CSDMS 2016 annual meeting poster MichaelTurzewski
Reconciling geomorphic observations with simulations of a modern landslide-dam outburst flood using GeoClaw software, eastern Himalaya
Katharine Huntington, University of Washington Seattle Washington, United States. kate1@uw.edu
Randall LeVeque, University of Washington Seattle Washington, United States. rjl@uw.edu
Abstract:
High-magnitude (>10^5 m^3/s) outburst floods have the potential to dramatically alter landscapes and greatly impact human lives and infrastructure. Numerical modeling can help us understand the hydraulics of these infrequent and difficult to observe floods, but their scale makes simulation challenging and computationally expensive, particularly where rugged mountain topography produces complex flow hydraulics. Here we simulate the second largest historical outburst flood on record using GeoClaw open source software for modeling geophysical flows, and ground-truth the results of these simulations using observations and geomorphic evidence of the event. This landslide-dam outburst flood was sourced in Tibet on the Yigong River in June 2000, scouring vegetation, triggering landslides and depositing flood sands in hydraulically sheltered areas downstream. We mapped these features in the field and remotely using Google Earth and Landsat-7 imagery, and simulated the flood with a reconstructed 2 km^3 impounded lake using instantaneous dam failure. Our simulations overestimate the reported peak discharge just downstream of the outburst, but produce flow depths that match reported flood stage at locations up to 450 km downstream. Key flood characteristics for hazard prediction like downstream patterns of inundation and flow depth are relatively insensitive to the chosen roughness parameter in GeoClaw. While the magnitudes of simulated velocities and momentum fluxes can vary greatly as a function of the chosen Manning coefficient, the spatial patterns of velocity and momentum flux are robust over a range of chosen values. GeoClaw simulations (1) produce peak velocities and momentum fluxes in locations that correlate with landslides that were observed directly after the event and (2) produce inundation patterns and flow depths consistent with the style of deposition observed in locations far downstream, displaying a clear link between flood hydraulics and geomorphic change due to erosion and deposition. Results suggest that GeoClaw can accurately simulate high-magnitude outburst flood events through mountainous topography, showing the potential of this modeling approach to improve both hazard predictions and our understanding of the geomorphic impact of outburst floods.
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