In this paper the important role that physical modeling can play in supporting the efficient and optimized design of ports, harbors and marinas will be reviewed and discussed. While the power and capability of numerical modeling approaches has increased dramatically in recent decades, some important gaps remain where physical modeling approaches can deliver better, more reliable answers. Physical modeling facilities and technologies have also improved in recent decades, and physical modeling studies, particularly those conducted at large scale, remain the preferred approach to optimize the layout and design of rubble-mound breakwaters to suit local conditions, and validate the performance of proposed designs prior to construction. Physical model studies also remain the best approach to predict the magnitude and character of wave-induced uplift pressures on the underside of pile-supported deck structures, and to develop and evaluate alternative strategies for attenuating the uplift pressures. Physical model studies are also the best approach for predicting overtopping flows due to waves at complex three dimensional structures, and predict the behavior of ships moored within harbors. All of the important physical processes governing wave propagation and wave structure interactions, such as wave refraction, diffraction, reflection, wave breaking, non-linear wave‑wave interactions, wave run-up, overtopping, interstitial flows, and armor unit stability, can be reproduced in a realistic manner in a large-scale physical model.
The important role that a 3D physical model study can play in supporting the design of a new harbor will be illustrated through reference to a specific example. Gateway Harbor has been proposed as a new harbor to be constructed beside Navy Pier on the shore of Lake Michigan near the center of the City of Chicago, Illinois, USA. Gateway Harbor will be located just south of Navy Pier, and will offer sheltered moorage mainly for recreational yachts, tour boats and passenger ferries. The project site is located behind an outer breakwater which offers partial sheltering during storms. However, because the outer breakwater is a low-crested structure that experiences a large amount of overtopping during extreme events with high water levels and on-shore winds, the site is exposed to moderate wave action during design events.
A 3D physical model study was commissioned to support the design of the new harbor. Key issues to be addressed included:
- wave agitation within the new harbor, which is strongly influence by the wave overtopping passing over the low-crested outer breakwater.
- Wave uplift pressures on the underside of a lengthy pile-supported deck structure
- Potential optimizations to the harbor layout and the design of the new structures to reduce wave disturbance and wave loads, reduce costs, and improve constructability.
A three-dimensional 1/30 scale physical model of the proposed harbor was constructed in a 36m by 30m directional wave basin the Ocean, Coastal and River Engineering Research Centre (OCRE) of the National Research Council of Canada (NRC). Accurate reproductions of a range of extreme wave conditions were generated in the model by means of a sophisticated 60-segment directional wave generator. The model was fitted with instrumentation to measure wave agitation within the harbor and uplift pressures on the existing deck-on-pile structure running along the south side of Navy Pier, and with several video cameras to monitor conditions in the model.
An initial series of tests was conducted to verify the incident wave conditions in the model for existing conditions without the new harbor. Following this, a 1:30 scale model of the eastern part of the new harbor was constructed, and tested in a wide range of extreme water levels and wave conditions particular to the site. The new breakwater structures were constructed using rock materials that were selected to reproduce the hydraulic performance and submerged stability of the materials specified in the prototype design. More than twenty alternative harbor layouts were simulated in the model, and the results of these studies have been assessed to help develop an optimized, cost-effective design which minimizes wave uplift forces, wave agitation and construction costs. After modifying the model to simulate the inner (western) part of the proposed harbor, a final series of tests was performed to investigate wave agitation throughout the inner harbor.
The study results showed that the initial harbor layout generated significant uplift pressures on the deck-on-pile structure running along the south side of Navy Pier under certain extreme wave conditions and water levels. Numerous design modifications to mitigate the issue were subsequently developed and verified in the model. The results of the study are being used by the design team to guide the final detailed design for Chicago Gateway Harbor. The role that physical modeling can play in optimizing the design of a new harbor and validating the performance of the new structures in design conditions will be discussed throughout the paper. The methods developed and tested to reduce wave agitation and mitigate wave impact loads at Gateway Harbor will also be discussed in detail.