Project Title: Modeling the Spectrum of Post-Fire Phenomena (Runoff, Erosion, Sediment Transport, and Deposition)
Mendenhall Fellow: David A. Kinner, (303) 273-8608, dakinner@usgs.gov
Duty Station: Golden, CO
Start Date: October 5, 2003
Education: Ph.D (Geology), University of Colorado, Boulder, 2003
Research Advisors: Susan Cannon, (303) 273-8604, cannon@usgs.gov; John Moody, (303) 541-3011, jamoody@usgs.gov
Project Description: Fires in semi-arid mountainous regions of the Western U.S. have profound impacts on the hydrologic and sediment cycles, particularly if intense rainstorms follow watershed burning. Fires remove vegetation, alter the soil surface and remove natural barriers to erosion. Post-fire, rainfall-runoff events can lead to any number of geologic hazards including flash flooding, rill and sheet erosion, excavation of stored channel material and debris flows. These phenomena can affect the safety of nearby populations and destroy existing infrastructure. The general objective of this work is to develop, test and field- parameterize models of post-fire runoff, erosion and deposition. Models allow for both an improved conceptual understanding of post-fire processes and, ultimately, a demarcation of areas at risk.
Although agricultural erosion models have been developed over the last century, their ability to predict runoff and erosion on steep slopes and for coarse-grained soils that have been altered by fire is just beginning to be examined. Steep, alluvial-filled channels, sometimes blocked by debris dams, present an additional challenge for physical modeling of the post-fire system. We will adapt existing hillslope and channel runoff models to the steep topography and develop new modeling techniques where necessary. Initially, the work will focus on implementing hillslope infiltration models so the delivery of water to channels can be reasonably quantified. A critical issue related to this infiltration work is whether ash seals the surface and leads to increased runoff. Hillslope experiments will also be used to quantify the impact of roughness on hillslope shallow-water flows and examine the role of micro-topography in controlling drainage structure. After developing models of hillslope runoff, detailed modeling will focus on the highly dynamic channel systems and the role of sediment availability at different points in the drainage network on erosion and deposition.
An integral part of the modeling work is the accompanying field data collections and experiments. These field activities will be critical in establishing model boundary conditions and validating results. The study will examine the spatial variability of infiltration parameters and the appropriate scale to measure these parameters to later use in modeling.
Given a developed modeling and field framework, some questions that we hope to begin to answer include:
These questions support our general goal of improving our understanding of post-fire phenomena.
- What are threshold environmental and precipitation conditions necessary for debris flow development through sediment bulking?
- What is the change in infiltration properties with time after a forest fire?
- What is the appropriate law to quantify shallow flow friction?
- How are post-fire eroded channel networks similar to regional drainage patterns?
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