Wildfire impacts on stream sedimentation

Sediment delivery to streams can be highly episodic as a result of the influence of highmagnitude, low-frequency disturbance events such as major storms or wildfires. Fires are catalysts  for erosion and sediment transport in many landscapes, and a large portion of the total long-term erosion can be associated with short periods after fires. Intense fires result in loss of ground cover and reductions in infiltration rates due to ash or fine sediment, enhancing runoff and surface erosion. Landslides and debris flows in burned areas can also enhance sediment supply. Another aspect of sediment delivery after fires is the transport of ash into streams, which can have major impacts on water quality and aquatic communities.

Key Points:

• Post-fire rainstorms can cause significant flooding, debris flows, and channel incision or aggradation.
• First year post-fire observations showed a fivefold increase in suspended sediment yield, followed the next two years by less elevated loads and a return to baseline values by 3 years post-fire.
• Recent work showed that suspended sediment loads 8 years post-fire were more than double the estimates obtained from the pre-burn period.
• Estimates of channel bank erosion indicate that up to half of the annual sediment load may be contributed from this source.