Modelling of wave climate and sediment transport patterns at a tideless embayed beach, Pirita Beach, Estonia

Nearshore sand transport patterns along the tideless, embayed Pirita beach, Tallinn, Estonia, have been investigated utilizing high-resolution modelling of wave processes combined with bathymetric surveys and sediment textural analyses of the nearshore sea floor. Textural analysis showed the mean grain size is about 0.12 mm. Fine sand (0.063–0.125 mm) accounts for about 77% of the sediments. Coarser-grained sand (0.28 mm) dominates along the waterline. Based upon the spatial distribution of the mean grain size and basic features of the local wave activity, properties of the Dean Equilibrium Beach Profile were determined. Alongshore sediment transport was calculated based upon a long-term time series of wave properties along the beach, and the CERC formula applied to about 500 m long beach sectors. The time series of wave fields and the properties of the local wave climate were modelled using a triple nested WAM wave model with an extended spectral range for short waves. The model is forced by open sea wind data from Kalbådagrund for the years 1981–2002. Results indicate that typical closure depth at Pirita is 2.5 m. The width and mean slope of the equilibrium profile are 250 m and 1:100, respectively. Southward transport dominates in the northern sections of the beach whereas no prevailing transport direction exists in the southern sections. This pattern has several nontrivial implications for the planning of beach protection activities

Beach face dynamics as affected by ground water table elevations

This report presents the results of laboratory studies which were carried out in the Coastal and Oceanographical Engineering Laboratory to investigate the effects of ground water table elevations on the beach profile changes over the swash zone. The experiment was conducted at three different water table levels while the other experimental conditions were fixed to constant values with regular waves. The water table levels included (1) normal water table level which is the same as mean sea level, (2) a higher level and (3) a lower level than the mean sea level. Special attention was given to the higher water level to investigate whether this level enhances erosion of the beach face and also to methods of interpreting the experimental data. The experiment described herein was carried out with a fairly fine sand and has demonstrated the significance of beach water table on profile dynamics. The increased water table level caused distinct effects in three definite zones. First, erosion occurred at the base of the beach face and the sand eroded was carried up and deposited on the upper portion of the beach face. Secondly, the bar trough deepened considerably and rapidly and the eroded sand was deposited immediately landward. This depositional area changed from mildly erosional to strongly depositional. Third, the area seaward of the bar eroded with a substantial deepening. The lowered water table appeared to result in a much more stable beach and the resulting effects were much less. The only noticeable trend was a limited deposition in the scour area at the base of the beach face. (Document has 37 pages.

Sixteen years of bathymetry and waves at San Diego beaches.

Sustained, quantitative observations of nearshore waves and sand levels are essential for testing beach evolution models, but comprehensive datasets are relatively rare. We document beach profiles and concurrent waves monitored at three southern California beaches during 2001-2016. The beaches include offshore reefs, lagoon mouths, hard substrates, and cobble and sandy (medium-grained) sediments. The data span two energetic El Niño winters and four beach nourishments. Quarterly surveys of 165 total cross-shore transects (all sites) at 100 m alongshore spacing were made from the backbeach to 8 m depth. Monthly surveys of the subaerial beach were obtained at alongshore-oriented transects. The resulting dataset consists of (1) raw sand elevation data, (2) gridded elevations, (3) interpolated elevation maps with error estimates, (4) beach widths, subaerial and total sand volumes, (5) locations of hard substrate and beach nourishments, (6) water levels from a NOAA tide gauge (7) wave conditions from a buoy-driven regional wave model, and (8) time periods and reaches with alongshore uniform bathymetry, suitable for testing 1-dimensional beach profile change models

INVESTIGATION OF THE MULTI-SCALE VARIABILITY OF BEACH PROFILES

This work focuses on the multi-scale variability of beach profiles. This includes the spatial variability over a range of scales of surveyed beach profiles and the complex temporal variability of beach elevation at given positions along the profile. The aims of this work are to characterize the variability of beach profiles in both time and space, to identify the predominant spatial and temporal patterns of beach profile changes, to identify the extreme profile changes due to infrequent storms/storm groups, to understand the nature of beach profile change in depth, to quantify the non-stationarity of beach profile and to provide insight into the prediction of beach profiles. This thesis includes a critical literature review of the existing profile models, such as numerical and data-driven models, to predict beach profiles. Particular focus is on the data-driven models since they characterize the beach in a site-dependent manner. The main weakness of the existing data-driven approaches is that many of the techniques assume stationarity and yet the processes in question are non-stationary, which necessitates more advanced techniques for investigating the variability of beach profiles. Hence in this thesis the wavelet technique is introduced, which is a relatively new technique. It is also shown how the use of a wavelet basis for decomposing the profile signals spatially allows a more satisfactory value for the depth of closure associated with a data set to be defined. Particular interests are in the beach profile data from the Field Research Facility (FRF) at Duck, North Carolina, USA. The field data and previous works by other researchers are introduced and preliminary studies are conducted including the interpolation of data and the empirical orthogonal function (EOF) analysis. A connection is established between EOF and wavelet analysis. In addition to the identification of basic patterns of beach profile changes, emphasis is given to the non-stationary investigation of beach profile changes in both time and space locally. In this way, the infrequent events are identified at different temporal scales. The responses of beach profile changes to different wave/storm conditions are discussed. The intermittent character of beach profile change is displayed in both time and space, providing much insight to the argument by Southgate and Moller (2000). Also, the depth of closure is presented by analysing the local components of wavelet variance in space, which is scale-dependent. The results agree with Larson and Kraus(1994). The wavelet analysis is validated on the beach profile data at the Coastal Research Station (CRS), Lubiatowo, Poland. Focus is on the spatial variability across the beach profile. Due to the multi-bar system, the spatial scale contents of beach profile changes at Lubiatowo are more complicated than Duck. The predominant spatial scales indicate that wave breaking may be the major factor of bar formation at this site. This is consistent with Pruszak et al. (1997)

