Journal of Irrigation and Drainage Engineering

The availability of a process-based coupled surface-subsurface model can lead to improved surface irrigation/fertigation management practices. In this study, a one-dimensional zero-inertia model is coupled with a one-dimensional unsaturated zone water-flow model: HYDRUS-1D. A driver program is used to effect internal iterative coupling of the surface and subsurface flow models. Flow depths calculated using the surface-flow model are used as Dirichlet boundary conditions for the subsurface-flow model, and infiltration amounts calculated by the subsurface model are in turn used in surface-flow mass balance calculations. The model was tested by using field data collected at the University of Arizona, Yuma Mesa, research farm. The maximum mean absolute difference between field-observed and model-predicted advance is $2\min$ . Applications of the coupled model in improved irrigation management are highlighted. In addition, the significance of the effects of soil moisture redistribution on irrigation water availability to crops and the capability of the coupled model in tracking those changes in soil water status over time are discussed using examples.

A stepwise multilevel scheme is developed to sequentially calibrate infiltration and roughness parameters for free-draining furrow irrigation systems. The scheme is one dimensional at each level, thereby simplifying computations and providing more robust and unique solutions using field data which exhibit variation. The scheme is easily programmed and implemented within any kinematic wave, zero inertia, or hydrodynamic analysis and will provide straightforward initiation and convergence. Applications to two comprehensive data sets are made and shown to be substantially more accurate and extensive than traditional two-point fitting algorithms. In addition to the field length and slope, the flow cross section, and the duration of the irrigation, the multilevel model only requires measurements of the inflow and outflow hydrographs. Field data collection is therefore simpler than required for traditional methods which require spatial and temporal advance and recession measurements.

Analytical equations for direct hydraulic analysis of a multidiameter center-pivot lateral with and without an end gun were developed. The pressure head profile along the multidiameter center-pivot lateral is described by simple analytical functions. The analysis is based on both continuous outlet and discrete outlet approaches. Friction losses can be calculated using the Darcy–Weisbach or the Hazen–Williams formulas. The proposed equations simplify important practical applications such as the economic design and evaluation of a multidiameter center-pivot system. A comparison test with a numerical stepwise method indicates that the proposed analytical approach is sufficiently accurate for practical applications.

Hourly evapotranspiration $\left({\mathrm{ET}}_o\right)$ rates were measured during the irrigation season in a highly advective area in Southern Spain, using a precision weighing lysimeter. Close to the lysimeter, an automatic weather station was located to register hourly values of the most relevant climatic variables. Several methods to estimate ${\mathrm{ET}}_o$ were evaluated for hourly and daily estimates. Accuracy was assessed from ordinary regression and from error analysis of the comparisons against measured values. FAO-24 methods showed a strong tendency to overestimate throughout the whole range of evaporation. Ritchie-type and Hargreaves equations had a similar behavior, underpredicting for ${\mathrm{ET}}_o>5.3\mathrm{mm}{\text{day}}^{-1}$ and vice versa. Penman locally adjusted and ASCE-PM performed the best, followed by FAO-PM. Penman-63 also gave excellent daily estimates. The poor behavior of the Priestley–Taylor equation improved after applying the Jury and Tanner correction, but still remains at a very high noise level. With the exception of ASCE-PM and FAO-PM, the rest of the methods showed a tendency to underpredict more with increasing advective intensities. However, that tendency is very mild in the case of Penman locally adjusted.

Modified Bellani plate atmometer has been offered as an alternative and simpler technique to combination-based equations to estimate evapotranspiration (ET) rate from green grass surface. However, there is a lack of information on its’ accuracy in humid climates. The evaporation rate $\left(E_A\right)$ from one type of atmometer marketed under the brand name ${\mathrm{ET}}_{\text{gage}}$ ® (or ETG) with a Number 30 green canvas cover that simulates the ET rate from a green grass surface was tested against the reference ET of a short green grass canopy $\left({\mathrm{ET}}_o\right)$ computed using the Food and Agriculture Organization of the United Nations Paper No. 56 Penman–Monteith (FAO56-PM) equation in two sites in north-central Florida. The ETG underestimated the ${\mathrm{ET}}_o$ as much as 27%. The root mean square error (RMSE) of daily estimates of $E_A$ ranged from 1.03 to $1.15\mathrm{mm}$ . Data analyses indicated that the most of the poor performances and underestimations of the ETG occurred on rainy days. Using only the nonrainy day $E_A$ versus ${\mathrm{ET}}_o$ relationship, the daily RMSE was as low as $0.47\mathrm{mm}$ and $r^2$ was as high as 0.89, and the underestimations were within 3% of the ${\mathrm{ET}}_o$ . Averaging daily ETG readings over 3 and 7 day periods considerably improved (lower RMSE and percent error, $\%E$ , and higher $r^2$ ) ${\mathrm{ET}}_o$ estimates. The ETG performed quite well on nonrainy days. The adjustment factors were developed and tabulated as a function of rainfall amount to adjust the $E_A$ values on rainy days. Results showed that an average adjustment factor of $0.84(E_A∕0.84=\mathrm{E}{\mathrm{T}}_o)$ can be used as a practical number if rainfall observations are not available. The underestimations of the ETG on rainy days were attributed, in part, to the wetting of the green canvas cover due to the rainwater accumulations on it and to the lower diffusivity (higher resistance) value of the canvas cover $\left(112–294\mathrm{s}{\mathrm{m}}^{-1}\right)$ compared to the diffusivity of a green grass surface used in the ${\mathrm{ET}}_o$ definition $\left(70\mathrm{s}{\mathrm{m}}^{-1}\right)$ . Although it is found that the ETG is feasible and practical device, the $E_A$ values measured on rainy days require careful interpretation in humid and rainy climates such as Florida. The rainy day $E_A$ values should be used cautiously with the proper regression equation and adjustment factors to estimate ${\mathrm{ET}}_o$ for irrigation scheduling if the input variables are not available to use the FAO56-PM equation for ${\mathrm{ET}}_o$ estimates.

