Moose Lake Dam Spillway Replacement
Why is the spillway being replaced?
A required hazard rating assessment in 2010 concluded that the dam could flood downstream
development in the event of a dam failure. The Wisconsin DNR assigned a high hazard rating to the
dam. A high hazard dam must safely pass the 1,000-year flood. In its current configuration, the Moose
Lake Dam does not have sufficient spillway capacity to pass the 1,000-year flood. The existing spillway
structure is 90 years old and has some minor structural deficiencies. A new spillway will provide the
necessary flood capacity and provide a structure that will have a long service life.
How will the spillway change from its current design?
The new spillway will look similar to the existing spillway, but will be significantly larger. There will be
three gates, each measuring 12 feet wide as compared to the two existing gates that are 8.5 feet wide.
The new stainless steel gates will function in the same manner as the existing gates by lifting them and
allowing flow under the gates. The downstream concrete flume will remain and be expanded to match
the width of the new spillway. The Town of Round Lake will construct a new two-lane concrete bridge
over the spillway.
Why is a drawdown necessary for construction?
The water levels on Moose Lake will be maintained 1.5 to 2.5 feet lower than the normal full elevation
throughout 2015. The drawdown will be limited as much as possible to balance the construction needs
with local desire to use the lake. We hope to keep the drawdown to no more than 1.5 feet, pending
receipt of construction proposals. Depending on ice and flow conditions, Moose Lake may be filled to
its normal level prior to construction.
The drawdown is necessary for the following reasons:
1. Dam safety – The spillway construction will require the use of a cofferdam – a temporary dam
used to keep the construction area dry. During construction, the spillway capacity will be
diminished. The drawdown will mitigate the risk of overtopping the cofferdam or embankment
in the event of a large flood or a flood with significant debris by providing increased storage
capacity.
2. Worker safety – A lower water level will increase the buffer between the lake level and the top
of the cofferdam and reduce the loading on the cofferdam. The risk of cofferdam overtopping
or failure will be reduced with a lower lake level, providing for safer working conditions.
3. Cost effectiveness – Cofferdams and construction dewatering are major contributing costs for
dam construction. The reduced lake level results in a smaller, less expensive cofferdam that
provides a cost-effective means for the contractor to keep the construction site dry and safe.
Will the new spillway change the normal operating levels at Moose Lake?
After construction, the dam will be operated to maintain the historic lake levels, including the winter
drawdown.
What is the proposed construction schedule?
Construction is expected to begin in early May, pending Wisconsin DNR plan approval and suitable ice
and flow conditions. The spillway construction is anticipated to be complete by the middle of
September. Bridge construction will begin following completion of the spillway this fall if time and
conditions allow.
What long-term benefits will the new spillway provide?
The new construction will provide a safe dam that will serve Chippewa and Flambeau Improvement
Company and the local area for years to come:
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A safe dam protects the interests of residents upstream and downstream of the dam.
The new spillway will extend the service life of the dam for 50 or more years.
Increased spillway capacity will reduce the frequency and magnitude of rising lake levels during
flood events.
The construction and future operation and maintenance costs are borne by Chippewa and
Flambeau Improvement Company and not local residents.
The spillway provides the foundation for the new bridge, reducing the bridge construction cost
and thereby costs to the Town of Round Lake.