Journal of Irrigation and Drainage Engineering

Typical engineering design of rock weirs rely on simplified one-dimensional equations dependent on empirical coefficients. However, most simplified methods fail to accurately predict the hydraulics through rock weirs because they do not consider flow through interstitial spaces between rocks and the way interstitial flow alters the head-discharge relationship. To improve the design methodology and better capture the complex hydraulics past rock weirs, a three-dimensional high-resolution computational fluid dynamics model was utilized to study the problem. The simulation results demonstrate that the flow phenomena and head-discharge relationship are significantly different between broad-crested weirs and rock weirs. The interstitial spaces between rocks not only drain a portion of total discharge, but also accelerate the weir overflow. Based on the results, a flow decomposition approach is proposed to quantify the discharge through a rock weir. The decomposition includes contributing flows from (1) weir flow over the individual rocks, and (2) interstitial flow between rocks. Discharge coefficients for both contributing flows were found to be approximately linearly proportional to the porosity. The applicability of the proposed decomposition was demonstrated with an independent case. Despite the success, future improvement is needed with more rock weir variations.

Erosion management is a major environmental challenge facing highway construction. A research study was undertaken to analyze possible sustainable improvements to current standard procedures for final grade turfgrass establishment on disturbed lands at both field and greenhouse scale. Pure compost, biosolids and greenwaste, and two topsoil/compost blends were compared with a topsoil standard (with additional straw and fertilizer application) in their ability to reduce sediment and nutrient runoff and improve green vegetation (GV) establishment. Differences in field GV rates were only observed during initial establishment (biosolids and topsoil had 11%–35% greater GV). This period coincided with an initial flush of nutrients and sediment that was 3- to 17-fold greater than later phase runoff. After this initial runoff phase, tested materials exported largely comparable nutrient and sediment runoff. In the controlled greenhouse studies, only the biosolids treatment reduced runoff volume, by 40%–98%, compared to the standard practice. Evidence of soil sealing from rainfall impact was seen for topsoil/compost mixtures, resulting in 20- to 28-fold greater total runoff volume and 28- to 224-fold greater sediment export than topsoil. Compost addition increased nutrient export 1.5- to 51-fold and 2.2- to 3.3-fold for phosphorus and nitrogen, respectively, due to increased runoff concentrations (pure compost) or volume (topsoil/compost mixtures). It was hypothesized that the additional straw mulch layer for the standard topsoil offered increased surface resistance and physical protection from rainfall impact and surface flow compared to the nonmulched compost treatments. Inclusion of a straw mulch layer with compost may provide similar, or better, slope stability performance.

The proper hydraulic design of microirrigation system subunits requires the characterization of minor losses. To this end, machine learning models based on artificial neural networks [multilayer perceptron (MLP)], support vector machines [support vector regression (SVR)], and an ensemble of decision trees [extreme gradient boosting (XGB)] were developed and validated to predict minor losses caused by fittings commonly used in microirrigation subunits. The databases for learning are collections of experiments with commercial fittings classified as I, Y, and T. The features considered were fluid properties along with geometric and operational characteristics. Semiempirical models based on dimensional analysis were less accurate than machine learning–based models. The MLP model presented the best performance for the evaluated processes, although it requires a considerable amount of data and an extensive calibration of the hyperparameters. The SVR model was predominantly more appropriate based on the radial basis function. However, it is computationally expensive, and the estimator may be more compromised by noise. The XGB model achieved the lowest computational cost and provided good accuracy with the test set but was less related to the theoretical power-law function expected in these hydraulic phenomena. An open-source web application was developed to support the use and comparison of the models; it can serve as an online tool for the design and simulation of minor losses.

The use of treated wastewater for irrigation is associated with the dispersion of fine droplets containing possibly pathogens. Their inhalation could expose workers and people in the surroundings to health problems. Wind and other atmospheric conditions may increase dispersion. The risk is difficult to assess, especially with water cannons and sprinklers, whose initial droplet conditions in airborne dispersal are not well characterized. In this study, the airborne dispersion of fine droplets (smaller than $300\mathrm{\mu m}$) was investigated numerically. A simplified Eulerian drift-flux model was used to obtain airborne profiles in windy conditions (between 1 and $3\mathrm{m}{\mathrm{s}}^{-1}$), and experiments in a wind tunnel were used for validation. The model was one-way coupled, evaporation was not taken into consideration, and droplet displacement was driven by fluid drag and gravity. Two main conclusions were drawn. First, single-diameter simulations provide a qualitative evaluation of the rapidity of sedimentation but are not exhaustive to represent the entire spray. Second, more precise predictions can be obtained by introducing an approximated size distribution, resulting from a slight improvement of the initial conditions.

Population growth and increasing food demand require cropping systems that produce higher yields with less water. Microirrigation can fulfill this demand but has a high investment cost, which can be reduced with adequate irrigation design and management. The design is based on pre-established emission uniformity (EU) by combining equipment characteristics and hydraulic configurations. This study evaluated the influence of EU and irrigation depth on the emission uniformity obtained after the design (${EU}_{ad}$), yield uniformity, and the expected profit for a microsprinkler-irrigated citrus orchard on sloping terrain for the growing conditions of Leme, Sao Paolo, Brazil. The research was developed under different scenarios of EU values, negative slope gradients in the irrigation subunit, and critical period irrigation depths, resulting in practical guidelines for irrigation practitioners and farmers. To design a system under level conditions, an EU value of 85% is recommended, because the resulting ${EU}_{ad}$ was always higher than the EU value considered at the design stage. For sloping conditions, the EU should be at least 90% in microirrigation subunits, and the higher the slope gradient, the greater the EU must be. Although the microirrigation system design was based on high values of the pre-established EU, the evaluated variation in the EU did not significantly modify the net crop profit. With a water supply, a 50% reduced irrigation depth generated a net profit 16.2% lower than that of the best option but had the highest irrigation water-use efficiency (${IWU}_E$) among the studied treatments. To obtain production uniformity and higher profit, not only the irrigation system uniformity but also the irrigation adequacy must be considered when selecting the appropriate water depth to be applied.

The design and calibration of a simple rectangular flume with central cylindrical contraction is presented. The flume is designed based on principles of critical flow in open channels. Critical flow is created through contraction of flow cross section by installing a vertical cylindrical column at the center of a rectangular open channel. The stage–discharge relationship was calibrated using a laboratory prototype with various configurations. A previously developed model was recalibrated using the laboratory data for the proposed flume. The results of the proposed stage relationship were also compared with results from a computational fluid dynamics model (CFD). The results and analysis show that if the piezometric head is measured at midstream at the upstream side of the contracting column, then stage–discharge relationship can be developed, which is independent of the contraction ratio. The stage–discharge function developed in this paper can be used for design and calibration of the flume regardless of the flume size or contraction ratio. The stage–discharge relationship equation is also compared with another set of independently measured laboratory data.