Lower Nine Mile Reservoir Report

Last Updated: December 5, 2025

Lower Nine Mile is a privately owned gravity dam located on Nine Mile Creek in Oneida County, Wisconsin.


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Summary

Constructed in 1907, the dam serves primarily for hydroelectric power generation and flood risk reduction purposes. Standing at a height of 12 feet and spanning 186 feet in length, the dam has a storage capacity of 2,617 acre-feet and a maximum discharge of 704 cubic feet per second.

Managed by the Federal Energy Regulatory Commission, Lower Nine Mile has a low hazard potential and is categorized as a very high-risk structure. Despite its age, the dam has not undergone condition assessment, but emergency action plans have been prepared and updated periodically. The dam features a controlled spillway with a width of 26 feet and is equipped with slide and tainter gates for water release.

Enthusiasts in water resource management and climate change can find interest in Lower Nine Mile for its historical significance and the operational challenges it faces as a key infrastructure for hydroelectric power generation in the region. The dam's location within a state-regulated jurisdiction in Wisconsin offers a unique insight into the regulatory framework governing dam safety and maintenance practices, making it a valuable case study for sustainable water resource management in the face of changing climate conditions.

Year Completed

1907

Dam Length

186

Dam Height

12

River Or Stream

Nine Mile Creek

Primary Dam Type

Gravity

Drainage Area

29

Nid Storage

2617

Outlet Gates

Slide (sluice gate) - 1, Tainter (radial) - 2

Hazard Potential

Low

Foundations

Soil

Nid Height

12
       
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.