Hillsboro West (Lagoon) Reservoir Report
Last Updated: December 13, 2025
Hillsboro West (Lagoon) is a key water management infrastructure located in Hillsboro, Oregon, serving as a vital resource for irrigation purposes since its completion in 1984.
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Summary
This earth dam structure stands at a height of 12 feet and has a hydraulic height of 9 feet, with a maximum storage capacity of 120 acre-feet. The dam spans 3000 feet in length and covers a surface area of 14.9 acres, making it a significant contributor to the local water supply.
Managed by a public utility agency and regulated by the Oregon Water Resources Department, Hillsboro West (Lagoon) plays a crucial role in the safe and efficient distribution of wastewater effluent for irrigation needs. With a low hazard potential and a history of regular inspections, this dam ensures the reliability and sustainability of water resources in the region. Equipped with outlet gates for controlled release of water, this structure exemplifies responsible water management practices in alignment with state regulations.
As part of the broader water infrastructure network in the area, Hillsboro West (Lagoon) stands as a testament to the importance of efficient water resource utilization in the face of climate challenges. With its strategic location and purposeful design, this dam serves as a cornerstone for irrigation activities, supporting agricultural productivity and environmental conservation efforts in Washington County, Oregon.
Year Completed |
1984 |
Dam Length |
3000 |
Dam Height |
12 |
River Or Stream |
WASTEWATER EFFLUENT |
Primary Dam Type |
Earth |
Surface Area |
14.9 |
Hydraulic Height |
9 |
Nid Storage |
120 |
Structural Height |
12 |
Outlet Gates |
Slide (sluice gate) |
Hazard Potential |
Low |
Nid Height |
12 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Tualatin River Near Dilley
|
1130cfs |
Fanno Creek At 56th Ave
|
3cfs |
Fanno Creek At Durham
|
36cfs |
East Fork Dairy Creek Near Meacham Corner
|
21cfs |
Columbia Slough At Portland
|
5cfs |
Willamette River At Newberg
|
52600cfs |
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.
Hillsboro West (Lagoon)