Prototype measurements and small-scale model tests of wave overtopping at shallow rubble-mound breakwaters: the Ostia-Rome yacht harbour case     

Leopoldo Franco  Jimmy Geeraerts  Riccardo Briganti  Marc Willems  Giorgio Bellotti  Julien De Rouck 《Coastal Engineering》2009

The paper presents the comparison between the results of small-scale model tests and prototype measurements of wave overtopping at a rubble-mound breakwater. The specific structure investigated is the west breakwater of the yacht harbour of Rome at Ostia (Italy) and is characterized by a gentle seaward slope (1/4) and by a long, shallow foreshore. The laboratory tests firstly aimed at carefully reproducing two measured storms in which overtopping occurred and was measured. The tests have been carried out in two independent laboratories, in a wave flume and in a wave basin, hence using a two-dimensional (2-D) and a three-dimensional (3-D) setup. In the 2-D laboratory tests no overtopping occurred during the storm reproductions; in the 3-D case discharges five to ten times smaller than those observed in prototype have been measured. This indicates the existence of model and scale effects. These effects have been discussed on the basis of the results of several parametric tests, which have been carried out in both laboratories, in addition to the storm reproductions, varying wave and water level characteristics. Final comparison of all the performed tests with 86 prototype measurements still suggests the existence of scale and model effects that induce strong underestimation of overtopping discharge at small scale. The scale reproduction of wave breaking on the foreshore, together with the 3-D features of the prototype conditions and the absence of wind stress in the laboratory measurements, have been individuated as the main sources of scale and model effects. The paper also provides a comparison between the data and a largely used formula for wave overtopping discharges in the presence of structures similar to the one at hand. The suitable value of a roughness factor that appears in that formula is investigated and good agreement is found with other recent researches on rubble-mound breakwaters.  相似文献   

Benthic macrofauna and productivity regimes in the Barents Sea — Ecological implications in a changing Arctic     

Sabine K.J. Cochrane  Stanislav G. Denisenko  Paul E. Renaud  Christopher S. Emblow  William G. Ambrose Jr.  Ingrid H. Ellingsen  Jofrid Skarhamar 《Journal of Sea Research》2009,61(4):222-233

Benthic faunal assemblages were analysed from 47 stations in the central and southern parts of the Barents Sea, together with sedimentary and water column parameters, daily ice records and modelled integrated primary productivity. Sampling spanned areas influenced by Atlantic Water (AW) to those lying under Arctic Water (ArW), and included stations with mixed water masses. Ice cover suppressed water column productivity in the northern areas. Three main faunal groups were identified, based on similarity of numerical faunal composition. The northern and southern faunal groups were separated by the northernmost penetration of AW in the bottom water and the third group, the Hopen group, was influenced by modified bank water. Faunal abundances were significantly higher within the southern faunal group relative to the northern group, but the numbers of taxa present were similar. The particularly rich fauna of the Hopen group reflected sediment heterogeneity and tight pelagic–benthic coupling. These results suggest that a retreat and thinning of the ice cover in the Barents Sea likely will result in the northern parts of the Barents Sea becoming more Atlantic in character, with a higher productivity at the sea floor.  相似文献   

GPS for real-time earthquake source determination and tsunami warning systems   总被引：1，自引：0，他引：1  

Geoffrey Blewitt  William C. Hammond  Corné Kreemer  Hans-Peter Plag  Seth Stein  Emile Okal 《Journal of Geodesy》2009,83(3-4):335-343

We identify the key design aspects of a GPS-based system (and in the future, GNSS-based systems) that could contribute to real-time earthquake source determination and tsunami warning systems. Our approach is based on models of both transient and permanent displacement of GPS stations caused by large earthquakes, while considering the effect of GPS errors on inverted earthquake source parameters. Our main conclusions are that (1) the spatial pattern, magnitude, and timing of permanent displacement of GPS stations can be inverted for the earthquake source and so predict the 3D displacement field of the ocean bottom, thus providing the initial conditions for tsunami models, and (2) there are no inherently limiting factors arising from real-time orbit and positioning errors, provided sufficient near-field GPS stations are deployed. This signal could be readily exploited by GPS networks currently in place, and will be facilitated by the IGS Real-Time Project as it comes to fruition.  相似文献   

