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51.
Ocean Dynamics - A new approach for analysis of spatiotemporal variability across ocean basins was tested using global 1° × 1° monthly sea level reconstruction (RecSL)... 相似文献
52.
Ocean Dynamics - A regional numerical ocean model of the Gulf Stream (GS) and the US East Coast was used to conduct sensitivity experiments of the dynamic response to temperature anomalies... 相似文献
53.
Can the Gulf Stream induce coherent short-term fluctuations in sea level along the US East Coast? A modeling study 总被引：1，自引：1，他引：0
Tal Ezer 《Ocean Dynamics》2016,66(2):207-220
54.
Predicting gully initiation at catchment scale was done previously by integrating a geographical information system (GIS) with physically based models, statistical procedures or with knowledge‐based expert systems. However, the reliability and validity of applying these procedures are still questionable. In this work, a data mining (DM) procedure based on decision trees was applied to identify areas of gully initiation risk. Performance was compared with the analytic hierarchy process (AHP) expert system and with the commonly used topographic threshold (TT) technique. A spatial database was used to test the models, composed of a target variable (presence or absence of initial points) and ten independent environmental, climatic and human‐induced variables. The following findings emerged: using the same input layers, DM provided better predictive ability of gully initiation points than the application of both AHP and TT. The main difference between DM and TT was the very high overestimation inherent in TT. In addition, the minimum slope observed for soil detachment was 2°, whereas in other studies it is 3°. This could be explained by soil resistance, which is substantially lower in agricultural fields, while most studies test unploughed soil. Finally, rainfall intensity events >62.2 mm h‐1 (for a period of 30 min) were found to have a significant effect on gully initiation. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
55.
A new method of integrating satellite remote sensing data and inundation models allows the mapping of extensive tidal mudflats
in a sub-Arctic estuary, Cook Inlet (CI), Alaska. The rapid movement of the shorelines in CI due to the large tides (~10 m
range) is detected from a series of Landsat imagery taken at different tidal stages, whereas GIS tools are used to identify
the water coverage in each satellite image and to extract the coordinates of the shoreline. Then, water level along the shoreline
for each satellite image is calculated from the observed water level at Anchorage and the statistics of an inundation model.
Several applications of the analysis are demonstrated: 1. studying the dynamics of a tidal bore and the flood/ebb processes,
2. identifying climatic changes in mudflats morphology, and 3. mapping previously unobserved mudflat topographies in order
to improve inundation models. The method can be used in other regions to evaluate models and improve predictions of catastrophic
floods such as those associated with hurricane storm surges and tsunamis. 相似文献
56.
Effects of vegetation on channel morphodynamics: results and insights from laboratory experiments 总被引：1，自引：0，他引：1
A series of laboratory experiments demonstrates that riparian vegetation can cause a braided channel to self‐organize to, and maintain, a dynamic, single‐thread channel. The initial condition for the experiments was steady‐state braiding in non‐cohesive sand under uniform discharge. From here, an experiment consisted of repeated cycles alternating a short duration high flow with a long duration low flow, and uniform dispersal of alfalfa seeds over the bed at the end of each high flow. Plants established on freshly deposited bars and areas of braidplain that were unoccupied during low flow. The presence of the plants had the effect of progressively focusing the high flow so that a single dominant channel developed. The single‐thread channel self‐adjusted to carry the high flow. Vegetation also slowed the rate of bank erosion. Matching of deposition along the point bar with erosion along the outer bend enabled the channel to develop sinuosity and migrate laterally while suppressing channel splitting and the creation of new channel width. The experimental channels spontaneously reproduced many of the mechanisms by which natural meandering channels migrate and maintain a single dominant channel, in particular bend growth and channel cutoff. In contrast with the braided system, where channel switching is a nearly continuous process, vegetation maintained a coherent channel until wholesale diversion of flow via cutoff and/or avulsion occurred, by which point the previous channel tended to be highly unfavorable for flow. Thus vegetation discouraged the coexistence of multiple channels. Varying discharge was key to allowing expression of feedbacks between the plants and the flow and promoting the transition from braiding to a single‐thread channel that was then dynamically maintained. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
57.
