Vernon Marsh-Mid.Flowage Reservoir Report

Last Updated: December 5, 2025

Vernon Marsh-Mid.Flowage is a state-owned dam located in Waukesha, Wisconsin, that serves as a crucial water resource for the area.


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Summary

Completed in 1962, this earth dam stands at a height of 7 feet and has a storage capacity of 830 acre-feet, with a normal storage level of 330 acre-feet. The dam controls the flow of Mill Brook and covers a surface area of 250 acres, providing important water management functions for the surrounding drainage area of 3.4 square miles.

Despite its low hazard potential, Vernon Marsh-Mid.Flowage is classified as having a very high risk level due to various factors. The dam is regulated by the Wisconsin Department of Natural Resources (WIDNR) and undergoes regular state inspections, with the last one conducted in June 2010. While the condition assessment is currently not rated, the Emergency Action Plan (EAP) for the dam was last revised in January 2016. Overall, Vernon Marsh-Mid.Flowage plays a significant role in water resource management in the region and is essential for maintaining the environmental balance of the area.

Water resource and climate enthusiasts will find Vernon Marsh-Mid.Flowage to be an intriguing structure that highlights the importance of proper dam management and maintenance. With its controlled spillway and history of state oversight, this dam serves as a key element in the water infrastructure of Waukesha, Wisconsin. As a significant water storage facility with a risk level that warrants attention, Vernon Marsh-Mid.Flowage stands as a reminder of the critical role that water resources play in shaping our environment and the need for sustainable water management practices to ensure the safety and well-being of local communities.

Year Completed

1962

Dam Length

4000

Dam Height

7

River Or Stream

MILL BROOK

Primary Dam Type

Earth

Surface Area

250

Hydraulic Height

7

Drainage Area

3.4

Nid Storage

830

Structural Height

7

Hazard Potential

Low

Nid Height

7
       
Seasonal Comparison

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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.