Garrison Creek Stormwater Detention Dam Reservoir Report
Last Updated: December 15, 2025
Located in King County, Washington, the Garrison Creek Stormwater Detention Dam stands as a vital structure designed for flood risk reduction along Garrison Creek.
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Summary
Owned by the local government and regulated by the Washington Department of Ecology, this earth dam with a hydraulic height of 45 feet was completed in 1991 to provide storage capacity of up to 40 acre-feet, serving a drainage area of 0.86 square miles. With a maximum discharge capacity of 307 cubic feet per second, the dam plays a crucial role in managing stormwater runoff and reducing flood hazards in the region.
The dam's strategic location within the Seattle District ensures effective flood control measures for nearby communities, with a fair condition assessment as of 2016. Despite its high hazard potential, the dam's structure and operation are continuously inspected and enforced by state authorities to ensure public safety. The dam's primary purpose of flood risk reduction aligns with its design as a multi-arch earth dam, utilizing rock and soil foundations to support its 117-foot length and 2-acre surface area. With an emergency action plan in place and regular inspections, the Garrison Creek Stormwater Detention Dam remains a crucial asset in safeguarding the local environment and residents against potential flooding events.
As climate change intensifies the frequency and severity of storms, the Garrison Creek Stormwater Detention Dam plays a pivotal role in managing stormwater and reducing flood risks in the region. With Congressman Adam Smith representing the area in Congressional District 09, Washington, the dam's importance in protecting communities and infrastructure from extreme weather events cannot be overstated. As part of the state's regulatory framework, the dam's continued operation and maintenance ensure its effectiveness in mitigating flood impacts and preserving water resources for future generations.
Year Completed |
1991 |
Dam Length |
117 |
River Or Stream |
Garrison Creek |
Primary Dam Type |
Earth |
Surface Area |
2 |
Hydraulic Height |
45 |
Drainage Area |
0.86 |
Nid Storage |
40 |
Structural Height |
45 |
Hazard Potential |
High |
Foundations |
Rock, Soil |
Nid Height |
45 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Mill Creek At Earthworks Park At Kent
|
8cfs |
Spring Brook Creek At Orillia
|
7cfs |
Mill Creek Near Mouth At Orillia
|
44cfs |
Cedar River At Renton
|
5160cfs |
Duwamish River At Golf Course At Tukwila
|
6700cfs |
Green River Near Auburn
|
10100cfs |
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.
Area Campgrounds
| Location | Reservations | Toilets |
|---|---|---|
Point Robinson Campground
|
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Dash Point State Park
|
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Dash Point Campground
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Garrison Creek Stormwater Detention Dam
Lake Tapps Near Sumner
Lake Fenwick Trail Kent