Reinforced soil walls commonly include facing elements which affect the mechanical behavior of the system. However, the design procedures involved in the existing codes and manuals (e.g. FHWA, BS8006, AASHTO, etc.) do not consider the structural contribution of the facing to the wall stability. Recently, a new computer based method for the analysis of reinforced soil walls which takes into account the interaction between the facing and the soil reinforcement layers was presented [Klar A and Sas T. Rational approach for the analysis of segmental reinforced soil walls based on kinematic constraints. Geotextiles and Geomembranes 2009;27:332-340]. This method demands full compatibility between the reinforcement layers and the deforming wall, and is solved as an optimization problem on this constraint. This kinematic compatibility (KC) method entails several assumptions regarding the interaction between the three components of the system (soil, wall, and reinforcement). This paper compares the KC method to a more rigorous continuum analysis. Results show that the KC method is capable of replicating the behavior of the more rigorous system, with a good agreement on both the value of maximum tensile forces in the reinforcement and shear and bending moment distributions along the wall. The KC method has a certain advantage over continuum methods, such as finite element or finite difference, since it requires limited input data that can easily be obtained from field tests. 相似文献
58.
The sigma coordinate, Princeton Ocean Model (POM) has been configured for the North Atlantic Ocean between 5°N and 50°N as part of data assimilation, model predictability and intercomparison studies. The model uses a curvilinear orthogonal grid with higher resolution in the western North Atlantic and lower resolution in the eastern North Atlantic. A series of experiments, each one of a 10-year duration, are performed to evaluate the sensitivity of the ocean mean state and variability to model parameters and model configuration; these experiments include open vs. closed boundary conditions, low vs. high resolution grids, and different choices of diffusion and viscosity. The results show that the use of closed boundaries together with near-boundary buffer zones where temperature and salinity are relaxed towards the observed values give less realistic flows, weaker recirculation gyres and less realistic Gulf Stream separation than do open boundary conditions. The experiments show that the sensitivity of the ocean variability in the model to the choice of the Smagorinsky diffusion and viscosity coefficients significantly differs from one region to another and largely depends on other attributes such as the mean position of the Gulf Stream in each simulation. A 50% change in model resolution in the Gulf Stream region has a larger effect on ocean variability than a change of diffusivity by a factor of 10. In areas where either the high or the low resolution models have sufficient resolution, as in the Gulf of Mexico, they are able to produce variability comparable to that observed from altimeter data; elsewhere, model variability is underestimated. 相似文献
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60.
An instrumented trial-fill dike was constructed on soft, laminated soils of the Lisan Peninsula foreshore of the Dead Sea.
The earthwork had base dimensions of 180 m by approximately 70 m wide and was raised in two stages to a maximum height of
12.5 m above original ground level. The geotechnical data of the dike were monitored in order to: assess the short- and long-term
strength of the foundation, obtain and analyze the pore-pressure response of the foundation soils for potential use in construction
control, obtain data on embankment settlement in order to refine end-of-construction and post-construction settlement assessments,
and optimize the height of the dike to be constructed by providing information on the construction sequence for use in calculation
of capital costs and alternative layouts and dike heights. The successful completion of the trial dike has demonstrated that
steep-side dikes up to 12.5 m high can be constructed rapidly on soft soils. The construction of the trial dike has therefore
proved a very substantial benefit to the evaluation of the likely performance of a dike constructed along the Lisan shore.
The key factor which made this fast construction possible was the unexpected, very rapid consolidation of the majority of
the foundation soil which has been shown to occur. The principal observations from the trial dike were: (1) end of construction
settlements may be calculated using drained stiffnesses where E′/su initial has a value of around 65; (2) post-construction settlements can be calculated using a coefficient of secondary compression,
Cα equal to 0.015; (3) a rapid increase in undrained shear strength occurred when loading the soil up to a value of su equal to around 30 kPa. The value of su/σv′ was as high as 0.5 at this stage. With further loading the strength increase was more modest and su/σv fell to around 0.25 for a vertical effective stress of 160 kPa; (4) for the undrained stability analyses of the trial dike,
the mean vane shear-strength profile provided an appropriate assessment of the short-term factor of safety against failure,
5) For the drained stability analyses of the trial dike, lower bound effective strength parameters for the foundation and
embankment fill (c′=0, φ′=30° and c′=2 kN/m2, φ′=33°, respectively), combined with field measurements of end of construction pore water pressures provided an analysis
which was broadly compatible with the undrained analysis; and (6) the trial dike has been stable, pre- and post-construction,
because of the well drained nature of its foundation which prevented the build up of high pore water pressures and led to
rapid consolidation.
Received: 22 June 1998 · Accepted: 30 October 1998 相似文献