A new study by the Institute of Earth Sciences and the Israel Geological Survey examined how pebbles move along beaches, in order to design more stable and protected beaches in the future. Doctoral student Hagi Eyal: "If we understand the movement of pebbles, we can better prepare for powerful storms"
In the reality of a changing climate, an alarming increase in the frequency and intensity of storm waves affecting the world's coasts is expected. A new study at the Institute of Earth Sciences and the Israel Geological Institute, which was recently published In the journal "Geophysical Research Letters", focused on understanding and quantifying the movement of pebbles along beaches under the influence of storm waves. The research was conducted as part of Hagai Eyal's doctoral thesis under the guidance of Prof. Yehuda Anzel and Prof. Nadav Lenski. The team of researchers measured and then developed a physical model describing the movement of the particles. The research, which took place on the shores of the Dead Sea, makes it possible to predict the height of the wave needed to transport a pebble of a certain mass and how far along the coast the pebble will move under the influence of the waves created in the storm. These findings will make it possible to plan beaches in a more efficient way and thus protect them from strong wave storms in the future.
Eyal's research was born from observing the sorting of pebbles of different sizes along the modern coastal ridges that form in the Dead Sea. These ridges are formed every year at a lower height than the previous year as a result of the level drop. In other places in the world the beaches are relatively stable and therefore storms work and create one beach ridge along which the pebbles move for years at the same height. Therefore, it is not possible to link a single wave storm or even several storms in any period to the movement of pebbles. According to the researchers, the receding Dead Sea allows for unique observations without which it is difficult to quantify, model and predict the process. In recent years, research has focused on developing methods by which it will be possible to measure the movement of pebbles in real time in the complex coastal environment. In order to measure the movement of pebbles, the researchers developed an innovative measurement method using 'smart pebbles'. "These are natural pebbles of different sizes, in which we drilled holes and implanted sensors that measure the accelerations and rotations of the pebbles, similar to the sensors in our phones," explains Hagai Eyal. These are sensors with an energy package that is adapted to measure at a high frequency for about ten days, so that the researchers were able to place the 'smart robes' along the coast before an approaching storm as predicted meteorologically, locate them after it and collect the data recorded inside the robe.
Prof. Anzel describes that "By comparing the movement data collected from the pebbles with parallel measurements of waves, winds and currents in the Dead Sea - it is possible to learn about the movement of the pebbles in real time during the storm and also about the causes of the movement. The research allows an initial glimpse of the process of the movement of the pebbles along the coast and this is an unprecedented innovation in the world" . The team of researchers specifies that according to the accelerations and rotations that the robe records, it is possible to know when a robe of any size moved from its position and started moving, what strength and height of wave caused it to change position and at what distance. The research is of applied importance beyond the basic and theoretical questions of earth scientists about the formation of sorting along the coasts.
"According to the observations and analyses, it seems that it is possible to draw a law that explains the movement of pebbles in other parts of the world as well, but this is currently an initial experiment, albeit a very successful one, in the Dead Sea. Future studies will examine other environments", emphasizes Il. The applicability of the research makes it possible to predict the stability of beaches and beach defenses, therefore it is also important in the protection of infrastructures, population areas and artificial beaches. The researchers conclude that "The research makes it possible to understand the movement and stability of pebbles, and therefore will help in the future planning of beach defenses against powerful wave storms."
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