Dillon Reservoir Report

Last Updated: December 4, 2025

Dillon Dam, located in Silverthorne, Colorado, is a vital water supply structure on the Blue River.


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Summary

Constructed in 1963, this Earth dam stands at a height of 310 feet and has a storage capacity of 305,000 acre-feet, serving the dual purposes of water supply and recreation. With a surface area of 3,300 acres and a drainage area of 338 square miles, this dam plays a crucial role in managing water resources in Summit County.

The dam has undergone modifications in 1986 and 2002 to enhance its hydraulic and mechanical systems. It features an uncontrolled spillway with a width of 15 feet and is equipped with slide and valve outlet gates. Despite being classified as having a high hazard potential, the dam's condition is rated as satisfactory, with regular inspections and a comprehensive emergency action plan in place. Managed by public utility agencies, Dillon Dam is a key infrastructure ensuring water security in the region.

Dillon Dam's strategic location and design make it a significant asset for water resource management in Colorado. The dam's role in regulating the flow of the Blue River and providing a reliable water supply underscores its importance for the surrounding communities. With a focus on safety and efficiency, Dillon Dam stands as a testament to successful water infrastructure development and management in the face of changing climate conditions.

Years Modified

1986 - Hydraulic, 1986 - Mechanical, 2002 - Hydraulic, 2002 - Mechanical

Year Completed

1963

Dam Length

5900

Dam Height

231

River Or Stream

BLUE RIVER

Primary Dam Type

Earth

Surface Area

3300

Hydraulic Height

231

Drainage Area

338

Nid Storage

305000

Structural Height

310

Outlet Gates

Slide (sluice gate) - 4, Valve - 5

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

310
       
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.