South Ridge Stormwater Detention Dam Reservoir Report

Last Updated: December 15, 2025

The South Ridge Stormwater Detention Dam, located in Issaquah, Washington, is a private-owned structure designed by Concept Engineering to reduce flood risk along the North Fork Issaquah Creek.


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Summary

Completed in 2002, this earth dam stands at a hydraulic height of 10 feet and a length of 430 feet, with a storage capacity of 25 acre-feet. The dam serves as a crucial tool in managing stormwater runoff and protecting the surrounding community from potential flooding events.

With a hazard potential rated as high, the South Ridge Dam undergoes regular inspections to ensure its structural integrity and effectiveness in flood risk reduction. The condition assessment conducted in 2018 deemed the dam to be in satisfactory condition. The Washington Department of Ecology regulates the dam, and it is subject to state permitting, inspection, and enforcement to maintain compliance with safety standards. The dam's location in King County, Washington, adds to its significance in managing water resources and climate challenges in the region, highlighting the importance of sustainable infrastructure for resilient communities.

As a key component in the flood risk reduction strategy for the area, the South Ridge Stormwater Detention Dam plays a crucial role in safeguarding the community from potential inundation events. With its design focused on earth and stone materials, the dam efficiently manages stormwater runoff from a drainage area of 0.1 square miles, providing a storage capacity of 22 acre-feet under normal conditions. The dam's presence underscores the importance of proactive water resource management in mitigating the impacts of climate change and enhancing community resilience to extreme weather events.

Year Completed

2002

Dam Length

430

River Or Stream

NF Issaquah Creek - Offstream

Primary Dam Type

Earth

Surface Area

1.9

Hydraulic Height

10

Drainage Area

0.1

Nid Storage

25

Structural Height

10

Hazard Potential

High

Foundations

Soil

Nid Height

10
       
Seasonal Comparison

Weather Forecast

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.