A monument should be erected, or at least an alley near the coastal pier should be dedicated, to the dedicated official who between July 1870 and 1874 spent more than three years measuring the insignificant oscillation of the Mediterranean Sea in the port of Alicante. But his name does not appear in the abundant documentation that commemorates that event, which in 2024 marks 150 years.
From July 1870 to 1874, that methodical public servant carried out four observations daily: at nine in the morning, at noon, at three and six in the afternoon, using a metal ruler graduated in double millimeters.
Why did the National Geographic Institute, then recently created, choose Alicante to carry out those measurements? As Professor Enrique Aparicio Arias explains, in a work published by the University of Alicante, “because the fluctuations (elevations and falls) of the land tide in Alicante, which occur daily in the Mediterranean Sea, rise or fall on an average of about 20 centimeters. This value is considered the one with the lowest variation in terrestrial tides compared to other cities located along the coast of the Spanish peninsula.”
Hence, Alicante was designated in 1874 by the Geographic Institute as a reference city, creating the altimetric datum or origin of altitudes for the peninsula, establishing the zero level in the tide gauge of the port of Alicante. The Madrid-Alicante railway connection, in operation since 1858, given that the railway lines were useful for leveling itineraries, also influenced the decision.
Once the place was chosen, the tidal fluctuations had to be measured in situ. To do this, the now anonymous technician from the Geographic Institute was writing down the values ??on a metal tide ruler for more than three years. With these data, an average value of the variations of the sea in Alicante of 0.430 meters was established with respect to the metal sign of the step where the graduated tide staff rested, said step being the value of the zero level.
The work had only just begun. Since, once the zero elevation was established, it was necessary to transfer the altitudes to the respective cities in Spain. To do this, from Alicante the methodology of geometric or height leveling was used, through the midpoint method, and in this way the different slopes and altitudes were obtained.
The first point of altitude was the first step of the staircase that is still found today inside the Alicante City Hall, at 3.4095 meters. This point is considered the first altimetric point NP-1; From there, the different altitudes of the cities of Spain were obtained, leading to the placement of bronze nails and reference plaques along the different railways and roads, indicating the altitude. For this reason, in most railway stations there is a plaque embedded in the wall indicating its average altitude over the Mediterranean Sea in Alicante.
Three main lines left from NP1 in Alicante, one to the North, towards Barcelona, ??another to the center, to Madrid and another to the South towards Murcia and from there to the Cádiz Observatory. From Madrid, new leveling lines were started to the different capitals of the interior.
The Alicante I tide gauge, located on the outer dock of the port of Alicante, is the oldest operational tide gauge of the National Geographic Institute, whose construction dates back to 1925; He will be 100 years old next year. It was designed to measure sea level in Alicante, which is the origin of altitudes in peninsular Spain, to be part of the IGN tide gauge network and to support the leveling work carried out at that time.
During the civil war, according to the Geographic Institute, the building suffered significant damage, “although the greatest damage occurred in 1962 due to the impact of strong storms.” It had to be rehabilitated and it was precisely in that year when the first consolidation works were carried out by building a retaining wall to protect the building from future storms. Finally, in 1993, large concrete blocks were added to the breakwater in order to protect the building, since said wall had fractured due to the erosive action of the sea.
On October 5, 2023, rehabilitation works on the Alicante tide gauge were completed, which were necessary to recover the building, isolating the interior from humidity, weather and saltpeter.
The work consisted of refurbishing the interior walls and ceilings, as well as the exterior facades and roof. The windows, the entrance door and the electrical installation have also been replaced. And finally, a pillar has been built for the new permanent station.
With this reform, the National Geographic Institute now has two fundamental tide gauge stations in Alicante (Alicante I and Alicante II), both equipped with permanent continuous recording stations, which will allow the recording of sea level also through a global navigation system. by satellite, as well as with radar sensors.
