Last Chance No. 1 Reservoir Report

Last Updated: December 5, 2025

Last Chance No.


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Summary

1, also known as Upper Twin Lake, is a privately owned earth dam located in Westminster, Colorado. Completed in 1892 for irrigation purposes, this historic structure stands at 14 feet high and spans a length of 810 feet, with a storage capacity of 150 acre-feet. Situated on Big Dry Creek-OS, this dam serves multiple functions including fire protection, stock watering, and recreational use in addition to its primary irrigation role.

Despite its age, Last Chance No. 1 has a low hazard potential and is currently rated as not assessed for condition. The last inspection took place in 1986, with a moderate risk assessment given a ranking of 3. While the dam meets state regulatory requirements for permitting, inspection, and enforcement, there is no Emergency Action Plan (EAP) in place, indicating a potential area for improvement. Overall, this structure presents an intriguing blend of historical significance and modern challenges in water resource management.

For water resource and climate enthusiasts, Last Chance No. 1 offers a glimpse into the intersection of past engineering achievements and contemporary dam safety considerations. With its location in a picturesque setting in Jefferson County, Colorado, this dam serves as a reminder of the importance of maintaining and monitoring aging infrastructure to ensure both water supply reliability and public safety. As efforts continue to address potential risks and enhance emergency preparedness, Last Chance No. 1 remains a fascinating case study in the ongoing management of water resources in the face of changing environmental conditions.

Year Completed

1892

Dam Length

810

Dam Height

14

River Or Stream

BIG DRY CREEK-OS

Primary Dam Type

Earth

Surface Area

18

Hydraulic Height

10

Nid Storage

150

Structural Height

14

Hazard Potential

Low

Nid Height

14
       
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.