It is essential to standardize the definitions and approaches to quantifying various irrigation per formance measures. The ASCE Task Committee on Defining Irrigation Efficiency and Uniformity provides a comprehensive examination of various performance indices such as irrigation efficiency, application efficiency, irrigation sagacity, distribution uniformity, and others. Consistency is provided among different irrigation meth ods and different scales. Clarification of common points of confusion is provided, and methods are proposed whereby the accuracy of numerical values of the performance indicators can be assessed. This issue has two companion papers that provide more detailed information on statistical distribution uniformity and the accuracy of irrigation efficiency estimates.

Irrigation is widely criticised as a profligate and wasteful user of water, especially in watershort areas.Improvements to irrigation management are proposed as a way of increasing agricultural production and reducing the demand for water. The terminology for this debate is often flawed, failing to clarify the actual disposition of water used in irrigation into evaporation, transpiration, and return flows that may, depending on local conditions, be recoverable. Once the various flows are properly identified, the existing literature suggests that the scope for saving consumptive use of water through advanced irrigation technologies is often limited. Further, the interactions between evaporation and transpiration, and transpiration and crop yield are, once reasonable levels of agricultural practices are in place, largely linear-so that increases in yield are directly and linearly correlated with increases in the consumption of water. Opportunities to improve the performance of irrigation systems undoubtedly exist, but are increasingly difficult to achieve, and rarely of the magnitude suggested in popular debate.

Abstract:The Imperial Irrigation District is a large irrigation project in the western United States having a unique hydrogeologic structure such that only small amounts of deep percolation leave the project directly as subsurface flows. This structure is conducive to relatively accurate application of a surface water balance to the district, enabling the determination of crop evapotranspiration (ETJ as a residual of inflows and outflows. The ability to calculate ETc from discharge measurements provides the opportunity to assess the accuracy and consistency of an independently applied crop coefficient-reference evapotranspiration (K ET o ) procedure integrated over c the project. The accuracy of the annual crop evapotranspiration via water balance estimates was ±6% at the 95% confidence level. Calculations using K and ET o were based on the FAa-56 dual crop coefficient approach and included separate calculation of evaporation c from precipitation and irrigation events. Grass reference ET o was computed using the CIMIS Penman equation and ETc was computed for over 30 crop types. On average, Kc-based ET computations exceeded ETc determined by water balance (referred to as ETc WB) by 8% on an annual basis over a 7 year period. The 8% overprediction was concluded to stem primarily from use of K c that represents potential and ideal growing conditions, whereas crops in the study area were not always in full pristine condition due to various water and agronomic stresses. A 6% reduction to calculated Kc-based ET was applied to all crops, and a further 2% reduction was applied to lower value crops to bring the project-wide ET predicted by Kc-based ET into agreement with ETc WB' The standard error of estimate (SEE) for annual ETc for the entire project based on K c , following the reduction adjustment, was 3.4% of total annual ETc, which is considered to be quite good. The SEE for the average monthly ETc was 15% of average monthly ETc. A sensitivity analysis of the computational procedure for K c showed that relaxation from using the FAa-56 dual K method to the more simple mean (i.e., single) K curve and relaxation of specificity c c of planting and harvest dates did not substantially increase the projectwide prediction error The use of the mean K curves, where effects c of evaporation from wet soil are included as general averages, predicted 5% lower than the dual method for monthly estimates and 8% lower on an annual basis, so that no adjustment was required to match annual ET derived from water balance. About one half of the reduction in estimates when applying the single (or mean) K c method rather than the dual K c method was caused by the lack of accounting for evaporation from special irrigations during the off season (i.e., in between crops).

Literature regarding evaporation from soil, wet plant surfaces, and sprinkler droplets was examined, normalized, and inter preted. Much of the evaporation literature is difficult to compare and interpret; this paper offers comparisons and discussions of various findings by others as well as by the writers. Techniques of measuring and estimating evaporation from irrigation and rainfall are discussed. The partitioning between increased evaporation and decreased transpiration from a variety of research is quantified. Factors that impact the various forms of evaporation are listed and quantified. This review and summary will provide practitioners and researchers with theoretical and practical guidance on measurement techniques and estimates of evaporation under a wide range of conditions.

