Posted by Kendall Bell-Enders and Robin H. Gary on October 10, 2014
The drilling of irrigation wells is a recent trend. As water suppliers restrict water use, many homeowners are looking to irrigation wells to maintain lush landscapes, rather than paying high water bills or converting to drought-tolerant, native plants. In areas with groundwater conservation districts, permit requirements, and a public process, there are far less irrigation wells. Many years ago the Texas Commission on Environmental Quality had identified Western Travis County as a Priority Groundwater Management Area, because of possible critical groundwater problems including shortages of surface water or groundwater. Recent well activity could introduce those problems sooner than later.
While the District is not immune to the recent irrigation well drilling trend, the majority of new wells drilled in the District are for domestic use (homes that don’t have another water source available). However, the interest in new irrigation wells has substantially increased over the last few years and those interested soon realize that Freshwater Edwards Aquifer permits are only available in non-drought conditions and that firm-yield Historic Trinity Aquifer permits are the most viable option. They are also informed that the Trinity Aquifer typically has higher salinity, can be low yielding, and may be restricted by District rules to limited amounts of production.
It is District policy to ensure that the annual permitted volume be commensurate with reasonable non-speculative demand; making it necessary to accurately estimate landscape water requirements and demand for irrigation applications. To support this policy, the District hired Dennis Pittenger, a professional urban horticulturist and researcher, to assist in developing a science-based methodology for calculating reasonable demand estimates for irrigation of landscape elements such as: mixed plantings, trees, and turfgrasses in the region.
The recommended methodology is a climate-based approach relying on local reference evapotranspiration (ETo), precipitation and research-based plant factors (PF’s). A “plant factor” is a fractional adjustment to ETo for specific landscape plants that accounts for plant morphology, physiology, and irrigation management. This methodology can provide reasonable and rational water requirement estimates because it is based on the fact that plant water demand is in large part a function of the local climate. An allowance for irrigation system and/or management inefficiencies is commonly applied when calculating landscape irrigation requirements and distribution uniformity of the irrigation system is the most common measurement of efficiency used for this purpose.
This methodology was vetted internally and adopted by the Board to serve as an objective and science-based tool to be used by District staff to ensure that the permitted volumes for requested irrigation permits are reasonable and commensurate with the actual water demands of the irrigated landscape. The report is available at the Guidance Documents section of the Permitting page.