Journal of Irrigation and Drainage Engineering

The application of agricultural chemicals to crops in the form of aqueous solutions or emulsions blended with irrigation water (often referred to as chemigation) is widely practiced in modern farming systems. Optimal chemigation management can help reduce crop production costs and mitigate the environmental effects of agricultural chemicals. As a step toward the development of a field-scale sprinkler irrigation chemigation systems management model, a solute transport model that can simulate the time and distance evolution of the concentration of a nonreactive solute in an irrigation lateral is developed and evaluated in the study reported here. For modeling purposes, a lateral is conceptualized as a branched hydraulic network consisting of a series of connected pipes, each delimited by outlet nodes. At the pipe scale, solute transport is modeled as a one-dimensional advective process in which the applicable differential equation is solved with a quasi-Lagrangian integration scheme. Solutions to the transport problem, in a pair of consecutive pipes, are coupled through what is described here as the nodal condition, which can be stated as: the concentration computed at the downstream-end node of a pipe constitutes the upstream boundary condition for the advective transport problem in the pipe just downstream. The model was evaluated in two phases. First, the soundness of the formulation and programmatic implementation of the numerical solution to the pipe-scale advective transport problem was tested through comparison of model outputs with analytical solutions. Evaluation of the predictive capacity of the lateral-wide model, in the context of a real-world application, was then conducted by comparing computed breakthrough curves of a nonreactive tracer with data measured along a pair of laterals. The results suggest that model performance is satisfactory.

Abstract

Culvert blockage is a recognized problem known to increase the risk of cross-drainage failure. Presently, the effects of bottom-up inlet blockage can be estimated using the theoretically derived energy loss method (ELM) and reduced area method (RAM). Both methods imply that hydraulically efficient inlets are more resilient to blockage effects but have not been verified experimentally for bottom-up blockages. In this study, a physical culvert model was used to determine the entrance loss coefficients and head-discharge relationships for commonly used pipe culvert inlets under different combinations of bottom-up blockage ratio, shape, and roughness. The experimental results confirm that hydraulically efficient inlets are more resilient to bottom-up blockage. Under submerged outlet control conditions, it was found that both blockage ratio and shape significantly influence the entrance loss coefficient and that ELM overestimated the entrance loss coefficient by up to 124%. Under inlet control conditions, it was found that only the blockage ratio significantly influenced the head-discharge relationship and that RAM underestimated the blockage discharge ratio by up to 38%. Comparisons to the experimental results show that ELM and RAM do not account for the increased efficiency of the unblocked part of the inlet under conditions of bottom-up blockage. Comparison to embedded inlets shows that they result in significantly lower entrance loss coefficients than partially blocked inlets under outlet control but yield similar discharge capacity ratios under inlet control. Uncertainties and estimation errors are given for the results, and validity for use in minimum performance design frameworks is evaluated for the different flow types used in hydraulic culvert design.

Practical Applications

The results show the importance of evaluating blockage effects as part of hydraulic culvert design and verify the general predictions of the energy loss method and reduced area method; that hydraulically efficient inlets are more resilient against blockage effects. The results are valid for type 1 and 5 (inlet control) and 4, 6, and 7 (outlet control) flows and can be used with existing design methods in the following ways: (1) informing the choice of inlet design, for both unblocked and blocked conditions; (2) including a blockage ratio in the design of culverts, based on registered blockage data or risk assessments; (3) evaluating necessary maintenance regimes based on acceptable blockage ratios; and (4) evaluating the effects of blockage on stream continuity. Given the large variation in in situ inlet blockage conditions, it is recommended to use the maximum values of entrance loss coefficients ($k_{eb}$) and the minimum discharge ratio ($Q_b/Q$) as a conservative approach for bottom-up blockage effects. Recommended design blockage ratios given in design manuals should be supplemented with registered data on blockage history for specific locations. For data registration and monitoring, the blockage ratio ($A_b/A$) should be recorded.

