Mann Reservoir Report

Last Updated: December 5, 2025

Mann is a privately-owned dam located in Jefferson County, Colorado, near the city of Littleton.


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Summary

Completed in 1877, Mann serves multiple purposes including fire protection, stock and small fish pond, irrigation, and recreation. The dam is primarily an Earth type structure with a height of 15 feet and a length of 400 feet, holding a maximum storage capacity of 98 acre-feet and a normal storage capacity of 21 acre-feet. It is situated on the Dochan Gulch river, within the Omaha District of the US Army Corps of Engineers.

Despite being classified as having low hazard potential and fair condition as of its last inspection in 2007, Mann poses a high risk due to its location and the potential impact of a failure on the surrounding area. The dam does not have a spillway and is not associated with any locks or outlet gates. While it meets state permitting and inspection requirements, the dam's Emergency Action Plan (EAP) status and risk assessment measures are unclear. For water resource and climate enthusiasts, Mann represents a historic structure with the potential for significant risk management challenges in the future.

Year Completed

1877

Dam Length

400

Dam Height

15

River Or Stream

DOCHAN GULCH

Primary Dam Type

Earth

Surface Area

4

Hydraulic Height

15

Drainage Area

1

Nid Storage

98

Structural Height

15

Hazard Potential

Low

Nid Height

15
       
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.