Will Walls Worsen Rio Grande Flooding? U.S. IBWC Can’t Give a Straight Answer

By Scott Nicol

The United States section of the International Boundary and Water Commission (US IBWC) recently hosted a meeting in Rio Grande City to explain their decision to allow Customs and Border Protection to build new border walls in the Rio Grande floodplain.  While they should be commended for reaching out to local residents, they seemed completely unprepared, unable to answer the most basic questions about their decision or the new walls.

When, for example, landowners asked whether there had been any on-the-ground surveys, and what the wall would mean for access and impacts to their property, they got no response. 

The manager for Rio Grande City’s international bridge and port of entry asked how they would be able to access the riverbank to carry out ongoing erosion control efforts.  US IBWC did not know. 

Residents asked whether walls crossing the washes that feed into the Rio Grande might become blocked with debris, preventing normal drainage and causing flooding.  At that point US IBWC admitted that even though they approved these new walls months ago, Customs and Border Protection still has not provided them with the walls’ design specifications, so they could not answer that question either.

2007 Bureau of Land Management photo of debris in the Arizona wall

 

US IBWC was also unable, or unwilling, to answer a key question about the flood model that they are using to justify their approval of border walls in the floodplain. 

Using the Freedom of Information Act the Sierra Club has gotten a copy of the flood model, as well as a number of related documents.

In 2011 Customs and Border Protection paid Baker Engineering to produce a model that claimed that flood water would pass harmlessly through the 4-inch wide spaces between the border wall’s six-inch wide bollard posts.  Baker’s accompanying report stated that, “A debris blockage of 10% was adopted where the fence is aligned parallel to the flow and 25% at locations where the fence is aligned perpendicular to the flow.”

The model’s computer program cannot add to this number, cannot decide that it is too low and that in reality more debris will clog the spaces between bollards.  By telling the computer that 75% to 90% of floodwater will pass through the wall, Baker effectively predetermined the model’s end result.    

At the meeting in Rio Grande City, surrounded by residents whose lands and lives will depend on whether or not these walls will actually let water pass through or will dam it up, US IBWC could not explain where the suspiciously round and suspiciously low estimate of 10% - 25% debris blockage came from.

In earlier reports Baker Engineering came to a very different conclusion about how much debris border walls were likely to catch.

After border walls in Arizona became clogged with debris and acted as dams in 2008, inflicting millions of dollars of damage on both sides of the border and causing two deaths, Baker Engineering was hired to follow the wall from El Paso to San Diego and report back to Customs and Border Protection.  Baker found that, “PF 225 fencing obstructs drainage flow every time a wash is crossed. With additional debris build-up, the International Boundary Water Commission’s (IBWC’s) criteria for rise in water surface elevations (set at 6” in rural areas and 3” in urban areas) can quickly be exceeded.” The report included photographs of bollard-style walls nearly identical to those planned for the Rio Grande floodplain filled with debris, and documented “debris build-up which sometimes reached a height of 6 feet.”

 Photo from the 2009 Baker report showing debris in the Arizona border wall

In examining on-the-ground evidence of debris clogging border walls, it bolstered a 2008 Baker Engineering white paper that looked at the likely impacts of the walls planned for Roma, Rio Grande City, and Los Ebanos.  In discussing the wall’s transfer capacity - the ability of water to pass between the bollards - it stated that,

“The transfer capacity estimate has been shown to include a significant allowance for “clogging” due to the accumulation of debris.  In the case of fence segments O-1 [Roma] and O-2 [Rio Grande City], the transfer capacity was estimated to allow for a minimum of 85% and 67% clogging, respectively.  For fence segment O-3 [Los Ebanos], a minimum allowance of 36% was estimated.  It is important to keep in mind that these estimates apply to portions of the fence that are generally parallel to the direction of flow.  Areas that are oriented generally perpendicular to the direction of flow should (for reasons of prudence) be modeled as completely blocked, primarily due to the hydraulic effects of bollards themselves.”

Map of the three new border walls from the 2011 Baker flood model

 



So how did Baker’s estimates of clogging drop from 85%, 67%, and 36% down to 10% where the wall is parallel to the Rio Grande, and from 100% down to 25% where it is perpendicular?

The US IBWC has yet to give the public an answer to that question.

The new flood model, with its low debris estimate, is cited by the US section of the International Boundary and Water Commission as the basis for its decision to allow these border walls.  The Mexican section has rejected the model’s assumptions, countering in late 2011 that these walls would likely obstruct 60% - 70% of flood flows even before the clogging effect of debris is factored in. 

On February 9, 2012 the two sections of the bi-national organization met to discuss their disagreement.  Meeting notes written by the same US IBWC engineer who was unable to answer questions about the model’s assumptions at the Rio Grande City public meeting say that,

“It was recognized that the Mexican Section may prefer a higher percent debris blockage.  It was explained that the U.S. Department of Homeland Security (DHS) wanted minimum debris blockage and a percentage that was felt to be reasonable was agreed upon in the meeting on February 23, 2011, during which the modeling methodology was finalized between USIBWC, DHS, the U.S. Army Corps of Engineers and Michael Baker Jr., Inc.”

So even when they met with their Mexican counterparts, US IBWC gave no concrete evidence that the lower estimate was more accurate than the earlier, much higher one.  The nice, round, low number was \simply “felt to be reasonable”, despite conflicting with empirical evidence from Arizona, and was adopted because it matched up with the Department of Homeland Security’s desire for a model showing a “minimum debris blockage.”

Not only was Mexico’s estimate ignored, they were not even invited to participate in the 2011 modeling methodology meeting.  And six days after the 2012 meeting the US section, flouting its treaty obligations, unilaterally approved Customs and Border Protection’s request to build walls in the floodplain.

Customs and Border Protection photo of debris backed up behind the border wall

Customs and Border Protection (CBP) has not hosted a public meeting on border walls in South Texas since 2007, but they did send a representative to the recent Rio Grande City meeting.  He declined to present any information, and remained silent unless he was asked a direct question. 

When asked when CBP would begin construction he said that at this time they do not have the funds to build these walls.  He failed to mention that CBP bought the steel years ago and currently has it in storage.  More importantly, he failed to mention that the new fiscal year for federal agencies begins on October 1, at which time their bank accounts will be refilled. 

If border residents want answers, we need to demand them now. 

Representative Cuellar and Senators Hutchison and Cornyn need to pressure the US IBWC to reverse its bad decision, and direct Customs and Border Protection to finally give up on these dangerous walls.  They need to take concrete action, and they need to do it now.

But of course they won’t, unless we, their constituents and voters, tell them to.

October is only three weeks away.  The clock is ticking.