I would have agreed with the width/length of the tank/dam doesn't matter ...
but ... then why are dams so thick at the top? Dams can be 20 / 30 / ...
feet thick at the top where the water is only a few inches deep. There is
more to this than me thinks!


Many dams have a service road across the top, a place to stage heavy equipment
if need be for repairs, etc. That will require a certain practical width. You
also need some structural mass to frame spillway gates, etc- often located near
the top of the dam. Hoover Dam has a highway across the top, and so is probably
75 feet "thick" many feet above the surface. :-)