scholarly journals Natural and Human-Induced Flow and Sediment Transport within Tidal Creek Networks Influenced by Ocean-Bay Tides

Water ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1493 ◽  
Author(s):  
Carmen Zarzuelo ◽  
Andrea D’Alpaos ◽  
Luca Carniello ◽  
Alejandro López-Ruiz ◽  
Manuel Díez-Minguito ◽  
...  
Keyword(s):  
Salt Marshes ◽  
Bottom Topography ◽  
Open Ocean ◽  
Tidal Asymmetry ◽  
Linear Interaction ◽  
Tidal Waves ◽  
Future Challenges ◽  
Cadiz Bay ◽  
Tidal Constituents ◽  
Set Up

Improving current understanding of hydrodynamics and sediment dynamics in complex tidal embayments is of major importance to face future challenges derived from climate change and increasing human pressure. This work deepens the knowledge of the hydro-morphodynamics of complex creek networks that connect basins with different characteristics, identifying their morphodynamic trends and the potential impacts of channel deepening. We selected two tidal creeks which flow through salt marshes and tidal flats of the Cádiz Bay (SW Spain) in a singular network due to their double connection to the Atlantic Ocean and the inner bay. We study the interactions between tidal waves that penetrate into the creeks from these two different bodies of water, analyzing the tidal asymmetry and the morphodynamic tendencies of the system. For the analysis, we set up a hydro-morphodynamic model specifically developed for areas with very shallow and complex channels. Results show that the tidal wave penetrates within the tidal network both from the inner Bay and the open ocean with different amplitudes, phases and flow velocities. There is also an asymmetric pattern for the tidal flows caused by the deformation of the dominant astronomical tidal constituents, M2 and M4, due to the non-linear interaction of tidal currents with the irregular creek geometry and bottom topography. Tidal asymmetry promotes the progressive infilling of the area where the tidal waves meet closing the connection between the open ocean and the inner bay, such an infilling trend being accelerated by human interventions.

scholarly journals Model Based Assessment of the Reflection Behavior of Tidal Waves at Bathymetric Changes in Estuaries

Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 489
Author(s):  
Vanessa Sohrt ◽  
Sebastian S.V. Hein ◽  
Edgar Nehlsen ◽  
Thomas Strotmann ◽  
Peter Fröhle
Keyword(s):  
Cross Sectional ◽  
High Agreement ◽  
Tidal Waves ◽  
Level Data ◽  
Water Level Data ◽  
Abrupt Changes ◽  
Water Effects ◽  
Potential Impact ◽  
Tidal Constituents ◽  
Harmonic Components

Estuaries are often modified by human activities. Adjustments in the morphology of an estuary have a potential impact on the hydrodynamics and on the reflection behavior of the tide. The influence of such system changes on the complex tidal regime with a large number of superimposed tidal constituents is not fully understood yet. The reflection properties of estuaries that are characterized by abrupt changes in geometry are systematically investigated on the basis of simplified estuary model approaches to improve the understanding of the oscillation and reflection behavior of tidal waves in estuaries. The reflection coefficients at abrupt cross-sectional changes are determined by two different methods, i.e., an analytical energy-based approach and a hydrodynamic numerical (HN) model. Comparisons indicate a high agreement of the results of the different methods when evaluating the reflection coefficient. The tidal constituents are reflected at partial and total reflectors and amplified by shoaling depending on the water depths, the height of the bottom step and the horizontal constriction. A harmonic analysis of simulated water level data partly shows the formation and amplification of higher harmonic components as a result of shallow water effects. The interaction with reflectors results in an increasing amplification of the tidal constituents and the tide.

scholarly journals Global Observations of Open-Ocean Mode-1 M2 Internal Tides

2016 ◽  
Vol 46 (6) ◽  
pp. 1657-1684 ◽  
Author(s):  
Zhongxiang Zhao ◽  
Matthew H. Alford ◽  
James B. Girton ◽  
Luc Rainville ◽  
Harper L. Simmons
Keyword(s):  
Energy Loss ◽  
Internal Tide ◽  
Field Measurements ◽  
Open Ocean ◽  
Internal Tides ◽  
Global Integration ◽  
Tidal Waves ◽  
Topographic Features ◽  
Midocean Ridges ◽  
The Pacific

