There are several different ways of harnessing tidal energy.
https://en.wikipedia.org/wiki/Tidal_power
1. You can simply mount a turbine in a place with high but intermittent tidal flow.
https://en.wikipedia.org/wiki/Tidal_power#Tidal_stream_generator
2. You can build two reservoirs connected to the sea, one kept high by high tides, the other kept low by low tides. Hydroelectric generation from the high to the low reservoir can be a continuous process without interruption. The infrastructure is expensive.
3. Dynamic tidal power employs a dam from the coast that amplifies the oscillating coastal tidal current wave. Bidirectional turbines in the dam wall extract available energy. By using multiple dam systems, in different tidal phase positions on the coast, power can be generated continuously by the regional system. The infrastructure is expensive.
https://en.wikipedia.org/wiki/Dynamic_tidal_power
This thread specifically refers to "Dynamic Tidal Power" on the coast of South Korea, where the tidal oscillation currents are enhanced by the natural position of the Korean peninsula.