Please scroll down to view the document. FIELD MEASUREMENTS OF SHEET FLOW SEDIMENT TRANSPORT IN THE SWASH ZONE
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Gravel beach morphologic change is a function of combined cross-and alongshore transport. At pres... more Gravel beach morphologic change is a function of combined cross-and alongshore transport. At present, numerical methods deal with these processes separately. We present observations from Start Bay, UK, of extreme storm response and recovery, across five gravel subembayments (lengths 250 m to 5 km). An easterly storm sequence in Feb-Mar 2018 forced massive alongshore transport (rotation and headland bypassing) and cross-shore transport including erosion of the barrier, destruction of barrier-crest roads, and distribution of material offshore. We demonstrate that profile response is a function of embayment length and headland proximity, such that: (i) pocket embayments (~250 m) experience a uniform response; (ii) short embayments (~500 m) rotate around a pivot point; (iii) longer bays (>1 km), exhibit a weak cut-fill response near the mid-point; and (v) long beaches (>5 km) show a strong cross-shore response, with rotation near the headlands. This study aids development of fully-coupled gravel transport models.
The role of seagrass in sediment dynamics is studied through observations and model simulations f... more The role of seagrass in sediment dynamics is studied through observations and model simulations focused on the Zostera marina seagrass meadows in the Isles of Scilly UK. Observations are presented which indicate a clear selection for fine grained sediments inside seagrass meadows and coarser sediments surrounding them. A recent modification of the 1DV General Ocean Turbulence Model (GOTM) known as mGOTM has been performed and is presented including a validated methodology for simulating the suspension of a distribution of sediment sizes. Using hind cast wave data from the study site, mGOTM simulations are used to demonstrate how the interactions between seagrass and flow can lead to both a reduction of bed stress but an enhancement of turbulent kinetic energy throughout the flow and how this contributes to the grain size selection observed in this location.
Abstract: Gravel beach morphologic change is a function of combined crossand alongshore transport... more Abstract: Gravel beach morphologic change is a function of combined crossand alongshore transport. At present, numerical methods deal with these processes separately. We present observations from Start Bay, UK, of extreme storm response and recovery, across five gravel subembayments (lengths 250 m to 5 km). An easterly storm sequence in Feb-Mar 2018 forced massive alongshore transport (rotation and headland bypassing) and cross-shore transport including erosion of the barrier, destruction of barrier-crest roads, and distribution of material offshore. We demonstrate that profile response is a function of embayment length and headland proximity, such that: (i) pocket embayments (~250 m) experience a uniform response; (ii) short embayments (~500 m) rotate around a pivot point; (iii) longer bays (>1 km), exhibit a weak cut-fill response near the mid-point; and (v) long beaches (>5 km) show a strong cross-shore response, with rotation near the headlands. This study aids development...
Wave tank testing is a useful tool to assess the performance of Wave Energy Converters (WEC) at d... more Wave tank testing is a useful tool to assess the performance of Wave Energy Converters (WEC) at different technology readiness levels (TRL). At early TRL the use of systematically varying wave conditions is acceptable, however at later stages there is a need to use testing conditions representative of potential prototype deployment sites. Environmental data at these deployment sties can be collected by various instruments, such as buoys, ADCP, radars etc. The most commonly used method to recreate the measured environmental testing conditions in a wave tank is to represent a sea state using the measured significant wave height and peak period and a parametric wave spectrum such as the JONSWAP or PiersonMoskowitz spectrum. Although a useful tool, these parametric spectra represent a simplification which omits much of the site specific spectral information, such as the directional information of the sea state, which has the potential to significantly impact WEC performance. In most wav...
Development of a Data Management Platform for the integration of European Wave Energy Impact Asse... more Development of a Data Management Platform for the integration of European Wave Energy Impact Assessment datasets
The concept of depth of closure, denoted by DoC , is of fundamental importance in evaluating coas... more The concept of depth of closure, denoted by DoC , is of fundamental importance in evaluating coastal sediment budgets, investigating shoreface morphodynamics, and in many coastal engineering applications. This key concept has been fully described in the literature, providing several approaches for its identification and parameterisation, but is not straightforward to apply to alongshore non-uniform macrotidal coastlines. The overall objective of the present research is to apply different criteria to identify the active zone in the nearshore system, using as a study site the embayed, macro-tidal and high-energy coastline of North Cornwall and Devon (United Kingdom). Different approaches are implemented to identify the depth of closure, and theoretical and observational time-dependent interpretations are applied to assess DoC at the medium-term and on the regional scale.
