Showing papers on "Shore published in 1981"

Physical Processes and Fine-grained Sediment Dynamics, Coast of Surinam, South America

Abstract: The prograding Holocene mud wedge between the Amazon and Orinoco Rivers in the trade wind belt of northeastern South America provides a modern-day example of muds accumulating under moderate wave-energy conditions. Gigantic shore-attached mudbanks (10 km 20 km), composed partly of thixotropic fluid-mud gel, front this coast every 30-60 km to form a buffer to wave attack and a temporary storage for fine-grained sediments. This mesotidal coast (tide range 2.0 m) with gentle offshore slope (0.0006) allows the exposure twice a day of extensive tidal flat deposits, which are backed by mangrove swamps on a well-developed chenier-plain complex. Field experiments were conducted in Surinam du ing 1975 and 1977 to provide new information on process-form relationships in this interesting but unusual muddy environment. Simultaneous measurements of waves, currents, tide elevation, suspended-sediment concentration, and variations in mud density show that soft intertidal and subtidal muds are suspended at both tide and wave frequency. Suspended-sediment concentrations typically exceed 1,000 mg/l at the surface as incoming solitary-like waves partially disperse fluid mud into overlying water on a falling or rising tide. Redeposition of mud may occur near time of high tide. The strong attenuation of shallow-water waves by these muds provides conditions that are favorable for further sedimentation. High concentrations of suspended fluid mud, together with solitary-like waves from the northeast throughout the year, can lead to extraordinarily high net sediment transport rates in the nearshore zone. Calculations based on solitary-wave theory and on data obtained from this study indicate that 15-65 106 m3 of mud can move along shore each year without involving breaking waves, the concept of radiation stress and a nearshore circulation cell, or bedload transport. Farther offshore, outside the zone of wave dominance, wind-driven currents and the Guiana Current combine to transport muds to the northwest, consistent with the observed direction of mudflat migration.

Fatal errors in set as a cost of dispersal and the influence of intertidal flora on set of barnacles.

Abstract: Cyprid larvae of Balanus cariosus settle preferentially on slate plates with a biota characteristic of the lower intertidal shore, and the cyprids also prefer plates with more algae. Cyprid larvae of Balanus glandula had the same preferences in two out of three experiments. We conclude that some component of the flora guides both species during settling and metamorphosis. Data on vertical distribution and fecundity of B. glandula show that the preference for the lower shore decreases fitness of B. glandula at the site of the settling experiments and at most other sites sampled in or near the San Juan Islands, though in some restricted habitats in the San Juans and extensive areas in the adjacent regions of Puget Sound a preference for the lower shore is appropriate. Extensive dispersal among sites is possible in the planktonic period of 2 to 4 weeks. This example supports the hypothesis that a cost to large scale dispersal is lower fitness at many sites within a species' range. In this case the cost is through poorer correlation between stimuli guiding choice of habitat and favorability of habitat.

Inertial Oscillations on the Continental Shelf of the Gulf of Lions—Observations and Theory

Abstract: Observations in the Gulf of Lions (northwestern Mediterranean Sea) in summer have shown that gusts of wind lasting a few days generate transient upwellings and inertial motions. Oscillations at the inertial frequency were observed in current meter data near the shore and at a frequency 10% greater in the temperature data. Vertical coherences in current meter data show a strong baroclinic mode at frequencies greater than inertial frequency. A simple one-dimensional two-layer transient model suggests that these motions are associated with two different physical processes. The first process describes the local response of the ocean to meteorological forcing, the second is associated with the propagation of long internal waves generated in the transient phase of the geostrophic adjustment process. As suggested by the model, the direction of propagation of the internal waves is computed from current and temperature data measured at one point and it is found that the shore is the source zone.

Shoreline Changes on the Louisiana Barrier Coast

Abstract: Deltaic barrier systems in Louisiana are presently experiencing a period of severe erosion. By using detailed photogrammetric measurements and digitization of individual island areas, it has been possible to provide a new and comprehensive evaluation of shoreline change along 250km of the Louisiana barrier coast. When combined with a new model for deltaic barrier evolution, these data provide an understanding of the natural mechanisms and man-made interventions underlying the present erosion problems.

