Flood, Starr
- When
- July 8, 1:20 PM CST to July 31, 11:59 PM CST
- Where
- Starr County, 0.49 mi W of Falcon Hgts to 1.05 mi NNW of Chapena
- Cause
- Planned Dam Release
- Property damage
- $37 million
- Crop damage
- $500,000
- Reported by
- River/Stream Gage
- Coordinates
- 26.551, -99.138
Incredible rainfall estimated to be more than 50 inches in around 10 days' time between June 30th and July 9th across the front range and peaks of the Sierra Madre Oriental in Coahuila Province, Mexico, ultimately flowed through the entire Lower Rio Grande basin for much of the summer of 2010. The rare and extreme event rapidly produced major flooding along the river in Starr County, the result of planned dam releases from Falcon International Reservoir, which lasted for nearly a month, beginning on July 9th and continuing through August 3rd.
Releases of water from reservoirs behind dams on both sides of the border began soon after the heaviest rains from Alex ended. On July 4th, releases began at the Marte R. Gomez Reservoir, flowing into Mexican Floodways but also toward the Rio Grande bordering Starr and western Hidalgo County. On July 5th, water levels had increased sufficiently at Amistad Dam, located much farther upstream near Del Rio, Texas, to begin releases down the river. By the 7th, with waters from Amistad having created major flooding in and near Laredo, Falcon Reservoir, located along the Rio Grande including Starr and Zapata County, began releasing water.
The initial rate of 15,000 cubic feet per second (cfs) was initially within capacity of the United States side of the flood control system, and the expectation for a potentially critical flood area between Falcon and Anzalduas Reservoir just upstream from Mission (Hidalgo County) was high water, but little if any flooding. That would quickly change on July 8th, when releases from Falcon Dam were more than doubled to 39,700 cfs (1125 cubic meters per second, cms). Soon after these releases were increased,the river quickly rose from just above flood stage (50 feet) at Rio Grande City to above major flood stage (53 feet) on July 9th. The time it took to rise from flood stage (1320 CST July 8th) to above major flood (630 AM July 9th) was a little more than 17 hours.
By July 14th, outflow from Falcon Dam was raised to 60,000 cfs (1700 cms) in order to relieve pressure on the dam from the reservoir pool, which had risen steadily above conservation stage of 301.2 feet at 822 AM CST July 12th. This release rate would both raise and swell the Rio Grande downstream; reports from local emergency management noted the river up to 2 miles wide in some spots. Prior to the peak outflow, the river crested at 57.63 feet at 6 AM July 11th, the second highest level ever recorded. A secondary peak occurred five days later - 57.31 feet at 4 PM CST July 16th.
All this water would continue to remain high and spread, and hundreds, of structures were impacted during the event. The city of La Grulla was under mandatory evacuation by July 15th as increasing water levels and currents threatened more of the community than earlier in the week; these orders would continue until July 22nd when the waters began to recede slowly. As a precautionary measure in the city of Roma, three small subdivisions located in the low lying areas and along the bank just south of the Port of Entry were placed under mandatory evacuation. These included De La Cruz sub-division about (20 to 25 homes), Campo Verde (4 homes), and Garza sub-division (1 home). By July 22nd, the flooding in Starr County had impacted 178 homes/businesses, including 65 in La Grulla and 39 in Roma. 166 families required temporary housing. Preliminary damages to highways and bridges in Starr County was at $19 million; preliminary public and private property estimates were listed at an additional $18 million. Agricultural damage was also notable in flooded areas. Full accounting of both crop and property damage will be available during autumn, 2010.