Shallow Topography Research Articles

Analysis and forecasting of shoreline changes in Amurang Bay

Amurang Bay has a very high development potential with the characteristics of a sloping and shallow topography and one of the areas as the capital of the South Minahasa district which is vulnerable to changes in the coastline. This analysis is used in order to analyse the changes that occur to the coastline in Kawangkoan Bawah and to see the changes over the next 10 years. Changes in the coastline can be monitored using remote sensing satellite technology, in a multi-temporal method as the comparative method or time series image analysis (last 5 years). The data analysis technique was carried out through ArGIS software using an additional tool, named DSAS. results of analysis of shoreline changes using NSM and LRR calculations in 2017-2022. Overall, the indications are that abrasion and accretion always occur every year so that they can change the shape of the beach over the last 5 years. The speed of movement of the coastline -5.9m/year. As for the speed of retreat of the coastline is -0.37m/year. The results of observation and analysis show that the coastline of Kawangkoan Bawah Village in Teluk Amurang is basically dynamic because it is found that abrasion and accretion occur every year. Recommended further studies related to land use patterns, sea level rise, and morphological changes to the existence and sustainability of the coast. We also recommend conducting in-depth studies that rely on field measurements to include the effect of momentary water levels in shoreline position monitoring

Evaluation of CFOSAT Wave Height Data with In Situ Observations in the South China Sea

The wave spectrometer operated by the China–France Oceanography Satellite (CFOSAT) can provide global ocean wave observation data. Although a lot of work on calibration and verification has been carried out in the open oceans dominated by swells, the quality of the data in the relatively enclosed sea area with complex terrain still lacks sufficient examination. The objective of this study is to assess the performance of the significant wave height data of the CFOSAT in the South China Sea (SCS), a unique sea area characterized by semi-enclosed basin and multi-reef terrain, and to recognize the environmental factors affecting the data quality. Compared against the long-term observations from five mooring or buoy sites, we find that the data is well performed in the relatively open and deep areas of the SCS, with an average correlation coefficient as high as 0.87, and a low average root-mean-square error of 0.47 m. However, the combined effects of complex topography, monsoons, and swell proportion variation will affect the performance of data. In the southern deep areas, the waves may be affected by a large number of dotted reefs, leading to wave deformations and energy dissipation in different seasons. In the northern nearshore areas, waves tend to be sheltered by the land or distorted by the shallow topography effects. These processes make it difficult for the swell to fully develop as in the open oceans. The low proportion of swell is a disadvantage for the CFOSAT to correctly observe the wave data and may lead to possible errors. Our results emphasize the importance of more verification when applying the CFOSAT data in certain local seas, and the necessity to adjust the algorithm of inverting wave spectra according to specific environmental factors.

Exploring Influences of Shallow Topography in Stable Boundary Layers: The SAVANT Field Campaign

Abstract Stable boundary layers are still a relatively problematic component of atmospheric modeling, despite their frequent occurrence. While general agreement exists that Monin–Obukhov similarity is not applicable in the stable boundary layer (SBL) due to the nonhomogeneous, nonstationary flow, no universal organizing theory for the surface SBL has been presented. The Stable Atmospheric Variability and Transport (SAVANT) field campaign took place in the fall of 2018 to explore under what conditions shallow drainage flow is generated. The campaign took place in an agricultural setting and covered the period of both pre- and postharvest, allowing for not only a basic exploration of the boundary layer but also a robust dataset for applied agricultural understanding of aerosol dispersion and impacts of changes in surface cover on drainage flows. This article provides a description of the field campaign. Examples of publicly available data products are presented, as well as examples of shallow drainage flow and corresponding lidar measurements of dispersion. Additionally, the field campaign was used to provide educational opportunities for students from several disciplines, and the outcomes of these joint educational ventures are discussed as models for future collaborations.

