Journal of Waterway, Port, Coastal, and Ocean Engineering

Though environmental impacts of dredging have been studied, no efforts have been applied to the evaluation of air emissions from comparable types of dredging equipment, as in this study. This study provides a procedure to include air emissions resulting from the combustion of diesel fuel during dredging operations into the dredging equipment selection decision-making process. The proposed procedure includes a limited life cycle assessment and is demonstrated for typical dredging methods and data from the Illinois Waterway as performed by the United States Army Corps of Engineers, Rock Island District, Ill. It was found that commonly used rules of thumb in the dredging industry hold true by indicating that mechanical bucket dredges are better suited for long transport distances and have lower air emissions and cost per cubic meter $\left({\text{m}}^3\right)$ for smaller quantities of dredged material. In addition, the results show that a cutterhead pipeline dredge would be preferable for moderate and large volumes of dredged material when no additional booster pumps are required. Finally, the results indicate that production rates can be a significant factor when evaluating the air emissions from comparable dredging equipment.

Often, nearshore radiation stresses are approximated using the monochromatic wave assumption, although this can have significant errors when the incident waves have finite frequency and/or directional spread. Consequently, the resulting wave-driven currents could be predicted erroneously or, when fitting to observations, biased model parameters such as the bottom friction coefficient may result. We develop and test a moments-based reduced spectral wave model which includes the leading order effects of wave frequency and directional spreading. This model solves the evolution equations of wave moments, which are integrations of the wave action balance equation multiplied by weighting functions over frequencies and directions. An assumption of analytical Gaussian distribution for the frequency-direction spectrum is made to develop a simple five-parameter system that contains information on the wave height, period, direction, frequency bandwidth, and directional bandwidth. Using this model, we investigate the finite bandwidth effects on the wave field and radiation stresses. The directional spreading is found to have a strong impact on the radiation stress, with a larger directional bandwidth resulting in smaller radiation stresses. However, the frequency spreading has much less impact. The spectral wave breaking based on the roller concept is considered in this wave model. After coupling with a circulation model based on the shallow water equations, simulation results compare favorably with the DUCK94 field data for waves and longshore currents but show strong dependence on the directional bandwidth.

In this paper, long $\left(>40\text{years}\right)$ hourly tide gauge records from the North Atlantic are analyzed. A new time series clustering approach which combines Bayesian methodology, extreme value theory, and classification techniques is adopted for the analysis of the regional variability of sea-level extremes. The tide gauge records are clustered on the basis of their corresponding predictive distributions for 25-, 50-, and 100-year return values. The results of the cluster analysis show a clear distinction between the higher latitude stations for which the return values are largest and the remaining locations. This distinction reflects in the U.S. east coast the transition between the Scottian shelf and Gulf of Maine area and the mid-Atlantic Bight area. For the stations at lower latitudes the results show a grouping based on return levels that is not a function of geographical proximity but reflects local effects in extreme sea levels associated with the specific location of each tide gauge.

A numerical modeling study, using an Eulerian tracer and Lagrangian particle-tracking methods, was carried out to map the age of water and residence-time distribution in the tide-dominated East Scott Creek Estuary, South Carolina. A coupled hydrodynamic, solute-transport, and particle-transport model was developed. The flow and solute-transport models were based on depth-integrated conservation equations and the particle-transport model was quasi-three-dimensional. The equations were discretized using the total variation diminishing finite-volume method. The numerical model predictions were verified against a set of field-measured hydrodynamic data, with the model-predicted water elevations and velocities in good agreement with the field measurements. Different methods of computing the age of water and the residence time that are applicable to tide-dominated estuaries and suitable for high-resolution flow and transport numerical modeling setup were investigated. An Eulerian method, based on the tracer-age theory, and a Lagrangian particle-tracking method were each used to map the age and the residence-time distribution throughout the main channel of East Scott Creek. The performance of the two methods in the given tide-dominated environment was investigated through a series of numerical experiments. The effects of the particle and tracer release time and tidal amplitude in the computation of tidal exchange-time scales were also investigated. The residence time computed by the Eulerian method scaled well with that of the Lagrangian method and produces a relatively smooth monotonic profile of the residence time in space. The Lagrangian method, unlike the Eulerian method, consistently showed a more detailed distribution of significant and varying nonmonotonic profile of residence times; yet, the two methods produce, in the tidally averaged sense, reasonably comparable residence-time distributions. The residence time computed by the Lagrangian method is very sensitive to the phase of the tidal forcing at the beginning of the computation.

Several types of equations have been proposed in the past 30 years to describe the planform of crenulate-shaped bays in static equilibrium: a logarithmic spiral, a parabolic curve, a hyperbolic tangent curve, and a set of circle arcs. Although several authors pointed out that these models have some physical and mathematical weaknesses, they find much use in practical applications, particularly the parabolic form. Several expressions of the parabolic shape have been proposed. Hsu and Evans’ original ones fit best the experimental values of Ho’s model tests and of Australian bays in equilibrium used to determine these expressions. The formula proposed by Tan and Chiew respects the tangent condition of the incident wave crest line at the control point and the crossing of the beach line through this point. The expression proposed in Italy by Mita also respects the conditions on the critical angle of a bay in equilibrium, as experimentally determined by Hsu and Silvester; but it poorly fits the data of Ho’s model tests and of Australian bays in equilibrium. This article proposes a new cubic equation to describe crenulate-shaped bays in static equilibrium. The proposed relationship includes the advantages of the three parabolic expressions mentioned above. In fact this proposed third-order equation interpolates the experimental data used by Hsu and Evans to the same degree of approximation as in their original second-order relationship. It also rigorously respects the theoretical conditions at the control point on the downdrift beach line as well as the condition of the critical angle experimentally determined by Hsu and Silvester. Finally the indentation ratio values proposed by Silvester and Hsu for bays in equilibrium are well approximated by the cubic equation across the whole application range. In short, the current formalism is mathematically inconsistent and the proposed modification resolves this as a relatively straightforward amendment of the formulas which leads to moderate changes in the results of the shoreline, but reduces some of the errors in the process of applying this type of model in engineering practice.