Irrigation Audits: A Task That Can Be So ‘Irrigating’, Or Does It?
Post-Audit: From here, after a successful irrigation-audit, DU can be calculated through the mathematical formulas seen below:
By Travis Roberson, Graduate Research Associate
I
rrigation audits (IA) are conducted across all areas of turfgrass that are intensively managed such as golf courses (greens, tees, and fairways), athletic fields, and commercial lawn care. An audit is performed to evaluate the efficiency of an irrigation system known as the distribution uniformity (DU). Using an audit to spatially calculate DU values also helps to identify areas with problems not seen through macro-observations by engaging the system. While it is recommended to perform multiple IA per year, the most optimal time is in the late winter to early spring seasons to allow any modifications to be implemented prior to the onset of elevated evapotranspiration rates. Evaluating irrigation systems requires a few key procedures: PreAudit, Irrigation-Audit, and Post-Audit to successfully capture viable information and determine the presence of problems that require professional attention. Pre-Audit: a successful IA is conducted when the entire system is functioning at an optimal level but ‘optimal’ must be determined by the manager himself. Inconsistencies of the system can occur based on instances such as tree roots heaving irrigation heads, major leaks (at the irrigation head or pipe), clogged screens, sunken sprinkler heads, etc. You may elect to not fix these issues prior to an audit if you are using the audit to display major defects in the system, so the goal of the IA must be determined to assess the effort required for the ‘Pre-Audit’ step. Irrigation-Audit: prior to actually performing the audit, it is important to document relevant information such as sprinkler head operating pressure, number of heads tested at a single IA cycle, head spacing and location, type of irrigation controller/ management software, current watering schedule and a root zone depth assessment, relative soil moisture content before and after irrigation application, windspeed and pre-determined test zone runtime. After all these ancillary details are documented, a comprehensive map documenting the irrigation zone layout and number of catch cans/placement is documented. From here, the irrigation zone is activated and the catch cans that are laid out in a systematic fashion (previously established based on the site location and irrigation head layout) collect the water during this runtime. Site inspection sheets are used after the runtime to measure each catch can and to make any specific notes such as leaks seen during the audit, nozzle issues, arc misalignments, etc.
DU =
VLQ VT
Where DU is distribution uniformity, Vlq is average of the lowest 25% of catch can volumes and Vtotal is the average of all of the catch can volumes. It is important to note that the industry standard is a DU of 70%, where anything above this value is considered a functionally operating irrigation system but also varies based on the type of irrigation heads being tested. As seen, it is a very intensive process to determine the effectiveness of an irrigation system that requires a substantial amount of time and set up to be performed effectively. Within our lab at Virginia Tech, we are experimenting with a newer way to evaluate the same detailed information in a more rapid fashion through drone thermal imagery. At Independence Golf Club in Midlothian, Virginia, in the summer of 2023, we went through the same industry processes to evaluate catch can volume data compared to aerial thermal imagery collected through a Mavic 3T drone, one of the newer ones on the market. We evaluated four greens and tee locations to study areas that are all sand-based medium rootzones but with little to no slope and/ or undulations. Using many different software packages we used drone flights, high overlapping thermal imagery to make larger orthomosaic, extract pixel data values, and compare to catch can volumes and have seen promising results. Our data suggests there is a negative relationship with the more water caught in a specific area decreasing thermal canopy values for bermudagrass greens and tees. These trends are promising to expedite irrigation auditing processes in the future, however, there is still a considerable amount of training required to post-process all of the necessary data. As technology (more so the ease of application for current technology) develops, thermal imagery may be an effective means for turfgrass managers to essentially run an irrigation zone for a specific runtime, collect thermal images, and upload to a repository for automatic data processing for DU outputs. Our end goal is to have this technology streamlined to reduce any friction turfgrass managers may have with wanting to identify irrigation limitations and wanting to improve their systems, ultimately maximizing water consumption of all intensively managed turfgrass areas!
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20 | VIRGINIA TURFGRASS JOURNAL January/February 2024 www.vaturf.org
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