Lihwa Lin

Recent Capabilities of CMS-Wave: A Coastal Wave Model for Inlets and Navigation Projects

Abstract The Coastal Inlets Research Program (CIRP) of the U.S. Army Engineer Research and Development Center (ERDC), Coastal and Hydraulics Laboratory (CHL) has developed a nearshore spectral wave transformation numerical model to address needs of the U.S. Army Corps of Engineers (USACE) navigation projects. The model is called CMS-Wave and is part of Coastal Modeling System (CMS) for wave estimates in the vicinity of coastal and estuarine navigation channels. It can simulate important wave processes at coastal inlets including wave diffraction, refraction, reflection, wave breaking and dissipation mechanisms, wave-current interaction, and wave generation and growth. This paper describes recent improvements in CMS-Wave that include semi-empirical estimates of wave run-up and overtopping, nonlinear wave-wave interactions, and wave dissipation over muddy bottoms. CMS-Wave may be used with nested grids and variable rectangular cells in a rapid mode to assimilate full-plane wave generation for circulation and sediment transport models. A brief description of these recent capabilities is provided.

Numerical study of sandbar migration under wave-undertow interaction

Reliable simulation of onshore-offshore sandbar migration under various wave and current conditions has remained a challenging task over the last three decades because wave-undertow interaction in the surf zone has been neglected in the existing numerical models. This paper presents the development of an improved sandbar migration model using a phase- and depth-resolving modeling approach. This new model includes interactions between waves and undertow and an empirical time-dependent turbulent eddy viscosity formulation that accounts for the phase dependency of turbulence on flowvelocity and acceleration.The authorsdemonstrate through extensive model-data comparisons thattheseenhancementsresultedinsignificantimprovementsinthepredictivecapabilityofthecross-shoresandbarmigrationbeneathmoderate and energetic waves. The comparison showed wave-undertow interaction playing a crucial role in cross-shore sediment transport. Waves increased the undertow-induced suspended-load flux during offshore sandbar migration, and a weak undertow suppressed the wave-induced onshore bed-load transport during onshore sandbar migration. The proposed empirical time-dependent turbulent eddy viscosity significantly improved the prediction of onshore-directed bed-load transport during onshore sandbar migration. DOI: 10.1061/(ASCE)WW.1943- 5460.0000231.

LABORATORY AND NUMERICAL STUDIES OF HYDRODYNAMICS NEAR JETTIES

Numerical and physical modeling studies were performed by the Coastal Inlets Research Program (CIRP) of the U.S. Army Corps of Engineers to investigate the spatial and temporal behavior of waves and wave-induced currents near jetties of an idealized coastal inlet. Hydrodynamics were examined in the vicinity of two extreme types of jetty structure: a highly absorbing jetty (resembling fairly porous rock rubble structure) and a fully reflective jetty (resembling a vertical sheet pile or caisson type breakwater). Laboratory experiments in a Froude scale of 1:50 were conducted with regular and irregular shore-normal (0°) and obliquely incident (20°) unidirectional waves. Current and wave measurements were made on the up-wave side and inside the inlet as well as in the bay, along a number of cross-shore and along-shore transects. Wave directions were measured by a remote-sensing video-camera system and Acoustic Doppler Velocimeters (ADV). Numerical modeling was performed with the Coastal Modeling System (CMS) consisting of a two-dimensional circulation model coupled to a spectral wave model. Calculated current and wave fields from CMS in the area around and between absorbing or reflected jetties were compared to measurements. The highly reflecting jetty created a circulation cell on the up-wave side of the inlet, whereas the absorbing jetty did not.

Evaluation of Breakwaters and Sedimentation at Dana Point Harbor, CA

Abstract : A flow, wave, and sediment transport model, the Coastal Modeling System (CMS), was applied to evaluate current and sedimentation patterns at Dana Point Harbor on the southern California coast. The permeability of breakwaters is the main interest in the study for the structural integrity and functioning to protect the harbor. Two Acoustic Doppler Current Profilers (ADCP) were deployed in November 2009 to collect current, water level, and wave data inside and outside the harbor. The model was validated by the field measurements. Wave transmission, flow penetration, and sediment seepage through the breakwaters were verified by the historical dredging information.

