The author says a caisson is kept free of water
because it is like

on this day in 1833, president andrew jackson announces that the government will no longer use the second bank of the united states, the country's national bank. a national bank had first been created by george washington and alexander hamilton in 1791 to serve as a central repository for federal fund

i actually have a suggestion instead of an answer, how about next time instead of spending the time to time up the question you take that time and try to figure something out for yourself, do you understand?

explanation:

leave a 5 star and a and brainliest answer if you understand, hope this betters you day, or not i don't really care either way. xd