The Klang and Langat Rivers flow into the Straits of Malacca to limn the compound Klang Delta and Klang Strait (Fig. 1). TIIC delta is distinguished by its complex network of inter-connecting tidal channels which also serve as distributaries of the rivers. Extensive low tidal flats of sand-mud sediments are present and are intimately related to the delta formation. Lying between the tidal channels are mangrove swamps, which are now essentially confined to the six most offshore islands for the state of Selangor. The innermost island, Indah Island, had lost most of its mangroves in 1999 for the development of West Port and industrial estates.

This was a study of produced formation water (PFW) discharged into a shallow tropical marine ecosystem on the Northwest Shelf of Australia. A combination of oceanographic techniques, geochemical tracer studies, chemical and biological assessment methods, and dispersion modelling was used to describe the distribution and fate of petroleum hydrocarbons and added nutrients discharged from an offshore production platform. Using fine scale volatile hydrocarbon data, the horizontal and vertical diffusion parameters for a three dimensional dispersion model were calibrated under local conditions. Trace hydrocarbon chemistry studies and integration of the data into a mass balance model, facilitated a comprehensive description of dispersion and degradation pathways and rates. Bio-accumulation into bivalves and water column microbial growth inhibition studies confirmed the chemistry and model predictions that the area of potential biological impact extended to 0.5 nautical miles (∼900 m) from the discharge with additional skewing in the direction of the predominant tidal flows. Impact would be expected to be concentrated in transient surface slicks and near surface seawater. Dispersion and degradation processes were fast enough to prevent any long-term build-up of contamination within the system. Trace levels of oil in the near field sandy sediments were directly related to the magnitude of the daily discharge. The study is a benchmark to help predict the effects of further oil industry expansion in this pristine coastal region.

Oceanographic studies were carried out from August 1994 to March 1995 on the intrusion of the Fly River plume in Torres Strait. Measurements at offshore coral reefs revealed an event of decreased salinity (≈24) while salinity of the water over the reefs fluctuated between 30–34 the rest of the time. Modelling suggests that this event resulted from the reversal of longshore currents advecting old river plume water back past the river mouth. There the new river water mixed with the old river plume water generating a patch of low-salinity water. While such events may be infrequent, they have the potential to leave a terrestrial signature on offshore coral reefs, in terms of (1) an input of terrigenous sediment and (2) the possible incorporation of riverine particulate metal into the food chain. The impact during an intrusion event may be significant. In the long term the riverine material is diluted in calcareous sediment produced throughout the year by bio-erosion of coral reefs.

Six oceanographic moorings were maintained in 1993 and 1994 and provided data on the water circulation and the flushing characteristics of the Gulf of Thailand. The concentration of dissolved and dispersed petroleum hydrocarbons (DDPH) was measured at 78 sites in 1994 and 1995 in coastal waters of the Gulf. The water circulation was sluggish and the Gulf was poorly flushed; the mean currents were generally <0.07ms-1. Under the influence of the South China Sea, an anticyclonic gyre existed in the southeast monsoon, a cyclonic gyre in the northwest monsoon, and sluggish currents the rest of the time. Even in the dry season brackish water was found inshore; this suggests that freshwater, that arrived in the Gulf in the previous wet season, was trapped along the coast and that little mixing occurred between offshore and coastal waters. In coastal waters of the Inner Gulf and the Eastern Sea Board there were occasional acute pollution events (DDPH>40μgl-1), superimposed 25% of the time upon chronic pollution (DDPH≈4μgl-1) due to limited flushing of the Inner Gulf and the Eastern Sea Board, and the presence of slightly contaminated water elsewhere (DDPH<1.2μgl-1) 75% of the time. Only the Outer Gulf seems relatively uncontaminated (DDPH≈0.01–0.1μgl-1). The seasonal distribution of the DDPH appeared to be controlled by the water circulation; indeed the highest DDPH values in the Inner Gulf occurred in November–December because of the net currents were weak and variable. The highest DDPH values on the Eastern Sea Board occurred in April–August when the region simultaneously received contaminated coastal water from the Inner Gulf. The smallest DDPH values on the Eastern Sea Board occurred in September–November because strong westward currents prevailed which flushed the contaminants. The observed currents and DDPH data were used to drive an oil spill model which predicted that acute contamination occurs at least once a year everywhere in the Inner Gulf.

