Shoreline variability of an urban beach fronted by a beachrock reef from video imagery

This contribution presents the results of a study on the shoreline variability of a natural perched urban beach (Ammoudara, N. Crete, Greece). Shoreline variability was monitored in high spatio-temporal resolution using time series of coastal video images and a novel, fully automated 2-D shoreline detection algorithm. Ten-month video monitoring showed that cross-shore shoreline change was, in some areas, up to 8 m with adjacent sections of the shoreline showing contrasting patterns of beach loss or gain. Variability increased in spring/early summer and stabilized until the end of the summer when partial beach recovery commenced. Correlation of the patterns of beach change with wave forcing (as recorded at an offshore wave buoy) is not straightforward; the only discernible association was that particularly energetic waves from the northern sector can trigger changes in the patterns of shoreline variability and that increased variability might be sustained by increases in offshore wave steepness. It was also found that the fronting beachrock reef exerts significant geological control on beach hydrodynamics. Hydrodynamic modelling and observations during an energetic event showed that the reef can filter wave energy in a highly differential manner, depending on its local architecture. In some areas, the reef allows only low-energy waves to impinge on the shoreline, whereas elsewhere penetration of higher waves is facilitated by the low elevation and limited width of the reef or by the presence of an inlet. Wave/reef interaction can also generate complex circulation patterns, including rip currents that appeared to be also constrained by the reef architecture.     

The structure of the interplanetary medium during the first stip interval (September–October 1975) and prerelease of energetic solar particles

An analysis of the interplanetary medium structure is made during STIP 1. (September–October, 1975). Using a simple extrapolation method a reconstruction of the stream lines is made which shows that the interplanetary space during this time period was very quiet. Such a behaviour is expected because this interval is close to the minimum of the solar cycle activity.The evolution of two fast solar wind streams, which dominated the interplanetary medium for very long time periods, is studied.A peculiar solar proton event, with onset time before the optical flare, is explained according to Elliot mechanism — i.e., that energetic particles are stored for a long time and released, sometimes, before the optical flare.These particles can be seen only when the interplanetary medium is very quiet, (without shock waves) and the flare very isolated.     

Risk acceptance criterion for tanker oil spill risk reduction measures

This paper is aimed at investigating whether there is ample support for the view that the acceptance criterion for evaluating measures for prevention of oil spills from tankers should be based on cost-effectiveness considerations. One such criterion can be reflected by the Cost of Averting a Tonne of oil Spilt (CATS) whereas its target value is updated by elaborating the inherent uncertainties of oil spill costs and establishing a value for the criterion’s assurance factor. To this end, a value of $80,000/t is proposed as a sensible CATS criterion and the proposed value for the assurance factor F = 1.5 is supported by the retrieved Protection and Indemnity (P&I) Clubs’ Annual Reports. It is envisaged that this criterion would allow the conversion of direct and indirect costs into a non-market value for the optimal allocation of resources between the various parties investing in shipping. A review of previous cost estimation models on oil spills is presented and a probability distribution (log-normal) is fitted on the available oil spill cost data, where it should be made abundantly clear that the mean value of the distribution is used for deriving the updated CATS criterion value. However, the difference between the initial and the updated CATS criterion in the percentiles of the distribution is small. It is found through the current analysis that results are partly lower than the predicted values from the published estimation models. The costs are also found to depend on the type of accident, which is in agreement with the results of previous studies. Other proposals on acceptance criteria are reviewed and it is asserted that the CATS criterion can be considered as the best candidate. Evidence is provided that the CATS approach is practical and meaningful by including examples of successful applications in actual risk assessments. Finally, it is suggested that the criterion may be refined subject to more readily available cost data and experience gained from future decisions.