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My sump generates a lot of output during some weeks. Enough that I need a better plan than dumping into the grass and gravel driveway downslope from the house. My first step in improving my driveway is calculating the amount of water I am dumping into it. What is the easiest way to measure? The 2 inch discharge pipe is about 18 inches off the ground. I guess I could dump the water into a kiddy pool and measure the amount of water in it after a 24 hour period. That leaves me with a kiddy pool I'd have to throw away in a month. I would prefer a method that allows me to measure into the future.

Is there a simple flow meter for a 2 inch pipe that will measure the amount of water flowing through it? I have found some, but they appear to be industrial grade and industrial priced.

I could estimate the volume of water discharged when the sump cycles on, and then count the number of times the sump runs. But how would I count the number of cycles?

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Time how long it takes to fill a 1 gallon bucket, then divide that time into a minute, that gives you GPM; Gallons Per Minute, a standardized flow rate. So for example if, while it is fully flowing, you put the bucket in the stream, someone else starts a stopwatch and you see that it takes 6 seconds to fill the bucket, 60 seconds / 6 seconds = 10 GPM.

Then if you want, get what's called an "elapsed time meter" that works on the same voltage as your pump, and wire it in parallel with the pump so that it records how long the pump runs. Multiply that run time (in minutes) during a time period by the flow rate to get a larger averaged flow over that time period, i.e. per hour or per day or per week to make it more useful for deciding what you want to do with it. So for example if, during a given week, the sump pump ran for 3.2 hours, that is 192 minutes, x 10GPM = 1920 gallons per week that you need to figure out how to safely dispose of.

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You can get the water volume from the sump pit (area based on pit diameter, height based on the difference between trigger and stop levels). Ignore the volume of the pump if you want to be conservative. On a heavy pumping day, count how many times the pump cycles during a several minute period and extrapolate to an hourly basis. Note how many hours the pump runs during a heavy period. That will estimate the total volume.

That said, a couple of thoughts:

  • It isn't clear what you would do with the information if you are discharging the water on a sloped gravel driveway or grass. The precise amount of water wouldn't really affect the solution unless you're calculating dry well or self-contained system requirements. A sloped gravel driveway will diffuse a lot of water, and spread it out as it goes. Is the water actually creating a problem you need to solve?
  • A discharge pipe 18" above the ground is unusual. If it's discharging right at your house, some portion of the water will seep back to the foundation no matter how much slope you have. If it is discharging a good distance away, you've got a pipe at a height where it's a trip hazard and exposed to damage. Ideally, you would want to add angles and pipe to bring it down to below ground level, run it at least 10 feet from the foundation (the farther the better), and use the ground slope to discharge it at ground level onto the gravel.
  • I am just trying to build some facts. My immediate problems are the water that currently drains from the driveway through the driveway apron and sidewalk to the street gutter. Enough water that I have icy sidewalks during the winter. As you implied, the house sump drainage isn't longer than 36" away from the house. So, I run the risk of dumping water into the ground so that it cycles directly back into my sump. It gurgles without the extension pipes to get it away from the foundation. So I want to store it in a cistern or build a dry well in clay soil. How much to store or dissipate per hour? – Brett Osiewicz Jun 28 '18 at 2:57

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