A 3-dimensional hydrodynamic model was employed to simulate a flood of freshwater from the Burdekin River into the coastal waters of the Great Barrier Reef (GBR). The model was verified for the entire 1981 flood event using actual discharge data and actual wind data for the river, against the historical field data. This flood was chosen for the validation of the model as it as the only flood event for which an extensive survey and data set of the river plume existed. The river delivered almost 19 billion tonnes of freshwater to the GBR lagoon from 3 separate flood events over the period, with peak discharges exceeding 12,000 tonnes of water per second. Comparisons between model results and field data for 3 different days of field surveys shows very good agreement between the observed and predicted salinity distribution in coastal waters at corresponding times.Sensitivity analysis on the model runs showed that the main driving influences on the fate of the plume water were the discharge volume of the river and the local wind forcing. Thus each ear, one would expect different plume trajectories depending on the time-varying nature of both he wind and the rainfall/catchment. The model simulations also showed that patchiness in the ar-field salinity field was enhanced by discharges from neighbouring rivers and by tidal interactions with headlands along the coast.From a management perspective, the simulations can identify the fate of the Burdekin ver plume in isolation to other freshwater discharges which cannot be done with field observations alone. This information should provide useful information on catchment management implications of the Burdekin region and its impact on shelf and Great Barrier Reef waters.

Six oceanographic moorings were maintained for 8 weeks across the mouth of the mangrove-fringed Fly River estuary from April to June 1995 in the southeast trade wind season. A further 4 moorings were deployed for 8 weeks along the estuary channel in 1992, also in the southeast trade wind season. These data were used to estimate net exchange of suspended sediment between the estuary and the Gulf of Papua. A net inflow of fine sediment into the estuary from the coastal ocean was found to be considerable, about 40 tonnes s-1 or about 10 times the riverine inflow rate, resulting in a calculated, spatially averaged vertical accretion rate of 2 mm year-1. Mangroves may account for trapping 6% of the riverine sediment inflow or about 1/4 of the riverine clay inflow. If this sediment was distributed only over the observed accumulation zones near islands the local accumulation rates in these zones would reach 4 cm year-1. Estimates of soft sediment mass accumulation rates (1–10 kg m-2 year-1) in the channel from Pb-210 and C-14 measurements from cores of deltaic mangrove mud cannot account for this accumulation rate on a 100–1000 year time scale. The fate of the remaining sediment is unknown, it may be exported from the estuary in the monsoon season.

Field studies of tidal flows in largely pristine mangrove swamps suggestthat the momentum equation simplifies to a balance between the water surfaceslope and the drag force. The controlling parameter is the vegetation lengthscale LE, which is a function of the projected area ofmangrove vegetation and the volume of the vegetation. The value ofLE varies greatly with mangrove species and water depth. It isfound that the drag coefficient is related to the Reynolds number Re definedusing LE. The drag coefficient decreases with increasingvalues of Re from a maximum value of 10 at low value of Re (<104), and converges towards 0.4 for Re < 5 ×104.

Intensive field and model studies were undertaken into the dynamics of the Fly River estuary, Papua New Guinea. The estuary has three dominant channels forming a shallow, fan-shaped delta, and receives a mean freshwater discharge of approximately 6,000 m 3 s -1 with little seasonal variation. The estuary is vertically well-mixed in salinity by strong tidal currents. The saline water is distributed unevenly between the channels. Model studies verified by field data suggest that this due to the dynamics of the estuary which are controlled by shallow water frictional effects that generate higher tidal harmonics, the shoaling of the tidal wave from the funnel shape of the estuary, a low value of the bottom friction coefficient resulting from the presence of fluid mud, and the along-channel water surface gradient. This gradient is in turn controlled by two dominant forcings, namely the freshwater discharge and the dominant offshore trade wind. This gradient is also modulated by the spring-neap cycle of the tidal currents which controls the low-frequency friction coefficient. The absence of strong cross-channel salinity gradients and of axial convergence zones is attributed to enhanced horizontal mixing by the lateral velocity shear due to the sinuosity of the thalweg meandering between numerous islands and shoals.

