Spectral quantification of nonlinear behaviour of the nearshore seabed and correlations with potential forcings at Duck, N.C., U.S.A

Local bathymetric quasi-periodic patterns of oscillation are identified from monthly profile surveys taken at two shore-perpendicular transects at the USACE field research facility in Duck, North Carolina, USA, spanning 24.5 years and covering the swash and surf zones. The chosen transects are the two furthest (north and south) from the pier located at the study site. Research at Duck has traditionally focused on one or more of these transects as the effects of the pier are least at these locations. The patterns are identified using singular spectrum analysis (SSA). Possible correlations with potential forcing mechanisms are discussed by 1) doing an SSA with same parameter settings to independently identify the quasi-periodic cycles embedded within three potentially linked sequences: monthly wave heights (MWH), monthly mean water levels (MWL) and the large scale atmospheric index known as the North Atlantic Oscillation (NAO) and 2) comparing the patterns within MWH, MWL and NAO to the local bathymetric patterns. The results agree well with previous patterns identified using wavelets and confirm the highly nonstationary behaviour of beach levels at Duck; the discussion of potential correlations with hydrodynamic and atmospheric phenomena is a new contribution. The study is then extended to all measured bathymetric profiles, covering an area of 1100m (alongshore) by 440m (cross-shore), to 1) analyse linear correlations between the bathymetry and the potential forcings using multivariate empirical orthogonal functions (MEOF) and linear correlation analysis and 2) identify which collective quasi-periodic bathymetric patterns are correlated with those within MWH, MWL or NAO, based on a (nonlinear) multichannel singular spectrum analysis (MSSA). (...continued in submitted paper)Comment: 50 pages, 3 tables, 8 figure

Wave Climate in the Gulf of Gdańsk vs. Open Baltic Sea near Lubiatowo, Poland

The paper analyses long-term variability in the wave climate near Lubiatowo, ca. 15 km east of Łeba harbor, and in the Gulf of Gdańsk, near the Vistula river mouth. The wave climate was reconstructed for the 1958-2001 period by the German Institute for Coastal Research (GKSS). Using basic statistical tools - empirical mean values of significant wave height, estimation of the number of threshold crossings above a prescribed value of that height and conditional empirical probability density functions of wave approach directions - a comparison of wave height at the two locations was executed. A substantial reduction in wave height inside the Gulf (sheltering effect) was measured. Further, the increased storminess over the winter season was estimated for the open sea location. Finally, the analysis of wave approach direction in the open sea location revealed substantial growth in extreme waves from the western sector. Given the geographic configuration of the Gulf and the combined rise in storminess and evolution in extreme wave direction, it can be inferred that the sheltering effect of the Gulf can vary depending on locations within the Gulf. Identification of sheltering patterns in the Gulf emerges as obvious follow-up research. This study could also prove useful in analyses aiming at integrated management of coastal zones in the Gulf, mainly in the implementation of Coastal Protection Law (Apr. 2003), which postulates maintenance of the 2001 shoreline configuration along the entire Polish coast

Co-variability of bars in a multi-bar nearshore zone determined with canonical correlation analysis (CCA)

Nearshore bed variations of the southem Baltic shore were investigated with the aim of detecting co-variability among bed forms of a multi-bar system. The studied area is located at IBW PAN Coastal Research Station at Lubiatowo. The beach consists of fine sand of median grain equal to 0.22 mm, is mildly sloping and boasts multiple (usually 4) bars, which is typical for the coast in the southem Baltic. Data on bed topography were collected along 27 lines, equally spanned every 100 m, since 1987 to 1999, usually twice a year. Fairly high alongshore bed homogeneity made it possible to choose one representative profile for which the CCA method was employed. The method demonstrated considerable potential for detecting co-variability of bed features in the nearshore zone. The results show that some 80% of variability in the region of the offshore slope of the outermost bar can be attributed to variations of Dean equilibrium profiles. The portion of variability of the two innermost bars due to variations of equilibrium profiles equals 40%. Horizontal counter-movements of outer and inner bars can be responsible for same 20%. The remaining 40% should be related to highly variable short time scale phenomena like breakers and wave driven currents in the vicinity of inner bars

Local Wave Energy Dissipation and Morphological Beach Characteristics along a Northernmost Segment of the Polish Coast

This paper analyses cross-shore bathymetric profiles between Władysławowo (km 125 of the Polish coastal chainage) and Lake Sarbsko (km 174) done in 2005 and 2011. Spaced every 500 m, they cover beach topography from dune/cliff crests to a seabed depth of about 15 m. They were decomposed by signal processing techniques to extract the monotonic component of beach topography and to perform a straightforward assessment of wave energy dissipation rates. Three characteristic dissipation patterns were identified: one associated with large nearshore bars and 2–3 zones of wave breaking; a second, to which the equilibrium beach profile concept can be applied; and a third, characterized by mixed behaviour. An attempt was then made to interpret these types of wave energy dissipation in terms of local coastal morphological features and the underlying sedimentary characteristics

Calculation of Wave Run-up Height in South Baltic Sea: Case Study at Coastal Research Station at Lubiatowo, Poland

The paper presents recent investigations of beach run-up phenomena at the Coastal Research Station of the Institute of Hydro-Engineering of the Polish Academy of Sciences at Lubiatowo, Poland. The local beach is typical of open-sea coasts of the south Baltic Sea, featuring multiple longshore bars that form predominantly dissipative systems. Measurements were taken to verify the existing formulas for the run-up height, bearing in mind that they had been derived for entirely different, oceanic conditions. The results indicate that these formulations can be adapted to south Baltic Sea conditions. This however, will require significantly larger data sets, which we intend to obtain in the near future

Coastal Processes at Selected Shore Segments of South Baltic Sea and Gulf of Tonkin (South China Sea)

The paper presents a comparative analysis of physical processes occurring at two different coasts, which belong to two different geographic zones, namely a subtropical region exposed to monsoons and typhoons and a region of temperate climate with ice-snowy winter season. The former coast comprises sandy shores nearby Lubiatowo and the Hel Peninsula, located at the south Baltic Sea in Poland. The shore at Lubiatowo is relatively stable in the long run, while the shore along Hel Peninsula is mostly vulnerable to erosion and strongly protected by use of various measures (groins, seawall and artificial beach nourishment). The second site is the eroded (and partly protected by dikes) coast at Hai Hau in the Gulf of Tonkin (the South China Sea, Vietnam). This shore segment is built of mixtures of sandy and cohesive material, comprising both marine sands and river-borne sediments which nourish the coastal zone at the Red River mouth, located northwards of the Hai Hau beach. The present analysis is focused on differences and similarities of hydro- and morphodynamics between the above coastal zones in various time and spatial scales. The analysis shows that regional climatic and environmental conditions, associated with geographical zones, play a key role in dynamic evolution of the coastal regions and necessitate different engineering activities against erosion and flooding