Research Areas > Stormwater > Effects of Fires on Runoff

Project: Effects of Regionwide Fires on Deposition, Runoff, and Emissions to the SCB

Background and Objective

Wildfires, both natural and manmade, can have significant effects on downstream receiving waters and the near-shore coastal environment. Severe burns have been shown to increase stormwater runoff and sediment generation; thus, fires may be problematic for management of already impaired waters. Most research on post-fire water quality has focused on sediment and nutrient enrichment, although burns also have potential to increase loadings of carbon, organic compounds like PAHs, and trace metals. These contaminants may be introduced through debris, ash deposition, stormwater runoff, or input from upland streams. Investigating the magnitude and duration of fire effects in watersheds is a critical step in accounting for its influence on water quality and therefore attainment of water quality standards.

The goal of this project was to design a monitoring program to investigate the fate of water quality constituents released during wildfires in southern California.

Status

This project was initiated in 2007 and completed in 2011.

Methods

To assist in this effort, a workshop was held in 2008 to develop a regional monitoring strategy that could be implemented following wildfires to help address these questions. More than 15 agencies participated in developing a plan that outlines the sampling approach, constituents, and quality control procedures for post-fire water quality assessment. Under this plan, the magnitude, duration, and effects of post-fire runoff on downstream loads of metals and organic compounds can be quantified.

Findings

A regional post-fire water quality monitoring program was developed by a team of technical experts, stormwater managers, and regulators from academia, government, and the private sector to help address the current information gaps. The monitoring plan provides agreed upon water quality sampling procedures, an implementation plan, and a funding strategy. The ready response plan can be quickly implemented after fires, and investigates the following priority management questions:

1. How does post-fire runoff affect contaminant flux?
2. What is the effect of post-fire runoff on downstream receiving waters?
3. What are the factors that influence how long post-fire runoff effects persist?

The monitoring plan includes site selection criteria that allow for prioritization of potential sampling sites based on the sensitivity of potentially affected resources, presence of previous and available monitoring data, feasibility, accessibility, and ability to coordinate with other monitoring programs. Pre-selection of sites and up-front coordination will allow for more rapid and effective response following fires. Finally, the plan includes preliminary recommendations for quality assurance procedures, data management, and communication that will facilitate information sharing and ongoing coordination. Ongoing program development and coordination will be accomplished through a post-fire runoff working group that consists of the US Forest Service, US Geological Survey, California Department of Forestry and Fire Protection, regional water quality control boards, major municipalities, key landowners, and local researchers.

An initial monitoring effort took place in 2009-2010 before and after the Station fire in the San Gabriel Mountain Range. The loss of vegetation and changes in soil properties due to fire reduced lag time and greatly increased the magnitude of storm runoff, resulting in sediment-laden floods carrying high concentrations of particulate-bound constituents. Post-fire concentrations and loads were up to three orders of magnitude greater than pre-fire values for many trace metals, including lead and cadmium. A shift was also observed in the timing of chemical delivery, where maximum sediment, trace metal, and cation concentrations coincided with peak discharge in the post-fire runoff. These results highlight the need for treatment of sediment-bound chemicals, in order to mitigate potentially detrimental impacts on downstream water quality.

Partners

This project was conducted in collaboration with the Southern California Stormwater Monitoring Coalition (SMC) and the project working group. The main technical partner on this project was UCLA, with additional support from the US Geological Survey.

Presentation

Effects of Southern California Wildfires on Storm Water Metals & PAHs - January 2009 presentation to SCCWRP member agencies describing potential pathways for fire effects on downstream waters, current scientific knowledge quantifying these effects, and SCCWRP’s research directions.