A concrete section of a border wall designed to keep illegal immigrants from entering Nogales, Ariz., became a dam that compounded flood damage in Mexico.

Floodwaters over the weekend designed to flow through an underground wash spilled onto Calle International in Nogales, Sonora, hitting the concrete wall and pooling up as high as 6 feet along storefronts, pictures taken Saturday evening obtained by the Santa Cruz County Flood Control District show.

The water stood only inches to a few feet high along East International Street in Nogales, Ariz., on the other side of the border fence, the pictures show.

The Mexican street is directly east of the Dennis DeConcini Port of Entry. All stores within about 300 feet of the border had significant damage, said Francisco Octavio Gastelum Ceballos, director of urban planning and ecology for Nogales, Sonora. And at least 50 vehicles parked in the areas were swept away, he said.

With the wash underneath the two cities not working properly, the concrete section of border wall could become a hazard to Nogales, Ariz., too, said John E. Hays, flood-plain coordinator with the Santa Cruz County Flood Control District.

In a worst-case scenario, a strong rush of water could knock the wall over, sending a flooding wave into downtown Nogales, Ariz., businesses, he said. In addition to the water, it would bring debris and pieces of concrete.

With more than two months left in the monsoon season — declared by the National Weather Service this year from June 15 to Sept. 30 — the nearly impermeable concrete structure is a looming disaster, Hays said.

"It really doesn't behoove anybody to have it like that," Hays said. "The water should be able to come across freely."

City officials in Nogales, Sonora, have sent a formal petition to the mayor of Nogales, Ariz., asking that something be done to allow for some water to pass through the concrete section, Gastelum Ceballos said.

The wall serves as a firm barrier to stop smugglers and illegal immigrants from dashing through or over the fence, said Brian Levin, Customs and Border Protection spokesman. It is surrounded on each side by steel "landing mat" fence.

It remains unclear if any plans are in place to evaluate the structure. Levin and Rob Daniels, spokesman for the U.S. Border Patrol, were unsure whose responsibility the wall would be.

Nogales, Ariz., Mayor Octavio Garcia-Von Borstel and officials with the International Water and Boundary Commission could not be reached for comment.

The concrete wall was built to replace a section of steel landing-mat fence in the late 1990s after community leaders urged federal officials to build a more visually appealing barrier, said Santa Cruz County Sheriff Tony Estrada.

"It was just an ugly landing-mat wall that they had up there, and it was an insult to both countries," Estrada said.

Designers of the federally funded fence didn't anticipate having to deal with floodwaters on the street because the Nogales Wash was working properly at the time, said John Kissinger, deputy city manager in Nogales, Ariz.

The growth of Nogales, Sonora, has stressed resources in the border city and in its sister city, Nogales, Ariz., Kissinger said. "When they designed and built the wall, they weren't anticipating the channel would fail," he said.

He agreed that the wall design should be re-evaluated in light of the weekend's events but said a working wash also would alleviate the problem.

"If the channel was redesigned and was working correctly, it would be a moot point," Kissinger said.

Nogales, Ariz., has declared a state of emergency and is waiting for a response from the state. Mayor Garcia-Von Borstel is planning to meet with Arizona's congressional delegation to ask for funds for repairs to the wash.

The repair estimate for the damaged 200-foot section of wash is estimated at $500,000. In May, the U.S. Section of the International Boundary and Water Commission paid $500,000 to repair the 150-foot section of wash damaged last year.

In Mexico, the federal government's National Water Commission has approved a $3 million project to completely reconstruct a 1,000-foot stretch of the wash, starting at the border and running south, Gastelum Ceballos said.

Officials and residents in both border cities remain concerned about possible damage from rainfall. On Tuesday afternoon, storms in Mexico dropped up to 2.5 inches of rain in about 45 minutes, said Craig Shoemaker of the National Weather Service.

The water flow in the wash rose to 7 feet, washing away sandbags and rock that had been placed in a 200-foot damaged section of the wash earlier in the day, Hays said. It was the second straight day crews' work had been swept away.

A 30 percent chance of rain was forecast for today, and a 20 percent chance for Thursday and Friday, said the weather service's Shoemaker.

● Contact reporter Brady McCombs at 573-4213 or bmccombs@azstarnet.com.