Guide to Estimating Irrigation Water Needs of Landscape Plantings
Guide to Estimating Irrigation Water Needs of Landscape Plantings
Guide to Estimating Irrigation Water Needs of Landscape Plantings
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Chapter 5—<br />
<strong>Irrigation</strong> Efficiency<br />
and Calculating the<br />
Total Amount <strong>of</strong> <strong>Water</strong><br />
<strong>to</strong> Apply<br />
The first four chapters have described the process<br />
for estimating plant water needs. To calculate the<br />
<strong>to</strong>tal amount <strong>of</strong> water <strong>to</strong> apply, irrigation efficiency<br />
needs <strong>to</strong> be addressed. This chapter introduces the<br />
formula for calculating <strong>to</strong>tal water needs and discusses<br />
the irrigation efficiency fac<strong>to</strong>r. How this<br />
information applies <strong>to</strong> irrigation management is discussed<br />
in Chapter 6.<br />
The ETL formula calculates the amount <strong>of</strong> irrigation<br />
water needed <strong>to</strong> meet the needs <strong>of</strong> plants. This<br />
is not the <strong>to</strong>tal amount <strong>of</strong> water needed <strong>to</strong> apply,<br />
however. Since every irrigation system is inefficient<br />
<strong>to</strong> some degree, the landscape will require<br />
water in excess <strong>of</strong> that estimated by ETL. In this<br />
chapter, irrigation efficiency will be discussed and<br />
then used <strong>to</strong> calculate the <strong>to</strong>tal amount <strong>of</strong> water <strong>to</strong><br />
apply.<br />
<strong>Irrigation</strong> Efficiency<br />
Efficiency can be defined as the beneficial use <strong>of</strong><br />
applied water (by plants). The following formula<br />
is used <strong>to</strong> calculate irrigation efficiency:<br />
<strong>Irrigation</strong> Efficiency (%) = Beneficially Used <strong>Water</strong> x 100<br />
Total <strong>Water</strong> Applied<br />
An efficiency <strong>of</strong> 100% would mean that all applied<br />
water was used by the planting. This rarely occurs.<br />
Consequently, irrigation efficiency is less than 100%<br />
Not all water applied <strong>to</strong> landscapes is used by plants. Some is lost<br />
due <strong>to</strong> run<strong>of</strong>f, windspray, or deep percolation. <strong>Irrigation</strong> efficiency<br />
losses need <strong>to</strong> be included in water budget calculations.<br />
in virtually all cases and additional water should be<br />
applied <strong>to</strong> account for efficiency losses.<br />
A determination <strong>of</strong> irrigation efficiency (IE) for<br />
landscape plantings is challenging. As yet, a standard<br />
method has not been established. The approach<br />
used for turf irrigation, distribution uniformity (DU),<br />
is not appropriate for most landscape plantings.<br />
Three approaches are considered here: calculation,<br />
estimation, and goal setting. Each method has significant<br />
limitations, and are presented here only as<br />
possible options <strong>to</strong> consider.<br />
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