Examples
Example 1
If each emitter had a discharge rate of one gallon per hour, how many hours of irrigation time are necessary per day to meet the requirement?
The Process
51-gph emitters = a flow rate per tree of A gph.
The total gallonage required per day per tree is B
Total gallonage C / Flow rate per tree D = Equals E hours.
If the 5 emitters were 2-gph emitters, how long would it take to irrigate the tree?
5 emitters at 2 gph = flow rate per tree of F gph.
With a total gallonage per day required of G
Daily Total of H / The flow Rate Per Tree I = J hours of System Operating Time(or simply divide 13.6 hours by 2).
Example 2
If you had a plant requiring 26 gallons per d and three emitters covered its area, what flow rate per emitter would you choose if only 4. hours were available for drip irrigation?
The Process
Total gallons per plant per day = A
Number of emitters available = B
Hours available for drip = C
Total gals. Required D / Hrs. available E = F Flow Rate Required Per Plant
With a flow rate per plant of G to be provided through H emitters, each emitter would have to discharge I gph.
Rounding up to the next common emitter flow rate, the emitters would be rated at J gph each.
Mixing & Matching Plant Groups
Prior to the section on circuiting emitters and plants into groups to be watered together, the possibility of mixing and matching some plant flow rates should be discussed.
For example, the tree from the previous example (number two) could be matched on the same pipe or tubing lateral with other plant flow rates if the emitters all are rated at the same pressure for their desired discharge and operating time is the same.
Example: 26 gallons per day required
3 emitters
2 gph emitters @ 20 psi
6 gph flow rate for the tree
4.5 hours watering time
Using the same number of hours for running time (4.5), what flow rates would you specify for the emitters on the plants in the following examples?
Plant #1 9 gallon per day required
2 emitters per plant @ 20 psi
9 gallons / A time available =a flow rate per hour of B gallons per plant.
The flow rate per plant of C GPH / 2 emitters equals what flow rate per emitter? D GPH
Plant #2 2.3 gallons per day required
1 emitter per plant @ 20 psi.
What common emitter flow rate is closest to the required flow rate for this plant? E
The other factor that should influence your decision about mixing and matching plants on the same circuit is frequency of irrigation. With plants and trees that have larger deeper root systems the daily water requirements can often be grouped into multiples of a few days' worth per application with corresponding days off between cycles. Plant groups with differing irrigation frequencies should not be circuited on the same valve.
Soil type, rooting depths and seasonal conditions all influence irrigation frequency. Though frequency is best determined on an individual plant type/soil type/climate type basis here are some rough guidelines:
Plant Types
Frequency
Small shrubs, vines
2-3 Days
Large shrubs, small trees
3-4 Days
Medium to large trees 5-6 Days
If the longer watering time required per cycle causes puddling or runoff, decrease the irrigation time and water more often.
Answers To Examples
Example 1
A.5
B.68
C.68
D.5
E.13.6
F.10
G.68
H.68
I.10
J.6.8
Example 2
A.26
B.3
C.4.5
D.26
E.4.5
F.5.77
G.5.77
H.3
I.1.92
J.2
Answers To Mix & Match Exercises
Plant #1 A.4.5
B.2
C.2
D.1
Plant #2
E.0.5 gph
2.3 gallons per day 4.5 hours
= .51 gph for the plant and its one emitter
Remember, emitter operating time and pressure need to be the same for the various emitters on the circuit to match them up properly.