Deformation and patterns of sedimentation,South San Clemente Basin,California Borderland     

Douglas L. Smith  William R. Normark 《Marine Geology》1976,22(3):175-188

Seismic reflection profiling in the South San Clemente Basin and the southern portion of the San Diego Trough has revealed at least six sedimentary units exhibiting varying stages of deformation. Four of the units are interpreted to be marine turbidites supplied by adjacent submarine canyons. Sediments comprising the Descanso Plain and correlative material within the South San Clemente Basin are attributed to a southerly source (Banda Canyon), while the more recent Quaternary turbidites from Coronado Canyon filled the southern San Diego Trough and then spilled over into South San Clemente Basin. The relatively high but intermittent rates of sedimentation, together with shifting sources and areas of deposition, have resulted in sedimentary units that were emplaced in comparatively short episodes but which were subjected to relatively continuous tectonic activity. Consequently, the sedimentary layers of each unit appear uniformly affected by deformation which increases in successively older units.  相似文献   

Structure and development of the southern Moroccan continental shelf     

William P Dillon 《Marine Geology》1974,16(3):121-143

The structure of the continental shelf off southern Morocco was studied by means of 2,100 km of seismic reflection profiles, magnetic and bathymetric surveys, and dredge samples. The research area lies off four geologic divisions adjacent to the coast: the Atlas Mountains; the Souss Trough; the Anti-Atlas Mountains; and the Aaiun Basin. The continental shelf, along with the western Atlas Mountains, the western Souss Trough, and the entire Aaiun Basin, has subsided along a normal fault-flexure system. This system runs along the shore at the Anti-Atlas Mountains, and cuts off this cratonic block from the shelf subsidence. The shelf is narrow and characterized by out-building off the Anti-Atlas range, whereas it is broader and characterized by upbuilding to the north and south. Deposition was essentially continuous at least from Early Cretaceous through Eocene time. Published work suggests that the last cycle of sedimentation began during Permian rifting. After Eocene time, most sediments carried to the shelf must have bypassed it and gone to construct the slope and rise or to the deep sea. Tertiary orogenies caused extensive folding of Mesozoic and early Tertiary deposits off the Atlas Mountains.  相似文献   

The world ocean: An introduction to oceanography: William A. Anikouchine and Richard W. Sternberg. Prentice Hall,Englewood Cliffs,N.J., 1973     

William R. Normark 《Marine Geology》1975,18(3):136-137

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Finite-amplitude mountain waves in a compressible atmosphere including the effects of dissipation     

William Blumen 《地球物理与天体物理流体动力学》2013,107(1-3):89-104

Abstract

Adiabatic, two-dimensional, steady-state finite-amplitude, hydrostatic gravity waves produced by flow over a ridge are considered. Nonlinear self advection steepens the wave until the streamlines attain a vertical slope at a critical height z_c. The height z_c , where this occurs, depends on the ridge crest height and adiabatic expansion of the atmosphere. Dissipation is introduced in order to balance nonlinear self advection, and to maintain a marginal state above z_c. The approach is to assume that the wave is inviscid except in a thin layer, small compared to a vertical wavelength, where dissipation cannot be neglected. The solutions in each region are matched to obtain a continuous solution for the streamline displacement δ. Solutions are presented for different values of the nondimensional dissipation parameter β. Eddy viscosity coefficients and the thickness of the dissipative layer are expressed as functions of β, and their magnitudes are compared to other theoretical evaluations and to values inferred from radar measurements of the stratosphere.

The Fourier spectrum of the solution for z ≫ z_c is shown to decay exponentially at large vertical wave numbers n. In comparison, a spectral decay law n ^?-8/3 characterizes the marginal state of the wave at z = z_c .  相似文献   

Examination of climate risk using a modified uncertainty matrix framework—Applications in the water sector     

Marie Ekström  Natasha Kuruppu  Robert L. Wilby  Hayley J. Fowler  Francis H.S. Chiew  Suraje Dessai  William J. Young 《Global Environmental Change》2013,23(1):115-129

