Cedar Way Stormwater Detention Dam Reservoir Report
Last Updated: December 15, 2025
The Cedar Way Stormwater Detention Dam, located within Mountlake Terrace in Snohomish, Washington, serves as a crucial infrastructure for flood risk reduction along Lyons Creek.
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Summary
Built in 1985, this earth dam with stone core stands at a hydraulic height of 30 feet and a structural height of 22 feet, providing a storage capacity of 40 acre-feet and a maximum discharge of 860 cubic feet per second. With a surface area of 3 acres and a drainage area of 1.63 square miles, this dam plays a vital role in managing stormwater runoff and reducing the risk of flooding in the surrounding area.
Managed by the local government and regulated by the Washington Department of Ecology, the Cedar Way Stormwater Detention Dam undergoes regular inspections to ensure its structural integrity and functionality. Despite its high hazard potential, the dam has been assessed to be in satisfactory condition, meeting safety standards and guidelines. The emergency action plan (EAP) for the dam was last revised in 2010, reflecting the commitment to preparedness and risk management in case of any unforeseen events. As a key component in the flood risk reduction strategy, this dam showcases the importance of sustainable water resource management and climate resilience efforts in the region.
Overall, the Cedar Way Stormwater Detention Dam stands as a testament to the collaborative efforts between local government agencies and regulatory bodies in safeguarding communities against the impacts of extreme weather events and climate change. By providing essential flood risk reduction measures and storage capacity for stormwater runoff, this dam plays a crucial role in ensuring the safety and well-being of residents in the surrounding area. With continued inspections, maintenance, and emergency preparedness measures in place, the Cedar Way Dam exemplifies best practices in water resource management and climate adaptation for a more resilient future.
Year Completed |
1985 |
River Or Stream |
Lyons Creek |
Primary Dam Type |
Earth |
Surface Area |
3 |
Hydraulic Height |
30 |
Drainage Area |
1.63 |
Nid Storage |
40 |
Structural Height |
22 |
Hazard Potential |
High |
Foundations |
Unlisted/Unknown |
Nid Height |
30 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Thornton Creek Near Seattle
|
41cfs |
Snohomish River Near Monroe
|
28500cfs |
Mercer Creek Near Bellevue
|
12cfs |
Pilchuck River Near Snohomish
|
1020cfs |
Snoqualmie River Near Carnation
|
9660cfs |
Issaquah Creek Near Mouth Near Issaquah
|
300cfs |
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.
Cedar Way Stormwater Detention Dam
Sammamish Lake Near Redmond
Beach Drive Northeast 17218, Lake Forest Park