The effect of tidal inlets on open coast storm surge hydrographs

Bridge scour modeling requires storm surge hydrographs as open ocean boundary conditions for coastal waters surrounding tidal inlets. These open coast storm surge hydrographs are used to accurately determine both horizontal and vertical circulation patterns, and thus scour, within the inlet and bay for an extreme event. At present, very little information is available on the effect that tidal inlets have on these open coast storm surge hydrographs. Furthermore, current modeling practice enforces a single design hydrograph along the open coast boundary for bridge scour models. This study expands on these concepts and provides a more fundamental understanding on both of these modeling areas. A numerical parameter study is undertaken to elucidate the influence of tidal inlets on open coast storm surge hydrographs. Four different inlet-bay configurations are developed based on a statistical analysis of existing tidal inlets along the Florida coast. The length and depth of the inlet are held constant in each configuration, but the widths are modified to include the following four inlet profiles: 1) average Florida inlet width; 2) 100 m inlet width; 3) 500 m inlet width, and 4) 1000 m inlet width. Results from these domains are compared to a control case that does not include any inlet-bay system in the computational domain. The Advanced Circulation, Two-Dimensional Depth-Integrated (ADCIRC-2DDI) numerical code is used to obtain water surface elevations for all studies performed herein. The code is driven by astronomic tides at the open ocean boundary, and wind velocities and atmospheric pressure profiles over the surface of the computational domains. Model results clearly indicate that the four inlet-bay configurations do not have a significant impact on the open coast storm surge hydrographs. Furthermore, a spatial variance amongst the storm surge hydrographs is recognized for open coast boundary locations extending seaward from the mouth of the inlet. In addition, a storm surge study of Hurricane Ivan in the vicinity of Escambia Bay along the Panhandle of Florida is performed to assess the findings of the numerical parameter study in a real-life scenario. The main conclusions from the numerical parameter study are verified in the Hurricane Ivan study: 1) the Pensacola Pass-Escambia Bay system has a minimal effect on the open coast storm surge hydrographs; and 2) the open coast storm surge hydrographs exhibit spatial dependence along typical open coast boundary locations. The results and conclusions presented herein have implications toward future bridge scour modeling efforts. (c) 2006 Elsevier B.V. All rights reserved