This project involves the movement of sediment from a navigational lane (presently obstructed) with subsequent placement upon remnant sections of the old dredge bank created in the late 1800s by a USACE navigation improvement project. Although the USACE project was abandoned in the 1920s, much of the original dredge spoils remained as a bank of sand/silt extending across much of the lakes east-west axis. These dredge spoil structures served as breakwaters for much of the 20th century, protecting critical habitat threatened by artificially high WLF.
Specific locations of the historical dredge bank are identifiable on existing and older aerial images. This specific proposal is focused on one segment of the dredge bank complex located in the southeast corner of the east lake basin. This site is characterized by relatively shallow depths of 0.25m to 1 m depths. Lake bed composition is sand /silt. Older maps show the old dredge bank footprint that has since partially eroded. This eroded site condition is common along other segments of the historical dredge bank not included in this project proposal.
This is the general area map;
You can see the large open gap between the 2 ends of the original dredge bank. This gap is proposed to be the specific project site.
As part of this project we also propose to reinforce the existing island structure (aka east island dredge bank ) with natural materials including dredged sediment from the partner navigation lane project. Select trees on island will also be cut to enable these actions;
1) Open canopy for vegetative response, 2) install woody structural habitat, and 3) provide shore edge protection .
Hydraulic dredging is proposed to relocate approximately 3,000 cu meters of lake bed sediments. The material will come from an obstructed navigational lane near the lakes outlet (Fox River) and relocated to the dredge bank remnant gap segment described. Early estimates indicate approximately 350 meters of dredge bank remnant can be transitioned to stable and bioengineered break water structure. The site proposed for sediment enhancement is state owned
The navigation lane to be improved is located approx 600 meters from the
break water enhancement site. The deepening of this lane, although a
secondary outcome, will have value for improved navigation, habitat protection,
and support for lowered WLF to further advance the emergent plant goals
Permit considerations will address precedence, sediment composition,
structural life, height, width, and base materials.
A bathymetry survey scheduled for spring 2010, funded with WI planning grant, will characterize the depth contours of the remnant breakwaters (dredge banks).
Detailed designs will be developed upon completion of the dredge bank bathymetric survey in June 2010. These designs will be developed under the direction of a technical review team including Shawn Eisch, Derek Kavanaugh, Ted Johnson, and Mark Sesing, with review by engineering staff. Subsequent to permit approvals (Ch 30 ), final approval will be sought from the LPPRD as advised by the Adaptive Management Committee (AMC).