Influence of the degree of embayment on the formation and behavior of rip currents on the beaches of Santa Catarina, Brazil

The goal of this study was to use topographic control by microfabricated scaffolds with 3-dimensional surfaces to induce active tension development and enhanced contractility in engineered cardiac syncytium (a high density cardiac cell structure with reconstituted cell-to-cell connections and synchronized tissue-like behavior). Deeply microgrooved (feature height 50μm) elastic scaffolds were designed using polydimethylsiloxane molding, and neonatal rat cardiomyocytes were grown on them to confluency. Engineered cardiac cell constructs on the topographically modified (T) scaffolds showed higher order of intra and intercellular organization (fiber-like structures) compared to those grown on various flat surfaces (F), and developed self-organized persisting electrical and mechanical activity. These structural and functional changes were accompanied by a statistically significant (p < 0.001) increase in nuclear eccentricity (mean ± S.E.: 0.79 ∓ 0.01, n=137 in T vs. 0.64 ± 0.01, n=863 in F), and a preferential nuclear orientation, deviating from the axis of the grooves at a shallow angle. The orientation of the nuclei correlated well with the actin fiber arrangement in the T-samples, as well as with the direction of maximum displacement. Topography-induced nuclear deformation, a sign of tension development, implies further functional changes in transcription and cell signaling. In conclusion, we demonstrate topographic control of electromechanics in engineered cardiac syncytium, without external mechanical or electrical stimulation. These findings suggest a possibility to use controled microenvironments in the design of biological autonomous force generators with reconstituted excitable tissue.

Chapter 2 - The Physical Environment

Application of multivariate statistical techniques in alongshore differentiation of coastal barriers

Optimal solutions to the nonlinear, hydrostatic, Boussinesq equations are developed for steady, density-stratified, topographically controlled flows characterized by blocking and upstream influence. These flows are jet-like upstream of an isolated obstacle and are contained within an asymmetric, thinning stream tube that is accelerated as it passes over the crest. A stagnant, nearly uniform-density isolating layer, surrounded by a bifurcated uppermost streamline, separates the accelerated flow from an uncoupled flow above. The flows are optimal in the sense that, for a given stratification, the solutions maximize the topographic rise above the blocking level required for hydraulic control while minimizing the total energy of the flow. Hydraulic control is defined mathematically by the asymmetry of the accelerated flow as it passes the crest. A subsequent analysis of the Taylor–Goldstein equation shows that these sheared, non-uniformly stratified flows are indeed subcritical upstream, critical at the crest, and supercritical downstream with respect to gravest-mode, long internal waves. The flows obtained are relevant to arrested wedge flows, selective withdrawal, stratified towing experiments, tidal flow over topography and atmospheric flows over mountains.

Saddle points between neighboring deep ocean basins are the sites of unidirectional flow from one basin to the next, depending on the source of bottom water. Flow in these sites appears to be topographically controlled so the interface between the bottom water and the water above adjusts itself to permit bottom water flow from the basin that contains a source of bottom water into the next. Examples in the Atlantic include flow in the Romanche Fracture Zone, the Vema Channel, the Ceara Abyssal Plain, the Anegada‐Jungfern passage, and the Discovery Gap, but there are many more. Theoretical predictions of volume flux using a method that requires only conductivity‐temperature‐depth data archives and detailed knowledge of bathymetry near the saddle point are compared with volume flux estimates using current meters and/or geostrophic estimates for seven cases. The ratio of prediction to volume flux estimate ranges from 1.0 to 2.7. Some ocean straits that separate adjacent seas are also found to critically control bidirectional flows between basins. Theory of the influence of rotation on such critical flows is reviewed. Predictions of volume flux in eight cases are compared with ocean estimates of volume flux from traditional methods.

