Talus P5 Stormwater Detention Dam Reservoir Report

Last Updated: December 15, 2025

Located in Issaquah, Washington, the Talus P5 Stormwater Detention Dam is a vital structure designed by Montgomery Water Group to mitigate flood risk and protect the surrounding area from potential water-related hazards.


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Summary

Completed in 2002, this earth dam stands at a hydraulic height of 24 feet and a structural height of 22 feet, with a length of 440 feet. It has a storage capacity of 12 acre-feet, with a normal storage level of 1.1 feet and a surface area of 1 acre, serving the purpose of flood risk reduction in the region.

Managed by a private owner, this stormwater detention dam is regulated by the Washington Department of Ecology, ensuring compliance with state standards for inspection, maintenance, and enforcement. Despite having a high hazard potential, the dam is assessed to be in fair condition as of August 2019, with regular inspections scheduled every 5 years to ensure its continued safety and effectiveness. The structure is situated offstream from Tibbets Creek, providing crucial flood control measures for the surrounding community in King County, Washington.

With its strategic location and effective design, the Talus P5 Stormwater Detention Dam plays a crucial role in protecting the residents of Issaquah and the environment from the impacts of flooding. As part of a comprehensive flood risk reduction strategy, this earth dam serves as a key component in the area's water resource management infrastructure, highlighting the importance of proactive measures to safeguard against potential hazards and ensure the resilience of communities in the face of changing climate conditions.

Year Completed

2002

Dam Length

440

River Or Stream

Offstream - Tibbets Cr.

Primary Dam Type

Earth

Surface Area

1

Hydraulic Height

24

Drainage Area

0.05

Nid Storage

12

Structural Height

22

Hazard Potential

High

Foundations

Soil

Nid Height

24
       
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.