Water Main Breaks: May the Force Be With You!

Main breaks always make for a bad day at the water company.  You’re going to get wet and muddy, but that’s part of the job of a Distribution Operator almost every day.  No, it’s more than that.  Main breaks can have devasting effects on lots of things other than our water system.  And that’s when the day at work gets to be really, really bad.  Get a little glimpse into this issue from my local newspaper:


I was surprised by the assertion in the article that service was restored to all customers within 30 minutes.  Nice job, Valencia Water Company!  But this was only a small part of the problem.  When a 16-inch main breaks, a lot of bad things can happen.  Why?  Well, just ask Luke, or Yoda, or Obi-Wan: it’s the Force!

Let’s calculate the force of the water leaving this 16-inch main.  Force is equal to pressure x area.  Normal water pressure in a main such as this might be 80 psi — perhaps slightly higher, but we’ll use that for our calculation.  The cross-sectional area of the line is 0.785 x d2, or 201 square inches.  So the force of the water leaving this main was about 16,000 pounds.  That’s 8 tons!  With that kind of force, even well-compacted soils will give way.  And they did here, undermining a major roadway and causing a huge sink hole in the street.

All we needed to calculate the Force was the pressure and the pipe size — and of course, the formula, which we discuss in course WM-8 here at MOST.  Armed with that, you’re a Math Jedi: May the Force be with you!

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