Hydrologic conditions controlling runoff generation immediately after wildfire

Abstract

[1] We investigated the control of postwildfire runoff by physical and hydraulic properties of soil, hydrologic states, and an ash layer immediately following wildfire. The field site is within the area burned by the 2010 Fourmile Canyon Fire in Colorado, USA. Physical and hydraulic property characterization included ash thickness, particle size distribution, hydraulic conductivity, and soil water retention curves. Soil water content and matric potential were measured indirectly at several depths below the soil surface to document hydrologic states underneath the ash layer in the unsaturated zone, whereas precipitation and surface runoff were measured directly. Measurements of soil water content showed that almost no water infiltrated below the ash layer into the near-surface soil in the burned site at the storm time scale (i.e., minutes to hours). Runoff generation processes were controlled by and highly sensitive to ash thickness and ash hydraulic properties. The ash layer stored from 97% to 99% of rainfall, which was critical for reducing runoff amounts. The hydrologic response to two rain storms with different rainfall amounts, rainfall intensity, and durations, only ten days apart, indicated that runoff generation was predominantly by the saturation-excess mechanism perched at the ash-soil interface during the first storm and predominantly by the infiltration-excess mechanism at the ash surface during the second storm. Contributing area was not static for the two storms and was 4% (saturation excess) to 68% (infiltration excess) of the catchment area. Our results showed the importance of including hydrologic conditions and hydraulic properties of the ash layer in postwildfire runoff generation models.

Application of minidisk infiltrometer to estimate water repellency in Mediterranean pine forest soils

“…At the aim of estimating soil sorptivity, tension infiltration experiments are preferred to ponded ones to exclude the contribution of macropores that may overwhelm soil hydrophobicity (Cerdà, 1996;Ebel et al, 2012;Nyman et al, 2010). Miniaturized tension infiltrometers were proposed to determine SWR (Hallett et al, 2001;Vogelmann et al, 2013), but their use is confined to the aggregate scale and, for field use, standard infiltrometers are more suited.…”

Effects of wildfires on peak discharges in watersheds

“…These changes can be attributed to several physical processes occurring during fires, which result in the reduction of interception and infiltration rates due to the destruction of canopy cover, the alteration of the hydraulic proprieties of soils, the creation of ash and consequent water repellence phenomena (DeBano et al 1998, Inbar et al 1998, DeBano 2000, Robichaud 2000, Shakesby & Doerr 2006, Onda et al 2008, Malkinson & Wittenberg 2011, Ebel et al 2012, Stoof et al 2012.…”

Soil-water dynamics and unsaturated storage during snowmelt following wildfire

“…These impacts are far reaching, including dissolved and particulate constituents (e.g. heavy metals and nutrients), organic matter, and other solutes (Gresswell, 1999;Smith et al, 2011;Emelko et al, 2011). There have been many studies focused on soil-water storage in the unsaturated zone, including snowmelt-dominated environments (e.g.…”

“…1) in the Colorado Front Range, USA (see Ebel et al, 2012). After initiation on 6 September 2010, extremely dry conditions and high winds drove the rapid spread of the wildfire, which eventually covered 2500 ha and destroyed over 160 residences before full containment on 13 September 2010 (FEST, 2010).…”