Showing papers in "Journal of Irrigation and Drainage Engineering-asce in 2002"

Estimating Evapotranspiration using Artificial Neural Network

Abstract: This study investigates the utility of artificial neural networks (ANNs) for estimation of daily grass reference crop evapotranspiration (ETo) and compares the performance of ANNs with the conventional method (Penman–Monteith) used to estimate ETo. Several issues associated with the use of ANNs are examined, including different learning methods, number of processing elements in the hidden layer(s), and the number of hidden layers. Three learning methods, namely, the standard back-propagation with learning rates of 0.2 and 0.8, and backpropagation with momentum were considered. The best ANN architecture for estimation of daily ETo was obtained for two different data sets (Sets 1 and 2) for Davis, Calif. Using data of Set 1, the networks were trained with daily climatic data (solar radiation, maximum and minimum temperature, maximum and minimum relative humidity, and wind speed) as input and the Penman–Monteith (PM) estimated ETo as output. The best ANN architecture was selected on the basis of weighted sta...

A Paradigm Shift in Irrigation Management

Abstract: In coming decades, irrigated agriculture will be called upon to produce up to two thirds of the increased food supply needed by an expanding world population. But the increasing dependence on irrigation will coincide with accelerating competition for water and rising concern about the environmental effects of irrigation. These converging pressures will force irrigators to reconsider what is perhaps the most fundamental precept of conventional irrigation practice; that crop water demands should be satisfied in order to achieve maximum crop yields per unit of land. Ultimately, irrigated agriculture will need to adopt a new management paradigm based on an economic objective—the maximization of net benefits—rather than the biological objective of maximizing yields. Irrigation to meet crop water demand is a relatively simple and clearly defined problem with a singular objective. Irrigation to maximize benefits is a substantially more complex and challenging problem. Identifying optimum irrigation strategies wi...

Integrated Water Management for the 21st Century: Problems and Solutions

Abstract: Most of the projected global population increases will take place in third world countries that already suffer from water, food, and health problems. Increasingly, the various water uses (municipal, industrial, agricultural) must be coordinated with, and integrated into, the overall water management of the region. Sustainability, public health, environmental protection and economics are key factors. More storage of water behind dams and especially in aquifers via artificial recharge is necessary to save water in times of water surplus for use in times of water shortage. Municipal wastewater can be an important water resource but its use must be carefully planned and regulated to prevent adverse health effects and, in the case of irrigation, undue contamination of groundwater. While almost all liquid fresh water of the planet occurs underground as groundwater, its long-term suitability as a source of water is threatened by non-point source pollution from agriculture and other sources and by aquifer depletion due to groundwater withdrawals in excess of groundwater recharge. In irrigated areas, groundwater levels may have to be controlled with drainage or pumped well systems to prevent water-logging and salinization of soil. Salty drainage waters must then be handled in an ecologically responsible way. Water short countries can save water by importing most of their food and electric power from other countries with more water, so that in essence they also get the water that was necessary to produce these commodities and, hence, is virtually embedded in the commodities. This “virtual” water tends to be a lot cheaper for the receiving country than developing its own water resources. Local water can then be used for purposes with higher social, ecological, or economic returns or saved for the future. Climate changes in response to global warming caused by carbon dioxide emissions are difficult to predict in space and time. Resulting uncertainties require flexible and integrated water management to handle water surpluses, water shortages, and weather extremes. Long-term storage behind dams and in aquifers may be required. Rising sea levels will present problems in coastal areas.

Pan Evaporation to Reference Evapotranspiration Conversion Methods

Abstract: Reference evapotranspiration (ET0) is often estimated from evaporation pan data as they are widely available and of longer duration than more recently available micrometeorologically based ET0 estimates. Evaporation pan estimation of ET0 (=KpEpan) relies on determination of the pan coefficient (Kp), which depends on upwind fetch distance, wind run, and relative humidity at the pan site. The Kp estimation equations have been developed using regression techniques applied either to the table presented in FAO-24 or to the original data upon which this table was based (from lysimeter studies in Davis, Calif.). Here, the relative performances of the FAO-24 table and six different Kp equations are evaluated with respect to reproducing the original data table using the FAO-24 table as a standard. Evaporation pan- and CIMIS-based estimates of ET0 are also compared for stations having ranges of mean humidities (48–66%) and mean wind runs (156–193 km/day) located in the Sacramento and San Joaquin valleys, and for a ...

Irrigation Performance using Hydrological and Remote Sensing Modeling

Abstract: Development of water saving measures requires a thorough understanding of the water balance Irrigation performance and water accounting are useful tools to assess water use and related productivity Remote sensing and a hydrological model were applied to an irrigation project in western Turkey to estimate the water balance to support water use and productivity analyses Remote sensing techniques can produce high spatial coverage of important terms in the water balance for large areas, but at the cost of a rather sparse temporal resolution Hydrological models can produce all the terms of the water balance at a high temporal, but low spatial resolution Actual evapotranspiration for an irrigated area in western Turkey was calculated using the surface energy balance algorithm for land (SEBAL) remote sensing land algorithm for two Landsat images The hydrological model soil-water-atmosphere-plant (SWAP) was setup to simulate the water balance for the same area, assuming a certain distribution in soil proper

Decision Support System for Estimating Reference Evapotranspiration

Abstract: Evapotranspiration (ET) is a major component of the hydrologic cycle and its accurate estimation is essential for hydrological studies. In the past, various estimation methods have been developed f...