Ocean circulation over the Saya de Malha Bank in the South West Indian Ocean

The Saya de Malha Bank is one of the major banks of the Mascarene Plateau in the South West Indian Ocean. It is known for its unique ecosystem, remoteness (nearest island is about 300 km away) and complex oceanographic conditions. This study presents the results of a survey conducted in May 2018 on-board the R/V Dr Fridtjof Nansen, and aims to provide a descriptive overview of the interaction of the large-scale South Equatorial Current (SEC) over the shallow Saya de Malha Bank. The analysis of the current pattern revealed a two-layered structure of the current over the shallow topography of the bank compared to the vertically rigid-structure of the SEC throughflow in its deeper region. This two-layered flow consists of a surface layer and a sub-thermocline layer. The top layer flow, carrying the lower salinity mass (Tropical Surface Water) is driven by the Ekman dynamics observed in the southern hemisphere whereas the sub-thermocline current layer is most likely governed by the tidal and internal wave dynamics generated by the topographic relief of the bank.

Iron Exports From Catchments Are Constrained by Redox Status and Topography

AbstractFe(III) hydroxides stabilize organic carbon (OC) and P in soils. Observations of rising stream Fe concentrations are controversially posited to result from a flushing of iron‐rich deeper soil layers or a decrease of competing electron acceptors inhibiting Fe reduction ( and ). Here, we argue that catchment topography constrains the release of Fe, OC, and P to streams. We therefore incubated organic topsoil and mineral subsoil and modified the availability of . We found that Fe leaching was highest in topsoil. Fe, OC, and P released at quantities proportional to their ratios in the source soil. Supply of reduced Fe leaching to 18% and increased pore water OC:Fe and P:Fe ratios. Subsoil, however, was an insignificant Fe source (<0.5%). Here, the leached quantities of Fe, OC and P were highly disproportionate to the soil source with an excess of released OC and P. We tested if experimental findings scale up using data from 88 German catchments representing gradients in concentration and topography. Average stream Fe concentrations increased with decreasing and were high in catchments with shallow topography where high groundwater levels support reductive processes and topsoils are hydrologically connected to streams; but Fe concentrations were low in catchments with steep topography where flow occurs primarily through subsoils. OC:Fe and P:Fe ratios in the streams similarly varied by and topography. This corroborates the findings from the laboratory experiment and suggests that catchment topography and competing electron acceptors constrain the formation of Fe‐reducing conditions and control the release of Fe, OC, and P to streams.

Short-Term Variability of Biological Production and CO2 System Around Dongsha Atoll of the Northern South China Sea: Impact of Topography-Flow Interaction

The short-term variabilities in temperature, salinity, nitrate, chlorophyll a (Chl a), and carbonate chemistry data (i.e., pH, partial pressure of CO2 (pCO2), total alkalinity, and dissolved inorganic carbon) were concurrently investigated in the shallow (~50 m) and deep (~300 m) water areas around Dongsha Atoll of the northern South China Sea (NSCS). The results show that surface temperature and pCO2 were lower but that upward nitrate flux and Chl a were higher in the upper euphotic zone at the shallow-water area than those at the deep-water area. We suggest that the observed contrasting biogeochemical properties between the two areas could be attributed to the impact of topography-flow interaction. As tidal currents (or any other horizontal currents) interacted with the shallow topography, they may induce vertical isotherm displacements (e.g., internal tides/internal waves) that may enhance turbulent mixing, and thus can transport more nutrient-replete subsurface water into the euphotic zone and stimulate phytoplankton production. The stimulated biological production and the cooling effect induced by topography-flow interaction may collectively drive surface pCO2 down in the shallow water area. Though the present short-term hydrological and CO2 data, which to our knowledge were concurrently investigated for the first time in the NSCS, reveal that the topography-flow interaction could be a favorable mechanism for atmospheric CO2 uptake around Dongsha Atoll, more long-term observations are still needed to confirm that the similar processes can repetitively take place in topography-flow interaction prevalent areas.

