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<br />i.'>", <br /> <br />;.!] <br /> <br />I.J <br /> <br />STUDY AREA <br /> <br />..'~ <br />~: ~1 <br /> <br />The Rio Grande Region, i.e. Water Resources Region 13 as designated by <br />WRC [3], is defined as the study area for the 13(a) assessment. It includes <br />all of the land areas in the United States encompassed within the watershed <br />of the Rio Grande and its major tributary, the Pecos River. The extent of <br />the study area is indicated in Figure 1. Just over half of the Region is in <br />New Mexico with about 40 percent in Texas and six percent in Colorado. <br /> <br />. <br /> <br />The headwaters of the Rio Grande originate on the eastern slopes of the <br />Continental Divide in a basin formed by the San Juan and the Sangre de Cristo <br />ranges of the Rocky Mountains in Colorado. The River flows south the full <br />. <br />length of New Mexico to enter Texas near the city of E1 Paso. From there, it <br />flows generally in a southeasterly direction for 1,244 miles, forming the <br />international boundary between the United States and Mexico until it reaches <br />the Gulf of Mexico near Brownsvil1e, Texas. Approximately 335,000 square <br />miles are included within the boundaries of the watershed [14], of which, <br />only about half actually drains to the Rio Grande. The remaining lands are <br />located within closed basins and do not contribute direct runoff to the <br />River. The actual drainage area of the entire River (176,333 square miles at <br />Brownsvil1e) is about equally divided between Mexico and the United States. <br /> <br />~ <br /> <br />The largest tributary in the Region is the Pecos River which rises in <br />north-central New Mexico, flows south into Texas, and then southeasterly to <br />join the Rio Grande near Langtry, Texas. The Pecos drains about 35,000 <br />square miles of watershed. Other principal tributaries of the Rio Grande in <br />the study area are the Rio Puerco (7,350 square miles) and the Rio Chama <br />(3,144 square miles) in New Mexico and the Devils River (4,035 square miles) <br />in Texas. <br /> <br />The extreme lower part of the Rio Grande Basin, below La Joya, Texas, <br />is confined by levees maintained by the International Boundary and Water <br />Commission (IBWC). Flood waters in the Rio Grande are diverted into f1ood- <br />ways which discharge into the Gulf through Laguna Madre north of the mouth <br /> <br />. ~ r .. . ,~. <br />I.J' i"/ ,. \ <br />. ..... '*-, .J... ...... \.. <br /> <br />3 <br />