The one-dimensional hydrodynamical equations of motion and continuity and the equation of transport of salt in a narrowand relatively shallow estuary are derived and solved numerically. Four different numerical solutions of the hydrodynamical equations are presented. These are based on: i) two explicit finite difference schemes (leap-frog and two-step Lax-Wendroff), ii) a four point implicit finite difference scheme, and iii) a Galerkin finite element method. These four numerical methods are used to develop mathematical models for the tidal dynamics in the Tay estuary. The finite element model is shown to be the most advantageous technique for the mathematical simulation of the tidal dynamics in branching estuaries. A combined hydrodynamical and salt intrusion model for a one-dimensional branching estuary based on the finite element method is successfully used to simulate water levels, discharges and salinities throughout Upper Milford Haven estuary between Carr Jetty and tidal limits of Eastern and Western Cleddau.

Simultaneous time-series measurements of the bidirectional, horizontal velocity field and free surface elevation were obtained using a two component electromagnetic current meter and a pressure transducer respectively. Field measurements were obtained within the inner 100m of the surfzone, on a high energy, dissipative beach, (Llangennith, Gower, S. Wales), during both storm (H$ = 2.75m) and calm (H(, = 0.75m) conditions. Of particular interest is the response of infragravity band, (0.003-0.05 Hz) oscillations to incident wave forcing. Shorewards dissipation of incident wave energy in the saturated region of the surfzone, (H,/ft = 0.44), is accompanied by a shorewards growth in infragravity energy. Shoreline levels of infragravity variance increase linearly with the squared breaker height, leading to a pronounced dominance of infragravity energy during high energy conditions, particularly within the inner surfzone. Cross-spectral analysis of shore-normal velocity components and surface elevation time-series show infragravity motions to be standing in the cross-shore direction with at least three zero crossing nodes in the offshore decay structure of the long waves. Analyses of the infragravity band were carried out in terms of a spectral transformation function, (M(x,f)), the predicted spectrum observed by an offshore located sensor, if the shoreline amplitude spectrum is white with unit spectral energy density. The spectral transformation function accurately predicts significant peaks and valleys in the onshore velocity and surface elevation spectra, but not in the longshore current spectra. These observations in combination with theoretical arguments indicate that the infragravity spectra are dominated by free, edge waves forced near resonance with significant contributions from high modes. Storm day infragravity run-up spectra forced from short crested, swell dominated incident waves, (f,-= 0.0769Hz), were essentially white. Contrastingly, calm day long wave run-up spectra resulting from high frequency, (0.106 < f,-< 0.172) wind driven waves were significantly blue. Semi-empirical models for the prediction of (a) gravity and (b) infragravity band variance are developed which, when combined, provide a means of estimating the total free-surface elevation variance in the nearshore zone with a knowledge of the beach profile and incident wave conditions. A spectral transformation function driven by Eckart's (1951) solution for high mode (n= 4) edge waves forms the basis for infragravity band variance model.

No description available.

Investigations into the dynamic environment and structure of some sedimentary areas in the Bristol Channel were carried out. The main area of study was the Helwick Sands, a 14 km long linear sand bank. The surface sand cover of this bank extends northwards into Carmarthen Bay, but is more varied to the south. Sand wave areas were found in association with the bank. These sedimentary features and hydrological measurements indicate the flood tidal current (eastwards flowing) to be dominant to the north of the bank and the ebb current (westwards flowing) to be dominant to the south. These current directions are sub parallel to the long axis of the bank. Near bed currents tend to be more oblique to this axis than surface ones. The area is open to attack by waves and swell travelling into the Bristol Channel from the west and southwest. It is shown that the energy input from both waves and tidal currents is sufficient to move the sea bed sediment. Investigations of the subsurface structure has shown no subsurface control on the siting and development of the bank and it is concluded that it has been hydrodynamically controlled throughout its history. Initiation of the bank started during the Flandrian Transgression, with glacial sediments being eroded by wave action and redistributed by wave and tidal current energy. The present day distribution of sediment on and around the bank is explained in terms of relative wave and unidirectional current dominance. As a part of the investigation into sediment movement, results of experiments on an intertidal sandbank in the Loughor Estuary are presented. Environmental parameters concerned with sand movement on the sea bed are considered and it is concluded that a simple approach to measurements of movement will yield as meaningful result as more sophisticated ones.

