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HTM-NET

Hydrodynamics and Matter Transport - Water Levels and Temperatures



1. The project

Coastal dynamics along the Provençal coast, forced at the mesoscale by the Liguro-Provençal current (Northern Current, NC) and by weather episodes, are complex and still hardly modelled at the bay scale. The HTM-NET project, initiated in 2013, aimed to provide original, continuous and sustainable information through instrumentation located in various ports or sheltered sites and allowing water levels and temperatures to be monitored.

Initially deployed on the Toulon urban area coastline, it has extended from 2019 further west on the Provençal coast to Cape Couronne, at the west of Marseilles. Two instruments are also deployed on the Etang de Berre, in order to better understand the tilting of water bodies or basin seiching, sometimes observed under strong wind conditions in semi-open or closed bays.

The Provençal coastline has very varied characteristics (sandy beaches, rocky coasts, abrupt bathymetry, bays, archipelagos, absence or presence of a continental shelf), diverse exposure to storms (swells and associated surges) and highly anthropised areas. The Liguro-Provençal current, which runs along the coast from the Côte d'Azur, has a more complex structure from the Hyères islands, with the formation of meanders off Toulon. Further west, it mainly follows the continental slope of the Gulf of Lion, but may also have a component along the coast. This current variability, as well as upwelling or downwelling episodes, are linked to variations in weather conditions, dominated for wind by the Mistral and the east wind. These marine weather conditions can be accompanied by significant variations in water levels and temperatures.

2. Objectives of the project

The programme consists in providing original measurement data for a better understanding and modelling of interactions and couplings between coastal dynamics and dynamics at bay scale, through the development of a long-term (several years) observation system. It is at the interface of the research axes in continental shelf dynamics and coastal dynamics of the MIO laboratory, a component of the PYTHEAS Observatory.

3. Instrumentation and implementation

The choice was made for a network of low-cost instruments, which makes it possible to obtain a number of measurement points supposed to be representative of the variability of temperature and level fields at the scale of the coastal fringe studied (with regard to its exposure to meteorological conditions). The instruments, which are autonomous in terms of memory and energy capacity, consist of an underwater pressure and temperature sensor, and an emerging pressure and temperature sensor, which also integrates the battery and the data storage system. Most have a GSM transmission system that allows levels and temperatures to be viewed in delayed time (a few hours) on the network's website.

The instruments are installed in accessible and protected areas (mainly ports). The acquisition of measurements, temperature and pressure in water and air, was initially done every 10 minutes, it has gradually increased to 2 minutes since 2018 throughout the network in order to better study level variations on a scale of a few dozen minutes.

Acknowledgements:

The HTM-NET observation programme initially benefited from a programme specifically dedicated to the Toulon urban area coastline, "Hydrodynamics and MES Transport: Water Levels and Temperature, HTM-NET" co-financed by the TPM urban community, now Toulon Métropole, and recurrent co-financing since 2013 from the CNRS/INSU, as part of the national "Observation and Experimental Systems for Environmental Research" programme over the long term (SOERE) Littoral - Trait de Côte (PYTHEAS observatory management).

The installation of the sensors was made possible thanks to the support or partnership of various organizations: the Port-Cros National Park, the Syndicat Mixte Ports Toulon Provence (SMPTP), which became a stakeholder in Toulon Métropole, the City of Hyères, the CCI du Var, the Conseil Départemental 13, La Ciotat Shipyards.


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