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The Rio Grande ( or ; (スペイン語:Río Bravo del Norte), or simply Río Bravo) is one of the principal rivers in the southwest United States and northern Mexico (the other being the Colorado River). The Rio Grande rises from south-central Colorado in the United States and flows to the Gulf of Mexico. Along the way, it forms part of the Mexico–United States border. According to the International Boundary and Water Commission, its total length was in the late 1980s, though course shifts occasionally result in length changes. Depending on how it is measured, the Rio Grande is the fourth- or fifth-longest river system in North America. The river serves as part of the natural border between the U.S. state of Texas and the Mexican states of Chihuahua, Coahuila, Nuevo León, and Tamaulipas. A very short stretch of the river serves as the boundary between the U.S. states of Texas and New Mexico. Since the mid–20th century, heavy water consumption of farms and cities along with many large diversion dams on the river has left only 20% of its natural discharge to flow to the Gulf. Near the river's mouth, the heavily irrigated Rio Grande Valley is an important agricultural region. The Rio Grande is one of 19 Great Waters recognized by America's Great Waters Coalition. The Rio Grande's watershed covers .〔(【引用サイトリンク】title= Rio Grande NASQAN Program )〕 Many endorheic basins are situated within, or adjacent to, the Rio Grande's basin, and these are sometimes included in the river basin's total area, increasing its size to about . ==Geography== The Rio Grande rises in the western part of the Rio Grande National Forest in the U.S. state of Colorado. The river is formed by the joining of several streams at the base of Canby Mountain in the San Juan Mountains, just east of the Continental Divide. From there, it flows through the San Luis Valley, then south into New Mexico, passing through Española, Albuquerque, and Las Cruces to El Paso, Texas and Ciudad Juárez, Chihuahua. Below El Paso, it serves as part of the border between the United States and Mexico. The official river border measurement ranges from to , depending on how the river is measured.〔 A major tributary, the Rio Conchos, enters at Ojinaga, Chihuahua, below El Paso, and supplies most of the water in the border segment. Other well-known tributaries include the Pecos and the smaller Devils, which join the Rio Grande on the site of Amistad Dam. Despite its name and length, the Rio Grande is not navigable by ocean-going ships, nor do smaller passenger boats or cargo barges use it as a route. It is barely navigable at all, except by small boats in a few places. The Rio Grande rises in high mountains and flows for much of its length at high elevation; El Paso is above sea level. In New Mexico, the river flows through the Rio Grande rift from one sediment-filled basin to another, cutting canyons between the basins and supporting a fragile ''bosque'' ecosystem on its flood plain. From El Paso eastward, the river flows through desert. Only in the subtropical lower Rio Grande Valley does extensive irrigated agriculture exist. The river ends in a small, sandy delta at the Gulf of Mexico. During portions of 2001 and 2002, the mouth of the Rio Grande was blocked by a sandbar. In the fall of 2003, the sandbar was cleared by high river flows around .〔(【引用サイトリンク】title= 2003 Annual Report )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rio Grande」の詳細全文を読む スポンサード リンク
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