Silver Lake Dam Fish Passage Modification
The City of Rochester is proposing to modify the Silver Lake Dam with a fish passage rock arch rapids in 2025. This project is the first step in a comprehensive, long-term approach to modify all low head dams in the City to improve habitat connectivity in the South Fork Zumbro River network. The existing dam will be moved 700-ft upstream from the Broadway Avenue bridge, and fish passage ramp and wave pools constructed downstream of the dam crest. The dam conversion will add 16 miles of connected habitat and benefit state-threatened and native mussel species, as well as smallmouth bass.
The Silver Lake Dam was constructed in 1937 and is located at the Broadway Avenue bridge over the South Fork Zumbro River. Nine other low head dams were constructed in the 1990's as flood control structures within the City of Rochester. These dams form fish barriers between the South Fork Zumbro River, Cascade Creek, Silver Creek, and Bear Creek.
The City of Rochester is proposing to modify the Silver Lake Dam with a fish passage rock arch rapids and wave pool channel by 2025. This project is the first step in a comprehensive, long-term approach to modify all low head dams in the City of Rochester for habitat connectivity. The existing concrete dam will be removed, and 700-ft of the upstream river channel will be shaped with rock fill with a cutoff wall control section at the upstream end of the fill. The City has an agreement with U.S. Army Corps of Engineers to maintain Silver Lake as a flow channel. The City will construct a 120-ft wide rock ramp in the existing riverbed directly downstream of the cutoff wall control section based on DNR guidance for Natural Channel Design in Dam Removals and Fish Passage. The fish passage channel will include a ramp slope no steeper than 3 percent, a series of 12-14 rock arch weirs with drops no greater than 0.8-ft between each weir, randomly placed fish gaps between weir stones, and a low flow channel to maintain fish movement under low flow conditions. Adjacent to the rock arch rapids fish ramp, the City will construct a series of 4-5 stepped, plunge pools formed by stone weirs that create wave features for tubers and kayakers, as well as fish habitat pools.
The proposed project was identified as a priority based on: 1) safety hazard of the recirculating currents that trap boaters and swimmers at the base of the dam, 2) increasing maintenance requirements of the aging Silver Lake Dam originally built in 1937, and 3) public support for environmental improvements to Silver Lake.
The proposed project is urgently needed to address the safety hazard the Silver Lake Dam poses to river users. The Silver Lake Dam is #23 on the 2021 MN DNR Dam Safety Project Priority List Legislative Report as a dam modification to restore fish passage. Modification of the largest dam in Rochester for fish passage is also a publicly visible first step to modifying all low head dams in Rochester and reconnecting river habitat along the South Fork Zumbro River network.
The City has used many different media events to get input on the project from a diverse and large number of community members: March 2019 open house attended by 80 people, November 2020 virtual open house attended by 1,607 people, post card mailings to 480 residents around Silver Lake, and social media posts viewed by 15,000 people. More than 500 people have responded to online surveys with an overwhelming majority supporting the project. An EAW was approved in 2021.
$2,368,000 the second year is to the commissioner of natural resources for an agreement with the city of Rochester to restore and enhance aquatic habitat in Silver Lake and the south fork of the Zumbro River by modifying the existing low-head dam in Rochester.
Rivers, streams, and surrounding vegetation provide corridors of habitat - The outcome of the proposed habitat corridor will be measured by the removal of the habitat barrier at the Silver Lake Dam and the miles of river habitat reconnected by the Silver Lake fish passage dam modification. The outcome of the proposed habitat corridor will be evaluated by partnering with MN DNR and other local mussel and fish biologists to complete pre- and post-construction mussel and fish species richness and abundance surveys to better quantify the benefits of fish passage dam modifications to native mussel assemblages and fish populations
City of Rochester Flood Control Program, City of Rochester Flood Control Program, City of Rochester Storm Water Utility Fund and Rochester Public Utilities