Experimental insights into cross-shore morphodynamics of beaches and cliffs

A morfodinâmica nas praias oceânicas da planície arenosa de Almofala varia em função de parâmetros oceanográficos (ondas, marés e correntes costeiras), meteorológicos (ventos, tempestades e chuvas) e antrópicos (fazendas de camarão). Os objetivos do trabalho são analisar os processos de progradação e retrogradação da linha de costa e a morfodinâmica das praias. As praias de Almofala, da Barreira e de Torrões localizam-se na costa oeste do Ceará. A metodologia consistiu na aquisição de dados topográficos (DGPS), oceanográficos (ondas - período, direção e altura da onda, e maré) e de amostras de sedimentos praiais. Estas praias apresentaram RTR com onda dominante. O parâmetro ε mostrou sistema barra e calha longitudinal nas praias de Almofala e de Torrões, e estágio reflectivo na praia da Barreira. O parâmetro Ω apresentou estágios predominantes de terraço de maré baixa na praia de Almofala, e dissipativo nas praias da Barreira e de Torrões, com predomínio de areia fina (44%) nas praias de Almofala e Torrões, e areia média (29%) na praia da Barreira. Estas praias são semi-expostas, com atuação de ventos (5,5 m/s) e ondas (0,56 m de altura), com erosão nas praias da Barreira (-64,5 m³) e de Torrões (-72,1 m³), e acresção (62,83 m³) na praia da Almofala, segundo dados de 2007.

The modelling of coastal morphodynamics has often been hindered by the lack of robustness/accuracy of constituent formulae, especially sediment transport formulae in the breaking and swash zones. Consequently, modellers are often forced to rely on crude calibration efforts and practical models consisting of empirical tuning-constants, to obtain favourable model results. Such methods are often unavoidable however due to theoretical limitations of existing models. The aim of this thesis is therefore to improve accuracy and applicability of suspended sand transport models for breaking wave conditions, for implementation into morphodynamic modelling studies. Several existing suspended sand transport models (6 reference concentration C₀ + 5 concentration profile C[z]) models were evaluated quantitatively and qualitatively against one another, and against state-of-the-art high-resolution datasets which were collected under large-scale breaking wave conditions. Numerous limitations were observed in existing models, with the most common of these being their inability to accurately replicate suspended transport patterns in multiple cross-shore regions. This was due to various issues, such as not adequately accounting for the effects of breaking-induced turbulent kinetic energy on resulting sand transport. This resulted in large discrepancies between computed and measured transport particularly in the highly turbulent breaking zone. Such poor performance in computing C₀ and C[z] had residual effects on the resulting suspended flux (uC[z]) and current-related transport rate (qsc) computations also, which are essential to the accurate modelling of morphodynamics, particularly in the medium- to long-term. A novel set of suspended sand transport (C₀ + C[z]) models (“L19”) were developed for breaking wave conditions and evaluated against the aforementioned existing models and datasets. The L19 formulae showed significantly greater performance than all existing models, indicating excellent agreement with measured data in all tested cross-shore regions. These improvements led to considerably better estimations of uC[z] and qsc, which have promising implications for future morphodynamic modelling.

Observing and mapping the long-term coastal morphodynamics because of the human and physical induced factors using conventional methods could not give expected outcomes. State-of-the-art technology and tools are the best methods to do so. Thus, this study is to explore the long-term coastal morphodynamics of coastal strip from Nintavur to Addalaichenai area using the Landsat satellite images of the years 1991, 2001, 2011 and 2019, downloaded from the Earth Explorer website. Google Earth (GE) historical images were also used for the comparison of periodic coastal morphodynamics. Normalized Difference Water Index (NDWI) was processed for land and water separation. Direct observation, perspective of the respective officials and inhabitants, reports concerning the departments and authorities were also considered as the sources for this study. In conclusion, this study has found that the coastal morphological changes have been made because of the both human and physical induced factors of which waves and river flooding withing the study area are the physical factors and construction activities; port and breakwaters are the human activities which have modified the beach in the study area. In comparison, after the construction of the port, remarkable coastal morphodynamics have been recorded in the period from 2011 to 2019 in the study area.
 
 Received: 11 February 2021 / Accepted: 22 March 2021 / Published: 10 May 2021

Coastal morphodynamics and Holocene environmental changes in the Pearl River Delta, southern China: New evidence from palynological records

