| Abstract | Originally constructed between 1885-1939, the three jetties protecting the Mouth of the Columbia River (MCR), the North Jetty, the South Jetty, and Jetty A have been progressively damaged due to storm wave attack and the loss of the sand shoal material that comprise their foundation. The MCR jetties are an essential part of maintaining the Columbia/Snake River navigation system, a significant export gateway for the west coast. In late 2014 Moffatt and Nichol (M and N) and the National Research Council of Canada (NRC) were commissioned by the US Army Corps of Engineers (USACE) to conduct physical model studies to inform and guide the design of repair works for two of the jetties, the North Jetty and Jetty A. Due to the exposed Pacific North-west conditions, strict environmental constraints, and the historic evolution of the existing structures, most notably a substantial relic stone foundation, the proposed repair works were complex and unconventional. Two separate three-dimensional physical models were constructed and used to investigate the performance of the proposed repairs for the two unique physical and functional settings at each jetty. Alternatives included rock armour and concrete armour units, tested under a range of site-specific design conditions, including extreme water levels and harsh wave conditions. This paper summarizes the physical modelling studies, the unique challenges presented by the complex bathymetry, and the important role physical modelling had in verifying and optimizing the reconstruction proposed for the North Jetty and Jetty A. The physical modelling provided essential identification of the near-structure three-dimensional interactions and guided the quantification of damages leading to optimization of the final designs. |
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