Chaplain Lake South Dam Reservoir Report

Last Updated: December 15, 2025

Chaplain Lake South Dam, located in Sultan, Washington, serves as a critical water supply infrastructure for the region.


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Summary

Completed in 1930, this earth dam stands at a hydraulic height of 75 feet and has a structural height of 50 feet, with a storage capacity of 17,800 acre-feet. The dam is situated on Chaplain Creek, with a drainage area of 2.6 square miles, providing essential water resources for the surrounding communities.

Managed by the Washington Department of Ecology, Chaplain Lake South Dam is regulated and inspected regularly to ensure its structural integrity and safety. With a high hazard potential, the dam's condition is assessed as satisfactory, with the last inspection conducted in July 2019. Despite its age, the dam continues to effectively meet its primary purpose of water supply, demonstrating its importance in maintaining a reliable water source for the area.

As a key component of the local water infrastructure, Chaplain Lake South Dam plays a crucial role in water management and supply for Snohomish County, Washington. With its strategic location and significant storage capacity, the dam serves as a vital resource for the region, highlighting the importance of ongoing monitoring and maintenance to ensure its continued functionality and safety in the face of evolving climate conditions and water resource management challenges.

Year Completed

1930

Dam Length

900

River Or Stream

Chaplain Creek

Primary Dam Type

Earth

Surface Area

450

Hydraulic Height

75

Drainage Area

2.6

Nid Storage

17800

Structural Height

50

Hazard Potential

High

Foundations

Soil

Nid Height

75
       
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.