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| Titel |
Predicting the delivery of sediment and associated nutrients from post-fire debris flows in small upland catchments |
| VerfasserIn |
Petter Nyman, Gary Sheridan, Hugh Smith, Patrick Lane |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250099903
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| Publikation (Nr.) |
 EGU/EGU2014-15748.pdf |
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| Zusammenfassung |
| Post-fire debris flows are extreme erosion events that can dominate the long term supply of
sediment from headwaters to streams in upland catchments. Predicting the location,
frequency and magnitude of debris flows is therefore important for understanding sediment
dynamics in upland catchments and providing a basis on which to manage hydro-geomorphic
risk in burned areas. In this study we survey 10 post-fire debris flow events in southeast
Australia with aims to i) identify rainfall conditions underlying the debris flow response, ii)
quantify erosion rates in hillslope and channel source areas, and iii) estimate the delivery of
sediment and water quality constituents to receiving waterways. Rainfall events that triggered
debris flows had an annual exceedance probability ranging from 0.1 to 0.6, and 30-minute
intensities, I30, ranging from 17-60 mm h-1. Sediment delivery by debris flows
(100-200 t ha-1) is similar to that which has been reported for similar events in the
western US and Spain. In terms of eroded volume, there was on average an equal
contribution from hillslopes and channels to debris flows, which is in agreement with the
calculations of surface and subsurface source contributions obtained from radionuclide
concentrations. In terms of the potential water quality impacts from post-fire debris flows, the
hillslopes had much higher concentration of constituents such as fine clay and silt,
plant available phosphorous and total carbon. The data on debris flow magnitude
was used to evaluate two different approaches for predicting sediment delivery
from debris flows. A statistical debris flow model developed by the US Geological
Surveys and parameterized for catchments in western US performed well (R2 = 0.92)
in terms of predicting the overall volume of material delivered at the catchment
outlet. An alternative modeling approach, using local slope and contributing area
as predictors of erosion, also produced good results, and could be used to obtain
more detailed predictions of sediment entrainment, deposition, the overall source
contribution and the associated constituents. Future work will aim to link models of
debris flow magnitude with models of initiation and debris flow frequency after fire. |
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