Salt Lake Co.-Big Cottonwood (Spencer`S) Reservoir Report

Last Updated: December 5, 2025

Salt Lake Co.-Big Cottonwood (Spencer's) dam, located in Holladay, Utah, plays a crucial role in flood risk reduction along Big Cottonwood Creek.


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Summary

Constructed in 1984, this earth dam stands at a structural height of 31 feet and a hydraulic height of 26 feet, with a storage capacity of 132 acre-feet. The dam serves the primary purpose of flood risk reduction and is regulated by the Utah Division of Water Rights, ensuring that it undergoes regular inspections and enforcement measures to maintain its functionality.

With a drainage area of 48.3 square miles and a maximum discharge capacity of 1030 cubic feet per second, Salt Lake Co.-Big Cottonwood (Spencer's) dam is designed to mitigate the high hazard potential associated with flooding in the region. The dam's fair condition assessment and inspection frequency of every two years demonstrate its ongoing commitment to safety and risk management. Although the dam does not have an emergency action plan in place currently, its strategic location and design contribute significantly to the protection of downstream communities and infrastructure from potential flooding events.

As a vital infrastructure owned by the local government, Salt Lake Co.-Big Cottonwood (Spencer's) dam stands as a testament to proactive flood risk reduction efforts in the area. With its modest height and storage capacity, the dam serves as a critical line of defense against flooding along Big Cottonwood Creek, safeguarding residents and properties in Salt Lake County, Utah.

Year Completed

1984

Dam Length

1420

River Or Stream

BIG COTTONWOOD CREEK

Primary Dam Type

Earth

Hydraulic Height

26

Drainage Area

48.3

Nid Storage

132

Structural Height

31

Hazard Potential

High

Nid Height

31
       
Seasonal Comparison

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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.