Western Mobile Lake 4 Reservoir Report

Last Updated: December 5, 2025

Western Mobile Lake 4, located in Boulder, Colorado, is a state-regulated dam situated along the St.


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Summary

Vrain River. This earth dam stands at a height of 31 feet, with a structural height of 33 feet and a length of 1050 feet. The reservoir has a storage capacity of 710 acre-feet, with a normal storage level of 598 acre-feet and a surface area of 32 acres.

Despite being classified as having a low hazard potential, Western Mobile Lake 4 is considered to have a high risk level due to certain factors. The dam's condition assessment is currently labeled as "Not Rated," and there is no existing Emergency Action Plan (EAP) in place. The risk management measures, as well as the overall risk assessment and characterization of the dam, are currently not specified in the available data.

Water resource and climate enthusiasts interested in Western Mobile Lake 4 can delve into the specifics of its design, construction, and regulatory oversight. The dam has not been modified in recent years, and its inspection frequency is set at 6 times per year. While the dam is state-regulated and undergoes regular inspections, more information is needed to fully assess its condition and potential risks. Further research and monitoring may be necessary to ensure the safety and integrity of Western Mobile Lake 4 for the surrounding community and environment.

Dam Length

1050

Dam Height

31

River Or Stream

ST VRAIN

Surface Area

32

Hydraulic Height

31

Nid Storage

710

Structural Height

33

Hazard Potential

Low

Nid Height

33
       
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.