Journal of Waterway, Port, Coastal, and Ocean Engineering

This paper presents analyses of a coastal stability indicator, recently introduced in Poland, that was based on a nearshore sediment volume found between +2 and −6 m ordinates. This purely empirical indicator was developed on the basis of long-term observations (made between 1957 and 2002) of the morphologies of emerged beaches and detailed nearshore seabed monitoring consisting of 969 cross-shore profiles spaced every 500 m that were surveyed between 2004 and 2006 along the entire Polish coast. It was introduced to quantify the requirements for beach nourishment and adopted as the main erosion-control instrument dictated by the Coastal Protection Act of 2003. Extensive seabed monitoring provided data for determining the shoreface sediment volume and led to the conclusion that a mean sediment volume (between 2 m above and 6 m below mean sea level) in excess of 1,500 m³ was a strong indicator of a stable coast. This assumption and the implications of it are discussed. Specifically, simple theoretical considerations pointed to a possible relationship of this indicator with the mean sediment diameter, D₅₀, which was between 0.20 and 0.22 mm, and to a general relationship between D₅₀ and shoreface sediment volumes.

Measuring the free-surface displacement on a vertical wall of a marine structure is not a trivial problem. In this context, the efficacy of ultrasonic probes is affected by the interaction between the signal emitted by the sensor and the vertical wall, whereas image-based techniques are computationally demanding, especially if long-time series are utilized. Considering these difficulties, this paper proposes a novel approach for measuring the sea surface elevation on vertical breakwaters. The proposed methodology involves the use of pressure measurements and a reconstruction algorithm based on a compressive sensing (CS) technique in conjunction with a generalized harmonic wavelet (GHW) basis. In particular, a constrained CS optimization approach is proposed by utilizing the known values of the free-surface data to reconstruct all other missing data while adhering at the same time to prescribed upper and lower bounds at all time instants. The reliability of the methodology was assessed against field data pertaining to a vertical wall equipped with pressure transducers recorded at the Natural Ocean Engineering Laboratory of Reggio Calabria. It was shown that direct application of an unconstrained GHW-based CS optimization approach yielded physically inconsistent minima and maxima values; thus, it was inadequate for reliably reconstructing the free surface. These drawbacks were removed by the constrained GHW-based CS. Furthermore, examination of the reconstructed sea surface profiles in the vicinity of extremely high wave crests or wave troughs showed that they are in agreement with pertinent theoretical data obtained by using the nonlinear quasi-determinism theory.

Coastal wave-induced nearshore currents are likely present as waves propagate and break on shallow-water zones. Accurate and efficient predictions of coastal waves and wave-induced nearshore currents in coastal areas are essential for coastal engineering. In this article, an efficient numerical model consisting of adaptive multilevel quadtree meshes for coastal waves and nearshore currents is presented. The numerical model consists of coastal wave and wave-induced nearshore-current models. In the model, coastal waves are modeled using the elliptic mild-slope equation that accounts for wave refraction, diffraction, reflection, and breaking-induced energy-dissipation effects, and nearshore currents are modeled using two-dimensional horizontal (2DH) depth-integrated shallow-water equations for which the wave radiation stresses for driving currents are provided by the wave model. The numerical model is solved using the finite-volume method on a Cartesian grid with an adaptive multilevel quadtree mesh system. The numerical mesh is adaptively refined according to local wavelengths, and the primary numerical grid is divided into four secondary grids if the local wavelength is smaller than eightfold the grid length. This allows the effective and accurate simulation of coastal waves and nearshore currents over complex topographies by a locally flexible refining grid resolution. The numerical model is validated by comparing the numerical results with experimental and field-measured results. The agreement between the numerical and measured data shows that the numerical model is both effective and efficient in modeling coastal waves and nearshore currents.

An important aspect that must be considered in harbor design and construction is the water quality within the basin, which depends on the water exchange between the harbor and surrounding water body. Of the most internationally distinguished methods for this purpose (mechanical shakers, overflows, pumps, permeable breakwaters), the most cost-effective method is to use flushing culverts through the body of the breakwater structure. This paper presents physical model results of a flushing culvert functioning with variations of the flushing culvert diameter (D), length (L_c), and vertical position in relation to the water surface level (W). A physical model (rubble mound breakwater) was placed in the wave channel with a piston-type wave generator, where spectral waves were generated. During the measurements, three different hydraulic processes of the wave transmission were observed, depending on the position of the water surface. The research results are presented as transmission coefficients (K_t).

Flume experiments examining the effects of a flexible mattress on bed scour around spur dikes were conducted. Results showed that scour induced subsidence damage to the flexible mattress. If the width of flexible mattress, $B$, was insufficient, then failure of the spur dike may occur. Results also revealed that (1) scour depth decreased as the area of the protective domain around the spur dike increased (e.g., it reduced 30%, from 20 to 14 cm, as the width $B$ increased from 0 to 0.35 m), and (2) higher approaching velocities resulted in deeper scour holes. On the basis of the experimental data and dimensional regression analysis, empirical formulas were proposed for calculating scour depth and the extent of the scour hole. The formulas were then used to obtain the optimum flexible mattress width.

This study presents results of the temporal development of propeller scour around a sloping bank. During the scouring process, the centerline scour profile along the propeller axis comprises a toe scour hole, a primary scour hole, or a combination of both. Their formation is dependent on the length of the toe clearances, which is defined as the longitudinal distance between the propeller face and toe of the slope. As a result, the overall maximum scour depth along the centerline profile may occur either in the primary or toe scour hole. The results show that the temporal development of the overall maximum scour depth for all the cases consistently exhibits an exponential form. An empirical method was obtained to estimate the maximum scour depth evolution throughout the scouring process.