Journal of Irrigation and Drainage Engineering

The flexible shape Palmer-Bowlus flume is a simple device for flow measurement in free-surface flow circular channels and conduits. In this study, the discharge-stage relation for Palmer-Bowlus flumes is determined based on the Bernoulli theorem. The proposed analytical method is able to account for geometric peculiarities and shape deformation of the flume for adaptation to pipes of different diameters, without need of experimental calibration. Experimental tests on different conduits demonstrate the robustness of the theoretical formulation for reliable free-surface flow measurement. Empirical criteria are also provided for assessing the limit of the proposed discharge-stage relation. The research will further encourage and support the use of these flexible and versatile flumes for hydraulic engineering applications.

Emitters are important components of drip irrigation systems, and the use of labyrinths as a mechanism of energy dissipation stands out in the drippers’ design. Relating the geometric characteristics of labyrinths with their operational and hydraulic characteristics is not trivial and generally requires the use of computational simulation tools. This study developed and evaluated models that can predict the discharge of labyrinth channels as a function of their geometry to make possible the rapid prediction of pressure–discharge curves due to modifications in the labyrinth geometry. An empirical mathematical model was developed based on nonlinear regression, and a computational model was trained based on artificial neural networks (ANNs). Twenty-four designs of prototypes were built in polymethyl methacrylate to operate at a discharge of approximately $1.4\mathrm{L}{\mathrm{h}}^{-1}$ under 100 kPa. The pressure–discharge curve of each prototype was determined in the laboratory in the range 50–350 kPa. Based on the experimental data, the coefficients of an empirical nonlinear model were fitted, and 11 single-hidden-layer ANN architectures were compared. The best accuracy was provided by an ANN architecture with an input layer with six neurons, six neurons in the hidden layer, and an output layer with a single neuron. The maximum relative errors of the predicted discharges were 9.5% and 9.4% for the ANN and nonlinear models, respectively. Both models were accurate and enabled rapid prediction of the emitter’s discharge. An open-source web application was developed to simulate the pressure–discharge curve of labyrinths within a range of geometric and operational characteristics.

Land leveling is used to correct soil surface irregularities to improve surface drainage and irrigation. It also makes the area more manageable for an array of agricultural activities such as planting and harvesting. The objective of this work was to evaluate two designs of land forming, one aimed at optimizing drainage and the other at optimizing surface irrigation, using fields with reliefs typical of the lowlands of southern Brazil. Seven commercial rice fields, ranging in size from 7 to 26 ha, were randomly selected and digital elevation designs generated for each. Land-leveling projects were developed using three designs: uniform slope (US) (control), land forming–drainage (LFD), and land forming–irrigation (LFI). Performance comparisons between the designs were evaluated through impacts on soil movement (SM), maximum cut in 99% of the area (MC), cumulative length of levees (LL), and total number of levees (NL). Results indicate that both LFD and LFI designs would reduce costs and require less soil disturbance compared to leveling to uniform slopes. LFD would require less soil movement and lower maximum cuts than LFI. However, LFI would reduce the lengths and numbers of rice levees that could have long-term economic and agronomic benefits not captured in these analyses. These results demonstrate that all land-leveling and land-forming alternatives should be thoroughly examined before undertaking field operations. Study outcomes will be useful to engineers and producers in evaluating options to improve the agricultural productivity of lowlands in southern Brazil, a region of national and international significance.

This paper presents a compilation of a large database consisting of 588 culvert scour experiments covering a wide combination of different culvert shapes, culvert outlet conditions, and sediment properties. The analysis shows that the maximum scour depth, when normalized with the hydraulic radius, can be expressed reasonably as a linear function of the particle densimetric Froude number for both full-flowing and non-full-flowing outlet conditions. In addition, the sediment nonuniformity effect is also considered by choosing $d_{84}$ (rather than $d_{50}$) as the representative grain diameter in the dimensional analysis, which improves the result of the data correlation.

This paper discusses the problem of low injection rates from Venturi injectors. The optimal combination of key structural parameters for Venturi injectors was investigated using a simulation software platform based on machine learning algorithms. The research considered different nozzle diameters under an inlet pressure of 0.3 MPa and outlet pressure of 0.1 MPa. For the various nozzle diameters, the optimal ranges of the contraction angle (20°–30°), diffusion angle (8°–10°), throat length (40–50 mm), and ratio of throat diameter to nozzle diameter (1.5–1.66) were found, and the parameter combinations that maximized the injection rate were determined. A regression model was used to predict the maximum injection rate with different nozzle diameters. For a nozzle diameter of 4 mm, the maximum injection rate increased by about 200% compared with the original model. In addition, a regression model for the prediction of the injection rate based on injector structural parameters was construction using data from physical injector models and verified by a three-dimensional printer. The model may be used to quickly and effectively design or predict the injection rate for different structural parameters of the Venturi injector.