A solid set sprinkler irrigation system with portable sprinklers was evaluated in a cluster of winter wheat fields in a semiarid area in the south of Iran. Irrigation performance indicators, including coefficient of uniformity (CU), distribution uniformity (DU), application efficiency (AE), potential application efficiency of the lower quarter (PELQ), application efficiency of the lower quarter (AELQ), deep percolation (DP), wind drift and evaporation losses (WDEL), and irrigation adequacy (${\mathrm{AD}}_{\mathrm{irr}}$) were analyzed in six irrigation events over three fields. Crop water productivity (WP) and final grain yield (GY) were also analyzed to assess the irrigation system efficiency. The results showed that in most irrigation events, the values of CU, DU, AE, PELQ, and AELQ were lower than 81%, 70%, 75%, 65%, and 65%, respectively, as the minimum recommended values in the literature. Furthermore, the ${\mathrm{AD}}_{\mathrm{irr}}$ values were between 0% and 80% in the irrigation events. The performance of different irrigation scheduling methods, including NETWAT software (known as the national reference method for irrigation scheduling), Penman–Monteith and Kc, Penman–Monteith and measured Kc, and calibrated Penman–Monteith and Kc were investigated based on monitoring the soil moisture deficit (SMD). Analysis showed that NETWAT estimated the lowest evapotranspiration for all of the wheat growth stages, which indicates an improper choice of irrigation scheduling method. This means that NETWAT highly underestimated the crop water requirement and resulted in a high soil water deficit, whereas the Penman–Monteith and measured Kc had the best match with the SMD. Moreover, in different fields, GY and WP varied between 2.7 and $3.55{\mathrm{Mg}\mathrm{ha}}^{-1}$, and 0.36 and $0.48\mathrm{kg}{\mathrm{m}}^{-3}$, respectively. Our detailed analysis revealed that the main reasons for the inefficient performance of the irrigation system were primarily related to the irrigation system design, scheduling, and setup. Therefore, accountability for the outdated design and subsequent system failure can be attributed to the irrigation system designer(s), the public agricultural agency responsible for approving the system design, and the scientific representative(s) responsible for the irrigation system. This study underscores the detrimental impact of inadequate management and design on the modern irrigation systems, highlighting their potential to reduce crop yields and water productivity significantly.

AquaCrop, a water-driven model, has been developed to simulate the response of crops, including wheat, to the amount of irrigation water. To estimate crop yield using this model, the calibration stage is applied first, employing the available data. Calibration accuracy guarantees the validation accuracy of this model. For this reason, before the calibration stage, the response of the AquaCrop model to changes in input parameters is investigated using sensitivity analysis. Most researchers use additive-subtractive methods. However, these methods do not provide much information about model sensitivity. In this research, three methods were used to analyze the sensitivity of AquaCrop to simulate winter wheat grain yield under different irrigation requirements. The methods included (1) an increasing-decreasing method; (2) a limit method; and (3) a Gamma test that was based on the nonlinear relationship between inputs and outputs. The irrigation treatments were 100%, 75%, 50%, and 0% of the irrigation requirement and were designated as I1, I2, I3, and I4. Six input parameters consisting of normalized water productivity (WP*), maximum crop coefficient for transpiration (${\mathrm{K}}_{\mathrm{CTR}}$), initial canopy cover (CCo), crop canopy growth coefficient (CGC), crop canopy decline coefficient (CDC) and harvest index (HI) were evaluated for sensitivity analysis. The results showed that the sensitivity of the AquaCrop model was extremely high to WP* changes and moderate to CCo changes. An inverse relationship between wheat grain yield and CDC and a direct relationship between wheat grain yield and other input parameters were observed. The sensitivity of the AquaCrop model to the CCo parameter was the same in all irrigation treatments. The increase in water stress decreased the sensitivity of the AquaCrop model to the input parameters. Therefore, in the case of large differences between simulated and observed grain yield, it is suggested to change WP* and Kctr values. In the condition of moderate difference, it is better to change two parameters, HI and CDC. To reduce the slight difference between the simulated and observed grain yield, it is suggested to change the two parameters, CGC and CCo. It should be noted that the results of the sensitivity analysis are specific to the experimental conditions, such as plant density, soil texture, and water supply, and may vary when applied to different regions. Therefore, it is recommended to obtain region-specific results and determine the sensitivity of the AquaCrop model to input parameters.

