Journal of Irrigation and Drainage Engineering

Clinoptilolite zeolite (CZ) is being considered as a wicking material for revegetation of riparian regions in arid environments where depth to groundwater is less than 3 m. Simulation of water fluxes and water contents in boreholes filled with CZ and in situ unamended riparian soil (RS) for the purpose of riparian revegetation was modeled using Hydrus-1D and compared to water content measurements. A review of the literature shows that Hydrus-1D model has never been used for the simulation of water fluxes in CZ. Water content, depth to groundwater, and climate data collected in 2012 and 2013 during a field experiment in the Rio Grande flood plain, New Mexico, were used to calibrate and validate the Hydrus-1D model. Predicted borehole water content agreed well with measurements taken at 15, 30, and 90 cm depths when the groundwater levels were nearly stable (coefficient of determination $[R^2]$ of 0.83 and root-mean square error (RMSE) of $0.023{\mathrm{cm}}^3/{\mathrm{cm}}^3$ for CZ; $R^2=0.90$ and $\mathrm{RMSE}=0.015{\mathrm{cm}}^3/{\mathrm{cm}}^3$ for RS). Results show that Darcian nodal velocities slowed down ($\sim 0\mathrm{cm}/\mathrm{day}$) within the top 60 cm of the CZ profile therefore limiting evaporation losses. However, this phenomenon can be a disadvantage for growing shallow-rooted plants.

Results of an experimental study into steady uniform flows in compound open channels with cylindrical obstructions designed to mimic emergent vegetation is presented. Two configurations—fully covered floodplain and one-line obstructions—are considered, and the hydraulic properties are compared to those of a smooth, unobstructed compound channel. Particular attention is given to the effect of obstruction (i.e., vegetation) density on the rating curve, drag coefficients, and spanwise profiles of streamwise velocity. Flow resistance is estimated using an established approach, and the results are in agreement with other experimental studies. It was shown that the obstruction configuration significantly influences the flow velocity in the main channel, and in the case of one-line obstructions the floodplain velocity is higher than for an unobstructed channel for a given flow rate. Spanwise velocity profiles exhibit markedly different characters in the one-line and fully covered configurations.

Numerical models are convenient for the management of basin fertigation. However, the characteristic line approach, commonly applied to solve the advection-dispersion equation, presents disadvantages such as numerical oscillation at the vertical position of the solute concentration wave caused by cubic spline interpolation. To address this problem, a new approach was constructed to solve the advection-dispersion equation. This new approach is a hybrid of the characteristic line and the finite-volume approaches. The zero-inertia equation with a standard diffusion wave type was used to describe the surface water flow, and a new model for basin fertigation was developed. Three basin fertigation experiments were carried out to validate the developed model. The results showed that the simulated solute transport processes did not exhibit any numerical oscillation and overcame the disadvantage of the characteristic line approach in conjunction with the cubic spline interpolation. Overall, the mass conservation ability of the developed solution for the advection-dispersion equation was significantly improved.

Indoor laboratory tests were carried out to determine the accuracy with which the coefficient of manufacturing variation ($CV$), the discharge coefficient ($K$), and the emitter discharge exponent ($x$) may be measured and calculated, and the number of significant digits to be reported in the published data. An error analysis and the propagation of the error in the formulas beginning from the experimental uncertainties of the instruments were used. Two calculation methods were used and compared to obtain $K$ and $x$: the method of the two measurements and the data regression analysis. The results showed that, because of a calculation error of 15%, the maximum precision of the $CV$ obtained in this analysis allowed the use of only one decimal of significant digits. As regards $K$ and $x$, the method of the two measurements showed high levels of uncertainty (9% for $K$ and 3.6% for $x$, respectively) despite the accuracy of the measurements; therefore, only two significant decimal digits for $x$ and no decimals for $K$ were indicated. The regression analysis method was more precise, with a precision of 1.7% and one decimal significant digit for $K$ and a precision of 0.5% and three decimals for $x$. Therefore, the results showed that, when publishing the values of the parameters to characterize trickle emitters, the calculation method used should be reported along with the degree of accuracy of the measurements in order to improve the assessment of their actual characteristics, allowing a more objective comparison among similar products of different companies.

Tailwater recovery (TWR) systems are being implemented on agricultural landscapes to create an additional source of irrigation water. Existing studies have sampled TWR systems using grab samples; however, the representation of solids and nutrient concentrations in these samples to water being irrigated from TWR systems has yet to be investigated. In order to test whether grab samples are representative of water pumped from TWR systems for irrigation use, this study compared concentrations of total suspended solids (TSS), total phosphorus (TP), total nitrogen (TN), total Kjeldahl nitrogen (TKN), nitrate-nitrite (${\mathrm{NO}}_3^{-}{\mathrm{NO}}_2^{-}$), and ammonium (${\mathrm{NH}}_4^{+}$). Grab samples were collected simultaneously from the surface water and from the respective outflow of irrigation infrastructure in six TWR systems. Comparison of 14 irrigation events showed TSS, TP, TN, TKN, ${\mathrm{NO}}_3^{-}{\mathrm{NO}}_2^{-}$, and ${\mathrm{NH}}_4^{+}$ did not differ (Pillai’s ${\mathrm{trace}}_{\mathrm{5,1}}=0.307$, $p>0.5$) between surface water grab samples and irrigation water samples. No differences ($p>0.05$) were found for TN, TP, ${\mathrm{NH}}_4^{+}$, and TKN across sites. This research suggests surface water grab samples from TWR systems represent the solid and nutrient concentrations being irrigated at that moment of time.