Uniformity coefficients should be high for high value crops, especially shallow rooted and container crops, with UC greater than 87%. For typical field crops the UC should be greater than 81%. For deep rooted orchard and forage crops, if chemicals are not injected, CU should be above 72%.
The UC in this case is good, being above 87%.
**D. **__Scheduling Coefficient (SC)__. Scheduling Coefficient is a measure of uniformity in an area that compares the lowest precipitation rate (volume) for a defined contiguous area to the average precipitation rate (volume) over the entire test area.
**Scheduling Coefficient (SC) = Average Catch (volume) overall / Average Catch in Critical Dry Area.**
The SC becomes a multiplier that tells how many times longer the watering must be done in order to water the dry area as much as the average area was getting at the time of the test.
Irrigation efficiency takes a back seat when there is an area that does not receive enough water. A grower must water to meet the requirements of the driest area. Thus, in Figure 3.4b of Section 4.3, the low quarter of volumes were 0.24, 0.25, 0.27 and 0.28 inches while the average depth collected was 0.31 inches. Using this scheduling coefficient calculation we can expect the grower to apply water to satisfy the dry area that is receiving 0.24 inches. With this in mind,
SC = 0.31 in. / 0.24 in. = 1.29 or about 1.3 times the amount of water needed on the average in order to satisfy the driest area which is 1/16 (6.25%) of the area. Of course, the 0.25 in. value is not much better, compared to the average.
This calculation points out the need to achieve high water application uniformity in order to conserve both water and energy.
**E. **__Flow Rate from a Nozzle.__ This equation is not required for the evaluation of uniformity but may be used to estimate the flow discharge of a nozzle if it is not known. It requires a good measurement of the nozzle size if the size is not given on the nozzle. Also, the water pressure at the nozzle must be measured.
Q = 28.62 (d x d) (square root of p)
Where: Q = flow rate of nozzle {gpm}
d = nozzle diameter {in.}
p = pressure at nozzle {psi}
28.62 = constant to convert units
__F. Precipitation Rate (gross).__ This is the gross amount coming out of the nozzle and does not account for losses to evaporation in the air before reaching the ground. Use this equation when the nozzle flow rate and the sprinkler spacing are known.
PR = (96.3 Q) / Area = (96.3 Q) / (S1 x S2)
PR = average precipitation rate in area {in./hr}
Q = flow rate into the area {gpm}
S1 = sprinkler spacing in one direction {ft}
S2 = sprinkler spacing in other direction {ft}
Area = area associated with the precipitation {sq ft}
96.3 = constant to convert units
**References:**
Rochester, E.W. August 2005. Irrigation System Performance Audit. Irrigation Association Education Foundation, 6540 Arlington Boulevard, Falls Church, VA 22042-6638. __www.iaef.org__. Notebook of instructor manual, powerpoint CD, worksheets, student manual.
Smajstrla, A.G., B.J. Boman, G.A. Clark, D.Z. Haman, D.J. Pitts and F.S. Zazueta. May 1997, reviewed 2005 by Haman. Bulletin 266. Agricultural and Biological Engineering Department, Florida Cooperative Extension, Institute of Food and Agricultural Sciences, University of Florida. 9 pp. http://edis.ifas.ufl.edu/pdffiles/AE/AE38400.pdf |