Flash floods push New Mexico dam to the brink of failure, forcing evacuations

Floodwaters swollen by the remnants of Hurricane Polo pushed an aging earthen dam in southern New Mexico to the brink of failure on Tuesday, forcing evacuation orders for five communities in Doña Ana County and capping two weeks of flash flooding that has killed at least four people across the state.

The McLeod Dam, a flood-control structure outside the village of Rincon, was overtopped by rushing water Tuesday afternoon as storms dumped several inches of rain on the surrounding watershed in a matter of hours. Dam operators and county emergency officials warned of "imminent failure and potentially life-threatening flooding downstream," and the National Weather Service office covering the region issued an emergency alert directing residents to move to higher ground immediately. By Wednesday morning, local radio reported the dam had not breached, though water was still passing over the top of the embankment.

What happened

Doña Ana County ordered evacuations in Rincon, Hatch, Salem, Garfield and Placitas late Tuesday as the dam's earthen embankment absorbed the brunt of a fast-moving storm cell. Most residents of Hatch, Salem, Garfield and Placitas were allowed to return home later that night after water levels stabilized, but Rincon, the community directly downstream of the dam, remained under evacuation orders into Wednesday. County officials said crews worked through the night assessing the structure and reinforcing an arroyo channel that had failed to carry the runoff.

New Mexico State Police Sgt. Ricardo Breceda said no deaths or injuries had been reported in connection with the dam emergency as of Tuesday evening, even as officers, New Mexico National Guard swift-water teams and federal resources fanned out across the county to assist stranded drivers and monitor road washouts.

The numbers

The McLeod Dam was built in 1951 and is classified as a high-hazard structure, meaning its failure could threaten lives downstream. According to the U.S. Army Corps of Engineers' National Inventory of Dams, the earthen embankment stands roughly 18 to 25 feet tall, depending on the measurement point, and is designed to hold several hundred acre-feet of water back from the Rio Grande valley below. Some parts of the Desert Southwest received more than 4 inches of rain in the 36 hours before the dam was overtopped, with a statewide flood watch warning of another 1 to 3 inches, and locally up to 6 inches, through Wednesday. Statewide, the two-week flooding spell tied to Hurricane Polo, Tropical Storm Odalys and a late-season monsoon surge has now been linked to at least four deaths and multiple emergency declarations across Doña Ana, Santa Fe, Socorro, Mora, San Miguel and McKinley counties.

How we got here

Hurricane Polo exploded from a disorganized tropical depression into a Category 5 hurricane in the eastern Pacific in roughly 42 hours this month, one of the fastest rates of intensification ever recorded in the Western Hemisphere, with sustained winds reaching 180 mph and a central pressure that made it the second-most-intense eastern Pacific hurricane on record after Hurricane Patricia in 2015. Though Polo stayed offshore of the U.S. mainland, its moisture plume combined with the remnants of Tropical Storm Odalys and an unusually persistent late-season monsoon pattern to pour repeated rounds of heavy rain onto New Mexico, Arizona and West Texas through September.

Ground across much of New Mexico was already saturated from earlier storms, including flash floods on the Navajo Nation on Sept. 16 that killed three people, including a 7-year-old girl, near the community of Newcomb, prompting Navajo Nation President Buu Nygren to declare a state of emergency. A Farmers' Electric Cooperative lineman, Ian Massey of Clovis, was electrocuted on Sept. 25 while repairing a storm-damaged utility pole that had toppled into standing water. New Mexico's Department of Homeland Security and Emergency Management activated its statewide emergency operations center on Sept. 22, pre-positioning National Guard swift-water crews near Las Vegas and Ruidoso and distributing thousands of sandbags, anticipating exactly the kind of compounding flood risk that materialized this week.

Who is affected

The immediate threat centers on hundreds of residents across the Rincon, Hatch, Salem, Garfield and Placitas area, a stretch of small farming communities along the Rio Grande known for chile and onion production. Farmland and employee housing near the dam sustained heavy damage from mountain debris and rushing water even before the embankment was overtopped. Flooding has also struck far beyond Doña Ana County: in Santa Fe County, the Tierra Real Mobile Home Community saw water reach residents' doorsteps, and multiple rural roads were closed by washouts. In Socorro County, a person was swept away in Brown Arroyo before emerging from the floodwaters unharmed, and county officials closed schools as roads around Socorro and San Antonio threatened to become impassable. In Clovis, which received 8 to 11 inches of rain the previous week, city officials warned that retention ponds and lakes were already near capacity heading into more rain.

Reaction

The scale and speed of the flooding, after a summer of drought concerns in parts of the state, has left some residents with a bitter irony to reckon with.

"We've been praying and praying and praying for rain. I just don't think anyone expected everyone's prayers to be answered all at once on one day."

That was Alessandra Alanis, a farmer near the McLeod Dam, describing the whiplash of a dry year turning into a flood emergency in a matter of hours. In Socorro County, Commission Chair Joe Gonzales offered a similar assessment of the storms' timing: residents had asked for relief from dry conditions, he said, and "we just got a little bit more specific" than intended. In Santa Fe County, longtime resident Javier Talavera, whose mobile home took on water, called it the worst flooding his family had seen in 30 years. County officials across the affected region have repeated variations of the same warning to drivers: do not attempt to cross flowing water or drive around barricades at flooded low-water crossings.

What happens next

The Doña Ana County government said engineers would continue inspecting the McLeod Dam and the arroyo channel below it through the week before deciding when to lift the evacuation order for Rincon. A statewide flood watch from the National Weather Service remains in effect, with forecasters warning that additional moisture drawn north from Polo's remnants could bring more rain to already-saturated ground into the weekend, raising the risk of renewed flash flooding and further strain on aging flood-control infrastructure. Federal and state forecasters said the wider pattern tied to Polo's remnants was not expected to clear the region for several more days, and state officials said the recovery in the hardest-hit counties would likely stretch on for weeks. The McLeod structure, built in 1951 to standards that predate much of the region's current growth, is a reminder that New Mexico's network of aging, high-hazard earthen dams is now being tested by rainfall patterns its engineers did not anticipate.