Implication of Shoreline and Nearshore Morphological Changes on Sediment Budget of Wave-Dominated Chennai Beach, India

The study examines the shoreline (1990-2019) and nearshore morphological changes (seasonal) to understand the littoral drift and sediment budget variability. Shoreline change rate depicts erosion (-0.06 m/yr) in the northern sector and accretion (+0.12 m/yr) in the southern sector. Seasonal nearshore morphological changes from non-monsoon to monsoon period signifies net erosion (-1.8x10^4 m^3 ) in northern sector and net accretion (+2.5x10^4 m^3) in the southern sector. Although the lost sediment during monsoon is regained in non-monsoon period, the quantity of sediment gain is reduced in areas with human interventions. The results of the investigation depict the dominance of littoral drift towards north from February to October, when wave approach from east-southeast to south-southeast direction and southwards from November to January when the wave direction was from east-northeast to east-southeast. The net longshore sediment transport rate estimated during the study period was 2.6x10^5 m^3/year in the northern sector and 1.5x10^5 m^3/year in the southern sector with higher rate attributed to monsoon than the non-monsoon. Sediment budget results in deciphering the causes of erosion (-1.27×10^4 m^3/yr) in northern sector and accretion (3.91×10^4 m^3/yr) in southern sector in the wave-dominated Chennai beach.

Analysis of Long-Term Shoreline Observations in the Vicinity of Coastal Structures: A Case Study of South Bali Beaches

Recently, many rigid structures have been installed to cope with and efficiently manage coastal erosion. However, the changes in the coastline or isocenter and the movements of coastal sediment are poorly understood. This study examined the equilibrium shoreline and isocenter lines by applying a Model of Estimating Equilibrium Parabolic-type Shoreline (MeEPASoL) as an equilibrium shoreline prediction model. In addition, the inverse method was used to estimate littoral drift sediment transport from long-term beach profile observations. The movement of coastal sediments was analyzed using long-term beach profile observation data for three Indonesian beaches, namely, Kuta Beach for 13 years, Karang Beach in Sanur for 15 years, and Samuh Beach in Nusa Dua for 18 years. The littoral drift at every site was dynamically controlled by seasonal changes in the monsoon, the erosion and deposition patterns coupled with the presence of coastal structures, and limited sediment movement. Shoreline deformation in Kuta is generally backward deformed, with a littoral drift from south to north. In Sanur, the littoral drift vector carries sediment from the right and left sides and forms a salient behind the offshore breakwater. The littoral drift at Nusa Dua is dominantly from south to north, but the force of sediment transport decreases near the breakwater towards the north. Furthermore, the methods applied herein could aid the development of strategic coastal management plans to control erosion in subcells of coastal areas.

The Shoreline Deformation in Convex Beach due to Sea Level Rise

Sea level rise (SLR) is become more serious on a global scale and has become one of the main reasons causes shoreline changes, and erosion, even on an extreme scale can cause the sinking of coastal areas and islands. It was recorded that many big cities were damaged by SLR. The Bruun rule is the most widely used method for predicting the horizontal translation of the shoreline associated with a given rise in sea level. In this study, however, the change in the average shoreline at the convex beach, which is more vulnerable to erosion due to sea level rise, is investigated. The increase in water depth by sea level rise causes a change in the wave crestline, ultimately leading to a linearization of the shoreline. In general, it is assumed that the annual average shoreline is parallel to the annual mean wave crestline. Moreover, assuming that the equilibrium depth contour is formed according to the crestline, the retreat of the shoreline is predicted. The shoreline change is indirectly predicted through the wave crestline deformation obtained from a wave model and this method is applied to the convex beach. Our result showed that for a convex beach with a length of 1 km has open ends with free littoral drift at both ends, the sea level rise of 1 m cause the erosion of 10 m in the protruding area, and the sea level rise of 2 m causes erosion of 23 m. However, if the convex beach is blocked at both ends, sea level rise of 1 m causes the erosion of 6.3 m in the convex area, but the shoreline advance of 3.8 m at both ends, and if the sea level rise of 2 m occurs, the erosion of 14.3 m can occur in the convex area and shoreline advance of 8.6 m can occur at both ends.

Littoral drift analysis based on long-term observation of mesotidal beach profile in Kuta Beach, Bali for coastal retreat assessment

The beach profile survey in the intertidal zone is crucial for a temporal variability study of shoreline and beach profile change for coastal management. The combination of numerical modelling and field data has proven to be successful in identifying the primary hydrodynamic and sediment transport processes such as littoral and cross-shore drift. Those parameters are relevant to the sandbar migration process and shoreline changes. The purpose of the present study is to analyse the littoral drift that caused temporal variability shoreline change in mesotidal beach for coastal retreat mitigation. Beach profile data of Kuta Beach was analyzed by 7 years of long-term field observation data both east monsoon and west monsoon situation. The shoreline definition used mean sea level (MSL)1.3 m and high water level (HWL) 2.6 m as reference. By using the MeEPASoL program as a graphical user interface program, shoreline changes converging to an equilibrium state can be simulated by taking into account the existing breakwater. Temporal shoreline position resulting from littoral drift and beach width change from its initial position is estimated for coastal erosion analysis. The result showed that dominantly, the littoral drift pattern moved from south to north. Furthermore, this study can be used in the process of identifying the primary hydrodynamic analysis in erosion disaster management as assessment of the beach erosion.

