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Measurement and modelling of deep sea sediment plumes and implications for deep sea mining
No full textDeep sea mining concerns the extraction of poly-metallic nodules, cobalt-rich crusts and sulphide deposits from the ocean floor. The exploitation of these resources will result in adverse ecological effects arising from the direct removal of the substrate and, potentially, from the formation of sediment plumes that could result in deposition of fine sediment on sensitive species or entrainment of sediment, chemicals and nutrients into over-lying waters. Hence, identifying the behaviour of deep-sea sediment plumes is important in designing mining operations that are ecologically acceptable. Here, we present the results of novel in situ deep sea plume experiments undertaken on the Tropic seamount, 300 nautical miles SSW of the Canary Islands. These plume experiments were accompanied by hydrographic and oceanographic field surveys and supported by detailed numerical modelling and high resolution video settling velocity measurements of the in situ sediment undertaken in the laboratory. The plume experiments involved the controlled formation of benthic sediment plumes and measurement of the plume sediment concentration at a specially designed lander placed at set distances from the plume origin. The experiments were used as the basis for validation of a numerical dispersion model, which was then used to predict the dispersion of plumes generated by full-scale mining. The results highlight that the extent of dispersion of benthic sediment plumes, resulting from mining operations, is significantly reduced by the effects of flocculation, background turbidity and internal tides. These considerations must be taken into account when evaluating the impact and extent of benthic sediment plumes
Impact Assessment of Major Flood Events on Agriculture and Infrastructure in Kerala, India from Remote Sensing Data
No full textClimate-related hazards in India cause large loss of life and damage to property, as well as critical infrastructure on an annual basis. Between 1995 and 2015 it is estimated that some 805 million people in India were affected by weather-related hazards. A recent report put India among the 10 most disaster-prone countries in the world and ranked floods as the climate-related hazard posing the greatest risk to people. Kerala state in particular endured devastating floods in 2018 and 2019. 2020 is expected to be another year with high monsoonal rainfall in Kerala.
The economic damage and loss assessment for buildings, infrastructure and agriculture can only be completed in detail after the initial response phase. However, a much earlier, initial estimate would be of benefit to discussions on fund mobilization and response strategies. Although several approaches and tools are already being used for post-disaster damage and economic loss assessment, their response time can be lengthy and their levels of detail and accuracy vary significantly.
As part of the Weather and Climate Science for Service Partnership India (WCSSP-India), Satellites for Impact and Vulnerability Assessment in India (SIVA) is researching and developing methods for using Earth Observation data to infer the short-term and long-term impact of severe flooding events in India on buildings, key infrastructure and crops.
SIVA uses optical and SAR data as well as freely available third party products in combination with machine learning algorithms with the aim of developing and testing methodologies to provide fast, reliable information about impacts of flooding to facilitate disaster response and recovery. The same methods can also be applied retrospectively to provide information about the impact of previous flood events for use in future disaster modelling
Lessons learned in assessing underwater noise potential impacts for an offshore seismic survey in southern Adriatic Sea
No full textWithin the Environmental Impact Assessment of an offshore 3D Seismic Survey in Southern Adriatic Sea, a comprehensive approach to address potential underwater noise impacts was developed to protect marine fauna. The study was based on applicable international guidelines about underwater noise such as ACCOBAMS, JNCC, and IAGC. The approach allowed to define, and agree with local authorities, consistent mitigation measures to protect marine fauna species in the study area.
Primary data on marine mammals, sea turtles and fish species were collected and integrated with secondary data from literature. An underwater sound propagation model based on the Range dependent Acoustic Model (RAM), producing 3D sound maps, was used to simulate the noise propagation of the 5085 cu. in. seismic array, consisting of 24 airguns at a depth of 8 m. Broadband metrics of cumulative SEL (Sound Exposure Level) and SPL (Sound Peak Level) were used to assess the distance from the source within which TTS (Temporary Threshold Shift) and PTS (Permanent Threshold Shift) might have occurred. The simulation considered potential impacts on cetaceans, sea turtles, pinnipeds and fish species, based on internationally recognized sound thresholds for TTS and PTS (i.e. NOAA). The model indicated an exclusion zone of 700 m to be implemented around seismic sources to avoid permanent injuries or deaths of the considered species. A model sensitivity analysis as well as a measurement test in the field were performed prior to the commencement of the seismic survey in order to validate the calculated exclusion and verify the validity of the model in other periods of the year. The field validation test was performed prior to the survey by recording airguns emissions along a 7 km streamer. The measured sound levels were lower than those predicted confirming the validity of the previously identified 700 m exclusion zone.