In urban drainage networks, manhole structures are used to dissipate energy and to decrease flow velocity, especially in steep slope areas. The purpose of this study is the numerical and experimental modeling of a new drop manhole in which an internal hanging baffle wall (IHBW) is used for increasing energy losses. Using open-source computational fluid dynamics (CFD) software called OpenFOAM, the proposed model is simulated numerically. Four types of regimes (R1–R4) are identified using impact parameters ($I_1$, $I_2$, and $I_3$) based on factors such as the jet impact point, the IHBW opening, and the pool depth. A semianalytical relationship is proposed based on the momentum equation to find the pool depth, which is in good agreement with the experimental data. By examining the coefficients of contraction and discharge, it was found that this system passes less discharge than an ordinary sluice gate due to the formation of a water curtain at the IHBW opening, but outperforms the existing rectangular drop manholes in terms of energy dissipation efficiency. It is mandatory to avoid the occurrence of Regime R4 in manhole design. For $I_1<0.9$ and $I_3<0.7$, lower and upper nappes may be submerged, which increases the possibility of manhole overflow and decreases energy dissipation efficiency. Numerical simulation results and laboratory observations are also in good agreement.

A comprehensive review of evaporation losses and evapotranspiration (ET) dynamics in sprinkler irrigation revealed substantial differences in the magnitudes of the different components of evaporation. Field studies reported that droplet evaporation losses ranged from 0.5%–45%, whereas theoretical studies indicated losses of less than 1%. A recent experimental study using advanced instruments and methodologies estimated that canopy evaporation is the major evaporation loss and droplet evaporation could be assumed to be negligible. Other studies showed that evaporation increased and transpiration decreased in evapotranspiration dynamics during wet canopy conditions. Sensible and latent heat fluxes in sprinkler irrigated crops act in opposite ways, but both positively contribute to the available energy and total ET.

New methods using analytical relationships to design drip irrigation laterals and subunits have been introduced in recent years based on the assumption that minor losses can be neglected. This assumption could be relaxed by applying the equivalent method, which makes it possible to account for minor losses, such as those caused by emitter connections, through formulas based on the rationale that an equivalent length of the drip lateral produces the same losses. However, equivalent length formulas are empirical; thus, they do not necessarily cover the entire range of conditions in the real-world contexts in which the formulas will be applied, and their extrapolation could lead to erroneous results. In this paper, theoretical equivalent lengths were calculated and linked to the kinetic energy fraction, which was considered as an alternative general procedure to compute minor losses. Therefore, the results obtained here are valid in all general contexts, because they were not affected by experimental calibrations. A methodology was suggested that extends the use of analytical relationships to design drip laterals from a previous method that neglects minor losses to a new method in which minor losses are considered. Several applications were performed for drip laterals in horizontal and in sloping fields. Results showed the reliability of this new design procedure.

The analysis of friction head-loss spatial distribution along center pivot lateral lines represents an important step when evaluating energy-use efficiency of center pivot irrigation systems. This work compares head-loss spatial distribution along center pivot lateral lines computed with the hydraulic simulator EPANET 2.0 with head-loss spatial distribution predicted by four different analytical models. For the different center pivot lateral line configurations considered in this study, two different sets of friction head-loss values were analyzed. These two sets represent head-loss estimates obtained with different values of the flow rate exponent ($\alpha$) in two main friction head-loss equations: Darcy–Weisbach ($\alpha =2$) and Hazen–Williams ($\alpha =1.852$). On both sets, the four analytical solutions assessed in the current work estimated head-loss values similar to those computed by the hydraulic simulator EPANET 2.0. These results show that the detailed description of flow rate distribution along the center pivot lateral line required by the numerical method did not improve the accuracy of the calculated head-loss distribution. On the data set of values produced by using the Hazen–Williams head-loss equation, the analytical solution associated with the most complex mathematical expression provided the lowest deviation in relation to head-loss values computed by EPANET 2.0. On the data set of values produced by using the Darcy–Weisbach head-loss equation, assuming a fully turbulent flow regime, the four analytical models presented the same deviation in relation to the values computed by EPANET 2.0.

Weirs and orifices of different shapes are widely used as flow-measuring devices or adjusting the upstream water level. These water structures can be combined, yielding a simultaneous flow over the weir and through the gate. A combined weir–gate (weir–orifice) structure can be used for flow measurement with the added benefit that sediment deposition behind the structure will be limited. This study introduces a sharp-edged plate installed at the end of a circular open channel in which flow is discharged into the atmosphere as a simple flow-measurement device. This weir–gate system yields a simultaneously free outflow over and under the plate. Most of the floating materials and sediments will pass through this flow-measurement device because the structure has no lateral contraction. The energy principle (results in weir and orifice relations) helps to deduce a suitable mathematical form for the stage-discharge equation. The energy principle and Buckingham’s theorem of dimensional analysis both were used to deduce the stage-discharge relationships. A series of laboratory experiments (626 runs) was conducted in two circular open channels to calibrate the deduced stage-discharge relationships under free-outflow conditions. The results showed that the best model to describe the stage-discharge relationships could be obtained using the energy principle (physically based approach) and dimensional analysis. The proposed general stage-discharge relationship had an average error of 1.89% with a maximum error less than 9.82% for the experimental trials. The results also showed that the dimensional analysis is not powerful enough alone for obtaining an accurate stage-discharge model. The theoretical considerations can make the dimensional analysis powerful enough to obtain an acceptable stage-discharge equation, as shown in this research.