Hi @rizzyk, I’m a data scientist working on some concepts for how we can support single-point irrigation using drip systems and emitters, i.e. all the problems discussed in this thread. I’m going to help you find some settings that will work for your problem, and provide some background. This is long winded but unfortunately it is quite a complex topic (one we are hoping to make much simpler!).
The community has rightly pointed out that the Rachio interface and conceptual model was designed and built for solving lawn irrigation and related types of zones which can be generally parameterized by the et demands of the crop and the watering output of the system in linear units (e.g. in/hr). This system is area-agnostic because we assume that sprinklers are distributing water evenly across their zones, and then provide the efficiency parameter to account for system waste. This is the way the ag and irrigation industries typically calculate watering, and it’s a good system for calculating irrigation according to weather, where the fluxes (et, precip) are all in linear units. However customers here are rightly pointing out that both the emitter hardware and the available info for watering trees etc are often strictly in volume per time. The way our system currently works, you basically need to find a linear nozzle rate that meets the volume/time application rate of the emitters, which usually requires some manual tuning.
OK, so let’s try to set up your zones so you can tune them. You have your hardware dialed, so we just need to get the software parameterized right.
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set efficiency at 100%. Drip systems don’t really have waste. Efficiency <100% will add runtime to compensate for waste.
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zone area will not matter
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I would start with the defaults for available water and root zone depth. 16% is reasonable for a compact soil you have re-worked. For most soils it is a little less than the bulk porosity, but compaction history and clay complicate this. Root zone depth default for trees is 25 inches. These and managed allowed depletion (a unitless fraction) combine to create the “allowed depletion” parameter. This is essentially the “size of the bucket” we will try to fill. It will affect BOTH duration and frequency, so tuning it can have complex results.
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The two knobs you want to play with are crop coefficient and nozzle rate. Crop coefficient will determine your zone’s sensitivity to ET demand, and nozzle rate will throttle your runtimes.
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For crop coefficient, we set trees at a 0.75 default (75% of daily reference ETo). The higher the crop coefficient, the more quickly our system will estimate that your soil has dried out, which will trigger another watering. If you want to water more frequently, try increasing in increments of 0.1, and visa-versa.
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Nozzle rate: this is the tricky one. I agree it is an obscure process trying to get from a volume rate to a linear rate. There are many resources offering calculators and tables to do this conversion, some use area, some use the linear length of the drip tubing, and some use neither, so it can be confusing. I’ll append some below.
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With this in mind, there are really two ways to approach the nozzle rate question: calculate it from first principles and trust that runtime OR start with a target runtime and tune until you reach it.
1st approach: elegant from an engineering perspective, but you need to make measurements to be accurate. Emitter valves will often have a published flow rate (e.g. 4 gal/hour) but this is for an “average” water pressure. To dial this in, you need to measure the flow rate at your pressure using a measuring cup and a timer. Once you’ve calculated gallons per hour, you can convert to a linear application rate using a conversion table, assuming 1 ft2 of area per emitter (common, but not always accurate):
- 1.6 in/hr = 1.0 gph/ft²
- 1.44 in/hr = 0.9 gph/ft²
- 0.96 in/hr = 0.6 gph/ft²
- 0.64 in/hr = 0.4 gph/ft²
So that requires some on-site measurement and some assumptions about the application area. That can be measured too, but it’s hard. I’m personally surprised how often this detail is hand-waved over, even by the state of CA in their water use calculations for residential irrigation. So there is some uncertainty.
The 2nd approach is to use heuristics about the runtime for trees, like the UCANR equations you used to derive 6.43 gal/week and 25.7 gal/week @ ETo = 0.15 inches for trees A and B, and experiment to find a good application rate. Use your emitter flow rates to calculate runtime per week (again, measuring these rates will give you the best results), then, in month with average ETo = 0.15 and with all other Rachio advanced settings constant, vary the nozzle rate until you reach that runtime. If you need to get more waterings in a week for the runtimes to be reasonable, tune frequency with crop coefficient, within reason. You can then keep that nozzle rate and let a Flex Schedule throttle the watering according to ET.
You might learn the most by setting a Flex Daily schedule on this zone and watching the calendar change as you tune settings. If the calendar is too irregular for you, you could set a Flex Monthly, which will water in regular intervals, however this will not respond to sub-monthly heat trends (something we are planning on addressing). I would want that functionality for fruit trees.
Please let me know what you try and what the results are. I’m sorry it is so un-obvious how to do this right with our system in its current form.