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, M��xico 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 western 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.
In all, major flooding continued for nearly a month, starting at 730 AM CDT 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 at 330 am CDT. In total, the river was in flood at Rio Grande City, and at points immediately upstream in Starr County, from the afternoon of July 8th through the early morning of August 10th, 33 days in total!
A number of small communities along the Rio Grande west of the Lower Rio Grande Valley Flood Control System were impacted by the now sprawling river for most of July, soon after the large releases began at Falcon International Reservoir. These included locations from Starr County immediately downstream of the dam, extending along the river to the Hidalgo County line.   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 transmigrants 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 Starr and Zapata (due to flooding). Property and Crop damages from the flood in Starr and Zapata Counties will ultimately total over $50 million when all assessments are completed. As of July 29th, property damage estimates in Starr County had reached $37 million; additional property damage values had not been received from Zapata County. Crops planted in flood zones were destroyed by the long duration of nutrient rich waters.  As of September 17th, FEMA had approved more than $8.3 million in state and federal grants for Texans affected by the flooding.  The value will likely rise as assessments continue across Starr, Zapata and Webb County, which will likely take most of the disbursements.

Flood in ZAPATA, TEXAS
From 14-JUL-10 04:00:00 to 24-JUL-10 08:00:00 (CST-6)
Location: ZAPATA ARPT
Flood cause: Planned Dam Release
Property damage: 1.00M
Crop damage: 25.00K
Reported by: Emergency Manager

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 ultimately led to increasing water levels at both Amistad International Reservoir (northwest of Del Rio, TX) and Falcon International Reservoir (adjacent to Zapata County), the result of inflow from Mexican tributaries and upstream reservoirs along the Rio Salado and Rio Conchos in Nuevo Leon and Coahuila State, Mexico.
At Falcon International Reservoir, where inflow from both the upstream Mexican tributaries and Amistad International Reservoir, which had begun releases of 35,000 cubic feet per second (cfs) on July 5th, the pool level rose above conservation stage (301.2 feet) during the morning of July 12th, and would continue a steady rise, reaching moderate flood stage (306.7 feet, the point where impacts begin along the shoreline) during the pre-dawn hours of July 14th. Despite an increase in releases from 39,700 cfs to 60,000 cfs from the Reservoir, the pool level continued to rise,  peaking at a new record stage of 309.31 feet during the evening of July 17th. The continued high pool level required maintaining releases of 60,000 cubic feet per second for nearly 14 consecutive days, in order to maintain a manageable water level at the dam. At Falcon, the previous record of 308.1 feet (set in October, 1958) was not only broken, but the pool level remained above the prior record for nearly 7 full days, from around 130 AM CDT on July 15th through 930 PM on July 22nd.  The pool level was above conservation level (301.2 feet) from the morning of July 12th through 4 PM on August 13th, more than a month.
Releases were gradually lowered toward the end of the month as the pool level began to fall more steadily heading into early August.
During the period of time when the reservoir was in moderate flood, or above 306.7 feet, structures and infrastructure was impacted along the shoreline.  At least 33 homes had some level of water incursion; damages were still being assessed as of this writing.  Lakefront roads were under some water for weeks as well.  Individual damage reports included an estimated $35.5 thousand to water pumps and related equipment.  Business losses also mounted at the Reservoir, where bass fishing is popular.  At least $15.3 thousand in losses was reported at Falcon State Park.
As of late September, a best estimate for property and infrastructure damage in Zapata County was at least $1 million; more is likely when the assessments are completed in autumn 2010.