Previous climate risk assessments provide important methodological insights into how to derive tractable research questions and the appropriate use of data under uncertainty, as well as identifying steps that benefit from stakeholder involvement. Here we propose the use of a framework for the systematic and objective exploration of climate risk assessments. The matrix facilitates a breakdown of information about aim and context, main results, methodological choices, stakeholder involvement, sources and characteristics of uncertainties and overall weaknesses. We then apply the matrix to three risk assessments in the water sector to explore some methodological strengths and weaknesses of approaches strongly linked to climate model outputs (top-down) versus those that originate from local knowledge of climate exposures (bottom-up), and demonstrate that closer integration with social and physical sciences is more likely to yield robust climate risk assessments.  相似文献   

Planetons: An example of large amplitude solitary waves     

William K. Dewar 《地球物理与天体物理流体动力学》2013,107(1-4):53-85

Abstract

The term ‘‘solitary wave'’ is usually used to denote a steadily propagating permanent form solution of a nonlinear wave equation, with the permanency arising from a balance between steepening and dispersive tendencies. It is known that large-scale thermal anomalies in the ocean are subject to a steepening mechanism driven by the beta effect, while at the smaller deformation scale, such phenomena are highly dispersive. It is shown here that the evolution of a physical system subject to both effects is governed by the ‘‘frontal semi-geostrophic equation'’ (FSGE), which is valid for large amplitude thermocline disturbances. Solitary wave solutions of the FSGE (here named planetons) are calculated and their properties are described with a view towards examining the behavior of finite amplitude solitary waves. In contrast, most known solitary wave solutions belong to weakly nonlinear wave equations (e.g., the Korteweg—deVries (KdV) equation).

The FSGE is shown to reduce to the KdV equation at small amplitudes. Classical sech² solitons thus represent a limiting class of solutions to the FSGE. The primary new effect on planetons at finite amplitudes is nonlinear dispersion. It is argued that due to this effect the propagation rates of finite amplitude planetons differ significantly from the ‘‘weak planeton'', or KdV, dispersion relation. Planeton structure is found to be simple and reminiscent of KdV solitons. Numerical evidence is presented which suggests that collisions between finite amplitude solitary waves are weakly inelastic, indicating the loss of true soliton behavior of the FSGE at moderate amplitudes. Lastly, the sensitivity of solitary waves to the existence of a nontrivial far field is demonstrated and the role of this analysis in the interpretation of lab experiments and the evolution of the thermocline is discussed.  相似文献   

Characterization of seafloor pockmark seepage of hydrocarbons employing fractal: A case study from the western continental margin of India     

Sumanta Dandapath  Bishwajit Chakraborty  Nicolas Maslov  Siddaiah M. Karisiddaiah  Dhrupad Ghosh  William Fernandes  Andrew Menezes 《Marine and Petroleum Geology》2012,29(1):115-128

Here we apply quantitative technique to describe the seafloor seepages based on the multi-beam backscatter and bathymetric investigations to characterize the pockmark morphology. The variable seafloor backscatter strength for coarser seafloor sediments are related to the diagenesis derived from biodegraded seepages. In this regard, box counting method is used to estimate ‘fractal dimension’ for backscatter imagery data of 398 blocks. These blocks are further sub-grouped into six classes depending on the spread of pockmark related seepages. The study area lies 102 km west off Marmagao along the central west coast of India which contains pre-dominantly (70%) gas-charged sediments. Comparison between the estimated self-similar fractals reveals that there is approximately 97% correlation between the box (D_box) and information (D_info) dimensions. Box dimension–derived fractal dimension values, suggest that the seepages are more along the fault trace in deeper waters, in comparison to sparsely distributed shallow water seepages. Besides, this poor seepage is confined within the smooth to moderately rough seafloor. It is established that the high backscatter strength along the upper slope of the pockmark region having higher fractal dimensions reflects multifractal behavior of seepage distribution. Entire area indicates patchy seepage patterns as supported by estimated fractal values showing intermittent fluctuations, which emphasizes non-linear behavior. Estimated self organizing criticality (SOC) parameters for six representative blocks reveal that the nature of pockmark, fault trace, sediment nature coupled with slumping of pockmark’s wall, sediment movement due to bottom currents are controlling the dynamic balance in the area seepage system. Further, our study emphasizing the multifractal behavior of seepage blocks, clearly depicts the drift in the seepage pattern.  相似文献