Pierson-Upper Reservoir Report
Last Updated: December 13, 2025
Pierson-Upper is a private dam located in Oregon, specifically in the Tualatin River watershed.
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Summary
Built in 1965, it serves primarily for irrigation purposes, with a capacity of 18 acre-feet and a normal storage level of 16.5 acre-feet. The dam stands at a height of 31 feet and spans 120 feet in length, providing water for individual residences in the area.
Managed by the Oregon Water Resources Department, Pierson-Upper is classified as a low hazard potential structure, with a needle outlet gate for water release. While it has not been rated for its condition, the dam undergoes inspections every six years to ensure its safety and integrity. The surrounding area has a drainage area of 0.82 square miles, with a maximum discharge capacity of 205 cubic feet per second.
Despite being a relatively small dam, Pierson-Upper plays a crucial role in providing water for agricultural purposes in the region. Its location in the scenic landscape of Washington County, Oregon, highlights the importance of sustainable water resource management in the face of changing climate conditions.
Year Completed |
1965 |
Dam Length |
120 |
Dam Height |
31 |
River Or Stream |
TUALATIN RIVER, TRIB TO |
Primary Dam Type |
Earth |
Surface Area |
1.6 |
Hydraulic Height |
29 |
Drainage Area |
0.82 |
Nid Storage |
18 |
Structural Height |
31 |
Outlet Gates |
Needle |
Hazard Potential |
Low |
Nid Height |
31 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Tualatin River Near Dilley
|
1130cfs |
Willamette River At Newberg
|
52600cfs |
Fanno Creek At Durham
|
36cfs |
East Fork Dairy Creek Near Meacham Corner
|
21cfs |
Fanno Creek At 56th Ave
|
3cfs |
South Yamhill River At Mcminnville
|
8310cfs |
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.
Pierson-Upper