Gary P. Merkley

Decision support for irrigation project planning using a genetic algorithm

This work presents a model based on on-farm irrigation scheduling and the simple genetic algorithm optimization (GA) method for decision support in irrigation project planning. The proposed model is applied to an irrigation project located in Delta, Utah of 394.6 ha in area, for optimizing economic profits, simulating the water demand, crop yields, and estimating the related crop area percentages with specified water supply and planted area constraints. The user-interface model generates daily weather data based on long-term monthly average and standard deviation data. The generated daily weather data are then applied to simulate the daily crop water demand and relative crop yield for seven crops within two command areas. Information on relative crop yield and water demand allows the genetic algorithm to optimize the objective function for maximizing the projected benefits. Optimal planning for the 394.6 ha irrigation project can be summarized as follows: (1) projected profit equals US

Field calibration of submerged sluice gates in irrigation canals.

114,000, (2) projected water demand equals 3.0310 6 M 3 , (3) area percentages of crops within UCA#2 command area are 70.1, 19, and 10.9% for alfalfa, barley, and corn, respectively, and (4) area percentages of crops within UCA#4 command area are 41.5, 38.9, 14.4, and 5.2% for alfalfa, barley, corn, and wheat, respectively. Simulation results also demonstrate that the most appropriate parameters of GA for this study are as follows: (1) number of generations equals 800, (2) population sizes equal 50, (3) probability of crossover equals 0.6, and (4) probability of mutation equals 0.02. # 2000 Published by Elsevier Science B.V.

Assessing whole-field sprinkler irrigation application uniformity

Four rectangular sluice gates were calibrated for submerged-flow conditions using nearly 16,000 field-measured data points on Canal B of the B-XII irrigation scheme in Lebrija, Spain. Water depth and gate opening values were measured using acoustic sensors at each of the gate structures, and the data were recorded on electronic data loggers. Several gate calibration equations were tested and it was found that the rectangular sluice gates can be used for accurate flow measurement. The Energy-Momentum (E-M) equations proved to be sound. The calibration of the contraction coefficient, to be used in the energy equation, allowed good estimations of the discharge for three of the four gates studied. The gate for which the E-M method did not perform satisfactorily was located at the head of the canal with a unique nonsymmetric approach flow condition. Alternatively, we investigated the performance of the conventional discharge equation. The variation of the discharge coefficient, Cd , with the head differential,...

Center-pivot uniformity analysis with variable container spacing

In order to assess whole-field sprinkler irrigation uniformity, an experiment was conducted to obtain water distribution profiles at 23 different pressures for each of five different sprinklers: Nelson R33, Nelson R33LP, Nelson R33 with road guard, Nelson R33LP with road guard, and Rainbird Mini Paw/LG-3. A mathematical model was developed to account for pressure variation throughout a fixed sprinkler system on a 10-ha field and to evaluate sprinkler irrigation uniformity for the whole field using interpolated water distribution profiles from the experimental data. The relationships between irrigation application uniformity and sprinkler pressure, sprinkler spacing, pressure variation, sprinkler type, and field topography were studied using the model. The results show that the coefficient of uniformity, CU, decreases rapidly when the pressure is below the low end of the manufacturer-recommended range; however, CU changes very little with pressure within the manufacturer-recommended range. The system application uniformity, CUsys, is usually less when pressure variations at different locations in a field are considered, and a simple previously published equation to predict CUsys is shown to closely approximate the CU from a more stringent calculation method. It was found that the impact of pressure variation (within the tested ranges) on application uniformity is less than that of the sprinkler spacing. Also, the effect of field topography on sprinkler application uniformity is relatively small for the cases tested herein.

Velocity profile modeling in rectangular and compound open-channel cross sections

Evaluation procedures for determining water application uniformity under center-pivot sprinkler systems have been documented in various technical publications. The so-called “catch cans” (open containers) are placed along one or more radial legs from the center of the field to obtain sample water application measurements, from which standard performance indices can be calculated. All of the published procedures for calculating indices such as the coefficient of uniformity (CU) and distribution uniformity (DU) are based on equal radial spacing of the containers, but in practice some evaluators choose to decrease the spacing toward the outer end of the leg, whereby more measurement samples are taken at locations which represent larger relative fractions of the total irrigated area. It is also common to have inadvertently non-uniform container spacing when one or more tip over during the test, or when avoiding placing a container along a wheel track at a tower. Modified equations and procedures are presented herein to correctly account for variable container spacing, along with spreadsheet macros to perform the calculations.

