The turbulent properties of flow in rivers are of fundamental importance to aquatic organisms yet are rarely quantified during routine river habitat assessment surveys or the design of restoration schemes due to their complex nature. This thesis uses a detailed review of the literature to highlight the various ways in which plants and animals modify the flow field, how this can deliver beneficial effects; and how turbulence can also generate threats to growth and survival. The thesis then presents the results from detailed field assessments of turbulence properties undertaken on low, intermediate and high gradient rivers to advance scientific understanding of the hydrodynamics of rivers and inform effective habitat assessment and restoration. A reach-scale comparison across sites reveals spatial variations in the relationships between turbulent parameters, emphasising the need for direct measurement of turbulence properties, while a geomorphic unit scale assessment suggests that variations in turbulence at the scale of individual roughness elements, and/or within the same broad groupings of geomorphic units (e.g. different types of pools) can have an important influence on hydraulic habitat. The importance of small-scale flow obstructions is further emphasised through analysis of the temporal dynamics of turbulence properties with changes in flow stage and vegetation growth. The highest magnitude temporal changes in turbulence properties were associated with individual boulders and vegetation patches respectively, indicating flow intensification around these sub-geomorphic unit scale features. Experimental research combining flow measurement with underwater videography reveals that more sophisticated turbulence parameters provide a better explanation of fish behaviour and habitat use under field conditions, further supporting direct measurement of turbulent properties where possible. The new insights into interactions between geomorphology, hydraulics and aquatic organisms generated by this work offer opportunities for refining habitat assessment and restoration design protocols to better integrate the important role of turbulence in generating suitable physical habitat for aquatic organisms.

In recent years, the actuator disc approach which employs the Reynolds-Averaged Navier-Stokes (RANS) solvers has been extensively applied in wind and tidal energy field to estimate the wake of a horizontal axis turbine. This method is simpler to administer and requires moderate computational resources in modelling a tidal turbines rotor. Nonetheless, the use of actuator disc approximation in predicting the performance of tidal devices has been limited to studies involving an extremely small disc (e.g. rotor diameter of 0.1 meter). The drawback of a small scale actuator disc model is the overestimation of essential parameters such as the mesh density and the resolution of the vertical layers, making them impractical to be replicated in a regional scale model. Hence, this study aims to explore the methodology on implementation of the Three- Dimensional (3D) actuator disc-RANS model in an ocean scale simulation. Additionally, this study also aspires to examine the sensitivity of the applied momentum source term and its validity in representing full-size tidal devices. Nonetheless, before the effectiveness of an actuator disc in a regional model can be tested, tidal flow models for the area of interest needed to be set up first. This was essential for two reasons: (a) to ensure accurate hydrodynamic flow conditions at the deployment site were replicated, (b) to give confidence in the outputs produced by the regional scale actuator disc simulations, since in-situ turbine measurement data from a real deployment site were difficult to source. This research was undertaken in two stages; in the first stage, a numerical model which can simulate the tidal flow conditions of the deployment sites was constructed, and, in the second stage, the actuator disc method which is capable of modelling an array of real scale-sized tidal turbines rotors has been implemented. In the first stage, tidal flow simulations of the Pentland Firth and Orkney Waters (PFOW) were conducted using two distinct open-source software - Telemac3D, which is a finite element based numerical model, and Delft3D, which is a finite difference based model. Detailed methodologies in developing a 3D tidal flow model for the PFOW using both numerical models were presented, where their functionality, as well as limitations were explored. In the calibration and validation processes, both models demonstrated excellent comparison against the measured data. However, Telemac3D was selected for further modelling of the actuator disc considering the model's capability to perform parallel computing, together with its flexibility to combine both structured and unstructured mesh. In the second stage, to examine the actuator disc's accuracy in modelling a full size tidal device, the momentum source term was initially applied in an idealised channel study, where the presence of a 20-meter diameter turbine was simulated for both single and array configurations. The following parameters were investigated: (i) size of the unstructured mesh utilised in the computational domain, (ii) variation in disc's thickness, (iii) resolution of the imposed structured grid to represent turbine's enclosure, (iv) variation in the vertical layers, and (v) influence of hydrostatic and non-hydrostatic formulations on the models' outputs. It is to be noted that the turbine's support structures have not been included in the modelling. The predicted velocities and computed turbulence intensities from the models were compared against laboratory measurement data sourced from literature, where excellent agreement between the model outputs and the data from literature was observed. In essence, these studies highlighted the efficiency and robustness of the applied momentum source term in replicating the wake profiles and turbulence characteristics downstream of the disc, hence providing credence in implementing the actuator disc method for a regional scale application. Subsequently, the validated actuator disc method was applied to the Inner Sound region of the Pentland Firth to simulate arrays of up to 32 tidal turbine rotors. The wake development, flow interactions with the rotor arrays, and flow recovery at the Inner Sound region have been successfully mapped. Also, this study highlighted the importance of employing optimal numerical margins, specifically for the structured grid and horizontal planes, as both parameters were relevant in defining the disc's swept area. As published materials on the implementation of actuator disc approach within a regional scale model is still scarce, it was aspired that this work could provide some evidence, guidance and examples of suggested best practice in effort to fill the research gap in modelling tidal turbine arrays using the actuator disc approach.

