Risk analysis & planning

Wildfire

It's important that dam owners understand the potential impacts of wildfire on dams, especially if heavy rains follow. Wildfires can damage:

• The surface of a dam or spillway, especially grass cover on embankment slopes or grass lining in a spillway channel.
• Associated facilities, especially wood structures or plastic pipes.

Wildfires also change the water conditions of a watershed, such as how fast water can move and how vulnerable land is to erosion. Heavy rains in a burned area can create:

• More and faster runoff from rainfall, especially high-intensity storms.
• Large amounts of sediment, which may reduce storage capacity in a reservoir.
• Debris flows (mudslides) or downed timber, which may obstruct spillways or access to a dam.
• More floating debris (dead trees, branches, sticks, etc.) in a reservoir, which may obstruct spillways.

What to do after a fire

If a wildfire occurs at or near a dam or within the watershed, dam owners should consult a qualified engineer or engineering hydrologist to assess the increased hydrologic risk; this is especially true if the dam is classified as "significant hazard" or "high hazard." The following resources are intended as a potential starting point for qualified consultants to assess dam safety after a fire:

• Recommended dam safety protocols for burned watershed hydrology calculations — guidance for calculating post-fire watershed parameters
• Spreadsheet for calculating post-fire watershed parameters — read the above guidance document before using this spreadsheet

In addition to this guidance from the dam safety office, the Natural Resources Conservation Service compiled their own more comprehensive guidance for performing post-wildfire hydrologic analyses:

• Hydrology Technical Note 4 – Hydrologic Analyses of Post-Wildfire Conditions — August 2016

If rain is forecast after a fire

Dam owners must closely monitor runoff and spillway performance especially after heavy rain or flash flooding. Dam owners need to be ready to implement their emergency action plans in case the spillway capacity is exceeded.

Flooding

Washington is among the most flood-prone states west of the Mississippi River. In Washington, the costs of flood damages exceed the cost of all other natural hazards. Here are resources for dam owners:

• Floods and floodplain management planning and project resources for communities
• Magnitude, frequency, and trends of floods at gaged and ungaged sites in Washington, based on data through water year 2014 — USGS

Earthquakes

• The Pacific Northwest Seismograph Network

Tsunami

• Tsunami tips, preparedness information, and tsunami evacuation maps by county

Important notice

The information and methods shared on this page and in attached documents should not be used without first securing competent advice on the suitability of any general or specific application. We make 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 therefore. Neither the state of Washington, the Department of Ecology, nor our reviewing engineer(s) are authorized to accept any of the design engineer’s professional responsibility and/or potential liability.