Journal of Irrigation and Drainage Engineering

The Central Arizona Project (CAP) has been supplying Colorado River water to Central Arizona for roughly 25 years. The CAP canal is operated remotely with a supervisory control and data acquisition (SCADA) system. Gate-position changes are made either manually or through the use of automatic controls with a controlled-volume approach. In this paper, the writers examine the potential application to the CAP canal of water-level difference control, a new feedback canal-control method. The main objective of this method is to keep the downstream water-level errors in equal pools. The control model is a multiple input and multiple output (MIMO) system, and the controller is solved as a linear quadratic regulator (LQR). A feed-forward routine called volume compensation was also used to route the flow changes. Simulation results show that this method is stable and can deal with different kinds of changes relatively quickly. For small changes, the water-level difference controller can operate well even without routing flow changes. For large flow changes, the water-level difference control alone can take up to 12 h to stabilize all water levels. Performance is greatly improved with the inclusion of the feed-forward routine. This new method provides better water-level control than the current method, and it is much less sensitive to errors in gate calibration. The writers suggest that this water-level difference-control method is quite promising, especially for large canals.

Transpiration and evaporation rates from irrigated pastures can be adequately assessed by conventional methods and more recently, by the use of stable isotopes $\delta {}^2\mathrm{H}$ and $\delta {}^{18}\mathrm{O}$. However, the salinity effects that transpiration and evaporation have on infiltrating irrigation waters and residual soil-waters have not been independently assessed in a flood irrigation setting. In this study, oxygen-18, deuterium and chloride concentrations of irrigation water, soil-water, and groundwater were monitored with soil-water content over time to independently assess the salinization effects of evaporation and transpiration. This study was carried out across four flood irrigation sites that overlie a heterogeneous loam-sand and limestone vadose zone. Results showed that minor evaporation losses were detected across most flood irrigation sites through the use of stable isotopes $\delta {}^2\mathrm{H}$ and $\delta {}^{18}\mathrm{O}$. The associated increase in chloride concentration of irrigation water as a result of evaporation (minor fractionating water loss) was low ($0\mathrm{mg}/\mathrm{l}$ to $129\mathrm{mg}/\mathrm{l}$) compared to the chloride increase as a result of transpiration ($150\mathrm{mg}/\mathrm{l}$ to $2,800\mathrm{mg}/\mathrm{l}$) noted in shallow soil-water. Across all sites, the fractionating water loss detected in soil-water was minor ($<1‰$ $\delta {}^{18}\mathrm{O}$ from the source) with isotopic signatures reflecting partially evaporated irrigation waters. The high soil-water chloride concentrations, minor fractionating loss, and corresponding decrease in soil-water content suggest that transpiration is the dominant cause of water loss and therefore the largest contributor to salinity effects during flood irrigation. Salinity effects caused by transpiration (0.4 to $2.6\mathrm{t}/\mathrm{ha}$) were 3 to 50 times greater than the salinity effects caused by evaporation from irrigation and soil-waters (0.01 to $0.3\mathrm{t}/\mathrm{ha}$).

The loss of water to the atmosphere during flood irrigation occurs through evaporation and transpiration. Whereas transpiration can be estimated through the FAO56 methodology, actual evaporation is difficult to quantify in water balance studies. In this study, two analytical models, previously developed to quantify evaporation from lakes on the basis of stable isotopes, were applied to determine evaporation losses from four flood irrigation sites of varied characteristics. Evaporation losses were determined by empirical relationships derived between heavy isotope enrichment and percentage of water loss in evaporation pan experiments. Validation of the two isotopic models in this setting was achieved by comparison with conventional nonisotopic methods, carried out in parallel. Results showed that heavy isotope enrichment of applied irrigation waters varied among each of the study sites. Isotope enrichment was notably different among irrigation bays that drained rapidly [$+0.05$ to $+0.18$ per mil (‰) for $\delta {}^{18}\mathrm{O}$ and $+1.7$ to $+2‰$ for $\delta {}^2\mathrm{H}$] from those in which ponding occurred for up to 18 h after application ($+1$ to $+2‰$ for $\delta {}^{18}\mathrm{O}$ and $+2$ to 7.5‰ for $\delta {}^2\mathrm{H}$). When compared with local pan enrichment, these isotope enrichments corresponded to evaporation losses of 0.2–2.7% (0.5–4 mm) and 2–5% (4.5–7 mm), respectively. This study demonstrated that the use of stable isotope data for irrigation waters provided valuable new insights into evaporation losses across different flood irrigation systems. The use of these techniques may be useful in suggesting which management strategies are most effective in improving water use efficiency and water quality.

