wAbstract
@We use a record of sedimentation in a small reservoir within
the Cerro Grande burn area, New Mexico, to document postfire delivery
of ash, other fine-grained sediment carried in suspension within
floods, and coarse-grained sediment transported as bedload over
a five-year period. Ash content of sediment layers is estimated
using fallout 137Cs as a tracer, and ash concentrations
are shown to rapidly decrease through a series of moderate-intensity
convective storms in the first rainy season after the fire. Over
90 of the ash was delivered to the reservoir in the first year,
and ash concentrations in suspended sediment were negligible after
the second year. Delivery of the remainder of the fine sediment
also declined rapidly after the first year despite the occurrence
of higher-intensity storms in the second year. Fine sediment loads
after five years remained significantly above prefire averages.
Deposition of coarse-grained sediment was irregular in time and
was associated with transported by snowmelt runoff of sediment
stored along the upstream channel during short-duration summer
floods. Coarse sediment delivery in the first four years was strongly
correlated with snowmelt volume, suggesting a transport-limited
system with abundant available sediment. Transport rates of coarse
sediment declined in the fifth year, consistent with a transition
to a more stable channel as the accessible sediment supply was
depleted and the channel bed coarsened. Maximum impacts from ash
and other fine-grained sediment therefore occurred soon after
the fire, whereas the downstream impacts from coarse-grained sediment
were attenuated by the more gradual process of bedload sediment
transport.
Keywords: sediment load; sedimentation rates; erosion rates; fires;
cesium; New Mexicox
Introduction
Setting
Methods
@Calculation of ash content
Results
Discussion and conclusions
Acknowledgments
References cited