Seattle Port Lagoon No 3 Expansion dam
Seattle Port Lagoon No 3 Expansion
Seattle Port Lagoon No 3 Expansion is a critical flood risk reduction project located in King County, Washington. Owned by the local government and regulated by the Washington Department of Ecology, this expansion was completed in 2001 by Kennedy-Jenks Consultants. The dam, primarily constructed of earth and rockfill, stands at a hydraulic height of 31.5 feet and has a storage capacity of 256 acre-feet, with a normal storage level of 221 acre-feet.
With a surface area of 0.9 acres and a maximum discharge of 140 cubic feet per second, this project plays a key role in managing flood risks in the region. The dam's hazard potential is classified as high, but its condition assessment in 2018 deemed it to be in fair condition. The dam undergoes inspections every five years, with the last inspection taking place in May 2017. Despite its importance in flood risk reduction, there are no associated structures or outlet gates in place.
Overall, the Seattle Port Lagoon No 3 Expansion serves as a vital infrastructure for protecting the surrounding areas from potential flooding events. Its strategic location along Des Moines Creek - Offstream and its compliance with state regulations highlight its significance in water resource management and climate resilience efforts in Washington state.
Dam data reference
Condition Assessment
- Satisfactory
- No 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.
- 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.
- 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.
Hazard Potential Classification
- High
- Dams 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, environmental 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.
Plan around the weather
Same NOAA / yr.no feed Snoflo's iOS app uses. Watch the precipitation column on the meteogram -- rain on the basin upstream typically lifts inflow 24-72 hours later.
Next 5 days, hour by hour
Temperature line with weather symbols on top, snow + rain accumulation as columns, humidity as a dotted line.
5-day forecast table
Every 3 hours, broken out across temperature, snow, rain, humidity, and wind. Each cell is colour-coded relative to the column min/max.
| Time | Condition | Temp (°F) | Snow (in) | Rain (in) | Humidity (%) | Wind (mps) | Wind dir |
|---|---|---|---|---|---|---|---|
| Loading detailed forecast… | |||||||
15-day temperature & precipitation
Daily temperatures, snow, and rain projected over the next two weeks.
Nearby streamflow gauges
USGS streamgauges around Seattle Port Lagoon No 3 Expansion -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Mill Creek Near Mouth At Orillia | 6 cfs | → |
| Spring Brook Creek At Orillia | 6 cfs | → |
| Duwamish River At Golf Course At Tukwila | 6,700 cfs | → |
| Mill Creek At Earthworks Park At Kent | 1 cfs | → |
| Cedar River At Renton | 339 cfs | → |
| Green River Near Auburn | 746 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near Seattle Port Lagoon No 3 Expansion.
Boat launches
- Lake Fenwick Trail Kent
- King County
- 47th Avenue Southwest 10203, Seattle
- Southwest Harbor Drive 8900, Vashon
- Fauntleroy Way Southwest 9345, Seattle
- Duwamish River Boat Ramp
Campgrounds
- Point Robinson Campground
- Dash Point State Park
- Dash Point Campground
- Cascadia Marine Trail
- Gig Harbor Rv Resort
- Manchester State Park
Paddle runs
- Snoqualmie Falls To Plum's Landing
- Confluence With Taylor River To Confluence With North Fork Snoqualmie River
- Wagner Bridge To Confluence With Middle Fork Snoqualmie River
- Huckleberry Creek To Confluence With Clearwater River
- Brothers Wilderness Boundary To Olympic Nf Boundary
- Quartz Road To Confluence With Middle Fork Snoqualmie River
Track Seattle Port Lagoon No 3 Expansion in the Snoflo app
Save this dam as a favorite and get the local NOAA / yr.no forecast plus regional flow context wherever you are.
About Seattle Port Lagoon No 3 Expansion
Where does the data for Seattle Port Lagoon No 3 Expansion come from?
Structural and regulatory data come from the U.S. Army Corps of Engineers' National Inventory of Dams (NID). Weather forecast comes from NOAA / yr.no -- the same feed Snoflo's iOS app uses.
How often is the report updated?
NID structural data refreshes annually as the Corps publishes updated assessments. The weather forecast refreshes throughout the day.
What does the High hazard rating mean?
The Corps of Engineers' hazard potential classification grades probable consequences if the dam fails: High = probable loss of human life; Significant = no probable loss of human life but possible economic loss / environmental damage; Low = no probable loss of human life, only minor economic / environmental losses. See the Dam Data Reference card above for the full definitions.
What's "% of normal"?
The current storage value compared to the historical average storage on this calendar day. 100% = right on average; values above 100% mean above-normal storage (wet year); values below mean below-normal (dry year or drought).
Can I get alerts when storage crosses a threshold?
Yes -- alerts are managed in the Snoflo iOS app. Favorite this dam, set a threshold, and you'll get a push the moment conditions cross.
Other water bodies near here
Snoflo-tracked reservoirs and dams within driving distance of Seattle Port Lagoon No 3 Expansion.