Journal of Waterway, Port, Coastal, and Ocean Engineering

The scope of the present work is the hydrodynamic study of the Huelva estuary inside an environmental impact project of a possible breaching of a mining sludge waste pond. This study is based on the numerical simulation of the mean river discharge and the tidal effect. The hydrodynamic models were validated against field measurements corresponding to the period in which the experimental data were registered. The measurements in the estuary primarily indicate that the currents oscillate according to the tidal variation along the river and these show that the currents evolve constantly with the tide so that the upstream speed increases until the end of the period of the tide’s rising and it subsequently diminishes until a change of direction at the end of the high tide. The speed of the downstream current increases rapidly during the period of maximum descent of the tide and it decreases again until a change of direction at the end of the low tide. Observations and numerical outputs showed an asymmetric trend in the temporal evolution of the speed of the current, reaching the maximum downstream speed approximately $2–3\mathrm{h}$ later than the high tide, while the maximum upstream speed was produced around $3–4\mathrm{h}$ later than of the low tide. The downstream current remains lower than the upstream current for the period of time studied and hence results in an upstream current that favors the retention of the hypothetical quantity of water that may be poured into the creek as a result of the rupture of the waste pond.

Details are given of a numerical model study to refine a layer integrated model, applied to scaled hydraulic model rectangular tidal basins with large aspect ratios (i.e., $L∕B=1∕4–4∕1$ ), and using two- and zero-equation turbulence models. For the zero-equation turbulence model the mixing length model was deployed to calculate the horizontal eddy viscosity coefficient, whereas for the two-equation model, the depth integrated $k\text{-}\epsilon$ turbulence model was used. Likewise, the layer integrated mixing length and $k\text{-}\epsilon$ turbulence models were used to determine the vertical eddy viscosity coefficient. The model was first applied to idealized channel flows, with the agreement between the predicted values and experimental data being satisfactory. The model was then tested by applying it to an idealized set of data for wind driven currents in a closed rectangular basin, with good agreement again being obtained between the numerical model results and published experimental data. The model was finally applied to a set of hydraulic model studies, undertaken by the writers for a number of different model rectangular tidal basin configurations (or aspect ratios), each with an asymmetric entrance, a flat bed, and vertical sidewalls. The numerical model results obtained using the $k\text{-}\epsilon$ and mixing length turbulence models in the horizontal plane were compared graphically with the experimental results to indicate the best model setup for these model basin configurations. Model simulations were also undertaken to investigate the sensitivity of the eddy circulation structure to the closed boundary representation, within the finite difference scheme, and three different boundary conditions were considered including: the no-slip, semislip, and partial-slip representations. The numerical model results showed that the horizontal current structure obtained using the $k\text{-}\epsilon$ model was similar to the results obtained using the mixing length turbulence model. The velocity distributions for the different layers were similar, except near the bed, and the horizontal velocity distribution only showed small variations through much of the water column. The three different representations of the closed boundary condition gave very different tidal circulation patterns within the basins, showing that the representation of the closed boundary was crucial for modeling vorticity in such basins. The model results for the $k\text{-}\epsilon$ and mixing length turbulence models were found to be in closest agreement with the experimental results when the no-slip and partial-slip conditions were used, respectively.

A video image processing technique has been developed for the study of free surface water waves. The technique allows detailed examination of continuous image sequences of progressing waves, providing a complete and precise geometric description of an evolving breaking wave. Wave breaking on sloping beaches has been investigated under monochromatic sea conditions and geometric parameters of a large number of breakers have been obtained. The bed slope was found to influence the breaking wave height and depth relationship. A number of new empirical equations have been derived defining the functional relationship between the nondimensional breaking height $H_b∕g{T}^2$ and breaking depth $d_b∕g{T}^2$ , between the breaking wave steepness $H_b∕L_b$ and relative depth $d_b∕L_b$ , and between the breaking height to depth ratio $H_b∕d_b$ and nondimensional breaking depth $d_b∕g{T}^2$ .

The morphology of intertidal multiple sand bars of Okoshiki Beach in Ariake Bay, Japan is examined to provide insight into the factors controlling the bar characteristics in the low wave environment. Cross-shore profiles of intertidal multiple sand bars were measured monthly for $2\text{years}$ from July 2003 to July 2005. Each measured profile is separated into a mean profile and a bar geometry using quadratic polynomial fitting. Superimposed on the mild foreshore $(1∕250)$ are at least seven low height $(0.1–0.6\mathrm{m})$ ridges with an average wavelength of $40\mathrm{m}$ . The sand bar morphology appears to be a permanent feature in both form and position. The bars occur approximately between the mean high and low water levels during neap tides. This bar zone is related to the zone where the tide-induced moving shoreline velocity is largest in the cross-shore. The calculated depth-averaged tidal currents indicate that sediment movement occurs less than 4% of the tidal period of $12.5\mathrm{h}$ . The bed load transport rate estimated from the bar height and migration velocity is on the order of $1\times {10}^{-4}{\mathrm{m}}^2∕\text{day}$ and very small.

Solitary wave interaction with porous breakwaters is studied by using a two-dimensional numerical model. In this model, flows outside of porous media are described by Reynolds-averaged Navier-Stokes equations. For porous flows, the spatially averaged Navier-Stokes equations, in which the effect of porous media is considered by including additional inertia and drag forces, are derived and implemented. The drag force is modeled according to Morison’s equation assuming uniform spherical particles within porous media. The corresponding drag force coefficient is expressed as the function of Reynolds number and hence the proposed porous flow model is valid in a wide range of porous flow regimes, i.e., laminar (linear friction), transitional, and turbulent (nonlinear friction) flows. The numerical model is validated against available theories and experimental data for both long wave and solitary wave interaction with porous breakwaters. The model is then employed to study solitary wave interaction with fully emerged rectangular porous breakwaters with different length and particle size. Based on the results, the characteristics of wave reflection, transmission and energy dissipation are discussed. Additional numerical tests are conducted to study the effects of depth of submergence and porosity of breakwaters on wave transformation. The scale effects in small scale and large scale model tests are also discussed by performing numerical experiments in the reduced and enlarged numerical wave flumes.

Guidance regarding equilibrium beach profiles has been well established, although limited knowledge exists regarding the spatial and temporal variability of the equilibrium beach profile parameter for engineering usage, and limited data have been published regarding such changes. Additionally, the controlling parameter in the equilibrium beach profile theory depends on assumed depth of profile closure. Equilibrium beach profile theory is utilized herein to assess the spatial and temporal variability of beach profiles along the Florida Panhandle Coast to provide added empirical guidance on this subject.

Tidal asymmetry, generated by nonlinear shallow water processes, controls to a large extent the long-term fate of noncohesive sediments in estuaries and lagoons. Since the accurate reproduction of this asymmetry is still a challenge for hydrodynamic models, it is important to quantify the effect of errors in the representation of tidal asymmetry on tidally averaged sediment fluxes. The effect of the accuracy in the amplitude and phase in the tidal velocity on the errors in the evaluation of residual sediment transport was analyzed analytically. Results show that errors of the order of 20% in velocity amplitude can lead to sediment transport errors on the order of 100%. Phase errors lead to smaller, but non-negligible, errors in sediment transport. Simple expressions to estimate these errors are provided.