Being in the coldest part of winter that we are now, makes me think of an interesting question. As I’m sure all of you know who live where it snows, when it goes below freezing, water mains will sometimes burst. This is because when water freezes, it naturally expands. Water mains are usually underground. Yet the water departments always seem able to find them. And odder yet, since centralized plumbing came into existence (I’m sure it has been widespread in the U.S. for at least a hundred years), water dept.'s have always been able to do this! They somehow did long before we have the high tech tools we have now. But how ?
It is difficult and sometimes can take weeks. Oftentimes the water will bubble to the surface because it is leaking out too fast to seep away in the ground. This is the best case scenario, but even then it can migrate dozens of feet from the leak which makes the search for the break more difficult. I believe they can also use microphones to try to listen for the sound of running water, but this can be difficult. I recall that maintenance workers will also put the “key” onto the water valve at various locations and listen for the sound of water transmitted through the metal. I’m sure there are other techniques as well, but I’m not aware of them.
There was a case just this week in Fergus Falls, Minnesota (west central part of the state) that had a water break. The water got to the surface, ran under the snow, into a series of culverts and eventually into the river. They even had planes out searching for the water. Luckily someone noticed the water flowing into the river and they traced it back. The lost 1 million gallons of water and had to close down the school and businesses.
By the way, in Minnesota the watermain is buried 7.5 feet deep to try to prevent freezing. (At least through to the centralpart of the state. Northeren Minnesota may be deepeer.)
One method is by who’s complaining and who isn’t, silly as it sounds. For real long pipes without branches (like gasoducts), sensors are put in places along the pipe, so you can check the pressure and see where the pressure is lower than it should.
Also if the pipe has a leak (but water still goes through) you can get a godd guesstimate of “where” the leak is by checking the water pressure up and down the line, I don’t have those notes here but we had exercises on that in my “Transfer of Matter and Energy” course, aka “Piping and Insulation”. This is with a handheld sensor, so you have to measure at points where the pipe is accesible. Getting a range of “plus/minus half a mile” is still better than having 300 miles to dig out.
We don’t have electric lines into our house. The lines are underground from the pole to a box several feet from the house and then underground from the box to our house. A couple of years ago, I heard a loud POP as the lights went out. The electric company sent out a large specialized truck that was able to tell exactly where they needed to dig. Thank goodness it was before the box or I would have had to help pay for that fancy truck (plus the digging, etc.)
Aside from the listening equiptment out there now, there’s tools that can pinpoint water mains exactly.
My company uses a transmitter that sends a signal (from an exposed water line) through the burried pipe and a reciever to trace the signal. This will give you the depth along with the location. Sometimes the signal will stop right where the break is because the break can prevent the signal from travelling any further.
There are different approaches (induction, conduction…blaa blaa) and there is even more sophisticated stuff that my company could never afford.
As for the past, a lot of people seem to think devining rods are/were accurate. There are municipalities still out there with a couple of bent wires as their most sophisticated tools. (this is probably why they hire us).
My field is more related to sewers than water mains though.
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