Journal of Irrigation and Drainage Engineering

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 unit inflow rate and tolerated runoff fractions, but when the supply inflow rate is fixed, adjustments to the unit inflow rate may be limited or not feasible. Because pump-back depends on the runoff fraction, it is desirable to limit runoff losses subject to their impact on irrigation system performance. Because of the 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.

Determining the pipe diameter is one of the principal problems encountered in designing and analyzing pipe flow lines. However, the direct determination of a pipe’s diameter is not possible because of the implicit form of the Colebrook resistance flow formula through commercial pipes. Traditionally, the pipe diameter is determined using a trial procedure. In this paper, the pipe diameter problem was solved using explicit equations in terms of the Lambert W-function. The maximum relative errors of the developed solutions are less than 0.013% for the rough and smooth flow regimes and less than 0.8% and 0.6% for the transition flow region between them. In addition, a method for determining pipe diameter under uncertainty, including design graphs, is presented. It is hoped that the developed solution for predicting pipe diameter will be helpful in the analysis of pipe flow and the design of pipelines and water distribution networks.

This technical note introduces a computational fluid dynamics (CFD)-based semiautomated flow rating methodology for hydraulic structures in South Florida. The approach uses the ANSYS Workbench, CFD code FLUENT, IronPython, and Visual Basic programming languages to incorporate the CFD flow data generation process into a semiautomated interactive flow rating platform. The framework includes multiple functions such as overall flow rating status, interactive planning of boundary conditions, automated CFD flow data generation, and hybrid flow rating development using field measurements and CFD-generated flow results. The platform can reduce the complexity of CFD application to flow data generation, optimize central processing unit (CPU) usage, greatly reduce simulation times, and significantly improve flow rating analysis efficiency for the water control structures maintained and operated by the South Florida Water Management District. About 30%–40% simulation time was saved by reducing CPU idle time and automizing geometry adjustments and mesh regeneration. In addition, a 40%–50% reduction in manual work for rating development was achieved with the approach presented.

This study detailed a novel semicoupled method for estimating the three-dimensional vertical velocity profile in an open channel with submerged flexible vegetation. A modified form of the two-dimensional shallow water equations coupled with the drag forces of the vegetation was derived by balancing the flux gradient and the source term. The bending profile of the flexible stems of different flow events was calculated based on the large cantilever beam theory. The vertical velocity profile in the free water and vegetation layers was estimated using Shannon’s entropy and Reynold’s stress equation theory, respectively. The derived semicoupled model was tested to replicate two popular laboratory flume experiments. The results showed that the model accurately predicted the velocity profiles under different flow conditions and patch density. The $R^2$ values of 0.76 and 0.81 indicate that the proposed model is well established and can be applied in complex flow scenarios.