A:I posted this answer on youtube a few weeks ago but here it is again. The storm drain cover is located in a lowlying area. If there is flash floodding in higher elavations, the water fills the storm drain faster than it empties to a level higher than the level of the cover. If the geyser shoots 20 feet in the air then the pressure needed to produce a 20 foot column of water is 240 inches of water or using a
conversion chart, 17.65 inches of mercury, or 8.67 PSI. If the cover is 6 feet in diameter that is little over 27 square feet. At just 2 psi differential, the water would exert 288 pounds per square foot or 8143 lbs of pressure against a 6 foot diameter cover. That's four tons of pressure lifting the cover off at just 2 psi. According to our calculations, the actual number would probably be closer to 16 tons of pressure lifting the cover off. Just water. One of Mother Natures little wonders.
