CGRG Bibliography of Canadian Geomorphology
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Author : Andrews, C.A.E.; and Eaton, B.C.
Date : 2008.
Title : Channel dynamics of a gravel-bed creek: four years of post wildfire response at Fishtrap Creek.
Publication : Joint Annual Meeting of the Canadian Geophysical Union and the Canadian Geomorphology Research Group. May 11-14, Banff, Alberta.
Issue :
Page(s) :
Abstract
In August 2003, a wildfire burned through Fishtrap Creek Watershed north of Kamloops British Columbia. This high intensity fire killed almost all of the trees within the watershed, including 90% of the riparian vegetation. It did not significantly alter the duration or magnitude of the peak flows, nor did it have detectable effects on the total suspended sediment concentrations. During the first two years after the fire, the channel morphology remained stable. The first evidence of morphologic adjustment occurred in 2006, when the channel began to widen and develop pronounced channel bars. While the channel in 2005 would have been classified as a plane bed channel, it had adopted a characteristically riffle pool morphology by the end of the 2006 freshet. However, the most dramatic channel reconfiguration occurred during the 2007 freshet, when the channel widened by as much as 12 m in places, and large volumes of large woody debris were recruited into the stream. As a result of this local increase in sediment supply and LWD loading, the channel aggraded by as much as 1.8 m in places, while at the same time it degraded by about 1.5 m in other places. For comparison, the pre-disturbance bankfull width at Fishtrap Creek was about 9 m, while the bankfull depth was about 0.6 m. Since we are fairly certain that the peak flow regime and the sediment supply from upstream have not been altered since the fire, this remarkable degree of channel change appears to be an endogenous instability associated with a loss of bank strength within the study reach. These results stand in contrast to the more commonly reported channel instability attributed to exogenous increases in sediment supply and/or peak flows. Unlike the exogenous post-fire changes, those that we have documented occurred only after a delay of about 3 years, when the root systems of the dead trees weakened enough to allow the channel to become laterally active.
Bibliography of Canadian Geomorphology