 Good morning. I'm going to talk on man-made objects, including old bombs, moving around at the seafloor during extreme storms. Modelling results. Millions of durable man-made objects litter the seafloor in many parts of the ocean. Many of those are heavy and stable, like this anchor in the picture. But don't underestimate the power of water movements under extreme storms and hurricanes. In shallow waters, oscillating fluid motions of up to six metres per second at the density of seawater can exert great forces, enough to shift objects around on time periods of days, months and years. In the North Sea, the focus of this study, millions of World War I and World War II munitions, bombs, mines and shells, lie in and on the seabed. They're called UXO, Unexploded Ordinance. In the same area, extreme storms of low hurricane scale strength occur several times a year. The well-published Storm Brita in 2006 broke equipment on a platform at 15 metres above calm sea level and produced waves of 20 metres height in water depths of just 30 metres. The research question of this study is, do old munitions move around on the seafloor under the influence of extreme events such as these storms? Where and how often? We constructed a data-driven numerical model to examine the problem. Spatial temporal data on sea surface, wave heights, periods and directions from the European Copernicus data system, seabed hardness from DBCBed, water depths from the SRTM 30 Plus data set were all brought to the same grid resolutions. We used Python, we're a Python shop, to do the programming. The strategy was to compute a decision matrix of object behaviour across the natural range of orbital velocities and wave period conditions and then to apply that across the North Sea area using joint probability distributions of the same variables. The challenge in compiling the decision matrix on whether an object under certain wave conditions could move is to accurately compute the forces on the small body which sits on or is it partially buried in the sediment. The object may be one of many shapes of course and may be damaged in some way or flooded. We worked with a flooded, intact cylindrical munition like a bottom-set ground mine because experimental validation data exists for similar objects. The sediment is also a complication. A scour pit will form around the object and depending on the type of sediment to the object's density it might sink or rise in the sediment as it is jostled by the wave actions. But in extreme storms much of the sediment will be uplifted into suspension. The inline horizontal forces on an object through the wave cycles can be calculated with extended Morrison equations. The integrated result is like this for one case which is fairly extreme 10 seconds wave period, 5 meters per second's maximum bottom orbital velocity. The movement of the object is finally classified as steady or rocking, shifting or moving. Given the bottom orbital velocities and periods we calculate drag force which is the fluid relative movement, added mass from hydrodynamic accelerational inertia and the Froude-Croiloff forces wave pressure field. Depending on the velocities and accelerations and also fluid density and the object's drag coefficient and dimensions. It's worth noting that Morrison was just a graduate student when he invented the equations which are still used industry-wide. Two extra restraining factors on movement are the rolling friction coefficient for a wheel on the bottom and uphill movement of the body over the edges of any scour pit that develop around it. The addition of these impulsive and resistant forces is complicated by their relative faces in the wave cycle and their dependence on the relative object fluid velocities and accelerations. That is why the plots are so complicated but the important graph is of displacements if and when the object breaks out of its scour pit and moves significantly. You can see that with the triangle on the diagram. The decision matrix that results is shown here in colour for the different scales of wave-induced bottom flows shown by period, vertical axis and by the maximum orbital velocity, the x-axis. The stipple shows the range of bottom flow conditions that are encountered in the area of study. The colours show the types of object motion that is possible in the varying conditions. As you can imagine, validation data for conditions at the seabed during severe storms is extremely difficult to come by. Here we're showing some as the blue circles. In recent decades, NATO entities have deployed instrumented cylindrical objects on the seabed where they have been subjected to storm conditions and similar shaped bottom objects have been tracked in the US before and after hurricanes. That gives us our validation data. The scatter in the movement data is wide as you see here with the circles but does appear to coincide with our modelling results. We have confidence that this modelling can help engineering energy and transportation projects to judge whether old munitions have moved in the times between root clearance surveys. To compute the likelihood of movement of the objects in any pixel of the map area the decision matrix is convolved with the joint spatial probabilities of the wave bottom orbital velocities and wave periods. These are the data that was supplied for instance from Coponicus. The likelihood of the chosen class of object moving is output supplied for this study in terms of return times for movement. You can see that the areas of predicted frequent movement correspond with shallow banks of this North Sea area but these are often areas of preferred industry development. The general conclusion from this and our other projects on extreme events is that researchers tend to be incredulous of records of extreme conditions and they stay close in their analysis to instrumented recorded data but instruments don't survive extreme conditions well and weekly quantifiable observations of extreme conditions have to be modelled too. We need to stretch the upper conditions of our numerical models of the sea bed. Thank you. Any questions?