Forty percent of freshwater withdrawals in the United States are for irrigated agriculture, which contribute more than $50 billion to the economy. Increasing diversions of water for urban, environmental, and other uses will likely decrease water available to agriculture. Water conservation in agriculture is touted as a good method for minimizing the impact of reduced agricultural diversions on production. Because “wasted” water is often reused until it reaches the ocean, there are limitations to the true water savings that result from programs that aim to increase irrigation efficiency. True water savings can come from four areas: reduction of unnecessary evaporation and transpiration, more effective use of rainfall, reduction of deep percolation water that becomes severely degraded in quality, and reduction of runoff from fields that is not reusable downstream. Any other reduction in net water consumption must come from reductions in evapotranspiration from the crops grown, which requires either reduction in acreage or reduction in crop yield brought on by intentional plant water stress. Other benefits of field or district‐level water conservation may include increased in‐stream flows (due to lower diversions) and energy conservation due to less pumping or more hydroelectric production, but not result in true water savings, since unconsumed water returns as a usable water resource. Understanding the hydrologic settings is critical to determining true water savings from conservation practices. On‐farm water conservation practices that provide true water savings at one location may be ineffective at another. In large irrigation projects, water delivery limitations often present obstacles to on‐farm water conservation efforts.

This paper evaluates how well the FAO-56 style soil water evaporation model simulates measurements of evaporation (E) from bare soil. Seven data sets were identified from the literature and in all but one case, the individuals who took the measurements were contacted and they provided the writers with specific weather and soils data for model input. Missing weather and soils data were obtained from online sources or from the National Climatic Data Center. Simulations for three possible variations of soil data were completed and compared. The measured and the FAO-56 simulated E/ETo and cumulative evaporation trends and values were similar. Specifically, the average evaporation weighted percent difference between the measured and the simulated cumulative evaporation was between -7.5 and -0.5%. This evaluation suggests model accuracy of about ± 15% with the use of sound weather data and a fairly generalized understanding of soil properties in the location being evaluated.

Abstract: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. CE Database subject headings: Optimization models; Canals; Open channels; Control structures; Hydraulic structures. Introd uctionCanals or open channels that convey water often consist of pools in series separated by control structures. Most automated canals have hydraulic check structures or simple proportional electrome chanical controllers. Although there is ample literature regarding the use of proportional integral (PI) algorithms for canal control, there are very few successful field implementations in irrigation districts. One of the reasons for the slow adoption of PI algo rithms for canal control is the lack of tools for tuning the algo rithm parameters. Finding these parameters can be a difficult and time-consuming problem for mainly two reasons. First, control actions of one PI controller disturb the water level in an adjacent pool. If this disturbing effect is not taken into account, distur bance amplification is likely to happen. Second, the dynamics of open-channel flow are highly nonlinear. Therefore, tuning the controllers for one flow condition does not guarantee satisfactory control in another flow condition. These two problems are not unique to PI control; they apply to any control algorithm, be it linear quadratic Gaussian, model predictive control, etc. This paper presents a procedure for tuning any linear control ler (including decentralized PI controllers) that guarantees stabil ity of the control loops. It minimizes a cost function that weights the water-level deviations from the target levels against the con trol efforts. The tuning procedure makes use of a set of linear models (each valid for small variations around one flow condi tion). Decentralized versus Centralized ControlDecentralized control (sometimes called "local control" or "dis tributed control") is where the control actions are computed using only measurements taken near the structure. With centralized con trol, measurements from all...

This paper details a study performed by the Irrigation Training and Research Center to determine motor performances under varying speeds [induced by a variable frequency drives (VFD) controller] and loads. A further goal of the study was to provide sufficient information to designers so that they could estimate total pumping plant power usage with a VFD-controlled installation. Motors were tested with a VFD as well as across-the-Iine. On average, the relative efficiency of the electrical system with a VFD may be approximately 8% lower than the relative efficiency of a properly designed, full-load across-the-line system. If one considers actual field operating conditions this 8% is misleading because overall energy savings can be obtained with VFDs due to their ability to properly adjust speeds to meet actual field conditions.