Coastal Configuration Research Articles

Oceanography and Coastal Topography of Herd-Stranding Sites for Whales in New Zealand

Physical aspects of sites of herd strandings by whales in New Zealand are compared with random sites at which strandings have not occurred. Both slope and indentation were significantly less for stranding than for random sites. The coastal configuration of multiple herd-stranding sites in New Zealand was compared with sites elsewhere in the world. Multiple herd-stranding sites all had similar coastal topography; specifically, gently sloping sandy beaches with an adjacent protruding section of coastline. There appeared to be a relation between local currents and herd stranding in Hawke Bay and Golden Bay (New Zealand). Wind-derived onshore currents are most common during the time of year when strandings occur in Golden Bay, New Zealand, and in Cap Vert, Senegal.

Numerical simulation of sea breeze interactions over the Auckland region, New Zealand

Abstract The Colorado State University mesoscale model is used to investigate the influence of gradient wind direction on migratory sea breeze convergence zones (SBCZs) that develop over an irregular coastline incorporating two narrow peninsulas. Results, which are in good qualitative agreement with observations, reveal that SBCZ dynamics are strongly influenced by the extent to which flow is either subparallel or perpendicular to the orientation of the major coastlines. The local coastal configuration is also shown to be the dominant factor controlling the location of zones of intense vertical motion associated with SBCZs. A notable aspect of the study was the simulation of a late afternoon mesoscale cyclonic eddy caused by the interaction of sea breezes during southeasterly gradient flow. Further observations are recommended to verify the existence of this phenomenon.

Dolomite formation in coastal Al-Khiran, Kuwait Arabian Gulf — a re-examination of the sabkha model

Recent dolomites are found in the subtidal, intertidal and supratidal sediments of the lagoons and sabkhas of coastal Al-Khiran, Kuwait. Two stages of diagenetic dolomite formation have been recognised in the sabkhas; one formed during the earlier lagoonal (transgressive) phase and the other during the later sabkha phase after progradation has commenced. In Al-Khiran, dolomite forms under geochemical conditions within the following ranges: (a) a Mg 2+ Ca 2+ molar ratio of 5.3 to 6.1 (in the lagoons) and 3.6 to 14 (in sabkhas); (b) reduced levels of dissolved SO 4 2− concentration, either through microbial sulphate reduction and/or achievement of seasonal mild schizohaline conditions (as in the lagoons) or by minor gypsum precipitation within the sediments; (c) a reducing environment in association with diagenetic pyrite formation; (d) a chloride concentration between 0.62 mol Cl − kg −1 (in lagoons) and 2.15−2.95 mol Cl − kg −1 (in sabkhas); (e) temperatures between 12°C and 35°C, and a pH between 6.4 and 8.4. In those areas of present-day optimum dolomite formation in the sabkha, the near-surface groundwater brines (the potential “dolomitizing” fluid) do not show major changes in chemical composition with time. The question of the dominant mechanism of dolomite formation (i.e. primary precipitation versus diagenetic alteration of host aragonite) is left open, but the balance of evidence (chemical and petrographic) favours a primary origin. Due to the coastal configuration and topographic barriers in the form of chenier ridges, marine flood recharge of the sabkhas and flooding frequencies (which control flow rates) are curtailed. The highest dolomite percentage is confined to intertidal channel areas, and in the absence of an efficient hydrodynamic flow mechanism, the volume of dolomite formed in the sabkha remains low (4 to 10% on average). Away from these areas, the intensity of dolomitization is reduced, even though the porosity and permeability of the host sediments are favourable. This occurrence is rather different from other well known areas of dolomite formation, as in the Caribbean and the southern Arabian Gulf (where the dolomite content is an order of magnitude greater), despite a similar host sediment stratigraphy and mineralogy. In Al-Khiran, it has not been possible to demonstrate a quantitative relationship between the dolomite content in the sediments and solution chemistry variables. It is surmised that the physical setting of the area, not solution chemistry, may be the major control on how much dolomite forms in the sabkha.

