"Un-canalizing" a river
by Kevin Bixby
The Rio Grande has long been the lifeline for humans living in the Chihuahuan Desert, making human inhabitation possible in places such as El Paso, Ciudad Juarez and Las Cruces.
It also has provided important habitat for an impressive array of wildlife species, including 95 species of mammals, 345 birds, 95 amphibians and reptiles, and 44 varieties of native fish. Unfortunately, human activities over the past century have altered the river ecosystem to the point where its ability to sustain such diversity has been compromised.
Ecologically, the Rio Grande can't function without curves. It turns out that the river's twists and turns create a variety of water velocities, which in turn produce a mix of slow and fast water habitats, which in turn sustain the aquatic life that comprise the river's ecosystem. Unfortunately, there is very little sinuosity remaining in the 200 miles of the river in southern New Mexico and west Texas.
Beginning in 1935, the International Boundary and Water Commission (IBWC)-a federal agency within the State Department--straightened the river below El Paso as part of its "Rectification Project," reducing the river's length by nearly half in the process. Levees were built and the river's banks armored to confine the river to its new alignment.
Several years later IBWC did the
same thing in southern New Mexico as part of its "Canalization
Project." The purpose of these projects was to ensure efficient water
deliveries, provide flood control and stabilize the international
boundary.
These projects eliminated more than meanders. They destroyed essential fish habitat, and were a major reason (along with the annual dewatering of the river every winter since Elephant Butte Dam was built in 1916) for the disappearance of two-thirds of the native fish species in the river.
Management of the projects through the years has also been detrimental to the river. IBWC mows between the levees every year, preventing native (and non-native) riparian vegetation from becoming reestablished. In some areas it allows grazing of livestock, which has the same effect as mowing. It also dredges the channel and stabilizes the banks with riprap. All these actions are inimical to a healthy river system.
Now, for the first time in its history, the IBWC is thinking seriously about other ways of managing the Canalization Project. The impetus is two fold. A 1996 study suggests the project may not be able to convey its design flood, so the agency is proposing to raise or rebuild 56 percent of the levees. The agency also pledged in a 1999 agreement with the Southwest Environmental Center to look at management actions that could support river restoration, including non-structural approaches to flood control.
A draft environmental impact study analyzing different management alternatives has been released and is currently open for public comment (until March 1, 2004). The importance of this study cannot be overstated. It will be impossible to restore the river to any significant degree of functionality and self-regulation without allowing it to reestablish a more natural meander pattern. It may be possible to do this within the existing levees in places, but it may also require setting back the levees or finding other ways to widen the effective floodplain, through the purchase of adjacent land or flood easements.
The Canalization Project EIS is a high priority for river advocates. We don't expect IBWC to restore the river by itself, but we do expect it to do its part. To date, IBWC has shown a reluctance to look outside the levees or to make more than band-aid management changes.
Of the four alternatives in the DEIS, at IBWC's website only one-"Targeted River Restoration"-takes an ecologically sustainable approach to restoring the river ecosystem. It calls for the timed release of water from Caballo Reservoir to mimic the river's natural (pre-dam) peak flows in the late spring. Such flows are essential for shaping a sinuous channel, inundating the land between the levees, and reestablishing riparian and aquatic habitats that have largely disappeared.
SWEC supports this alternative, and calls on IBWC to do even more to restore the river. (The Targeted River Restoration alternative does little to help restore the downstream half of the Canalization Project's 105 miles.) We are committed to helping IBWC come up with a management alternative for the Canalization Project that allows the agency to meet its legal obligations for water delivery and flood control, but also opens the door for restoring the Rio Grande ecosystem.
For more info, contact the Southwest Environmental Center at (575) 522-5552.