A dam holds back a lake that is 85m deep at the dam. If the lake is 20km long, how much thicker should the dam be if the lake were smaller, only 1.0km long?

the thickness of the dam should be the same if the level of water does not change.

Explanation:

the thickness of dam depends on the pressure of water that has to withstand.

Since the pressure exerted by the water depends only on the depth of the lake and not the length of the lake

P = 1/2 * ρ*g*h,

where P = pressure exerted by the water on the dam, ρ = density of water, g = gravity, h = depth of the lake

Then if the lake were smaller and the depth remains the same, the thickness of the dam should be the same