Direct personnel hazard in wave overtopping flows at seadikes
Sandoval, Claudio Alejandro
All the human activities at the coastal line are exposed to the wrath of the ocean, the action of waves being one of the most important. Every year in the UK alone, three or four people die due to wave overtopping flows, often including children among the casualties. Currently the design methods of the coastal defences restrict the wave overtopping discharge to a pre-defined level. The methods to calculate the overtopping discharge are well known and widely validated; on the other hand the definition of that admissible discharge is much less studied. This thesis is focused to explore the relation between wave overtopping flow and admissible levels for people at the crest of seadikes. The research is divided in two main areas. The first one is related with the human stability and the identification of the overtopping flow’s parameters responsible to generate a critical situation. Secondly is the link back between this critical flow parameters and the wave condition which can generate them on a seadike. These two main areas are treated separately, based on an exhaustive literature review for each topic, to then combine their results generating a risk prediction for overtopping flows. For the first topic few studies were found which have explored the human stability in overtopping flows, being necessary to extend the research to projects related with fluvial floods. In addition, and due to a lack of data from real overtopping flows a thorough analysis of video records of real overtopping accidents is conducted, yielding a new data of the flow condition that a person could be exposed in an actual overtopping flow. With this information two methods to estimate the critical flow condition which can produce instability on a person are improved and validated for nonviolent overtopping flows. More information was found regarding the prediction of the overtopping flow’s parameters. These finding are used to develop two methods which allow estimating the velocity and depth of the most hazardous flow for a wave condition and seadike geometry. With all this information a series of risk matrices and envelopes are derived, with which it is possible to predict if a certain wave condition will generate overtopping flows capable to unbalance a person at the crest of seadikes. The admissible overtopping for people calculated here are compared with present guidelines and a much more optimistic prediction is found, being the pedestrian prediction generated here more alike to a “trained personal”. Also a significant dependence of the overtopping limits to the seadike geometry is found, aspect which is not considered in the present recommendations. In addition, a great influence of the person characteristics, weight and height, on the tolerable overtoppings is detected. Due to a wide view of the process is considered in this thesis the area which are needed to explore deeper are detected and further work are proposed.