As developers seek to convert the energy of the tides into electricity, sub-sea turbines must be designed to perform well in increasingly harsh conditions. Such energetic seas have historically been avoided, hence measurements taken below the surface in strong tidal currents and large waves are relatively few, and the theory behind these interactions is underdeveloped. This thesis compares measurements of subsurface velocity taken in the field, at a UK site proposed for development, to the velocity outputs of a model capable of combining waves and currents in a number of ways. In particular the interaction between waves and currents is investigated. The methodology incorporates a novel virtual velocity measurement instrument to measure the model flow, replicating the physical instruments used at sea, such that direct comparisons can be made between the two data-sets. Model and field velocities show good agreement across a range of current speeds and wave heights, with a range of metrics used to demonstrate the suitability of the model, based on linear wave-current theory, for this site. The wave-current interaction module is calibrated, with linear superposition of wave and current velocities proving a suitable representation of field velocities. Calculation of a dispersion relationship affected by mean current velocity marginally improves calibration with field data. Analysis of other sites using the tools developed will further validate this type of model, which in combination with blade element momentum theory, is able to predict pre-construction site specific loads on tidal turbines. Doppler Current Profilers (DCPs) are able to measure subsurface water particle kinematics and sea surface elevation simultaneously, however assumptions made by these instruments jeopardise detail when recording in highly energetic seas, particularly where waves and turbulent tidal currents combine. Models developed to optimise the design of tidal turbines require correct site specific inputs to accurately reflect the conditions that a turbine may encounter through its lifetime, moreover, the kinematics of these models must be accurately validated. To overcome the limitations in DCP measurements a 'Virtual' Doppler Current Profiler (VDCP) is developed (Crossley et al. 2017), enabling quantification of error in site characteristics, and 'like for like' comparisons of field and model kinematics that has never previously been documented. The numerical model developed incorporates tidal currents, waves and turbulence combined linearly to output subsurface velocity based on conditions from the field which have been averaged over ten minute intervals. The inputs are simple, time averaged characteristics (current magnitude, direction, and profile; wave height, period and direction, turbulence intensity and turbulence length-scale) and the model outputs velocities over a two dimensional grid that develops with time. The VDCP samples this flow as if it were the very instrument in the field that recorded the data used for validation. Taking into account the heading, pitch and roll of the instrument a data set directly comparable to that measured in the field is generated. The VDCP is initially used in quantifying error in wave and turbulence statistics, demonstrating a phase dependency of velocity measurements averaged between beams and providing a theoretical error for wave and turbulence characteristics sampled under a range of conditions, in order to improve tidal site characterisation. Spectral moments of the subsurface longitudinal wave orbital velocities recorded by the VDCP can be between 0.1 and 9 times those measured at a point for certain turbulent current conditions, turbulence intensity measurements may vary between 0.2 and 1.5 times the input value in low wave conditions and turbulence length scale calculations can vary by over ten times the input value, dependent on both current and wave conditions. The methodology can be used to determine a theoretical error in any site characterisation parameter for any set of wave, current and turbulence conditions. Results of the model validation using the VDCP show that the tidal flow model, and in particular the newly developed wave-current interaction module, is effective in simulating field subsurface velocities over a range of depths, for waves of up to 3m significant wave height and currents of up to 3.5ms-1. The model is effective in reproducing the wave climate using both measured and modelled surface elevation spectra, and tests, with marginal improvements, the effect of modifying the dispersion equation to account for currents. Field and model velocities compare well over the frequency range dominated by waves, showing only small underestimations in model standard deviations with respect to those from field data, at depths close to the sea surface. At the low frequency end of the modelled spectra, where large turbulent eddies dominate, there is some deviation in model accuracy, particularly during the ebb tide where recorded turbulence parameters are extremely variable, creating uncertainty due to a relatively small sample size. Between field and model velocity maxima, some scatter is observed, potentially providing uncertainty in the estimation of ultimate loads. Model and field damage equivalent velocities, used in the determination of fatigue loads, agree well. Results suggest that a linear wave-current representation of subsurface velocities at this particular tidal site is applicable. Care should be taken when interpreting this result due to the relatively small sample size, and the possibility of site specific nuances, and as such further studies are proposed. The Virtual DCP model is a novel development which has proven its usefulness in the work contained in this thesis and in the analysis of commercial field data. It is extremely versatile, adapting to a range of configurations and set up criteria such that it can be used in the quantification of DCP measurement error for a range of flow characteristics. This information is useful in the design of tidal turbines (and other sub-sea structures) as well as for oceanographic and biological processes. The tidal flow model developed extends beyond the capability of similar numerical models with the capability to model the interaction between waves and currents according to a number of different options. Combined with the VDCP, which samples from the model flow field, a system is created that can be effectively calibrated to find the best model solution to replicate flows at a tidal site measured by a 'real' DCP over a broad range of sea conditions and water depths. The purpose is to ensure that models used to predict the sub surface velocities in the field are suitable and a key question was to understand whether the linear super-position of linear wave models and a turbulent current flow provides a realistic model of the particle kinematics with a view to undertaking loads analysis of a tidal stream turbine. Comparisons of this kind have not previously been documented, and this thesis lays out the path to improved site characterisation.

