Causes of tides

Causes of tides
Fig 5.0 - Being able to predict the effects of gravitational tides on sea level is crucial when cruising in coastal waters. As the tide floods and ebbs there is a change in sea level.
Fig 5.0 – Being able to predict the effects of gravitational tides on sea level is crucial when cruising in coastal waters. As the tide floods and ebbs there is a change in sea level.

Everyone in the UK has some experience of the tides and possibly due to a trip to the beach and watching the tide ebb and having to walk progressively further to reach the sea or watching a sandcastle being destroyed as the tide comes in or floods. Being able to calculate and predict whats happening with the tide and fluctuating sea level is very important to water users. When the tide is in and sea level high we may be able to pass over the top of rocks which would otherwise hit when the sea level is lower and tide is out (Fig 5.0).

You probably know that the moon affects the tides, but before we look at how to measure and calculate the tides, its probably best to have a closer look at what makes the tides ebb and flood. In the UK we have a high and a low tide roughly twice a day and called a semi-diurnal tide.