Radioelement distribution in river, beach, and offshore areas and their significance to Chavara placer deposit, Southern Kerala Coast of India

The radioelement and heavy mineral distribution in river, beach and innershelf areas of the southern Kerala coast is related to placer mineral concentration on the beaches at Chavara. Southern Kerala rivers—Neyyar, Karamana and Vamanapuram—transport higher amounts of radioactive elements than the larger Kallada River due to higher radioactive minerals in the hinterland rocks. Coastal configurations and the seasonal longshore current pattern seems to control along-shore distribution of minerals. The proposed model for placer concentration suggests that the energy difference and seasonal current direction along this coast is important.

Ground‐Water Discharge to Lakes: Focusing in Embayments

AbstractSeepage of ground water to Green Bay and Lake Michigan from a fractured dolomite aquifer beneath the Door Peninsula of Wisconsin is examined to determine the influences of embayments on the relative amounts of ground‐water discharge. A digital simulation has been used to calculate the quantity and distribution of that discharge. The simulated results are based on the net recharge which occurs on the land portion of the study area. They compare favorably with discharges calculated by flow net using observed hydraulic gradients and conductivities, and are in relative agreement with direct measurements made by seepage meters. The simulation has not been verified (due to lack of independent observations), but the similarity of the discharges from the three methods is argued to indicate the model's validity.In the study area, 66,000 m3/day of ground water is discharged directly to Green Bay (26,000 m3/day) and Lake Michigan (40,000 m3/day). Almost 60% of this total occurs in 20 embayments along the shore, even though they occupy only about 33% of the shoreline length as measured parallel to the long axis of the peninsula.Discharge is focused into embayments by distortion of equipotential lines caused by a bay's penetration into the ground‐water system. In the study area, it is shown that flow amplifications of up to 500% vary directly with two measures of the shoreline shape at bays, horizontal penetration (defined as the ratio of a bay's axial length to the distance to the ground‐water divide), and vertical penetration (the ratio of the maximum bay depth to aquifer thickness). Both factors have equal influence on the amplification of discharge. A graphical means of predicting the effect of coastal configuration on other bays is presented, but its applicability outside the study area is unknown.

Duration of post‐weaning fast and local dispersion in the southern elephant seal, Mirounga leonina, at Marion Island

Post‐weaning behaviour of southern elephant seals, M. leonina, was studied at Marion Island. Duration of fast in both sexes increased in direct proportion to weight at weaning, while it decreased with weaning date in males. Both sexes appear to fast until they have reached a lower weight ‘threshold’ of around 70% of weaning weight. Local dispersion after the fast was studied by resighting tagged animals at weekly intervals. Only 460 (7.0%) resights out of 6530 involved a move between sites, representing 378 (16.8%) of the 2246 pups that were tagged. Males moved more frequently between tagging sites and covered greater distances than females. Moves between sites are more frequent and distances travelled are greater in December than November. Differences in dispersion patterns between Marion Island and lies Kerguelen may be caused by differences in coastal configuration. Underyearlings spent 105.0±19.6 days at sea before returning for between 10 and 20 days in the autumn. Weaning weight had no effect on likelihood of hauling out in autumn. Movements between sites during the autumn haulout are infrequent and no fidelity to birth site is evident at this stage.

SYSTEMS MODEL OF COASTAL CIRCULATION

The numerical model presented simulates two-dimensional hydrodynamic conditions in order to predict both components of the average velocity, vertically integrated, as well as the free surface elevation of the sea in coastal waters. The equations supporting the model are the well-known shallow-water equations, or quasi-static equations. In the classical theory for long waves in shallow water, the vertical accelerations of the fluid particles are neglected because these accelerations are very small with respect to gravity. In the same manner, vertical velocities may be neglected when compared with the horizontal ones. Integration of the system of differential equations in partial derivatives has been performed by using a “leapfrog” finite-difference technique under explicit solving. The computer program was developed in FORTRAN 77. Results and their agreement with coastal configuration are shown for two applications of this model: the Delta del Ebro, on the Mediterranean coast of Spain, and the Ria de Pontevedra, on the Atlantic northwestern coast of Spain. Here attention is focused on the application to the Delta del Ebro area.

