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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

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,

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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. (Author 's abstract)

Additional Publication Details

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
Edition:
-
Year Published:
1988
Language:
ENGLISH
Publisher:
U.S. Geological Survey,
Description:
iv, 20 p. :ill., map ;28 cm.