Storm Wave Forces on Selected Prototype Coastal Bridges on the Island of Oahu

Submitted to: Hawaii Department of Transportation Coastal Bridge and Port Vulnerability to Tsunami and Storm Surge Project Project No: DOT-08-004, TA 2009-1RHydrodynamic study of storm wave loads on four selected coastal bridges (prototype scale) around the Island of Oahu is presented here. These include NewMakaha Stream bridge, New South Punaluu Stream bridge, Maili Stream (Maipalaoa) bridge and Kahaluu Stream bridge on the Island of Oahu. Maximum water level at the location of the selected bridges is determined under extreme conditions of a Category 5 Hurricane making landfall on the island. The maximum wave height and wave period are estimated theoretically based on the highest water level. Several different scenarios are considered for each of the selected bridges. The wave loads on the bridges are calculated by use of several theoretical methods. One is based on Euler’s equations coupled with the Volume of Fluid method, for which OpenFOAM, an open access computational fluid dynamics (CFD) package is used to perform the computations, and another one is based on the Green-Naghdi (Level I) nonlinear shallow water wave equations, and is applied to the cases in which the bridge is fully submerged. Existing theoretical and empirical relations, including the Long-Wave Approximation for a fully submerged bridge, developed based on the linear potential theory, and the empirical relations for an elevated bridge deck are also used. Re- sults are compared with each other. The condition that results in the maximum wave forces for each of the bridges is summarized at the end of the report.This work is partially based on funding from State of Hawaii’s Department of Transportation (HDOT) and the Federal Highway Administration (FHWA), grant numbers DOT-08-004, TA 2009-1R. Any findings and opinions contained in this paper are those of the authors and do not necessarily reflect the opinions of the funding agency

Bore impact on decks of coastal structures

Bore impact on horizontal fixed decks of coastal structures is studied by use of the Level I Green–Naghdi (GN) equations and the Navier–Stokes (NS) equations. The bore is generated by the breaking of a water reservoir, and may represent the propagation of a tsunami on land or broken storm waves. The bore-induced horizontal and vertical forces are determined and their variation with the bore and deck conditions is studied in this work. Various conditions of deck location with respect to the water level are considered, including cases with the deck under or above the still-water level. Two types of bore are considered, namely (i) a bore generated by a dam break, where the reservoir water depth is substantially larger than the downstream depth, and (ii) a bore generated by an initial mound of water, where the reservoir water depth is comparable to the downstream depth. It is shown that these mechanisms result in the formation of significantly different bore shapes. It is also shown that the relative height of the reservoir and the downstream water depth play a significant role in the bore generation and its impact on coastal structures. It is also found that the bore-induced forces vary almost linearly with the change in amplitude of the reservoir, while a change in the length of the reservoir has little effect on the loads. The horizontal force on submerged decks is shown to be independent of the submergence depth of the deck; this is due to the uniform velocity distribution over the water column of the bore. Results of the GN and NS models are compared with each other for submerged cases and the limitations, accuracy, and efficiency of these models in studying this problem are discussed. Results of the GN equations are in close agreement with the NS equations, making them a computationally efficient alternative for the study of this problem.<br/