The remnants of Hurricane Alex brought a large area of 10 to 20 inches of rain to the upper Rio Grande basin and mountains from July 1 to July 5, 2010. The Rio Grande Valley of Mexico and Texas also received widespread 3 to 7 inches of rain contributing to the inflow to the Rio Grande. During the period July 8 to 9, 2010 another tropical cyclone, depression number 2, brought additional significant rainfall to South Texas and the Rio Grande Basin, but its contribution was much less significant.
The excessive rainfall inundated the tributaries to the Rio Grande and resulted in large releases to the water storage system. A large flood wave of water was tracked from Del Rio to Eagle Pass and set new record river crest levels when it reached Columbia Bridge and Laredo between July 8 and 9th. The Rio Grande crest of 42.45 feet surpassed the 35-foot reading recorded after Hurricane Charley in August 1998 and the 39-foot flood crest of late June 1971, both of which many long-time residence recall as major flooding. The all-time record at Laredo is 62.48 feet recorded on January 1, 1965. At Columbia Bridge, a preliminary crest of 49.46 feet occurred July 8th.
|Topographic map depicting the Rio Grande||Detailed map of the Rio Grande System including tributaries and dams|
The excessive runoff from the rainfall caused interior Mexico and International Boundary and Water Commission (IBWC) reservoirs to conduct significant releases. The pool elevation at Amistad Dam rose over 15 feet since July 1, which was 12 feet above conservation pool levels. This reservoir began releasing 35,000 cubic feet per second, the largest release from the dam since 1974.
|Hydrograph for the Rio Grande at Laredo depicted the peak level of 42.45 feet.||Historic flood crests at Laredo on the Rio Grande. The Map depicts the gage location.|
|Rainfall total from June 30 through July 6 2010 depicted a large area of 10 to 20 inches.|
|The 14 day percent of normal rainfall depicted 400 to 800 percent of normal rainfall between June 27 and July 10, 2010.|
The city of Laredo issued mandatory evacuation orders for several subdivisions along Chacon and Quail Creeks due to backwater effect from the Rio Grande. Other evacuations ordered included La Posada Hotel, Los Martinez and Cheyenne subdivision, Masterson Road, Allen street, Ventura and Vidaurri by Riverbanks. Road closures included bridge 1, Columbia bridge, Meadow bridge, SH-359 at Ejido, US-83 at SH-359 and the 3 Points area. At the peak of the flood all roads out of Nuevo-Laredo were closed.
|The track of Hurricane Alex from June 25 to July 2 2010. The tropical system weakened over the Sierra Madre mountains in Mexico. It was slow to exit between July 2 and July 5 and therefore produced massive rains.|
|GOES infrared satellite loop of Hurricane Alex|