Post‐wildfire changes in suspended sediment rating curves: Sabino Canyon, Arizona

Abstract

Abstract:Wildfire has been shown to increase erosion by several orders of magnitude, but knowledge regarding short-term variations in post-fire sediment transport processes has been lacking. We present a detailed analysis of the immediate post-fire sediment dynamics in a semi-arid basin in the southwestern USA based on suspended sediment rating curves. During June and July 2003, the Aspen Fire in the Coronado National Forest of southern Arizona burned an area of 343 km 2 . Surface water samples were collected in an affected watershed using an event-based sampling strategy. Sediment rating parameters were determined for individual storm events during the first 18 months after the fire. The highest sediment concentrations were observed immediately after the fire. Through the two subsequent monsoon seasons there was a progressive change in rating parameters related to the preferential removal of fine to coarse sediment. During the corresponding winter seasons, there was a lower supply of sediment from the hillslopes, resulting in a time-invariant set of sediment rating parameters. A sediment mass-balance model corroborated the physical interpretations. The temporal variability in the sediment rating parameters demonstrates the importance of storm-based sampling in areas with intense monsoon activity to characterize post-fire sediment transport accurately. In particular, recovery of rating parameters depends on the number of high-intensity rainstorms. These findings can be used to constrain rapid assessment fire-response models for planning mitigation activities.

Geology and geomorphology control suspended sediment yield and modulate increases following timber harvest in temperate headwater streams

“…The a parameter is considered a metric of erosion severity whereas the b parameter is a function of the erosive power of a stream (Desilets et al, 2007), with larger values indicating new sources of sediment availability at higher Q (Sheridan et al, 2011). Both Q s and Q were normalized by drainage area to account for differences in catchment contributing areas, allowing for unbiased comparison among sites (Leopold et al, 1964;Milliman and Meade, 1983).…”

Wildfire, morphologic change and bed material transport at Fishtrap Creek, British Columbia

“…Studies that explicitly consider forest fires have focussed on: erosion of hydrophobic soils by overland flow (Inbar et al, 1998;Benavides-Solorio and MacDonald, 2001;Moody and Martin, 2001;Cerda and Lasanta, 2005;Desilets et al, 2006;Moody et al, 2008); the generation of debris flows from hydrophobic soils (Wells, 1987;Cannon and Reneau, 2000); or the aggradational landforms formed by post-fire increases in sediment supply to fluvial networks (Meyer and Wells, 1997;Benda et al, 2003;Legleiter et al, 2003). Furthermore, most of these studies tend to focus on fires that produce either a large increase in peak flows of a dramatic increase in sediment supply to the stream channel (see Wondzell and King, 2003).…”

At the nexus of fire, water and society

“…Observed post-fire effects range from no observed change in stream hydrology or chemistry to higher peak flows, base flow, suspended sediment (also reported as turbidity) and bedload [41,42], and increases in several chemical constituents such as nutrients, dissolved organic carbon (DOC), heavy metals and polycyclic aromatic hydrocarbons (PAHs) [43][44][45][46][47]. Variations in post-fire hydrology and water quality can only be captured by high-frequency water sampling that includes storm sampling [20], a point reiterated in case studies in the US states of Arizona [48], New Mexico [49] and Colorado [47,50].…”