Analysis of multi-scale morphodynamic behavior of a high energy beach facing the Sea of Japan

Monthly cross shore beach profiles measured at the Ogata Wave Observation pier located in Joetsu-Ogata Coast, Niigata Prefecture, Japan, was analysed to investigate multi-scale morphodynamic beach behaviour. The Ogata beach, facing the Sea of Japan, is subjected to high energy wave conditions with that has a strong winter/summer seasonal signature. The measured beach profiles at the beach show very significant variability where cross-shore movement of shoreline position and lowering of the beach at the location of measurements exceed 20 m and 4 m respectively. The shoreline position seems to follow the seasonal variability of incident wave climate where a correlation coefficient of 0.77 was found between monthly averaged incident significant wave height and the measured monthly shoreline position. During the summer months, the beach variability mostly concentrated to in the sub-tidal part of the profile, while a significant amount of upper beach change was observed during the winter months. The beach profile shape was found to rotate between three different beach states in time; (i) concave reflective profile; (ii) profile with sub-tidal berm; and (iii) gentle, dissipative profile. Empirical Orthogonal Function (EOF) analysis of the profiles show that the variability of beach profile shape is dominated by (a) upper shoreface steepening; (b) sub tidal berm development and dissipation; and (c) variability of the overall profile slope, which have some longer than seasonal cyclic signatures. Comparison of temporal EOFs with climate indices such as Southern Oscillation Index and Pacific Decadal Oscillation index shows notable some correlations between profile change and climatic variability in the region. The analysis also shows that the morphological variability of Joetsu-Ogata Coast has similarities and some distinct spatial and temporal differences to beaches of similar kind found elsewhere

Getting that Sinking Feeling: Analysis and Impacts of Sea Level Rise on Three National Parks along the East Coast, USA

Due to global climate change, sea level rise (SLR) has become a threat for future generations, but the extent of this danger is unknown. To help understand the possible effects of SLR on the east coast of the United States, we studied three national parks: Acadia National Park (ACAD), Assateague Island National Seashore (ASIS) and Everglades National Park (EVER). We predicted that ACAD would be less affected by SLR than ASIS and EVER due to the construction of its beach profile. By measuring the beach profile, we found that Sand Beach in ACAD was reflective with an average slope of 3.2 cm/m while South Ocean Beach in ASIS had an intermediate morphology with an average slope of 1.57 cm/m. The Snake Bight Channel beach in EVER was dissipative and had no slope. Using historical Landsat imagery from 1984 to 2016, we estimated that ACAD’s water area increased by 1.61%, that ASIS’s water area increased by 2.47%, and that the EVER’s water area decreased by 0.22% between 1992 and 2011. Using RCP scenarios from the latest IPCC report, we estimated future inundation levels in each park along with the percent change between the best and worst-case scenarios. Under the RCP8.5 scenario, ACAD had 1.36 km2 of inundation, ASIS had 37.11 km2, and EVER had 366.47 km2. ACAD had the highest percent change between the worst and best RCP scenario at 15.70%. ASIS had a slightly smaller percent change at 14.25% and EVER had even less at 10.42%. This study suggests that continued SLR will cause national parks billions of dollars in property damage and the loss of their inherent ecological value

