Estimating Main Breaks 1

[benjiw]

What is the best or most realistic method to estimate water main breaks? I have situations where our field guys find a leak and report back something like "it was a 10 inch broke straight around" and then ask me to determine the flowrate. I'm not sure of the best method to attempt to estimate such a leak.
Thanks

 

[rconner]

(I noticed after several weeks no one had yet attempted to answer your question.) If there were no more direct way to measure what you are talking about, I guess one might attempt to apply Greeley's formula to this situation (as expressed e.g. at

http://www.google.com/url?sa=t&rct=...KICQ&usg=AFQjCNH7INUJA3f6MgbPI4LWMkZcTZXtBA),

that would require either measuring the gap or estimating as best one could the breech area, "A" created. AWWA Manual M36 would probably be a good reference for questions like this.

 

[hydrae]

Estimating the flow out of a main break is tricky

The best way is to monitor meters feeding the area if they exist and comparing flows during the leak and after the leak is fixed.

It can also be estimated during the repair, but keep in mind that as the leak is excavated the flow increases since the soil around the pipe was also holding back some of the pressure. Another method is to measure how much water was needing to be pumped during the excavation, such as we had two 2 inch pumps going full out to get the water below the level of the break. The pump says it flows 173 gpm, subtract some losses and figure 125 gpm each so that would be 250 gpm for that leak when exposed.

Hydrae

 

[greggy]

I've used our pipe model with an outlet about the size of the break hole set up as a reservoir to check the order of magnitude of a break's flow. The hole size is adjusted for restrictions such as soil or broken pipe. I've compared the model break flow rate with the actual tank drain rate and have been fairly close for estimating purposes.

 

[gerhardl]

I have met this question, and also asked clients to come up with an answer for it in connection with emergency shutdown valves.

As indicated by the three good answers above, you have to approach this by a 'guesstimate', taking all variables into considerartion.

The first question is calculation for what purpose, and consequences if the estimation is too high or two low.

Next, very often, a double consideration/calculation will do: probably not higher than contra most possibly not lower than, and an avarage.

Your considerations should contain the data (as figueres) of your calculations and modifications (example : buried pipeline reducing leak in estimated area (xxx square) at mean water pressure ( yy bar) with ( zz backpressure) and (aa percentage reduced area) - or whatever depending on method, enabling later control or repetition of the estimate.

 

[bimr]

Water main breaks occur infrequently and trying to estimate the volume of water lost is difficult. Develop an estimate by recording the time of the break and the time it took to isolate or shut down the break. That time is used to identify the amount of water lost in the storage tanks during that duration. Use the tank volume charts as shown on the control system or SCADA. (Note that the SCADA system may also record the time of the water break as a pressure fluctuation.) Also during period of the water break, account for the amount of water that was pumped from the water supply (well or river intake, etc.). Depending on the time of day from historical records, you can estimate a percentage of water used by customers as compared to water lost.