Garrison Creek 98th Avenue Detention D Reservoir Report

Last Updated: December 15, 2025

Garrison Creek 98th Avenue Detention D is a vital water management structure located in Kent, Washington, designed to mitigate flood risks and manage water resources effectively.


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Summary

Owned by the local government and regulated by the Washington Department of Ecology, this detention dam was completed in 1996 with a primary purpose of flood risk reduction. With a hydraulic height of 29.8 feet and a structural height of 27.34 feet, this earth dam plays a crucial role in safeguarding the surrounding area from potential hazards.

Covering a surface area of 1 acre and with a drainage area of 0.52 square miles, Garrison Creek 98th Avenue Detention D has a storage capacity of 50 acre-feet, providing essential water storage during periods of high discharge. Despite being classified as having a high hazard potential, the dam is assessed to be in fair condition, with inspections conducted every 5 years to ensure its structural integrity. The dam's location along Garrison Creek in King County underscores its significance in water resource management and climate resilience efforts in the region, making it a key asset for environmental enthusiasts and stakeholders alike.

Year Completed

1996

Dam Length

981

River Or Stream

Garrison Creek

Primary Dam Type

Earth

Surface Area

1

Hydraulic Height

29.8

Drainage Area

0.52

Nid Storage

50

Structural Height

27.34

Hazard Potential

High

Foundations

Soil

Nid Height

30
       
Seasonal Comparison

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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. 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

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, 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.