Precipitation rate calculations


#1

I’m confused about how to calculate precipitation rates.

To collect data, I used the standard .Orbit catch cups with a 16 square inch opening on the top. For each zone I put out 12 of them and ran the zone for 20 minutes.

Here is an example zone.

Total water collected in 12 catch cups = 359ml or 21.9cu. in. That is an average of 30ml or 1.83cu. in.

When I enter those values into the Rachio online calculator it results in 5.5 inches/hour.

This seems incredibly high as the Rachio default for a rotor head is 1.5, and the system will not permit an entry over 5.0

On the other hand, if I use the formula of (average volume/catch cup area) * 0.06 = PR for the run time I get 0.09 inches in 20 minutes and 0.27 inches per hour.

This formula comes from aces.nmsu.edu/pubs/_h/H510.pdf.

Similarly, the formula of (3.66 x average catch can volume in mL)/ Run time x 16
also gives me a rate of 0.27 inches per hour.

This formula is from
www.bozeman.net/Smarty/media/Public_Works/Water%20Conservation/pdf/CoB-DIY-Irrigation-Audit-Kit-Procedures_1.pdf

The advertised specifications on my Hunter and RainBird rotor heads indicate and average precipitation rate of 0.3-0.4, so those last 2 calculations of 0.27 make a lot more sense than the Rachio 5.5 result.

What do I not understand???


#2

Did you plug your ml’s into the orbit’s website: http://irrigationaudit.hydrorain.com/get-started/#/stations/getStarted


#3

Thanks for the response. However that link doesn’t seem to work. Maybe their server is down.
The other Orbit url at wateringschedule.com calculates efficiency but not precipitation rates.


#4

I think their site might be screwy right now because it can’t find Phoenix in their system. Anyways, when you get to the screen that shows your results and zone efficiency, click on each zone and it’ll take you to a new page (granted that their site is working correctly) and it’ll give you detailed information including PR

Here’s a link to another thread on my comment about this


#5

The link you provided from a previous thread is super, and would provide just the information I need. However, when I now go to the url that didn;t work the other day, it opens now, but to the same place as wateringschedule.com. Both are Orbit, so maybe after having difficulty with the Irrigation Audit app page they realigned it to the other one. So the new one provides effciiency and run time recommendations, but not precipitation rate.

Unless my computer is throwing me to the wrong url for some reason. Does it still work for you?


#6

Ahhhhh! Not it looks like the Audit websit is back fully operational and it does calculate all teh data you mentioned. As far as precipotation rate, it derives the exact same figure from the other 2 URLs I mentioned in my original post — which is MUCH, MUCH less than that calculated by the Rachio online calculator.


#7

There was conversation on the forum before about the different websites actually being from the same company. I’m glad you were able to find the info correctly.


#8

So any idea why Rachio calculate precipitation rate so much differently than other sources?


#9

I do not. Definitely good question for anyone else out there who are more into these types of calculations to figure out.