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<br />002J79 <br /> <br />the City of Tijuana. Sediment flows (due to erosion upstream) in the Alamar and Tijuana <br />rivers could result in the destruction of one of the largest coastal wetlands in Southern <br />and Baja California that is at the mouth of the Tijuana River. Located in the United <br />States, the Tijuana National River Estuarine Research Reserve (TRNERR) includes 2,500 <br />acres of coastal wetlands. As with most wetlands in Southern California and Baja <br />California, coastal estuaries are a rarity since most have been paved over by urban <br />development or river channelization (Michel 2000). Coastal estuaries, and other wetlands <br />in the Alamar and Tijuana rivers, are significant in terms of preserving biodiversity, since <br />these wetlands are part ofthe Pacific Flyway, a network of wetlands that are a wintering <br />habitat for a variety of waterfowl, songbirds, and other migratory species (Vincent 1999). <br /> <br />Storm water flows from Tijuana carry not only pollutants from the city and other <br />upstream locations, but also large amounts of sediment. For example, during the 1994-95 <br />winter rains, storm water flows deposited 30 centimeters of sediment in the Tijuana River <br />estuary. The average range of sediment accumulation is between one millimeter to one <br />centimeter per year (Southwest Wetlands Interpretive Association 1999). The increasing <br />rate of sediment deposition is filling up the estuary habitat, resulting in its loss. <br /> <br />Besides pollution prevention and treatment of discharges into the river, wetlands or <br />riparian habitats can be utilized to improve water quality in the Alamar River Corridor. <br />What makes wetlands uniquely suitable to improving water quality? The filtration of <br />pollutants is a natural function of wetland or riparian ecosystems. Wetlands improve local <br />water quality by trapping sediment and removing nutrients and toxic contaminants <br />(Husted 1997: 12). Because a riparian habitat is positioned between water and land, it <br />serves as a buffer zone that intercepts and even breaks down pollutants found in nonpoint <br />source pollution or polluted runoff. <br /> <br />Expansion of human development in river corridors has caused the destruction of <br />riparian habitats. Unfortunately, when riparian or wetland habitats are destroyed, the <br />quality of water inevitably deteriorates. An economic analysis conducted in California <br />estimated that the water purification benefits provided by the wetlands are worth <br />approximately $6,600 per acre (Husted 1997 citing Allen et. al. 1992). To replace or <br />destroy the natural pollution control functions of riparian habitats imposes more costs to <br />residents that use local water resources. <br /> <br />To summarize, riparian habitat destruction that comes along with river channelization <br />has led to a number of fundamental environmental problems including the following <br />(adopted from Dallman and Piechota 2000): <br /> <br />. Decreased wildlife habitat and biodiversity <br />. Decreased groundwater infiltration <br />. Decreased stream base flows <br />. Decreased surface and groundwater storage <br />. Increased storm water runoff and volume <br />. Increased storm water peak discharge rate <br />. Increased channel erosion <br /> <br />33 <br />