At AZTI premises at Pasaia, different equipment used to record sea water level in situations where forecasts announced imminent storms of extraordinary characteristics (known nowadays as explosive cyclogenesis, Klaus, Hércules, etc.) have been deployed over the last ten years. The purpose of these measurements is to assess the flood risk of these phenomena in areas protected from wave swell such as harbours, estuaries and river mouths.
Pasaia tide gauge, installed in 2015, collects information above sea level with a frequency of 0,2 Hz. This intensive data series enables the separation of the different processes involved in the sea level signal: astronomical tide, meteorological tide and harbour agitation.
- Astronomical tides are gravitational in origin and due to the attraction of the Sun and the Moon on the surface fluids of the ocean; and as they are associated with stars movements they are predictable far in advance.
- Meteorological tides are caused by the atmosphere on the water surface and especially due to fluctuations of atmospheric pressure (anticyclones make sea level fall while violent storms cause it to rise).
- Moreover, in sheltered areas such as bays, estuaries, rivers, harbours, etc., the swell produces changes at sea level for a much shorter period compared to astronomical and meteorological tides within tens of seconds or even up to minutes, which is known as harbour agitation.
The three processes together (along with astronomical tide and meteorological tide) have a significant impact on the coastal waters which may be flooded and affected by waves in strong gale situations.
List of sensors and parameters
- Total sea level height every 5 minutes (instant level)
- Astronomical contribution to instant sea level
- Meteorological contribution to instant sea level
- Harbour agitation