E. Bautista

Structured Application of the Two-Point Method for the Estimation of Infiltration Parameters in Surface Irrigation

The two-point method is one of the best known procedures for estimating empirical infiltration parameters from surface irrigation evaluation data and mass balance, mainly because of its limited data requirements and mathematical simplicity. However, past research have shown that the method can produce inaccurate results. This paper examines the limitations of the method, reviews alternatives for improving two-point method results based on data that are collected or can easily be collected as part of a two-point evaluation, and suggests strategies for estimation and validation of results for different levels of evaluation data. Results show the limitations of formulating the estimation problem with advance data only and the benefits of using instead an advance and a postadvance mass balance relationship in the analysis. Because different combinations of parameters can satisfy the mass balance equations, the estimated function cannot be extrapolated reliably beyond the times used in formulating those relationships. While results can be used with confidence to characterize the performance of the evaluated irrigation event, they need to be used carefully for operational analysis and design purposes.

Improved Surface Volume Estimates for Surface Irrigation Volume-Balance Calculations

Abstract This article reviews procedures for estimating surface storage in surface irrigation volume balance calculations. Those procedures are based on the assumption of a power law relationship for flow depth as a function of distance along the stream. The analysis uses zero-inertia simulation and a system of dimensionless variables to examine how the depth profile varies as a function of hydraulic conditions when infiltration is given by the empirical extended Kostiakov equation. Alternatives for approximating the exponent of the depth profile power law (β ) are suggested. The magnitude of the resulting errors relative to zero-inertia model predictions is quantified. Results show that the range of variation for the parameter β increases with field slope, with increasing advance length relative to the maximum advance distance, and when infiltration rates are relatively constant with time during the irrigation event. Estimating β as a function of advance distance is most challenging under these condition...

External Iterative Coupling Strategy for Surface-Subsurface Flow Calculations in Surface Irrigation

Coupling the unsteady open-channel flow equations of surface irrigation with the equation of variably saturated porous media flow is a computationally complex problem because of the dependence of infiltration on surface-flow depths. Several models of this coupled process have been developed, all of which solve the surface and subsurface flow iteratively at each time step of the surface-flow solution. This study presents an alternative strategy, in which stand-alone surface and subsurface-flow models are used to conduct the calculations sequentially and iteratively at the time level of the irrigation event. At each iteration, the subsurface-flow results are computed using the surface-flow depths generated by the surface-flow model at the current iteration. Infiltration results computed at selected computational nodes are fitted to an empirical infiltration function, and then fed back to the surface-flow model. The proposed strategy, labeled external iterative coupling, was prototyped for border and basin irrigation systems using the WinSRFR and HYDRUS-1D models. The proposed procedure produced irrigation performance results comparable to those generated with an internally coupled model, even when using a single representative location to calibrate the empirical infiltration equation used by the surface-flow model. In comparison with models that iterate at each time step, the proposed coupling strategy reduces the computational effort and improves convergence. The approach provides a practical alternative for coupling existing and future surface and subsurface flow models.

The SRFR 5 Modeling System for Surface Irrigation

AbstractThe SRFR program is a modeling system for surface irrigation. It is a central component of WinSRFR, a software package for the hydraulic analysis of surface irrigation systems. SRFR solves simplified versions of the equations of unsteady open channel flow coupled to a user-selected infiltration model. SRFR was reprogrammed using a modern object-oriented architecture with the objective of facilitating its continued development and, thus, the addition of new modeling options and functionalities. The upgraded software is SRFR 5. An important component of the modeling system is the code that manages computational incidents. While the computational methods used by SRFR 5 have been widely tested and are generally robust, calculations are prone to failures due to problems with the solution of the nonlinear finite difference system of equations, discretization problems, and problems with the determination of the appropriate boundary condition at each computational time step. Code that manages computationa...

Routing demand changes to users on the WM lateral canal with SacMan.

Most canals have either long travel times or insufficient in-canal storage to operate on demand. Thus most flow changes must be routed through the canal. Volume compensation has been proposed as a method for easily applying feedforward control to irrigation canals. Software for automated canal management (SacMan) includes both feedforward routing with volume compensation and distant downstream-water-level control. SacMan was implemented on the WM canal of the Maricopa-Stanfield Irrigation and Drainage District, Stanfield, Ariz. Field testing was conducted for a 30 day period during 2004 where more than 50 deliveries to users were made with feedforward control. This paper presents results from some of these field tests and demonstrates the degree of water-level control achievable with combined feedforward (routing)-feedback control.

Errors in Infiltration Calculations in Volume-Balance Models

Abstract Volume-balance models of surface irrigation calculate the infiltrated volume at a given time as a product of the stream length, upstream infiltration, and shape factors. The best-known expression of this type was derived by combining the Lewis-Milne equation with empirical power-law expressions for infiltration and advance as functions of time. This expression results in systematic errors that are not well understood by users of volume-balance methods. This article examines those errors in furrow irrigation by comparison with infiltrated volumes computed with zero-inertia simulation. The potential for errors is greatest with light soils and where the bottom slope is large enough to produce kinematic flow conditions. An example is presented to show how these errors in a parameter-estimation problem based on a volume balance can be corrected iteratively with the help of zero-inertia simulation.

Surface Volume Estimates for Infiltration Parameter Estimation

Volume balance calculations used in surface irrigation engineering analysis require estimates of surface storage. These calculations are often performed by estimating upstream depth with a normal depth formula. That assumption can result in significant volume estimation errors when upstream flow depth evolves slowly with time and cannot be used under zero-slope conditions. This article examines the errors incurred when calculating upstream depth with an approximation to the zero-inertia equation instead of the normal depth formula. The approximation, which uses an empirical adjustment factor, gives reasonable results under a wide range of hydraulic conditions.

WinSRFR: Current Advances in Software for Surface Irrigation Simulation and Analysis

Significant advances have been made over the last decade in the development of software for surface irrigation analysis. WinSRFR is an integrated tool that combines unsteady flow simulation with tools for system evaluation-parameter estimation, system design, and operational optimization. Ongoing efforts are focusing on coupling the simulation engine to physically-based infiltration modeling applications and adding modules for simulation of sediment and solute transport. The current and planned integration of these components have made evident the need to re-engineer the SRFR simulation engine and reevaluate some of its computational components. This paper briefly discusses WinSRFR and provides an overview of surface irrigation modeling advancements relevant to the WinSRFR project.

Evaluation of basin inflow cutoff criterion in the irrigation districts of southwest Arizona

Low irrigation efficiencies persist in irrigated areas near Yuma, Arizona due to poorly designed irrigation systems, poor condition of existing systems, inaccurate delivery of flow rates, and inadequate criteria for determining irrigation cutoff to individual basins. In farms where growers lack adequate control over the water supplied to individual basins, conventional irrigation cutoff criteria, based on precise measurement of inflow rates, are ineffective. A joint research project, involving the USDA-ARS-ALARC, University of Arizona, and the USBR, is exploring the management of these systems using the time of advance to half the field length as a criterion for cutoff when inflow rates are not know accurately. Preliminary simulation studies have shown the potential benefits and limitations of such a strategy. This strategy is being tested in the field, to assess its sensitivity to uncertain system properties. This article describes the general research methodology and some of the initial simulation and field results.