Shore platform morphology and the tidal duration factor

Abstract: A simple wave erosional model was used to simulate the profiles of shore platforms in eastern Canada, Australia, New Zealand, and Britain. The model assumes that the rate of intertidal erosion is determined by the time that still water level occupies each elevation within the tidal range (the tidal duration factor), by an erodibility factor related to wave energy and rock hardness, by platform gradient, and by the rate of submarine erosion. Simulated profiles were broadly similar to actual platforms in nearly all areas. All profiles eventually reached states of dynamic equilibrium, as the platforms assumed gradients which caused erosion rates to become equal at all points along their surfaces. Equilibrium was attained in periods which suggest that wave-cut platforms are essentially postglacial features. The model explains the effect of tidal range and erodibility on platform gradient and width, and the prominence of ramps and low tide cliffs in microand mesotidal environments, as well as identifying those factors which determine the elevation of platforms. The morphology characteristics of shore platforms are determined by a variety of morphogenic and geological factors. Bed dip, jointing, thickness, and other structural and lithological factors may be responsible for considerable variation in platform geometry within short distances along a coastline (Bird and Dent, 1966; Trenhaile, 1971). These local variations may be most marked along indented shorelines, and headland platforms are often quite different from those in the adjacent embayments; although few generalizations about the precise nature of these differences appear to be justified (Bartrum, 1935; So, 1965; Wright, 1970; Trenhaile, 1972). At the regional scale, however, differences in mean platform morphology between areas largely reflect differences in their morphogenic environments. The secondary role of geological factors at the regional scale is indicated by the relationship between aspects of platform geometry and a number of morphogenic factors (Wright, 1967, 1970; Trenhaile, 1972, 1974a, 1978, 1980). The geological contribution at the regional and larger scale is essentially limited to producing local deviations about morphological means which are determined by the morphogenic environments. Platform morphology also varies at the global scale. Davies (1964) has emphasized differences between the morphogenic environments of world shorelines, and Trenhaile (1974b) has applied this concept to shore platforms. The wave-cut platforms' in the storm wave, macrotidal environments of England and Wales, are generally wide, quasilinear surfaces, with gradients between 0-5 and 3'. They extend from a cliff-platform junction, generally close to high tide level, to low tide level or Trans. Inst. Br. Geogr. N.S. 6, 82-102 (1981) Printed in Great Britain This content downloaded from 207.46.13.146 on Tue, 23 Aug 2016 04:00:36 UTC All use subject to http://about.jstor.org/terms N .........iiiiiiiiiiiii!i!iii!!!i~~i~ii~~iiiii~iiiiii~~i . . . . . . . . . ...~iiiiiiiiiiiiiiiii~i~i~iiii!i~~ii~ i~iiiiiiiiiii!!iiiiiiiiiiiii~~ii~i!iiiiiii~ii~ ~~~~iliiiiiiiiii~iii~iii~ii~iii~iiiiiiiiiiiiilii~ i~i~i!i!ii~i~~iiiiii~iiiiiiii~iiiiiiiiiiiiiiiiiii~ i~ ~iiiiiii~iiiiiiiiiiiiiiii~iiiiiiii~i~i ii~i!ii!iiiiiii!i~ ~ii iii~ ~iiiiiiii~ ii~i~ iiii~iiiiiiiiiiiiii~ii~i~iiiii!iiii ii~ ~~~ii~i~ii~ii~iiiiiiiiiiiiiiiiiiiiiiiiiiiiii i i ii~ ~iiiiii~iiiiiiii~ii~iiiiiiiiii~iiii!!iii i iii~ii i~~iiiiiiiiiii~iiii~iiii!i!!!i~ ~iiiii~ iiiOW Nii~iii~i~i!~!iiiiiii~ii! i!!i! ii i iii% !i~!i~i!!!.!!.!%.l.i . ii.i.ii.i%.i.

