Photos: 'Manhole' Covers Feature Form and Function

It's likely that almost since there have been sewer and water systems, there have been so-called manhole covers. The covers serve an obvious purpose: to prevent people and large, unwanted objects from falling in to the holes.

Manhole covers usually weigh more than 100 pounds, according to an article on Wikipeidia.com. The heavy weight keeps them in place when traffic passes over them and helps keep them from being stolen.

Not entirely, though. Manhole-cover theft  first became a serious problem in India and China, where missing manhole covers caused at least eight deaths in 2004, again according to an article on Wikipeida.com. Hundreds of manhole covers are stolen in the city of Bangalore, India every month.

Most of those in and around Northport are in place. And, once you start looking for them, they are everywhere.  And they aren't just to cover sewer system access holes. They are used to protect other utility systems, as well, such as water and gas.

But why are they round? There have been many answers through the years, but the most common seems to be that a  round manhole cover cannot fall through its circular opening, whereas a square manhole cover may fall in if it were inserted diagonally in the hole.