Twin Branch Reservoir Report

Last Updated: December 5, 2025

Twin Branch is a gravity dam located on the St.


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Summary

Joseph River in Mishawaka, Indiana, with a primary purpose of hydroelectric power generation. Constructed in 1903, this historic structure stands at a height of 41 feet and spans 946 feet in length, boasting a storage capacity of 10,000 acre-feet and a maximum discharge of 37,600 cubic feet per second. The dam is equipped with seven Tainter (radial) gates for water regulation and has a surface area of 1,065 acres, serving a drainage area of 3,530 square miles.

Managed by the Federal Energy Regulatory Commission, Twin Branch presents a high hazard potential due to its age and condition assessment not being available. Despite its risk profile, the dam plays a crucial role in providing renewable energy and water resource management in the region. With no state jurisdiction or regulatory agency oversight, the responsibility for inspection and maintenance falls under federal jurisdiction, emphasizing the importance of ongoing monitoring and risk management measures to ensure the safety and reliability of this vital infrastructure for both water resource and climate enthusiasts.

As a significant landmark in the region, Twin Branch serves as a reminder of the intersection between water resource management, climate resilience, and renewable energy production. Its historical significance, coupled with its high hazard potential, underscores the need for proactive risk assessment, emergency preparedness, and ongoing maintenance to safeguard both the dam's structural integrity and the surrounding ecosystem. With a focus on sustainability and innovation, Twin Branch stands as a symbol of the ongoing efforts to balance the dual priorities of energy production and environmental stewardship in the face of a changing climate.

Year Completed

1903

Dam Length

946

Dam Height

41

River Or Stream

St Joseph River

Primary Dam Type

Gravity

Surface Area

1065

Hydraulic Height

22.1

Drainage Area

3530

Nid Storage

10000

Structural Height

37

Outlet Gates

Tainter (radial) - 7

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

41
       
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.