A preliminary study about methods for harvesting energy from marine resources

We’ve already written about tides and their origins in the previous chapters: the gravitational pull of the moon and the sun and the rotation of the earth. The current rise and fall of tide is accompanied by a regular movement of water: this phenomenon is the tidal current. Tidal currents and tides are obviously related to each other, but the relation between them is complex to identify and, especially, it is variable.

While nearshore water seems to move forward and backward, offshore the direction of the flow of the tidal current is not restricted by barriers: the result is a rotary movement (Figure 4-I). When tidal currents are directed toward the land, water levels rise in harbors and rivers and these are called flood tides. Tidal currents flowing seaward with falling sea levels are called ebb tides. Between flood and ebb tides there are slack water periods (little or no horizontal movement) [17], [20].

The current at anytime and anywhere in the ocean is a combination of tidal and non-tidal currents: the observation of tidal currents is not simple at all because of the superimposition of other currents. As tidal barrages could produce energy both with the rise and fall of the tide, both the flood and the ebb of the reversing nearshore current can produce mechanical energy.