An article says 7.5 million acre feet would raise the lake level 10 feet. 20,000 acre feet is .002 of 7.5 mill. .002 of 7.5 mill is .02 ft., just under 1/4 inch. Still a very small amount, but 24,000 times greater than your estimate.

"The lake needs to be about 10 feet deeper to cover up most of the dust emission hot spots in Farmington Bay, which is the bay closest to residents along the Wasatch Front, Perry says. It would take about 7.5 million acre-feet of water to fill the lake to this level."