Model Estimate of the Coastal Constructions’ Impact on the Hydrodynamic Regime of the Neva Bay Water Area Adjacent to the 300th Anniversary Park of St. Petersburg in August and December 2011

PT. Teluk Lamong Terminal is one of the busiest port terminals in Indonesia. Such conditions require the development of the facility area for reclamation. This reclamation can potentially change the seabed’s contours and current patterns in the Lamong bay area of Surabaya. Therefore, the Author will conduct a research study to determine the impact of reclamation on the speed and current pattern of the existing and post-reclamation conditions in Lamong bay, Surabaya. This research conducted numerical modeling with Delft3D software. The simulation results show that the current pattern at the highest tide in the existing and reclamation models tends to have a dominant current direction from east to the northwest in the Madura strait. In contrast, some currents from the Madura strait are deflected into the Lamong bay area. On the other hand, during the lowest low tide conditions, both existing and reclamation conditions, the current pattern has a dominant direction coming from the northwest to the east, and the current in the Lamong bay area tends to exit or towards the Madura strait. There is an increase or decrease in current velocity when reclamation is carried out in each tidal condition. The highest increase in current velocity occurs at high tide with a value of 0.02 m/s, while the highest decrease in current velocity occurs at the high tide of 0.13 m/s. At the lowest ebb conditions, the highest current speed increase is 0.12 m/s, and the highest current velocity decrease is 0.03 m/s.

The primary source of environmental problems in Jakarta Bay’s waters is the change in hydrodynamics caused by reclamation and land-derived waste from the 13 watersheds that discharge into the bay. In June and December 2006 and 2015, hydrodynamic and trajectory simulations were conducted in Jakarta Bay to determine the distribution of plastic debris in pre- and post-reclamation conditions. The hydrodynamic conditions and particle trajectory in Jakarta Bay were described numerically using the Hamburg Shelf Ocean Model (HAMSOM). Secondary tidal data and primary ADCP data are used to validate the simulation results. The distribution of plastic debris released during the simulation depicts a distribution that follows the monsoon pattern, moving west during the east monsoon and moving east in the west monsoon and spreading along the coastline in both conditions. The percentage of plastic debris increased by 21.42% in June and 4.07% in December. The increase in the percentage of plastic debris that remains in the waters of Jakarta Bay is due to a 0.03 - 0.05 m/s decrease in current velocity following the formation of the reclamation island. Due to the decrease in current velocity within the bay, trajectory simulations indicate that plastic debris will take an additional 69.52 – 304.25 hours to exit. The accumulation of plastic debris around the reclamation islands demonstrates that the islands act as waste traps, necessitating proper waste cleanup, particularly in the canal area and around the reclamation island.

This study of modern river deposits substantiates and extends flume studies of regressive and sand waves by Jopling (1961) and Allen (1965). As first proposed by Jopling, regressive are a sequence of climbing oriented in a direction opposite that of the general current flow. At the risk of introducing another new term, they are herein termed climbing ripples rather than regressive ripples, because regression has a specific meaning in geology. Four types of sedimentary features were observed in an exposure of a large (4.5 ft high and 35 ft long) sand wave in a cut bank of the Arkansas River near Tulsa, Oklahoma. In downstream sequence they are: (1) accretionary foresets with tangential bases; (2) avalanche foresets with abrupt basal contacts; (3) reversed climbing ripples; and (4) normal or ripples. The accretionary foresets show a progressive decrease in mean grain size down the foresets, have an angle of slope (28°) less than that of the avalanche foresets (31.5°), and contain no reversed climbing ripples. In contrast to this, the avalanche foresets show a progressive increase in mean grain size down the foresets, a steeper slope, and development of reversed climbing ripples. The change from accretion to avalanche foresets apparently was the result of a decrease in current velocity. As velocities decreased, excessive deposition took place near the head of the foresets resulting in oversteepening and avalanching. At the same time a reverse eddy formed near the toe of the sand wave and produced the reversed climbing ripples. The reversed climbing are finer grained (2.82 vs. 2.43^phgr), poorer sorted, and more strongly fine-skewed than the foreset deposits. In the accretion foreset sands the sorting decreases progressively from top to bottom. The accretionary foreset sands tend to be more positively skewed near the base than they are near the top, whereas the avalanche foreset sands tend to be more positively skewed near the top and more nearly symmetrical near the base. End_of_Article - Last_Page 552------------