This paper proposes an efficient mathematical model of an automatic upstream water-level control gate, called a Begemann or flap gate. This automatic gate controls the upstream level close to a reference level for free gate flow, using a counterweight to compensate for the hydraulic pressure on the gate. The proposed gate model is designed to be included in a hydraulic simulation model. A discharge law for the gate is first derived using simple physical assumptions. Then a method to compute the static equilibrium is obtained by modeling the opening force exerted by the water on the gate. This mathematical model is validated on experimental data from a small-scale gate and on other data from the literature in order to show the ability of the model to simulate various gates.

Canals or open channels that convey water often consist of pools in series separated by control structures. Successful implementation of water-level control with these structures using decentralized proportional integral (PI) controllers depends heavily on the tuning of the control parameters. These parameters are hard to determine due to the interactions between the pools and the varying flow conditions in the canal. This paper presents a procedure for tuning any linear controller (including decentralized PI controllers) that guarantees stability of the controlled canal. It minimizes a cost function that weights the water-level deviations from the target level against control efforts at both low- and high-flow conditions. The procedure is tested on a model of the Umatilla Stanfield Branch Furnish Canal in Oregon. The tests show the capability of the procedure to deal with the pool interactions. The results of a realistic turnout schedule applied to the controlled canal show the high performance of the controllers (small water-level deviations in all pools) over varying flow conditions.

Extensive field data and calibrated flow and salt-transport models characterize the spatial and temporal patterns of salinity and waterlogging in an irrigated western river valley. Over three irrigation seasons, average seasonal aquifer recharge from irrigated fields in a $\mathrm{50,600}\mathrm{ha}$ study area ranges from $0.59\text{to}0.99\mathrm{m}$ , including contribution from precipitation. The salinity of irrigation water varies from $618\text{to}\mathrm{1,090}\mathrm{mg}∕\mathrm{L}$ . The water table is shallow, with 16 to 33% of irrigated land underlaid by an average water table less than $2\mathrm{m}$ deep. Average water table salinity ranges from $\mathrm{2,680}\text{to}\mathrm{3,015}\mathrm{mg}∕\mathrm{L}$ , and average soil salinity from $\mathrm{2,490}\text{to}\mathrm{3,860}\mathrm{mg}∕\mathrm{L}$ . Crop yield reductions from salinity and waterlogging range from 0 to 89% on fields, with regional averages ranging from 11 to 19%. Annual salt loading to the river from subsurface return flows, generated in large part by dissolution from irrigation recharge, averages about $533\mathrm{kg}∕\text{irrigated}\mathrm{ha}\mathrm{per}\mathrm{km}$ . Upflux from shallow water tables under fallow ground contributes to about $65\text{million}{\mathrm{m}}^3$ $\left(\mathrm{52,600}\text{acre}\text{-}\mathrm{ft}\right)$ per year of nonbeneficial consumption. Beyond problem identification, the developed database and models provide a basis for effectively addressing these problems through a systematic and comparative assessment of alternative solutions.

By applying the kinematic wave method to a homogeneous, rectangular overland plane, the influence of the constant and proportional-loss models on the design discharge are examined. The examination shows that with the use of the proportional-loss model, there is no partial-area effect and the design discharge is governed by the full-area contribution. On the other hand, with the use of the constant-loss model, there is no partial-area effect if the loss rate is small. For larger loss rates, there is a partial-area effect; and for this case, the design is complicated, since there is a need to search for the critical storm that governs the partial-area effect. The characteristic of the critical storm is that its rate of decrease in rainfall intensity with duration equals the corresponding rate of increase in the contributing area. The preceding findings are consistent with the design concept in the rational method that uses the proportional-loss model, and the results from earlier studies that used the constant-loss model.