Parshall flumes were developed in the early 1900s as a simple and inexpensive way to provide accurate flow measurement in open channels. Unfortunately, many Parshall flumes in use today do not follow essential design parameters that prevent them from accurately measuring flow. Two design parameters that are commonly overlooked are: the need to measure upstream head in the correct location and the need to have appropriate entrance wingwalls attached to the flume. With recent advancements in computational fluid dynamics (CFD), numerical modeling has made it possible to accurately model nonstandard Parshall flume designs of varying sizes without extensive financial commitments for physical modeling. This paper utilizes numerical modeling to create a correction procedure for 2–8-ft nonstandard Parshall flumes. Basic background information regarding Parshall flumes and the numerical model used are presented. In addition, the results and correction procedures determined when head measurements are taken at any location (other than the standard design location) on the converging wall or along the longitudinal centerline of the flume with either standard or nonstandard entrance wingwalls.

Air vents in low-level outlet works are installed downstream of control gates or valves to mitigate subatmospheric pressures locally and reduce the potential for damaging cavitation. Published air-vent-sizing methods, which have been limited to large-dam outlet geometries (in-line vertical slide gate), are not applicable for small- to medium-sized embankment dam low-level outlet geometries in which the slide gate is installed on the upstream sloping face of the dam. The water-discharge and air-demand characteristics of a lab-scale low-level outlet works, with the inlet installed on a $3H:1V$ sloping floor (representing the upstream face of an embankment dam), were evaluated experimentally with respect to gate design (round or rectangular), gate opening, driving head, and outlet submergence; the results are reported herein. Discharge coefficients for predicting low-level outlet works discharge rates (vented or nonvented), and a methodology for air-vent sizing for small- to medium-sized embankment dams are also presented.

To predict hydraulic jump characteristics for channel design, jump height may be determined by calculating the subcritical sequent depth from momentum theory. In closed conduits, however, a hydraulic jump may fill the conduit entirely before the expected sequent depth is reached. This paper reviews momentum theory as applicable to closed-conduit hydraulic jumps and presents general solutions to the sequent depth problem for four commonly shaped conduits: rectangular, circular, elliptical, and pipe arch. It also provides a numerical solution for conduits of any shape, as defined by the user. The solutions assume (1) the conduits are prismatic, fairly horizontal, and relatively frictionless within the jump length; (2) the pressure is hydrostatic and the velocity is uniform at each end of the jump; (3) the effects of air entrainment and viscosity are negligible; and (4) atmospheric conditions exist at the entrance. The implications of these assumptions are discussed briefly. In practice, the derived solutions may be used to predict the size and location of potential hydraulic jumps within culvert barrels or storm water sewers to facilitate a cost-effective design for energy dissipation.

Hydraulic performance of the emitter is crucial in drip-irrigation systems. Considering the limitations of evaluating an emitter’s hydraulic performance, a new method was proposed by using a pressure loss coefficient (PLC) as the evaluation index, which was derived from frictional and local losses of the fluid in labyrinth channels. The value of PLC can be obtained through numerical calculations of flow rates and pressure heads of the emitter by a Reynolds stress model (RSM). In addition, experiments were also carried out to measure the emitter’s PLC, and the results are found to be consistent with those obtained through numerical analysis. The new evaluation method can be used to predict and compare the hydraulic performance of this specific type of labyrinth channel with a range of dimensions.

Calculation of stormwater flow passage underneath two ancient Roman bridges supporting an aqueduct in southern France provides insight into the Roman engineers’ design of aqueduct bridges. The bridges are quite different although the watersheds they cross have similar characteristics. At a height of 5.4 m (18 ft), the Simian Bridge has four arches while the Charmassone Bridge [height of 2 m (7 ft)] has a culvert to pass stormwater flows. The Simian Bridge was designed to maintain the needed elevation across the valley by use of arches, and it easily passes flood flows. In contrast, the Charmassone Bridge may have been designed to manage flood flows as evidenced by the sizing of its culvert and use of buttressing to support upstream hydrostatic pressures due to stormwater retention behind the bridge.