Directional Wave Numerical Modeling on Fringing Reefs at Hilo Harbor, Hawaii

Abstract

Hilo Harbor is a major deep-draft commercial port located in Hilo Bay on the northeastern coast of the Big Island of Hawaii (HI), USA. It is protected by a two-mile long rubble-mound breakwater, also known as the tsunami barrier to locals, built on a submerged reef ridge along the NNE perimeter of Hilo Bay. The fringing reefs outside of the bay, at the entrance, and inside the bay control waves and currents which impact navigation to the harbor. Unfavorable navigation and berthing conditions in the harbor are caused by high-energy swells and storms from NNW, N, and NNE, as well as strong trade winds from NE. A numerical directional wave modeling was conducted to assisting the investigation of breakwater, ship channel, and turning basin modifications to improve navigation and docking at the harbor. The wave model used in the study is based on the generic, fully-integrated Navier-Stokes equations over depth. Both depth-integrated dynamic and static pressures induced by waves and tides are presented and included in the model. Because model governing equations are the exact integration of three-dimensional equations of the incompressible fluid motion, all nonlinear wave processes are preserved in the modeling. Model results compare well to wave and current data collected inside the bay and to harbor seiching problem caused by occasional infra-gravity waves observed inside the bay.