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<br />002020 <br /> <br />Today, nearly all of the Colorado River water entering Mexico passes through dams and <br />reservoirs in the United States. The last such' facility before the river enters Mexico is Imperial Dam <br />located about 20 miles upstream from the United States-Mexico border. Water released from <br />Imperial Dam is delivered to Mexico at the Northerly International Boundary and then is diverted at <br />Morelos Dam (constructed in 1950) into the Mexicali Valley for agricultural, municipal, and <br />industrial uses. Water that is not diverted at Morelos Dam flows southwest into the river corridor in <br />Mexico. When large flows pass Morelos Dam, they reach the river's confluence with the Rio Hardy, <br />eventually crossing miles of mud flats in the inter-tidal zone before they reach the Gulf of California <br />("Gulf'). The entire corridor constitutes a rich biotic resource. The southernmost portion of the <br />river, together with the upper Gulf and Cienaga de Santa Clara, are included in an International <br />Biosphere Reserve. <br /> <br />Today, Mexico's 1.5 million acre-feet per year treaty allocation from the Colorado River <br />ordinarily does not reach most portions of the Delta or the Gulf. For many years in the past decade, <br />however, natural runoff exceeded consumptive uses and storage capacity in the United States so that <br />Mexico received significantly larger releases of water. In 1995, for example, Mexico received 61~OOO <br />acre-feet of excess water; in 1997, 634,000 acre-feet; in 1998,2.4 million acre-feet; in 1999,900,000 <br />acre-feet; and in 2000, 337,000 acre-feet. While the 1997-99 excess flows were caused by flood <br />control releases, the excess flows in 2000 were from operational over-deliveries. Some of these <br />excess deliveries have not reached the Delta, but have been diverted and used in Mexico for <br />agricultural and municipal purposes. <br /> <br />B. Ecosystems of the Delta <br /> <br />The additional waters available to the Delta in recent years significandy improved the quality <br />of the habitat in some areas. Wetland and riparian areas connected to the river have gained in size <br />and diversity. Two large wetland lakes exist in the Delta. The Laguna Salada is located to the west <br />of the river and varies in depth, size,. and salinity depending on rainfall runoff, fann runoff, river <br />flows that occasionally back up into the area, and the length of time that the water remains in the <br />area before completely evaporating. The ephemeral nature of the Laguna Salada, its 'incompletely <br />defined ecological resources and the limited technical understanding of its operation suggest that its <br />potential for management be assessed separately from the overall Delta protection and restoration <br />activities. <br /> <br />The Cienaga de Santa Clara is on the east side of the river, and owes its current size primarily <br />to brackish flows of agricultural drainage water coming down the Bypass Drain from the Wellton- <br />Moh~wk District in Arizona. The Cienaga encompasses an area of 50,000 acres, of which 11,000 <br />acres are vegetated.o4 <br /> <br />As the ecological health of the Delta gready improved in the 1990s, universttIes, <br />environmental NGOs, local communities, and Ducks Unlimited began to identify and prioritize <br />opportunities for Delta restoration.s These efforts. assessed the ecological conditions of the riparian <br />corridor from Morelos Dam to the Gulf as well as opportunities for restoration~ <br /> <br />Researchers have divided the Delta into seven zones based on vegetation structure and <br />landscape conditions (Figure 2).6 <br /> <br />5 <br />