Rockwell Reservoir Report

Last Updated: December 5, 2025

Rockwell, a privately owned dam located in Weld County, Colorado, serves primarily for irrigation purposes on the Big Hollow river.


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Summary

Built in 1885, this Earth-type dam stands at 16 feet high and 1100 feet long, with a storage capacity of 441 acre-feet. Despite its low hazard potential, Rockwell has been deemed unsatisfactory in its condition assessment as of October 2016.

The dam's spillway is uncontrolled with a width of 24 feet, and it has a maximum discharge capacity of 1050 cubic feet per second. Although Rockwell has not been modified in recent years, it undergoes inspections every 6 years to ensure its safety and compliance with state regulations. The risk assessment for Rockwell is considered moderate, with a rating of 3 out of 5, indicating the need for ongoing risk management measures.

For water resource and climate enthusiasts, Rockwell presents a historical landmark in Colorado's irrigation infrastructure. Its location in the scenic city of Johnstown, along with its vital role in water management on the Big Hollow river, makes it a significant structure worth monitoring and preserving for future generations. As climate change impacts water resources, understanding and maintaining dams like Rockwell becomes increasingly crucial to ensure sustainable water usage and management in the region.

Year Completed

1885

Dam Length

1100

Dam Height

16

River Or Stream

BIG HOLLOW

Primary Dam Type

Earth

Surface Area

15

Hydraulic Height

16

Drainage Area

7

Nid Storage

441

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.