|MadSci Network: Engineering|
You ask several good questions here. 1. Sea life endangered by tidal power? Almost always, sea life living in tidal areas has adapted to the covering/uncovering by water due to tides. In fact, many species need the exposure to air to survive. 2. Locks are indeed expensive to build, although necessary for ships to travel up rivers. The problem here is that fish have difficulty with locks and, more important, the locks destroy some marine habitats. 3. Siphons are much easier on the bottom-growing marine species than locks due to the fact that you don't have to dig up a lot of ground to install one. The problems are that you can't use the canal for ships and fish have trouble going up the siphons to spawn. So each system has its good and bad points; you have to consider all the tradeoffs before making a decision.
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