2024 CSDMS meeting-114
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Modeling the effects of bed-sediment entrainment on the dynamics and runout of outburst floods and emergent debris flows with the granular-fluid model D-Claw.
David George,
(he/him),U.S. Geological Survey Vancouver, WA , United States. dgeorge@usgs.gov
Outburst floods and debris flows often incorporate large volumes of erodible bed sediment along their runout path. Although this phenomenon is widely recognized and often implicated for volumetric growth of debris flows, the effect of this process on the dynamics and runout extent of large flows has not been directly modeled extensively or systematically. Rather, models that account for this process traditionally utilize simple static volumetric and/or rheological adjustments. However, this process dynamically influences flood and debris-flow evolution in a complex spatiotemporal fashion.
We used D-Claw, a depth-averaged granular-fluid model that accommodates the incorporation of bed material into overlying flow and resultant changes in flow rheology across a wide range of solid concentrations, from dilute suspensions to dense-granular debris flows. We modeled hypothetical lake outburst floods from Spirit Lake, WA into the erodible sediment rich Toutle River Valley. Downstream flood dynamics of clear-water flows were compared to floods that entrain material and transform into down-valley debris flows. We found that while the entrainment of bed material may significantly increase total flow volume (>150%), downstream discharge and runout extent are more similar to clear-water floods than might be expected by volumetric considerations alone. We postulate that the relationship between entrained volume and flow extent depends on complicated site-specific factors such as location of erodible sediment and evolving rheological factors.
