Sprinkler Uniformity Evaluation
By Paul Vermeulen
Agronomist, Western Region, USGA Green Section
Reprinted from the USGA Green Section Record
1991 March/April Vol 29(2): 30
IN THE PROCESS of evaluating the performance of an irrigation
system, many of us have become well versed with the importance of
proper sprinkler head spacing, mainline looping, and pumping
station and operational pressure. Having checked all of these
major system components, the final step is to take a closer look
at how evenly the sprinkler head itself distributes water over
the course.
The distribution of water from a sprinkler head using information
taken from a typical rain gauge test is plotted on a graph. The
X-axis is the distance of the rain gauge from the sprinkler head,
and the Y-axis is the amount of water captured in each rain
gauge. While this chart shows us the water distribution for a
single sprinkler head, it fails to reveal the water distribution
when operated in relation to its neighboring, or backup sprinkler
heads.
A computer program developed at the University of California,
Fresno, Center for Irrigation Technology under the direction of
Kenneth H. Solomon reveals a figure showing what happens with
respect to water distribution. This figure, referred to as a
"denso-gram," is based on the same information as the
graph for the single sprinkler head. The lightly shaded areas of
the denso-gram indicate wet spots, whereas the darker areas
indicate dry spots.
To interpret the meaning of the denso-gram, the computer also
generates a scheduling coefficient. This value indicates the
amount of extra water required to provide enough moisture to the
dry areas indicated on the denso-gram. For example, if the
pumping station is capable of applying 0.2 inches of water every
30 minutes, then the irrigation cycle must be scheduled for 51
minutes (30 x 1.17) in order to adequately moisten the critical
areas. Naturally, this is a waste of water and a needless expense
from the standpoint of water and electrical costs.
In the Southwest, reducing the scheduling coefficient is vital
for water conservation; however, this Turf Tip can also be used
in other areas of the country for improving turfgrass quality.
For example, take a case where dry spots in the fairways require
hand watering during the summer months, or where wet spots are
affecting playability. More than likely an effort has been made
to check sprinkler head spacing, mainline looping, and pumping
station and operational pressure. If so, the time has come to
check sprinkler head water distribution by using this new
technology.
If you would like information, contact: The Center for Irrigation
Technology, California State University, Fresno, CA 93740, (209)
278-2600.