This was proved by construction of a tidal barrage at St. Malo in France in the mid 1960s. Despite the success of La Rance, no other major tidal barrages have been built since, due in some part to environmental concerns. However, sea water has a much higher density than air, meaning that currents of 5-8 knots generate as much energy as winds of much higher velocity. In addition, unlike the wind rushing through a valley or over hilltops, tidally-generated coastal currents are predictable. The tide comes in and out every twelve hours, resulting in currents which reach peak velocity four times every day.
Coastal currents are strongest at the margins of the world's larger oceans.
South East Asia is one area where it is likely such currents could be exploited for energy. In particular, the Chinese and Japanese coasts, and the large number of straits between the islands of the Philippines are suitable for development of power generation from coastal currents. As discussed above, if deployed across the mouth of an estuary they can be very environmentally destructive. However, in the 1990s their deployment in channels between small islands or in straights between the mainland and island has increasingly been considered as a viable option for generation of large amounts of electricity. Also, by decreasing the cross-section of the channel, current velocity through the turbines is significantly increased.