Abstract

In Burkina Faso, surface drip irrigation is promoted as a water-saving technique to overcome the decline of agricultural water through the increase of water productivity. However, there is little proof up to now about the suitable dripper-plant spacing optimizing water uptake for high productivity. A field trial was undertaken to assess the effects of the dripper-plant spacing in improving yield and water productivity. The design was complete randomized blocs in four replications with the dripper-plant spacing of 0, 5, 10, and 15 cm. It is shown that placing the dripper 15 cm away from the plant resulted in higher water distribution, fruit size, and productivity. The increase of 91%, 131%, 51%, and 11% was registered for wetted area, fruit length, fruit diameter, and fruit weight, respectively. Yield and water productivity increased up to 143%. Implementing the system of drip irrigation at the dripper-plant spacing of 15 cm should be suggested for improving both yield and water productivity in the dry areas.

Practical Applications

The distance between the dripper and the plant is an important component for designing and implementing a drip-irrigation system for a specific crop on a specific soil since the crop water uptake and productivity depend on this parameter. Up to now, there is no evidence of suitable distance for fruits, more precisely for tomatoes. Technicians are implementing the drip system and farmers are still producing based on an old belief suggesting that the dripper should be as close as possible to the plant. The present study tested different distances (0, 5, 10, and 15 cm) between the dripper and the plant in an experimental field to identify the optimal spacing. Based on the obtained data, this paper suggests that the spacing of 15 cm between dripper and plant is adapted for improving water productivity and yield, and it should be adopted to optimize the efficiency of the drip-irrigation system for field-grown tomatoes.

The paper presents three-dimensional (3D) simulations conducted to study scour around a pair of twin piles arranged in different skew angle ($\alpha$) configurations under combined wave-current flow conditions, utilizing a computational fluid dynamics (CFD) model, REEF3D. The Reynolds-averaged Navier-Stokes (RANS) equation is solved using the $k\text{-}\omega$ turbulence model in this study. The Exner equation is employed to measure variations in bed elevation, while the level-set approach accurately captures the free surface. The numerical model integrates a hydrodynamic module with a morphological module to simulate the scour process. The pressure component within the RANS equations on a staggered grid is characterized through Chorin’s projection method. For discretizing the convective term of the RANS equations, the 5th order weighted essentially nonoscillatory (WENO) scheme is employed. van Rijn formula is used to calculate bed load transport, for suspended load transport standard convection diffusion formula is utilized. The numerical model is utilized to explore how the gap ratio ($G/D=1$ and 2) and the combined wave-current parameter ($U_{cw}=0$ and 0.2) impact piles arranged at different skew angles. Furthermore, it is observed that the flow gap between the piles substantially amplifies the scour depth. The scour depth is influenced by both the gap ratio and skewed arrangement (staggered with 30°, 45°, and 60° approach flow angles) of piles. In the case of only wave conditions, the interference between piles vanishes when the skew angle is set at 30° and the gap ratio ($G/D$) is 2. Conversely, under combined wave-current scenarios, the interference effect remains evident at a gap ratio of 2. Moreover, this interference effect persists at skew angles of 45° and 60° for both wave-only and combined wave-current conditions, when gap ratios ($G/D$) are 1 and 2. For a fixed Kuelegan-Carpenter (KC) number, the stretch of scour hole reduces as the gap ratio increases in combined wave-current flow, while the extent of scour hole perpendicular to the flow direction increases as the gap ratio and combined wave-current parameter increases. Additionally, it is noticed that the normalized scour depth decreases as the gap ratio increases when the $KC$ number and $U_{cw}$ are fixed.