Other pools, which you then empty on low-tide. That way you can start draining your main pool as soon as high-tide is reached - you don't need to wait for low-tide. With a set of pools you can keep draining 24 hours a day.
Schemes such as this have been proposed, see the Swansea Tidal Lagoon [0]. The bottom line is that they are crazy expensive for the power they deliver and just don't compete against other renewables.
