Gap Road Reservoir Reservoir Report
Last Updated: December 15, 2025
Gap Road Reservoir, located in Prosser, Washington, is a private earth dam built in 2004 for irrigation purposes along the Yakima River.
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Summary
Managed by the Washington Department of Ecology, this reservoir has a storage capacity of 47 acre-feet and covers a surface area of 3.3 acres. With a maximum discharge rate of 10 cubic feet per second, the dam has a structural height of 17 feet and spans 1800 feet in length.
Despite its satisfactory condition assessment, Gap Road Reservoir poses a high hazard potential, emphasizing the importance of regular inspections and emergency preparedness. With a 5-year inspection frequency, this reservoir plays a crucial role in water resource management for agricultural irrigation in Benton County. Additionally, its location in Congressional District 04, represented by Dan Newhouse, underscores its significance in supporting local farming communities and sustaining the region's water supply.
As a vital offstream storage facility in the Seattle District, Gap Road Reservoir serves as a key component of the irrigation infrastructure in the area. Its presence enhances water security and provides essential resources for agricultural activities in Benton, Washington. With its strategic design by SCM Consultants and state-regulated operations, this reservoir exemplifies the intersection of water resource management, climate resilience, and agricultural sustainability in the region.
Year Completed |
2004 |
Dam Length |
1800 |
River Or Stream |
Yakima River - Offstream |
Primary Dam Type |
Earth |
Surface Area |
3.3 |
Hydraulic Height |
17 |
Drainage Area |
0.01 |
Nid Storage |
47 |
Structural Height |
17 |
Hazard Potential |
High |
Foundations |
Soil |
Nid Height |
17 |
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.
Gap Road Reservoir