Prosser Diversion Reservoir Report
Last Updated: December 15, 2025
Prosser Diversion, located in Benton County, Washington, along the Yakima River, is a Federal-owned irrigation structure managed by the Bureau of Reclamation.
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Summary
Constructed in 1916, this concrete arch dam stands at 9 feet tall and spans 661 feet in length, with a storage capacity of 350 acre-feet. Primarily serving irrigation purposes, Prosser Diversion plays a crucial role in supporting agricultural activities in the region.
With a low hazard potential and a moderate risk assessment rating of 3, Prosser Diversion is a key component of water resource management in the area. Although the condition assessment is currently listed as "Not Available," the Bureau of Reclamation conducts inspections every 6 years to ensure the structure's safety and functionality. As an uncontrolled spillway dam, it is essential for the proper operation and maintenance of Prosser Diversion to mitigate potential risks and address any necessary improvements for long-term sustainability.
Climate enthusiasts and water resource stakeholders interested in the management and operation of irrigation structures will find Prosser Diversion a fascinating case study. With its historical significance and ongoing role in supporting agricultural activities along the Yakima River, this Federal-owned dam highlights the importance of sustainable water resource management practices in the face of changing climatic conditions and increasing demands for water resources.
Year Completed |
1916 |
Dam Length |
661 |
Dam Height |
9 |
River Or Stream |
YAKIMA RIVER |
Primary Dam Type |
Concrete |
Hydraulic Height |
7 |
Nid Storage |
350 |
Structural Height |
9 |
Hazard Potential |
Low |
Foundations |
Rock |
Nid Height |
9 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Yakima River At Mabton
|
28900cfs |
Yakima River At Kiona
|
23800cfs |
Granger Drain At Granger
|
13cfs |
Columbia River Below Priest Rapids Dam
|
124000cfs |
Umatilla River Near Umatilla
|
516cfs |
Yakima River Above Ahtanum Creek At Union Gap
|
14200cfs |
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.
Prosser Diversion