| This study compares documented debris flow runout distances with numerical
simulations in the Yosemite Valley of California, USA, where about 15%
of historical events of slope instability can be classified as debris flows
and debris slides (Wieczorek and Snyder, 2004).
To model debris flows in the Yosemite Valley, we selected six streams with
evidence of historical debris flows; three of the debris flow deposits have
single channels, and the other three split their pattern in the fan area
into two or more channels. From field observations all of the debris flows
involved coarse material, with only very small clay content.
We applied the one dimensional DAN (Dynamic ANalysis) model (Hungr, 1995)
and the two-dimensional FLO-2D model (O'Brien et al., 1993) to predict and
compare the runout distance and the velocity of the debris flows observed in
the study area. As a first step, we calibrated the parameters for the two
softwares through the back analysis of three debris- flows channels using a
trial-and-error procedure starting with values suggested in the literature.
In the second step we applied the selected values to the other channels, in
order to evaluate their predictive capabilities.
After parameter calibration using three debris flows we obtained results
similar to field observations We also obtained a good agreement between the
two models for velocities. Both models are strongly influenced by
topography: we used the 30 m cell size DTM available for the study area,
that is probably not accurate enough for a highly detailed analysis, but it
can be sufficient for a first screening. |