The present investigation examines the growth and decay of an ephemeral creek system produced in response to a managed realignment at Freiston Shore, The Wash. In addition, the natural and anthropogenically enhanced developments of the creek system are compared.The creation of a managed realignment caused sheetflow to occur on the adjacent intertidal zone, approaching and throughout the period of low water, during spring tides. The resultant creek development led to annual headward (landward) extension rates of up to 400 m yr − − − − −1 , over 20 times greater than those taking place during natural conditions. Rapid development of the creek system continued for 2 years, following initiation of the managed realignment. Over the succeeding 12 months, the creek system degenerated; it silted up and reverted to a similar pattern to its original geometry, prior to the managed realignment. Siltation of the creek system coincided with the cessation of sheetflow from the managed realignment. The natural creeks connected to the breaches in the embankment (as part of the scheme) became enlarged sufficiently to accommodate the increased flow produced by the drainage of the managed realignment site, without overbank flow occurring. The natural and anthropogenically enhanced developments of the creek system were similar to those described in the fluvial models described by Schumm et al. (1987): expansion by headward growth, followed by the extension of rapidly growing, long creeks, with tributaries added to fill the drainage network.

The performance of three different hydrodynamic modelling packages is compared in this study, namely Delft3D, Delft3D FM (both developed by Deltares) and MIKE 21 FM (developed by DHI). Delft3D and MIKE 21 FM are internationally known software packages while Delft3D FM (formerly known as D-Flow FM) is a relatively new package. The models use structured approaches (Delft3D), unstructured approaches utilising triangular and quadrilateral elements (MIKE 21 FM) and unstructured approaches utilising elements ranging from linear to six sided (Delft3D FM). Models of Western Port, Australia, were developed using the three different packages to allow a comparison of performance and to determine if there are any differences in using structured versus unstructured approaches. Model performance has been assessed based on model calibration, representation of channel flows and computational efficiency. Despite the inherent differences in the grid configuration and the implementation of the numerical schemes between structured and unstructured approaches, both approaches have been shown to be able to accurately predict hydrodynamic conditions in a complex estuarine environment. The unstructured approach was found to be the most computationally efficient both when run on multiple cores (MIKE 21 FM was the most efficient) and when run on a single core (Delft3D FM was the most efficient).

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An important consideration in the design of ¢sh farms is the fate of the resultant particulate wastes. Consequently, this study is aimed at investigating the validity of an existing near-¢eld regulatory model that assesses the fate of particulate wastes arising from ¢sh farms. The results from the near-¢eld regulatory model have been compared with those from a far-¢eld model to assess the implications of the near¢eld model focusing on a 1km-by-1km area around the ¢sh farm and ignoring any cumulative impacts of other ¢sh farms in the area. The study has been undertaken at a site located on the west coast of Scotland encompassing Loch Shuna and Loch Melfort, which contain eight ¢sh farms. The far-¢eld dispersion modelling was undertaken using a layered three-dimensional tidal model with a coupled dispersion module. This study has demonstrated a number of bene¢ts through using a far-¢eld model to simulate particulate waste dispersion resulting from ¢sh farms as opposed to using a near-¢eld model. The far-¢eld model accounts for the spatial variability in tidal currents, which can be important in coastal areas; it also allows the impacts of multiple ¢sh farms operating in combination to be assessed over a larger area. In addition, it was found that compared with the far-¢eld modelling, the near-¢eld modelling has the potential to underestimate the benthic impacts of ¢sh farms.