The migratory activity of Gammarus zaddachi and Gammarus chevreuxi is investigated in a current chamber, in which a tidal cycle can be simulated. In fresh running water the number of animals drifting with the current is of about the same magnitude as the number of animals actively swimming against the current. A diurnal periodicity is recorded in the migratory activity. The migratory activity is influenced by the population density and the food supply. In the current chamber a tidal cycle can be simulated by varying the factors current velocity, current direction, salinity, and temperature. The combination of a decrease in current velocity, followed by a slow current in the opposite direction, an increase in the salinity, and a rise in the temperature of the medium causes a significant increase in the activity of both species investigated. An increase in only one of the environmental factors mentioned above can also produce an increase in the migratory activity, but less pronounced than when all the factors coordinate in simulating a complete tidal cycle. Both G. zaddachi and G. chevreuxi react in a similar way on the simulation of a tidal cycle. In both species no great differences have been found between juveniles and adults with regard to the migratory activity. The results of the simulation experiments are discussed in connection with the migration cycles of G. zaddachi and G. chevreuxi as recorded in the field.

Biostratigraphy and depositional environment of algal stromatolites from the Mescal Limestone (Proterozoic) of central Arizona

The Thakuran River is truly a major tidal creek in the low-lying, tropical coastal plains of the Ganges-Brahmaputra delta. It is fed by to-and-fro-moving flood and ebb flows without any headwater discharge. The Thakuran River basin is intersected by numerous creeks and characterised by the mudflats on the river margins as well as in the riverbed. Lateral sedimentation takes place on meandering tidal creeks and gullies, whereas vertical sedimentation is found in the mudflats. Morphological features like mud ridges, mud microdelta, mud pellets, and mud lumps are recognised in their relationships to creek sedimentation. Depositional features typical of tidal environment like mud couplets, tidal bedding and tidal bundles have been recognised. The laminae of sand and clay in the core samples from the mudflat indicate a gradual decrease in current velocity in the upward direction.

A series of pyroclastic density currents were generated at Tungurahua volcano (Ecuador) during a period of heightened activity in August 2006. Dense pyroclastic flows were confined to valleys of the drainage network, while dilute pyroclastic density currents overflowed on interfluves where they deposited isolated bodies comprising dune bedforms of cross-stratified ash exposed on the surface. Here, the description, measurement, and classification of more than 300 dune bedforms are presented. Four types of dune bedforms are identified with respect to their shape, internal structure, and geometry (length, width, thickness, stoss and lee face angles, and stoss face length). (1) “Elongate dune bedforms” have smooth shapes and are longer (in the flow direction) than wide or thick. Internal stratification consists of stoss-constructional, thick lensoidal layers of massive and coarse-grained material, alternating with bedsets of fine laminae that deposit continuously on both stoss and lee sides forming aggrading structures with upstream migration of the crests. (2) “Transverse dune bedforms” show linear crests perpendicular to the flow direction, with equivalent lengths and widths. Internally, these bedforms exhibit finely stratified bedsets of aggrading ash laminae with upstream crest migration. Steep truncations of the bedsets are visible on the stoss side only. (3) “Lunate dune bedforms” display a barchanoidal shape and have stratification patterns similar to those of the transverse ones. Finally, (4) “two-dimensional dune bedforms” are much wider than long, exhibit linear crests and are organized into trains. Elongate dune bedforms are found exclusively in proximal deposition zones. Transverse, lunate, and two-dimensional dune bedforms are found in distal ash bodies. The type of dune bedform developed varies spatially within an ash body, transverse dune bedforms occurring primarily at the onset of deposition zones, transitioning to lunate dune bedforms in intermediate zones, and two-dimensional dune bedforms exclusively on the lateral and distal edges of the deposits. The latter are also found where flows moved upslope. Elongate dune bedforms were deposited from flows with both granular-based and tractional flow boundaries that possessed high capacity and competence. They may have formed in a subcritical context by the blocking of material on the stoss side. We do not interpret them as antidune or “chute-and-pool” structures. The dimensions and cross-stratification patterns of transverse dune bedforms are interpreted as resulting from low competence currents with a significant deposition rate, but we rule out their interpretation as “antidunes”. A similar conclusion holds for lunate dune bedforms, whose curved shape results from a sedimentation rate dependent on the thickness of the bedform. Finally, two-dimensional dune bedforms were formed where lateral transport exceeds longitudinal transport; i.e., in areas where currents were able to spread laterally in low velocity zones. We suggest that the aggrading ash bedsets with upstream crest migration were formed under subcritical flow conditions where the tractional bedload transport was less important than the simultaneous fallout from suspension. This produced differential draping with no further reworking. We propose the name “regressive climbing dunes” for structures produced by this process. A rapid decrease in current velocity, possibly triggered by hydraulic jumps affecting the entire parent flows, is inferred to explain their deposition. This process can in principle hold for any kind of particulate density current.Electronic supplementary materialThe online version of this article (doi:10.1007/s00445-013-0762-x) contains supplementary material, which is available to authorized users.