I assessed the composition of zooplankton communities at the three tidal inlets connecting Lake Pontchartrain to Lake Borgne and subsequently to the Gulf of Mexico. The objectives of my research were to better understand the factors contributing to both spatial and temporal differences in zooplankton communities at the three locations. Monthly samplings of the neuston were conducted from September 2009 until April 2011 and then again from September 2012 until May 2013. Sampling consisted of triplicate tows using SeaGear “Bongo” nets. Water quality data along with water turbidity were recorded at each site and during each sampling effort. All specimens collected during the survey were quantified and identified to the lowest taxonomical unit. The results indicated that there were significant differences among the aquatic invertebrate communities composition among the three sites groups averaged across months (ANOSIM, R= 0.162, p = 0.001). The outcomes from this study could have strong implications for fisheries management and will provide a baseline for future research.

Blind Pass, a heavily structured wave-dominated tidal inlet on the west central coast of Florida, has undergone substantial morphologic changes in the past 150 years. Initially Blind Pass was a mixed-energy inlet. In 1848 a hurricane opened a new inlet to the north called Johns Pass, which captured a large portion of the tidal prism of Blind Pass. Since then Blind Pass migrated southward until it was structurally stabilized in 1937. The decreasing tidal prism resulted in significant inlet channel filling. The channel has been dredged 12 times since 1937. The present inlet is stabilized by two jetties and a series of seawalls. Detailed time-series field measurements of bathymetry and tidal flows were conducted between 2001 and 2004, after the last channel dredging in the summer of 2000. The measured depositional rate in the inlet channel approximately equals the net southward longshore transport rate. This suggests that the inlet has served as a trap for the southward longshore transport allowing negligible bypassing to the eroding downdrift beach. Most of the active sedimentation occurs on the northern side of the inlet. The sediment in the thalweg is largely coarse shell lag, indicating adequate sediment flushing by the ebbing tide. The cross-channel flow measurements revealed that ebb flow was approximately twice as high in the channel thalweg as compared with the rest of the channel. The flood flow was largely uniform across the entire inlet and dominated over the northern portion of the inlet due to the weak ebb flow there. This cross-channel flow pattern is crucial to the understanding of the sedimentation patterns in the Blind Pass channel. Two years after the last dredging the mouth has become shallow enough to induce wave breaking across the shoal area. Distinctive seasonal patterns of sedimentation were measured thereafter in the inlet channel, influenced by seasonal wave climate. The sedimentation is event driven from passage of cold fronts bringing elevated wave energy that accelerates the southward longshore transport. During normal conditions the sediment deposited in the mouth area is redistributed further into the inlet by the flood current combined with wave-driven current.

