Effectiveness of Pocket-Wave Absorbers in Vertical-Wall, Coastal Entrance Structures: Fid-Bau Portal

Effectiveness of Pocket-Wave Absorbers in Vertical-Wall, Coastal Entrance Structures

E. F. Thompson / J. R. Bottin / J. P. Selegean

This Coastal and Hydraulics Engineering Technical Note (CHETN) provides preliminary information on the effectiveness of pocket wave absorbers (relative to wave conditions) in vertical steel sheet-pile coastal entrance structures. The U.S. Army Corps of Engineers is responsible for dozens of harbor entrances in the Great Lakes constructed with parallel jetties. These jetties, many in operation for more than 100 years, were typically constructed of rock-filled timber cribs. Over time, the wood cribbing has experienced significant deterioration, thus causing the jetty to be rather porous. Many of these structures have been rehabilitated. The typical rehabilitation approach has been to drive steel sheet pile around the existing structure and place a concrete cap on top, thereby encasing the original structure. After completion of the rehabilitation projects, the wave climate between the jetties appears to increase significantly causing navigational difficulties and damage to moored vessels within the harbor. This is apparently due to the fact that the timber crib jetties were rough, porous structures, especially in their deteriorated state, and were much more effective at dampening wave energy than the rehabilitated, sheet-pile encased jetties. The steel sheet-pile structures, being considerably more reflective than the deteriorating timber structures, are largely responsible for the increasingly energetic wave climate. To mitigate for the more energetic wave climate, the Corps has removed short sections of steel sheet piling at selected harbors and replaced them with pocket wave absorbers.