Technology Lends a Hand

Several geotextile products were used by the Garden to help protect shoreline plantings. A Geoweb product placed parallel to the shoreline helps prevent failure of shoreline slopes during high water levels. Constructed from polyethylene (plastic), the Geoweb is 9 feet wide, installed with about 3 feet extending below the normal water line and the other 6 feet above the water line. After securing the Geoweb into the shoreline soils with ½-inch steel reinforcing bars pounded to a level below the frost line (about 4 feet), the honeycomb-shaped "cells" are filled with soil to a level 2 inches above the top of the Geoweb. Each of the cells is planted with one or more native shoreline plantings. The fibrous nature of many native plants' root systems spread through the holes in the cell walls. As the plants mature, this combination of plastic reinforcement together with the plant roots creates an extraordinarily effective barrier against wind and wave erosion.

Another specialized product the Chicago Botanic Garden has used to help protect new shoreline plantings is a plastic "benthic mesh." This plastic webbing was originally developed by Wetlands Research, Inc. to help reduce water turbidity in wetland and lake environments by protecting lakebeds and wetland soils from the feeding behavior of rough fish (such as carp). The Garden modified the product's original design by enlarging its openings to about 1 square inch, thereby allowing a more diverse assemblage of shoreline vegetation to grow through the mesh. The benthic mesh also serves to provide a firm footing for Garden maintenance staff over the underlying soft lakebed soils. During the production process, the plastic mesh is injected with a form of calcium to make it heavier than water and thereby resistant to floating. The product is staked to the lakebed using hoops of ½-inch reinforcing rods to resist upheaval by ice in the spring. And, since the mesh is faintly visible in shallow water areas, the Garden custom-colored the plastic during the production process to match the color of our clay soils found in northeastern Illinois.

This method provides long-term shoreline stabilization and at the same time creates valuable wetland and aquatic habitat. The primary disadvantage to this approach is that it requires the lake system to be drawn down during construction to allow compaction of the clay planting shelves.

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