation. Records are available covering practically the entire period
during which these diversions have been made. Consumptive use was
estimated for the few periods or diversions for which no records were