Archive for March, 2011

By Stefanie Herweck

The International Boundary and Water Commission’s proposal to cut down the trees that line the banks of the Arroyo Colorado in the City of Harlingen has raised alarm among Harlingen residents, city officials, and conservationists.

Citizens brought their concerns to the IBWC Citizen’s Forum last month in Mercedes. But the gulf between the citizens’ views and those of the IBWC was revealed almost as soon as IBWC Principal Engineer Carlos Peña opened his mouth.

“The Arroyo Colorado was designed to carry 21,000 cubic feet of water per second,” Peña began.

In the standing-room-only audience a hand went up. “Could you clarify? Who designed the Arroyo Colorado and when did they design it?”

Peña seemed not to understand the thrust of this question. He discussed the revisions to the flood map that IBWC made after the flooding brought on by 1967’s Hurricane Beulah. He explained how the Arroyo Colorado was “designed” to carry 21,000 cubic feet per second (cfs) during a hundred year flood event, and that data from last year’s Hurricane Alex suggested it was only capable of handling a quarter of that flow.

The forested area on its banks, he said, had to be cleared to speed up the water moving through the arroyo.

The hand went up again: “Wouldn’t it be more accurate to say that you have designated that the Arroyo Colorado handle a particular flow amount? After all, it is God who designed the arroyo, not the IBWC.”

Peña seemed to think that this distinction was only a matter of words, but it lies at the heart of the conflict between the citizens and the IBWC. To the citizens, the Arroyo Colorado is a natural asset that God has blessed them with. To the agency, the Arroyo Colorado is just another part of the elaborate flood control system that they designed. It is this conflict that brought so many citizens out to speak up for their arroyo.

Concerned Harlingen residents and City leaders came to the Citizens Forum because the Arroyo Colorado is the reason their city was founded back in 1904. Generations of Harlingen children have explored the forest on the arroyo’s banks. And they know that, as the only city in the Valley with a natural stream running through its heart, the Arroyo Colorado is what makes Harlingen Harlingen.

For the conservationists in the audience, the Arroyo Colorado is an ancient natural stream, a part of the Rio Grande Delta that drains northward into the Laguna Madre. Over centuries it has deposited the rich alluvial soils that make agriculture possible north of the Rio Grande. It supports the last remaining streamside ecosystem in the Valley aside from remnants scattered along the Rio Grande. It also forms a natural streamside corridor that could allow wildlife to travel from the Rio Grande to Laguna Atascosa National Wildlife Refuge.

This corridor could be the key to the survival of the ocelot and the jaguarundi, critically endangered cats that once roamed the entire Rio Grande Delta. Last year, two ocelot kittens were born in Laguna Atascosa National Wildlife Refuge. There isn’t enough habitat in the Refuge to support them all, and as they prepare to strike out and find their own territory, their future is uncertain. The Arroyo Colorado, with its mouth on the northern edge of Laguna Atascosa, offers the ocelots a pathway to new habitat.

Some in the audience were among the citizens who banded together to create the Hugh Ramsey Nature Park on the arroyo’s banks. Still maintained in part by local community groups such as garden clubs and boy scout troops, this unique park has become a popular destination for residents and tourists alike.

The World Birding Center has opened another jewel on the Arroyo Colorado, the 40-acre Harlingen Thicket. These two natural streamside parks bring thousands of ecotourists to Harlingen every year and are helping to make the City the center of the lucrative ecotourist industry in the Rio Grande Valley. The birds that draw people to these parks and to Harlingen’s Rio Grande Valley Birding Festival are dependent on the forest along the arroyo.

But where the citizens see a heritage, a habitat, and a worthy investment in the economic future of a city, IBWC sees only a drainage ditch.

This failure to see the whole river with its range of important functions shows that IBWC is behind the curve when it comes to the latest research and best practices. It reveals that the agency is in desperate need of a paradigm shift.

Evidence is mounting that highly-engineered flood control systems on rivers create as many problems as they solve. This is because the man-made flood control structures are at odds with natural flood protection systems like wetlands, streamside forests, and natural floodplains.

By containing the river in a channel without regard to the floodplain and natural meanders, the man-made system starves the surrounding wetlands of water. Areas that once acted like living sponges dry up, die, and no longer absorb and store floodwaters.

Removing streamside trees also decreases this natural capacity to absorb water. A single large tree, such as one of the majestic cedar elms that line the arroyo, can soak up 40,000 gallons of water per year, which it releases into the atmosphere. In the process, the trees and other vegetation also act as natural filters, purifying the water of pollutants from urban and agricultural runoff.

The roots of streamside trees also anchor the soil on the banks. When they are removed, storm water runoff speeds into the river, tearing deep channels through the bank. When the unnaturally fast waters of the river hit the now undermined bank, erosion can be extreme. It could spell disaster for Harlingen neighborhoods along the arroyo.

The eroded material in turn leads to silt deposits and sandbars which block the channel and increase the risk of flooding.

This problem often requires yet another engineering fix: dredging the river to remove sediment. An eroded bank might also be lined with concrete to keep it from eroding further.

Maintaining a system like this becomes increasingly expensive and increasingly destructive to the river as a natural system. It often ends with a concrete-lined drainage ditch that bears little resemblance to a natural river.

Realizing that unnatural and over-engineered systems are unsustainable and damaging, communities and agencies across the country have begun taking steps to restore their rivers. They are taking innovative approaches to flood control that work with, instead of destroy, the river’s natural systems.

Preserving and enhancing native vegetation along the riverbanks is a key component of these efforts.

If the IBWC continues to operate single-mindedly as “designer” and clears the banks of the Arroyo Colorado, they will doom the arroyo’s future as a natural stream, strip Harlingen citizens of their greatest natural asset and seriously set back the establishment of a Lower Rio Grande Valley wildlife corridor.

Instead, the agency should break out of this outdated, destructive paradigm and approach their mission with a deeper understanding of the many vital functions of healthy rivers both for natural ecosystems and for human communities. They should see the current challenge posed by the Arroyo Colorado as an opportunity to innovate and to create sustainable flood control systems that work with nature.

The IBWC will truly serve the communities of the Lower Rio Grande Valley when the agency realizes that we need healthy rivers as much as we need flood control.

Originally published in the Rio Grande Guardian.


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