This study presents a classification of morphodynamic beach states monitored along the South Brittany coast, on the western part of France. The investigated area faces the Atlantic Ocean and it is exposed to prevailing wind and waves mainly coming from the NW to SW and experience similar waves and wind climates as most beaches located on the French Atlantic coast. However, morphological settings of Brittany coast display more specific characteristics which contribute to make the morphodynamic beach behaviours more complex. To characterise the morphodynamic beach states, a beach survey programme was carried out from February 2008 to June 2009. Twenty five beaches were surveyed. Beach profiles were levelled from the toe of the dune to the water level line using a TRIMBLE electronic theodolite. Wave data were obtained from two offshore buoys, named l’Ile d’Yeu Nord (8503) and Le plateau du Four (04403), and owned by CETMEF (Centre d'Etudes Techniques Maritimes Et Fluviales). Wave characteristics used include significant wave height (Hs) and its associated period (Ts). Morphodynamic beach states were determined by the surf scaling and the surf similarity parameters using breaker wave’s height values derived from offshore wave height. Temporal changes of morphodynamic beach states were assessed in relation with beaches profiles and hydrodynamic factors variations. Six different morphodynamic beach behaviours were identified, mainly varying between reflective and intermediate states. Multivariate statistical analyses were then carried out to assess the main factors driving morphologic and morphodynamic beach disparities. Obtained results are related to both coastline orientation and nearshore bedrocks distribution, enhancing the role of these specific morphologic constraints in the complex behaviour of South Brittany coast.

The modelling of swash zone hydrodynamics and sediment transport and the resulting morphodynamics has been an area of very active research over the last decade. However, many details are still to be understood, whose knowledge will be greatly advanced by the collection of high quality data under controlled large-scale laboratory conditions. The advantage of using a large wave flume is that scale effects that affected previous laboratory experiments are minimized. In this work new large-scale laboratory data from two sets of experiments are presented. Physical model tests were performed in the large-scale wave flumes at the Grosser Wellen Kanal (GWK) in Hannover and at the Catalonia University of Technology (UPC) in Barcelona, within the Hydralab III program. The tests carried out at the GWK aimed at improving the knowledge of the hydrodynamic and morphodynamic behaviour of a beach containing a buried drainage system. Experiments were undertaken using a set of multiple drains, up to three working simultaneously, located within the beach and at variable distances from the shoreline. The experimental program was organized in series of tests with variable wave energy. While a positive effect was observed under low energy conditions, for medium and high energy conditions the benefit of having the drains operative was not always clear. In any case, it was evident that any positive effect of the drains on the beachface was confined by the position of the cone of depression in the aquifer’s surface. The tests carried out in the large wave flume at UPC had the intent to investigate swash zone under storm conditions. The main aim was to compare beach profile response for monochromatic waves, monochromatic waves plus free long waves, bichromatic waves and random waves. Both erosive and accretive conditions were considered. The experiments suggest that the inclusion of long wave and wave group sediment transport is important for improved nearshore morphological modelling of cross-shore beach profile evolution, and provide a very comprehensive and controlled series of tests for evaluating numerical models. It is suggested that the large change in the beach response between monochromatic conditions and wave group conditions is a result of the increased significant and maximum wave heights in the wave groups, as much as the presence of the forced and free long waves induced by the groupiness. The equilibrium state model concept can provide a heuristic explanation of the influence of the wave groups on the bulk beach profile response if their effective relative fall velocity is larger than that of monochromatic waves with the same incident energy flux.

Modelling the role of self-weight consolidation on the morphodynamics of accretional mudflats

The main objective of this study is to unravel the physical processes that control typical coastal systems in Central Vietnam while challenged by the fact that it is a data limited environment. Inlets and bays are the typical coastal system along the central coast of Vietnam. These coastal systems are strongly influenced by tropical monsoon conditions, which are characterised by variations in seasonal wave conditions and seasonal river flow. These systems are even more vulnerable to extreme weather conditions, such as floods and storms, because of the complex topography of a relatively narrow and steep mountain range which is directly connected to a dense river network in the low-lying coastal plains at the downstream end. Economic and ecological values in the coastal area are under pressure as a result of the intensification of natural disasters and human interventions. Notable examples of this are Cua Dai beach and Da Nang bay. Cua Dai beach lies adjacent to the Cua Dai inlet which is a typical seasonal varying tidal inlet connected to the catchment area of the Vu Gia-Thu Bon River. Cua Dai beach has suffered extreme erosion in the recent decade. Da Nang bay is a complex bay beach headland downstream of the Vu Gia River that discharges into this bay. Also, this system is affected by human interventions. Due to the common downstream basin of the Vu Gia-Thu Bon River system, both being typical coastal systems in Central Vietnam that experience data limitations, this study attempts to combine and understand the hydrodynamics and morphodynamics of Cua Dai inlet and the complex Da Nang embayment. In order to identify and quantify the main processes governing the evolution of Cua Dai beach to explain the morphological changes and extreme erosion in recent years, a new approach was developed. Historical shoreline positions and sediment budget changes are the two parameters of main importance in the approach to quantify the erosion processes in the Cua Dai coastal inlet. Historical shoreline changes were derived fromsatellite images and associated sediment budgets were estimated based on shoreline change rates using additional assumptions, such as defining a closure depth and a time invariant beach profile. To gain insight into the sediment transport along the Cua Dai beach, additional numerical models and empirical equations are used to investigate the variation in alongshore sediment transport induced by waves. Further analysis on how seasonal variation in both waves and river discharge impacts the morphodynamics of the ebb tidal delta and its adjacent coasts is performed based on process-based modelling.

