FLAGSTAFF, Ariz. — Coconino National Forest’s Cinder Lake—a natural depression that has been used to store runoff from areas affected by the 2010 Schultz Fire—can store about 4,000 acre-feet of water, or enough to fill about 2,000 Olympic-sized swimming pools, according to a new U.S. Geological Survey report. These findings will be used by the federal, state, and local agencies developing a comprehensive plan to mitigate flooding in the neighborhoods affected by the Schultz Fire.
"Time will eventually heal the scars left on the landscape impacted by the Schultz fire, as biological communities become re-established and physical and chemical weathering recreate fertile soils," said USGS director Marcia McNutt. "Until then, the good news is that Cinder Lake has copious capacity to mitigate flood risk for downslope communities."
The 2010 Schultz Fire burned more than 15,000 acres northeast of Flagstaff, making the burned areas susceptible to larger and more frequent flood events. Flooding increases because the charred ground where vegetation has burned away cannot easily absorb rainwater. Neighborhoods downslope of the burned areas have experienced extensive damage to homes, property, municipal waterlines, and roads as the result of post-fire flooding.
"This study is a cooperative effort between the USGS, Coconino County, and U.S. Forest Service to develop sound information in response to wildfires," said Jamie Macy, a USGS hydrologist with the Arizona Water Science Center and the study’s lead author. "In a time of shrinking resources, this effort is a really wonderful example of federal and local agencies working together to address critical community needs."
Coconino County implemented emergency measures to protect homes in downslope communities in response to extensive flooding during the summer of 2010. These measures included widening and deepening roadside ditches to carry runoff from the burned areas away from affected neighborhoods to Cinder Lake and other undeveloped national forest land.
"Determining how much water Cinder Lake can store was a critical question, and the County turned to the USGS to find the answer because of its water science expertise," said Mandy Metzger, Coconino County Supervisor. "The USGS findings indicate that Cinder Lake provides substantial storage capacity that can be used to help protect homes from flooding."
The USGS conducted subsurface surveys and drilled four boreholes to estimate the area’s potential for water storage. The highly porous layer of cinders and sedimentary deposits at the surface of Cinder Lake extends to a depth of about 30 feet, below which is a less porous layer of basalt. By volume, 43% of this very porous uppermost layer is available for water storage.
On the basis of these findings, the 300 acres occupied by Cinder Lake can store an estimated 1.3 billion gallons of water. For reference, the flood events that occurred during the 2011 summer monsoon season produced about 50 acre-feet of runoff, or 16 million gallons, that was moved to Cinder Lake.
"The USGS study shows that Cinder Lake is an integral, highly effective component of the current floodwater mitigation network,” said Coconino County Supervisor Liz Archuleta. “Moving forward, this information will help us implement the flood control measures necessary to protect the surrounding community."