Refresh my memory on the moisture chart

So I have made a change to my root depths for my turf zones to 9 inches. I,did this about a month ago. Looking at the moisture chart below, the pr event put out .53 inches of water. I’m a touch confused by that number based on my zone setup, I can’t firgure out where .53 comes from. The closest I can get is .521 (.64 inches an hour * .8 efficiency) but this assumes that the zone ran for an hour. But still this difference is outside floating roundoff tolerances.

Currently my schedule runs this zone for 35 minutes so the actual should be much lower (we get tons of ran this time of year so I’m trying a different way to conserve).
Everything else on the graph looks correct:
9 inch root depth *.15 awc = 1.35 inches field capacity.
1.35 * .45 (allowed deplition) = .60 inches to replenish.
Which .53 / .89 = .60 (rounded up) so that lines up with field capacity.
I just can’t explain the .53

Now you have me really curious too – I keep all my zone setups in a spreadsheet, and I used to take Available Water Inches * Root Depth Inches * Allowed Depletion and come up with the water in inches spot on. But I just did that calculation with your data and come up with .61 inches - so I don’t get it either. Something appears to be different now.

I haven’t looked at my own data yet - we’ve had lots of rain so my system is still off. Now I’m really curious to see what it’s going to do.

@plainsane @Linn

Thanks for the detailed information, having the engineering team review.


@plainsane Did you adjust the zone settings after the irrigation event on the 1st, can you please check the graph for next week? We do not modify the past depth of water. I am looking at “side yard” zone" which looked like the closest to what you posted in the picture and it’s future irrigation amount is .66 inches which matches the formula (8 inch RZD * .55 AD * .15 AWC = .66). It has different configuration now, probably changed since the post, but the math seems to be correct. Let me know if I am looking at the wrong zone.

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That is the correct zone. I did change the zone settings last night after I posted, because I was playing around.

The screen shots that I posted were the same for the graph I posted but 9 * .45 * .15 != .53. Again, my zone run times will not apply .53, I’m running short because of our periodic rain. Does my run time need to be aligned with the depletion amount?

I’ll see what happens in another next time it runs. I was just curious how .53 is derived.

I’m trying to stretch my roots which is why I was at 9 and I was going to walk back the ad. But for now I reverted back to my tried and true after I was finished playing around

@plainsane Yes you currently have a runtime coefficient on that zone. If you adjust the actual duration for the zone, it will not adjust the depletion/fill amount, just the duration. You will effectively tell the system how long it takes to reach the desired depletion amount.

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Yes I didn’t ask my question correctly. I still do not understand .53, I will wait for the next run

@plainsane Have you adjusted duration for that zone since the run on the 1st? If runtime is adjusted after the irrigation event, then irrigation events for previous 2 days will be adjusted. The system uses the currently configured duration as the basis for depth of water. So if you increase the duration, then the system will lower the moisture for those past events, because those events have shorter duration than what is required for full bucket.

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Ok so this math adds up to .66 which is what the precipitation event records.

So back to my previous question, is the zone run time in the flex schedule required to match this .66 inch deplition volume?

Currently mine does not.

Pr is .64
Efficiency is .8

.8 * .64 / 60 (minutes) * 40 (minutes) = .34 inches, not .66

This is on front yard.

I still have no clue where .53 came from but I’ll drop that…

The formula for calculating moisture level based on duration is a bit different.

scheduling multiplier = 1 / (.4 + .6 * efficiency)
level = duration * precipRate / (runtimeAdjustment * scheduling multiplier)

Your runtime adjustment on that zone is 0.622935346861727 (means it was lowered from what the system recommended by user).
Runtime in seconds is 2627 ~ 43.783 minutes

schedulingMultiplier = 1.136
level = 43.783 *(0.64 / 60) / (0.622935346861727 * 1.136) ~ .65995 inches

The recommended duration for .66 in depth of water is 4217 seconds ~ 70 minutes.

So if you set your runtime on that zone to 70 minutes you will have the duration for that depth of water based on characteristics. All systems are different and precipitation rate is hard to measure, but this is the recommended value assuming the values are correct.

Couple of things to consider:
Recreating the schedule always gives you recommended duration based on settings.
Adjusting duration only adjusts the coefficient. So if you change your zone settings, duration will also change but it will still by multiplied by the coefficient.


The @theflexdude be like…




Question for the gurus, I need my memory refreshed (or maybe expanded), too. Does the amount watered always equal the full amount to replenish the root zone from allowed depletion, or can it vary depending on previous day moisture level, and expected precipitation for the irrigation date? In this example, if the watering was done early in the day, that it would have brought the zone up to 100% with the 0.53, then some ET later in the day dropped it some.