Multibeam sonar surveys in the past decade, augmented by single‐beam data from the OLEX charting system, reveal landsystems on Atlantic Canadian shelves that are diagnostic of Late Wisconsinan ice‐sheet dynamics. Four landsystems are described. (1) The Bay of Fundy landsystem comprises two contrasting sets of bedforms, and is interpreted as evidence of topographically controlled fast‐flowing ice adjacent to slower‐moving ice. (2) The German Bank landsystem off southwest Nova Scotia is comprised of glacially fluted terrain overprinted by De Geer moraines and arcuate recessional moraines. We infer that a flow of grounded glacial ice out of the Bay of Fundy was followed by steady retreat, punctuated by at least one major re‐advance. (3) The Placentia Bay landsystem consists of a convergent field of streamlined landforms with superimposed De Geer moraines, overprinted in one area by flutings. We infer that this landsystem was formed in the onset zone of fast‐flowing ice, and that overprinting was due to a re‐advance of ice from offshore. (4) The south coast of Newfoundland landsystem, which includes arcuate, fjord‐mouth moraines and a coast‐parallel, fluted moraine, indicates strong topographic control on a retreating marine ice margin as it reached a fjord coastline. These submarine glacial landsystems are not inconsistent with a conceptual model showing Late Wisconsinan ice advance to shelf edges, rapid calving retreat along deepwater channels and slower retreat of ice margins grounded in shallow water. The re‐advances documented two of the study areas have parallels in the Last British Ice Sheet, confirming that the reorganization of marine‐based ice sheets, caused by calving in embayments, led to internally forced re‐advances.

Neutrally buoyant floats, deployed across the northern slope of the Iceland‐Faroe Ridge at 800m depth, reveal tight topographic control of their movement: a cluster of 22 floats drifts southeast to the Faroe‐Shetland Channel where it bifurcates such that floats deployed over the upper slope turn south and eventually exit the Norwegian Sea through the Faroe Bank Channel, and floats over the deeper slope turn north in the Norwegian Sea. A subset of the latter group moves quickly north along the western slope of the Vøring Plateau and divides with most of the floats turning east into the Lofoten Basin and the remainder circulating cyclonically around the Norwegian Basin. This study establishes that i) the Faroe Bank Channel overflow waters must come from along the slope north of the Faroes, not the interior of the Norwegian Sea, and ii) exchange of intermediate waters between basins takes place along topographically controlled routes.

We present a theoretical and experimental study of the propagation of gravity currents in porous media with variations in the topography over which they flow, motivated in part by the sequestration of carbon dioxide in saline aquifers. We consider cases where the height of the topography slopes upwards in the direction of the flow and is proportional to the$n\text{th} $power of the horizontal distance from a line or point source of a constant volumetric flux. In two-dimensional cases with$n\gt 1/ 2$, the current evolves from a self-similar form at early times, when the effects of variations in topography are negligible, towards a late-time regime that has an approximately horizontal upper surface and whose evolution is dictated entirely by the geometry of the topography. For$n\lt 1/ 2$, the transition between these flow regimes is reversed. We compare our theoretical results in the case$n= 1$with data from a series of laboratory experiments in which viscous glycerine is injected into an inclined Hele-Shaw cell, obtaining good agreement between the theoretical results and the experimental data. In the case of axisymmetric topography, all topographic exponents$n\gt 0$result in a transition from an early-time similarity solution towards a topographically controlled regime that has an approximately horizontal free surface. We also analyse the evolution over topography that can vary with different curvatures and topographic exponents between the two horizontal dimensions, finding that the flow transitions towards a horizontally topped regime at a rate which depends strongly on the ratio of the curvatures along the principle axes. Finally, we apply our mathematical solutions to the geophysical setting at the Sleipner field, concluding that topographic influence is unlikely to explain the observed non-axisymmetric flow.