On coastal currents off Tehuantepec

The Gulf of Tehuantepec is of particular oceanographic interest because it is one of the few places in the world where intense winds, known as Tehaunos, blow normal to shore in events of a few days duration. A short experiment with floats deployed within a few kilometres off the coast during one of these events, indicates that a remarkably coherent pattern of circulation results. Winds blew offshore with speeds between 10 and 18 m s −1 during several days, driving a cross-shelf jet of about 0·25 m s −1. Close to shore, a compensating alongshore flow of up to 0·80 m s −1 developed in order to feed the offshore flow of the jet and this, in turn, appeared to drive small cells of circulation, whose scales are defined by the coastal configuration. Very rough estimates of the vertically integrated balances of momentum suggest that the sea surface slopes that develop in both the cross-shelf and alongshore directions in response to the wind are of O(10 −6) and, hence, should be quite measurable in a more detailed examination of this region.

Nuclear strategy: the geography of stability

Most of the strategic studies literature on nuclear strategy ignores the role of geographical factors, assuming them to be unimportant. This paper examines the ways in which geography (in terms of state size and location, number of neighbours, distance, coastal configuration, population distribution, etc.) may be relevant to nuclear strategy, and in particular how such factors can contribute to, or hinder, nuclear stability. It is argued that geographical factors and geographical context lead to major asymmetries in both the perceptions and situations of the two superpowers, and this makes arms control agreement much more difficult. The paper concludes by suggesting that the more extensive deployment of nuclear weapons at sea might contribute to improved nuclear stability.

Census of pre‐sixteenth‐century portolan charts

Census of pre‐sixteenth‐century portolan charts

Tidal-Inlet Fills as Hydrocarbon Reservoirs: Example from Halfway Formation, Alberta: ABSTRACT

When placed within the context of their depositional setting and compared to modern analogs, the proven hydrocarbon reservoirs of the Middle Triassic Halfway Formation provide models for future exploration of similar sequences in the stratigraphic record. The Halfway sandstones accumulated along the northeastern margin of the Triassic seaway. Barrier-strandplain deposits amassed along a depositional embayment in western Alberta downdrift of an area of sediment influx into the basin in eastern British Columbia. Along the Halfway coastline, porous deposits accumulated either in the wave-reworked upper shoreface-foreshore zone of barrier islands or in tidal-inlet areas. The barrier-island reservoir sandstones are thin (less than 5 m) and elongate with depositional strike, whereas the tidal-inlet deposits are thick (up to 20 m) with abundant shell-hash lag conglomerates and elongate with depositional dip. Similar to modern coastal configurations, the frequency and thickness of tidal-inlet sequences increase toward the center of the depositional embayment because of tidal amplification. There, more conduits through the barriers were necessary to exchange the larger volumes of water during a tidal cycle. Most of the significant Halfway hydrocarbon reservoirs have been inlet-fill sequences. An excellent example is the Wembley field. Positioned near the center of the Halfway depositional embayment, this field contains 37.5 million bbl of oil. A majority of the reserves are found in inlet deposits. Porosities and permeabilities have been significantly enhanced by secondary solution of the shell lags. Other Halfway inlet reservoirs exist along depositional strike. They are most abundant near the axis of the embayed shorelines where tides were amplified. Future hydrocarbon exploration along other embayed coasts should emphasize the locations and abundance of inlet-fill deposits. End_of_Article - Last_Page 267------------