The physical characteristics of the Loughor Estuary have been studied by field data collection on selected tidal cycles along the Central Channel of the Estuary, and monthly sampling programmes at its periphery. Data has been collected on water levels, salinity of the water mass and current speed and direction over a range of tides and low to medium freshwater inputs. The tidal wave is symmetrical at the mouth of the Estuary (eastern Carmarthen Bay), becoming asymmetrical as it propagates up the Estuary. Within the Estuary, the tidal response is a combination of a standing (symmetrical) wave and progressive (asymmetrical) wave, with the progressive component increasing towards the head of the Estuary. The flushing time of the Estuary is only of the order of a single tidal cycle; therefore, this estuarine area is one of high energy dissipation and turbulence. The general pattern of tidally-induced surface water circulation is directed along the main longitudinal axis of the Channel. In addition, the orientation of the current system in the main Channel, local variations in the current direction can occur due to the effect of abrupt coastal discontinuities and shallow bathymetry. Salinity variation across the Estuary is very small, with salinities along the southern shoreline being slightly higher than the corresponding northern values. The general pattern of the longitudinal (and vertical) salinity distribution at both High and Low Water, at least under low to medium freshwater discharge, demonstrates that, the lower portion of the Estuary is almost vertically homogeneous, with stratification increasing slightly towards the head of the Estuary. The correlation between salinity and salinity gradients along the Estuary and the total freshwater discharge (based on observations of the River Loughor and extrapolation to the remaining rivers) and tidal range, have demonstrated that there is a strong negative correlation between the salinity at each of the Stations and river discharge. Mixing is influenced slightly more by river discharge than by tidal range. Based on Ilansen and Rattray classification, the Estuary is "laterally homogeneous and well mixed". Net flow is seaward of all depths in the water column; consequently, upstream salt transport must be by diffusion. The net transport of salt upstream, across any of the sections, at the time of the observations, is indicative of flood waters of higher salinity than those on the ebb. The nature of the tidal current system at the mouth of the Loughor Estuary, based on tile analysis of self-recording current meter data is rectilinear immediately opposite to the main Channel axis; rotatory current systems predominate at the peripheral (shallower water) stations. Residual currents demonstrate that waters from the mouth of the Loughor Estuary take about 3 to 4 days to reach the Ilelwick Sands, a linear sandbank adjacent to the northern Bristol Channel coastline; presumably, they then mix with the water masses of the northern Bristol Channel.

No description available.

Data from 80 oceanographic cruises, carried out between 1931 and 1973, were analysed to describe the upper water masses, general circulation, coastal upwelling and "E1 Nino" events along the S.E. Meridional Pacific. Four main water masses were found to be present in the upper 1000 metres of the zone: (a) Subtropical surface water - found at the northern part characterized by a salinity maxima of 34.8-35.0"/oo. (b) Sub-antarctic water - the dominant feature in the surface layers, characterized by low salinities fluctuating between 32.0°/oo and 34.8°/oo, at depths of between 20 metres and 130 metres. Oceanic spreading of these waters varies seasonally, in accordance with the S.E. Pacific anticyclonic gyre; similarly, coastal spreading is seasonally controlled by the fresh-water input in the south. (c) Equatorial subsurface water - present at depths of 300 to 350 metres at the northeastern half of the zone with salinity maxima ranging from 34.5 to 34.9°/oo; in the north this maxima appears associated to an oxygen minimum layer. In the N.E. corner (the Arica-Mejillones region), interaction between "fiords waters" coming from the south and surface and sub-surface waters with high salinities, defines a different water mass - the Arica-Mejillones water, characterized by a higher subsurface salinity maxima (34.7-34.0°/oo) which, coastally, spread_ towards the south at depths of 100 metres. (d) Antarctic Intermediate water - defined by a (lower) salinity minima of 34.2°/oo to 34.6°/oo; its spreading takes place at depths between <500 to >600 metres and it is apparently associated with an oxygen maxima decreasing towards the north. The horizontal circulation follows, in general, the spreading path of the water masses listed above: (a) On the western side, around 1000km offshore, a sluggish northerly motion dominates with velocities (relative) ti 4cm/sec; (b) Further to the east, a flow enters the zone at about 79°W and spreads southerly, at about 5OOkm offshore, with velocities ti 6cm/sec; (c) Nearer to the shore, a somewhat faster northerly flow is found (velocities ti l8cm/sec) at 300-400km offshore; (d) Within the remaining coastal region, three other currents may be found: a coastal counter current, flowing southerly at 200km offshore, with velocities ti l2cm/sec; the "fiords current", which spreads northerly at about 100km offshore with velocities fluctuating between 6 and l6cm/sec; and, a third current, flowing south and very close to the coastline, with velocities ti 20cm/sec (mainly corresponding to the spreading of the Arica-Mejillones water). Coastal upwelling is mainly observed during Spring-Summer, along the northern and central regions. The main source for upwelling is provided by the coastal (fiord) salinity minima. The expressions, in the SE Meridional Pacific, of the air-sea phenomena known as "El Nino", may be summarized as follows: (a) Oceanic Subtropical and Equatorial Subsurface southerly penetrations are reinforced and extended towards the west; (b) The oceanic part of the Subantarctic System progressively weakens; (c) The Iumboldt-Fiords coastal part of the Subantarctic System is reinforced, in the southern regions, and further north is split into the "proper" Humboldt current and a coastal "Fiords Current"; (d) In the N.E. corner, high salinity surface waters (> 35.0°/oo) approach the coastline and, from there, extend south; (e) Waters in the Arica-Mejillones Area stabilizes and further develop the strong Spring Summer thermocline; this, in time, extends to the coastline. Coastal upwelling, on these occasions, ceases and downwelling is observed in areas close to the shore.

No description available.

No description available.

No description available.