Holly Reservoir Report

Last Updated: December 5, 2025

Holly, located in Arapahoe County, Colorado, serves as a critical flood risk reduction structure along Little Dry Creek.


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Summary

Built in 1979, this earth dam stands at a height of 40 feet and spans 1170 feet, providing a storage capacity of 455 acre-feet. Despite being classified with a high hazard potential, the dam's condition assessment was rated as satisfactory during the last inspection in November 2018.

Managed by local government authorities, Holly is regulated by the Colorado Department of Water Resources with state permitting, inspection, and enforcement in place. With a spillway width of 200 feet and uncontrolled spillway and outlet gates, this structure plays a vital role in mitigating flood risks for the surrounding area. While the dam's risk assessment is moderate, ongoing risk management measures are not explicitly documented.

For water resource and climate enthusiasts, Holly presents a fascinating case study in dam infrastructure and flood risk management. Its strategic location, design features, and regulatory oversight highlight the complex interplay between human interventions and natural forces in safeguarding communities against water-related hazards. As efforts continue to ensure the structure's safety and effectiveness, Holly stands as a testament to the ongoing challenges and opportunities in sustainable water resource management.

Year Completed

1979

Dam Length

1170

Dam Height

40

River Or Stream

LITTLE DRY CREEK

Primary Dam Type

Earth

Surface Area

23

Hydraulic Height

40

Drainage Area

2

Nid Storage

455

Structural Height

45

Outlet Gates

Uncontrolled

Hazard Potential

High

Foundations

Soil

Nid Height

45
       
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.