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BAER Scientists Evaluate the Washburn Fire for Flooding Risks

While many wildfires cause little damage to the land and pose few threats to natural resources and people downstream, some fires create situations that require special efforts to prevent additional damage after wildfires. Loss of vegetation exposes soil to erosion; water runoff may increase and cause flooding, sediments may move downstream and damage houses or fill reservoirs and put endangered species and community water supplies at-risk.

An interagency Burned Area Emergency Response (BAER) team is assessing federal lands burned in the Washburn Fire, with the goal of keeping visitors and employees safe while recreating and working in Yosemite National Park and the Sierra National Forest. BAER team assessments focus on emergency actions that are necessary to protect human life and safety, property, critical cultural resources, and critical natural resources such as soil productivity, hydrologic function, and water quality. Emergency actions are intended to minimize any further damage during rainstorm events.

BAER hydrologists, soil scientists, road engineers, recreation specialists, botanists, archeologists, and GIS specialists are currently assessing the condition and response of the watersheds within the Washburn burned areas. These BAER specialists evaluate other critical values that could be at risk during major rainstorm events such as national park and forest roads and trails, campgrounds, and other park and forest infrastructures.

BAER soil scientists evaluate the burned watersheds to determine post-fire effects to soil and watershed conditions. This includes testing whether the soil is hydrophobic – aka repels water. Post-Fire burned areas of hydrophobic (water repellent) soils can act as a “tin roof” by reducing infiltration capacity of soils, enhanced overland flow, and accelerated soil erosion. This is important because the amount of hydrophobicity is an important component to determining how much increased water runoff we can expect after a fire. The hydrophobic layer is the result of a waxy substance that is derived from plant material burned during a hot fire. The waxy substance penetrates the soil as a gas and solidifies after it cools, forming a waxy coating around soil particles. Hydrophobicity repels water from soil and is considered when mapping watershed response to rainstorms after a wildfire.

Below, this photo shows Forest Service soil scientist and BAER team leader Todd Ellsworth assessing soil hydrophobicity (water repellency) and changes to soil structure in a high soil burn severity (SBS) area of the Washburn burned area. Todd captures a drop of water placed on the burned soil which was determined to be hydrophobic.
 

In this next photo, National Park Service soil scientist Catherine Fong is gathering SBS data to evaluate and map the level of severity within this burned area of the Washburn Fire.
 

This photo below shows a portion of a mosaic burn pattern for a watershed slope in the Washburn Fire which describes multiple burn scar characteristics left by a fire. In wildland fires burn patterns are influenced by topography, wind direction, length of exposure, and type of fuel. They are also influenced by the fire severity and intensity within a stand of trees.