Beach systems of the Sydney region

Abstract: Summary The Sydney coast exhibits some of the world's most dynamic beaches. This is a consequence of a combination of a moderate to high energy though highly variable wave climate, a steep inner continental shelf which allows most of this energy to reach the shore, and pronounced alongshore gradients in energy produced by varying degrees of headland protection along the highly embayed coastline. Consequently a high degree of variability exists both temporally and spatially within and between Sydney beaches both in terms of wave height and resultant beach form. This paper examines the results of this spatial variation as well as the nature and effect of wave climate on temporal variation in the typical beach form. Modes of beach erosion operating on the beaches are considered in terms of particular combinations of wave conditions and antecedent beach states.

Sediment Management for Southern California Mountains, Coastal Plains and Shoreline. Part C: Coastal Sediment Delivery by Major Rivers in Southern California

Abstract: In southern California the natural environmental system involves the continual relocation of sedimentary materials. Particles are eroded from inland areas where there is sufficient relief and, precipitation. Then, with reductions in hydraulic gradient along the stream course and at the shoreline, the velocity of surface runoff is reduced and there is deposition. Generally, coarse sand, gravel and larger particles are deposited near the base of the eroding surfaces (mountains and hills) and the finer sediments are deposited on floodplains, in bays or lagoons, and at the shoreline as delta deposits. Very fine silt and clay particles, which make up a significant part of the eroded material, are carried offshore where they eventually deposit in deeper areas. Sand deposited at the shoreline is gradually moved along the coast by waves and currents, and provides nourishment for local beaches. However, eventually much of this littoral material is also lost to offshore areas. Human developments in the coastal region have substantially altered the natural sedimentary processes, through changes in land use, the harvesting of natural resources (logging, grazing, and sand and gravel mining); the construction and operation of water conservation facilities and flood control structures; and coastal developments. In almost all cases these developments have grown out of recognized needs and have well served their primary purpose. At the time possible deleterious effects on the local or regional sediment balance were generally unforeseen or were felt to be of secondary importance. In 1975 a large-scale study of inland and coastal sedimentation processes in southern California was initiated by the Environmental Quality Laboratory at the California Institute of Technology and the Center for Coastal Studies at Scripps Institution of Oceanography. This volume is one of a series of reports from this study. Using existing data bases, this series attempts to define quantitatively inland and coastal sedimentation processes and identify the effects man has had on these processes. To resolve some issues related to long-term sediment management, additional research and data will be needed. In the series there are four Caltech reports that provide supporting studies for the summary report (EQL Report No. 17). These reports include: EQL Report 17-A Regional Geological History EQL Report 17-B Inland Sediment Movements by Natural Processes EQL Report 17-C Coastal Sediment Delivery by Major Rivers in Southern California EQL Report 17-D -- Special Inland Studies Additional supporting reports on coastal studies (shoreline sedimentation processes, control structures, dredging, etc.) are being published by the Center for Coastal Studies at Scripps Institution of Oceanography, La Jolla, California.

18 O modelling of freshwater inputs in Baffin Bay and Canadian Arctic coastal waters

Abstract: 18O–salinity modelling of marine environments has been proposed for various areas, including some Arctic seas. The present report concerns Arctic coastal waters collected along the west coast of Greenland, northern Baffin Bay, the Arctic archipelago and the north shore of Alaska. Measurements of 18O versus salinity allow the identification of three main components: marine standard water, continental freshwater and sea ice meltwater. Continental waters may be represented by either glacial meltwater (western Greenland), land drainage (Mackenzie areas) or both. Quantitative determinations of the respective parts involved in mixed coastal waters imply a precise knowledge of the isotopic characteristics of the local continental waters. These determinations may be achieved either numerically or graphically.

National survey of planted salt marshes (Vegetative stabilization and wave stress)

Abstract: There have been many recent attempts to establish salt marshes in the coastal United States. Plantings are generally made for the purpose of shore protection, dredged material stabilization, or habitat development. During 1980 a survey was made of recent and historic salt marsh planting projects. Data were collected in 104 planted marshes in 12 coastal states. The relative stability of these plantings was compared to physical indicators of wave climate severity (fetch, shore slope, offshore depth, shore configuration, sediment grain size, orientation with respect to prevailing and storm winds, and proximity to boat traffic).

