Journal of Irrigation and Drainage Engineering

In a traditional automated upstream controlled canal with a downstream buffer reservoir, the process to fill the buffer reservoir requires one step: the inflow to the canal is increased, and the flow change eventually arrives at the buffer reservoir. This paper describes an attempt to shorten the time necessary to stabilize the new flow rate at the buffer reservoir. The method requires calculated, remote manual adjustments to all the canal check structure gate positions in addition to two flow rate changes made at the head of the canal, followed by a return to automated upstream control. The method was tested in the Upper Main Canal of the Central California Irrigation District both through simulation and in the field. With a canal flow of approximately 20% of the maximum, simulation modeling predicted that a flow rate change arrival at the reservoir would be about 5.5 h in a typical operation, with final stabilization in about 16 h. Simulation of an improved procedure indicated an almost instantaneous increase in flow at the reservoir of half the flow change, with final flow stabilization at 11 h. The field test resulted in almost the full flow change arriving at the reservoir after about 20 min, with gradual stabilization occurring over the next 11 h. Important differences between simulation and actual results are discussed.

Labyrinth weirs present an effective solution for high discharge efficiency in space-restrictive situations. However, these weirs exhibit negative effects (vibrations, noise, and instability) when the nappe clings to the downstream surface of the weir because of subatmospheric pressures. Nappe breakers are used to limit the occurrence of this behavior. Currently, only a limited number of investigations have focused on the performance of nappe breakers when applied to circular labyrinth weirs. The present study has been designed to provide detailed performance data for sharp-crested circular labyrinth weirs for the case of a simple weir as well an augmented weir (with nappe breaker). Three-dimensional (3D) computational fluid dynamics (CFD) models were verified by comparison with the experimental observations, and then the pressures under the jet flow at the downstream of the weir were scrutinized using a two-phase (water-air) turbulent numerical model. The results of both the numerical simulations and experimental observations confirm the positive outcomes obtained through the use of the nappe breakers to control subatmospheric pressures on the downstream face of the weir.

Knowledge of the maximum length for paired drip laterals facilitates the economic optimization of microirrigation systems. The methodologies proposed to date have been based on complicated mathematical procedures that make certain restrictive assumptions, such as fixed pressure head variation, and disregard emitter flow variation; this has limited their application. The methodology presented in this study, which assumes the basic equations for the analysis of a drip lateral based on the energy gradient line, allows evaluation of the maximum length of paired drip laterals with non-pressure-compensating emitters when diameter and slope are known and pipe is laid on a uniformly sloping field. The results show that the maximum length of a paired drip lateral with a given diameter is almost constant for any slope, although there is a maximum slope above which the lateral pipe diameter needs to be reduced. The maximum slope can be obtained when the ratio between the difference in elevation and the head loss due to friction of the downhill lateral exceeds 1. A method is also proposed to determine the lateral pipe diameter for a fixed length.

Maize water use was measured by water balance in a 6-year field trial in the west-central Great Plains of the United States. Seasonal water use of the 102-day maturity class variety varied from 616 to 774 mm, with an average of 666 mm. About 10% of the seasonal crop evapotranspiration from the drip-irrigated crop was estimated to be evaporation from the wet soil surface following precipitation or irrigation. Seasonal crop evapotranspiration averaged 68% of tall (alfalfa) reference evapotranspiration and 82% of short (grass) reference evapotranspiration. Derived basal alfalfa-reference crop coefficients, $K_{cb}$, matched the ASCE Manual of Practice 70 (MOP #70) [Jensen, M. E., and Allen, R. G., eds. (2016). Evaporation, evapotranspiration, and irrigation water requirements, ASCE Manual of Practice 70, 2nd Ed., ASCE, Reston, VA] values fairly well during crop development, but mid-season values were about 1.05, which exceeded MOP #70 values by about 10%. Short reference $K_{cb}$ values matched MOP #70 {and Food and Agricultural Organization Irrigation and Drainage Paper #56 [Allen, R. G., Pereira, L. S., Raes, D., and Smith, M. (1998). Crop evapotranspiration: Guidelines for computing crop water requirements, FAO Irrigation and Drainage Paper 56, Food and Agriculture Organization of the United Nations, Rome.]} recommended values fairly well. The derived basal crop coefficients were linearly related to crop canopy ground cover, which provided an excellent way to scale $K_{cb}$ during both the crop development and maturation stages.

This paper describes and discusses the available experimental investigations concerning vertical pipe flow in order to understand possible differences caused by different intake types and inflow conditions. Specific attention is given to the difference between drain pipes and overflow pipes and to the influence of the inflow conditions on the head–discharge relation. Data from the available literature are systematized and treated in a unified manner to provide a comprehensive view of possible flow regimes, among which four main types are selected, namely Borda free and full flow, governed by pipe cross section; weirlike flow, governed by pipe diameter; and full pipe flow, governed by pipe cross section and length. For each, both data from the literature and novel data are used to calibrate both dimensional and nondimensional head–discharge equations, along with prediction equations for the discharge coefficients. The equations describing the critical head, marking the passage to full pipe flow, and the vortex critical head, marking the passage to a vortex-free full pipe flow, are provided.

Unsustainable groundwater use for agricultural irrigation has led to declining aquifer levels across the United States, necessitating implementation of water conservation practices. One conservation practice being implemented throughout the lower Mississippi River alluvial valley (LMAV) that collects and stores surface water for irrigation is a tailwater recovery (TWR) system. Accordingly, the overall objective of this study was to develop a water budget for TWR systems. Eight TWR systems were continuously monitored for water depth, allowing rates of water gain and loss to be quantified. Volumes of water movement were calculated based on change in water depth and system dimensions. Using water budgets derived from TWR systems the water volume was calculated and found to be gaining, except during months of irrigation. Extrapolating the water budget to all TWR systems shows a total offset of 15% of the annual groundwater deficit. Tailwater recovery system efficiencies show designs may be altered to improve the water savings and use of these systems.

This paper presents the potential of remotely sensed data in addressing spatially distributed irrigation equity, adequacy, and sustainability. The surface energy balance algorithm for land (SEBAL) was implemented to map actual evapotranspiration (ET) over an irrigation district in southern California. Potential ET was also mapped based on the Priestley–Taylor method, modified to account for the effect of horizontally transported energy on enhancing/suppressing ET. Remotely sensed products were integrated with ground-based data in a Geographical Information System (GIS) environment to quantify several irrigation and drainage performance indicators. The among- and within-field coefficients of variation of actual ET were comparable to previous studies, suggesting that water consumption was uniform across the irrigation district. The relative ET was high, indicating that irrigation supply was adequate. The extensive network of open drains was also found to be functioning at an optimal level according to the results of two performance indicators based on the magnitude and uniformity of groundwater depth.