Low dissolved oxygen in the Pearl River estuary in summer: Long-term spatio-temporal patterns, trends, and regulating factors

Several large semi-enclosed seas and coastal bodies have formed seasonal hypoxic water masses over large areas. The dominant cause for such formations is believed to be the increasing inflow of nutrients from watersheds and urban areas into estuaries and coastal waters. Several studies have reported hypoxic events in the Pearl River estuary (PRE). However, hypoxia events appear to be episodic, which are neither seasonal nor estuary-wide. The reasons for such occurrences are not understood fully. The objectives of this study are to use 24-year time series data obtained during 1988–2011 to analyze the long-term variability in dissolved oxygen (DO) in summer over the entire estuary from urban areas to estuarine coastal waters and examine regulating factors for the occurrences of hypoxia. The results showed that various regulating factors were responsible for the variability of DO in different regions of the PRE. DO decreased in the urban reach, upstream and main estuarine zones of the PRE from about 2000. It was hypoxic (DO <2.0 mg L−1) in the urban reach zone and periodic low DO (DO <3.5 mg L−1) and episodic hypoxic in the upstream zone after 2000, mainly influenced by the increasing sewage discharge. The main estuarine zone experienced episodic low DO and sporadic hypoxia after 2000. The ecosystem buffering capacity was characterized by turbidity, well vertical mixing and short residence time which diluted the pressure for the formation of hypoxia. The eastern shelf appeared to be more vulnerable to hypoxia because of its deeper topography, plume front position, and stratification of the water column compared with the western shelf. Its bottom waters experienced seasonal low DO but seldom hypoxia. In comparison, low DO rarely occurred in the western shelf because of its shallow topography and short residence time. In brief, 24-year series data captured from 1988 to 2011 showed a lack of seasonal and estuary-wide hypoxia in the PRE.

Vorticity Balance off the South Shore of Oahu, Hawaii, Derived by High-Frequency Radio Doppler Current Observations

AbstractHigh-frequency radio Doppler surface current observations off the south shore of Oahu, Hawaii, are used to calculate the vorticity equation at a ~2-km spatial resolution in terms of a time-dependent and time-mean surface balance. First-order terms are mean advection of mean vorticity, vortex stretching, and a residual, which is treated as unquantified terms such as wind stress curl, bottom pressure torque, and noise. The most striking feature in the 2-yr time-mean vorticity balance is the anticorrelation between advection of vorticity and vortex stretching implying that potential vorticity (PV) advection is the most dominant mechanism in the area. Several terms in the depth-integrated vorticity balance were also estimated. The bottom pressure torque acts as a first-order term only in areas of shallow topography. A PV analysis resulted in the 50-m Penguin Bank steering the westward Hawaiian Lee Current.

First Evidence of Coherent Bands of Strong Turbulent Layers Associated with High-Wavenumber Internal-Wave Shear in the Upstream Kuroshio

The upstream Kuroshio flows through Okinawa Trough and the Tokara island chain, the region near the continental shelf of the East China Sea and shallow seamounts, where the Kuroshio can induce strong mixing over the shallow topography. Also, tidal currents over the rough topography may produce internal tides, and associated turbulence. The previous observations show energetic high vertical wavenumber near-inertial wave shear in the Kuroshio thermocline, which implies strong turbulent mixing. However, direct turbulence measurements in this region are very scarce. Using high lateral resolution (1–2 km) direct turbulence measurements, we show here, for the first time, that strong turbulent layers form spatially coherent banded structures with lateral scales of >O(10 km), associated with bands of near-inertial wave/diurnal internal tide shear of high vertical wavenumber in the upstream Kuroshio. The turbulent kinetic energy dissipation rates within these turbulent layers are >O(10−7 W kg−1), and estimated vertical eddy diffusivity shows >O(10−4 m2 s−1) on average. These results suggest that the high vertical wavenumber near-inertial waves propagating in the upstream Kuroshio could have large impacts on the watermass modifications, momentum mixing, nutrient supply, and associated biogeochemical responses in its downstream.

Mapping the mantle transition zone beneath Hawaii from Ps receiver functions: Evidence for a hot plume and cold mantle downwellings

