Design of tailwater recovery systems accounting for irrigation system operation and performance

Authors: Bautista, Eduardo; SCHLEGEL, JAMES; FRENCH, ANDREW

Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2022
Publication Date: 6/29/2022
Citation: Bautista, E., Schlegel, J.L., French, A.N. 2022. Design of tailwater recovery systems accounting for irrigation system operation and performance. Journal of Irrigation and Drainage Engineering. 148(9). Article 04022029. https://doi.org/10.1061/(ASCE)IR.1943-4774.0001703.
DOI: https://doi.org/10.1061/(ASCE)IR.1943-4774.0001703

Interpretive Summary: Tailwater recovery systems help reduce water losses in free-draining surface irrigation, either by temporarily storing the runoff for later use on the same or a downstream field, or by recirculating the water to the head of the field during an irrigation event. In the U.S., general design guidelines are provided in the USDA-NRCS National Irrigation Guide. Those guidelines are based on design procedures developed over 40 years ago, prior to the development of unsteady flow simulation models for irrigation and to the development of current technologies for regulating pumping rates. Existing design methods do not consider the relationship between operation ad performance of the irrigation system with tailwater system design specifications. As a result, tailwater systems can be difficult to operate result due to large imbalances between inflows and outflows. This study examines the design of tailwater systems considering the range of unit inflow rates and irrigation targets of the irrigation system. Results show that when the tailwater system is designed for a fixed inflow rate supply, there is a range of irrigation targets and unit inflow rates for which volume balances can be minimized. Imbalances can also be mitigated by adjusting the inflow supply rate based on specified runoff fraction targets. The study also describes operational adjustments that can be used during an irrigation event to mitigate volume imbalances of the tailwater system. This information should be of interest to irrigators that use tailwater recovery systems and to system designers, including NRCS engineers.

Technical Abstract: The design of tailwater recovery system design for furrow irrigation was examined. The analysis expands on procedures developed by previous authors and aims to account for the operation and performance of the irrigation system on tailwater system design. The method is demonstrated with a hypothetical test case which was examined under a range of inflow rates per furrow and target application depths. While the required tailwater sump capacity largely depends on the area to be irrigated and the maximum target irrigation depth, capacity requirements will increase if large imbalances between inflows and outflows occur by design. Imbalances can be reduced by a judicious selection of the unit inflow rate and tolerated runoff fractions, but when the supply inflow rate is fixed, adjustments to the unit inflow rate may not be feasible or limited. Since pump-back depends on the runoff fraction, it is desirable to limit runoff losses subject to their impact on irrigation system performance. Because of uncertainty and variability of infiltration and runoff, a tailwater system will inevitably be subject to imbalances. If runoff from the initial irrigation set can be measured and the tailwater pump-back rate can be adjusted, the configuration of the tailwater system can be modified before pump-back begins to mitigate imbalances caused by infiltration variability.