AbstractA global map of open-ocean mode-1 M2 internal tides is constructed using sea surface height (SSH) measurements from multiple satellite altimeters during 1992–2012, representing a 20-yr coherent internal tide field. A two-dimensional plane wave fit method is employed to 1) suppress mesoscale contamination by extracting internal tides with both spatial and temporal coherence and 2) separately resolve multiple internal tidal waves. Global maps of amplitude, phase, energy, and flux of mode-1 M2 internal tides are presented. The M2 internal tides are mainly generated over topographic features, including continental slopes, midocean ridges, and seamounts. Internal tidal beams of 100–300 km width are observed to propagate hundreds to thousands of kilometers. Multiwave interference of some degree is widespread because of the M2 internal tide’s numerous generation sites and long-range propagation. The M2 internal tide propagates across the critical latitudes for parametric subharmonic instability (28.8°S/N) with little energy loss, consistent with the 2006 Internal Waves across the Pacific (IWAP) field measurements. In the eastern Pacific Ocean, the M2 internal tide loses significant energy in propagating across the equator; in contrast, little energy loss is observed in the equatorial zones of the Atlantic, Indian, and western Pacific Oceans. Global integration of the satellite observations yields a total energy of 36 PJ (1 PJ = 1015 J) for all the coherent mode-1 M2 internal tides. Finally, satellite observed M2 internal tides compare favorably with field mooring measurements and a global eddy-resolving numerical model.

The time-varying characteristics in tidal duration asymmetry

2020 ◽  
Author(s):  
Guo Wenyun ◽  
Song Dehai ◽  
Guo Leicheng ◽  
Ge Jianzhong ◽  
Ding Pingxing ◽  
...  
Keyword(s):  
Neap Tide ◽  
Spring Tide ◽  
Time Variability ◽  
Tidal Asymmetry ◽  
Water Effect ◽  
The Changjiang Estuary ◽  
Tidal Constituents ◽  
Sea Area ◽  
Tide Interaction ◽  
Shallow Water Effect

<p>Tides always behaves different rising and falling durations, which can mostly attribute to the shallow-water effect and interactions among tidal constituents. The duration asymmetry may lead to an inequality in flood/ebb tidal current magnitudes, affecting the net sediment transport. Tidal duration asymmetry has time-dependent characteristics. We deducted a general framework for identifying the time-variability in tidal duration asymmetry. The application to the global tides showed that the fortnightly variability in tidal asymmetry is universal and that duration asymmetry can be stronger during neap tide than during spring tide. Then the framework is applied to the tides in the Changjiang Estuary. Prominent seasonal variation in tidal asymmetry is revealed, mainly relate to the river-tide interaction. Application to the tides in the Yangshan Harbor sea area revealed that the local-scale tidal asymmetry can be changed strongly by a large coastal engineering.</p>

scholarly journals On the Generation of Bottom-Trapped Internal Tides

2015 ◽  
Vol 45 (2) ◽  
pp. 526-545 ◽  
Author(s):  
Saeed Falahat ◽  
Jonas Nycander
Keyword(s):  
Energy Density ◽  
Energy Flux ◽  
General Circulation ◽  
Bottom Topography ◽  
Vertical Mixing ◽  
Internal Tides ◽  
The Arctic ◽  
Linear Wave ◽  
Tidal Constituent ◽  
Tidal Constituents

AbstractThe interaction of the barotropic tide with bottom topography when the tidal frequency ω is smaller than the Coriolis frequency f is examined. The resulting waves are called bottom-trapped internal tides. The energy density associated with these waves is computed using linear wave theory and vertical normal-mode decomposition in an ocean of finite depth. The global calculation of the modal energy density is performed for the semidiurnal M2 tidal constituent and the two major diurnal tidal constituents K1 and O1. An observationally based decay time scale of 3 days is then used to transform the energy density to energy flux in units of watts per square meter. The globally integrated energy fluxes are found to be 1.99 and 1.43 GW for the K1 and O1 tidal constituents, respectively. For the M2 tidal constituent, it is found to be 1.15 GW. The Pacific Ocean is found to be the most energetic basin for the bottom-trapped diurnal tides. Two regional estimates of the bottom-trapped energy flux are given for the Kuril Islands and the Arctic Ocean, in which the bottom-trapped waves play a role for the tidally induced vertical mixing. The results of this study can be incorporated into ocean general circulation models and coupled climate models to improve the parameterization of the vertical mixing induced by breaking of the internal tides.

scholarly journals Effects of large macropores on soil evaporation in salt marshes