Trigno River Mouth Evolution via Littoral Drift Rose

A mid-term analysis of shoreline evolution was carried out in the present paper for the Trigno river mouth area (5.2 km), located in the northern part of the Molise coast region (southeast Italy). The littoral drift rose (LDR) concept was employed, coupled to the GENESIS one-line model, to produce numerical simulations. The LDR graph was used to define a single, time-invariant, “equivalent wave” component (EW), which was supposed to entirely rule the shoreline changes. Given the inherent bimodality affecting the Molise wave climate, EW could result not significant in forecasting shoreline evolution, since both a climate inversion and a time-varying diffusion extra effect are expected. These aspects, never investigated in the literature, are deepened in the present paper, with the main aims of firstly assessing the explanatory power of the LDR equivalent wave and its significance within a bimodal climate, and secondly checking the role of a time-varying diffusivity. Results confirmed the reliability of the EW concept, even within a bimodal climate. Moreover, the possible effect of a time-varying diffusion, which is expected with a large directional variability, produced insignificant results with respect to the EW.

California harbor dredging: History and trends

California is a major shipping point for exports and imports across the Pacific Basin, has large commercial and recreational fisheries, and an abundance of marine recreational boaters. Each of these industries or activities requires either a port or harbor. California has 26 individual coastal ports and harbors, ranging from the huge sprawling container ports of Los Angeles and Long Beach to small fishing ports like Noyo Harbor and Bodega Bay. Almost all of California’s ports and harbors were constructed without any knowledge or consideration of littoral drift directions and rates and potential future dredging issues. Rather, they were built where a need existed, where there was a history of boat anchorage, or where there was a natural feature (e.g. bay, estuary, or lagoon) that could be the basis of an improved port or harbor. California’s littoral drift rates and directions are now well known and understood, however, and have led to the need to perform annual dredging at many of these harbors as a result of their locations (e.g. Santa Cruz, Oceanside, Santa Barbara, Ventura, and Channel Islands harbors) while other harbors require little or no annual dredging (e.g. Half Moon Bay, Moss Landing, Monterey, Redondo-King and Alamitos Bay). California’s coastal harbors can be divided into three general groups based on their long-term annual dredging volumes, which range from three harbors that have never been dredged to the Channel Islands Harbor where nearly a million cubic yards is removed on average annually. There are coastal harbors where dredging rates have remained nearly constant over time, those where rates have gradually increased, and others where rates have decreased in recent years. While the causal factors for these changes are evident in a few cases, for most there are likely a combination of reasons including changes in sand supply by updrift rivers and streams related to dam construction as well as rainfall intensity and duration; lag times between when pulses of sand added to the shoreline from large discharge events actually reach downdrift harbors; variations in wave climate over time; shoreline topography and nearshore bathymetry that determine how much sand can be trapped upcoast of littoral barriers, such as jetties and breakwaters, before it enters a harbor; and timing of dredging. While there is virtually nothing that can be done to any of these harbors to significantly reduce annual dredging rates and costs, short of modifying either breakwater or jetty length and/or configuration to increase the volume of sand trapped upcoast, thereby altering dredging timing, they are clearly major economic engines, but come with associated costs.

Quantitative interpretation of risk potential of beach erosion due to coastal zone development

Coastal erosion is more severe due to human-induced coastal zone development in addition to natural climate change. Anthropogenic development affecting coastal erosion is divided into three areas; watersheds, coastal waters, and coastal land areas. In this study, the ultimate effect of anthropogenic development on changes in the amount of sand, changes in the littoral drift, and changes in shoreline variability in these three planar areas is expressed as quantitative risk potential of beach erosion damage, defined as a change in the planar surface of the sand beach. The change in the amount of sand is due to the law of conservation of matter, and the littoral drift characteristic of sand is interpreted as a change in the main crest line at the breaking point, and the response characteristics of shoreline position is interpreted as change in the erodibility and recovery characteristics of beach sand. This quantitative method was applied to Bongpo-Cheonjin Beach of erosion grade D (frequency of erosion damage within 5 years) in Gangwon-do, Korea to identify the cause of erosion and evaluate the detailed applicability of this method. It was interpreted using a series of aerial photographs taken from 1972 to 2017 and survey data obtained from the erosion rating project started in 2010. In the erosion rating project, the GPS shoreline survey of 4 times per year and the sand sampling at the swash zones of base line at 150 m intervals are mainly carried out. We showed the feasibility of methodology evaluating the risk potential for beach erosion proposed in this study, and it can be expected that this method will be applicable to eroded beaches elsewhere.