Hawaii is the archetypal example of hotspot volcanism. Classic plume theory suggests a vertical plume ascent from the core–mantle boundary to the surface. However, recently it has been suggested that the plume path may be more complex. Determining the exact trajectory of the Hawaiian plume seismic anomaly in the mantle has proven challenging. We determine P-to-S (Ps) receiver functions to illuminate the 410- and 660-km depth mantle discontinuities beneath the Hawaiian Islands using waveforms recorded on land and ocean-bottom seismometers, applying new corrections for tilt and coherence to the ocean bottom data. Our 3-D depth-migrated maps provide enhanced lateral resolution of the mantle transition zone discontinuities. The 410 discontinuity is characterised by a deepened area beneath central Hawaii, surrounded by an elevated shoulder. At the 660 discontinuity, shallow topography is located to the north and far south of the islands, and a deep topographic anomaly is located far west and east. The transition zone thickness varies laterally by ±13 km depth: thin beneath north-central Hawaii and thick farther away in a horseshoe-like feature. We infer that at 660-km depth a broad or possibly a double region of upwelling converges into a single plume beneath central Hawaii at 410-km depth. As the plume rises farther, uppermost mantle melting and flow results in the downwelling of cold material, down to at least 410 km surrounding the plume stem. This result in the context of others supports complex plume dynamics including a possible non-vertical plume path and adjacent mantle downwellings.

The post-Duluth Interval revisited

Abstract Recent work has identified two post-Duluth Interval events not previously reported: a minor glacial readvance, with its newly recognized end moraine, and a possible jokulhlaup associated with catastrophic flooding. In addition progress has been made refining isobase trends for the post-Duluth Interval. Also, the position of the earliest Lake Minong shoreline along the northern rim of the central Upper Peninsula has been identified and its relationship to the highest Minong shorelines in eastern and western Superior basin clarified. Green-spectrum LiDAR data were used to map the shallow water bottom topography of Lake Superior between Munising and Marquette, Michigan. These maps reveal three newly-discovered ice-marginal channels graded to Lake Minong. Together with previously reported sub-aerial channels, these channels have been instrumental in refining our understanding of early Lake Minong in the south central Superior basin.

Analysis of current–topography interaction in remote sensing imaging procedures for shallow water topography

Underwater topography can be imaged using remote sensing methods. Numerous studies have been conducted to understand the imaging mechanism of shallow water topography. However, current–topography interaction constitutes the weakest link in the remote sensing imaging mechanism of underwater topography. In addition, few studies focused on different topography patterns. Current velocity is highly correlated with bathymetry, and velocity gradient is used as an indicator of sea surface roughness. In this research, we analyzed the distribution characteristics of current velocity and velocity gradient in different cases using a 3-dimensional (3-D) hydrodynamic model to discuss the current–topography interaction part of the remote sensing imaging mechanism, especially the modulation by current parallel or normal to the underwater topography, both positive and negative. Results showed remarkable agreement between 3-D current analysis and surface velocity analysis. Parallel and normal currents had different responses to different topography types. The distribution of surface current gradient showed opposite features over negative and positive topography in parallel and normal current fields. This can be used to distinguish negative topography from positive topography with different current directions to a certain extent.

Modeling glacial flow on and onto Pluto’s Sputnik Planitia

Observations of Pluto’s surface made by the New Horizons spacecraft indicate present-day N2 ice glaciation in and around the basin informally known as Sputnik Planitia. Motivated by these observations, we have developed an evolutionary glacial flow model of solid N2 ice that takes into account its published thermophysical and rheological properties. This model assumes that glacial ice flows laminarly and has a low aspect ratio which permits a vertically integrated mathematical formulation. We assess the conditions for the validity of laminar N2 ice motion by revisiting the problem of the onset of solid-state buoyant convection of N2 ice for a variety of bottom thermal boundary conditions. Subject to uncertainties in N2 ice rheology, N2 ice layers are estimated to flow laminarly for thicknesses less than 400–1000 m. The resulting mass-flux formulation for when the N2 ice flows as a laminar dry glacier is characterized by an Arrhenius–Glen functional form. The flow model developed is used here to qualitatively answer some questions motivated by features we interpret to be a result of glacial flow found on Sputnik Planitia. We find that the wavy transverse dark features found along the northern shoreline of Sputnik Planitia may be a transitory imprint of shallow topography just beneath the ice surface suggesting the possibility that a major shoreward flow event happened relatively recently, within the last few hundred years. Model results also support the interpretation that the prominent darkened features resembling flow lobes observed along the eastern shoreline of the Sputnik Planitia basin may be the result of a basally wet N2 glacier flowing into the basin from the pitted highlands of eastern Tombaugh Regio.