Bunces Pass is an unstructured tide-dominated inlet just north of the main entrance to Tampa Bay, Florida. The inlet has been stable for at least 130 years, as the size, shape, and orientation have remained unchanged. The morphological evolution of the Bunces Pass ebb-tidal delta is influenced by adjacent inlets. Historically, the ebb tidal delta was extremely large, due to the presence of the south channel of Pass-A-Grille Pass. As the tidal prism decreased through the south channel, the sheltering effect produced by the large ebb tidal delta diminished, and large volumes of sand began migrating shoreward. Sediment from the ebb tidal delta accreted along "the Reefs", formed both North Bunces Key and South Bunces Key, and accreted on Mullet Key south of the inlet. Tidal currents at Bunces Pass are primarily ebb-dominant during both summer and winter seasons, though there is flood dominance for several days during neap tides. The ebb dominance is primarily due to the large back-barrier embayment of Tampa Bay, which results in a spring ebb tidal prism of 2.02 x 107 m³. This tidal prism is more than 400 times the corresponding littoral drift. It is primarily responsible for maintaining the inlet's stability, as well as the development of its large ebb-tidal delta. Sediments from the ebb tidal delta at Bunces Pass reflect different degrees of wave versus tidal energy. The strongest tidal currents present throughout the entire ebb tidal delta complex mechanically weather shell gravel in the main channel, producing a shelly, fine quartz sand with relatively high amounts of shell gravel and carbonate sand. This sub-facies is also present on the north channel margin linear bar, due to the interaction of waves, tidal currents, and a southerly littoral drift along this coastal reach. Fine, quartz sand dominates the off shore and swash platform environments. The present situation at Bunces Pass shows a stabilized, tide-dominated inlet with a large, elongate ebb delta that is unlikely to change significantly in the future if present conditions are maintained. The prevalent ebb-dominance suggests that the inlet is hydraulically connected to the adjacent and much larger Egmont Channel inlet system, which also serves Tampa Bay. Strong ebb-tidal currents have kept Bunces Pass in dynamic equilibrium with its surrounding environment. The large ebb tidal prism is responsible for explaining how a tide-dominated inlet is maintained in a microtidal environment.

Thesis (Ph. D.)--Murdoch University, 2003. / Title from PDF title page (viewed on Apr. 23, 2007). Includes bibliographical references (p. [363]-422).

Thesis (M.C.E.)--University of Delaware, 2006. / Principal faculty advisors: Dominic M. Di Toro and James T. Kirby, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Nowadays, renewable energy is in full growth. In particular, offshore wind farms will be at the centre of UK energetic strategy in the coming years. However, other types of marine renewable are still at an early development stage. That is the case for tidal energy. Many projects have been undertaken but there is no candidate for competitive commercial applications yet. Deltastream is one of these numerous pioneering projects. It consists of a set of three marine current turbines mounted on a triangular base put down onto the seabed. The device is not moored and no harm is done to the environment. However, that makes the structure more sensitive to water flows. And it is important to ensure that it will remain at its location and not being carried along with the tidal streams. Using CFD, the present study aims to evaluate the drag on the nacelles of the structure and come up with solutions to reduce it as much as possible.

The purple sandpipers (Calidris maritima) are the most common waders in the high arctic archipelago of Svalbard, Norway. There they have to cope with a very short summer season and high metabolic costs of migrating far north and breeding in an arctic environment. The food on land is usually scarce, whereas there are rich feeding grounds in the littoral zone, such as in the intertidal zone of river flats. These feeding grounds are though only available to the purple sandpipers during low tide and as long as the estuary is not covered by sea ice. One of these intertidal flats was used as the fieldwork area in this study. To study when the birds are coming to this intertidal flat for feeding, a count study was performed during the entire stay of the purple sandpipers in Svalbard in summer 2010. Point counts were performed at low tide during 118 different days. Additionally, point counts were performed at twenty days during the six hours of the entire low tide period, to study when during the tidal cycle most sandpipers were feeding at the estuary. Most sandpipers were counted at the intertidal flat at the beginning of June with the highest number, 921 individuals, on 8th June. When the tundra was free of snow and the birds could start breeding, numbers where rapidly declining with very few sandpipers left in the estuary in July and the first part of August. From the end of August numbers were increasing again with a second but lower peak in the end of September and beginning of October. By the end of October all sandpipers had left the estuary. The study on the appearance of purple sandpipers at the estuary at the different periods of low tide showed that there were significantly more sandpipers between low tide and half an hour later than at the rest of the low tide period. This might be due to better access to their prey at that time. This knowledge could be used in future studies aiming at recording the maximum numbers. The result of the phenologic study could be included in a long term monitoring to see if the numbers and the timing of purple sandpipers are stable in this area or not: Are the peak numbers differing significantly? Is the timing of the arrival, the stay on the tundra and the timing of leaving the archipelago in the fall changing? Long-term monitoring would be especially interesting in the view of possible influences of the climate change on the purple sandpipers. Rising sea level as a result of the climate change would change the morphology of the estuaries and thereby influence the food resources available for sandpipers.