Blocking of Steady Circulation by Coastal Geometry

Along the southern Turkish continental shelf, the intensity of the observed mean flow has a considerable degree of variability. The relatively strong currents along the straight portion of the coast is reduced significantly in the nearshore region upon encountering irregularities in the form of bays and headlands. As a possible explanation of such blockage by coastal irregularities, a linear, homogeneous wind-stress free model is presented incorporating the constraints of topographic steering and linear bottom friction. Solutions are given for an idealized case of an abrupt indentation on a straight coast adjoining a linearly deepening shelf. The directions preference of blocking and the applicability of boundary layer approximations am discussed. Numerical solutions are obtained for the realistic bathymetry and coastal configuration along the southern Turkish continental shelf. The concepts developed are applied to the observed blocking features.

Relative Role of Waves and Tides in Development of Transgressive and Regressive Coastal Sequences: ABSTRACT

Close examination of coastal morphology and related sediment bodies reveals that the commonly used terms and tide are in many places applied improperly. Such terminology provides little data that the geologist can use in establishing the various process parameters that prevailed in ancient coastal depositional environments. In addition to the absolute and relative size of waves and tides, it is also necessary to consider other factors which contribute to coastal morphology such as tidal prism, sediment availability, topographic relief, and rates of relative sea level change. Interaction of these factors may create a wide variety of stratigraphic sequences. Several of these additional factors differ strikingly depending on whether or not the setting is one of shoreline progradation or marine transgression. In the absence of a delta, progradation generally leads to a simple, relatively straight shoreline, which tends to limit tidal currents to inlets, if present. Transgression caused by a relative rise in sea level may promote shoreline irregularity and embayment, and thus the potential for a larger tidal influence. Progradation occurs under conditions of ample sediment supply relative to the rate of sea level change, whereas transgression causes entrapment of sediment in coastal bays and rivers, thus reducing the amount of sediment available to the open marine setting. Nondeltaic progradational deposits, accordingly, are likely to be considered wave dominated regardless of wave size or tidal range. Waves are more effective in distributing and reworking the sediment along a straight progradational coast than are tidal currents, and, in addition an ample amount of sand is available on the shoreface for this reworking. Shoreface deposits typically are the major component of a nearshore progradational sequence. Transgressive deposits, however, are more likely to be considered tide-dominated even where wave size and regional tidal range are unchanged from those prevailing under conditions of progradation. Coastal irregularity creates refraction patterns that dissipate wave energy over broad areas, and so tidal flow within embayments becomes an important process. Most of the available sediment resides in these embayments and bears the stamp of reworking by tidal currents. Shoreface deposits are likely to be sporadically distributed and of inconsequential volume. Deltas constitute a potential exception to the foregoing generalization. Many deltas are dominated by riverine processes and little influenced by either waves or tides. Moreover, deltas that form in areas of extreme tidal range can generate a complex shoreline during progradation and thereby mimic the embayed coast. Such tide-dominated deltas, however, typically form in areas of broader irregularity of coastline. Sufficient progradation may smooth this larger scale coastal configuration and thereby diminish the tidal influence. End_of_Article - Last_Page 439------------

The effect of coastal geometry on the location of peak surge

An attempt has been made to study the dynamic effect of a curving coast and the angle of incidence of the tropical cyclone track relative to shore-line on the location of the peak surge. The experiments have been performed by a numerical storm surge prediction model for the east coast of India.
 
 Using a forcing wind-stress distribution representative of a severe cyclonic storm. with a core of hurricane winds, a comparison of the results is made for different tracks of a cyclone Striking at three different places along the east coast of India which have different type of coastal configurations, viz. .(i) almost straight line coast. Running approximately from Nagapatinam in the south to Ongole in the north, which is parallel to meridian. (ii) Crescent coast running from Nellore in the south to Masulipatnam in the north, which resembles the crescent of the moon and (iii) a slant coast. running approximately from Visakhapatnam in the south to Patadeep in the north, which is an almost straight line coast inclined to meridians.
 
