Simulation of three lahars in the Mount St Helens area, Washington using a one-dimensional, unsteady-state streamflow model
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Abstract
A one-dimensional, unsteady-state, open-channel model was used to analytically reproduce three lahar events. Factors contributing to the success of the modeling were: (1) the lahars were confined to a channel, (2) channel roughness was defined by field information, and (3) the volume of the flow remained relatively unchanged for the duration of the peak. Manning 's 'n ' values used in computing conveyance in the model were subject to the changing rheology of the debris flow and were calculated from field cross-section information (velocities used in these calculations were derived from super-elevation or run-up formulas). For the events modeled in this exercise, Manning 's 'n ' calculations ranged from 0.020 to 0.099. In all lahar simulations, the rheology of the flow changed in a downstream direction during the course of the event. Chen's 'U ', the mudflow consistency index, changed approximately an order of magnitude for each event. The ' u ' values ranged from 5-2,260 kg/m for three events modeled. The empirical approach adopted in this paper is useful as a tool to help predict debris-flow behavior, but does not lead to understanding the physical processes of debris flows.
Study Area
| Publication type | Report |
|---|---|
| Publication Subtype | USGS Numbered Series |
| Title | Simulation of three lahars in the Mount St Helens area, Washington using a one-dimensional, unsteady-state streamflow model |
| Series title | Water-Resources Investigations Report |
| Series number | 88-4004 |
| DOI | 10.3133/wri884004 |
| Year Published | 1988 |
| Language | English |
| Publisher | U.S. Geological Survey |
| Contributing office(s) | Oregon Water Science Center |
| Description | iv, 20 p. |
| Country | United States |
| State | Washington |
| Other Geospatial | Mount St. Helens area |