The paper studies the impact of nourishment with coarse sand at Locos beach in Torrevieja, Spain, in January 2020, on coastal dynamics. The objective is to model the changes in wave heights, currents, and potential sediment transport due to the nourishment. The SMC 2.5 software was used to model the beach evolution. The results show that the nourishment caused a reduction in wave height in some directions, especially in the ENE direction, and a decrease in current velocity in all directions. The potential sediment transport was reduced by three times in all directions after nourishment, and in the northern part, it almost disappeared. Nourishment also decreased the number and intensity of eddies in the surf zone, implying a reduction in rip currents, and enhancing safety for beachgoers. Additionally, nourishment led to a reduction in potential sediment transport, improving the stability of the cross-shore beach profile against storms. The findings suggest that coarse sand nourishment at Locos beach improved stability and safety, providing valuable insights for future coastal beach management and design.

Following promising results from demonstration projects, the next stage in the development of tidal stream energy is the commercial exploitation of this resource. Many high energy density tidal sites are in interconnected channels and hence an interaction between nearby tidal farms is expected. In this study, the impacts of farm interactions are analyzed based on changes in the capacity factor and the length of offshore work windows estimated using results from a three-dimensional numerical hydrodynamic model. This study focuses on four nearby farms in the Goto Islands: two farms that are side-by-side in the same channel, and two other farms that are in parallel channels. The side-by-side farms reduce each other’s capacity factor by 5.37% and 2.22% due to velocity deficits in the turbine wakes of the adjacent farm. This decrease in current velocity leads to an increase in the length of offshore work windows, as these windows are defined by periods for which the current velocity at the turbine installation points is below a given threshold. Conversely, the interactions of farms in parallel channels are negligible in the case of the Goto Islands. These results highlight the importance of considering inter-array interactions to maximize energy generation and minimize installation and maintenance costs.

Hydrodynamics and sedimentation induced by large-scale coastal developments in the Keum River Estuary, Korea

Development time and growth rate of the marine calanoid copepod Temora longicornis as related to food conditions in the oosterschelde estuary (Southern North Sea)

Influence of shoreface morphological changes since the 19th century on nearshore hydrodynamics and shoreline evolution in Wissant Bay (northern France)

Sedimentology of the Bengal shelf, Bangladesh: comparison of late Miocene sediments, Sitakund anticline, with the modern, tidally dominated shelf

A Gulf Stream-like meandering current is kinematically modeled using a streamfunction ψ = Uλ(1 − tanh[(y − yc)/λ cos(α)]. Under suitable parameter values a “front” exists along the velocity maximum across which there is no transport, but with mixing occurring on either side. An analogous barrier exists in the Gulf Stream but appears to fade with depth. The conditions for mixing across the model front are studied using the Chirikov overlap criterion, which indicates the front breaks down for meander amplitude above a critical threshold that is inversely dependent on the ratio of meander phase speed and current speed, c/U. It is suggested that the increase in cross-frontal mixing in the deeper levels of the Gulf Stream is the result of current meandering and the decrease of current velocity with depth. The mechanism for this is interaction of different meander modes traveling along the Gulf Stream. These ideas are shown to be consistent with field measurements of tracers in the ocean.

Summary Detailed sampling using a very small sample size and grain-size analysis with a Coulter Counter of three fine-grained turbidites enabled a distinction to be made between the well-sorted single-grain Stokes’-deposited and unsorted ‘whole suspension’ floc-deposited grain-size populations. The results indicate that each turbidite is a continuous sequence deposited from the same source suspension. Particles settle to the bottom as flocculated masses. Initially flocs are broken up by near-bottom shear forces and only the coarsest silt and sand remains on the bed. The remaining mud forms a temporary mud suspension near the bottom which reflocculates and intermittently deposits at some critical concentration producing mud interlayers between silt laminae. Decrease in current velocity eventually allows simultaneous deposition of single grains and flocs with the latter becoming progressively more abundant resulting in formation of graded beds. Eventually, all deposition occurs in the form of mud flocs and a massive sediment results. The study essentially confirms the basic mechanism of the fine-grained turbidite deposition model proposed by Stow & Bowen (1978).