Mccaslin Reservoir Report

Last Updated: December 5, 2025

Mccaslin is a privately owned dam located in Boulder, Colorado, specifically in the city of Longmont, along the St Vrain Creek-TR.


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Summary

Completed in 1908, this earth dam stands at a height of 16 feet and spans 435 feet in length, with a storage capacity of 167 acre-feet. Its primary purpose is for irrigation, serving the local agricultural community in the area. Mccaslin is regulated by the Colorado Department of Water Resources (DWR) and undergoes regular inspections to ensure its structural integrity and compliance with state regulations.

Despite being classified as having a low hazard potential and fair condition assessment, Mccaslin poses a moderate risk due to its location and the potential impacts of a breach or failure. Its spillway, of uncontrolled type with a width of 44 feet, can handle a maximum discharge of 600 cfs. The dam has not been significantly modified over the years, and emergency action plans and risk management measures are not explicitly outlined in the available data. Joe Neguse, a Democratic Representative, oversees the congressional district where Mccaslin is situated, emphasizing the importance of maintaining the safety and functionality of this vital water resource infrastructure amid changing climate conditions and increasing water demands in the region.

Year Completed

1908

Dam Length

435

Dam Height

16

River Or Stream

ST VRAIN CREEK-TR

Primary Dam Type

Earth

Surface Area

16

Hydraulic Height

16

Drainage Area

1

Nid Storage

167

Structural Height

16

Hazard Potential

Low

Nid Height

16
       
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.