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.
Suggested Citation
Laenen, A., Hansen, R.P., 1988, Simulation of three lahars in the Mount St Helens area, Washington using a one-dimensional, unsteady-state streamflow model: U.S. Geological Survey Water-Resources Investigations Report 88-4004, iv, 20 p., https://doi.org/10.3133/wri884004.
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 |