Wildfires can threaten dam safety , ECOconnect
As a dam owner, you are responsible for the proper care and management of your dam. (See disclaimer below) With wildfires in Washington State on the rise, it is important to understand the potential impacts of wildfires on your dam, especially if heavy rains follow.
In 2014, wildfires burned six times as many acres as usual: 363,000 acres. The average amount of acres burned in each of the previous five years was 61,000. Rising temperatures, more and longer lasting heat waves, and drier summers are expected to contribute to larger, more severe and more frequent wildfires in the future.
Although only owners of dams classified as high hazard and significant are legally required to have Emergency Action Plans (EAPs) in place, all dam owners should have plans for emergency situations. Being aware of the potential impacts of wildfires is an important part of that planning. Here are some basics:
The Dam Safety Office (DSO) uses three levels to describe emergency situations. Level 1 incidents are characterized as non-emergency, unusual events, which need a response to reduce the risk or likelihood of a more serious problem (Level 2 or 3 incident).
Wildfire at or near your dam or within the watershed where your dam is located is a Level 1 incident. Remember that water moves differently through a burned watershed than it does through an undamaged one. This is true even for rainfall events that previously would have been considered rather minor.
For more information about burned areas and flash flooding, see article on Burn Scars Have an Increased Risk of Flash Flooding and Debris Flows, courtesy of the National Weather Service, Pendleton and Boise offices.
For additional safety tips regarding debris flows (mudslides), see article on Post-Fire Hazards: Debris Flows, courtesy of the Okanogan-Wenatchee National Forest 2014 BAER team and the Colorado Geological Survey.
Your watershed will need assessment by a qualified engineer or engineering hydrologist to assess the increased hydrologic risk, especially if your dam is classified as “high hazard” or “significant hazard.” DSO has prepared guidance for consultants see disclaimer, below):
In addition to this guidance from DSO, the Natural Resources Conservation Service (NRCS) compiled their own more comprehensive guidance for performing post-wildfire hydrologic analyses:
Disclaimer: The dam owner should know more about their dam than anyone else. In Washington State, liability can be imposed upon a dam owner if they fail to maintain, repair or operate the dam in a safe and proper manner. It is uncommon that a dam owner has all of the technical skills needed to monitor the condition of the dam. Thus, the role of the consulting engineer is critical to dam safety.
The information provided herein [the guidance materials] is intended as a potential starting point for hired consultants to assess dam safety in the event a forest fire occurs at or near the site of a specific dam. The information and methods shared on this webpage and in the attached reports should not be used without first securing competent advice with respect to its suitability of any general or specific application. Ecology makes no representation or warranty of any kind, whether express or implied, concerning the accuracy, completeness, suitability or utility of any information, apparatus, product, or process discussed herein, and assumes no liability therefor. Neither the State of Washington, the Department of Ecology, nor Ecology’s reviewing engineer(s) are authorized to accept any of the design engineer’s professional responsibility and/or potential liability.
Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.htm