Allis Reservoir Report

Last Updated: December 4, 2025

Allis is a privately owned dam located in Castle Rock, Colorado, constructed in 1906 for irrigation purposes along Carpenter Creek.


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Summary

Standing at 45 feet high and stretching 690 feet in length, the dam has a storage capacity of 225 acre-feet, with a normal storage of 140 acre-feet and a surface area of 12 acres. With a low hazard potential and a moderate risk assessment, the dam is classified as unsatisfactory in condition as of the last inspection in 2013.

Despite its age, Allis continues to serve its primary purpose of irrigation along with providing fire protection, stock, and small fish pond services. The dam's uncontrolled spillway width of 12 feet allows for a maximum discharge of 4100 cubic feet per second. The dam is under state jurisdiction and regulated by the Colorado Department of Water Resources, with permitting, inspections, and enforcement regularly conducted to ensure its safety and compliance.

Located in Douglas County, Allis plays a crucial role in water resource management in the region. While classified as having a moderate risk assessment, the dam's low hazard potential indicates a manageable level of risk. With its rich history dating back over a century, Allis stands as a testament to the importance of maintaining and regulating water infrastructure for both agricultural and environmental purposes in the face of changing climate patterns.

Year Completed

1906

Dam Length

690

Dam Height

45

River Or Stream

CARPENTER CREEK-TR

Primary Dam Type

Earth

Surface Area

12

Hydraulic Height

45

Drainage Area

1

Nid Storage

225

Structural Height

45

Hazard Potential

Low

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.