Every week, we present you with a question about your boating license. To help you validate your knowledge, or to discover new and unexplored areas. This week, we tackle a question about the weather.
Weather-related water level
Water heights are subject to weather conditions according to 3 criteria:
- Atmospheric pressure
Air pressure causes water levels to vary. An anticyclone, or high pressure, "presses on the sea and lowers the level". Conversely, a depression, or low pressure, causes the water level to rise. Each hectopascal more or less corresponds to 1 cm more or less of water height. Tide forecasts are always based on a pressure of 1013 hpa. Between a barometric pressure of 1013 and 1003 hectopascals, the sea will be 10 cm higher than calculated from the chart alone. - The wind
A sea wind can "push" the sea, particularly at the bottom of a bay, increasing the water level. Conversely, an onshore wind will lower the water level. - The waves
Waves and swells can cause water levels to rise higher than forecast. This is often the fear of coastal dwellers in stormy weather.
To answer this week's "Boating Licence" question, you had to tick answers A and C. As a low-pressure system is approaching, the water level will be higher than calculated on the charts.
