Coastal Water Circulation Research Articles

Applications of a 3-D Numerical Model to Circulation in Coastal Waters

A three dimensional baroclinic numerical model which consists of hydrodynamic, transport and turbulence model components, has been applied to two test cases, including: the wind induced flow in a laboratory basin and tidal flow in a model rectangular harbor. The agreement between the physical and numerical model results is highly encouraging. Model has been implemented to Ölüdeniz Lagoon located at the Mediterranean coast of Turkey to simulate tidal and wind driven currents. M2 tide is the dominant tidal constituent for the area. There exist some field measurements performed on water salinity, water temperature and current pattern in Ölüdeniz Lagoon. Even though measurements provide only some preliminary data for the site, favorable results have been obtained from the application of the model to a real coastal water body.

A three-dimensional multi-level turbulence model for tidal motion

A three-dimensional multi-level turbulence model is developed to simulate tide induced circulation in coastal waters. Based on the bathymetry data, the coastal waters are divided into a number of layers. In every layer, the velocities are integrated along the layer depth. The eddy viscosity and diffusivity are computed from the Prandtl mixing length turbulence model. This multi-level model solves for the water surface elevations and currents in different water depths. Comparison of numerical results with the measured data shows good conformity.

Multiple states in doubly driven flow

It has been known since 1961 that if two components effect density, a convecting fluid may possess multiple stable states for the same boundary conditions. Until recently, analytical and numerical calculations have been conducted for application to climate models. Laboratory observations were absent. Experiments have now produced the anticipated multiple states and also give new insight into their physical nature. A new, wider range of applications to estuary and coastal water circulation is indicated. In the experiments a chamber of water was heated from below and exposed to a constant volume flux of salty water from above. This was connected to a large reservoir of fresh room temperature water through two horizontal tubes, one near the top and the other near the bottom. Parameters were such that the time constant for change of temperature was less than the time constant for change in salinity. The experiments confirmed the principal prediction of theory — that two states can exist for the same boundary conditions. The range of two stable states was mapped as a function of the temperature forcing for fixed salinity flux. For low thermal forcing, the salinity driven state was found. This had very slow exchange of warm and very salty water with the reservoir. Density due to salinity was greater than that from temperature. Above a critical forcing an additional state could exist. This possessed exchange with the reservoir in the opposite direction of warm and much lower salinity water above approximately 1.5 times the critical forcing, only the thermal state was found. A second example driven by stress and heat flux also exhibits multiple states. Two examples are analyzed.

Distribution of intertidal isopods in relation to geographical changes in macroalgal cover in the Bay of Biscay

The distribution of intertidal isopods with respect to algal species was investigated over a range of 250 km on the shores of north Spain. A survey of 25 localities included three zones with a distinct composition of algal species: a western zone comprising shores facing Atlantic waters and the outer part of the Bay of Biscay; a narrow transition zone (about 70 km in length); and an eastern zone extending to the inner part of the Bay of Biscay. Thirty two isopod species were collected, 11 of which were present in high densities. Response to geographical change was observed to occur clearly in three species,Ischyromene lacazei, Idotea pelagicaand I.baltica, and to a lesser degree in I.granulosa; the former two and the latter two were abundant in the eastern and western zones respectively. All four species were found to be closely associated with macroalgae species which display geographical changes in abundance (e.g. Laminaria ochroleucaandComllina elongata). In addition,Idoteaspecies were found to inhabit a reduced number of algal species compared with other European shores. Spanish shore of the Bay of Biscay probably constitutes the geographic limit of the distribution of the four species. A sampling artefact might also be responsible to some extent for the patterns of distribution observed. Differences in the physico-chemical properties of sea water along the coast and circulation of coastal waters are not thought to influence the distribution of isopods.

Evidence for an eddy over the continental shelf in the downstream lee of Otago Peninsula, New Zealand

Circulation of coastal waters around Otago Peninsula, south-eastern New Zealand, was investigated by hydrographic surveys from 1978–1982, satellite imagery and a simple numerical model. Two distinct water masses were identified over the continental shelf: (i) Southland Current water occurred over the outer shelf at the surface but penetrated inshore to at least the mid-shelf region near the bottom; and (ii) Neritic waters occurred over the inner shelf, often with a surface band of low salinity water that extended offshore NE from Cape Saunders. Core salinities of this mid-shelf band were inversely related to flow of the Clutha River, located south of the Peninsula. Satellite images show that low salinity nearshore river plumes are squeezed into a core which is then deflected seawards as it flows northward past Cape Saunders. Further north, this water extends back towards shore and sheds a southward counter-current into Blueskin Bay, thereby forming an eddy. A numerical model indicated that asymmetric tidal flow around the Peninsula induces a counter-clockwise eddy within Blueskin Bay. The eddy was enhanced by northward flow of the Southland Current along the outer shelf and an associated meander at the Karitane Canyon. Inclusion of alongshore wind stress into the model suggested that the eddy is further enhanced under moderate steady wind conditions from the north-east but broken down by strong south-west winds. Analysis of local wind data indicates that the eddy is a relatively persistent feature in the northern lee of Otago Peninsula.

