Modelling hydrodynamic and bacterial processes through linked river, floodplain and coastal systems : with particular application to marine turbines, barrages and embankment breaches
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Hydro-environmental models have provided robust tools for efficient planning of water resources, flood risk and water quality, as well as increasingly being used for new challenges such as marine renewable energy, and have increasingly attracted growing interest. The new challenges ahead for use of hydro-environmental modelling tools has led to an increasing interest in considering the water system as a whole, and with a larger system framework, with this being achieved by expanding the modelling domain further than the area of the interest to capture the whole hydrodynamic and water quality and/or sediment transport processes. This study has focused on the enhancement of hydro-environmental modelling tools through improving the link between 1-D and 2-D models for the purpose of modelling river, estuarine and coastal water basins. The study has considered traditional boundaries, as well as the development and implementation of less conventional boundary conditions such as momentum absorbing boundaries which were used in simulating the marine renewable energy schemes. A GIS based 2-D hydro-environmental numerical model, namely DIVAST GIS, has been developed in this study and has been dynamically linked to a 1-D model using various linking methods, such as water levels discharges and overlapping methods. The model was augmented with a user-friendly GUI (Graphical User Interface), which was developed using OpenMI standards and thereby facilitate the opportunity to link with other models. The models were applied to two practical and site specific studies. Firstly, the linked models were refined in an application to undertake a hydro-environmental impact assessment study for two different marine renewable energy schemes proposed to extract energy from the Severn Estuary and Bristol Channel. These schemes included the Severn Barrage and an array of tidal stream turbines. The 1-D and 2-D models were linked using the overlapping method and validated against field and laboratory data. Faecal bacteria indicator levels were modelled by considering the interactions between the bacteria and the sediments and a dynamic decay rate, based on turbidity and solar intensity, was deployed for enhanced accuracy in modelling the bacterial fluxes. The linked model showed promising potential in modelling the hydro- environmental impact of marine renewable energy devices and structures. Secondly, the linked models were refined to predict breach failure and flood risk predictions of an artificial breach and flood inundation in the Greenwich Embayment, London. Comparisons were made implementing 1-D/2-D linked models using two different 2-D numerical schemes, namely the ADI and TVD schemes, and using three different 1- D/2-D linking methods, namely water levels discharges and discharges with momentum conservation. The results showed that the predicted flood inundation extent was different when using the two different schemes, as to be expected, and with the results also showing that the link method with the momentum transfer not making a significant difference to the model predictions for this study. Moreover, it was found that the flood inundation and extent predicted using the ADI and TVD methods were similar when the 1-D and 2-D models were linked through the discharge method, while the results were significantly different when the water level method was used to link the models. Consequently, it is recommended that the discharge link method should be used for linking 1-D and 2-D models in applications as for flood defence breaches as reported herein.