SENAT
Report n° 117 (2007-2008) by M. Roland COURTEAU, Senator (for the parliament office for the evaluation of scientific and technological choices) - Appendix to the minutes of the 7 December 2007 session
Disponible au format Acrobat (21 Moctets)
(2) Using appropriate measuring devices
Every effective warning system relies on seismic stations, tide gauges and tsunamimeters that transmit their data in real-time. In addition, taking into consideration the tsunami-risk linked to landslides necessitates the installation of such specialized sensors as hydrophones.
With regard to tide gauges, there exist several networks. Via the RONIM 71 ( * ) network, SHOM manages 30 tide gauges scattered about metropolitan France, the West Indies, the Indian Ocean and the Pacific. LEGOS 72 ( * ) is responsible for the ROSAME 73 ( * ) network, which includes 4 tide gauges installed off of D'Urville and Amsterdam Islands and in the Crozet and Kerguelen Islands. Furthermore, the departmental bodies responsible for public works, the harbour authorities and certain local governments also manage tide gauges. Finally, within the context of tsunami warnings, the OVSG ("Vulcanologic and Seismologic Observatory of Guadeloupe") is creating its own network in Guadeloupe and CEA proposes that tide gauges must be installed in the Pacific in order to set up a tsunami warning system to protect New Caledonia and Wallis and Futuna.
Many of the Overseas Territories' tide gauges are - or will soon be - capable of transmitting their data in real-time. On the other hand, among those tide gauges managed by SHOM in metropolitan France, only Le Conquet device meets this criterion. However, according to the information gathered by your rapporteur, 13 tide gauges belonging to SHOM (including 11 in metropolitan France) could be rapidly updated to transmit their data in real-time, because they already have the necessary outlets. The estimated cost is €2,500 in equipment and one work day per tide gauge. It is therefore urgent that SHOM's governing body provide it with the necessary means to rapidly adapt the tide gauges in question.
In the Mediterranean, only 2 tide gauges could rapidly transmit their data in real-time: that of Port-Vendres and that of Sète. It is therefore essential to accelerate SHOM's planned replacement in the medium term of the sea-level measuring devices off Ajaccio, Toulon, Marseille and Nice, so that they may be integrated into the warning system before the end of 2008.
Furthermore, your rapporteur insists on the fact that data transmission can be free, if the tide gauges allows for the direct sending of data via the Global Telecommunication System. Therefore, all that needs to be done is to acquire a receiving system to receive the data from all of the tide gauges using GTS. This system, whose energy source and transmissions are autonomous, is particularly recommended for the more isolated islands and coastlines, which is the case with many sites in the Overseas Territories and in foreign countries.
Given the multitude of sea-level networks, it is particularly important to create a "one-stop" set up, by designating a single body in charge of centralizing and archiving the data, as well as making it available to all interested users. In addition, this body could advise all those organizations interested in installing sea-level measuring devices in order to ensure that the planned devices meet the criteria defined by the Global Sea-Level Observing System (GLOSS), and thereby serve as many applications as possible.
Your rapporteur would like to point out that SHOM is responsible for navigational security in the French zones via the establishment of nautical charts and tide tables. Therefore, all bathymetric and tidal information is supposed to be transmitted to SHOM - though, in reality, this is not done by the various organizations on a systematic basis. Indeed, SHOM only learned of the existence of the network managed by the OVSG after these tide gauges were damaged by Hurricane Dean.
To get round this difficulty, the GLOSS national representative 74 ( * ) has taken charge of this mission. However, this solution is not ideal, because it relies on the good will of a single individual, which renders the initiative very vulnerable over time.
Therefore, SHOM should be officially commissioned to coordinate the sea-level measurement activities in France by its board of governors and it should be provided with all the financial and human-resource means necessary for it to carry out this task.
In this regard, your rapporteur would like to point out that the board of governors is currently negotiating SHOM's "objective-means agreement" for the next five years. It would therefore be appropriate to take into account during this process France's needs with regard to the national coordination of its sea-level measuring activities and the network's rapid updating to real-time. The presence of a representative of the Ministry of Ecology and Sustainable Development and a representative of the Ministry of the Interior and of the Overseas Territories on the governing board of SHOM should raise this board's awareness of the fundamental role that SHOM is brought to play in rendering the tsunami warning system effective.
With regard to the seismic stations, France's broadband network should be installed within a few years in metropolitan France. It should correctly cover our territory, while the network's communications are switched over to satellite. Nevertheless, the data-transmission costs are great and should be included in the operating costs of the various organizations responsible for managing the seismic stations.
Finally, the French Mediterranean coastline will only be well protected if at least two tsunamimeters are installed off the coast of Algeria. Other tsunamimeters will be necessary in the Mediterranean basin, including one between Corsica and the mainland and another in the northeast Atlantic. The significant costs engendered by these measuring devices in terms of equipment, installation and maintenance should be shared out at least partially at the European level.
* 71 Sea-level monitoring network.
* 72 Laboratoire d'Etudes en Géophysique et Océanographie Spatiales ("Space-Based Geophysics and Oceanography Research Laboratory").
* 73 Réseau d'Observation Subantarctique et Antarctique du niveau de la MEr ("Subantarctic and Antarctic Sea-Level Observation Network").
* 74 Also a research professor at the University of La Rochelle.