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The Colorado River
Colorado River
Delta is the region where the Colorado River
Colorado River
flows into the Gulf of California
Gulf of California
(also known as the Sea of Cortez). The delta is part of a larger geologic region called the Salton Trough.[1] Historically, the interaction of the river’s flow and the ocean’s tide created a dynamic environment, supporting freshwater, brackish, and saltwater species. Within the delta region, the river split into multiple braided channels and formed complex estuary and terrestrial ecosystems. Use of water upstream and the accompanying reduction of fresh water flow has resulted in loss of most of the wetlands of the area, as well as drastic changes to the aquatic ecosystems. However, a scheme is currently in place which aims to rejuvenate the wetlands by releasing a pulse of water down the river delta.[2]

Contents

1 Natural history 2 Human history

2.1 Early history 2.2 After dam construction 2.3 High flows in 1980s

3 Ecology 4 Biosphere
Biosphere
reserve 5 View 6 References 7 External links

Natural history[edit]

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Until the early 20th century, the Colorado River
Colorado River
ran free from its headwaters in the Rocky Mountains
Rocky Mountains
of Colorado
Colorado
southwest into Mexico, where it flowed into the Gulf of California. Significant quantities of nourishing silt from throughout the Colorado River
Colorado River
Basin were carried downstream, creating the vast Colorado River
Colorado River
Delta. Prior to the construction of major dams along its route, the Colorado River fed one of the largest desert estuaries in the world. Spread across the northernmost end of the Gulf of California, the Colorado River delta’s vast riparian, freshwater, brackish, and tidal wetlands once covered 7,810 km² (1,930,000 acres) and supported a large population of plant, bird, aquatic, and terrestrial life. Because most of the river’s flow reached the delta at that time, its freshwater, silt, and nutrients helped create and sustain a complex system of estuarial wetlands that provided feeding and nesting grounds for birds, and spawning habitat for fish and marine mammals. In contrast to the surrounding Sonoran Desert, the Colorado
Colorado
River delta’s abundance was striking. Human history[edit] Early history[edit] Early explorers reported jaguars, beavers, deer, and coyotes in the delta, in addition to the abundance of waterfowl, fish, and other marine and estuary organisms (Spamer, 1990; Aldo Leopold, 1948 ). Early explorers also encountered local people known as the Cucapá, or the people of the river. The Cucapá are descendants of the Yuman-speaking Native Indigenous peoples of the Americas
Indigenous peoples of the Americas
and have inhabited the delta for nearly a thousand years. Spanish explorer Hernando de Alarcón made the first recorded contact with the Cucapá in 1540 and reported seeing many thousands. The Cucapá used the delta floodplain extensively, for harvesting Palmer’s saltgrass (Distichlis palmeri), a wild grain which grows in salty soil; and for cultivating maize (corn), beans, and squash.

On the map the Delta was bisected by the river, but in fact the river was nowhere and everywhere, for he could not decide which of a hundred green lagoons offered the most pleasant and least speedy path to the Gulf.

--Aldo Leopold, from A Sand County Almanac, describing the Colorado River Delta as it existed in 1922