Macropores are important components of soil hydrology. The spatial distribution of macropore flow as a proportion of saturated hydraulic conductivity was tested on six humid–temperate slopes using transects of tension infiltrometer measurements. Automated water table and overland flow monitoring allowed the timing of, and differentiation between, saturation‐excess overland flow and infiltration‐excess overland flow occurrence on the slopes to be determined and related to tension‐infiltrometer measurements. Two slopes were covered with blanket peat, two with stagnohumic gleys and two with brown earth soils. None of the slopes had been disturbed by agricultural activity within the last 20 years. This controlled the potential for tillage impacts on macropores. The proportion of near‐surface macropore flow to saturated hydraulic conductivity was found to vary according to slope position. The spatial patterns were not the same for all hillslopes. On the four non‐peat slopes there was a relationship between locations of overland flow occurrence and reduced macroporosity. This relationship did not exist for the peat slopes investigated because they experienced overland flow across their whole slope surfaces. Nevertheless, they still had a distinctive spatial pattern of macropore flow according to slope position. For the other soils tested, parts of slopes that were susceptible to saturation‐excess overland flow (e.g. hilltoes or flat hilltops) tended to have least macropore flow. To a lesser extent, for the parts of slopes susceptible to infiltration‐excess overland flow, the proportion of macropore flow as a component of infiltration was also smaller compared with the rest of the slope. The roles of macropore creation and macropore infilling by sheet wash are discussed, and it is noted that the combination of these may result in distinctive topographically controlled spatial patterns of macropore flow. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Topographic control of soil microbial activity: a case study of denitrifiers

The water mass distribution in the western Barents Sea, the thermohaline structure of the western Barents Sea Polar Front, and the local formation of a dense water mass are described on the basis of an analysis of historical hydrographic data. This study concentrated on the frontal region between Bjørnøya and Hopen Island where Arctic water is found on the Spitsbergen Bank and Atlantic water in the Bear Island Trough and Hopen Trench. The distributions of Atlantic and Arctic waters in relation to topography were consistent with the hypothesis that the location of the polar front is fixed at about the 250 m isobath by the barotropic circulation of Atlantic water within the Bear Island Trough and Hopen Trench. In winter, vertical gradients of temperature and salinity were weak throughout the frontal region, consistent with a barotropic, topographically controlled front. In summer, vertical gradients remained weak below 100 m depth but increased in the upper layer as a result of the presence of fresh, warm surface water produced by melting ice. The topographic control of thermohaline properties at the surface was disrupted by the meltwater pool, and the meltwater contributed to water mass modification in the frontal region. The following seasonal cycle of water mass formation was hypothesized: Summer heating melts the sea ice on the Spitsbergen Bank and produces the surface meltwater pool. This meltwater not only increases vertical thermohaline gradients on the bank but also crosses the front and freshens the surface layer throughout the western Barents Sea. Subsequent winter cooling, which creates ice over the bank, also forms dense water in the Bear Island Trough and Hopen Trench by convective mixing of Atlantic water and the overlying meltwater.

Globally rip currents are the primary physical hazard facing swimmers on surf beaches. However, beach swimmers also face other hazards such as large waves, tidal influenced currents, and shorebreak waves. The aim of this study was to investigate factors leading to the increased likelihood of surf lifeguard rescues. Rescue data from Surf Life Saving Queensland’s Lifesaving Incident Management System and Operations Console for 54 wave dominated beaches in South–East Queensland, Australia, from July 1st, 2016 to October 6th, 2021 was linked with wind speed and direction, air temperature, phase of tide, wave height and period, beach type, beach hazard rating, and beach swimmer numbers. Stepwise regression was performed to find independent predictors of rescue. There were 8515 rescues, with 3345 (39.3%) females and 5109 (60.0%) males (61 sex not recorded). There were no independent predictors of surf rescue but swimming outside the lifeguard patrol area was nine times more likely to result in rescue than swimming inside the patrol area. Increased rescues were noted at periods of increased rip activity. Rip currents (2992/6523, 45.8%) were the most frequently recorded contributing factor. Rescues occurred most frequently (5902, 69.3%) during the six hours of lower tide levels and during onshore winds (5463, 64.2%). Surf rescues increased with increasing wave height and period, air temperature, and wind speed but decreased as average values for each variable were surpassed. Beaches protected from the prevailing wave direction by headlands had a stronger relationship between rescues and wave height. Beaches adjacent to inlets with tidal flow had a stronger relationship between rescues and the ebb tide. Beach morphology, and hazard rating did not have a relationship with ratio of rescues per 100,000 swimmers. We found no independent predictors for surf rescue, however this study has, for the first time we believe, quantified the increased risk (× 9) posed by swimming outside the patrol area. Open beaches, beaches protected by headlands and beaches with tidal inlets all had different relationships between rescues, tides and wave size. Our findings suggest that lifeguards may need to adopt new approaches to prevent rescues adjacent to the patrol area, as well as a revision of the general hazard rating being required.

