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City proposes wider critical water quality zone to protect Colorado

Tuesday, January 22, 2008 by Mark Richardson

Changes in the way critical water quality zone (CWQZ) buffers are measured in the Colorado River south of Longhorn Dam, approved last week by the Environmental Board, are designed to improve water quality and preserve the river’s economic and recreational values.


A proposal developed by the city Watershed Protection and Development Review Department (WPDR) would amend the City Code to measure the CWQZ buffer from the bank rather than from the centerline of the river.


“Currently, with parts of the Colorado up to 300 feet wide, there are places where most of the protective buffer is under water,” said Matt Hollon with WPDR. “This change will push future mining operations and development back a safe distance and stabilize the river bank.”


City Code currently calls for a 200-foot buffer along the Colorado River on the 28 miles from Longhorn Dam to the end of the city’s five-mile extraterritorial jurisdiction boundary. Landowners that are currently using the 200-foot setback from the water’s centerline will be grandfathered under the amended code.


However, Hollon said that most of the property along the city’s stretch of the river remains undeveloped, so the amendment should be effective in stopping pollution and halting the encroachment of mining operations.


“This will only affect a small portion of the undeveloped tracts along the river,” he said. “Currently, 13 percent of undeveloped land is in the CWQZ. With the changes, that will only increase to 17 percent.”


Some of the benefits of the change include water quality factors such as temperature moderation, sediment control and base flow maintenance. From a flood control standpoint, it will moderate extreme flows and resulting damage, intercept and store rainfall and runoff, and promote bank stability.


Hollon also said it would protect the ecosystem near the river by protecting riparian trees, plains and soils, preserve wildlife corridors, and prevent encroachment by vehicle traffic.


He also noted that at two points along the river, mining operations have seriously eroded parts of the riverbank, and breakthroughs in the bank have at times rerouted the river stream. The new buffers should help prevent that as well.


Chair Dave Anderson said the amendment was an important change to the City Code.


“This will help resolve a problem that was created years ago and will help keep the river clean,” he said.


The proposed amendment will go the Planning Commission, then the City Council. City officials also plan, once it is approved, to present it to the Travis County Commissioners.

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