Tidal scour

Tidal scour is when the moving water in a river or sea bed is flowing really hard and it's like a big giant vacuum cleaner that can suck up and move all the little rocks and dirt on the bottom of the river or sea.

Imagine your bathtub drain when you're pulling the plug, and all the water starts swirling really fast and then all the little hairs and dirt just go swoosh and disappear. It's kind of like that in the river or sea.

This tidal scour can create holes or ditches in the river or sea bed, kind of like when you scoop out sand in the sandbox. Sometimes, these holes or ditches can be really deep, and boats have to be careful not to get stuck in them.

Overall, tidal scour is just a fancy way of saying really strong water currents that can move dirt and rocks around in the river or sea.