Former sea-levels and ice limits in part of Wester Ross, northwest Scotland

Abstract: All well-developed fossil marine features along 190 km of the coastline of Wester Ross have been mapped and instrumentally levelled. Glaciated intertidal rock platform fragments are interpreted as interglacial. Some pre-existing high rock platform fragments were considerably modified by Lateglacial marine erosion but others stand above the Lateglacial marine limit. Outside the area covered by the Wester Ross Readvance the marine limit represents an approximately synchronous shoreline corresponding with the culmination of the readvance. This shoreline slopes down towards the NNW at between 0.33 and 0.39 m/km. A relative fall of sea-level as ice retreated from the readvance maximum is demonstrated especially by outwash deposits merging into raised beaches. The Main Postglacial Shoreline is tentatively identified but it is inferred that the Main Lateglacial Shoreline is below present sea-level. The raised marine features are compared with certain modern shore features of the study area as well as with some fossil features elsewhere in Scotland.

Storms and shoreline configuration

Abstract: Spectral analysis of the 1962 great Atlantic coast storm penetration (overwash) along the Outer Banks of North Carolina and Fenwick Island, Maryland, reveals along-the-coast periodicities ranging in wavelength from 14 km to 15 km. Periodicities with similar wavelengths exist in long-term mean rates of change of the shoreline and storm-surge penetration line. This suggests the location and magnitude of storm deposits and storm hazards along the Atlantic coast are systematically distributed.

Water circulation and shelf waves in the northern Great Barrier Reef lagoon

Abstract: Currents and sea levels were measured at a number of locations in the Great Barrier Reef (GBR) lagoon from about 10 to 13o S., during the period October-December 1979. A strong non-tidal, low-frequency modulation of all sea-level and current data was found. The currents nearshore were driven northward by the wind, and then at least partially blocked by the dense network of reefs to the north of 10o s. The water then flowed southward in deeper water adjacent to the reef, driven by a longshore pressure gradient. The low- frequency sea-level data, though not the current records, showed northward phase propagation at speeds characteristic of a first-mode shelf wave trapped in the lagoon between the shore and the reef. Data are presented revealing the intrusion of low-salinity water, through Bligh Entrance, in the GBR lagoon, as a result of river discharges in the Gulf of Papua. It is suggested that low-frequency longshore currents may periodically flush these river plumes from the GBR lagoon and enhance interaction between reefs. In the Coral Sea in front of reef passages, the large horizontal velocities may result in forces upwelling by selective withdrawal and jet entrainment.

Structure of the Flow within the Coastal Boundary Layer of the Great Lakes

Abstract: Properties of the nearshore flow have been observed in some detail in Douglas Point, Lake Huron. Time series flow data obtained from a network of current meters deployed in a coastal chain perpendicular to the local shoreline have been analyzed to resolve the mean flow properties, horizontal turbulence characteristics and the kinetic energy (in the mean flow and fluctuations) within the coastal boundary layer. The variability of these parameters as a function of the distance from shore for an episode during which persistent short-parallel currents prevailed for several days has revealed two distinct boundary layers, an inner boundary layer dominated by bottom and shore friction (FBL—frictional boundary layer) and an outer boundary layer as a consequence of the adjustments of inertial oscillations to the lateral boundary (IBL—inertial boundary layer). If one takes the width of the frictional boundary layer as the distance to the point where the kinetic energy of currents peak, it is ∼2 km at Dougl...

