42. Rainfall-Infiltration-Runoff Processes for Soil Affected by Wildfire

The transformation of rainfall into runoff in burned watersheds is an essential component of watershed scale models to predict erosion, floods, sediment transport, debris flows, and sediment deposition after fires. Specifically, a need exists to understand and to model the soil infiltration processes (see fig. 1) in burned mountainous watersheds where (1) fire effects, as measured by burn severity, can cause extremely dry soil and water repellency, and (2) rainfall is often dominated by orographic convective storms (Underwood and Schultz 2004). The infiltration rate controls such parameters as the time-to-ponding, time-to-concentration (Overton and Meadows 1976; Saghafian and Julien 1995), time of peak discharge, as well as the general shape of the runoff hydrograph (Woolhiser and Liggett 1967; Moore and Foster 1990; Hillel 1998; Smith 2002). The infiltration process depends on such characteristics as: antecedent soil moisture; initial abstraction (Steenhuis and others, 1995); sorptivity, a capillary process (Hillel 1998; Smith 2002); hydraulic conductivity, a gravity process (Hillel 1998; Smith 2002); rewetting process (Blonquist and others 2006); and various possible surface-sealing processes (Morin and Benyamini 1977; Sumner and Stewart 1992; Wang and others, 1998). These processes depend in turn on mosaic patches of burn severity creating (1) extremely dry soils, (2) changes in soil particle or aggregate sizes, and (3) possible chemically induced water repellency coupled with some magnitude of natural water repellency.

Figure 1.  Infiltration into a two-layer system subjected to the heat from the 2000 Cerro Grande Fire consisting of about 1 cm of dark ash over soil, which is white. The darker ash represents the area where sorptivity dominated hydraulic conductivity and caused lateral spreading. Diameter of the hole is about 15 cm.

Research under the project will provide a Mendenhall Fellow an opportunity:

1. to develop innovative laboratory and field methods and perhaps instruments to measure some of the fundamental physical soil parameters such as critical water content, sorptivity and saturated hydraulic conductivity in soils subjected to temperatures associated with wildfires (Haverkamp and others 1994; Martin and Moody 2001; Robichaud and others 2008).
2. to modify existing infiltration theory or possibly develop new infiltration theories to adequately predict the excess rainfall and runoff on burned hillslopes with bare and ash-covered soils during unsteady convective rainfall.  Differences from current theory may be needed to predict excess rainfall during the different stages of rainfall and infiltration: (a) prior to runoff when hydrophobic soil and sealing processes may be important; (b) after ponding and during runoff, especially if sorptivity varies; and (c) during the later stages of rainfall when runon infiltration may be significant (Moore and Foster 1990; Overton and Meadows 1976; Haverkamp and others 1994; Smith 2002).
3. to investigate how the spatial distribution of burn severity is linked to the infiltration-runoff process and how this process determines the actual land surface area that contributes water to drainage networks during unsteady rainfall events at the scale of hillslope segments up to the larger scale of watersheds with well developed channels (Moody and others, 2008; Stone and Paige 2003).

Additionally, this research can provide the opportunity to develop process-based computer algorithms of the rainfall-infiltration-runoff processes that can be linked to process-based watershed models designed to predict runoff and erosion from burned watersheds.

References

Blonquist, J. M., Jr., Jones, S. B., Lebron, I., and Robinson, D. A., 2006. Microstructural and phase configurational effects determining water content: Dielectric relationships of aggregated porous media: Water Resources Research, v. 42, W05424, doi:10.1029/2005WR004418, 13 p.

Haverkamp, R., Ross, P.J., Smettem, K.R.J., and Parlange, J.Y., 1994. Three-dimensional analysis of infiltration from the disc infiltometer, pt. 2, Physically based infiltration equation: Water Resources Research, v. 30, no. 11, p. 2931–2935.

Hillel, D., 1998. Environmental soil physics: New York, Academic Press, 757 p.

Martin, D.A., and Moody, J.A. 2001, Comparison of soil infiltration rates in burned and unburned mountainous watersheds: Hydrological Processes, v, 15, p. 2893–2903.

Moody, J.A., Martin, D.A., Haire, S.L., and Kinner, D.A., 2008, Linking runoff response to burn severity after a wildfire: Hydrological Processes, v. 22, no. 13, p. 2063–2074.

Moore, I.D., and Foster, G.R., 1990, Hydraulic and overland flow, chapter 7, in Anderson, M.G., and Burt, T.P., eds., Process studies in hillslope hydrology: New York, John Wiley & Sons, p. 215–254.

Morin, J., and Benyamini, Y., 1977, Rainfall infiltration into bare soils: Water Resources Research, v. 13, no. 5, p. 813–817.

Overton, D.E., and Meadows, M.E., 1976, chapters 3, 4, and 5, in Stormwater modeling: New York, Academic Press, p. 42–97.

Robichaud, P.R., Lewis, S.A., and Ashmun, L.E., 2008, New procedure for sampling infiltration to assess post-fire soil water repellency:  U.S. Department of Agriculture, Forest Service Report RMRS-RN-33, 14 p.

Saghafian, B., and Julien, P.Y., 1995, Time to equilibrium for spatially variable watersheds: Journal of Hydrology, v. 172, p. 231–245.

Smith, R.E., 2002, Infiltration theory for hydrologic applications, in Water Resources Monograph 15: Washington, D.C., American Geophysical Union, 212 p.

Steenhuis, T.S., Winchell, M., Rossing, J., Zollweg, J.A., and Walter, M.F., 1995, SCS runoff equation revisited for variable-source runoff areas: Journal of Irrigation and Drainage Engineering, May-June, p. 234–238.

Stone, J.J., and Paige, G.B., 2003, Variable rainfall intensity rainfall simulator experiments on semi-arid rangelands, in Proceedings of the First Interagency Conference on Research in the Watersheds, Oct. 27-30, 2003, Benson, Arizona: p.83–88.

Sumner, M.E., and Stewart, B.A., eds., 1992, Soil crusting, in Chemical and physical processes advances in soil science series: Boca Raton, Fla., Lewis, 401 p.

Underwood, S.J., and Schultz, M.D., 2004, Patterns of cloud-to-ground lightning and convective rainfall associated with postwildfire flash floods and debris flows in complex terrain of the western United States: American Meteorological Society, October 2004, p. 989–1003.

Wang, Z., Feyen, J, van Genuchten, M.T., and Nielsen, D.R., 1998, Air entrapment effects on infiltration rate and flow instability: Water Resources Research, v. 34. no. 2, p. 213–222.

Woolhiser, D. A., and Liggett, J.A., 1967, Unsteady, one-dimensional flow over a plane—The rising hydrograph: Water Resources Research, v. 3, no. 3, p. 753–771.

Proposed Duty Station: Boulder, CO

Areas of Ph.D.: Hydrology, soil physics, soil science, meteorology, geology

Qualifications: Applicants must meet one of the following qualifications: Research Hydrologist, Research Physicist, Soil Scientist, Research Chemist, Research Geologist, Research Geophysicist

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisor(s): John Moody, (303) 541-3011, jamoody @usgs.gov; Deborah Martin, (303) 541-3024, damartin@usgs.gov; Roger Smith (Colorado State U), (970) 493-2662, gedrathsmith@q.com

Human Resources Office contact: Vanessa Chambless, (303) 236-9584, vchambless@usgs.gov

Summary of Opportunities