Correct. Crop Coefficient only changes the amount of water over time (without changing how much water is applied each day it waters). Nozzle rate changes both. It’s best, but also hardest, to accurately know nozzle rate.
You’re right, the advanced sliders only really change two parameters. But by adjusting the advanced sliders, it gets you in the ballpark for those two parameters. Otherwise, you’d have to just guess at minutes and frequency, and adjust from there, with nothing to start with. I do agree that after setting the advanced parameters as best you can, changes from then on would be better done with only two sliders: 1. More water at once. 2. More water per week.
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I use closed loop control. Water is put on lawn via sprinklers and rain. 5 moisture sensors report soil % saturation. I then apply common sense and adjust fixed schedule if needed. Trying to accomplish same open loop seems hopeless to me but many are doing successfully (I guess)
Hey Rraisley, your posts are super helpful in helping to decode what on earth the Rachio app is up to! I wondered if you’d be willing to write a brief guide that lists out each variable in the Advanced Setting and what it does if you increase or decrease it? Also, a specific question, do you understand what the unit in/in means for Available Water? Is it inches of water per hour per inch of dripline? Cheers!
Thanks. While I was learning, I did write up this topic that might be of help to you:
A Beginners Guide on Understanding and Using ALL THOSE ***** NUMBERS!
Available water is the amount of water per unit that a given type of soil can hold. If I’d have invented the term, I’d have simply used Percent as the value (my soil, per a site that lists values based on actual location, is 17%). However, the Industry states it differently: They state the inches of water per inch of soil (yes, that’s the same as just a fraction); in this case my soil would be 0.17 in/in. And if you’re working with metric, to confuse things further, it’s written as 0.17 cm/cm or 0.17 mm/mm. It could have been 0.17 miles/mile!
So, it’s just a fraction/decimal/portion of the soil that is water, based on the soil type. That number times the root depth (D) gives a total inches of water that the top D inches of soil can hold, and if we want it to decrease by 50% before watering, it tells us we can apply AW x D x AD (Available Water x Root Depth x Allowed Depletion) at once, and then wait for it to use that much water before watering again. In my case that’s 0.17 x 6 x 0.50 = 0.51" of water. This calculated number is important because the amount of water applied by Rachio is calculated directly from it, and the length of time Rachio waits to water again is also calculated from it. Sandy soil can’t hold much water, so no sense in overwatering it, so you apply less, but more often.
Hope this helps.
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Hey Rraisley, that makes sense, thanks for clarifying that it is actually a dimensionless number!
I have another question about nozzle inches per hour. I have a long planting bed with a pipe running along the back, and a combination of dripper lines and dripper nozzles branching off it. How would you get to accurate nozzle inches per hour number?
I’ve not done that much with drip lines, except for my one, and I’m not sure it’s right. But basically, there are two methods:
If, as you say, the area is narrow, and you end up watering the entire area (not just around each plant spaced far apart), then you can use the same Flow & Area system (GPM / Area x 96.25). Another method is to calculate how much water each plant needs, multiply by the number of plants to calculate how much water is required per week, then calculate the minutes needed to give that many gallons. A third method would be to use the first method, but estimate how much of the bed area you’re using for plants (say half of it), and modify time accordingly.
All of them, IMHO, require measuring the actual GPM flow, because it can vary TREMENDOUSLY, and that will directly affect the time you need to water. I still use Flex Daily for my drip zone, but it applies a lot of water at once, about once a week or less, due to root depth, and vary the Crop Coefficient if it gets too wet or too dry. Once dialed in, it should work well as the temperature changes.
OK, thanks. How would you go about measuring the actually GPM, other than putting buckets under all the dripper and drip lines?
While that sounds like a heck of a lot of fun, I’d simply read the number of gallons on the meter, run the zone for a while, read the gallons on the meter again, subtracting to find the gallons used, and divide the result by minutes. If the flow is /really/ low, you can time with a stopwatch the seconds for a gallon or whatever, but I’d start the other way.
Well, now I feel dumb for asking that question! Haha, very simple solution. Who would’ve thought an irrigation system could be so confusing!? Cheers!
Wow. Rachio…I sure hope you’re paying Richard.
Richard, you’re awesome. I gave up on the flex daily. It was “fun” playing with it but not while I watched everything die. My original sense of it was correct. The algorithms, or the underlying measurements critical to them, do not work in Southern California. “Customer service” is hesitant to acknowledge this, but in trying to trouble shoot, it became clear. I was inspired by all you helped me learn and converted most of my 11 zones to a drip system. It should save a lot of water and since we’re in for another drought, it will help. Thank you again, for all your time and patience.
Debbie
Nope. I just like helping where I can.
Thanks. Please tell my wife. 
Sorry it didn’t work for you. The only underlying calculations really involve the same factors (standard and Advanced) with Flex Daily that the other schedules use, but it appears more sensitive to being dialed in.