The coastal circulation off Mauritania

Abstract: In January and February 1977, during the local upwelling season, RV “Meteor” carried out an ecological field experiment (“Auftrieb '77”) along the coast of Mauritania. This paper describes the winds, currents and T/S properties of the upwelling waters between 17o N and 19o N during the field experiment. Eleven moorings with current meters, tide gauges and a meteorological buoy collecting wind data worked on the shelf. Another meteorological buoy together with a current meter mooring recorded the wind and currents 40 nautical miles offshore the shelf break. While the moorings were installed (23 January to 22 February) “Meteor” surveyed at about weekly intervals the hydrographic conditions along standard cross-sections. The wind conditions during “Auftrieb '77” resemble those of previous cruises into the Mauritanian upwelling area in the same season. The wind blows from northeasterly directions with a mean strength of 4 Beaufort. It is, however, remarkable that the wind direction on the shelf, 30 km from the coast, is distinctly more offshore (by 40 degrees, clockwise) than the wind direction 120 km away from the coast. Wind, atmospheric pressure and air temperature exhibit typical diurnal and semi-diurnal variations. Inshore and midshelf the mean currents are directed towards south. The subsurface onshore current component, within the compensation layer, is on average two to three times smaller than observed during previous years further north. This might be caused by the relatively weak along shore component and strong offshore component of the wind over the shelf in January and February 1977. Along the continental slope the poleward flowing undercurrent prevails. In contrast to previous cruises further north, the undercurrent emerges as typical feature on the outer shelf at some places. Offshore, the undercurrent seems to extend up into the surface layer. The current boundary (two-sided convergence) between southward flow on the shelf and northward flow offshore is marked by a pronounced front, at times. Sinking movements may occur along this transitional zone. The location of the current boundary relative to the coast determines the spatial cross-shelf extension of occasional three-dimensional recirculations over the shelf, and accordingly the speed of recycling. Eddies along the boundary probably contribute to a great extent to the recycling. During a period of weak offshore winds a northward flow spreads over the entire shelf at all depths for several days. The onshore advancement of the counter current is also relfected in a local pressure rise and in a temperature increase. Such counter current events are probably not exceptional and represent an effective recycling process of the upwelling waters in this area. The hydrographic and chemical sections clearly indicate the effect of upwelling during “Auftrieb '77”. The actual depths, from which thh waters ascend to the surface are not greater than 100 to 200 metres. The largest proportion of the upwelling waters between 17o N and 19o N is provided by South Atlantic Central Water (SACW), which is carried by the undercurrent northwards. No fundamental changes of the hydrography on the shelf occur during the approximately one month long experiment. Interruptions of local upwelling for several days, as observed for example in connection with the counter current event, are too short to significantly alter the hydrographic conditions characterised by upwelling.

Dynamics of the shore vegetation of a North Swedish hydro-electric reservoir during a 5-year period

Abstract: Dynamics of the shore vegetation of a north Swedish hydro-electric reservoir during a 5-year period

The Use of Ground-Water Flow Models for Estimating Lake Seepage Rates

Abstract: Ground-water flow models developed for the flow systems around Bass Lake and Nepco Lake, Wisconsin, show that models can be useful tools for estimating lake seepage rates. A two-dimensional profile model for Bass Lake illustrates that the ratio of horizontal to vertical hydraulic conductivity of the aquifer around the lake is related to both the magnitude of vertical hydraulic gradients near the lake and the distribution of seepage from the lake as a function of distance from shore. The model also shows that it is important to know the vertical hydraulic conductivity of littoral lake-bed sediments to estimate lake seepage rates. A three-dimensional model constructed for an unusual ground-water flow system around Nepco Lake provides a more realistic simulation of the flow system than does a comparable two-dimensional model. Both models were useful for identifying additional data that could be used to quantify the ground-water portion of the lake's water budget more accurately. It is suggested that a combination of two-and/or three-dimensional models could be used to estimate seepage rates at many lakes for which sufficient data exist.

