Journal of Irrigation and Drainage Engineering

Treated wastewater (TWW) reuse in crop or landscape irrigation is beneficial for water resource preservation, both quantitatively and qualitatively. However, TWW reuse based on sprinkler irrigation remains limited. This is principally due to a poor understanding of the risks resulting from aerosolization and transport, particularly those associated with the inhalation of pathogenic or toxic contaminants during sprinkler irrigation. Pathogen dissemination is intrinsically linked to fine droplet dispersion and their transport over long distances. Such mechanisms have not been adequately addressed in sprinkler irrigation studies with regard to potential contamination of the environment or their impact on human health. In previous work, droplet dispersion was analyzed by conducting field measurements, and an empirical model was proposed. However, this model remained rather empirical and did not sufficiently take into account all the variables that are thought to act on evaporation. In this work, further measurements were made under a wider range of operating pressure and climatic conditions to improve the model. The set-up was improved by use of a new collecting device and methodology to avoid sampling pollution. Tracer concentration was increased, and the trial duration shortened to limit wind velocity variation effects on measurement accuracy. The objective was to model fine droplet volumes transported beyond the wetted perimeter of the sprinkler. This empirical modeling relies on climate variables and uses dimensionless numbers that characterize atomization and evaporation. Models that combine the key evaporation demand variables with Reynolds or Weber numbers better fit experimental data. They can account for more than 80% of transport variability, including very small volumes of water ($0.1\mathrm{mL}·{\mathrm{m}}^{-2}·{\mathrm{h}}^{-1}$) that are transported or deposited on the surface downwind from the wetted area.

Research was conducted to help rice (Oryza sativa L.) farmers increase rainfall capture to offset groundwater use in the Lower Mississippi River Valley (LMRV). The LMRV is where a majority of US rice is produced and irrigated using groundwater withdrawn from the declining Mississippi River Valley Alluvial aquifer (MRVAA). Increasing rainfall capture in rice fields should reduce the region’s reliance on groundwater. Kolmogorov–Smirnov (K-S) frequency analysis was used to determine 50%–99% quantiles for daily rainfall occurring at nine LMRV locations. The rainfall quantiles were used as freeboard settings in a generalized water-balance model that simulates multiple-inlet rice irrigation (MIRI) of a 16-ha field. Compared with the case when freeboard was not intentionally managed, average irrigation use was reduced by up to 60 mm or approximately 10%. Average rainfall capture (RC) estimates increased from approximately 60% to 80% when at least 28-mm freeboard was maintained throughout an 86-day flood. Rainfall capture decreased when rain occurred in intense, closely-spaced events. Improved RC and application efficiency (AE) were each responsible for about half of the total irrigation use reductions estimated by the model. By maintaining at least 28-mm freeboard and promptly halting irrigation when the target flood depth is achieved, rice producers can reduce groundwater withdrawals, energy use, and runoff.

Accurate prediction of shear stress distribution along the boundary in an open channel is the key to the solution of numerous critical engineering problems. This paper investigated the distribution of boundary shear force at the cross section of meandering compound channels. The research focused on developing a model for predicting shear force using a machine learning (ML) method, the multivariate adaptive regression spline (MARS). A nonparametric regression methodology was adopted in MARS for developing a model of shear force percentage in the floodplain of two-stage meandering channels. The width ratio, relative depth, sinuosity, bed slope, and meander belt width ratio of the channel were input variables to the model. The influence of each parameter on predicting the percentage of shear force in the floodplain was also analyzed by adopting a sensitivity analysis. Performance of the MARS model was evaluated by three different machine learning techniques—the group method of data handling (GMDH), support vector machine (SVM) and $k$-nearest neighbor (KNN)—through different statistical measures. The results indicated that the proposed MARS model predicted the shear force percentage in the floodplain satisfactorily, with a coefficient of determination ($R^2$) of 0.94 and 0.93 and a scatter index (SI) of 0.053 and 0.044 for the training and testing phases, respectively. Moreover, the model was successfully applied for validating the two available overbank discharge values for the Baitarani River at Anandapur (drainage area of $\mathrm{8,570}{\mathrm{km}}^2$), giving the minimum errors of the evaluated methods in terms of mean absolute scaled error (MASE) of 0.014 and 0.066 for flow depths of 7.5 and 8.63 m, respectively.

Performance of a green infrastructure (GI) tree trench comprising planters, an underground rock infiltration bed, inlet structures collecting runoff, and a perforated underdrain pipe delivering water from the inlet structure into the rock bed was evaluated. Over 23 months of monitoring, the system removed 94% of the contributing rainfall primarily through infiltration; therefore, the current design achieved the design goal. The planters were found to be hydrologically isolated, so the tree trench underdrain delivery pipe and rock bed control system performance. Overflow occurred prior to the full utilization of the rock bed storage, indicating that the underdrain pipe limited inflow. Over the course of a rain event, the switch of flow control from the conduit to the pipe wall orifices reduced the maximum flow rate, generating overflow. Flow equations considering water heads variations were derived, and maximization of flow rate was presented based on the equations. The general recommendations for similar sites are to lower the delivery pipe to the bottom of rock bed and considering orifice density as the key element in design.