After dam construction[edit] Today, conditions in the delta have changed. Like other desert river deltas, such as the Nile Delta
Nile Delta
and the Indus River Delta, the Colorado River delta
River delta
has been greatly altered by human activity. Decades of dam construction and water diversions in the United States and Mexico
Mexico
has reduced the delta to a remnant system of small wetlands and brackish mudflats.[3] As reservoirs filled behind dams and captured floodwaters, freshwater could no longer reach the delta. The construction of Hoover Dam
Dam
in the 1930s marked the beginning of the modern era for the Colorado River
Colorado River
Delta. For six years, as Lake Mead filled behind the dam, virtually no freshwater reached the delta. Even spring flooding was captured. This ecologically devastating event was repeated from 1963 to 1981 as Lake Powell
Lake Powell
filled behind the Glen Canyon Dam. With these reservoirs now filled, the dams are used to regulate flow so that water can be reliably apportioned among the users of the Colorado River
Colorado River
Compact, and its use maximized. Most flood flows can be contained, regulated, and added to the river’s capacity to sustain the Western United States' urban centers and agriculture. Floodwaters are released only when the Bureau of Reclamation, the agency managing the dams, predicts flows that exceed the system’s capacity for use and storage. The loss of freshwater flows to the delta over the twentieth century has reduced delta wetlands to about 5 percent of their original extent, and nonnative species have compromised the ecological health of much of what remains. Stress on ecosystems has allowed invasive plants to out-compete native species along Colorado River
Colorado River
riparian areas. Native forests of cottonwood and willow have yielded to sand and mudflats dominated by the nonnative tamarisk (also known as salt cedar), arrowweed, and iodinebush, a transformation that has decreased the habitat value of the riparian forest (Briggs and Cornelius, 1997). High flows in 1980s[edit] Full reservoir conditions coupled with a series of flood events throughout the 1980s and early 1990s resulted in flood releases that reached the delta. These flows reestablished an active floodplain and revegetated many areas of the floodplain within irrigation and flood control levels, and helped to reestablish riparian forests. Ecology[edit] The delta supports a variety of wildlife, including several threatened and endangered species. Mexico’s Environmental Regulations on Endangered Species lists the following endangered species found in the terrestrial and aquatic regions of the delta (Diario Officiel, 1994):

the desert pupfish, also listed as an endangered species in the U.S., the largest remaining population anywhere is in La Ciénega de Santa Clara the Yuma rail, also listed as endangered in the U.S. the bobcat the vaquita porpoise, the world's smallest marine cetacean, listed as a species of special concern by the U.S. Marine Mammal Commission. There are thought to be less than 250 vaquita left in the world. the totoaba, now virtually extinct, a steel-blue fish that grows up to 2 m (7 ft) and 136 kg (300 pounds), and once supported a commercial fishery that closed in 1975 (Postel et al., n.d.). the Colorado
Colorado
delta clam, once an extremely abundant species and important in the trophic dynamics of the ecosystem.

Although not extensively studied, the delta’s significance for migratory birds is indisputable, as it is the principal freshwater marsh in the region. A total of 358 bird species have been documented in the Colorado River
Colorado River
Delta and upper Gulf of California
Gulf of California
region. From these, two are listed as endangered, six as threatened, and sixteen are under special protection in Mexico. Two wintering species and five breeding species have been locally extirpated, including the southwestern willow flycatcher, the Fulvous whistling duck, and the sandhill crane. Biosphere
Biosphere
reserve[edit] The Gulf of California
Gulf of California
lies within the jurisdictional boundaries of Mexico
Mexico
and its states of Baja California
Baja California
and Sonora. In 1974, the Mexican government designated portions of the upper Gulf and lower Colorado River
Colorado River
Delta as a reserve zone. The United Nations Educational, Scientific and Cultural Organisation (UNESCO) designated over 12,000 km² (3 million acres) of Upper Gulf of California
Gulf of California
and Colorado River
Colorado River
Delta Biosphere
Biosphere
Reserve as a Biosphere
Biosphere
Nature reserve
Nature reserve
in June 1993. Within this 12,000 km² (3 million acres), over 4,000 km² (1 million acres) nearest the Colorado River
Colorado River
Delta are designated as the Reserve “core area”, with the remaining 8,000 km² (2 million acres) of open water and shoreline designated as a “buffer area”.[4] UNESCO considers areas for designation as Biosphere
Biosphere
Reserves only after the nation in which the site is located submits a nomination. Once designated, Biosphere
Biosphere
Reserves remain under the sovereign jurisdiction of the countries where they are located. Federal Mexican governmental agencies with administrative authority over the Biosphere Reserve include the National Commission of Protected Natural Areas (CONANP) and the Secretary of the Environment, Natural Resources and Fisheries (SEMARNAP) . In addition to designation as a Biosphere
Biosphere
Reserve, 2500 km² (618,000 acres) within Colorado River
Colorado River
Delta (Humedales del Delta del Río Colorado) are designated as a Ramsar Wetland under the U.N. Convention on Wetlands. Ramsar Wetlands
Wetlands
are wetlands of international importance in terms of their ecology, botany, zoology, limnology or hydrology. The U.N.
U.N.
designation is considered following a nomination by the nation in which the site is located. View[edit]

The region from orbit.[5]

References[edit]