Detrital Quartz as an Indicator of Distance from Shore in Marine Mudrocks

Abstract: Eighty-nine surface samples and 17 subsurface samples of shale from the Blaine Formation (Permian) in western Oklahoma were examined to determine the variation in percentage of quartz and mean size of quartz with distance from a known shoreline. Samples were fused using sodium bisulfate to release the quartz from the mass of clay minerals. The surface samples gave areally and statistically meaningful trends; subsurface samples did not do so because of sampling difficulties. The mean percentage of quartz in surface samples decreases from 47 percent at a distance of 60 km from shore (more precisely, the sand-mud line) to 11 percent at 270 km from shore (r = .70), a loss of 10 percent quartz with each 60 km increase in distance. Mean grain size decreases from 5.2 at 60 km from shore to 6.9 at 270 km from shore (r = .71). Extrapolation of the data indicates that at the sand-mud boundary the percentage of quartz is 57 percent and the mean size of the quartz is between 4.75 and 5.1. The percentage of quartz in mudrocks can be a useful indicator of the position of the shoreline in ancient fine-grained epicontinental sea deposits.

Studies of Shores and Shore Displacement on the Southern Coast of Kenya—Especially in Kilifi District

Abstract: The raised terraces and similiar shore elements of Kilifi District, Coast Province, Kenya, between local Datum level and c. 20 m above Datum have been levelled. It was found that the shore elements...

The structure and composition of epilithic diatom communities of the St. Lawrence and Ottawa rivers in the Montreal area

Abstract: The structure and composition of epilithic diatom communities were studied at five stations in the St. Lawrence River and one station in the Ottawa River, adjacent to the south shore of the island ...

Shore protection structures: Effects on recession rates and beaches from the 1870s to the 1970s along the Ohio shore of lake Erie

Abstract: Shore-protection structures—largely groins and seawalls—have increased in number along the 300-km-long mainland Ohio shore of Lake Erie from about 60 in 1876–77, to about 1,400 in the late 1930s, to about 3,600 in the mid 1970s. Recession rates, on the other hand, have decreased from the early period (1876–1877 to the late 1930s) to the later period (late 1930s to 1973). Forexample, the length of shore that receded at the intermediate rate (0.3 to 0.9 m/yr) decreased from 76 to 54 km and the length of shore that receded at the lowest rate (less than 0.3 m/yr) increased from 151 to 171 km. Beach widths also have decreased; the length of shore fronted by wide (greater than 15 m) beaches decreased from 64 km to 35 km between 1876–1877 and 1968. Furthermore, the length of shore without a beach increased from 84 km in 1876–1877 to 112 km in 1968. The decreases in recession rates have been caused by the shore-protection structures, which have directly armored the shore from waves (seawalls) or reduced the wave energy reaching the shore by trapping sand (groins). Moreoever, because the shore is a major source of sand for the beaches, the decrease in recession has led to a reduced sand supply and narrower beaches. Ironically, by protecting the shore, the structures apparently have more than compensated for the loss of the best natural form of shore protection, beach sand.

Predicting adjustments in shore and offshore sand profiles on the Great Lakes

Abstract: : This report summarizes a procedure for calculating the ultimate advance or retreat of the beach profile in response to a semipermanent change in water level elevation. The method, applicable to sandy shores throughout the Great Lakes, is illustrated by two examples. Hands (1980 describes the development of the procedure. A strictly empirical correlation useful for estimating shore retreat on a 1- to 5-year basis is discussed in Hands (1979). The present procedure couples field measurements with a model of how the profile ultimately reestablishes equilibrium with a new water level elevation. The former procedure would generally underestimate this longer term change. (Author)

Trophic structure and biomass distribution on two East Cape rocky shores

Abstract: The distribution and biomass of macrofauna and macroalgae is described for two intertidal rocky shores near Port Elizabeth. The sheltered shore supported more macrofauna species (67) than the exposed shore (61), mainly owing to greater habitat heterogeneity; of 88 species recorded, 40 (46%) were shared. The shores had 13 and 23 macroalgal species respectively, with 9 shared. Ash-free dry biomass averaged 26 g m -2 over 200 m on the sheltered shore and 56 g m -2 over 80 m on the exposed shore for macrofauna and 81 g m -2 and 77 g m -2 for the algae. Lower animal biomass values on the sheltered shore may partly have been due to exploitation. Macrobenthic biomass was partitioned as follows on the sheltered and exposed shores respectively: grazers 86% and 82%, filter feeders 8% and 13%, carnivores 4% and 5% and deposit feeders 2% and 0%. Species warranting further study are listed.