No problem. Definitely, drip zones will save water, although I’ve found them more difficult to determine exactly how much water is needed. Everything has its inherent advantages and problems, it seems.
There are a couple of estimates that are made via climate/weather data that do not work for this area. I decided I did not need to know the names of these variables or coefficients, just needed to get my plants watered!
Debbie
I’d be curious to know what those estimated are that you feel are wrong. What is it about SoCal that makes it not work?
I’m in Arizona, and once dialed in, my system runs without issue.
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Another likely dumb question, but I measured the amount of water my lawn subsurface irrigation uses, and it comes to around 6.5 cubic ft per hour. How do I convert that to the “inches per hour” unit in the rachio app. Over what area is that inches per hour measured? Or is it cubic inches per hour (probably not as that would be a huge number)?
You have the flow (cfm or gpm works fine, just with the appropriate factor). The second part of calculating Nozzle Inches per Hour is the Area. You divide flow per unit time by area to get flow per inch.
Hmmm, I think you may have a decimal wrong (VERY easy to do with water meters, which often have a “0” written in at the end). One cubic foot is 1728 cubic inches. One gallon is 231 cubic inches. So 6.5 cubic feet per hour is 6.5 x 1728 / 231 = 48.6 gallons per hour or 0.81 gallons per minute. My zones run from 10.5 to 12.5 gallons per minute. So unless that is for a very small drip zone, it’s probably 65 cubic feet per hour or about 8.1 gpm. And to be honest, that’s probably hard to measure over a full one hour period, due to other water usage, etc.
Another way to measure flow (which should be done separately for each zone, IMHO) with a cubic foot meter is there’s usually an outer dial that makes one full revolution for one cubic foot of water. I’ve timed the number of seconds it takes to flow one cubic foot, and calculated the flow that way.
But the second part - Area - is what area of your yard or crop the zone irrigates. If it’s a 25 x 50 area, that’s 1250 square feet. If you have a Rachio 3, you can often have it calculate the area of each zone using its Yard Map feature on your phone.
So using the above numbers,
Nozzle Inches per Hour = Flow in Gallons / Time for Flow / Area in Square Feet x 96.25.
For the above that’s = 8.1 / 1 / 1250 x 96.25 = 0.62"/hour
Yep, you’re right on the missing decimal, I didn’t realize the number the dial points to needed to be tacked on the end of the numbers. See if this makes more sense:
The meter started at 158469 ccf
After 15mins it read 158532 ccf
Which is 65ccf / 15 min = 252 ccf/ hr
That’s 14101.5 ccin/hr
Area of grass = 163 sqft = 23329 sqin
So, 14101.5 / 23329 = 0.604 nozzle inches per hour.
While I thought I agreed with the result, I’m confused by the math:
158469 - 158532 = 63, not 65, but converting it to hours it does come out to 252 cf/hr.
The problem here is you said previously you measured 65 cf/hr, and now have 252 cf/hr.
Using my conversion, not yours, 252 cf/hr x 1728 / 231 / 60 = 31.4 gpm (gallons per minute). WOW, that’s a lot of flow. My flows are all in the 10-12 gpm area, so that just seems really high, unless it’s a commercial system with large pipe & tubing.
Using your calculations to convert from ccf to ccin (cubic feet to cubic inches), there would be 14101.5 / 252 = 55.95 cubic inches in a cubic foot. But there aren’t. There are 1728 cubic inches in a cubic foot.
Assuming the 65ccf/15 minutes is correct, I’d do the math like this:
The meter started at 158469 ccf
After 15mins it read 158532 ccf
Which is 63ccf / 15 min = 252 ccf/ hr
That’s 435,456 ccin/hr
Area of grass = 163 sqft = 23,472 sqin
So, 435456 / 23472 = 18.55 nozzle inches per hour, an incredibly high number
Doing the math a different way as a check:
63 ccf/15 min = 63 / 15 x 1728 / 231 = 31.42 gpm which as mentioned above seems really high.
Then 31.42 / 1 / 163sf x 96.25 = 18.55 in/hr, so that checks out.
The reason this answer is so much different than the previous calculations is previously you said you got 65 ccf/hr but now it’s almost 4 times that (63 x 4 = 252). And in my previous calculation I put in a guess of 1250 square feet, and you actually have 163. Yet your calculations just happened to almost match mine.
I’m not sure what to say. Even correcting the math results in an answer I don’t think is possible. And I hate to doubt your measurements.
Hi! I live north of the SF valley, so I feel your pain about our hot, dry summers!
If you really want to know the nozzle flow rate, and can’t get to the water meter (which I also feel for, given that mine is located in my neighbor’s yard and the cover regularly gets buried under bermuda grass), you could try a catch cup test. The easiest way of doing that is ordering some catch cups on line and then using the manufacturer’s handy website calculator to determine the answers. That will give you at least a ballpark figure on what the nozzle flow rate is, although the placement of the cups can affect that.