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Wave Action (wave + action)
Selected AbstractsInstability investigation of cantilevered seacliffsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2008Adam P. Young Abstract Wave action is a fundamental mechanism in seacliff erosion, whereby wave undercutting creates an unstable cantilevered seacliff profile and can lead to large catastrophic cliff failures, thus threatening coastal infrastructure. This study investigated the instability of two such failures that occurred in Solana Beach, California, by combining terrestrial LIDAR scanning, cantilever beam theory and finite element analysis. Each landslide was detected by evaluating the surface change between subsequent high resolution digital terrain models derived from terrestrial LIDAR data. The dimensions of failed cantilever masses were determined using the surface change measurements and then incorporated into failure stress analysis. Superimposing stress distributions computed from elastic cantilever beam theory and finite element modeling provided a method to back-calculate the maximum developed tensile and shear stresses along each failure plane. The results of the stress superposition revealed that the bending stresses caused by the cantilevered load contributed the majority of stress leading to collapse. Both shear and tensile failure modes were investigated as potential cliff failure mechanisms by using a comparison of the back-calculated failure stresses to material strengths found in laboratory testing. Based on the results of this research, the tensile strength of the cliff material was exceeded at both locations, thus causing the cliffs to collapse in tension. Copyright © 2008 John Wiley & Sons, Ltd. [source] Spawning site selection by Eurasian perch (Perca fluviatilis L.) in relation to temperature and wave exposureECOLOGY OF FRESHWATER FISH, Issue 1 2009W. N. Probst Abstract,,, The selection of spawning depth by Eurasian perch Perca fluviatilis was investigated in an experiment using artificial substrata in Lake Constance during the spawning season of 2007. The experiment compared spawning behaviour at substrata between 0.5 and 15 m depth at two sites exposed to different regimes of ship-generated wave action. The total abundance of egg ribbons did not differ significantly between the two sites, but the preferred spawning depth was deeper at the wave exposed site (5 m) compared to the sheltered site (2 m). While water temperatures could not account for the observations, differences in wave exposure may explain the different spawning depth preferences. At both sites, large egg ribbons were generally found in deeper water, and large egg ribbons occurred more frequently at the sheltered site. Because the egg ribbons of perch are likely to have a size-dependent susceptibility to hydrodynamic stress, large females may be expected to select deeper spawning locations where the effects of surface waves are considerably attenuated. [source] Deltas in the Abisko area, northern Sweden: the Abiskojokka delta in lake TorneträskGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3-4 2002Hans Andrén Several small river deltas are found within the Abisko area. This study deals with the Abiskojokka delta in Lake Torneträsk. The aim is to describe the recent delta and its morphological development since the middle 1960s. In the apex of the delta, bars consist of boulders and cobbles while the mouth,bars are built by pebbles, gravel and to some extent sand. Birch vegetation is found on the sandy levées while willows and sedges dominate the interlevée basins. Mouth bars close to the lake generally lack vegetation. A comparison of the map in the present study with a map from 1965 shows comparatively small changes since 1964. Similar results are achieved when comparing aerial photographs from 1959 and 2000. Thus, the growth of the Abiskojokka delta is rather small compared to several other deltas in the Scandinavian mountains. This low growth rate is a result of upstream lakes trapping the major part of the fluvial sediments. Therefore, most of the delta sediment is redistributed old glaciofluvial material from the terraces within the Abiskojokka valley. Some material might also emanate from the Abiskojokka canyon. Formation of the main part of the delta is probably associated with the lowering of the Torneträsk ice,lakes, during and after the deglaciation of the region. Although some extreme rainstorm events have occurred in the area during recent decades, the effects of these on the delta are small. The result of such events is, however, visible as deposition of sand and silt on the levées after flooding. On the other hand, the shoreline and the mouth bars are continuously changing due to rather high wave energy especially during northerly winds. Along several mouth bars, spits are formed and reformed due to wave action. Minor changes of, and within, the two main distributaries have also been noticed, especially as bank erosion and redistribution of bars. The project will continue with a survey of the distal slope (foreset slope) of the delta as well as a study (including X,ray radiography) of the bottom sediments in Lake Torneträsk close to the delta front. The upstream deltas within this drainage basin as well as other deltas within the Torneträsk region will be studied. [source] Effects of storm frequency on dune vegetationGLOBAL CHANGE BIOLOGY, Issue 10 2010ELISE S. GORNISH Abstract In the Gulf of Mexico, barrier islands absorb the majority of wind and wave action from storms, which modifies their dune morphology and vegetation dynamics. Storm frequency is predicted to increase as a result of climate change, yet the effects of this change