Journal of Irrigation and Drainage Engineering

A model describing the application pattern produced by a single sprinkler is proposed. Based on calibrated statistical distributions and free from any ballistic consideration, this model uses a mixture of beta probability distributions in which parameters are first estimated with water application data measured in zero wind condition. Data measured in field conditions are then used to assess the wind effect on the shift of the center of gravity of the irrigated area, on the range of the sprinkler in various directions, and on the values of the beta distributions' parameters. The computation of the water application amounts at any point of the irrigated area is finally resolved in the use of a single equation, which can be easily implemented in a software package to simulate application patterns under a series of sprinklers attached to a center pivot or moving lateral irrigation machine.

A distributional semiempirical model for the simulation of spatial distribution of water application under center pivot sprinklers has been developed by the writers. This method describes the probability of water application for a sprinkler using a combination of beta functions. The calibration of this model has been undertaken using laboratory tests conducted in controlled conditions and then in windy conditions. The parameters calibrated are listed. The minimum number of tests needed for calibration has been estimated. The model used can be calibrated from one test in controlled conditions and three or four tests in windy conditions covering the range of usual wind speeds. Validation should be performed using at least two more infield tests. This simulation model of spatial water distribution under sprinklers of center pivot will thereafter be used to simulate the distribution of water under a typical pivot machine.

A zero-inertia furrow irrigation model with specified space solution was used to investigate the effects of variability in furrow inflow rate and spatial variability in infiltration, geometry, and roughness on end-of-furrow advance, average infiltrated depth, and Christiansen's and distribution uniformities. Extensive field-gathered infiltration, geometry, and roughness data were used as input to the zero-inertia model. Simulations were performed on a single furrow as well as fieldwide. Variable furrow inflow was incorporated into the fieldwide analysis. Model simulations were evaluated to determine the importance to irrigation performance of variability in each input variable. Variability of furrow physical characteristics, in decreasing order of their relative impact on furrow irrigation performance, were furrow inflow rate, infiltration, geometry, and roughness for the conditions studied.

Level basins, when properly designed and managed, often attain very high irrigation efficiencies. Problems can arise when the infiltrated depth exceeds the soil water holding capacity or when the crops are sensitive to waterlogging. Both cases could benefit from allowing part of the applied water to run off the basin. This water can be reused for on-farm irrigation of the subsequent basin. Such a setup will be referred to as the “runoff rescue” (RR) system. In this work, an RR system composed of five adjacent terraced basins is described and evaluated. The basins were connected by outflow points located at the upstream and downstream ends of the fields. To provide terms for comparison, the performance resulting from conventional irrigation (without RR) of each basin was estimated using a simulation model. The RR system showed reductions of 14, 16, and 24% in irrigation time, infiltrated depth, and recession time, respectively. The average increments for distribution uniformity and application efficiency were 2 and 9%, respectively.

An optimal design method for a drip submain manifold is presented. The optimal design is based on the shortest route algorithm for acyclic networks. Different route lengths are represented by total annual costs of different pipe sizes between two successive laterals. An example is solved to compare the method with an existing graphical method.

Desalinization of soils, by flooding the surface completely and leaching salts through subsurface drains, removes salts rapidly above the drains but only slowly midway between the drains. More uniform leaching using less water can be obtained by constraining the seepage area with the use of bunds, initially flooding only the region midway between the drains and then progressively increasing the flooded area toward the drains until the whole area is flooded. The improvement in the efficiency of desalinization using this procedure was shown by obtaining an analytical solution of the flow regime for the seepage from a ponded surface strip to a 2D pipe-drain system using conformal transformations and then estimating the leaching of salts from the soil below the surface by assuming that salts were transported only by convection. The analysis shows that the progressive leaching procedure requires <16% of the water needed using the conventional method, in which the soil surface is completely flooded the entire time, and that it can be attained in <24% of the time.

Optimization-based models for simulation of tile drainage systems are formulated and solved with a finite-difference approximated Richard's equation as an embedded constraint. The solution methodology minimizes the sum of absolute violations of the discretized variably saturated porous media flow equations. The optimal design minimizes the sum of the pressure heads to obtain optimal drain locations and discharges for a given lateral spacing. The projected augmented Lagrangian method of nonlinear programming is used to solve the optimization models. The performance of the simulation is verified using the steady-state square embankment drainage problem. Thereafter, the simulation and design models are solved for a hypothetical tile drainage system. The results demonstrate the capability of the models.

Contamination of surface and subsurface waters has become a major problem related to agricultural practices. Nitrate, one of the principal plant fertilizers, is the chemical having the greatest effect. This research utilized closed system laboratory experiments to evaluate the effectiveness of an electrokinetic process in concentrating and retaining nitrates close to the anode and studied the effect of selected electrokinetic system design parameters on the performance of the process. The tests demonstrated that an electrokinetic process can effectively concentrate and retain nitrate close to the anode in saturated sandy soil.

A model is presented that uses a daily mean evapotranspiration ET_o rate to estimate energy-limited (potential or Stage 1) soil evaporation, and it also uses daily mean ET_o and a soil hydraulic β factor to estimate soil hydraulic property-limited (Stage 2) evaporation. The model provides good estimates of cumulative soil evaporation on both hourly and daily bases when compared to observed soil evaporation in three field trials. Crop coefficient K_c values from cumulative hourly and cumulative daily soil evaporation estimates and ET_o data were comparable. Using a soil hydraulic factor (β = 2.6) in the model gave a fair approximation for the widely used K_c curves for initial growth of crops presented in the United Nations Food and Agricultural Organization's Irrigation and Drainage Paper 24. However, using a site-specific β factor should improve soil evaporation and K_c estimates for site-specific applications.

Early drawdown data, for which the argument u of the well function is >0.01, have often been considered unimportant in evaluating aquifer parameters. This paper shows that these early drawdown data, especially in the neighborhood of u = 0.43, can yield accurate values of aquifer parameters. A simple method has been presented for explicit determination of aquifer parameters using early drawdown data. The method does not require curve matching, initial guess of the parameters, or special care to check for u < 0.01, and the computations involved can be performed on a calculator. Application of the method on published data sets shows that the estimates of the aquifer parameters using only a few initial drawdowns are as good as those obtained by Theis curve matching when all data, including the late drawdowns (u ≤ 0.01), are used. The new method converges with the Cooper-Jacob method when the late drawdown data are considered. Thus, the late drawdown data also can be analyzed using the new method.

The characteristics of a parabolic-bottomed triangle cross section are introduced. For this geometry the “best” hydraulic cross section is determined by using the undetermined multipliers method of Lagrange. For a given flow, roughness coefficient, and longitudinal slope, the best hydraulic section is the channel section having the least wetted perimeter or cross-sectional area. The cross-sectional parameters of this novel geometry are compared with those of trapezoidal, parabolic, and round-bottomed triangle cross sections. It is shown that for all values of side slopes, the flow area and wetted perimeter in a parabolic-bottomed triangle cross section are less than those of trapezoidal and parabolic cross sections for the same discharge. This indicates that less excavation and linings are involved and therefore implies that the parabolic-bottomed triangle cross section is more economical than trapezoidal and parabolic cross sections.