Flood — Hidalgo, Texas

2010-07-09 to 2010-07-31 · near Carrizelos, Hidalgo, Texas

Event narrative

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 southwest Hidalgo County, the result of planned dam releases from Falcon International Reservoir. River flooding likely began along the banks of the Rio Grande in Hidalgo County less than 18 hours after flooding began at river side locations in Starr County. Affected communities included Cuevitas, Havana, and the south portions of La Joya and Penitas - locations not protected by the Lower Rio Grande Valley Flood Control Project levee system. The city of Los Ebanos, surrounded on three sides by the river, was most impacted by the flood, which was well over a mile wide for several weeks. Significant flooding continued into the first days of August.

Mandatory evacuations were initiated on July 12th for Los Ebanos, in the southwest corner of the County; the evacuation level was reduced to voluntary on July 20th. The early evacuations proved fateful, as pressure on a retention pond dike caused it to rupture, spilling water into some neighborhoods and forcing most residents to leave the area. Additional impacts were noted between Los Ebanos and the Anzalduas Diversion Dam, where several residences and roadways were threatened prior to the levee south of Mission.

In all, hundreds of structures, as well as paved and unpaved roads, were damaged significantly by the long duration flood. Most of these were in Los Ebanos, but others were along or south of Military Highway between Cuevitas and the south portion of Penitas. Five homes were evacuated near Military Road in Havana where the river flooded them. Damage to property was estimated to be at least $5 million, with additional damage to crops in southwestern Hidalgo County.

Note: Total value of irrigated and non irrigated dryland crop (sorghum, corn, and cotton) was not available for locations west of Anzalduas; an early estimate of $1.5 million between Los Ebanos and Penitas will be updated as information arrives.

Wider weather episode

Torrential rainfall from Hurricane Alex and remains, followed by daily peltings of rain across the front range of the Sierra Madre Oriental, and concluding with the remnants of Tropical Depression Number 2 dropped perhaps 50 or more inches of rain across Coahuila Province, Mexico, which flowed steadily through the Rio Grande basin, requiring a series of planned flood control actions to mitigate the possibility of severe river flooding across the Lower and Middle Rio Grande Valley. Severe flooding in Monterrey, Nuevo Leon, Mxico from June 30th through July 2nd, from an estimated 30 inches of rain in this area was a portent of future impacts on the Rio Grande during the weeks to come.

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, the river surged to major flood levels in Starr and extreme southwestern Hidalgo County, where the river widened significantly and flooded rangeland, as well as several small communities along its banks, during the weekend of July 10th and 11th. 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 flood stage of 301.2 feet during the morning of July 12th . This release rate would continue until July 27th, followed by gradually reduced rates over the next several days. By August 2nd, releases were brought down to 30,000 cfs.

Major flooding continued for nearly a month at Rio Grande City - and by proxy, southwest Hidalgo County - starting on July 9th and continuing through August 3rd! Flood conditions (50 feet or higher) continued a few days beyond, with levels dropping below flood stage on August 10th. In total, the river was likely in flood at points downstream in southwest Hidalgo County, from the morning of July 9th through at least August 10th - more than month.

A number of small communities along the Rio Grande west of the Lower Rio Grande Valley Flood Control System were impacted by the sprawling river for most of July, soon after the large releases began at Falcon International Reservoir. These included locations in southwest Hidalgo County. The system of levees and floodways (spillways) downstream of Penitas (where improved levees begin along the river itself) largely worked as designed, containing and diverting water along the river and associated floodways extending through southern and eastern Hidalgo County into extreme northern Cameron and extreme southern Willacy County. However, additional water damage occurred to properties built inside the levees and floodways. Voluntary and mandatory evacuations were ordered for a number of threatened communities; as of this writing, no fatalities had been reported directly from the high waters. There were dozens of water rescues on the river through the period, many of them trans migrants attempting to cross from Mexico into Texas.

On August 3rd, President Obama declared most counties in the Rio Grande Valley a Major Disaster, eligible for federal funding to assist with the longer term recovery. Deep South Texas Counties included Cameron and Hidalgo.

Property and Crop damages from the flood may ultimately total well over $50 million when all assessments are completed. As of the end of July, private and public property damage estimates in Hidalgo County had reached more than $19 million. Crops planted in flood zones were destroyed by the long duration of nutrient rich waters; in addition to countywide lost yields due to Alex's heavy rainfall ($10 million), an additional $5.2 million was lost in sorghum, cotton, and corn production along the Hidalgo portion of the floodway system, with another $7.5 million required to re-grade the damaged agricultural infrastructure. Perhaps another $2 million was lost to crops along and near unimproved levee/no levee areas west of Anzalduas; data on these areas were still being processed as of this writing.

View location on OpenStreetMap → (26.2658, -98.5826)

Source: NOAA Storm Events Database, event_id 247517. Narrative written by the NWS forecast office that issued the report.