on coastal ecosystems remain poorly understood. Using estimates of plant growth in storm and nonstorm years from long-term census data describing the dynamics of dune vegetation on St. George Island, FL, we built a first-order model that predicts how dune communities will respond to a change in storm frequency. It predicts that an increasing frequency of storms will result in a change in the vegetation across the dunes. The fore- and interdune communities are predicted to become more similar to one another through the dominance of a small number of common storm-resilient species. Alternatively, the backdune community is predicted to become more distinct through an increase in rare species that represent primary succession. Finally, the model predicts that many species will not respond to an increase in the number of storms per year in the same manner in which they respond to current storm frequency. This model is beneficial both for the development of more complex approaches to predicting effects of climate change and for informing preventative management techniques. [source] Will increased storm disturbance affect the biodiversity of intertidal, nonscleractinian sessile fauna on coral reefs?GLOBAL CHANGE BIOLOGY, Issue 11 2008S. J. WALKER Abstract Relatively little is known about how the future effects of climatic change, including increases in sea level, temperature and storm severity and frequency, will impact on patterns of biodiversity on coral reefs, with the notable exception of recent work on corals and fish in tropical reef ecosystems. Sessile invertebrates such as ascidians, sponges and bryozoans occupying intertidal rubble habitats on coral reefs contribute significantly to the overall biodiversity and ecosystem function, but there is little or no information available on the likely impacts on these species from climate change. The existing strong physical gradients in these intertidal habitats will be exacerbated under predicted climatic change. By examining the distribution and abundance of nonscleractinian, sessile invertebrate assemblages exposed to different levels of wave action and at different heights on the shore around a coral reef, we show that coral reef intertidal biodiversity is particularly sensitive to physical disturbance. As physical disturbance regimes increase due to more intense storms and wave action associated with global warming, we can expect to see a corresponding decrease in the diversity of these cryptic sessile assemblages. This could impact negatively on the future health and productivity of coral reef ecosystems, given the ecosystem services these organisms provide. [source] Numerical simulation on joint motion process of various modes of caisson breakwater under wave excitationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 6 2006Wang Yuan-Zhan Abstract A caisson breakwater may experience various modes of motions under wave action. The elementary motion modes are classified into two categories, i.e. the horizontal and rotational vibration coupled motion and the horizontal slide and rotational vibration coupled motion. The motion modes of caisson will transform from one to another depending on the wave forces and the motion behaviours of a caisson. The numerical models of the two motion modes of caisson are developed, the numerical simulation procedure for joint motion process of the two modes of caisson breakwater under wave excitation is presented and tested by a physical model experiment. It is concluded that the simulation procedure is reliable and can be applied to the dynamic stability analysis of caisson breakwaters. Copyright © 2005 John Wiley & Sons, Ltd. [source] Effect of wave exposure dynamics on gut content mass and growth of young-of-the-year fishes in the littoral zone of lakesJOURNAL OF FISH BIOLOGY, Issue 7 2010S. Stoll Total length, body mass and gut content mass of young-of-the-year (YOY) perch Perca fluviatilis, dace Leuciscus leuciscus and bleak Alburnus alburnus were recorded over the summer of 2006 at three littoral sites at Upper Lake Constance. In P. fluviatilis and L. leuciscus, gut content mass correlated positively with wave-induced energy flux (EF) of the respective site and sampling day, while no correlation of gut content mass with EF was found in A. alburnus. It was assumed that benthivorous P. fluviatilis and L. leuciscus profited from suspended or uncovered benthic food items generated by wave action at sites and periods with high EF. Alburnus alburnus, in contrast, feeding mainly on zooplankton in upper parts of the water column, could not profit from increased EF. In P. fluviatilis, increased gut content mass during periods of high EF resulted in higher growth rates. For L. leuciscus, no real growth rates in local fish populations could be determined, as individuals were less sedentary, and when increased growth occurred at sites during the periods of high EF, migration of fish levelled out the resulting size differences within few days. The results of this study show that dynamic habitat variables affect site profitability in the littoral zone of lakes, especially in benthivorous fishes. Therefore, dynamic habitat variables should be considered in addition to fixed habitat properties in analyses of habitat choice of fishes in the littoral zone of lakes. [source] Nest site characteristics and nesting success of the five-spotted wrasse Symphodus roissali in the north-western Mediterranean SeaJOURNAL OF FISH BIOLOGY, Issue 1 2006N. Raventos The effects of site characteristics on the distribution of nests and nesting success were examined in the five-spotted wrasse Symphodus roissali in the north-western Mediterranean Sea. Nesting males selected nest sites mainly on flat