Hypothetical question for best land grade in a 1 mile diameter cylinder

what would be the best grade to ensure positive water movement in
the soil and allow for water effects (waterfalls, pools, etc)
when I figured a straight line across the land portion of cylinder I
had the same effect as a 400 foot rise to the center and would say
that this is too much - it would also put too much under the center to
the outside of the sphere. Has anyone figured out what it would take
for the best effect.