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How to build a waterfront erosion control retaining wall

Project Name: Beyond Hope II Marina

Customer Name: Beyond Hope II, LLC

Design / Specifying Engineer: John Mckervey of Whipple Consulting Engineers

Block Manufacturer: Wilbert Precast, Inc.

Wall Installer: Wilbert Precast, Inc.

Project Location: Hope, Idaho

Year Built:  Winters of 2007/2008

Project Scope

When developers purchased a popular RV park on 600 feet of Lake Pend Oreille frontage in Hope, Idaho, they had a vision to transform the property into a resort that includes high-end home and condominium sites. They envisioned the centerpiece of the development, called Beyond Hope II, LLC, to be a beautiful and unique 50 slip marina.

The marina that existed at Beyond Hope had decayed to the point that it was unsightly and unusable for boaters, so developers chose to begin the first phase of renovations with the marina overhaul. The goal of the marina renovation was to increase the size of the marina as well as improve its look and functionality. Included in the renovation were several retaining walls that would highlight the project.

Developers chose Redi-Rock retaining wall products due to Redi-Rock’s diverse product capabilities/applications and classy look that could be integrated throughout the entire development, as well as Redi-Rock’s proven track record in shoreline applications. Redi-Rock’s massive block size allowed designers to specify tall gravity walls without geogrid, allowing the project to progress quickly within the short window of low water on Lake Pend Oreille.

Wilbert Precast created docks for the marina using 96 precast dock sections for a total of 36 completed docks. The dock sections are mounted on steel posts driven into the lake basin. In total, the dock system created 50 usable boat slips and increased the size of the marina 25-35 percent.

The biggest installation and engineering challenge for this project was the abundance of natural springs running through the site. Originally the base of the blocks were set just above the low water mark; however concerns about springs behind the wall prompted Wilbert to make sure the base material drain rock was situated well below the low water mark to ensure that the footing was large enough and deep enough to prevent a washout.

In addition to retaining walls, the marina design called for a sea wall to protect the marina from waves and rough water. Originally, the designers had wanted to use Redi-Rock freestanding blocks to construct the break water; however, the water level at the base of the proposed sea wall was below the low water mark and the Department of Environmental Ecology would not allow the dredging the site preparation would have required.

To provide a creative and structurally sound solution for the sea wall and maintain the continuous look of Redi-Rock throughout the marina, Wilbert designed 3’ tall by 12’ long by 6” wide precast panels that have the signature Redi-Rock cobblestone face. The panels were then placed between steel I-beams driven into the lake bottom, creating a functional, durable sea wall with the appearance of Redi-Rock to create continuity throughout the project. In all, Wilbert installed 82 precast panels to create the seawall.

Construction of the Beyond Hope marina project was completed in February 2008. In total, 2,300 Redi-Rock blocks were installed, including retaining wall blocks, freestanding blocks, caps, and 72 steps. “This project used just about every Redi-Rock product we make at our shop,” Lindberg said. Wilbert completed close to half a million dollars worth ofwork at Beyond Hope out of the $1.5 to $2 million project.

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