 The results of the experiment show that the location of the highest surge is sensitive to the coastal geometry and the direction of motion of the storm relative to the coast.

Depositional Setting and History of the Tar Springs Sandstone (Upper Mississippian), Southern Illinois

The Tar Springs Sandstone (Upper Mississippian) crops out in a thin belt around the southern margin of the Illinois Basin. The formation is composed of fine-grained, well-sorted quartz arenites and sublitharenites. Four facies recognized by their lithologies, sedimentary structures, geometries, and geographical locations, comprise the Tar Springs Sandstone. These facies and their dominant characteristics are: 1) Facies A, cross-bedded sandstone; 2) Facies B, horizontally bedded sandstone; 3) Facies C, flaser- and lenticular-bedded sandstone and shale; and 4) Facies D, interbedded sandstones and shales. The Tar Springs Sandstone represents deposition by prograding fluvial-deltaic and paralic sedimentary environments. Specific depositional environments are fluvial and distributary channels (Facies A), shoreface and foreshore (Facies B), tidal flats (Facies C), and pro-delta, interdistributary bay, floodplain, and destructional bars (lower, middle, and upper Facies D). The distribution of the deposits reflects a longshore change in marine processes from wave-dominated in the southeast to tide-dominated in the northwest. This suggests that there was either a change in bathymetry or coastal configuration that resulted in diminished wave energy and an enhanced tidal regime in a longshore direction away from the major sediment sources. Interpretations of the depositional history of the Tar Springs Sandstone suggest the following sequence of events. Fluvial and distributary channels traversed a broad coastal plain and built high-constructive lobate deltas which prograded into a shallow eperic sea. Marine currents reworked the deltaic sand bodies, and northwest flowing longshore currents provided sands to strike-fed mainland beaches. To the northwest of the deltas, where fluvial sediment contributions were minor, thin marine sheet sands were deposited. In these distal areas, sedimentation was dominated by tidal processes, and extensive tidal-flats developed. With the cessation of terrigenous influx, deltaic deposits were reworked into destructional bars. Finally, conditions once again became favorable for clear-water carbonate deposition on the epeiric sea floor.

Storm surges in the Gulf of Thailand

The paper describes a linear model for computing storm surges in the Gulf of Thailand. The coastal configuration of this Gulf is similar to the Bay of Bengal, but the seabed contours are different. There is no extensive shallow region in the Gulf of Thailand as in the Bay of Bengal. In this paper we compare the response of these two basins to forcing by an idealized storm.

Numerical computations of the storm surges in tosa bay

The storm surges which occurred in Tosa Bay in August 21, 1970 were numerically simulated. First of all NOAA's model “SPLASH” (Special Program to List Amplitudes of Surges from Hurricanes) was used and the effects of the typhoon's parameters, the bottom topography, the coastal configuration and the coordinate systems of storm surges were examined. “SPLASH” was then modified to suit computations of storm surges in the open sea and open boundary conditions were studied. Finally a two layer model was developed and the effects of the two layer system on surges were investigated.

Ascension Island, south Atlantic: A survey of inshore benthic macroorganisms, communities and interactions

