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Simulation of three lahars in the Mount St Helens area, Washington using a one-dimensional, unsteady-state streamflow model

Water-Resources Investigations Report 88-4004
By:  and 
https://doi.org/10.3133/wri884004

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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
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