Next Meeting Presentation

Wednesday, September 26
 

Environmental Mitigation and Remediation
Applications of Sub-Surface Dredging

Michael J. Costello
Service Engineering Group

Presentation Synopsis:

In today’s world of habitat restoration, wetland mitigation, and sediment remediation, there are needs to:

• Preserve the sediment/wetland surface vegetation

• Prevent redistribution of contaminated surficial vegetation

• Armor natural caps

• Vary the bathymetry or surface sediment grain size to increase functions and values

• Deepen wetlands to reduce nutrient cycling

• Deepen navigational areas

• Dredge sand for construction projects

Subsurface Dredging is a technique to achieve all of these goals in saturated ground conditions where clean sand underlies the surficial sediments.  Developed in the Netherlands and being refined here in Minnesota / Wisconsin, SSD is a technique where lances pierce through the surficial sediments into underlying sand.  Through a process called “breaching,” the sand is dredged to the surface, the bed subsides and the free sand can be used in many ways.

This presentation outlines the technology and several of its many applications to habitat, mitigation and remediation projects.

Meeting Location:

June Meeting was at the U of MN's St. Anthony Falls Laboratory
 

The meeting began with an overview by Post President Bill Forsmark about the extensive studies and planning efforts that had taken place during the past several years in conjunction with Xcel Energy's FERC relicensing efforts for the St. Anthony Falls Hydropower Plant.  His portion of the presentation also covered the construction of a new dam about 30 feet upriver of the existing structure along with the development of the upper portion of Hennepin Island into a park with an access bridge that gives the public access to the island and riverfront area and up-close views of the main spillway, horseshoe dam and the downtown skyline. Charlene Roise, president of Hess Roise and Company, gave a very enthralling presentation about the history of the falls area and how it has evolved/changed over the past century and a half as it has become an industrialized area.  She has helped Xcel Energy develop a comprehensive Historical Property Management Plan for this area, and was instrumental in developing the interpretive displays in the new park area. Rob Olson, a regulatory specialist for Xcel Energy, discussed the FERC relicensing process, and all the additional steps that Xcel took to make what is now referred to as the St Anthony Falls Water+Power Park a reality. Omid Mohseni, the Associate Director for Applied Research and Engineering at the University of Minnesota's St Anthony Falls Laboratory, talked about several improvements made at the Lab, including new outdoor flumes in several of the old historic tailraces that will be used for studying erosion mechanics and the effectiveness of natural erosion control measures. The presentations concluded with a tour inside the historic hydropower plant.  It was inspiring to see how this rather old, but well maintained facility was continuing to produce electricity in such an efficient and non-polluting manner.