Study to be conducted by team of experts in meteorology and oceanography

Two-year study to be carried out on forecasting "rissagas"

Destruction. Result of the last major "rissaga" in June

Sensors to measure the sea level will be installed in the Mallorcan ports of Alcúdia, Cala Ratjada, the Channel of Menorca and in the port of Ciutadella

C.M.W..Maó

Ports de les Illes Balears has commissioned a study into the natural phenomenon known as "rissagas" which affect the port of Ciutadella; this investigation will be the most comprehensive to have been carried out in the last 25 years. The scientific team will be composed of experts in meteorology and oceanography from the Balearic University, the companies SENER and EMS and the GIOC group from the University lof Cantabria who will be co-ordinated by Agustí Jansà, the Director of the Balearic Meteorological Centre.

From March 2007 a system of sensors will be installed in the ports of Alcúdia and Cala Ratjada in Mallorca, in the Channel of Menorca (at a depth of some 50 metres and with a large buoy on the surface) and in the port of Ciutadella. Meteorological sensors will also be installed in the two Mallorcan ports to obtain atmospheric readings.

The sensor system will use mobile phone communications to send details of sea currents, waves and atmospheric pressure every second to a central computer. The scientists say that this is a pioneer system that is similar to technology used in the U.S.A. to predict tsunamis.

The study will last two years. Readings will be taken during the "rissaga" season, i.e. between April and October, next year and in 2008. Once the results are available the scientific team will be able to decide on measures to protect the port of Ciutadella. Two possibilities have been mooted: to continue with the present system of closing the port to maritime traffic whenever there is a "rissaga" alert (which should be more precise in future); or to study a flood barrier system.

The new system of sensors will allow more accurate predictions of "rissagas". The present system gives warning of "tidal bores" within the next 6-48 hours. The objective of this scheme is to reduce this prediction time to 1-2 hours.

Scientific unknown

The "rissaga" is a natural phenomenon which especially affects the port of Ciutadella and which became the subject of studies 25 years ago. However, scientists acknowledge that it is still relatively unknown. Agustí Jansà says that "there are hypotheses. The Œrissaga´ is a phenomenon of major changes in sea level which accompanies specific atmospheric and meteorological conditions."

At present the only forecasting service is offered by the Balearic Meteorological Centre and has operated since 1985. The centre makes predictions of a problematic type based on the observation of meteorological conditions. They broadcast three levels of alert: yellow or relative danger, when sea level will oscillate between 0.5 and 1 metre; orange or danger (between 1 and 2 metres); and red or extreme danger when the sea level will alter by more than 2 metres.

Jansà states that in the majority of cases when the centre has issued a warning, the phenomenon does occur. However, there are still deficiencies in the system: sometimes the "rissagas" have occurred without warning and at others there have been warnings followed either by no "rissaga" or else a minor one.

Since the last major tidal bore, on 15th June this year, the Ports Authorities have established a system of closing Ciutadella port to maritime traffic every time there is a "rissaga" warning.