Many countries have significant interests in generating electricity using waves and tidal current technologies. In energetic areas, waves and tidal currents interact for modifying the energy resource and impacting on the design conditions. Changes to the wave climate depend on the strength of the current and the relative wave direction. SWAN simulations of the wave climate around the Orkney Islands, with and without currents, show that considerable changes in the wave climate occur near sites of interest to wave and tidal energy project developers. Using circular statistics the effect of the relative angle between the waves and the current can be investigated. Local effects can lead to 150-200% increases in wave height when the waves oppose the current. These dramatic changes lead to an increase in wave power of over 100kWm −1 . The complex nature of the tides in the channels also leads to large changes in wave power during the so-called slack water period. Wave amplification diagrams are proposed to provide a convenient summary of wave-current effects at a particular site and allow a statistical analysis to be made. When performing resource analysis and site selection work for marine energy projects, wave-current interaction must be considered.

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A numerical method which fulfils the free-surface boundary conditions and extrapolates the fluid velocity in to empty grid cells outside the fluid region on a fixed Cartesian grid system is presented. The complex, three-dimensional, vortex structures formed via surface/vortex interaction and induction between vortices have been computed using the proposed technique implemented within a level-set method for both vertical and oblique droplet impacts in incompressible fluids. The present results have been validated through numerical tests which confirm zero tangential shear at the free-surface and comparisons with experimental observations of cavity and vortex ring formation underneath the impact location. In some cases, transitions from a concentric vortex ring to a fully three-dimensional vortex structure has been confirmed. Whilst the primary vortex ring is initiated at the highly curved contact surface between the droplet and receiving surface, azimuthal instabilities are manifested in the shear layer around the cavity crater developing after the vertical impact, resulting in axial counter-rotating vorticity between the cavity and descending vortex ring. Underlying mechanisms which induce local deformation of the free-surface, creating a so-called scar, due to the sub-surface vortices at the oblique impacts are also discussed.

A numerical computation of the 2011 Tohoku earthquake tsunami was performed to identify fundamental features of the tsunami evolution along the coast of Hokkaido, Japan. Edge waves formed at multiple locations where the refracted tsunami focused, governing local surface oscillations and regional variations in tsunami height along the Pacific coast of Hokkaido. The computation reasonably reproduced the distribution of surveyed tsunami height as well as the time records of surface elevation recorded at ports in Hokkaido. The major features of the frequency spectrum for the 2011 Tohoku tsunami were identical to those for the 2003 Tokachi-oki earthquake tsunami; inherent local properties of surface oscillation caused by the passage of edge waves existed, determined by the local bathymetry.

From Tuesday, December 16, 2014, until Thursday, December 18, Hokkaido was battered by strong winds and high sea waves caused by a passing low pressure system intensified to typhoon levels. In the city of Nemuro, a rise in sea level influenced by the storm surge which exceeded quay height in port areas was observed from predawn Wednesday, December 17, 2014. Flooding was experienced in areas of central Nemuro, the Nemuro Port and estuaries of rivers. This technical note provides a comprehensive meteorological analysis and the results of a local flood survey carried out by the authors from December 19 to 21, 2014, and summarizes the characteristics of the 2014 Nemuro storm surge disaster

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Extratropical cyclones that develop rapidly in the northwest Pacific Ocean, called explosive cyclones, have caused storm surges twice recently along the coast of Nemuro Bay, located in northeastern Japan, in 2014 and 2015. As the number and intensity of explosive cyclones have increased over the last three decades near the Japanese archipelago (Iwao, Inatsu, and Kimoto 2012), the frequency of extreme storm surges is anticipated to increase under future climatic conditions. Explosive cyclones formed in the northwest Pacific region can be categorized into three major types (Yoshida and Asuma 2004) based on their evolution: Type-I cyclones develop over the Sea of Japan and travel toward the Sea of Okhotsk, Type-II are generated on the continent and move toward the Pacific Ocean through the Sea of Japan, and Type-III travel northward in the Pacific Ocean along the Japanese archipelago. We performed computational experiments of past storm surges to find statistical fea-tures of local sea levels, depending on the types of the cyclone evolution under a realistic meteorological scenario of winter cyclones, with aim to provide possible sea level rise expected in the northeast Asia.Here, we show that amplification of local sea level, governed by the orientation of coastal lines with cyclone tracks, is defined by the evolution type that is classified by their trajectories, rather than the intensity, of the cyclone. Nemuro Bay is the most vulnerable site in the northwest Pacific region regardless of the evolution type; thus repeated disasters are anticipated therein. Severe storm surges are also expected along certain other semi-enclosed coasts facing the northern Sea of Japan and Sea of Okhotsk due to Type-I cyclones. The probabilistic evaluation of sea levels depending on the cyclone evolution type as introduced in this study may be useful for evaluating potential disasters.

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