Combination of Cobble and Sill Controls Erosion

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by Paul A. Kakuris, Great Lakes Environmental Marine, Ltd, Chicago, IL, USA,

Document Type: Proceeding Paper

Part of: Coastal Zone '87

Abstract: Two types of erosion controls that have had their own successes separately - cobble beach nourishment and a modular previous sill - were deployed in a successful combination to protect a seriously eroded coast on Lake Michigan north of Chicago. In the first combination of its kind, cobble nourishment was used to create a new perched beach where no natural beach was left, and the modular pervious sill (Surgebreaker offshore reef) was installed as a new shoreline. The cobble beach-sill system was designed to protect bluff toes that were being damaged by waves that overtopped and scoured a deteriorating sheetpile bulkhead at water's edge. Wave attack in the area has been increasing, with normally high-energy storm surges and century-high and still rising lake levels. Bluff toe damage has stopped. The perched cobble beach appears suitably stable, with the protective sill, and has recent system design adjustments that should increase stability. The sill appears responsible for substantial shoaling, from sill toe to at least 100 ft. offshore.

Subject Headings: Reefs and sills | Erosion | Coastal management | Beach nourishment | Lakes | Storm surges | Wave overtopping | Water waves | North America | Illinois | United States | Chicago | Lake Michigan

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