A combination of climate change, due to anthropogenic CO2 emissions and concerns over energy security, due to fluctuating fuel prices, has led to the UK pushing to increase its renewable energy production. Harnessing tidal stream energy is an infant sector in the UK’s renewable energy portfolio, despite the UK’s large tidal stream resource, and is harnessed through deploying tidal stream energy converters. This thesis focuses on the design of a novel vertical axis tidal turbine (VATT) called CarBine which is driven by drag force and therefore has several unique advantages, including slow rotational speed, omni-directionality and a simple design. This research focused on the optimisation of the CarBine design and was split into two areas: physical testing and numerical modelling. A conventional Savonius was also analysed in both of these respects and this enabled a direct comparison of CarBine to a competing drag force driven VATT. Physical testing measured the power of the turbines and was conducted in hydraulic flumes at both Cardiff University (CU) and IFREMER in Northern France for a range of flow conditions. Testing at IFREMER enabled the quantification of the blockage effect in the CU experiments. Physical testing resulted in the optimised design of CarBine being one with a four arm configuration. From physical testing at CU, CarBine showed inferior efficiency performance to that of the conventional Savonius, a Cp of 0.117 compared to 0.225 at U∞=0.72 m/s. As a result a hybrid of both the Savonius and CarBine was tested, namely a Savonius with flaps. However, results from physical testing showed the Savonius with flaps to have inferior performance to both CarBine and the conventional Savonius, with a Cp of 0.103 at U∞=0.72 m/s at CU. Numerical modelling was conducted using the commercial CFD software package, Ansys CFX. Both transient and steady state simulations along with 2D and 3D models were used to model both CarBine and the Savonius. Both the k-ε and SST turbulence models were used for comparison. The two degrees of rotational freedom present in the CarBine design resulted in CarBine being difficult to model precisely. The numerical modelling results were validated against the physical testing results and where available, 3D results showed closer validation than the 2D results.

Based on the concepts of water exchange timescales, a three-dimensional model has been refined to predict the age of water (AW). The model has been applied to two estuaries with very different characteristics. One estuary is a partially stratified micro-tidal estuary, i.e., the Pearl River Estuary (PRE), China and the other one is a well-mixed macro-tidal estuary, i.e., the Severn Estuary and Bristol Channel, UK (SEBC). The focus of this study is to investigate the influence of density-induced circulation on the estuarine water exchange process. A comparison between the predictions made using the barotropic mode and the baroclinic mode has been undertaken in the above two estuaries. The results indicate that due to the partially stratified phenomenon, in the PRE lower AW values are observed at the water surface, with higher AW values occurring near the bed. In the wet season, a more obvious AW stratification can be observed. The density-induced circulation causes an increase in the water mixing rate and a decrease in the timescales by a ratio greater than 50%. The stratification of the AW distribution is also enhanced. However, in the homogenous phenomenon of the SEBC, the baroclinic forcing’s impact on the water exchange process is very small. A model investigation is then carried out to predict the spatio-temporal variation of AW distribution in response to other dynamic factors. A regression analysis reveals that the age of freshwater exponentially decreases with the growth of discharge. Scenario analyses show that the tidal influence becomes more pronounced when the discharge is relatively small, and the varying tidal range mainly impacts on the fluctuation range of the AW, instead of its depth-averaged value. Moreover, the iv vertical variation in the AW is enhanced during neap tides due to less mixing. The age of seawater in the estuary is lowest near the estuary mouth and it increases further upstream. In the SEBC, the impacts of proposed tidal stream turbines with two different array arrangements on the water exchange process are analysed to investigate changes in the water level, current speed and AW distributions. A physical model investigation into the water exchange processes in a small scale model of the SEBC is then undertaken to estimate the travel time between different locations, and the water and tracer fluxes through two selected cross sections.

In this study, a hydro-environmental numerical model is utilised to further demonstrate the applicability of computer models to predict tidal flow in coastal waters. In particular, high resolution model simulations are performed at two selected sites: the Ogeechee Estuary, USA to assess the hydro-kinetic energy potential near Rose Dhu Island, a small island in the estuary; and at Swansea Bay, UK to assess faecal coliform pollution levels in the bay. Model results from the Ogeechee Estuary simulations revealed that better representation of branching smaller creeks located inshore enhanced the magnitude of tidal currents by approximately 30% near Rose Dhu Island. Evaluation of spatial and temporal distribution of currents revealed that local hot-spots of hydro-kinetic energy exist within the estuary and a maximum annual power of 4.75MW is available from the tidal streams surrounding the island. Investigation of the sensitivity of model parameters related to intertidal storage and bottom friction showed that ebb tide dominance in the estuary is reduced by lowering wetland elevation and by increasing bottom friction in the channel. Increasing the marsh friction to represent the resistance offered by marsh vegetation decreased the influence of intertidal storage on tidal distortion as ebb-dominance is reduced. Model results from the Swansea Bay simulations showed that three distinct flow patterns exist in the bay including re-circulating eddy like patterns, due to the presence of a headland located towards to the south-west end of the bay. The model-predicted distribution of Faecal Indicator Organisms (FIO) helped identify major pollution sources that negatively influence the rating of the Swansea Bay bathing water site. Investigation of the spatial distribution of FIO concentrations at the Designated Sampling Point (DSP) revealed that that the samples collected at DSP for compliance monitoring would correctly represent the pollution levels in the surrounding areas, however, at locations further off-shore significant spatial variability by up to five times was observed. As expected, intermittent peaks in FIO concentrations were noticeable following rainfall events, however, a strong temporal variability within a day was also observed at the DSP with concentration values varying by up to ten times in magnitude.

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This project implemented novel approaches to assess the source, age, concentration and mobility of fecal indicator microorganisms within a karst groundwater system. Research was conducted in the well-characterized Blue Hole Spring karst groundwater basin in Versailles, Woodford County, Kentucky. At this site the AC/TC ratio and fecal coliform (FC) bacteria counts were used to delineate sources of fecal inputs and determine relative age of the fecal matter. An aging experiment using indicator bacteria (total coliform (TC) and atypical colonies (AC)), which approximated subsurface conditions, indicated that changes in the AC/TC ratio are likely to be retarded during bacterial transport through karst conduits. Decreases in the AC/TC ratio during the monitoring period appear to be the result of sewage releases. Multiple logistic regression (MLR) modeling was performed to examine correlations between physiochemical parameters and FC concentrations. MLR models using physiochemical parameters correctly predicted “safe for contact” (< 200 cfu/100 mL FC) conditions 65.6% of the time and “unsafe for contact” (> 200 cfu/100 mL FC) conditions 69.2% of the time at Blue Hole Spring. Modeling using other indicators (TC and AC) predicted “safe for contact” conditions 87.5% of the time and “unsafe for contact” conditions 61.5% of the time. A series of tracer tests were performed to compare transport of solute and abiotic particle tracers (rhodamine WT fluorescent dye, bromide and fluorescent bacteria-sized microspheres) and bacteria (15N-enriched wild-type E. coli) within the karst system. The surrogate tracers did not suitably mimic microbial mobility within the basin. Solutes and 15N-enriched E. coli arrived concurrently during storm flow to Blue Hole Spring, whereas microsphere breakthrough corresponded with maximum solute concentrations. The 15Nenriched E. coli exhibited slightly more tailing during storm-flow recession than solute tracers, none of which exhibited remobilization. Microspheres demonstrated remobilization within the conduits that correlated with later increases in discharge related to secondary storm events.

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