A Hybrid Chemo-/Grapho-Epitaxial Alignment Strategy for Defect Reduction in Sub-10 nm Directed Self-Assembly of Silicon-Containing Block Copolymers

The directed self-assembly (DSA) of a 20 nm full-pitch silicon-containing block copolymer (BCP), poly(4-methoxystyrene-b-4-trimethylsilylstyrene), was performed using a process that produces shallow topography for hybrid chemo-/grapho-epitaxy. This hybrid process produced DSA with fewer defects than the analogous conventional chemo-epitaxial process, and the resulting DSA was also more tolerant of variations in process parameters. Cross-sectional scanning transmission electron microscopy (STEM) with electron energy loss spectroscopy (EELS) confirmed that BCP features spanned the entire film thickness on hybrid process wafers. Both processes were implemented on 300 mm wafers initially prepatterned by 193 nm immersion lithography, which is necessary for economic viability in high-volume manufacturing. Computational analysis of DSA extracted from top-down SEM images demonstrates the influence of process parameters on DSA, facilitating the optimization of guide stripe width, guide stripe pitch, and prepattern...

Inverse methods to gradient etch three-dimensional features with prescribed topographies using abrasive jet micro-machining: Part I – Modeling

Abrasive jet micro-machining (AJM) can be used to machine a wide range of features on the micro-scale. Given a set of process parameters, surface evolution models capable of predicting the shape of straight, constant-depth channels in a wide variety of materials are well-established. This paper presents a novel framework for solving the unaddressed more challenging and industrially relevant inverse problem of determining the erosive source traverse velocity and path required to machine a particular user-specified feature topography. It is shown that the problem can be expressed as a Fredholm integral equation of the first kind where, for a given desired topography, the source erosive efficacy is a difference kernel, and the unknown function to be determined is the dependency of the instantaneous source velocity on its location. For Gaussian sources typical of AJM, an analytical solution based on the Gaussian transform is presented that can be used for a wide range of desired topographies. For non-Gaussian sources, an approximate approach based on a point-source solution is suggested, and its accuracy is discussed. Once the velocity function to create the desired shallow topography has been determined, it can be used in existing surface evolution models to predict the shape at any depth. The methodologies are demonstrated to be applicable for the AJM of constant depth micro-channels with user-specified cross-sectional shape, gradient etched micro-channels with specified texture along their length, and pockets with texture in two perpendicular directions. The accompanying paper validates the methodology by comparison with measured three-dimensional profiles arising from the predicted velocity functions. The study is the first to consider the inverse problem for AJM, and to demonstrate the ability to etch and predict user specified three-dimensional topographies.

Linear long wave propagation over discontinuous submerged shallow water topography

The dynamics of an isolated long wave passing over underwater obstacles are discussed in this paper within the framework of linear shallow water theory. Areas of practical application include coastal defense against tsunami inundation, harbor protection and erosion prevention with submerged breakwaters, and the construction and design of artificial reefs to use for recreational surfing. Three sea-floor configurations are considered: an underwater shelf, a flat sea-floor with a single obstacle, and a series of obstacles. A piecewise continuous coefficient is used to model the various sea-floor topographies. A simple and easily implementable numerical scheme using explicit finite difference methods is developed to solve the discontinuous partial differential equations. The numerical solutions are verified with the exact analytical solutions of linear wave propagation over an underwater shelf. The scope of this simplified approach is determined by comparison of its results to those of another numerical solution and wave transmission and reflection coefficients from experimental data available in the literature. The efficacy of approximating more complicated continuous underwater topographies by piecewise constant distributions is determined. As an application, a series of underwater obstacles is implemented.

Interaction of aquifer–wetland in a zone of intensive agriculture: the case of Campo de Dalías (Almería, SE Spain)