Meandering rivers are interesting features of the landscape due to their aesthetically pleasing forms. There is an abundance of scientific studies on meandering rivers, however, their behaviour is still not fully understood. The complexity of the flow, bed morphodynamics and bank stability, the related uncertainties in water and sediment motion, sediment properties and geotechnical properties of the banks, as well as the large time and length scales suggest that it is impossible to exactly predict the evolution of a meandering river. Typical spatial and temporal scales of meandering rivers are too large to use detailed three-dimensional models and therefore reduced-order models, obtained by depth- and cross-section averaging are used. These models are faster but also less generic. In this study such models are used and extended (by means of theory and detailed numerical models) to predict the hydrodynamic and morphodynamic processes in (strongly) curved meander bends.

The need for sustainable energy is rising, and at the moment wind energy is one of the few forms of renewable energy that can be harvested efficiently.We investigated the influence of an offshore wind farm on the large-scale morphodynamics of the seabed.To this aim, we developed a morphodynamic model to investigate the effect of offshore wind farms on the seabed. By implementing the model in a GIS environment, the model allows us to calculate the effects of a wind farm using location specific and park design input parameters. By implementing an analytical model in a GIS, a rapid calculation of the effects of an offshore wind farmat a certain location in the North Sea can be made.

Sogut, E. and Farhadzadeh, A., 2021. Numerical study of longshore variation in beach morphodynamics along Eastern Lake Erie shoreline due to seiche. Journal of Coastal Research, 37(1), 92–103. Coconut Creek (Florida), ISSN 0749-0208.Extreme coastal events and abrupt changes in atmospheric pressure in an enclosed or semi-enclosed basin can trigger low-frequency water surface oscillations known as seiches. This exploratory study numerically quantifies the effects of seiche on morphological changes along the eastern Lake Erie shoreline. The quantification is made by simulating the hydrodynamics of the lake using a coupled circulation and spectral wave model (ADCIRC+SWAN), providing the flow boundary conditions to the two-dimensional nearshore morphodynamic model, XBeach. The process-based XBeach model is used to simulate the nearshore morphological variations under two water-level conditions: the lake's actual water level and the synthetically generated seiche-free water level. The XBeach model is cross-calibrated using the process-based nearshore morphodynamic model, CSHORE, which was extensively validated using lab and field data. It is found that the seiching motions have a contribution of ∼1.5% to the erosion of beaches along the 2-km stretch of the shoreline in eastern Lake Erie shoreline.

Microplastic pollution in Vietnamese sandy beaches: Exploring the role of beach morphodynamics and local management.

While hydrodynamic processes respond instantaneously to morphological change, morphological change requires the redistribution of sediment. As sediment takes a finite time to move, there is a lag in the morphological response to hydrodynamic forcing. Sediment can therefore be considered to be a time-dependent coupling mechanism. Since the boundary conditions of hydrodynamic forcing change regularly this may mean that the beach never attains equilibrium. Morphodynamic processes exhibit positive and negative feedbacks nonlinearities and threshold behavior. The present study deals with beach morphodynamics using Mopla module of SMC which is a numerical system called Coastal Modeling System ( SMC) is a part of the Spanish Beach Nourishment Manual (SBM). Mopla module of SMC further incorporated with wave propagation model (Karkby and Dalrym model), current model (Navier and Slokes equation) and the sediment model (Bailard and Soulsby model). Three study points (Kirtania, Choumukh and Rasalpur) have been chosen for beach morphodynamics using this wave, current and sediment model at the Balasore coast, Odish, India. The results shows that the significant wave height is 0.62–1.20 m in Kirtaniya, 0.00–0.90 m in Choumukh and 0.10–0.85 m in Rasalpur. The present study also reveals the potential transport of sediment at near shore region which is 0.25–0.1 m3/h/ml at Kirtaniya sector, 0.01–0.04 m3/h/ml at Choumukh and 0.015–0.06 m3/h/ml at Rasalpur sector. The height of sediment of erosion and accretion is bounded between −0.05 and 0.02 m at Kirtaniya, −0.01 and 0.001 m at Choumukh and −0.02 and 0.01 m at Rasalpur sector after the 48 h duration of model calibration. The area of erosion and accretion can also be presented at the each point of study. So one can easily estimate the volume of sediment mobilization by measuring the area under erosion and accretion respectively in a particular beach and also can take the management measures for that particular coastal area.

Swashed away? Storm impacts on sandy beach macrofaunal communities

The objective of the present study is to study the effects of beachrocks (i.e. of coastal formations consisting of beach material consolidated in situ by mainly carbonate cements) on beach morphodynamics. Towards this objective a detailed study of the beachrock-infected beach of Vatera Bay (Lesvos, Greece) has been carried out using both field sedimentological and morphological data and 1-D morphodynamic modelling. The results of the study show that (a) the beachrock spatial distribution along the Vatera beach is controlled by wave energy levels and beach sediment size; (b) beachrock-infected beaches are characterised by relatively small variability in the morphology of their upper part and their 'mean' profile is controlled by that of the exposed and/or buried beachrock surface and (c) beachrocks have significant impacts on beach morphodynamics as they facilitate the formation of characteristic morphological features (e.g. 'scour steps' at the offshore beachrock margins) and increase beach erosion.