[Robert A Cook PE]

The huge diameter of a pipeline equal in area to the canal would be very difficult (expensive) to build. But supporting the height of a concrete pipe is also difficult: you can't bury it: it's already below water level (burying the pipe wold just make pumping all that water much more difficult, and mean easily 3-8 times the diesel power and pump capacity). Also, the pipe can't be supported structurally by the loose muck and mud.

Canal (at lake level, with locks/ports to adjust for changing river levels) is the only practical means. Once you pump it "up" out of the city into the lake, (which is slightly "uphill" from the ocean), the water flows to the sea naturally and at no expense.

[gridlock]

But what is the velocity of water flow in the canal? I don't think the cross sectional area of a pipe would have to be nearly as large, because a pipe can operate at much higher velocities.

At some point, however, you have to trust the engineers who have been scratching their heads over this problem for the last couple hundred years or so. To my mind, the best solution involves either condemnations of large areas in order to build proper earthen dikes, or a decision to not build in these areas at all.