Generic Free-Flow Rating for Cutthroat Flumes

A 3-D hydraulic model was developed for computing velocity profiles, surface velocity coefficients, and discharge under steady, uniform flow conditions for rectangular and compound open-channel cross sections. Reynolds-averaged Navier–Stokes equations, Reynolds stress equations, and kinetic energy and dissipation equations were applied in the model using the finite-volume method with the k–ε turbulence model. Many previously unpublished approaches to solving the numerical details of this type of hydraulic model are presented herein. Four different sets of Reynolds stress equations (one using the Boussinesq hypothesis and three algebraic stress models of varying complexity) were tested. Only one of the four stress models was successful in predicting the depression of the maximum stream-wise velocity below the water surface. The model was verified using data collected at the Utah Water Research Laboratory. A companion paper (Marjang and Merkley in Irrig Sci, 2009, in press) describes the application of this model to the calculation of surface velocity coefficients for the float method to estimate discharge in rectangular and compound irrigation canals.

Experimental Determination of the Hydraulic Properties of Low-Pressure, Lay-Flat Drip Irrigation Systems

Computational fluid dynamics (CFD) software was used to generate water depth and discharge data for 51 Cutthroat flume sizes, including all 24 standard sizes published by the flumes developer and 27 intermediate sizes. The hydraulic model was validated by using data from several sources, including physical model testing for 15 standard sizes and three intermediate sizes. Grid-size independence was also confirmed for a range of computational cell sizes and the calibration results for 15 standard flume sizes were compared with previously published calibration parameters. Through the validated CFD simulations, a full set of calibration and validation data was generated for each of 51 flume sizes, filling the gaps in the experimental data and permitting a full analysis of the performance of the flume. The study resulted in a generic calibration for free-flow conditions for any Cutthroat flume in the dimensional range of the 24 standard sizes and specified dimensional ratios according to the original design criteria. The error in the predicted discharge for all flume sizes is less than 3% of the full-scale discharge. DOI: 10.1061/(ASCE)HY.1943-7900.0000732.

Improved calibration of Cutthroat flumes

The hydraulics of IDEal low-pressure drip irrigation system components were analyzed under controlled laboratory conditions. The hydraulic loss coefficient for the lateral-submain connector valves was determined based on laboratory measurements. It was found that the hydraulic loss due to friction in the lay-flat laterals can be accurately estimated with standard friction loss equations using a smaller effective diameter based on the wall thickness and inlet pressure head. The equivalent-length barb loss, expressed as an equivalent length of lateral, was calculated for button emitters, as well as for microtubes inserted to lengths of 5 and 10 cm. The head-discharge relationship and coefficient of manufacturer’s variation of prepunched lateral holes (without emitters), button emitters, and microtubes were determined. It was found that most of the head loss occurs in the connector valve, which has a relatively small hole through the hollow stopcock. The presence of manufacturing debris in the valve also inc...

Simulation of peak-demand hydrographs in pressurized irrigation delivery systems using a deterministic–stochastic combined model. Part II: model applications

An analysis of laboratory data for a 0.914-m (3-ft) length Cutthroat flume with four different throat widths is presented. Significant differences with previously published calibration parameters were found. Special attention was given to non-hydrostatic pressures at the upstream and downstream piezometer taps, and the variations are presented in a series of three-dimensional plots. Variation in relative pressure at different tap heights was observed and was concluded to represent a shift from a concave to a convex flow profile between the 0.305- and 0.203-m throat widths. This significant alteration in the flow profile correlates with a sharp change in the nf calibration parameter, describing a non-linear relationship with flume throat width. Alternative equation forms were explored in an attempt to increase the predictive accuracy of the calculated flow rates for free- and submerged-flow regimes. The alternative equations showed a decrease in the percent error, in the submerged-flow regime, by more than 50%. Transition submergence was observed to vary not only due to flume size, but also to flow rate. An empirically fitted equation was developed to calculate the transition submergence as a function of throat width and flow rate. In addition, a separate calibration for free-flow parameters was defined based on measurements from an upstream point gauge. The flow measurement accuracy of existing Cutthroat flumes can be significantly increased, especially for submerged-flow regimes.

Transitional Flow between Orifice and Nonorifice Regimes at a Rectangular Sluice Gate

This study describes a model named HydroGEN that was conceived for simulating hydrographs of daily volumes and hourly flow rates during peak-demand periods in pressurized irrigation delivery networks with on-demand operation. The model is based on a methodology consisting of deterministic and stochastic components and is composed of a set of input parameters to reproduce the crop irrigation management practices followed by farmers and of computational procedures enabling to simulate the soil water balance and the irrigation events for all cropped fields supplied by each delivery hydrant in a distribution network. The input data include values of weather, crop, and soil parameters, as well as information on irrigation practices followed by local farmers. The resulting model outputs are generated flow hydrographs during the peak-demand period, which allow the subsequent analysis of performance achievable under different delivery scenarios. The model can be applied either for system design or re-design, as well as for analysis of operation and evaluation of performance achievements of on-demand pressurized irrigation delivery networks. Results from application of HydroGEN to a real pressurized irrigation system at different scales are presented in a companion paper (Part II: model applications).