NAVIGATION IMPROVEMENTS, MOUTH OF THE COLORADO RIVER, TEXAS

This paper describes an ongoing analysis of coastal and inlet processes at the mouth of the Colorado River Navigation Channel, Texas. A weir jetty system with impoundment basin down drift of the weir was constructed at the mouth of the Colorado River in 1985 to reduce the expected rate of dredging of the shallow-draft entrance navigation channel. The required rate of dredging has been about double the design estimate, however, due in part to diversion of the Colorado River away from its entrance to the Gulf of Mexico. A study is underway to better understand the processes involved, design a more efficient entrance, and provide the reduced dredging interval and volume originally desired, while placing the inlet processes within a regional sediment transport framework.

Sediment Transport Modeling and Application for Ocean Beach and San Francisco Bight, CA

Abstract : The U.S. Army Corps of Engineers (USACE) San Francisco District (SPN) and Coastal Inlets Research Program (CIRP) are presently performing hydrodynamics, wave, and sediment transport numerical modeling study with the Coastal Modeling System (CMS) to evaluate a designated dredged-material placement site nearshore the beach erosion hot spot and onshore nourishment alternatives on Ocean Beach, California. Both model results and measurements reveal that tidal forcing is the main process in the nearshore area where the tidal current is predominantly along the shoreline. The calculated sediment transport shows more longshore movement than cross-shore shoreward the dredged-material placement site. The model result also indicates significant sediment erosion at Ocean Beach.

Understanding regional shoreline change and coastal processes at the Sunset Beach Region, Oahu, Hawaii

PURPOSE: This U.S. Army Corps of Engineers (USACE) Regional Sediment Management Technical Note (RSM-TN) reviews the development of a conceptual understanding of the complex regional coastal sediment processes at the Sunset Beach region on the island of Oahu, HI, which is a component of the USACE Hawaii Regional Sediment Management investigations. This document discusses the numerical modeling and volume change rate methodology used to identify sediment pathways in the region. This conceptual understanding of the sediment processes for the Sunset Beach region was developed to help inform future sediment management planning and decisions and to aid in identification of potential RSM actions within the region.

Identification of Alternatives to Reduce Shoaling in the Lower Matagorda Ship Channel, Texas

Regional Sediment Management Program (U.S.) United States. Army. Corps of Engineers. Galveston District.

Numerical modeling of wave overtopping of Buffalo Harbor Confined Disposal Facility (CDF4)

Abstract : This report provides details of a numerical modeling study conducted to provide estimates of wave overtopping of the Buffalo Harbor Confined Disposal Facility (CDF4). The CDF4 is situated adjacent to the South Entrance Channel to Buffalo Harbor, NY, along the south shoreline of the Lake Erie. This contaminated material holding facility experiences periodic overtopping during significant storm events. There is concern that overtopping waves may cause the contaminated fine-grain sediments inside the CDF to mobilize, some of which may get transported over the South Entrance Arm Breakwater (SEAB) into the south harbor entrance, navigation channel and harbor complex. The present study focused on predictive estimates of waves and wave overtopping, so flow and sediment transport modeling were not considered. Instead, it was assumed that if flow occurred over the SEAB, some sediment would exit also. Wave processes in the exterior and interior areas of CDF4 were investigated to determine wave runup and overtopping for the existing CDF system using two classes of wave models: CMS-Wave, a spectral wind-wave generation, growth and transformation model, and a nonlinear Boussinesq-type wave model (BOUSS-1D/2D). This report documents details of the modeling study, including data used in the study, results and recommendations.

Coupling Phase-Resolving Nearshore Wave Models with Phase-Averaged Spectral Wave Models in Coastal Applications

Phase-resolving wave models are best suited for the class of coastal applications with strong wave diffraction and reflection caused by coastal structures. Often, a deepwater spectral wave transformation model has to be coupled to a phase-resolving wave model to ensure accurate modeling of the local wave field near structures. This paper presents the development and evaluation of simplified methods for coupling a phase-resolving model CGWAVE with a phase-averaged model CMS-Wave. Four methods, which are, single point input, geometric mean, spatially varying wave height input, and quasi-spectral wave input, were tested at the Grays Harbor/Half Moon Bay area, a very dynamic site with complex geometry and bathymetry. Comparison of results with field data indicate that monochromatic CGWAVE solutions with a single-point wave input may not be reliable in certain applications since this method ignores the spatial variation and spectral properties of the incident waves at the open boundary. Results also indicate that directional wave spreading in the coupling of two wave models is important even for swell-like wave conditions. By combining a finite number of monochromatic CGWAVE solutions using the proposed quasi-spectral methods, the wave height estimates were improved in the Half Moon Bay as compared to data.