Field observation and numerical analysis of rip currents at Ten-Mile Beach, Hailing Island, China

Abstract. Wave climates are fundamental drivers of coastal vulnerability; changing trends in wave heights, periods and directions can severely impact a coastline. In a diverse storm environment, the changes in these parameters are difficult to detect and quantify. Since wave climates are linked to atmospheric circulation patterns, an automated and objective classification scheme was developed to explore links between synoptic-scale circulation patterns and wave climate variables, specifically wave heights. The algorithm uses a set of objective functions based on wave heights to guide the classification and find atmospheric classes with strong links to wave behaviour. Spatially distributed fuzzy numbers define the classes and are used to detect locally high- and low-pressure anomalies. Classes are derived through a process of simulated annealing. The optimized classification focuses on extreme wave events. The east coast of South Africa was used as a case study. The results show that three dominant patterns drive extreme wave events. The circulation patterns exhibit some seasonality with one pattern present throughout the year. Some 50–80% of the extreme wave events are explained by these three patterns. It is evident that strong low-pressure anomalies east of the country drive a wind towards the KwaZulu-Natal coastline which results in extreme wave conditions. We conclude that the methodology can be used to link circulation patterns to wave heights within a diverse storm environment. The circulation patterns agree with qualitative observations of wave climate drivers. There are applications to the assessment of coastal vulnerability and the management of coastlines worldwide.

Many coasts suffer from prevailing erosion, with them being particularly vulnerable to predicted climate change impacts, threatening coastal ecosystems, their services, infrastructures and populations. Understanding coastal morpho-sedimentary dynamics is thus essential for coastal management. However, coastal vulnerability may differ locally, depending on exposure/protection and local geological and morpho-hydrodynamical features, suggesting that a local approach to erosion risk assessment is needed to identify and understand local patterns. Digital elevation models of a 14 km long coastal stretch in northern Portugal that were extracted from aerial surveys obtained between November 2008 and February 2019 were analysed to quantify changes in shoreline position and sediment budgets, both for the whole study area and for distinct beach segments. The observed dynamics were subsequently analysed by considering prevailing wave and wind intensities and directions. Overall and during the decade analysed, the beach–dune system of the studied stretch slightly increased in volume (0.6%), although the shoreline retreated (by 1.6 m on average). Temporal variability in coastal dynamics was observed at all of the temporal scales considered—from seasons to 5-year periods—with them being related to variability in ocean and wind patterns. There was a trend from accretional to erosional conditions, with the first 5-year period showing a mean increase in the beach–dune system’s volume of 0.6% and a mean shoreline progradation of 1.5 m, followed by 5-years with 0.0% volume change and 3.1 m shoreline retreat. Locally, the dynamics were very variable, with shoreline dynamics ranging from 24.0 m regression to 51.5 m progradation, and sediment budgets from 213.8 m3 loss to 417.0 m3 gain, per segment and for the decade. Stretches with relatively stable morphologies and others with erosional or accretional trends were found, depending on the beach type, shoreline orientation and the presence of defence structures. Rocky beaches were the least dynamic and sandy beaches the most dynamic, with mean shoreline position changes of 0.0 m and −3.4 m, respectively, and mean sediment budgets of −1.1 m3 and −2.9 m3 per linear meter of coastline, respectively, for the studied decade. The observed dynamics showed how local conditions interacted with meteo-ocean conditions in shaping local morpho-sedimentary dynamics, stressing the importance of a local approach to coastal erosion monitoring and risk assessment.