Johnston Reservoir Report

Last Updated: December 5, 2025

Johnston is a privately-owned dam located in Littleton, Colorado, along the Lilley Gulch river.


°F

°F

mph

Wind

%

Humidity

Summary

Completed in 1974, this earth dam stands at a height of 11 feet with a hydraulic height of 17 feet, serving primarily for irrigation purposes. With a storage capacity of 1134 acre-feet and a surface area of 82 acres, Johnston plays a crucial role in water resource management in the region.

Maintained by the Colorado Department of Water Resources, Johnston has a significant hazard potential but is currently assessed to be in satisfactory condition as of February 2020. The dam has a moderate risk level, with regular inspections conducted every two years to ensure its safety and functionality. Despite its age, Johnston continues to provide vital water resources for irrigation and recreational activities in the area.

With its uncontrolled spillway and a maximum discharge of 3650 cubic feet per second, Johnston remains an important infrastructure for water management in Jefferson County, Colorado. As climate change continues to impact water resources, the maintenance and regulation of dams like Johnston are essential to ensure the sustainable use of water for agricultural and recreational purposes in the region.

Year Completed

1974

Dam Length

1530

Dam Height

11

River Or Stream

LILLEY GULCH

Primary Dam Type

Earth

Surface Area

82

Hydraulic Height

17

Nid Storage

1134

Structural Height

11

Hazard Potential

Significant

Nid Height

17
       
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.