The primary goal of fire protection in California is to safeguard a wide range of assets found across the wildland areas. These assets include life and safety, structures, range, timber, recreation, water and watersheds, air quality, unique scenic areas, cultural and historic resources, wildlife, plants and ecosystem health. Although loss of life or injuries and loss of structures are two of the more emotionally gripping and economically significant impacts of wildland fire in California, large, intense wildfires often have a negative impact on water quality and its beneficial uses, and fisheries habitat as well.

Perhaps the most significant impact to water quality as a result of a wildfire is increased erosion and, consequently, sedimentation. Sediment increases are measured in terms of additional cubic yards of material delivered to streams and to places of deposition. Additional sediment storage can alter a stream’s form and function in a deleterious manner. Water quality effects of wildfires are usually measured as increases in total dissolved solids (TDS) and total suspended solids (or turbidity). Large intense wildfires may also increase runoff and peak flows. The magnitude of impacts in a given watershed can vary greatly depending on the influence of a number of factors, including type and condition of vegetation, type of soil and its moisture content at the time of the fire, level of heat generated by the fire, slope, aspect, proximity to the nearest water course, and the timing and intensity of post-fire storms. Recently burned forest lands can produce an average of 20 to 50 cubic yards per acre of erosion per year, with approximately half of that amount (10 to 25 cubic yards per acre) reaching a stream channel to become sediment for the first two years following a fire. Recently burned chaparral watersheds generally yield sediment levels at 6 to 35 times of unburned areas and can reach as high as 312 tons per acre per year for the first three years following a fire! Increased water yield and peak flows, or maximum instantaneous discharges, are another potential impact of large, intense fires. These increases coupled with the addition of large amounts of debris entering stream channels can result in increases in the magnitude and frequency flooding that can cause substantial damage. Even a moderate storm following a fire can lead to a 200 percent increase in runoff dependent upon slope, type of soil, and the percentage of vegetative cover removed by the fire.

In Northern California, intense wildfires commonly burn in watersheds containing important spawning and rearing habitat for anadromous fish, including coho salmon and steelhead trout. The potential impacts to fisheries habitat from wildfires include increased water flow, sedimentation, water temperature and nutrient loading.

Increases in water flow can cause excessive channel deepening and scour of spawning gravels from the channel bottom, erosion of too much riparian vegetation, and lowering of summer groundwater levels. As the stream flows move faster emerging fry are literally washed downstream and/or forced out of their natural hiding places and exposed to predators. Those fish that manage to avoid being immediately eaten are forced to migrate all the way to the ocean, well ahead of schedule and will have little chance of survival.

Rainfall recharges the groundwater which then percolates back up creating summer water flow. Well vegetated hillsides are able to absorb rainwater and hold the soil against erosion. When vegetation is removed, runoff to the creeks increases and the water does not have a chance to infiltrate the soil. As a result of decreased infiltration in the winter, summer rearing pools may go dry.

Sediment entering the stream channels from increased runoff can be deposited on spawning gravel preventing the emergence of fry and the deposition of eggs. Sediment can also fill pools, widening and flattening the stream channel removing summer and winter rearing habitat for small fish.

Lack of vegetation, or riparian cover, results in increases of water temperature, dissolved oxygen levels and decreases the numbers and types of aquatic insects which are the primary food source for salmonids. Cold water is saturated with oxygen, when water temperatures rise fish can not breathe and die as do many of the aquatic insects that also rely on cold water for their habitat. Increases in levels of nitrogen may result which can lead to algal blooms that further increase the levels of dissolved oxygen in the stream channels.

Wildfires cause devastation. Whether it is the loss of a home or the destruction of vital fisheries habitat the affects of a fire can last a for many years. We should all do what we can to prevent fires, whether it is putting in a defensible space around your home or making certain your campfire is really out as the costs are simply to high.

Inside this edition:
Call for Associate Director
Wildfires - Impacts on Watersheds
Defensible Space
Farm Bill 2002

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