The Swan River estuary, a microtidal estuary in the south-west of Western Australia, has a largely seasonal cycle of salinity variation due to the low tidal amplitude and strongly seasonal rainfall. In contrast, macro- and mesotidal estuaries may have semi-diurnal, diurnal or fortnightly periodicities in salinity variation. The temporal variation of the position of the salt wedge in the upper reaches of the Swan River estuary was analysed using field data and a laterally averaged, two-dimensional numerical simulation model for very dry (1993–94) and very wet (1973–74) years in the recent rainfall history. The salt wedge dynamics in the estuary are considered to have three phases; salt wedge dominated during summer and autumn characterized by very low freshwater discharge; salt wedge waning or absent in late winter and early spring with high flow; and salt wedge emplacement during late spring and early summer with low flow. During 1974, when the river inflow was greater than that of other years and remained substantial until early summer, the upstream salt wedge propagation during spring and early summer was strongly inhibited by river discharge. The correlation between the longitudinal location of the salt wedge and the inflow for 1994 (r2=0·86) further suggests that freshwater inflow is the most important mechanism affecting the salt wedge position in the Swan River estuary. When applied to other years this predictive tool gave reasonable predictions of the salt wedge position. The recorded positions of the salt wedge for the 4 years of study were compared against results of numerical model simulations, inflow correlations and the Hinwood formulation. Each method provided an adequate description of the salt wedge location apart from Hinwood's formulation for low river discharges, which greatly overpredicted upstream movement of the wedge.

An investigation into the effect of rime step on a common photosynthesis algorithm reveals that the predicted phytoplankton production and biomass depend strongly on the length of the time step. This time step dependence is due to the assumption that a light limitation factor derived From integrating the irradiance over the time step is equivalent to the integrated light limitation factor over the time step. This subtle inaccuracy in defining the factor For light limited phytoplankton production produces a substantial difference in the biomass estimates derived from the two models. To illustrate the difference, the light limitation factor integrated over the time step is implemented in the one dimensional water quality model DYRESM-WQ. The new version of DYRESM-WQ is used to simulate chlorophyll a concentrations in Prospect Reservoir, New South Wales. These results are compared to concentrations predicted using the original algorithm. The comparison shows that the new algorithm for phytoplankton production is relatively insensitive to time step, which decreases the difficulty of calibrating the model for chlorophyll a.

In our work, we investigate systematically the deformation and instability of a rotating cylinder of compressible material under fixed end thrust using Neo-Hookean material model. We employ numerical methods to study the solution of the second order differential equation for the radial deformation, which represents the deformation of the cylinder under loading conditions. We further analyse the instability behaviour of the rotating elastic cylinder using the incremental deformation theory and obtain the critical value of angular velocity when buckling occurs. Finally, we plot a phase diagram, which illustrates the regions of stable, buckling and no solution with respect to angular velocity and end thrust.