Suspended-sediment response to wildfire and a major post-fire flood on the Colorado Front Range

Floods following wildfire cause rapid transportation of suspended sediment from watersheds, so the USDA Forest Service continues to work even when the fire is out. In the years following the 2012 High Park fire, the South Fork Cache la Poudre watershed in the Arapaho Roosevelt National Forests experienced high concentrations of suspended sediment, which peaked during a major flood in 2013 that exported 35 years’ worth of sediment from the watershed in a seven-day period.

Photo Credit

USDA Forest Service photo by Rene Freeland.

Colorado Front Range landscape view.

Using data from 2013 to 2015, researchers looked at precipitation, streamflow, water turbidity (cloudiness caused by the presence of sediment), and suspended-sediment concentration. The researchers used the relationships between turbidity and sediment concentrations to estimate the rate for sediment concentrations to return to baseline within the water column.

Suspended-sediment export from the watershed peaked during the 2013 flood and declined to pre-fire conditions within three years. This fast return to pre-fire sediment conditions could be explained by the combination of powerful flood events one-year post-fire and the area’s thinner soil types. The research shows that major floods following wildfire in landscapes with thin soils like the Colorado Front Range can expedite returns to background suspended-sediment levels.

Forest Service science supports the delivery of clean water to American households and businesses with applied science that helps providers and water managers make management decisions affecting water quality and quantity.