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

EXECUTIVE SUMMARY

Historically, the Colorado River fed one of the
greatest desert estuaries in the world. The
Colorado's delta consisted of vast riparian,
freshwater, brackish, and tidal wetlands that
covered 1,930,000 acres (780,000 ha) and
supported a legendary richness of plant, bird,
and marine life. Today, conditions are changed.
Decades of dam construction and water
diversions in the United States and Mexico have
reduced the delta to a remnant system of small
wetlands and brackish mudflats.

Recently, however, the delta has begun to
make a comeback. In the last two decades,
floodwater, releases from reservoirs in the
United States, agricultural return flows from
both countries, and municipal wastewater from
Mexico have proved beneficial. Although flood
flows are extremely unreliable and irregular,
and wastewater is high in salinity and pollut~
ants, this water has begun to restore some areas
of the delta. Current conditions have allowed
wetlands to flourish on about 150,000 acres
(60,000 ha).

The authors believe that key areas of the delta
might be saved through more efficient use of
water that now flows into the delta. This could
be accomplished without adverse effects on
other Colorado basin water users. While
demand for water by irrigators, cities, and other
important constituencies makes it unlikely that
a natural flow regime can be restored to the
delta, deliberate management of existing water
resources, such as agricultural drainage, waste-
water, and floodwater, could make a significant
difference. Although the delta's ecosystems

deserve greater consideration in the allocation
of Colorado River resources, the delta's mini-
mum requirements are surprisingly modest.

This report outlines the delta's natural and
cultural history, documents recent scientific
findings about the delta's partial recovery,
reviews its current political context, and makes
recommendations for securing, assuring, and
managing existing flows to further benefit and
sustain the delta's remnant wetland ecosystems.

The authors assessed habitat values in the
delta's vegetated riparian areas and wetlands,
and found relatively large areas of dense,
woody vegetation capable of supporting signifi-
cant bird populations. In addition, the authors
measured the quantity and rate of water flows
needed to sustain delta vegetation, and found
that annual flows of 32,000 acre-feet (4 x 107 m3),
supplemented by periodic (once every four
years on average) flood flows of 260,000
acre-feet (3.2 x 108 m3), should suffice. Research
documenting flows needed to support the
fisheries of the delta and the near-shore marine
environment of the Gulf of California has not
yet been conducted.

Finally, the authors outline recommendations
to manage existing flows for the benefit of delta
ecosystems; change international institutions
and agreements to support delta ecosystems;
establish market mechanisms and funding
sources for delta preservation; increase public
participation; conduct further research; and
implement site-specific restoration.

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