Showing papers by "Laurent O. Amoudry published in 2015"

Improving decadal coastal geomorphic predictions: An overview of the iCOASST project

Abstract: Coastal areas are already at high risk from a range of geohazards. The cumulative effect of human intervention on soft coastlines has frequently left them far from equilibrium under today’s conditions, especially in densely populated areas. Future changes in marine forcing due to climate change reinforce the need to understand and predict processes of change in shoreline position and configuration at management (decadal) scales. The UK-based iCOASST project is developing new and improved methods to predict decadal geomorphic evolution, linked to coastal erosion and flood risk management. This is based on a framework that links several components to develop a system-level understanding of this change. The framework includes: (1) new methods for system-level analysis and mapping of coast, estuary and inner shelf landform behaviour; (2) well validated ‘bottom-up’ hydrodynamic and sediment transport shelf models which can be applied at shelf scales to investigate inner shelf-coastal interactions; and (3) model compositions formed of existing or new ‘reduced complexity models’ of selected coastal landforms and processes that are suitable for multiple decadal length simulations. This will ultimately allow multiple simulations of coastal evolution which can explore uncertainties in future decadal-scale coastal response, including the effects of climate change and management choices. This paper outlines the current state of progress in the iCOASST Project.

Impact of scaled tidal stream turbine over mobilesediment beds

Abstract: Tidal stream turbines (TST) have been identified as a desirable technology for harnessing tidal energy. Measur ement and characterisation of wakes are critical for environmental and development reasons. Wake recovery length is an importa nt parameter for appropriate design of arrays, and wakes may result in altered dynamics both within the water column and at the seabed. Laboratory-scale experiments over mobile beds have been conducted to quantify the detailed wake structure and its impact on sediment transport dynamics. A 0.2 m diameter model turbine was installed and a steady current was driven over an artificial sediment bed using recirculating pumps. A Nortek acoustic current-meter Aquadopp was used to measure the three-dimensional mean current with vertical profiles at different locations from the turbine. A three-dimensional Acoustic Ripple Profiler was used to map the bed during the experiments. These measurements provide comprehensive da ta sets which can be combined to (i) characterise wakes, bed disturbances, and the impact on suspension processes and, ( ii) used to inform and validate numerical models. Keywords—Tidal stream turbines, laboratory experiments, environmental impact, mobile sediment bed, wakes. I. I NTRODUCTION The need of sustainable energy has led in recent years to the development of tidal stream turbines (TST) and has become a near reality. A number of renewable energy sources are avail able around the world from water, geothermal heat, sun, wind , biomass and wave-tidal sources. However, different issues have made their use extremely difficult: conversion process es, limited efficiencies, infrastructure, land availability, systems reliability and the impact to the environment are all import ant factors in energy extraction [1]. TST take advantage of the well known and predictable tidal current behaviour, which a lso represent a predictable energy generation. In addition, TS T are thought to be a better option than tidal barrages because of a smaller impact impact on the environment. Examples of this new technology are the prototype devices that have been test ed by different companies throughout government support such asMarine Current Turbines , Lunar Energy, SMD Hydrovision, PulseandTGL [2]. While a comprehensive list of impacts of TST on their environment has yet to be determined, effects on the flow field and the sea bed are important. An accurate characterisation of the changes in the flow field and thus the wake will help to determine the distance between turbines in order to achieve th maximum efficiency. The presence of the device will result in a decrease in current velocity but will recover after a certai n distance downstream. Determining the optimal distance betwee n turbines therefore has to balance the decrease in efficiency of energy extraction due to proximity with the increase in installation cost due to overall size of TST farm. The effect of a turbine on the sea bed is less known. Nevertheless, turbulence produced by TST can have an impact if they are too close to the sea bed with possible changes in the normal sediment transport pattern. Experiments with disks have sh own important changes in: i) turbulence structure depending on the proximity to the sea bed, ii) increase in turbulent intensit y over a roughened bed and, iii) far downstream, effects of the wake with a combination of distance to the sea bed and roughness [3]. Impacts of TST on sediment transport may take different forms. A first scenario could be to avoid the effects by placin g the turbines far enough from the sea bed. This will require the knowledge of the total water depth at which no impacts are expected and would limit the number of possible sites as deeper waters will be necessary. On the other hand, the TST will increase the erosion near the rotor, take sediment i n suspension and transport it downstream. This sediment coul d be added to the sediment eroded by the next turbine and finally deposited some distance downstream from the entire TST farm. However, the sediment could be transported again with the reversing of the flow. These mechanisms are not well known and depend on the modifications of the flow field by the presence of a turbine. The present study focuses on the

NOC Liverpool report for the miniSTABLE benthic lander deployments as part of the UK-SSB research programme

Abstract: A review of the key features of a series of seabed based scientific lander deployments undertaken by the National Oceanography Centre at Liverpool, UK as part of the UK Shelf Seas Biogeochemistry (UK-SBS) Programme (www.uk-ssb.org) is provided in this document. A bespoke lander design provided a unique platform for a broad range of scientific measurements to facilitate novel benthic or near seabed scientific research. A complex and diverse set of lander based instrumentation included dissolved oxygen flux or ‘eddy correlation’ sensors, sonar based localised seabed distance and contour profiling, high resolution water velocity measurements and measurements of suspended particulate matter in the lower water column. The sensor suite was complimented by an automated, water sampler for collecting and preserving samples with a programmable sample volume and collection time. These seawater samples were suitable for determining dissolved inorganic nutrient levels close to the seabed. Inline filters were used to assess the levels of particulate concentrations at the time of each sample collection. A series of scientific survey cruises, using the research vessel RRS Discovery, occurred from March 2014 to September 2015 as part of the UK-SSB programme. Within this sequence of scientific cruises four key Celtic Sea based sites were surveyed. The lander deployment sites used provided a diverse range of seabed based scientific study conditions.

Residual circulation modelling at the national UK scale to identify possible sediment pathways to inform decadal coastal geomorphic evolution models

Abstract: A coastal area model of the UK has been setup to investigate the coastal residual circulation to identify possible sediment sources and sinks to inform coastal geomorphic models of alongshore and cross-shore sediment pathways. This study investigates the sensitivity of the annual residual to more realistic forcing and wave-current coupling. Two contrasting case study sites, one in the northwest the other in the southeast of the UK, are analyzed in more detail to identify the vertical variability within the residual circulation to suggest how the transport pathways for suspended and bedload material may differ to inform the regional management schemes.