Ebb and flow- a phenomena that most of us know, just as low water and high water. But ebb and flow are not interchangeable to low and high water.

Low water describes the precise moment, when the water reaches the lowest level. In contrast to that is high water, when the water reaches its peak. Ebb describes the period from high to low water. The period from low water to high water is called flow.

In our part of the Wadden Sea, the altitude difference between high water and low water is around 175 centimetres (69 inches). High water is every 12 ½ hours and the same is true for low water. Thus it takes 6 ¼ hours from high to low water. This explains why high and low water are not always at the same time of day. Every day, it is about 50 minutes later.

A lot of factors influence the level of high water, e.g. the wind and the constellation of the Moon to the Earth.

The wind is able to accumulate the sea and hence a higher water level can be reached. If this happens, the tide is called storm tide. On 1 March 2008, Rømø was affected by a storm tide.

If the moon influences the tides, it is more complicated. Then the tides are influenced by the graviational force of the moon. In this case, the tides are called neap and spring tides.

A spring tide occurs 2-3 days after full moon and 2-3 day after new moon as well. At these times, high water is about 20 centimetres (7.9 inches) higher and low water is 20 centimetres (7.9 inches) lower than normal. Neap tide is between those phases of the moon. Here the graviational force of of the moon is at its minimum and this means that high water is about 20 centimetres (7.9 inches) lower and low water is 20 centimetres (7.9 inches) higher than normal.

Thus one can say that at spring tide, the altitude difference between high and low water raises about 40 centimetres (15.7 inches) compared to the normal altitude difference. The total altitude difference is 215 centimetres (84.6 inches).

At neap tide, the altitude difference is 40 centimetres (15.7 inches) lower than normal and hence the total altitude difference is 135 centimetres (53.1 inches).

If you plan to go for a mudflat hiking, you should either take a look at the tide calendar beforehand or join a guided tour. In this way you can prevent rude surprises.