Using Smart Irrigation To Conserve Water

By Linda Reekie, Research Manager, Water Research Foundation

Background

Using efficient irrigation for outdoor lawns is an effective way to save water and to delay the need for water utilities to develop new water sources. In 2005, Orange County Utilities (FL) began an effort to plan for alternate water sources in Orange County because its primary water source, the Floridan Aquifer, was predicted to meet its capacity to provide water. The expected population increase of 49 percent by 2035 in the Central Florida Water Initiative Regional planning area, of which Orange County is a part, along with a projected deficit of groundwater, prompted Orange County Utilities to pursue alternative water supplies as well as additional water conservation opportunities. Under the direction of Jacqueline Torbert, manager of the water department, Orange County Utilities took on Water Research Foundation project #4227, Smart Irrigation Controller Demonstration and Evaluation in Orange County, Florida, to mitigate the risk of expected groundwater limitations and to leverage the increased affordability of smart irrigation technologies to save water. The primary researcher was Dr. Michael Dukes of the University of Florida Agricultural and Biological Engineering Department. Other project funders included the South Florida Water Management District and the St. Johns River Water Management District.

Approach

The research project investigated the performance of two different smart irrigation technologies over time at both commercial and residential properties and in poorly-drained and well-drained soil conditions. The research also investigated an educational component, where half of the residential properties using smart irrigation technologies received instruction on the use of the technology installed and assistance in optimizing the control setting of the smart irrigation technology for site-specific parameters.

The two smart irrigation technologies installed and evaluated were soil moisture sensors (SMS) and evapotranspiration (ET) controllers. Soil moisture sensors are installed in the root zone of the soil. The sensors measure the amount of moisture in the soil and communicate to the SMS controller that the moisture is above or below the set threshold, thus signaling the controller to turn the irrigator off or on. ET controllers calculate the amount of needed irrigation through a soil moisture balance equation, using temperature and precipitation data collected onsite through a sensor and a rain gauge. An ET controller replaces the irrigation system’s existing timer and is connected to a temperature sensor and rain gauge to communicate weather data to the irrigation controller for irrigation scheduling. ET controllers also take into account such site parameters as soil type, landscape slope, plant type, sun exposure, and root depth to determine the amount of moisture needed.

About 167 residential properties were included in the research. Households were selected based on water records indicating a tendency to irrigate more than needed. The two smart irrigation technology treatments were distributed within specific geographic locations so that there were at least three replicates per treatment group and properties were spread across the two dominant soil types: flatwoods soils (somewhat poorly drained) and sandy soils (well drained). Treatment groups included: ET controller only, ET controller with educational component, SMS only, SMS with educational component, and a comparison group (no smart irrigation technology). The irrigation data collected and analyzed spanned a three-year period.

In addition to making comparisons between treatments, turf grass quality ratings were conducted seasonally throughout the treatment period and statistical analysis of the turf grass quality results were conducted.

Four commercial properties were also included in the research. These properties received ET controllers with site-specific programming. Nineteen months of data were collected for the commercial properties.

Results

For the residential properties in both the flatwoods and sandy soil locations, all treatment groups had significantly lower weekly irrigation compared to the comparison group. Differences between the two treatment technologies were not significant. However, in the flatwoods soils (somewhat poorly drained), the ET and SMS treatment groups that had received education had significantly less irrigation than the ET and SMS treatment groups that had not received education. It is speculated that the site-specific settings associated with the education component seems to have lowered the average irrigation application for both technologies in flatwoods soils.

Figure 1. Cumulative irrigation for the study period averaged across locations for the flatwoods soils (Source: Torbert et al. 2016)

In the sandy soils, the ET treatment technology irrigated significantly more than both SMS treatments and the ET plus education treatments. In the sandy soil locations, the ET treatment groups that had received education had significantly lower average irrigation application than the other groups. The educational component favorably impacted average irrigation application for the ET technology in the sandy soils.

Figure 2. Cumulative irrigation for the study period averaged across locations for the sandy soils (Source: Torbert et al. 2016)

On average, ET irrigation controller treatments reduced irrigation by 18 percent across both sandy and flatwoods soils for the non-education group, and 32 percent for the education group. The SMS technology reduced irrigation by 30 percent for the non-education group and 42 percent for the education group across both soils. The educated groups had a trend for less irrigation than their non-education counterparts. A post-test survey showed that the level of irrigation knowledge did not differ between the groups receiving education and the non-education treatment groups; therefore, it is speculated that the education groups irrigated less due to the optimized control settings for site-specific parameters.

Among the four commercial properties, all of which were installed with ET controllers, average irrigation was reduced across both soil types by 28 percent. Turf grass quality ratings were taken quarterly and the quality exceeded the minimum rating at all commercial properties throughout the study.

A post-test survey provided data on water use, conservation attitudes, satisfaction with the residential use of SMS and ET controllers, as well as satisfaction with yard appearance. A range of 61 to 87 percent of participants in each treatment group considered themselves satisfied or very satisfied with their irrigation practices. A range of 61 to 77 percent or survey participants were either satisfied or very satisfied with their yard appearance. A range of 65 to 81 percent of survey participants were satisfied or very satisfied with smart irrigation technology.

The study results demonstrate that smart irrigation controllers conserve water for both residential and commercial properties that historically over irrigate, by efficiently scheduling irrigation. The study participants were exempt from mandatory one- and two-day-per-week irrigation restrictions imposed at the time of the study by the water management districts. To realize the water conservation potential of smart irrigation technologies, alternatives to policy mandates such as irrigation restrictions based on days of the week should be examined.

Reference

Torbert, J. W., B. Tolley, T. Thill, L. M. Allen, M. D. Dukes, E. M. Breder, P. F. Monaghan, M. C. Morera, and O. Wells. 2016. Smart Irrigation Controller Demonstration and Evaluation in Orange County, Florida. Project #4227. Denver, Colo.: Water Research Foundation.