A coupled system of wind, wind wave, and coastal circulation models has been implemented for southern Louisiana and Mississippi to simulate riverine flows, tides, wind waves, and hurricane storm surge in the region. The system combines the NOAA Hurricane Research Division Wind Analysis System (H*WIND) and the Interactive Objective Kinematic Analysis (IOKA) kinematic wind analyses, the Wave Model (WAM) offshore and Steady-State Irregular Wave (STWAVE) nearshore wind wave models, and the Advanced Circulation (ADCIRC) basin to channel-scale unstructured grid circulation model. The system emphasizes a high-resolution (down to 50 m) representation of the geometry, bathymetry, and topography; nonlinear coupling of all processes including wind wave radiation stress-induced set up; and objective specification of frictional parameters based on land-cover databases and commonly used parameters. Riverine flows and tides are validated for no storm conditions, while winds, wind waves, hydrographs, and high water marks are validated for Hurricanes Katrina and Rita.

Southern Louisiana is characterized by low-lying topography and an extensive network of sounds, bays, marshes, lakes, rivers, and inlets that permit widespread inundation during hurricanes. A basin- to channel-scale implementation of the Advanced Circulation (ADCIRC) unstructured grid hydrodynamic model has been developed that accurately simulates hurricane storm surge, tides, and river flow in this complex region. This is accomplished by defining a domain and computational resolution appropriate for the relevant processes, specifying realistic boundary conditions, and implementing accurate, robust, and highly parallel unstructured grid numerical algorithms. The model domain incorporates the western North Atlantic, the Gulf of Mexico, and the Caribbean Sea so that interactions between basins and the shelf are explicitly modeled and the boundary condition specification of tidal and hurricane processes can be readily defined at the deep water open boundary. The unstructured grid enables highly refined resolution of the complex overland region for modeling localized scales of flow while minimizing computational cost. Kinematic data assimilative or validated dynamic-modeled wind fields provide the hurricane wind and pressure field forcing. Wind fields are modified to incorporate directional boundary layer changes due to overland increases in surface roughness, reduction in effective land roughness due to inundation, and sheltering due to forested canopies. Validation of the model is achieved through hindcasts of Hurricanes Betsy and Andrew. A model skill assessment indicates that the computed peak storm surge height has a mean absolute error of 0.30 m.

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Bender elements have surfaced as versatile transducers for low-strain testing of soils in a variety of cells and load conditions. However, lack of guidelines leads to different implementations among laboratories. The authors present an interesting evaluation of effective length and travel time determination. The purpose of this discussion is to contribute complementary information, summarizing our experience with bender elements in various short-term and long-term tests (a typical installation and examples of application are described in Fam & Santamarina (1995)).

The stiffness of soil at very small strain Go is a useful parameter for characterizing the non-linear stress–strain behaviour of soil for monotonic loading and it is required for analyses of the dynamic and small strain cyclic loading of soils. Tests were carried out on fine-grained soils in a hydraulic triaxial cell fitted with bender elements and with local axial gauges. From the results of these tests simple expressions were obtained which describe the variation of G>o with current state in terms of the current stress and overconsolidation ratio. The parameters in these expressions were found to depend on plasticity index. The simple expressions for Go were found to apply generally at larger strains, with the values for the parameters also depending on the current strain. Values of Go measured in laboratory tests on reconstituted London clay agree well with values measured in tests on undisturbed samples and in field tests which make allowance for the different states in the various tests. La rigidité Go d'un sol, sous très faible déformation, est un paramètre intéressant qui permet de caractériser la non-linéarité du comportement en contrainte-déformation de ce sol lors d'un chargement monotone et d'analyser les cycles de chargement dynamique à faible déformation. Des essais ont été réalisés en cellule triaxiale hydraulique sur des sols finement grenus équipés de capteurs en flexion et de jauges axiales locales. Les résultats obtenus au cours de ces essais ont permis de définir des relations simples donnant la variation de Go en fonction de la contrainte courante et du degré de surconsolidation. Les paramètres dépendent de l'indice de plasticité. Une expression simple de Go est applicable à de plus fortes déformations, les paramètres étant alors en plus fonction de la déformation courante. Les valeurs de Go mesurées en laboratoire sur de l'argile de Londres reconstituée sont en bon accord avec celles obtenues sur des échantillons intacts où lors d'essais in-situ et rendent compte des différents états rencontrés lors des différents essais.