Remote Sensing for Nuclear Power Plant Siting

It is shown that satellite remote sensing provides timely and cost-effective information for siting and site evaluation of nuclear power plants. Side-looking airborne radar (SLAR) imagery is especially valuable in regions of prolonged cloud cover and haze, and provides additional assurance in siting and licensing. In addition, a wide range of enhancement techniques should be employed and different types of image should be color-combined to provide structural and lithologic information. Coastal water circulation can also be studied through repetitive coverage and the inherently synoptic nature of imaging satellites. Among the issues discussed are snow cover, sun angle, and cloud cover, and actual site evaluation studies in the Bataan peninsula of the Philippines and Laguna Verde, California.

Offshore Developments that Minimize Environmental Impact

This paper identifies possible reasons for recent increased interest in offshore development and examines some aspects of offshore development technology. Existing offshore developments are citied by the author for purposes of illustrating types of activities which utilize offshore locations. With regard to offshore developments in the future, three types of potential tenants are: (1) site-related that require a marine environment; (2) site-related that are unwanted onshore; and (3) functionally related to other offshore facilities. Examples of each tenant-type are provided. Construction methods, such as conventional earth-fill, polder, pile-supported or caisson-supported deck, and floating structures, as well as the technologies reqired for offshore development are discussed. With regard to environmental considerations, the author states that potential benefits which may be accrued from offshore siting include filling of unsightly swamp areas, reduced shoreline erosion, improved flushing and circulation of coastal waters, expanded marine habitat, control of urban encroachment, less costly land in some cases, large quantities of water for cooling and waste dispersion, reduced visual impact, lessened noise impact, and reduced overall negative environmental impact. Conversely, careful planning of offshore developments to assure minimal adverse effects include considerations of: thermal pollution; destruction of valuable marine life; water, air, and noise pollution; dislocation of valuable endangered species of wild life; interruption of recreational uses; and despoiling of scenic beauty.

Aluminium telegraph wires

Long-term series of meteorological, hydrological and oceanographic data were compared with hypoxia occurrence, in order to define characteristics and trends of this phenomenon in the Emilia Romagna Coastal Zone (ERCZ) in 1977–2008. During this period, hypoxia was recorded at all sampling stations, up to 20 km offshore. In winter, spring and late autumn, hypoxia appearance was matched to significant positive anomalies of air and surface seawater temperatures (up to + 3.6 °C), whereas this effect was less pronounced in August–October. Hypoxia generally occurred with scarce precipitation (0–2 dm3 m2 d− 1) and low wind velocity (0–2 m s− 1), suggesting the importance of stable meteo-marine conditions for the onset of this phenomenon. Nevertheless, wind direction emerged as an indicator of hydrodynamic seasonal changes in the area and is thus a hypoxia regulator. In winter, spring and autumn, hypoxia was favored by large increases of biomass induced by river freshets. In contrast, summer hypoxia occurred during periods of low runoff, suggesting that pronounced stratification and weak circulation of coastal waters were more important in this season.Since the 1990s, a shift from widespread summer hypoxia to local hypoxia irregularly distributed across the year has occurred. This process was concomitant to long-term increases of air temperature (+ 0.14 °C yr− 1), wind speed (+ 0.03 m s− 1 yr− 1) and salinity (+ 0.09 yr− 1), and decreases of Po River flow (− 0.54 km3 yr− 1), oxygen saturation (− 0.2% yr− 1) and PO43 − (− 0.004 μmol P L− 1 yr− 1) and NH4+ (− 0.04 μmol N L− 1 yr− 1) concentrations in surface coastal waters. Despite that several of these changes suggest an ERCZ trophic level positive reduction, similar to that reported for the N Adriatic, the concomitant climate warming might further exacerbate hypoxia in particularly shallow shelf locations. Therefore, in order to avoid hypoxia development a further mitigation of anthropogenic pressure is still needed in the area.