Beach response due to the pressure equalization modules (PEM) system

Coastal erosion is a significant problem with dramatic effects on the coastline. There is an urgent need to introduce new and cost-effective measures that can mitigate the impacts on the shoreline. This study has been initiated to investigate the response of the beach at Teluk Cempedak due to the beach nourishment and Pressure Equalization Modules (PEM) system. The objectives of this study are the determination of closure depth and effectiveness of the system in treating the erosion process. The depth of closure was examined using both data from a series of beach profile surveys and from empirical formulae. The widely accepted Fixed Depth Change (FDC) method was explored and the hc before and after the installation of PEM system was investigated. The research found that multiple closure points can occur along the profile lines. The closure depth after the installation of PEM system was found to be deeper and the closure point is further seaward at the southern part of the beach. The Hellemeier’s equation over predict hc by 76 %, however it reveals that the equation is still robust in determining an upper limit of hc. The simplified equation was developed at Teluk Cempedak beach in predicting closure depth and can be equated to 0.98 times H0.137. From the survey data, it is found that after three years, the total sand volume and beach elevation are significantly higher in PEM areas. Generally, the result presented indicates the decreasing value of rate of erosion. Thus it revealed that PEM system is able to stimulate accretion of sand and yet slow down the erosion process. However, based on the sand volume distribution pattern, after three years, it is obviously seen that the accretion of sand occurring at the northern part while erosion process is taking place in the southern part of the beach. Based on the distribution pattern of bed elevation over the chainage, overall, the upper part of the beach is convex unlike earlier i.e before the installation of PEM system, where the beach was low and concave. This phenomena indicates that the system contribute to a significant accretion of sand and thus created a higher beach level at about 10 m to 55 m towards the sea. However, this trend only can be seen at a certain chainage. The PEM efficiency in terms of increment in bed elevation can only be observed at CH 400 till CH 800 while at CH 900 towards the south, the efficiency is decreasing. This shows that the accretion of sand is only occurring at the northern part and the beach is eroding at the southern part. Therefore, based on the available four years record of data, there is a certain part of the beach benefiting from the PEM system. However, some parts are still experiencing the erosion process

Morphological changes, beach inundation and overwash caused by an extreme storm on a low-lying embayed beach bounded by a dune system (NW Mediterranean)

The geomorphological evolution of a low-lying, micro-tidal sandy beach in the western Mediterranean, Pals beach, was characterized using airborne Light Detection and Ranging (LiDAR) data. Data were collected in prior to and six months after the impact of an extreme storm with a return period of approx. 50 years, with the aim of characterizing the beach's response to the storm. The use of repeated high-resolution topographic data to quantify beach geomorphic changes has allowed assessment of the accuracy of different proxies for estimating beach volume changes. Results revealed that changes in the shoreline position cannot accurately reproduce beach volume changes on low-lying beaches where overwash processes are significant. Observations also suggested that volume estimations from beach profiles do not accurately represent subaerial volume changes at large profile distances on beaches with significant alongshore geomorphological variability. Accordingly, the segmentation of the beach into regularly spaced bins is proposed to assess alongshore variations in the beach volume with the accuracy of the topographic data. The morphological evolution of Pals beach during the study period showed a net shoreline retreat (- 4 m) and a significant sediment gain on the subaerial beach (+ 7.5 m3/m). The net gain of sediment is mostly due to the impact of the extreme storm, driving significant overwash processes that transport sediment landwards, increasing volume on the backshore and dunes. The increase of volume on the foreshore and the presence of cuspate morphologies along the shoreline also evidence post-storm beach recovery. Observed morphological changes exhibit a high variability along the beach related to variations in beach morphology. Changes in the morphology and migration of megacusps result in a high variability in the shoreline position and foreshore volume changes. On the other hand, larger morphological changes on the backshore and larger inundation distances occur when the beach and the dunes are lower, favouring the dominance of overwash. The observed storm-induced morphological changes differ from predicted beach storm impacts because of spatial and temporal variations in the beach morphology, suggesting that detailed morphological parameters and indicators used for predicting beach vulnerability to storms should be regularly updated in order to represent the pre-storm beach conditions. Finally, observed morphological changes in Pals Bay evidenced a different behaviour between natural and urban areas, with better post-storm beach recovery on natural areas where the beach is not artificially narrowed.Peer ReviewedPostprint (author's final draft

Beach profile evolution towards equilibrium from varying initial morphologies

The evolution of different initial beach profiles towards the same final beach configuration is investigated based on large-scale experimental data. The same wave condition was performed three times, each time starting from a different initial profile morphology. The three different initial profiles are an intermediate energy profile with an offshore bar and a small swash berm, a plane profile and a low energy profile with a large berm. The three cases evolve towards the same final (equilibrium) profile determined by the same wave condition. This implies that the same wave condition generates different sediment transport patterns. Largest beach changes and differences in hydrodynamics occur in the beginning of the experimental cases, highlighting the coupling between morphology and hydrodynamics for beach evolution towards the same profile. The coupling between morphology and hydrodynamics that leads to the same final beach profile is associated with differences in sediment transport in the surf and swash zone, and is explained by the presence of bar and berm features. A large breaker bar and concave profile promote wave energy dissipation and reduce the magnitudes of the mean near-bed flow velocity close to the shoreline limiting shoreline erosion. In contrast, a beach profile with reflective features, such as a large berm and a small or no bar, increases negative velocity magnitudes at the berm toe promoting shoreline retreat. The findings are summarised in a conceptual model that describes how the beach changes towards equilibrium from two different initial morphologies