St. Helens Blast Related Sedimentation Modeling and Planning Realities in the Toutle/Cowlitz/Columbia River System

Abstract

Following the Mount Saint Helen’s eruption of May 18, 1980 a major planning effort was started by the United States Army Corps of Engineers to deal with potential flood and sedimentation problems related to that event. This paper reviews the four major reports to come out of that effort with emphasis on the role of sedimentation, frequency, and risk modeling in the planning process. New types of information concerning the assumptions of supporting models and the positive and negative consequences of selecting various management strategies were incorporated into the documents. The inherent stochastic nature of the modeling process emerged as an important issue in evaluation of recommendations from planners and engineers instead of being masked by single conclusions based on average conditions. A higher public profile for models and modelers and the attendant demands this new role implies is likely if the planning process exemplified in these documents is generally adopted.