^ David A. Alles, ed., "Geology of the Salton Trough", Western Washington University, Edited May 28, 2005. ^ Water, wildlife surge back into once-parched Colorado River
Colorado River
delta ^ Clifford, Frank (September 21, 2007), "A trickle of water might save estuary", Los Angeles Times  ^ "Archived copy". Archived from the original on 2012-04-08. Retrieved 2010-07-04.  . accessed 7/4/2010 ^ Salton Trough July 29, 2013

External links[edit]

Official Upper Gulf of California
Gulf of California
and Colorado River
Colorado River
Delta Biosphere Reserve website Map of the Biosphere
Biosphere
Reserve (in español) A Delta Once More: Restoring Riparian
Riparian
and Wetland Habitat in the Colorado River
Colorado River
Delta International Boundary and Water Commission
International Boundary and Water Commission
Site on Colorado
Colorado
River Operations IBWC Minute 306 (Conceptual Framework for U.S. - Mx Studies for Future Recommendations Concerning the Riparian
Riparian
and Estuarine Ecology of the Limitrophe Section of the Colorado River
Colorado River
and its Associated Delta.) Proceedings of IBWC Colorado River
Colorado River
Delta Symposium Colorado River
Colorado River
Delta Research Coordination Network

Coordinates: 31°44′N 114°40′W / 31.74°N 114.66°W / 31.74; -114.66

v t e

Colorado River
Colorado River
system

Jurisdictions

United States

Arizona California Colorado Nevada New Mexico Utah Wyoming

Mexico

Baja California Sonora

Canyons

Byers Canyon Gore Canyon Red Gorge Glenwood Canyon De Beque Canyon Horsethief Canyon Ruby Canyon Westwater Canyon Cataract Canyon Narrow Canyon Glen Canyon Grand Canyon

Marble Canyon Granite Gorge Middle Granite Gorge Lower Granite Gorge

Grand Wash Canyon Iceberg Canyon Virgin Canyon Boulder Canyon Black Canyon Pyramid Canyon Mohave Canyon

Natural features

River course Rocky Mountains Colorado River
Colorado River
Basin Colorado
Colorado
Plateau Grand Lake Horseshoe Bend Sonoran Desert Mojave Desert Lower Colorado River
Colorado River
Valley Mohave Valley Parker Valley Palo Verde Valley Colorado
Colorado
Desert Alamo River New River Salton Sea Imperial Valley Delta Montague Island Gulf of California/Sea of Cortez

Tributaries

Blue River Dirty Devil River Dolores River Escalante River Eagle River Fraser River Gila River Green River Gunnison River Kanab Creek Little Colorado
Colorado
River Paria River Roaring Fork River San Juan River Thunder River/Tapeats Creek Virgin River Las Vegas Wash Williams Fork Río Hardy

Engineering

Mainstem dams

Shadow Mountain Granby Windy Gap Grand Valley Price-Stubb Glen Canyon Hoover Davis Parker Headgate Rock Palo Verde Imperial Laguna Morelos

Major reservoirs

Fontenelle Reservoir Flaming Gorge Reservoir Blue Mesa Reservoir Navajo Lake Lake Powell Lake Mead Lake Mohave Lake Havasu Imperial Reservoir Theodore Roosevelt Lake San Carlos Lake

Aqueducts and canals

Grand Ditch Colorado River
Colorado River
Aqueduct San Diego Aqueduct Central Arizona
Arizona
Project All-American Canal Coachella Canal

Water projects

Boulder Canyon Project Colorado-Big Thompson Project Colorado River
Colorado River
Storage Project Grand Valley AVA Yuma Project

Designated areas

Arches National Park Canyonlands National Park Colorado
Colorado
National Monument Dead Horse Point State Park Glen Canyon
Glen Canyon
National Recreation Area Grand Canyon
Grand Canyon
National Park Lake Mead
Lake Mead
National Recreation Area Rocky Mountain National Park

Related topics

Arizona
Arizona
v. California Colorado River
Colorado River
Board of California Colorado River
Colorado River
Compact Floyd Dominy Lee's Ferry International Boundary and Water Commission Metropolitan Water District of Southern California Rapids and features U.S. Bureau of Reclamation

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