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USGS Measures the Response of the Rodeo/Chediski Burn
Released: 7/24/2002

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192
Mark Anderson 1-click interview
Phone: 520-670-6671 ext. 222

Chris Smith
Phone: 520-670-6671 ext. 251



Editors- Photographs are available at:
http://az.water.usgs.gov/newevents/rodeofire.html

Last week, USGS scientists began sampling sediment and organic-rich streamflow coming from the Rodeo/Chediski fire burn area to discern possible ecological and water-quality effects of this discharge. In addition, three new USGS streamflow gages are allowing advance warning of possible flooding to affected Arizona communities.

Monsoon thunderstorms of the last two weeks in the Rodeo/Chediski fire burn area have produced large peak streamflows in response to relatively small amounts of rainfall. The sediment-laden water running off the burn area contains organic debris, dissolved nutrients, and other chemical compounds released by the fire’s combustion, said Mark Anderson, chief of hydrologic investigations and research for the U.S. Geological Survey in Tucson.

This sediment and organic-rich water from the burn area significantly increased the flow of the Salt River, the major tributary of Theodore Roosevelt Lake. USGS scientists began collecting water samples of these first inputs to Roosevelt Lake, a primary water supply for the Phoenix metropolitan area, on July 17. The water samples collected by USGS scientists from the Salt River upstream from Roosevelt Lake will be analyzed to determine the types and amounts of dissolved nutrients, salts, metals, and organic carbon as well as suspended sediment flowing into the lake.

"Results from these samples will aid land and water managers in determining the amounts of nutrients and organic matter flowing into Roosevelt Lake that could affect drinking-water quality, aquatic habitat, and the ecology of the lake," Anderson said. "If amounts are too high, low oxygen levels, fish kills, and drinking-water taste and odor problems may develop later this summer."

Three new streamflow gages installed by the USGS in the burn area immediately after the fire, provided the advance warning that these monsoon flows were on the way. The gages, which were installed in cooperation with the White Mountain Apache Tribe, also provide flood warning for the communities of Carrizo and Cibecue where precautionary evacuations occurred during these storms based in part on the USGS data transmitted in real time from these new gages. The USGS in Arizona operates a network of 220 streamflow-gaging stations that are part of a nationwide network of more than 7,000 gages. This network of gaging stations safeguards lives and property and ensures adequate information is available for managing water resources. Key to that information network is a core of federall funded stations that are a part of a National Streamflow Information Program. Additional streamflow and water-quality monitoring by the USGS in Arizona will provide valuable data for understanding the hydrologic impacts of wildfires in Southwestern watersheds.

"Thanks to these new real-time gages, we were able to predict the arrival time of this first fire runoff into Roosevelt Lake and have scientists on the scene ready to measure and collect samples of this scientifically important first flush of water after the fires," Anderson said.

Field measurements taken by the USGS after the flood wave passed the sampling site on the Salt River above Roosevelt Lake revealed that dissolved oxygen concentrations had dropped dramatically from a typical 6 milligrams per liter to as little as 1 milligram per liter. "For comparison," said Anderson, "3 to 5 milligrams per liter of oxygen is required to sustain fish over a long period." "But," he noted, "USGS data show that it’s not all bad news for the Salt River— concentrations of dissolved salts in the river decreased as the added storm runoff diluted the normally salty summer streamflow."

Additional information about the USGS water-resources studies in Arizona can be obtained via email to webmaster@az.water.usgs.gov or by visiting the Arizona District home page at http://az.water.usgs.gov.


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