Siena Reservoir Report

Last Updated: December 5, 2025

Siena is a vital water supply infrastructure located in Lafayette, Colorado, along the Coal Creek-TR river system.


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Summary

This Earth dam, completed in 2004, stands at a height of 40 feet and has a storage capacity of 640 acre-feet, with a normal storage level of 450 acre-feet. The dam has a spillway width of 17 feet and a maximum discharge capacity of 690 cubic feet per second, ensuring proper water management in the region.

Owned and regulated by the local government, Siena is subject to regular inspections and enforcement measures to maintain its satisfactory condition and high hazard potential. The dam's design, by BASEPOINT DESIGN CORPORATION, incorporates stone core types and foundations of rock and soil, contributing to its structural integrity. With a risk assessment rating of moderate (3), the dam is equipped to handle emergencies, though the Emergency Action Plan (EAP) status and risk management measures could benefit from further updates to ensure maximum safety and preparedness.

Situated within the Omaha District of the US Army Corps of Engineers, Siena serves as a critical infrastructure for water supply purposes in Broomfield County, Colorado. The dam's strategic location and design underscore its essential role in water resource management and climate resilience efforts in the region, highlighting the importance of proactive maintenance and risk mitigation strategies to safeguard this valuable asset for the community.

Year Completed

2004

Dam Length

1250

Dam Height

40

River Or Stream

COAL CREEK-TR

Primary Dam Type

Earth

Surface Area

20

Hydraulic Height

31

Nid Storage

640

Structural Height

41

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

41
       
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.