2020 ◽  
Author(s):  
Tingzhang Zhou ◽  
Pei Xin ◽  
Jirka Jirka Šimůnek
Keyword(s):  
Water Flow ◽  
Salt Marshes ◽  
Evaporation Rate ◽  
Preferential Flow ◽  
Soil Surface ◽  
Soil Evaporation ◽  
Infrared Light ◽  
Soil Conditions ◽  
Set Up ◽  
The Impact

<p>The occurrence of macropores in salt marsh sediments is a natural and ubiquitous phenomenon. Although they are widely assumed to significantly affect water flow in salt marshes, the effects are not well understood. We conducted physical laboratory experiments and numerical simulations to examine the impact of macropores on soil evaporation. Soil columns packed with either sand or clay and with or without macropores were set up with water tables in the columns set at different levels. A high potential evaporation rate was induced by infrared light and a fan. The results showed that in the soil with a low saturated hydraulic conductivity (and thus a low transport capacity), macropores behaved as preferential flow paths, delivering water from the groundwater towards the soil surface and maintaining a high evaporation rate in comparison with the soil without macropores. This effect was more pronounced for sediments with lower hydraulic conductivities and shallower groundwater tables. These results not only improve our understanding of water flow and soil conditions in salt marshes but also shed light on soil evaporation in other hydrological systems.</p>

scholarly journals Experiences with Occupational Pensions in Denmark

2019 ◽  
Vol 88 (1) ◽  
pp. 11-30
Author(s):  
Svend E. Hougaard Jensen ◽  
Torben Möger Pedersen ◽  
Tove Birgitte Foxman
Keyword(s):  
Pension System ◽  
Wage Bargaining ◽  
Legislative Process ◽  
Occupational Pension ◽  
Bargaining Process ◽  
Future Challenges ◽  
Private And Public ◽  
Collective Wage Bargaining ◽  
The Government ◽  
Set Up

Summary: This paper focuses on the development of the funded, occupational pension (OP) system in Denmark. Launched in 1987, as a grand agreement between social partners backed by the government, and as part of the collective wage bargaining process, the Danish OP system differs from the set-up in most other countries, where OP schemes typically have been introduced as part of the legislative process. The OP schemes, being a major component of the overall Danish pension system, have attracted a lot of international attention in recent years and play a key role behind the system’s success with respect to achieving satisfactory coverage, providing high replacement rates and not least, for keeping fiscal policy on a sustainable path. Finally, the paper discusses a number of future challenges, mainly related to the interaction between private and public pensions in a welfare state.

scholarly journals A Plasticity Theory Approach to the Steady-State Shape of a Three-Dimensional Ice Sheet

1982 ◽  
Vol 28 (100) ◽  
pp. 431-455 ◽  
Author(s):  
Niels Reeh
Keyword(s):  
Steady State ◽  
Flow Pattern ◽  
Bottom Topography ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Theory Approach ◽  
Ice Streams ◽  
Perfectly Plastic ◽  
Set Up

AbstractThe differential equation determining the elevations of a perfectly plastic three-dimensional steady-state ice sheet is set up. Analytical solutions of the equation are obtained in two simple case, (1) an ice sheet on a horizontal base with an arbitrary edge curve, and (2) an ice sheet on a plane sloping base with a rectilinear ice margin. The solutions are discussed, particularly with reference to the development of ice divides and ice streams.For arbitrary base and ice-margin geometries, solutions are obtained by means of the method of characteristics, which reduces the problem to solving simultaneously three ordinary first-order differential equations. The integration, which is performed by numerical methods, is generally commenced at the ice margin, where the necessary boundary conditions are known.The method has been applied to model the elevation contours and the flow pattern of the central Greenland ice sheet, using the bottom topography revealed by radio echo soundings and the present ice margin geometry. The result is in surprisingly good agreement with our knowledge of the ice-sheet topography and flow pattern, all significant ice divides and ice streams being reproduced. This suggests, that the method can be applied to model the shape and flow pattern of ice sheets under glacial conditions, using information about former ice-margin positions.