substrata and close to a margin in the rocky littoral strip; however, substratum slope and degree of shelter from wave action were the determinants for a greater success. [source] Observations on the relationship between lake formation, permafrost activity and lithalsa development during the last 20,000 years in the Tso Kar basin, Ladakh, IndiaPERMAFROST AND PERIGLACIAL PROCESSES, Issue 4 2008Bernd Wünnemann Abstract A close relationship has existed between high mountain permafrost and lake history in the Tso Kar basin, Ladakh, India throughout the last 20,kyr BP. Analyses of sediment cores indicate phases of permafrost growth during low lake levels between >20,10,cal. kyr BP and after 5,cal. kyr BP. Palaeo-shorelines and lake carbonate outcrops indicate a maximum lake size at ca. 8,5,cal. kyr BP when permafrost is believed to have been absent in the basin. Regression of the lake with accompanying salinisation since about 4,cal. kyr BP allowed permafrost aggradation. Permafrost mounds and thermokarst features are inferred to have continued to develop in the last 60 years. Sections in two 6,10,m high unvegetated mounds revealed thick ice lenses and reticulate cryostructures leading to their classification as lithalsas. Mound collapse is induced by surface erosion and slumping, while sediment reworking by wave action and other processes appears to prevent rampart formation. If lake levels continue to fall, further permafrost aggradation is expected in this high elevation enclosed basin. Copyright © 2008 John Wiley & Sons, Ltd. [source] Habitat diversity relative to wave action on rocky shores: implications for the selection of marine protected areasAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2009Laura K. Blamey Abstract 1.Current selection of marine protected areas in South Africa is based on objective criteria including biogeographic representation and habitat heterogeneity. This paper specifically examines rocky shores on the west coast of South Africa to determine whether they are divisible into discrete ,habitats' that need independent conservation. 2.Seventeen rocky shores spanning the full spectrum of wave exposure were compared in terms of maximum wave forces, biomass, species richness and diversity among zones and sites. Three biotic assemblages were identified, characterizing sheltered, semi-exposed to exposed, and very exposed habitats. Differences among these were clear-cut low on the shore but disappeared at the top of the shore where wave action was attenuated and desiccation uniformly intense. 3.The recognition of three discrete biologically-defined habitats means that rocky shores cannot be regarded as a uniform habitat for conservation purposes. All three components need protection if the full spectrum of rocky-shore communities is to be conserved. 4.It is argued that this approach allows habitats to be defined in an objective manner, and that once this has been done, habitat heterogeneity constitutes a better measure of conservation value of an area than a ,hotspot' approach based on species richness and endemism. Copyright © 2008 John Wiley & Sons, Ltd. [source] A historical perspective of the genus Mytilus (Bivalvia: Mollusca) in New Zealand: multivariate morphometric analyses of fossil, midden and contemporary blue musselsBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2004JONATHAN P. A. GARDNER The taxonomic status of smooth shelled blue mussels of the genus Mytilus has received considerable attention in the last 25 years. Despite this, the situation in the southern hemisphere remains uncertain and is in need of clarification. Recent work suggests that contemporary New Zealand mussels from two cool/cold temperate locations are M. galloprovincialis. However, the distribution of Mytilus in New Zealand ranges from 35 ° to 52 ° south (, 1800 km), meaning that large areas of the subtropical/warm temperate north and the subantarctic south remain unsampled, an important consideration when species of this genus exhibit pronounced macrogeographical differences in their distributions which are associated with environmental variables such as water temperature, salinity, wave action and ice cover. This study employed multivariate morphometric analyses of one fossil, 83 valves from middens, and 92 contemporary valves from sites spanning the distributional range of blue mussels to determine a historical and contemporary perspective of the taxonomic status of Mytilus in New Zealand. The findings indicated that all fossil and midden mussels are best regarded as M. galloprovincialis and confirmed that contemporary mussels, with one possible regional exception, are also best regarded as M. galloprovincialis. Contemporary mussels from the Bay of Islands (warm temperate/subtropical) exhibited much greater affinity to M. edulis than they did to M. galloprovincialis, indicating that mussels from this area require detailed genetic examination to determine their taxonomic status. The analyses revealed a significant difference between the fossil/midden mussels and the contemporary mussels, consistent with levels of present day differentiation among intraspecific populations and not thought to reflect any substantive temporal change between mussels of the two groups. The continuous distribution of M. galloprovincialis in New Zealand from the warm north to the subantarctic south indicates that the physiology of this species is adapted to a wide range of water temperature conditions. Therefore, the distribution of this species on a worldwide scale is unlikely to be restricted by its adaptation to warm water alone, as has previously been widely assumed. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 329,344. [source] | ||||||||||||||||