Targeted mitigation measures were implemented in line with all considered guidelines, including Marine Fauna Observers and Passive Acoustic Monitoring. Starting from a deep analyisis of the international guidelines for the protection of the marine fauna, the selection of the most suitable mitigation measures was then driven by the local operational context and the national legislation. Local authorities and scientific bodies were involved in the mitigations design process; an innovative Emergency Response Plan, including a Stranding Action Plan, was drafted and approved by competent authorities to prevent and manage potential incidents.
The novelty of this study lies in the use of a robust modelling tool as a basis to define a series of mitigation measures based on a rigorous precautionary approach, such as the draft of an Emergency Response Plan and a Stranding Action Plan. This approach was developed in close collaboration with in-country authorities and scientific bodies. The consistency of the approach reassured local and international stakeholders regarding the mitigation of potential underwater noise impacts of the seismic survey on marine fauna species in the area
Beach and nearshore monitoring techniques
No full textMonitoring of beach and nearshore environments is essential for obtaining better insights into the functioning of the coastal zone. It has driven the understanding of these environments and worked beneficially alongside modelling studies. Hydrodynamics, water quality and sedimentological and morphological processes can be observed and quantified through field measurements. A successful monitoring programme has a well-considered design, reflecting the interests of all parties involved and balancing scientific requirements (such as measuring scales and resolutions in time and space) against available budgets and resources. The key to utilizing the monitoring result is a data management system that accommodates the FAIR principles – Findable, Accessible, Interoperable and Reusable – for data handling. For the future of coastal monitoring we foresee that recent technological developments will help define the way; particularly miniaturized sensors, data transmission advances, and remote sensing techniques. These developments, especially if embedded in high-profile, open-access coastal observatories, can pave the way towards now-casting of coastal systems
Morphological evolution of a barchan dune migrating past an offshore wind farm foundation
Get PDFAs the number of manmade structures installed on the seafloor is increasing rapidly, we seek to understand the impact of these immobile obstacles on marine geomorphological processes, such as the evolution of bedforms. A 5.8 m diameter monopile foundation was installed at the case study offshore windfarm approximately 30 m ahead of an approaching barchan (crescent‐shaped) dune. The impact of the monopile on the dune's evolution was analysed using six multibeam bathymetry surveys spanning 20 years. To substantiate this analysis, coupled three‐dimensional numerical modelling of flows and sediment was conducted in which the scour inducing bed shear stresses were calculated from the modelled turbulent kinetic energy. Following the installation of the monopile, the mid‐section of the dune accelerated and stretched in the direction of the wake of the monopile. Four years after the monopile's installation the rest of the dune had caught up, flattening out the slip face within half the dune's length downstream of the monopile. Due to the modified flow field, the dune was scoured deeply at the base of the monopile to a depth of 6.8 m (supported by the model results that predicted a scour depth exceeding 2 m over a period of just a few days). The surveyed volume of material scoured amounted to 8% of the total dune volume. Whilst the process of scouring occurs at a timescale of days to weeks, the dune migrated on average by 25 m/yr. The difference in the timescale of the two processes allowed the scouring to occur through the full thickness of the dune. The scoured dune profile recovered rapidly once the dune migrated downstream of the monopile. This article demonstrates how large geomorphological features can intercept and migrate past a monopile foundation without long‐lasting impacts on the integrity of the feature or the foundation
Explicit Relaxation Technique for Solving the Green-Naghdi Equations for Dispersive Waves
No full textWe introduce a relaxation technique for solving the Green-Naghdi equations for dispersive waves. We propose a numerical method that is explicit in time and uses continuous finite elements for the approximation in space. The numerical method is compatible with dry states and is provably positivity preserving under a CFL condition. The method is then numerically validated against manufactured solutions and is illustrated by comparison with laboratory experiments. We highlight some coastal engineering applications of the model such as tsunami and storm surge waves propagation over complex topographies. We show the robustness and reproducibility of the method by also implementing it in the open source software Proteus, which is developed at the U.S. Army Engineer Research and Development Center
Communicating simulation outputs of mesoscale coastal evolution to specialist and non-specialist audiences
