Why are tidal currents especially strong in narrow inlets and estuary mouths?

Tidal currents become especially strong in narrow inlets and estuary mouths due to the physical constriction of the coast through which tidal water must pass.1

The speed of these currents is determined by the volume of water—known as the tidal prism—that must flow through the opening during a single flood or ebb-tide cycle. The tidal prism is calculated as the product of the tidal range and the surface area of the coastal bay served by the inlet.1

Consequently, even in areas with a low tidal range, such as the Gulf of Mexico, currents can reach high speeds if the associated bay is sufficiently large, as a massive volume of water is forced through a restricted passage. These swift currents are significant in coastal landforms because they possess the energy necessary to transport sediment and erode bedrock, whereas tidal currents on open coasts typically lack the velocity to do so.1