Evaluation of Residential Irrigation Controller with On-Site Weather Station for Reduction of Water Use, Deep Percolation and Salt and Selenium Loading in Arid Landscapes
* Will a new type of irrigation controller, recently commercially available, significantly reduce water use and deep percolation as compared to traditional timer-based controllers?
The new controllers automatically adjust water application rates based on locally measured evapo-transpiration (ET), per-zone precipitation rates, plant type, soil type, slope of site, and latitude/longitude-derived solar radiation.
Reclamation and U.S. Department of Agriculture (USDA) are charged with managing Colorado River salinity levels. About two hundred and sixty million dollars have been invested in the lower Gunnison and Grand Valley as part of a six hundred million dollar Colorado River basin-wide effort. Extensive conversions of agricultural land to residential use threaten the benefits of those projects. If these new controllers are proven effective, promoting their use can help maintain those benefits, and possibly offset the need for new salinity-control projects that would have to be funded by Reclamation.
Need and Benefit
The Grand Valley in Mesa County in western Colorado contributes an average of 500, 000 tons of salt annually to the Colorado River as a result of salt pickup from irrigation. Mesa County is experiencing rapid population growth. Associated with the rapid population growth is the conversion of agricultural land to residential use. In some areas, lands not previously irrigated are being developed for residential use. Many of these areas are underlain by Mancos shale, containing high levels of salts and selenium. Irrigation water that percolates below the root zone (deep percolation) and leaks from unlined irrigation water delivery systems develop a shallow ground-water system with associated salt and selenium pickup that results in increased salt and selenium loading to small tributaries and the Colorado River. Deep percolation has been previously quantified for agricultural land use (oral communication, Dan Champion Colorado State University [CSU] Extension Grand Junction, Colorado) but has not been quantified for areas where land use is being converted from agricultural use to residential use. A two hundred and sixty million dollar joint effort between the USDA (on-farm) and Reclamation (off-farm) to reduce salt loading to the river has been underway for over 25 years in the Grand Valley and lower Gunnison River basin. The results have been successful with salt loading decreasing in tributaries in the Uncompahgre Valley, Grand Valley, and in the river at the Colorado-Utah border.
However, with current extensive land-use conversion, changes are occurring in use of irrigation water which impact deep percolation volumes and associated salinity loading. The proposed research will determine whether residential irrigation controllers which use onsite weather data and customized site specific programming such as per-zone precipitation rates, plant type, soil type, slope of site, and latitude/longitude derived solar radiation are a more cost-effective means of reducing irrigation water usage and associated deep percolation and salt loading in arid landscapes such as the Mancos Shale of western Colorado. Since a two-year U.S. Geological Survey (USGS) baseline study using the same or similar sites will be completed soon, a direct comparison between traditional irrigation time-based controllers and these more sophisticated controllers will be possible. Selected homeowners will receive a WeatherMatic Smartline irrigation controller and professional installation of the timer. At the end of the study, the homeowner may elect to keep the new timer or revert to their old equipment.
The soon-to-be concluded USGS two-year study would provide the baseline for this proposed research. USGS will be Reclamation's partner in this work, providing some in-kind services and utilizing the same personnel, expertise, and knowledge of sites and procedures from the previous study.
Reclamation needs the information to be developed in this study to determine if promoting and possibly providing incentives for use of this type of equipment for urban and suburban irrigation users would be a cost effective means of maintaining existing levels or even reducing salt and selenium loading in the Colorado River. The controllers would initially be promoted locally in the Grand Valley and lower Gunnison River basin but could have broad application across Reclamation states where salt and/or selenium loading is problematic or where there is a need to reduce water use. This technology could increase water availability for other uses and avoid the costs of constructing new water supply projects or implementing additional salinity-control projects. It is believed the new type of controller could be a significant improvement over existing technology by delivering irrigation only when needed and not just on a regular timed schedule.
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