Rock arch rapids and other features moderate river flow when a substandard dam is removed and natural river flow is restored.
When a flood damaged the Lake Shady dam beyond practical repair, Olmsted County saw an opportunity to return the upriver lake to a riverine, wetland, and upland bionetwork. The project needed to restore the river’s ecological health and natural beauty without impacting high water elevations during future flood events while also creating new recreational opportunities for the community.
Our design called for demolishing the existing concrete dam and constructing an 800-foot-long series of 10 rock arch rapids to withstand the tremendous stresses caused by an estimated 100-year storm event flow—approximately 2,800 cubic feet (79 cubic metres) per second. Using specially quarried four- to six-foot boulders, the arches were built under low river flow and frozen conditions to preserve the lakebed and support heavy equipment.
The project restored 1.05 miles (1.69 kilometres) of river channel with 120,000 cubic yards (91,700 cubic metres) of saturated sediment, 11 riffle structures, and 2,665 linear feet (812 metres) of woody debris structures to stabilize banks and improve fish habitat. The scenic overlook adapted from a modified dam abutment structure and a 1,100-foot (335-metre) portage way encourage a variety of encounters with this reach of the Zumbro River now restored to its natural beauty.
At a Glance
- Offices
- Award
- ACEC of Minnesota Engineering Excellence Awards - Grand Award, 2019
Joe Palen, Senior Associate, Community Development
We strive to provide exceptional customer service to our clients by providing trusted advice and creative, cost effective solutions.
George Athanasakes, Vice President, Ecosystem Restoration, Environmental Services
We analyze natural processes driving ecological functions and incorporate these processes into designs to create self-sustaining ecosystems.
Linda Brown, Senior Associate, Community Development
I work with private developers and governing entities to develop areas in communities that benefit everyone.
John Smyth, Associate
My job is to help communities protect and restore their water resources, so they can be enjoyed for generations to come.
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