Mount St. Helens Sediment Retention Structure Reservoir Report
Last Updated: December 15, 2025
The Mount St.
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Summary
Helens Sediment Retention Structure, located in Toutle, Washington, was completed in 1988 by the US Army Corps of Engineers to primarily reduce flood risks in the area. This Earth-type dam stands at a height of 186 feet, with a hydraulic height of 180 feet and a structural height of 239 feet. It spans 1800 feet in length and has a dam volume of 228,000 cubic feet. The dam is situated on the North Fork Toutle River and has a spillway width of 400 feet to manage a maximum discharge of 228,000 cubic feet per second.
The risk assessment for the Mount St. Helens Sediment Retention Structure indicates a low hazard potential, with routine evaluations ensuring the dam's safety and functionality. The US Army Corps of Engineers continues to monitor and assess the structure's condition, conducting regular inspections and equipping it with instrumentation for performance monitoring. An Emergency Action Plan is in place to guide response procedures in case of an emergency, and the Corps engages in emergency exercises with local stakeholders to enhance community awareness of flood risks. Overall, the structure's risk management measures are robust, with plans for an updated risk assessment in 2022 to address evolving earthquake and flood hazards.
In summary, the Mount St. Helens Sediment Retention Structure serves as a crucial flood risk reduction measure on the North Fork Toutle River in Washington. With its high hazard potential classification and routine risk assessments, the US Army Corps of Engineers ensures the safety and functionality of the dam. Through ongoing monitoring, emergency response planning, and community outreach efforts, the Corps remains committed to safeguarding the area from potential risks associated with the dam.
Year Completed |
1988 |
Dam Length |
1800 |
Dam Height |
186 |
River Or Stream |
NO. FORK TOUTLE |
Primary Dam Type |
Earth |
Hydraulic Height |
180 |
Drainage Area |
143 |
Structural Height |
239 |
Hazard Potential |
High |
Foundations |
Rock, Soil |
Nid Height |
239 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.
Hazard Potential Classification
HighDams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.
Mount St. Helens Sediment Retention Structure
Headwaters In Sw1/4 Sec 28, T9N, R5E To Mount St. Helens National Volcanic Monument Boundary