STREAM PIRACY ON THE RIO GRANDE - CHANGES IN THE CHANNEL OF THE RIO GRANDE, VAL VERDE COUNTY, TEXAS

Two changes in the channel of the Rio Grande at and near the town of Del Rio, County of Val Verde in southwest Texas are documented.

The most recent change occurred between 1944 and 1961, and most likely during the historic floods of 1954 that produced record flooding along the Rio Grande and Devils Rivers including the town of Del Rio and other towns downstream on the Rio Grande. The flooding was the result of record rainfall between Del Rio and the town of Pandale and within the drainages of the Pecos and Devils Rivers- the two major tributaries to the Rio Grande immediately upstream of the town of Del Rio. The rainfall was the result of the remnants of Hurricane Alice that moved inland from the Gulf of Mexico between June 23 and June 26, 1954. At the town of Del Rio a major bend in the Rio Grande was straightened out during the major flooding that occurred. As a result of this channel modification approximately 560 acres of land that were formerly on the Mexican side of the Rio Grande were transferred to the United States side.

A much older channel modification occurred in the vicinity of the confluence of the Devils River with the Rio Grande. This confluence is now drowned beneath of water of Amistad Reservoir. Evidence for channel modifications is preserved in gravel terrace deposits along the Evans Creek tributary to the Devils River. Gravel terraces along this unusually large tributary contain well rounded pebble to cobble gravel deposits including fragments of a reddish brown porphyritic volcanic rock. The drainage basin for the Box Canyon tributary does not, at present, contain any volcanic rocks. The only known sources of fragments are volcanic rock outcrops in the Big Bend region of Texas and adjacent regions of northern Mexico within the Rio Grande River basin upstream from this locality.