Tuesday, August 4, 2015

Wildfires can threaten dam safety

by Lynne Geller, communications and outreach, Water Resources Program

For dams in forested watersheds, fires, floods and failures can happen, and happen quickly. Ecology’s Dam Safety Office (DSO) is getting the word out about the potential impacts of wildfires on dams, especially if heavy rains follow. As a dam owner, you are responsible for the proper care and management of your dam. We all have a stake in dams functioning properly and safely. And wildfires in our state are on the rise.

Wildfires can damage the surface of a dam or spillway. Associated facilities, especially wood structures or plastic pipes, are vulnerable. Fire changes the water conditions of a watershed, such as how fast water can move, and how vulnerable the land is to erosion.

Heavy rains in a burned area can create an additional set of problems. These include more and faster runoff; large amounts of sediment which reduce storage capacity; and mudslides that can block spillways and access to the dam.

If there is a wildfire at or near your dam, or within the watershed where your dam is located, you must promptly evaluate the situation. Determine what, if anything, is needed to keep the dam and surrounding area safe, and take necessary action. This is your responsibility as a dam owner.

Pay close attention to rain predictions and events

It is important for dam owners to remember that water moves differently through a burned watershed than it does through an undamaged one. Rainfall events that previously would have been considered rather minor can now be very damaging.

If rain is forecast, especially heavy rain or flash flooding, you must closely monitor actual rainfall near your dam or in your watershed.

If rain actually occurs, especially heavy rain or thunderstorms, you must closely monitor actual runoff and spillway performance. Be prepared to implement your emergency action plan in case spillway capacity is exceeded.

Be prepared: the importance of planning

Although only owners of dams classified as significant hazard and high hazard 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.

Our DSO strongly recommends that you have a watershed assessment by a qualified consultant, especially if there is a risk of harm to people and property downstream. The Dam Safety Office just released burned watershed guidance for use by qualified engineers or engineering hydrologists to assess dam safety in the event a forest fire occurs at or near the site of a specific dam.

The problem isn’t going away

Wildfires in our state are on the rise. In 2014, wildfires burned six times as many acres as usual: 363,000 acres. Already this year, three have been more than 750 unintended fires that have burned 74,000 acres. Compare this to the average amount of acres burned in each of the past five years: 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.

For more information, see Ecology’s webpage on dams and fires. This page includes links to other resources.

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