Slack in the Oosterschelde
Slack water is an important moment when planning a dive in the Oosterschelde. Around this moment the current temporarily drops sharply before the water starts flowing in the opposite direction again. How long the period of low current lasts differs per dive site.
What is slack water?
During the flood tide the water in the Oosterschelde flows in one direction, and during the ebb tide in the other. Between these two current directions, the current speed temporarily drops sharply. The current then picks up again, but now in the opposite direction.
This moment of transition is called slack water.
For divers, it is mainly the period of low current around slack that is of interest. That period is not equally long everywhere, and the minimum current speed can differ per dive site.
Slack water versus high and low tide
Slack water and high or low tide are not the same thing.
High tide and low tide describe the moment at which the water level reaches its highest or lowest point. Slack water relates to the current. The two moments therefore do not automatically coincide.
Within one tidal cycle there is a slack after high tide and a slack after low tide. The exact time differs per location.
Read more about the full tidal cycle and the relationship between high tide, low tide and slack water at Tides in the Oosterschelde.
Why does slack water differ per location?
The shape of the Oosterschelde and its various channels and branches mean that the water does not flow the same way everywhere.
As a result, the current does not change at the same moment everywhere. The period during which the current stays low around slack can also differ per dive site.
When planning a dive, it is therefore not enough to look only at a general tide table. The conditions at the specific dive site are what count.
Expected slack per dive site
Do you want to know when the current at your dive site is expected to be lowest?
Use the Tide Planner to see the expected current speed and the corresponding dive windows per dive site. You can indicate for yourself which maximum current speed you find acceptable.
You can also look up a location directly via Dive sites.
Go to the Tide Planner →Frequently asked questions
How many slack periods are there per day?
Every tidal cycle of roughly 12 hours and 25 minutes has two slack periods: one after high tide and one after low tide. That works out to roughly four slack periods per day.
How long does the window around slack last?
That differs per dive site and per chosen limit in cm/s. The Tide Planner calculates the window times per site for limits of 15 to 30 cm/s.
Does slack change with the phase of the moon?
The moon influences the tide and therefore also the conditions under which slack occurs. Around spring tide the tidal range is larger and the current can be stronger. Around neap tide the tidal range is smaller and the current is generally weaker. The exact moment of slack is determined by the local tide and differs per location.
Is slack always the best moment to dive?
Not necessarily. At some dive sites the current is also relatively low outside of slack. At other locations the difference between slack and the rest of the tide is much larger. It is therefore more useful to look at the expected current speed at the specific dive site than only at the time of slack.
Can slack be predicted in advance?
Yes. The astronomical tide and the moments at which the current is expected to turn can be calculated far in advance. The actual conditions at a dive site can later deviate, for example due to wind and air pressure. The further ahead you look, the greater that uncertainty about the actual conditions can become. Duiken Centraal uses these predictions to show practical dive windows per dive site.
Slack at a specific dive site
The moment of slack differs per location. Check the expected slack periods and calm moments for a specific dive site in the Tide Planner.
Open the Tide Planner