St. John Commons Dam Reservoir Report

Last Updated: January 11, 2026

The St.


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Summary

John Commons Dam in Morgan, Indiana, stands as a testament to modern engineering and water resource management. Completed in 2002, this private-owned earth dam spans 300 feet in length and reaches a height of 29 feet, with a primary purpose that extends beyond traditional flood control. Situated on the Long Run river, the dam boasts a storage capacity of 150 acre-feet and a normal storage of 108 acre-feet, serving as a vital tool in regulating water flow and ensuring sustainable water management in the region.

Managed by the Indiana Department of Natural Resources, the St. John Commons Dam is classified as a high hazard potential structure, yet its condition assessment remains satisfactory. With a spillway width of 70 feet and a maximum discharge capacity of 4368 cubic feet per second, the dam is equipped to handle significant water flow during periods of heavy rainfall or flooding. Its risk assessment is moderate, reflecting a balanced approach to risk management and emergency preparedness.

Located in a picturesque setting in Morgan County, the St. John Commons Dam not only provides flood protection but also enhances the natural environment and supports the local ecosystem. With its sustainable design and satisfactory condition, this earth dam stands as a symbol of progress in water resource management and climate resilience, showcasing the importance of responsible stewardship in safeguarding our water resources for future generations.

Year Completed

2002

Dam Length

300

Dam Height

29

River Or Stream

LONG RUN

Primary Dam Type

Earth

Surface Area

15

Hydraulic Height

29

Drainage Area

0.79

Nid Storage

150

Structural Height

29

Outlet Gates

None

Hazard Potential

High

Foundations

Soil

Nid Height

29
       
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.