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<br />Water Resources in the Alamar River Watershed <br /> <br />According to a report for the period 1978-1991, the hydrologic parameters of the <br />Alamar River are as follows: (1) drainage area 1,387 km2; (2) annual average volume <br />74.738 Mm3; (3) average annual water consumption 2.528m3/sec; (4) annual average <br />discharge 2.528 m3; and (5) maximum discharge 383.8 m3 (IMPlan 2000; Ponce 2000). <br /> <br />The Alamar River watershed provides approximately 50 percent of surface water <br />flows within the Tijuana River basin. Besides surface water flows, the Alamar riverbed is <br />a vital recharge zone for a large groundwater basin or aquifer that lies beneath the Alamar <br />and Tijuana rivers (see Figure 2). This aquifer, known as the Tijuana River Aquifer, is <br />geographically delimited by hill formations to the north and southwest of the Tijuana <br />River; the mesa formations ofOtay Mesa; hill formations to the east in Los Alamos; and <br />topographical elevations like Cerro Colorado to the southeast. In the alluvial plains in the <br />riverbeds ofEl Florido Creek, the Alamar River, and the Tijuana River, there is a <br />semiconfined aquifer (Guzman 1998: 38). The alluvial fill in the riverbeds and <br />floodplains is composed of mostly medium-grained, fairly well sorted, and loosely <br />packed sand. This material readily transmits water to the wells (California Department of <br />Water Resources 1965). The groundwater flows generally westerly, and follows the <br />configuration of the Alamar and Tijuana rivers. <br /> <br />According to Guzman (1998), it is difficult to estimate the aquifer's water production <br />potential due to numerous factors. First, since precipitation can vary dramatically in the <br />Tijuana River watershed, recharge to the aquifer will vary. In addition, government <br />estimates do not consider water quality issues-a key variable in determining how much <br />water is potable. For example, it is unknown how much of Tijuana's uncontained sewage <br />flows and urban pollutants percolate into the aquifer (Guzman 1998). Finally, even <br />government estimates vary. According to the Comision Estatal de Servicios Publicos de <br />Tijuana (CESPT) (1994), groundwater wells of the Alamar and Tijuana rivers produce <br />approximately 370 liters per second. This was approximately 10 percent of the total local <br />water production for the Tijuana-Rosarito region in 1994 (CESPT 1994). In 1995, a <br />hydrological study revealed that the aquifer produced 18 millions of cubic meters (Mmc), <br />which was approximately 15-20 percent of the region's water production (Guzman <br />1998). In 1998, CNA estimated the water production at 14Mmc (Guzman 1998). The <br />conflicting data demonstrate the need for long-term studies of groundwater water <br />capacity, use, and quality in the Alamar River Valley, and in the entire Alamar-Tijuana <br />river groundwater basin (Guzman 1998). <br /> <br />Table 1 delineates results of a preliminary water use survey conducted in the Alamar <br />River Valley during the field research period. The water use categories are derived from <br />Mexico's National Waters Law (CNA 1998), the beneficial uses adopted by the State of <br />California (California Regional Water Quality Control Board 1994), and beneficial uses <br />adopted by the Campo Environmental Protection Agency (Campo EPA 1994). <br /> <br />10 <br />