I notice that in V3, when looking at moisture levels, it includes recent watering, so I am thinking the duration is more dynamic than in V2.

@jkb We always water for the entire depth of water, unless the day of depletion is restricted. In that case we water the previous non-restricted day for amount that is enough to fill the bucket including ET for the day. So during normal watering you will have (Previous balance + precip + depth of water - ET) as your end of day balance. On restriction fill up you will have depth of water as your end of day balance and irrigation amount will be computed as the following: (watering amount = depth of water - precip + ET - previous balance).

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So when the zone runs for 43 minutes instead of the recommended 70 (I think it really should be 77 minutes) and the graph shows .66 inches of water instead of a fraction of the amount, can you see where this draws confusion?
The graph tells me that .66 came from flex (the + sign).

So I’m back to the question: am I required to have my flex schedule to run for 70 minutes to actually get the .66 inches of water that the graph tells me I got?

Where are these constants coming from?

Also, am I wrong in thinking that a system with a pr of .64 with efficiency of .8 requires 77 minutes to reach .66?
.66 / (.64 *.8 / 60) = 77.34

This has been confusing me too. I’m coming at this a little differently, with a little less math, but I’m wondering if I’m starting to see a little of what is going on.

@plainsane , did you by any chance tweak your duration times on the previous version of the software? The comment

makes me think that you did.

Here’s what I’m seeing after playing around quite a bit this morning.

My zone 5 and zone 6 are set up identically. Last year I had problems with them getting too much water. They are in an area of my yard in mostly shade that just does not drain well. And the zones overlap. So last year I did a duration tweak of 65%. Under the old software, that tweak made the system THINK it was still putting down the .61 inches which was supposed to have a watering time of 45 minutes. But I was only watering for 30 minutes.

Here’s the weird thing I’m seeing now. I think that my 65% duration tweak from last year is still in place, and I can’t get it back to 100%. I set up a test phantom zone (zone 13) IDENTICAL to my zone 5, and it calculates out that it will water for 45 minutes. Went back to my zone 5 and changed characteristics (I was playing with root depth) to make sure I could see the duration changes. But when I make my zone 5 and my zone 13 exactly identical again, zone 5 wants to water for 29 minutes and zone 13 for 45 minutes. That 29 minutes is 65% of the 45 minutes. Which seems to me that it’s keeping my previous tweak (only it no longers tell me that I had tweaked it or what that tweak was).

Luckily, I keep track of all my zone settings (and changes) so I at least know what duration tweaks I had set.
But had I not recorded those tweak percentages, I wouldn’t now know how to change the durations to get them to what the schedule recommends. @plainsane, I think this is part of what is throwing you off.

And I did actually like that tweaking the duration time was a way to shorten watering time without getting into all the increase/decrease frequency/watering amount since I was having such a hard time with this area of my lawn.

I’m pretty sure the answer to this is yes.

I did my calculation slightly differently than @theflexdude did, but using the scheduling multiplier I also came up with approximately 70 minutes.

My calculation to come up with watering time:

Available water * root depth * allowed depletion = inches to water

((60 minutes * inches to water) / pr rate) * scheduling multiplier = minutes to water

((60 * .66) / .64) * 1.14 = 70.53

That’s precisely what user modification to duration does. It tells the system “this is how long a user thinks it takes to reach the depth of water for that zone”. @plainsane as @Linn quoted there is a 62.2935346861727% adjustment to your durations that is shortening the watering interval.

The easiest way to get to 100% is simply to delete the schedule and create a new one. All of your moisture levels will stay but the durations will be the ones recommended.

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@plainsane I will explain where scheduling multiplier comes from once I find the book.

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Scheduling multiplier is applied to adjust for non-uniformity in turf applications. Because the systems are not perfectly uniform, it’s a standard practice increase the run time in order to minimize dry spots. 0.4 and 0.6 are constants used for all calculations. So if we invert the moisture level formula for duration for entire depth of water, we have:

duration = depthOfWater * schedulingMultiplier * runtimeAdjustment / precipRate

For recommended duration runtimeAdjustmentCoefficient is 1.

depthOfWater = 0.66 in
schedulingMultiplier = 1.14 (based on 80% efficiency)
precipRate = 0.64 in/hr

duration = 0.66 * 1.14 * 1 / 0.64 = 1.1756 hours = 70.54 minutes

With runtimeAdjustmentCoefficient = 0.622935346861727 (user duration adjustment) we have:

duration = 0.66 * 1.14 * 0.623 / 0.64 = 0.7324 hours = 43.945 minutes

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