To find out the expected depth for a snorkel dive on a particular day requires the charted depth and tidalvariation to be combined. For example:The charted depth of the seabed is 2.2 metersThe tide tables for the day show that at 0800 low water is 1.0 meter.At 1405 high water is 4.0 meters. So, at low water there will be 1.0 meters of Water over the chart datum depth of 2.2 meters, which means that there will actually be 3.2 meters of water on this site at low water.At high water, the tide table shows 4.0 meters, so at high water there will be 4.0 meters of water over the chart datum depth of 2.2.m, which means there will actually be 6.2m of water on this site at high water This shows the importance of planning. For example, if the snorkel dive was planned just using the depth at chart datum, at 2.2 meters it would seem ideal as a site for a new Snorkel Diver, s first sea dive to build confidence and depth experience. But if the snorkel dive actually took place around 2 o'clock (1400) in the afternoon, the actual depth of 6.2 meters would be too deep for a newsnorkeller to really enjoy their dive.