First Application of Micro Coiled Tubing in Indonesia at Offshore Mahakam

2021 ◽  
Author(s):  
Rantoe Marindha ◽  
Pratika Siamsyah Kurniawati ◽  
Gerardus Pancawisna ◽  
Reyhan Hidayat ◽  
Gitani Tsalitsah Dahnil ◽  
...  
Keyword(s):  
Cost Saving ◽  
Time Frame ◽  
Micro Ct ◽  
Safety Issues ◽  
Coiled Tubing ◽  
Start Up ◽  
Future Challenges ◽  
Ct System ◽  
Set Up ◽  
Conventional Ct

Abstract In order to answer the future challenges associated with offshore logistics, minimalist platform and job simplicity, smaller footprint of coiled tubing set is required for pumping job. Although coiled tubing (CT) is one of the most efficient deployment method for multiple wellsite operations and various objectives. Often it is difficult to capture all the benefits of its application in some offshore wells. Limited crane capacity and deck space at the platform often provide challenges to efficiently execute a CT operation. Minimalist and crowded platforms may not allow conducive condition to set up a conventional CT system. As part of continuous improvement in Well Intervention, smaller size of CT called Micro CT is deployed to unload the completion fluid using nitrogen pumping. This is to provide sufficient drawdown prior to clean up or perforation jobs. Micro CT is a small coiled tubing typically with 1" outside diameter and 10,000 ft length. It is approximately half the weight and a third smaller compared to the conventional CT. The start-up project of 1st Micro CT job in Indonesia is commenced with unloading Job in Bekapai and South Mahakam wells. Five (5) unloading job are successfully performed within allocated time frame and budget. There were no major safety issues recorded. Total of 60% cost saving was generated from the reduced mobilization trips of supply boat while 40% cost saving is from improved diesel consumption efficiency. From operational aspect, less annular friction can be achieved and led save up to 35% in N2 consumption. Moreover, it saves10 – 20% rig up time in comparison to conventional CT. On top of that, those 5 unloading jobs was completed with liquid unloading efficiency of more than 70% from the target. This paper will elaborate the experience of an Asset Operator in deploying 1st Micro CT application safely and will discuss in detail some of the measurable milestone achievement from the project.

Forecasting landslide at slope-scale: past achievements, present challenges and future perspectives

2020 ◽  
Author(s):  
Emanuele Intrieri ◽  
Tommaso Carlà ◽  
Giovanni Gigli ◽  
Nicola Casagli
Keyword(s):  
Applied Mathematics ◽  
Warning System ◽  
Open Pit ◽  
Economic Losses ◽  
Open Pit Mines ◽  
Recent Advancement ◽  
Future Challenges ◽  
Set Up ◽  
The Stability ◽  
Kinematics Parameters

<p>In general, the most reliable parameters to forecast the occurrence of a landslide are kinematics parameters, such as displacement, velocity and acceleration, since they represent the direct indicator of the stability conditions of a slope. Despite recent advancement in satellite interferometry, the highest temporal resolution, necessary to set up an effective early warning system, are still achievable from ground-based instrumentation.</p><p>Within this framework a few methods to forecast the time of failure of landslides at slope-scale have been developed in the last decades and, in many instances, they have been successfully used to prevent casualties and economic losses.</p><p>Common applications include public safety situations and open-pit mines, for which accurate warnings are crucial to protect workers and at the same time avoid unnecessary interruptions of the extraction activities.</p><p>In this work, a review of the most relevant kinematics-based forecasting methods is presented. Some examples are shown to illustrate the respective advantages, limitations and range of applicability of each method. Future challenges, trends and opportunities provided by technological innovations and scientific advances, also in related fields such as Material Science and Applied Mathematics, are also presented.</p>

Challenges in Deep Water Experiments: Hybrid Approach

2002 ◽  
Vol 124 (2) ◽  
pp. 90-96 ◽  
Author(s):  
Carl Trygve Stansberg ◽  
Harald Ormberg ◽  
Ola Oritsland
Keyword(s):  
Deep Water ◽  
Experimental Verification ◽  
Hybrid Methods ◽  
Hybrid Approach ◽  
Offshore Structures ◽  
Future Challenges ◽  
On Line ◽  
Set Up

An overview of challenges within hydrodynamic verification of deep-water offshore structures is given first. The role of model testing in the verification, as well as a range of relevant measured responses, are discussed. Various solutions for experimental verification of deep-water structures are considered. In particular, the combination of model tests with truncated set-up and computer simulations—the hybrid approach—is discussed. Two basic groups of hybrid methods are identified: Active (on-line) and passive (off-line). Most published works are on passive systems, of which a particular method is described. Case study examples with this procedure are reviewed and discussed, and future challenges are commented.

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