The Campo de Dalias (Almeria, south-eastern Spain) was the backdrop for the development of intensive agricultural activity during the 1970s. Due to the poor natural soil development, the agriculturalists opted for a system that involved quarrying silt and clay deposits that could be used as soil in the greenhouses. In parallel, poor water quality in the upper aquifer caused the gradual abandonment of boreholes and a generalised rise in piezometric levels. These factors have favoured the formation of a series of artificial wetlands in the abandoned clay pits (Onayar, Cabriles and Balsa del Sapo (“Toad Pond”) being the most significant). In Balsa del Sapo, the water column rose 3.5 m between October 2007 and February 2011. There has been a continuous fall in the electrical conductivity of the surface water, which has gone from 14,500 µS cm−1 in 2004 to 4,100 µS cm−1 in 2013. The most recent concentrations are close to those found in the groundwater. The same situation is detected for Cl, SO4 and Na ion concentrations in the surface and groundwater. These data show the groundwater–surface water interaction in the Balsa del Sapo. Nevertheless, the sharp rise in surface water level has created a flood hazard (due to the shallow topography of the area), both for people living in the vicinity and their property. This is an endorheic zone where a number of ramblas (gullies) draining the southern face of the Sierra de Gador mountains converge. The Campo de Dalias is a spectacular example of the changes that can occur in a semiarid agricultural area as a result of intensive groundwater abstraction. These changes are directly related to the management of water resources, the most recent consequence of which is the increased risk of flooding. Hence, there is a need to consider the management of these water resources to achieve a more sustainable use, which is compatible with the environmental protection of the wetland and which will give some guarantee of flood protection for people and property.

Summer nitrogenous nutrient transport and its fate in the Taiwan Strait: A coupled physical‐biological modeling approach

In order to understand the fate of nutrients in the Taiwan Strait during summer, we built a coupled physical‐biological numerical ocean model, which can capture the basic hydrographic and biological features within the strait. The nutrient that we chose to model is dissolved inorganic nitrogen (DIN). The model includes individual reservoirs for nitrate (NO3) and ammonium (NH4). Both the observational evidence and model results show that NO3 in the strait originates primarily from the upwelling subsurface water in the northern South China Sea (SCS) that enters the strait via the eastern and western routes separated by the Taiwan Bank. The coupled physical and biological effects on the NO3 transport at these two routes are highlighted in the study. For the western route, the shallow topography and the coastal upwelling intensify the biological uptake of NO3 in the whole water column. Consequently, the nitrogenous contribution by this route is mainly in form of the particulate organic nitrogen (PON). In contrast, NO3 is transported conservatively below the nitricline at the deep eastern route, contributing the whole NO3 supply in the TWS. The model estimates the fluxes of DIN and PON into the TWS, from the northern SCS, are 1.8 and 4 kmol s−1, respectively. Over half (∼1 kmol s−1) of the DIN is synthesized into PON by the phytoplankton in the strait. Overall, this study estimates the physical and biological effects on the nutrient transport in the TWS during summer.

Storm surge and tidal interaction in the Tjeldsund channel, northern Norway

The aim of this study is to investigate tide–surge interaction in narrow channels with complex and relatively shallow topography. A high-resolution depth-integrated tidal and storm surge model has been implemented for the Tjeldsund channel which is an important sailing lane in northern Norway. A horizontal grid resolution down to 50 m is applied in order to represent the complex bottom topography and the formation of jets and small-scale eddies. Two typically storm surge events in December 2004 have been examined in detail. The tide–surge interaction is found to influence the generation of higher harmonics and the formation of eddies in the current field. In some cases, the magnitude of storm surge currents may reach the same magnitude as the tidal currents enhancing the formation of jets and eddies.

Numerical Investigations of Convective Initiation in Barbados

Localized convection in Barbados accounts for hazardous conditions and a significant percentage of the island’s annual rainfall. The feature results in rainfall accumulations exceeding 50 mm in 3 hours or less, over isolated locations. Weather Research and Forecasting model (WRF) simulations are conducted for a rapid convective initiated and heavy precipitation event of 26 August 2008 over Barbados. The simulation results from the 1 km grid resolution domain depict that the shallow topography on the island plays a significant role in enhancing convective activity under weak synoptically disturbed conditions. The model results also demonstrate that the driving forces for the development of deep convective clouds include low-level moisture convergence that form as a result of the temperature differential between the land and the ocean and forced low-level uplift as a result of the blocking by the topography. The high-resolution WRF simulations demonstrate its capability to accurately capture the low-level flow over the island, as well as the orientation of the divergence and convergence patterns throughout the depth of the atmosphere. These results are heartening to use the WRF as a resource for studying deep convection in Barbados for disaster managers and water resource managers.