Evaluation of Class A Pan Coefficients for Estimating Reference Evapotranspiration in Humid Location

Abstract: Evaporation pans Class A pan, U.S. Weather Bureau (USWB) are used extensively throughout the world to measure free-water evaporation and to estimate reference evapotranspiration (ET0). However, rel...

Monitoring and Modeling Flow and Salt Transport in a Salinity-Threatened Irrigated Valley

Abstract: Saline high water tables pose a growing threat to the world’s productive irrigated land. Much of this land lies along arid alluvial plains, where solutions must now be developed in the context of changing constraints on river management. Findings are presented from the preliminary phase of a project aimed at developing, through well-conceived data collection and modeling, strategies to sustain irrigated agriculture in the salinity-threatened lower Arkansas River Basin of Colorado. Extensive field data from a representative subregion of the valley reveal the nature and variability of water table depth and salinity, irrigation efficiency and salt loading, and soil salinity. The shallow water table had an average salinity concentration of 3,100 mg/L and an average depth of 2.1 m, and was less than 1.5 m deep under about 25% of the area. Evidence reveals low irrigation efficiencies and high salt loading under each of six canals serving the subregion. Water table depths less than 2.5–3 m contributed to soil sa...

Energy Dissipation and Air Entrainment in Stepped Storm Waterway: Experimental Study

Abstract: For the last three decades, research focused on steep stepped chutes. Few studies considered flat-slope stepped geometries such as stepped storm waterways or culverts. In this study, experiments were conducted in a large, flat stepped chute (~3.4 degrees) based upon a Froude similitude. Three basic flow regimes were observed: nappe flow without hydraulic jump, transition flow, and skimming flow. Detailed air-water flow measurements were conducted. The results allow a complete characterization of the air concentration and bubble count rate distributions, as well as an accurate estimate of the rate of energy dissipation. The flow resistance, expressed in terms of a modified friction slope, was found to be about 2.5 times greater than in smooth-chute flow. A comparison between smooth- and stepped-invert flows shows that greater aeration and larger residence times take place in the latter geometry. The result confirms the air-water mass transfer potential of stepped cascades, even for flat slopes (<5 degrees).

Determining Minor Head Losses in Drip Irrigation Laterals. I: Methodology

Abstract: Minor head losses at emitter insertions along drip laterals were predicted by a derivation of Belanger’s theorem and analyzed by the classic formula that includes a friction coefficient \iK multiplied by a kinetic energy term. A relationship was established for \iK as a function of some emitter geometric characteristic. These take into account the flow expansion behind the reduction of the cross-sectional area of the pipe due to obstruction by the emitter. Flow constrictions at emitter insertions were estimated by analogy with contraction produced by water jets discharging through orifices. An experimental procedure was also developed to determine minor losses in situ, in the laboratory or in the field. An approach is suggested to calculate either \iK or the emitter equivalent length \Ile\N as a function of lateral head losses, inlet head, and flow rate. Internal diameter and length of lateral, emitter spacing, emitter discharge equation, and water viscosity must be known. Approximate analytical relations to study flow in laterals were developed. They may be used to design and evaluate drip irrigation units. Analytical and experimental procedures are validated in the companion paper by Juana, et al.

Continuous Outflow Variation along Irrigation Laterals: Effect of the Number of Outlets

Abstract: Previous continuous-uniform outlet discharge approaches for the hydraulic analysis of irrigation laterals are generally valid for large (theoretically) infinite number of outlets. For a finite number of outlets, however, these approaches may lead to errors in hydraulic computation. A new continuous-uniform outflow approach that takes into account the effect of the number of outlets on the lateral hydraulics is presented. A new analytical equation describing the energy line shape along uniform sprinkle and trickle irrigation laterals and manifolds is developed. The effect of ground slope and velocity head on hydraulic computation is also considered. The method is however restricted by the simplified assumption of equal outlet discharge. An alternate improved analytical method considering the effect of non-uniform outflow distribution along the lateral is also included. Analytical expressions for determining the inlet pressure head and global statistical parameters characterizing the outflow distribution (Christiansen uniformity coefficient, pressure head variation) are developed for design and evaluation purposes. Comparison tests with an accurate numerical stepwise method indicated that the proposed simplified approach is more accurate than other previous works particularly when the number of outlets is relatively small. The improved method is the most accurate method for all cases examined even for low levels of uniformity.

