WSP12647 ‎(2)‎

• File Number: 8282.400
• Description: Colorado River Operations and Accounting - Deliveries to Mexico
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/1/1999
• Author: Environmental Defense Fund
• Title: A Delta Once More - Restoring Riparian and Wetland Habitat in the Colorado River Delta - Environmental Defense Fund - 06-01-99
• Water Supply Pro - Doc Type: Report/Study

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ENVHZONA1ENTAL DEFENSE fUND

TIDES AND FLOODS

Two sources of water-tides and floods-continue to
sustain parts of the delta much as they have for
centuries. Tides are a daily given in the delta, and the
topography of the long and narrow Gulf creates an
exceptionally high tidal swing of 10 feet (3 m) or greater
at its northern end. This allows high tides to flow more
than 34 miles (56 km) inland in some places (Glenn et
aI., 1996) and spread over a total of 81,500 acres (33,000
ha) (Thompson et aI., 1968). Tides have sustained vast
areas of the delta through the last several decades,
although without freshwater flows to dilute the seawa-
ter, tides can have a deleterious effect as well.

Since 1980, floods have once again reached the delta,
though they are no longer a guaranteed springtime
occurrence as they once were. The Colorado's system
of dams can regulate much of the variation between wet
and dry years, but extraordinarily wet years will
probably continue to bring flooding to the delta when
releases exceed the capacity of users in the United States

and Mexico to divert the water. Since the filling of the
Colorado River's reservoirs, these releases have
reestablished an active floodplain from Morelos Dam
to the tidal zone in the Gulf of California.

Near-record flood releases in the winter of 1983 were at
first considered an aberrant event, but occasional
flooding has continued, coinciding with El NiTIO events
(Glenn et aI., 1996). From 1980 to 1993, average annual
flood flows across the border (cross-border flows
minus Mexico's treaty allotment) were 3.9 maf
(4.8 x 109 m3). This is nearly three times Mexico's
1.5 maf (1.8 x 109 m3) treaty allotment, and 25 percent of
the historic flow into the delta before dam construction
(Glenn et aI., 1996). The largest releases occurred in the
early 1980's, with flows after 1986 more sporadic and
smaller in volume. In 1997-1998, flows exceeding 1.5
maf (1.8 x 109 m3) were released to the delta (Glenn et
aI., 1999).25 [SeeFigure4.]

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