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<br />Is important to consider the hydrology of the region with regard to the sustainable <br />supply of water for human use. Watersheds in Southern California-Baja California <br />usually consist of three primary geological water-bearing formations; sandy alluviums, <br />weathered tonalite, and fractured bedrock (Connolly 1997). These formations are <br />important because they have the ability to hold and contain water, as is the case of the <br />sandy alluviums. The weathered tonalite, however, is key to the hydrology of the area <br />because, after it recharges, it releases water slowly and thus is able to feed and sustain an <br />aquifer with enough water to survive years of drought (Connolly 1997). <br /> <br />.~ <br /> <br />An aquifer is unable to recharge without a sufficient vegetation cover on the surface <br />that allows water enough time to percolate into the surrounding land. Tree roots also help <br />by slowing the horizontal flow of groundwater. Both the trees and understory vegetation <br />keep water temperature low, minimizing loss to evaporation (Connolly 1997). Some <br />plants that grow back in restored areas in the Southern California-Baja California region <br />are watercress, nettle, duck weed, yerba mansa, sedges, celery, rushes, and cattails <br />(Connolly 1997). Willow and cottonwood are also favorable trees, for they assist in the <br />growth of smaller vegetation. Trees can form a canopy, supporting the water table <br />elevation increase and encouraging water aboveground to form ponds. Along the edge of <br />a pond, a canopy helps reduce evaporation of surface water and help keeps temperatures <br />cool and favorable to wildlife. The restored river invites nesting ducks, red-tailed hawks, <br />kestrels, migratory song birds, least bells vireos, as well as deer, bobcat, coyote, and <br />mountain lion, all of which are native wildlife species to the region. The diverse native <br />vegetation and wildlife are important to this region for they have learned to adapt to one <br />another and many have symbiotic relationships. <br /> <br />Prior to the arrival of European settlers, erosion in the Tijuana River watershed <br />(including the Alamar River) was kept to a minimum by the Kumeyaay (a Native <br />American tribe that inhabited western Baja and Southern California), with careful <br />management through controlled burning of native vegetation and other techniques. On <br />steep slopes in and near river corridors, the Kumeyaay placed small rock formations <br />parallel to the slope in order to slow rainfall that would carry silt down hill. These also <br />served to spread the flow of rainwater to other areas (Blackburn and Anderson 1993: <br />384). The slow pace of the storm water runoff also helped the ground absorb more of the <br />moisture and the areas behind the rock alignments were often used for planting. Riparian <br />vegetation (such as willows), of which some species are medicinal plants, were used to <br />slow the running of storm water down slopes and through valleys. Riparian vegetation <br />was planted along the stream sides, and if a cut would occur in the stream, willow would <br />be planted at the cut to encourage vegetation growth and help the break to close naturally <br />(Blackburn and Anderson 1993). Wet meadows, watery bogs, and groundwater were fed <br />by streams controlled by boulder-brush alignments and check dams. By using these <br />techniques, even in drought years, the Kumeyaay maintained groundwater levels close to <br />the surface, providing water for people and wildlife (Blackburn and Anderson 1993). <br /> <br />However, present land use conditions, river channelization, and the destruction of <br />riparian habitat have resulted in a decrease of groundwater levels and a significant <br />increase in erosion in not only the Alamar River valley, but in most arroyos throughout <br /> <br />32 <br />