Wildfires and the Impact on Water Quality

Background

In the summer of 2012, several major wildfires burned thousands of acres of Colorado forests.  The National Interagency Coordination Center reports that nearly 1.2 million acres have been burned in the Rocky Mountain region in 2012 alone.  Wildfire risk will increase in the near future, according to Colorado Senator Mark Udall in a recent letter to the United States Department of Agriculture, asking the department to help reduce the wildfire risk in the state’s overgrown forests through increased logging.  Senator Udall, who serves on the U.S. Senate Energy and Natural Resources Committee, cites drought, high rates of pine beetle kill, and higher population in fire risk zones as significant contributors to the increased wildfire risk.  Additionally, an article recently published in the Ecological Society of America journal, Ecosphere, estimates increased risk of wildfires in temperate zones, like Colorado, over the next few decades in response to global climate changes.

Compounding the immediate damage done by wildfires to public and private property is the subsequent negative effect on the water flow and quality downstream when the fires occur in forested watersheds.  Water users downstream of burned areas experience an increased risk of flash floods during rainstorms as well as dramatic declines in water quality for several years after the fire.  These effects pose problems for water utilities in particular.  Water utilities are obligated to meet federal regulation for safe and clean drinking water for their customers despite source water quality.  With an increased risk for wildfires in the future, they must look for possible solutions to the water quality problems.

Effects on Water and Soil

The Colorado State Forest Service lists several latent effects of wildfires on soil and water conditions.  With the associated loss of vegetation after wildfires, there is very little to slow water runoff during rainstorms.  In particularly severe wildfires, the burning of certain plants releases a waxy substance that settles in and coats the soil, making it more difficult for the soil to absorb water.  These two conditions substantially increase the rate of erosion in watersheds, along with the risk of flash floods downstream.  Simultaneously, fast-moving water can sweep up debris, sediment, and ash— turning the water black and transporting a large amount of material downstream.  This sediment and debris can eventually clog smaller streams and rivers or begin to fill-in reservoirs.

A 2012 report from the U.S. Geological Survey measured the effects of the September 2010 Fourmile Canyon Fire on the water quality of the Fourmile Creek Watershed.  The report showed large increases in turbidity, nitrate concentrations, and dissolved organic carbon (“DOC”) concentrations during the light rainstorms shortly after the fire.  The increases were less substantial during the spring snowmelt, but heavy summer thunderstorms increased turbidity, DOC, and nitrate concentrations well above the levels following the initial precipitation, and moved a large amount of sediment from hillsides into the creek.  Because of the presence of mine waste in the Fourmile Creek Watershed, the Survey also detected slightly elevated levels of metal concentrations downstream.  The report indicates that these increased levels are likely to increase operation and maintenance costs for water utilities that are dependent on burned watersheds for source water.  Also, increased levels of sediment can fill-in and compromise water reservoirs.  Nitrates exacerbate algae growth, creating negative effects on water taste and odor.  Higher turbidity and DOC concentration complicates the chemical treatment process and results in more hazardous byproducts, such as chloroform and trihalomethanes.  The report cites other studies that have found similar water quality problems from burned watersheds for up to ten years after the fire.

Addressing the Problems

The U.S. Geological Survey report suggests that water utilities measure surface water quality after wildfires to determine when to divert water or when to change water sources.  For many utility companies, though, there are very limited alternatives to potentially degraded source water.

In Colorado, intergovernmental Burn Area Emergency Response (BAER) teams have begun addressing the problems created by wildfires, and continue to take action to prevent watershed erosion and improve water quality.  These teams include specialists from the Natural Resources Conservation Service, the Colorado Department of Transportation, the U.S. Forest Service, and local governments.  The BAER teams mulch and seed the worst burn areas to promote vegetation recovery, and attempt to slow water runoff and erosion through the construction of culverts, silt fences, and log terraces.  A large amount of funding for these teams comes from the federal government through the Emergency Watershed Protection program.  However, the amount of funding has not been adequate to fully address the damage done.  In response, Senator Udall has requested additional relief money from the Federal Emergency Management Agency, in part to help water utilities recover from the high cost of repairing source watersheds and infrastructure.

Professor Tom Meixer and Pete Wohlgemuth, a US Forest Service hydrologist, suggested a more proactive means of lessening the impact of wildfires on water quality in an article which found similar negative effects as the U.S. Geological Survey report.  Meixner, with a Ph.D. in Hydrology and Water Resources, worked with Wohlgemuth to analyze several burned watersheds.  Their research showed that the levels of sediment runoff and nitrate concentrations were substantially lower in areas that had previously been the subject of prescribed fires.  These controlled burns would reduce the amount of fuel available in wildfires.  With less fuel comes less sever burning in the watershed, and thus less negative effect on downstream water.

Conclusion

As the risk for wildfires increases in areas like Colorado, it’s important to recognize the potential resultant issues with water quality, and to take appropriate steps to maintain the efficient supply of clean drinking water.  Much of what is being done today is reactive in nature, such as seeking to speed up the process of watershed recovery and reduce the rate of erosion.  However, proactive alternatives are available and should be implemented as well.  As Senator Udall mentioned in his letter to the USDA, many Colorado forests are overgrown.  The added potential fuel for wildfires is a significant contributor to water quality problems downstream.  With the reduction of fuel through logging and controlled burns, it might be possible to reduce the undesirable latent effects of wildfires on forested watersheds and water quality.


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