No full textCoastal geomorphologists and engineers worldwide are increasingly facing the non-trivial challenge of visualising and communicating mesoscale modelling assumptions, uncertainties and outcomes to both coastal specialists and decision-makers. Visualisation of simulation outcomes is a non-trivial problem because the more abstract scientific visualisation techniques favoured by specialists for data exploration and hypothesis-testing are not always as successful at engaging decision-makers and planners. In this paper, we show how the risk of simulation model outcomes becoming disconnected from more realistic visualisations of model outcomes can be minimised by using the Coastal Modelling Environment (CoastalME). CoastalME is a modelling framework for coastal mesoscale morphological modelling that can achieve close linkages between the scientific model abstractions, in the form of lines, areas and volumes, and the 3D representation of topographic and bathymetric surfaces and shallow sub-surface sediment composition. We propose and illustrate through the study case of Happisburgh (eastern England, UK), a transparent methodology to merge the required variety of data types and formats into a 3D-thickness model that is used to initialise a simulation. We conclude by highlighting some of the barriers to the adoption of the methodology proposed
A simple taxonomy for describing the spatio-temporal structure of environmental modelling data
No full textEnvironmental modelling practitioners are now seeking to move forwards together and build standards and technologies with more universal applicability and integration. With so many overlapping environmental modelling technologies and infrastructures being offered and with so many relevant supporting technologies contributing on the periphery, there is considerable scope to articulate and utilise underlying concepts which draw them together. As such, this paper offers the Spatio-temporal Modelling Taxonomy, a simple taxonomy for describing the spatio-temporal structure of environmental numerical modelling data used as input to, or produced as output from environmental numerical models. The taxonomy is motivated from common spatial structures, a set of feature-types to describe observed environmental data and the implementation of the OpenMI integrated modelling standard. It serves as a natural evolution of terminology that is in common use in environmental numerical modelling and is designed to strike the right balance between complexity and utility. It implements a structured, theoretical framework, whilst being essentially practical in nature to apply to the ‘real world’ facing numerical modellers and those seeking to integrate environmental numerical models and the data supporting them
Flood risk management in Africa (Editorial)
No full textThe continent of Africa comprises 54 states, and its climatic conditions are incredibly diverse, ranging from equatorial to desert. Rainfall and river flows in Africa show high levels of variability across a range of spatial and temporal scales (Conway et al., 2009; Hamandawana, 2007; Laraque, Mahé, Orange, & Marieu, 2001; Sutcliffe & Knott, 1987). This poses several complex challenges for the management of floods on the continent. These range from estimating extreme flood flows in ungauged catchments in arid zones in north Africa and managing flood regimes in large, transboundary river basins such as the Niger and Zambezi to reducing the vulnerability to floods of the 238 million people in sub‐Saharan Africa who live in informal settlements (United Nation [UN], 2019)
Using remote sensing to collect data on the impact of flooding on the built environment in Kerala, India
No full textFlooding displaces millions of people worldwide every year, causes billions of dollars’ worth of damage, and is only expected to worsen in coming decades. Measurements of floods’ socioeconomic impact are needed both to enable efficient targeting of relief resources for that event itself, and to act as verification data for the development and testing of impact-based forecast models. However, data about a flood event’s impacts can take months to collect in the aftermath of an event and are often not collected in a consistent fashion. Remote sensing data, while not equivalent to ground truth data, offers the capability to systematically collect data over large regions in a time-efficient way.
Here we present research into methodologies for using remote sensing to collect data on the impact of flooding on the built environment, using the case study of the 2018 Kerala, India floods. According to figures published by the Kerala State Disaster Management Authority, the 2018 floods affected over 800,000 houses and damaged over 9,000 km of roads. Methods based on interferometric coherence decrease have proved successful in detecting structural damage in urban areas caused by natural disasters such as typhoons, tsunamis and landslides. In this situation, however, those methods perform less well because they struggle to detect flood impact in non-urban areas which did not have high pre-event coherence and at buildings that were damaged by inundation but did not sustain the type of structural or roof damage that causes coherence decrease. We therefore assess the alternative approach of combining flood and built environment datasets and we compare the results of doing so using existing or routinely-produced datasets versus using datasets processed especially for this application