The sole responsibility for the content of this publication lies with the authors. It does not ne... more The sole responsibility for the content of this publication lies with the authors. It does not necessarily reflect the opinion of the European Union. Neither the EACI nor the European Commission are responsible for any use that may be made of the information contained therein" Deliverable D3.1
The shore mounted “Pico” OWC has a relief valve mounted in parallel to the turbine which connects... more The shore mounted “Pico” OWC has a relief valve mounted in parallel to the turbine which connects the chamber to the atmosphere. The aperture of this valve is adjustable and can be used to regulate the pneumatic power exposed to the turbine. Here we develop an algorithm to actively control the relief valve aperture so that the peak pneumatic power of each wave cycle approaches but does not breach the turbine stall threshold, thus providing the maximum pneumatic power possible without the turbine stalling. The relief valve aperture is slow to adjust so the hydrodynamic and pneumatic behaviour is forecasted to allow enough time to achieve the correct aperture before the wave reaches the chamber. The chamber hydrodynamics are forecasted using a neural network that considers hydrodynamic measurements made 60 meters up wave and other operational, environmental and preceding wave, parameters. Turbine stalls were identified approximately by the gradient in turbine vibration and the angular...
A semi automatic technique for Rapid Environmental Assessment in the coastal zone using Small Unmanned Aerial Vehicles (SUAV)
Vousdoukas M.I., Pennucci G. Holman R.A., Conley D.C., 2011. A semi automatic technique for Rapid... more Vousdoukas M.I., Pennucci G. Holman R.A., Conley D.C., 2011. A semi automatic technique for Rapid Environmental Assessment in the coastal zone using Small Unmanned Aerial Vehicles (SUAV). Journal of CoastalResearch, �SI �64 �(Proceedingsofthe 11th Inte The submission reports on the use of Small Unmanned Aerial Vehicles (SUAVs), to generate high quality time- averaged images that can provide information on the nearshore sand bar morphology, the locations of rip channels, and the dimensions of surf/swash zones. A set of ~6200 images obtained at altitudes ranging from 152 to 500 m is processed using a new semi-automatic technique to create geo-referenced snapshots, time-averaged and mosaic images of the nearshore zone. Geo-rectification and 'stitching' of the images is based on an image processing algorithm which automatically identifies common features between consecutive frames, after automatic sea masking and manual quality control. Only the initial frame of the video is geo...
Commercial development of the generation of renewable energy in the marine environment will be pr... more Commercial development of the generation of renewable energy in the marine environment will be predicated on the implementation of reliable methods for the assessment of the in situ energy resource. The most commonly utilized methods for assessments of the wave and current fields currently involves the deployment of in situ sensors. While the deployment of such instrumentation has a long pedigree and has led to numerous advancements in oceanography, there are significant shortcomings associated with the use of in situ instrumentation for resource characterization related to Marine Renewable Energy (MRE). In particular, such measurements are highly susceptible to environmentally related damage and even loss. Operationally, deployment and maintenance costs are high and reliability is low. Technically, the information is spatially constrained and, as relates to the horizontal plain, typically only provides point measurements. HF (High Frequency) radar in a beam forming configuration pr...
In order to ensure the sustainable character of any tidal energy extraction project, the assessme... more In order to ensure the sustainable character of any tidal energy extraction project, the assessment of its potential hydrodynamic impacts is required. As regards Tidal Current Turbine (TCT) arrays, a sustainable implementation would provide optimum power extraction with minimum impacts on the environment. A numerical approach is proposed in this work to create a decision-making tool for use in planning such TCT projects. The tool is built around an existing regional modelling framework (the 3 dimensional Regional Ocean Modeling System ROMS) which is being modified to enable the user to account for the effects of TCTs. In such a framework where farm layout optimization is significantly driven by TCT interactions, the hydrodynamic induced effects of a single TCT cannot be reduced to considerations of momentum alone but must also include the role of turbulence. Consequently, correction terms in the transport equations of the closure model has been implemented to compensate the turbulen...
An inverse methodology for offshore sea wave spectr um estimation and its application to data fro... more An inverse methodology for offshore sea wave spectr um estimation and its application to data from a comprehensive field campaign at Porto Ferro bay is presented in this paper. The required directional moments were computed from the instruments deployed inside the bay (one ADCP and five ADVs) and the data kernel matrixes we re built using a backward ray tracing model. Smoothness constraints and a zero boundary condition were added, the problem being so lved with the NNLS method. By comparison with the measurements fr om the two directional buoys, one may conclude that the offsho re estimates using the ADCP data alone are fairly good. As expected an due to its location, the inclusion of ADV data did not enhance th parameter estimation.
Power production at the Pico OWC WEC has fallen significantly short of early theoretical projecti... more Power production at the Pico OWC WEC has fallen significantly short of early theoretical projections. The main reasons for this that have been identified are: the collection of boulders in the chamber has reduced the water depth promoting wave asymmetry, a defect in the chamber front lip makes a pneumatic connection to the atmosphere at times resulting in pressure loss, and the maximum turbine rotational speed has been limited to below the optimum. In addition the turbulent flow shed from the Wells turbine under stall conditions causes significant stress in the mechanical system components resulting in accelerated fatigue and excessive noise emission. The constant need to maintain and recover fatigued components is an unsustainable drain on financial and human resources. In order to improve power production and reduce fatigue rate by minimising stall frequency and severity, a control strategy is considered to improve pneumatic power exposure to the turbine through relief valve contr...
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