Critics say the design of the border fence caused debris and water backup during a July 12 storm that led to flooding at the port of entry at Lukeville and Sonoyta, Mexico, and at the Organ Pipe Cactus National Monument.
"One of the reasons for it was the debris that accumulated on the fence itself," said Lee Baiza, superintendent of the monument, a 517-square-mile lush desert tract overseen by the National Park Service.
Environmental groups have criticized the manner in which the U.S. Army Corps of Engineers and contractors for federal agencies have designed and built a range of fencing and vehicle barriers at various points along the Arizona-Mexico border.
In particular, they've denounced Homeland Defense Secretary Michael Chertoff'sto hasten construction as the Bush administration pushes to complete 670 miles of fences and other barriers by year's end along the nearly 2,000-mile Mexican border.
The barriers are intended to deter illegal immigrants and drug smugglers.
Critics have said the design of the pedestrian fencing being put in on the Arizona border is flawed. Much of that fencing consists of 10-foot wide and 15-foot tall steel-mesh panels, some featuring a series of wide horizontal grates at the bottom designed to let water and sediment flow through.
"While the Bush administration may claim it's taking environmental impacts of the border wall into consideration, building wire mesh fences across washes prone to debris-laden floods is fundamentally flawed," Robin Silver, a spokesman for the Center for Biological Diversity, said in a statement.
Defenders of Wildlife spokesman Matt Clark said what happened at Organ Pipe validates the warnings voiced to Homeland Security before construction started.
"It doesn't take an expert hydrologist to anticipate the potential for these walls to become like dams," Clark said, "especially in flash flood type of storms, where a lot of water and debris are generated very quickly and can pile up against the fences very rapidly."
He noted that rapidly moving runoff in washes dislodged or eroded large chunks of concrete foundations, and debris stacking up against the fence created barriers that redirected water, creating gullies and causing even more erosion.
Federal officials maintain that while Chertoff has invoked his waiver authority three times in Arizona, he has ordered Customs and Border Protection and Border Patrol officials to adhere to environmental requirements.
"We are still required to follow every environmental rule, regulation and policy," said Robert Gilbert, chief of the Border Patrol's Tucson sector. "He does not waive us doing what we would have to do without the waiver. So it doesn't change anything in the environment."
The Organ Pipe monument's staff produced a report earlier this month on the pedestrian fence's effect on the 330,000-acre monument's drainage systems and infrastructure.
It concluded that the fence failed to meet hydrologic performance standards of the U.S. Army Corps of Engineers or standards set by the U.S. Border Patrol's final environmental assessment for the project.
That assessment determined that the 5.2-mile pedestrian fence would have no significant impact on the monument's environmental features.
But the recent monument report said its own staff had raised concerns last year over the fence-building plans, based on knowledge of local flash flooding.
The July 12 storm dumped as much as 2 inches of rain in about 90 minutes in the area, and water running through washes on the monument backed up as debris piled along the base of the fence.
It created pools up to seven feet deep and flows several hundred feet wide that eroded some areas along patrol roads. The waters even scoured some fence and vehicle barrier foundations.
"The monument had suggested that they take into consideration everything that can happen with a weather event," particularly an accumulation of debris, Baiza said. "We had a concern that this was going to happen."
Baiza said the fence designers are being asked to come back and study the drainages again to come up with alternatives.