With tidal data from the literature and the field, a two-dimensional (depth-averaged) numerical model was formulated to simulate the dominant semi-diurnal tidal hydrodynamics of the Central Great Barrier Reef continental shelf. Importantly, the individual mesh dimensions of the numerical scheme were set at approximately 2 × 2 km which was sufficient resolution to incorporate the topography of each reef within the matrix. The model provided a new detailed understanding of the influence of the reef matrix on the tidal currents of the outer shelf. In particular, the model demonstrated that the spatial variability in the tidal current's speed and direction exists down to the scale of the 2 km grid size. The model also demonstrated the significant tidally-induced residual currents that result from the interaction with the complex topography of the reef matrix. The advective effect of these tidal currents would be significant as the tidally-induced residual currents are of similar magnitude to the non-tidal currents of the region. Further, the spatial variability in the modelled and observed tidal currents suggests highly spatially variable advective processes operate within the reef waters.

Field studies in the Fly River estuary, Papua New Guinea, show that the turbidity maximum exists only at spring tides. The wind is important in wave-driven fluidization of the bed. The erosion rate varies with the sixth power of the water velocity. The suspended sediment settling velocity varies nonlinearly with the concentration. At least three-quarters of the river sediment inflow appears to be trapped in the estuary. A numerical hydrodynamics-sediment transport model is able to reproduce a number of the key features of the turbidity maximum, and suggests that the turbidity maximum is due to the simultaneous influence of the baroclinic circulation and the tidal pumping.

The Gulf of Papua has the shape of a half-moon of radius of about 200 km and mean depth <50 m. The freshwater inflow is large, about 15,000 m3 s−1 with little seasonal variation. The entire Gulf is stratified in salinity in the top 20 m. The halocline, sharpened by strong winds, inhibits tidal mixing in the Gulf, even in shallow coastal waters where tidal currents are >1 m s−1. The dominant M2 tide propagates from the Coral Sea through the Gulf to enter both Torres Strait and the large estuaries of Papua New Guinea. The low-frequency currents have, in costal waters, little vertical shear associated with the salinity stratification, but, at the shelf break, a strong vertical shear in the well-mixed layer typically 100 m thick. A dominant forcing of the circulation in the Gulf is the eastward-flowing Coral Sea Coastal Current in the Northwest Coral Sea. This current appears to generate a counter-clockwise rotating eddy in the Gulf. The wind fluctuations result in the brackish water leaving the Gulf alternatively at its western and eastern sides. The residence time of river runoff in the Gulf, estimated using a three-dimensional hydrodynamic model, is about 2 months and this estimate agrees with that from freshwater budget estimates. Brackish water intrudes in the Torres Strait where tidal mixing maintains vertical homogeneity. The tidal mixing front is located near the northern tip of the Warrior Reefs and the intrusion is strongest in the monsoon season.

The compaction rate of suspended mud depends not only on the sediment concentration but also on the turbulent intensity. This effect appears to be due to the turbulence plugging micro-channels used in the dewatering process. The compaction rate decreases by a factor of up to 10 with increasing stirring or turbulence in the inhibited settling (fluid mud) range. Our findings are based on the results of laboratory experiments where this effect was measured directly, and on observations of the suspended sediment stratification cycle at tidal frequency in the Normanby River estuary, Australia.

A two-dimensional (depth-averaged) numerical model is proposed to describe the hydrodynamics of Cleveland Bay and is used to investigate the water circulation within the Bay. By utilizing data from the field and the literature, the open boundary conditions used to force the model have been tailored to respond to variances in the behaviour of the dominant shelf- scale processes present in this region; namely: the tides and the wind field as well as the quasi-steady East Australian Current. Thus, the internal circulation dynamics of Cleveland Bay can be readily determined by simply specifying the period of interest and the corresponding wind field. The model can be run in real-time or be used to simulate futuristic events. This model has been verified with field data, and sensitivity tests demonstrate the applicability of the open boundary formulations. Local authorities, who are responsible for the economic and ecological management of the bay, can readily employ such a predictive model for assessing the influence that the water circulation has on present and future activities within Cleveland Bay.