TO: Moorings Bay System homeowners, condominiums, and CO-OPs.

FROM: The Moorings Bay Special Taxing District Advisory Committee, Ron Pennington, Chairman, Doug Finlay, Jim Rozzi, Dan Spina, and Michael Williams, and Jon C. Staiger, Ph.D., Natural Resources Manager

SUBJECT: Tutorial information regarding seawalls located in the Moorings Bay System

DATE APPROVED: 15 October 2002

Boundaries of the Moorings Bay System: The waterway between Banyan Boulevard on the south and Seagate Drive on the north, including Doctors Pass.

Purpose of the Tutorial: The referendum that created the Moorings Bay System Taxing District provided for Pass and waterway dredging, maintenance of aids to navigation, surface trash and debris removal, and inspection of seawalls.

The Natural Resources Manager provides consultation regarding inspection of seawalls. This tutorial is to help that process. The City of Naples does not provide engineering inspection of seawalls.

Contact: Jon C. Staiger, 239-213-1030

Basic Concept: The best solution to questions about seawall condition is to engage an experienced professional engineer to evaluate the wall. Such individuals are most qualified to differentiate between superficial problems, cosmetic problems and structural problems that could jeopardize a seawall.

A Partial List of Experienced Engineers:

• Coastal Engineering Consultants, Inc. 643-2324

• James E. Hirst & Associates, Inc. 261-4567

• W. J. Johnson Associates, Inc. 596-3200

• Suboceanic Consultants, Inc. 261-2025

Seawall Problems:

Seawall slabs: The slabs should be vertical, their seams parallel, and their faces should be in the same plane. Misalignment is usually a sign of an unwanted shift in slab position. Small cracks are present in most "mature" seawall slabs. Long horizontal cracks and areas where pieces of concrete have spalled off the face of the slab are causes of alarm, because they can indicate significant deterioration of the reinforcing steel, and potential wall failure.

Seawall caps: The caps should be level and continuous. Chipping or spalling of concrete from the lower edge of the cap is usually a sign that the reinforcing steel is too close to the surface, and corroding from salt penetrating through small cracks. If sufficient concrete breaks away the structural integrity of the wall will be jeopardized. Seawall caps will develop obvious torsion cracks if the slabs start kicking out at the toe (toe failure).

Tiebacks and deadmen: Tieback deterioration is a given. The original steel was rarely galvanized and, if otherwise treated to resist corrosion, the paint is long gone. Experience indicates that the tiebacks fail closer to the cap than to the deadmen, so an inspection requires some digging, but not complete excavation. If the tiebacks deteriorate sufficiently and water pressure builds up behind the seawall, either from heavy rain or a storm surge, the cap can crack through and the wall collapse outward.

Loss of soil: Subsidence behind seawalls can result from loss of soil through the joints or from beneath the toe. The former is much more prevalent that the latter, and more easily remedied. Excavation behind the joints, backing them with filter fabric, and backfilling with soil is the simplest solution. Continuing to dump fill in the voids is a cosmetic fix, but it does not address the cause. Some walls have been "repaired" by sealing the joints with cement grout, to prevent soil loss. This is not a wise practice, since there must be a way to relieve hydraulic pressure from behind the wall. If the space behind the cap has been covered with a sidewalk, there is a risk that subsidence could go undetected until a serious problem arises.

If you would like additional information or a list of seawall repair contractors, please call Dr. Jon Staiger, City of Naples Natural Resources Manager, at 213-1030.