REPORT:
Channel and Drainage-Basin Response of the Toutle River System in the Aftermath of the 1980 Eruption of Mount St. Helens, Washington

Table of Contents

• Abstract
• Introduction
  • Events leading to the May 18 eruption
  • Volcanic impacts, deposits, and areal distribution from May 18 eruption
    • Debris avalanche
    • Directed blast and ash fall
    • Pyroclastic flows
    • Lahars
  • Purpose and scope
• Setting
  • Climate and hydrology
  • Land use
  • Condition of study area immediately following the May 18 eruption
    • Upper North Fork Toutle River
    • Lower North Fork Toutle River
    • Upper Green River
    • Lower Green River
    • Upper South Fork Toutle River
    • Lower South Fork Toutle River
    • Toutle River main stem
• Hydrologic impacts and conditions
• Engineering works
  • Dredging
  • Temporary debris-retaining structures
  • Sediment-stabilization basins
  • Controlled releases from lakes
  • Permanent sediment-retention structure
    • Upstream effects
    • Downstream effects
• Data collection and compilation
  • Water discharge
  • Sediment discharge
  • Bed material
  • Sediment sources and volumes
  • Channel-network development
  • Channel hydraulics
  • Channel-bed aggradation and degradation
  • Channel widening and narrowing
  • Channel erosion and deposition
  • Sediment discharges
  • Bed-material characteristics
  • Stream-energy conditions
• Drainage-area integration and channel-network development
  • Integration of drainage area
  • Channel-network development
• Landscape response
  • Hillslopes
    • Physical factors controlling erosion rates
    • Eroded sediment
  • Stream channels
    • Vertical processes
      • Secondary vertical processes
      • System-wide trends of aggradation and degradation
    • Lateral processes
    • Relative roles of vertical and lateral processes
      • Discussion
      • Sediment eroded
    • Role of extreme events
  • Sediment discharge
    • Sediment yields
    • Temporal variations in sediment discharge
    • Particle-size characteristics of sediment
      • Suspended sediment
      • Bed material
    • Sediment discharge and volcanic impact
      • Debris avalanche -- upper North Fork Toutle River
      • Lahars -- South Fork Toutle River
      • Blast ashfall -- Green River
  • Estimates of long-term sediment discharge
  • Channel evolution
    • Debris avalanche -- upper North Fork Toutle River
    • Lahars -- lower North Fork Toutle River, South Fork Toutle River, lower Green River, and Toutle River main stem
    • Blast ashfall -- upper Green River
• Flow-energy relations and principles of channel adjustment
  • Physical principles controlling channel adjustment
  • Governing equations
  • Hydraulic modeling
  • Energy relations and the Toutle River system
• Summary and conclusions
• Selected references
• Appendixes
  • Appendix I - Peaks above base discharge for four sites in the Toutle River system
  • Appendix II - Highest mean discharge for one-day and three-days, and water year, for four sites in the Toutle River system, 1981-92
  • Appendix III - Monumented cross sections used in this study

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