Énergie marémotrice | EPFL Graph Search

thumb|Usine marémotrice de la Rance. L'énergie marémotrice est issue des mouvements de l'eau créés par les marées et causés par l'effet conjugué des forces de gravitation de la Lune et du Soleil. Elle est utilisée sous forme d'énergie potentielle ou sous forme d'énergie cinétique . L'exploitation de l'énergie marémotrice est ancienne. Les premiers moulins à marée dateraient de l'Antiquité sur la rivière Fleet dans la Londres romaine. Ils apparaissent à travers l'Europe au Moyen Âge comme ceux sur l'Adour, construits au . La première usine marémotrice produisant de l'électricité par la force des marées est l'usine marémotrice de la Rance, dans le nord-est de la Bretagne, mise en service en 1966. Principes Marée Le phénomène de marée est synchronisé par la différence des temps de rotation entre la Terre sur elle-même (24 heures) et la Lune dans son mouvement autour de la Terre (28 jours), avec en outre un effet de la rotation de la Terre autour du Soleil (une année), et

Effects of entrance conditions on tidal hydrodynamics in idealized prismatic estuaries under sea level rise

Steve Hottinger

Understanding tidal hydrodynamics response to sea level rise (SLR) in estuaries is essential to predict future potential issues such as shoreline erosion, more frequent and intense flooding, coastal wetland threatening, and their economic and ecological associated losses. By going beyond the classic static or “bathtub” approach, this study uses the RMA-2 modelling software to capture the full energy dynamic resulting from SLR and changes in entrance conditions. Indeed, entrance restrictions are seen as a key factor controlling tidal propagation within the entire system and only little knowledge exists on their effects on the flow under SLR. An innovative numerical approach using idealized prismatic estuaries is undertook to fill this gap. More than 150 simulation cases are performed, varying the channels geometry, restrictions dimensions and tidal forcing to capture most of existing prismatic estuarine dynamics. The resulting tidal flow is described using tidal ranges (TR), but also flow velocity, tidal asymmetry, wave types, tidal prism, etc. to find out potential interesting trends. In short channels, tidal reflection is found to be the dominant process influencing tidal propagation while in long channels the flow is mostly controlled by bottom friction. TR are amplified up to 10% per metre SLR, exacerbating the future flooding problematics linked to a higher mean sea level. However, strong TR attenuation is observed when entrance restrictions are implemented, leading to potential insights on SLR effects mitigation using narrower inlets. SLR acts on the flow velocities distribution and on the tidal asymmetry by increasing medium velocities and decreasing flood dominance. Both will impact sediment transport, leading to stronger coastal erosion. This increases therefore the pressure on sensitive ecosystem already struggling to stay in pace with SLR. SLR can bring the channels closer or further from their natural period of sway. This change in tidal resonance can lead to modifications of the flow parameters behaviour. When channels become more resonant with SLR, amplification of the above phenomena are usually seen, while when they are brought away from resonance, attenuation or even reverse effects can be observed. All these issues are not captured by the bathtub approach and arise from changes in tidal dynamics. Furthermore, instead of focusing on specific estuaries as most of the previous studies, this project is using an idealized approach allowing a global evaluation of the future tidal hydrodynamics. Understanding tidal response to sea level rise in estuaries is crucial to develop efficient coastal management plans able to mitigate this threat on estuarine ecosystems and populated areas. In particular, over 130 port cities having a population higher than 1 million people are concerned by SLR issues in estuaries.

2019

Tidal influence on soil conditions in an intertidal creek-marsh system

David Andrew Barry

To understand better how tides affect the soil conditions of salt marshes, pore-water flow in a modeled 3-D creek-marsh system was simulated under the influence of both monochromatic and spring-neap tides. In analyzing the simulation results, we examined six indices, viz., marsh surface elevation, hydroperiod, shortest distance to creeks, mean soil water saturation, soil saturation index and net water flux across the marsh surface. The results demonstrated that mean soil water saturation, soil saturation index and net water flux exhibited corresponding patterns of spatial variations, which were related to marsh surface elevation, hydroperiod, shortest distance to creeks and tidal regime. While the relationships could be described by a simple function under monochromatic tides, under spring-neap tides it was more complex with different behaviors in the lower and upper marsh areas. The shortest distance to creeks was a critically important factor affecting soil conditions. Well aerated and drained zones co-existed near the creek under both monochromatic and spring-neap tides. Spring-neap tides led to improved soil aeration in the upper marsh, including the interior section (away from the creek) where the hydroperiod and inundation frequency were reduced during neap tides. However, the local flushing condition did not improve correspondingly. The study suggests that single morphological index cannot describe the soil conditions adequately. A proper representation of the soil conditions for plant growth and distribution should take into account not only the aeration condition but also the flushing condition. For that purpose, a composite index is needed to combine the soil water saturation index and the net flux index.

American Geophysical Union2013

Effects of entrance conditions on tidal hydrodynamics in idealized prismatic estuaries under sea level rise

Steve Hottinger

2019