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<br />In the following discussion, the Rio Grande Project area has been divided into river <br />reaches for the Elephant Butte Reservoir area, the Caballo Reservoir area, the Rincon Valley, <br />the Mesilla Valley, and the EI Paso Valley. The emphasis in the discussion is on the river flows <br />that have occurred historically in these reaches and features of the Rio Grande Project that <br />presently exist. The historical operation of the project features is documented and analyzed in <br />later sectrons of this report. Plates 1 through 3 show the major water diversion, water <br />distribution, and stream gaging stations in the project area with Plate 1 covering the segment <br />from just above Elephant Butte Dam downstream through the Rincon Valley, Plate 2 covering <br />the Mesilla Valley, and Plate 3 covering the EI Paso Valley. Figures 2-3 through 2-6 are <br />schematic diagrams of the water diversion, drainage, and measurement facilities in the Rincon, <br />Mesilla, and EI Paso Valleys and in the HCCRD. Table 2-1 summarizes the gaging stations that <br />have been operated on the Rio Grande in this portion of the basin. <br /> <br />Elephant Butte Reservoir Area <br /> <br />This reach covers about 40 river miles beginning at the head of Elephant Butte <br />Reservoir at San Marcial and extl'nding to just below Elephant Butte Dam. Prior to the <br />construction of Elephant Butte Dam and the operation of the reservoir, this segment was known <br />as the Engle Valley. The downstream 16-mile portion of this river reach is shown on Plate 1. <br /> <br />Stream gaging facilities have been operated on the Rio Grande at San Marcial since <br />1895. The Rio Grande at this location is at an elevation of approximately 4,450 feet and drains <br />an area of about 27,700 square miles. Since the tributaries of the Rio Grande below this <br />location are arroyos and dry most of the time, the flow at this location reflects most of the water <br />available to the Rio Grande Project. Table 2-2 shows the monthly and annual flows during <br />1895-1995, a period of 101 years. Annual flows averaged 929,420 acre-feet and ranged from <br />114,147 acre-feet in 1951 to 2,831,334 acre-feet in 1941. Prior to 1950, these flows were <br />measured at a single gaging station located 1.1 miles downstream from the former San Marcial <br /> <br />r ~ C;;~;'-. <br />"i\.. vv <br /> <br />2-4 <br />