There are a ton of traditional ways to define a low tide. Check tide tables. Look at the moon. Lead lines, depth sounders. Steep gangplanks are a dead give-away.
See, that's steep. Ergo, it's low tide.
But that's old school. Nobody does that any more. Not when there is the highest of high tech available to the advanced sailor (btw, that's me, an advanced sailor). I refuse to cater to the old ways. Sure, they've gotten mariners through generations of bad times. But running aground is serious business. I have to KNOW when it's low tide. No guesses based on outdated methodology.
I use the shopping cart method. Not everyone knows about it. In fact, I might be the only sailor advanced enough to utilize this method. But it is foolproof.
If you're walking down the gangplank and can see the shopping cart, the tide is too low to go to the pumping station. Simple, elegant, high tech.