Ascension, an isolated volcanic island 07° 57′ south of the Equator, is about 145 km west of the mid-Atlantic ridge. The position and coastal configuration of the island results in a high level of wave-action throughout. Six categories of marine habitat are distinguished: (1) open littoral rocks (igneous formations; beach rocks); (2) blow-hole areas; (3) pools (tide pools; inland saline pools); (4) turtle ponds; (5) outfall channels from power stations; (6) sublittoral substrata (rocky areas; calcareous cobbles; conch shells). Except in the absence of barnacles, the characterising organisms on wave-exposed igneous rocks are distributed much as reported elsewhere along tropical Atlantic shores, i.e.: small snails define the littoral fringe; in the eulittoral are two subzones, the upper lacking characterising organisms, the lower with lithothamnia; on the sublittoral fringe exists the sea urchin Echinometra lucunter L. Luxuriant and diversified filamentous and fleshy algae develop only where the Ascension blackfish ( Melichthys niger Bloch), which are extremely abundant and widespread, can either not penetrate or not feed readily due to water movement (e.g. in inland pools; tide pools with rocky barriers; beach; rock slabs; the sublittoral in protective niches, crevices and holes). The contents of the blackfish digestive system show that algae, particularly articulated coralline algae, are widely taken by choice, necessity, or accident. Areas which are intensely grazed by fish carry prostrate or short growth forms of normally large or erect algae as a basal turf; only blue-green algae appear as unrestricted growths. Where sea urchins also are present (e.g. in the sublittoral fringe and certain tide pools) only the crustose lithothamnia persist.

Numerical case studies for oceanic thermal anomalies with a dynamic model

Numerical investigations to identify the physical processes responsible for the generation, evolution, and dissipation of oceanic thermal anomalies (OTA) were carried out using the numerical dynamic model of the North Pacific Experiment (Norpax). The Norpax model is based on time‐integrations of the finite‐difference forms of the primitive equations. It possesses an actual coastal configuration and 10 vertical layers, with a constant maximum depth of 4 km. The horizontal grid spacing, both longitudinal and latitudinal, is 2.5°. The seasonally varying model climatology is generated by integrating the model over 80 years of simulations under the climatological atmospheric forcing, of which the first 60 years are the long‐term annual mean conditions and the last 20 years vary with the seasonal cycle. Large‐scale features of the model ocean climatology compare favorably with observed large‐scale motions and structure in the North Pacific Ocean. The model is used for oceanic thermal anomaly studies. Two simulated cases are presented: one demonstrates the generation and evolution of OTA's under anomalous atmospheric wind forcing of winter 1949–1950, and the other portrays the evolution and dissipation of the OTA's under climatological atmospheric conditions in winter 1971–1972. The resulting model simulations are compared with observational data to examine to what extent change of the oceanic thermal structure is accounted for by the anomalous wind forcing and how much by the internal adjustments in the ocean. The model indicates that OTA's are generated by anomalous atmospheric winds and that thermal advection, both horizontal and vertical, plays the most important role in the generation. During winter, anomalous wind‐induced upwelling has more influence on a cold anomaly in the tropic and subtropic regions than anomalous downwelling has on a warm anomaly in the subarctic region under a weak stable state. The behavior of an initial anomaly under climatological conditions is closely related to large‐scale features, such as the circulation pattern and the thermal gradient in the ocean, and is also subject to modifications due to the presence of OTA's. Aside from limitations of the present course‐grid model, most discrepancies found between the simulated and observed anomalies can generally be attributed to the lack of reliable and accurate meteorological and subsurface data. As better oceanic and atmospheric data become available, further studies of anomaly dynamics through numerical experiments will lead to understanding anomalous heat distributions in the upper layers of the ocean and hence to better ocean predictions.

Numerical Simulation Studies of Oceanic Anomalies in the North Pacific Basin. I: The Ocean Model and the Long-Term Mean State

Abstract A three-dimensional, prognostic numerical model of the North Pacific Ocean, possessing an actual coastal configuration and ten layers (but constant depth), has been developed in order to show the physical nature of large-scale normal and abnormal characteristics of this ocean in response to various normal and anomalous seasonal meteorological conditions. Based on the simulated energetics, emphasis is given to the identification of the major physical processes and essential dynamic mechanisms responsible for the generation, evolution and dissipation of large-scale anomalies in the North Pacific Ocean. The model is based on time integrations of the finite-difference forms of the primitive equations. The oceanic circulation is driven by atmospheric forcing, namely, the surface wind stresses and the differential heating over the ocean. The flux form of numerical scheme for energy conservation and the rigid-lid approximation for filtering out the external inertia-gravity wave are used in the formulati...