Encouraging the use of smart technologies for residential
landscapes has become a popular trend in water conservation and rebate
programs by water utilities and agencies looking for ways to decrease waste due
to inefficient irrigation. Generally, these
technologies can be separated into two categories (Figure 1):
- evapotranspiration-based irrigation controllers (ET) The ET controller uses weather data, inputs chosen by the user based on landscape characteristics, and proprietary algorithms to determine when to irrigate and how much to apply.
- soil moisture sensors (SMS). The SMS measures the amount of moisture in the soil and skips irrigation if the soil is too wet.
If at once you don’t succeed
A recent ET
controller study was planned and implemented in Hillsborough County,
FL. A community-wide analysis of water
billing data was completed for the county and the three communities that showed
the highest estimated irrigation were Apollo Beach, Riverview, and
Valrico. A total of 36 volunteers were
selected across the three communities with 21 of them receiving Toro
Intelli-sense ET controllers. All ET
controllers were programmed with UF/IFAS-recommended
program settings (ET+Edu). The
remaining volunteers were monitored, but did not receive an ET controller
(comparison).
Unfortunately, results were not as positive as anticipated. Though the ET controllers decreased
irrigation application by 23% to 41%, irrigation increased by 14% for homes in
Valrico and 54% for homes in Riverview when compared to the respective
volunteers without technologies. Irrigation was high within these two
communities, but the volunteers were not necessarily over-irrigators. It was clear that there must be a better way
to identify the utility customers that would benefit from smart
technologies.
More technology, bigger canvas
A new study
was planned for Orange County, FL, that would evaluate the water conservation
potential of both types of smart technologies when installed on homes with
excessive irrigation habits. Instead of
focusing on communities, all customers in the Orange County Utilities service
area were evaluated individually for trends in over-irrigation. The UF/IFAS recommendation for irrigation is
based on a soil water balance approach where the change in soil moisture
depends on evaporation, transpiration, rainfall, and irrigation (Figure
2).
Figure 2. The soil
water balance is used to estimate the amount of irrigation needed to account
for evaporation and transpiration losses when rainfall is not sufficient.
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Landscape Irrigation Ratios (LIR) were calculated for every month over
a five year span for each utility customer.
The
LIR is a ratio of measured irrigation to UF/IFAS recommendations for the
same month. An LIR greater than 1
indicates over-irrigation whereas an LIR less than 1 indicates conservative
irrigation practices. Customers were
considered for the study when a minimum of three months in three consecutive years
had ratios greater than 1.5. Out of
140,000 accounts analyzed, there were only 7,408 accounts that exhibited this
behavior and out of these accounts, there were 843 volunteers willing to learn
more about the study.
After a detailed evaluation of many of the volunteering homes, the
study included 139 participants located in seven communities across the county. There were 28 that did not receive a
technology (comparison), 55 that received a Rain Bird
ESP-SMT (ET), and 56 that received a Baseline
WaterTec S100 (SMS). There were 28
homes of each technology that received additional educational opportunities and
UF/IFAS recommended program settings (+Edu).
Figure 3. Average
landscape irrigation ratios from before the Orange County smart controller
study began. Irrigation trends were high
with 6-8.3 times the recommendation.
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The average historical LIRs (five years of monthly irrigation
application to monthly UF/IFAS recommended irrigation) for Orange County study subjects ranged from 6.0 to 8.3,
meaning that these volunteers were applying 6 to 8.3 times the amount of
irrigation needed (Figure 3). When considering
historical LIRs in the aforementioned Hillsborough County study, they ranged
from 1.5 to 2.4 indicating that they were also over-irrigating but were already
much more conservative than the Orange County participants (Figure 4).
Diving into the numbers
Irrigation by the comparisons in Orange County decreased from
historical trends (6.9 before the study, 4.3 during the study). Though the real reason is unknown, possibilities
for the behavior adjustment include highly publicized droughts encouraging
water conservation, awareness of being monitored for the study, or even repairing
leaks discovered during their initial system evaluation. Implementing the technologies had a larger
effect, reducing the LIRs to 2-3.3 (Figure 5).
The additional education and programming was important for the SMS,
reducing the ratio significantly from 2.9 (SMS) to 2.0 (SMS+Edu). However, all of these treatments are still
well above a value of 1, which is the goal, so more savings are possible.
The takeaway
Smart technologies should be focused on homes
that exhibit habitual excessive irrigation.
In situations where marginal water savings are possible, such as in the
Hillsborough County ET controller study, a soil moisture sensor with UF/IFAS
recommended installation and programming is recommended. These sensors can be used in situations of
deficit irrigation schedules whereas ET controllers can increase water use to
maintain a well-watered landscape. Both
technologies were effective when used in the right situations.
Thanks to Hillsborough County
Water Resource Services, Tampa Bay Water, Orange County Utilities, Water
Research Foundation, St. Johns River Water Management District, and South
Florida Water Management District for providing the support to complete these
projects. These studies were co-authored
by Michael D. Dukes.
About the author:
Stacia L. Davis, Ph.D. is an assistant professor of irrigation
engineering with the Louisiana State University Agricultural Center located at
the Red River Research Station, Bossier City, LA. She studied the water conservation potential
of smart technologies at the University of Florida prior to moving to
Louisiana.
Awesome research! Thanks Stacia!! We should look at publishing multi-state extension documents!
ReplyDeleteThat sounds like a great plan!
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