Contrasting facies patterns between river-dominated and symmetrical wave-dominated delta deposits

Process-physics-based, coupled hydrodynamic–morphodynamic delta models are constructed to understand preserved facies heterogeneities that can influence subsurface fluid flow. Two deltaic systems are compared that differ only in the presence of waves: one river dominated and the other strongly influenced by longshore currents. To understand an entire preserved deltaic succession, the growth of multiple laterally adjacent delta lobes is modeled to define delta axial to marginal facies trends through an entire regressive–transgressive depositional succession. The goal is to refine a facies model for symmetrical wave-dominated deltas (where littoral drift diverges from the delta lobe apex). Because many factors change depositional processes on deltas, the description of the river-dominated example is included to provide a direct reference case from which to define the impact of waves on preserved facies patterns. Both systems display strong facies trends from delta axis to margin that continued into inter-deltaic areas. River-dominated delta regression preserved a dendritic branching of compensationally stacked bodies. Transgression, initiated by sea-level rise, backfilled the main channel and deposited levees and splays on the submerging delta top. Wave-dominated deltas developed dual clinoforms: a shoreface clinoform built as littoral drift carried sediment away from the river month and onshore, and a subaqueous delta-front clinoform composed of sediment accumulated below wave base. Although littoral drift in both directions away from the delta axis stabilized the position of the river at the shoreline, distributary-channel avulsions and lateral migration of river flows across the subaqueous delta top produced heterogeneities in both sets of clinoform deposits. Separation of shoreface and subaqueous delta-front clinoforms across a subaqueous delta top eroded to wave base produced a discontinuity in progradational vertical successions that appeared gradual in some locations but abrupt in others. Littoral drift flows away from adjacent deltas converged in inter-deltaic areas, producing shallow water longshore bars cut by wave-return-flow channels with associated terminal mouth bars. Transgression initiated by sea-level rise initially led to vertical aggradation of wave-reworked sheet sands on the subaqueous delta top and then retreating shoreface barrier sands as the subaerial delta top flooded. Pseudo inter-well flow tests responded to local heterogeneities in the preserved deposits. As expected, abandoned channels in the river-dominated case defined shoreline-perpendicular preferential flow paths and wave-dominated delta deposits are more locally homogeneous, but scenarios for development of more pronounced shore-parallel heterogeneity patterns for wave-influenced deltas are discussed. The results highlight the need to consider the dual clinoform nature of wave-dominated delta deposition for facies prediction and subsurface interpretation.

National geological and hazardous systematic cartography of the coastal zone as a contribution to the promotion of sustainability, defence and valorisation of the Portuguese coastal area

<p>The Portuguese coastal zone, where ¾ of the population lives and where the contribution to GNP is estimated at 85%, assumes an important role in the national economic context, which is not only presently reflected on the budget dedicated to the management and mitigation of current risks associated to climate change, but also for its strategic importance in environmental, social and leisure industry perspectives.</p><p>The geological and hazardous cartography of the coastal zone, of mainland Portugal, on a 1:3000 scale, has been developed, at LNEG, as an instrument to support the sustainability, protection and enhancement of the coastline [<em>2018, JCC, 22:1031-1043</em>].</p><p>The increase in knowledge concerning coastal hazard, based on the historical evolution of the shoreline, expressed on a systematic and digital cartographic basis at a scale of detail, in addition to the important contribution to the development of regional geology, is a vital contribution for the correct use and sustainable development of the coast. So far, shoreline evolution evaluation has been determined for two coastal sectors covering approximately 140 km of coastline: the western sector of Figueira da Foz to Nazaré and the southern sector of Algarve between Faro and Vila Real de Santo António [<em>2021, JCC, https://doi.org/10.1007/s11852-020-00791-3</em>].</p><p>The western sector evolutionary trend, from 1947 to 2015, shows an overall erosional behaviour, even though a prograding tendency is observed in some areas. Coastline evolution assessment reveals an average retreat of -13.6 m and a 702,558 m<sup>2</sup> land loss area. However, when looking only for the sectors where erosion occurred, a total of 1,164,888 m<sup>2</sup> of land loss was observed. Erosion, that is more severe in the northern part, reaching a maximum coastal retreat of -145 m and an erosion rate of 2.46 my<sup>-1</sup>, seems to be induced by a reduction of the littoral drift, but also by human interference in coastal dynamics, namely by the introduction and enlargement of the original rigid constructions and groins installation.</p><p>Regarding the south eastern Algarve coastline displacement, from 1950 to 2015, a seaward shift prevails, with a prograding coastline occupying approximately 54% of the studied sector. However, this progradation is mostly associated to human intervention on the coast, being related to up-drift accumulation against inlet jetties / groins. The erosional trend prevails predominantly in the central barrier island system of Ria Formosa, namely in the Culatra (with a maximum displacement of -163 m), Armona (maximum displacement of -83 m), the Tavira, (maximum displacement of -116 m), and the Cabanas islands, where maximum displacement observed is up to -235 m. Regarding land area changes, some sectors lost and others gained area due to coastline displacement. However, the overall analysis showed an area increase of 1.05 × 10<sup>6</sup> m<sup>2</sup> for this south-eastern coastal fringe.</p><p>The achievement of high-resolution, continuous and updated data, at a regional scale, likely favour successful application of the needed mitigation measures (as beach/dune nourishment, sand-shots and others) at the exact key target locations.</p>