Influence of sluice gate contraction coefficient on distinguishing condition

Abstract: Sluice gates are widely used for flow control in open channels. Flow through the gate may be free or submerged depending on tailwater depth. One may determine whether the flow will be free or submerged by determining the maximum tailwater level that permits free flow. This is called the distinguishing condition. This paper derives a theoretical equation for the distinguishing condition including the contraction coefficient as a parameter, based on the basic equations for free flow and the hydraulic jump. The equation is investigated using experimental data from two different gate types. The results show that the contraction coefficient varies with gate type and that this affects the distinguishing condition. The results also show that for a given upstream depth, tainter gates (radial gates) are less likely to become submerged than vertical gates due to larger contraction coefficients. The present study results are useful in the design and operation of sluice gates.

Infiltration variability in furrow irrigation

Abstract: In this paper, the contribution of different sources of variability to irrigation water depth variability was quantified using a combination of variance techniques. This method was applied using field measurements from irrigation events performed on a loamy soil with a low-infiltration rate. Infiltration variability was estimated with blocked furrow infiltrometers. The assumptions made for the application of the combination of variance techniques proved to be valid. The major variability source turned out to be the soil intake characteristics, whose variance accounted for 45-71% of the variance in infiltrated depth under first irrigation conditions. Opportunity time and wetted perimeter were less variable in subsequent irrigations and the soil intake characteristics variability accounted for a percentage of total variance beyond 76%, being at times beyond 95%. The combination of variance techniques can be used to complement standard evaluation methods in order to take into account the influence of different variability sources.

Equivalent Friction Factor Method for Hydraulic Calculation in Irrigation Laterals

Abstract: A simplified method for the resolution of lateral hydraulic problems in laminar and turbulent flow is presented. In the first stage, the head losses are calculated by applying the Darcy–Weisbach equation with a discrete and constant outflow model, which leads to a correction parameter equivalent to Anwar’s Ga factor. The difficulty that arises from variation of the friction factor along the lateral (due to discharge flow) is overcome by means of an equivalent friction factor (feqN). In the second stage, this head loss model is used together with a variable discharge model based on Taylor polynomials to make a better estimate of the flow rate distribution by means of a successive-approximations scheme. This new approach directly allows the computation of the real mean lateral’s outflow and the minimum and maximum discharges. In the third stage, the previous results can be improved (if desired) by taking into account the nonconstant outflow distribution model developed in the previous stage. The method prop...

Determining minor head losses in drip irrigation laterals. II: Experimental study and validation

Abstract: Values of friction coefficient K and equivalent length le were determined for various emitter models using analytical and experimental procedures developed in the companion paper by Juana et al. in 2002. Flow contraction coefficient Cc for water jets discharging through orifices with angle α=45° is suggested when the emitters have hydrodynamic geometry at the insertion. Otherwise, α=90° or, as an extreme value, α=180° is preferred. Both criteria K and le showed a reasonable agreement for minor losses evaluation produced at emitter insertions along drip laterals. Accuracy on their determination was analyzed. Larger dispersion of K and le values was observed when lateral head losses were small. Inlet head, Reynolds number, and emitter spacing did not show a clear effect on K and le values, whereas the effect of obstruction ratio r of the pipe cross-sectional area at the emitter location was of practical significance. Parameters of the emitter discharge equation determined with lateral tests were comparable ...

Efficient Algorithm for Gradually Varied Flows in Channel Networks

Abstract: This paper presents an efficient solution technique for one-dimensional unsteady flow routing through a general channel network system—dendritic, looped, divergent, or any combination of such networks. The finite difference method is used to solve the de St. Venant equations in all the branches of the network simultaneously. The number of equations to be solved at a time during any iteration is reduced to only four times the number of branches of the network. This results in a significant reduction in storage requirements and solution time. Importantly, the algorithm does not require any special node numbering schemes and the nodes can be numbered independently for each branch. The algorithm is also suitable for programming on a parallel-processing computer.

New strategy for optimizing water application under trickle irrigation

Abstract: The determination of water application parameters for creating an optimal soil moisture profile represents a complex nonlinear optimization problem which renders traditional optimization into a cumbersome procedure. For this reason, an alternative methodology is proposed which combines a numerical subsurface flow model and artificial neural networks (ANN) for solving the problem in two, fully separate steps. The first step employs the flow model for calculating a large number of wetting profiles (output), obtained from a systematic variation of both water application and initial soil moisture (input). The resulting matrix of corresponding input/output values is used for training the ANN. The second step, the application of the fully trained ANN, then provides the irrigation parameters which range from a specified initial soil moisture to a desired crop-specific soil moisture profile. In order to avoid substantial disadvantages associated with the common feedforward backpropagation approach, a self-organizing topological feature map is implemented to perform this task. After a comprehensive sensitivity analysis, the new methodology is applied to the outcome of an irrigation experiment. The convincing results recommend the new methodology as a positive contribution towards an improved irrigation efficiency.

Coupled Reservoir Operation-Irrigation Scheduling by Dynamic Programming

Abstract: This paper develops a forward dynamic programming (FDP) model to solve the problem of reservoir operation and irrigation scheduling. The typical scenario for application of the model is composed of a system of two reservoirs in parallel supplying water to as many as three irrigation districts. Two models are coupled. The interseasonal model defines seasonal deliveries from the reservoir system. The intraseasonal model uses area and water allocations generated from the interseasonal model to produce an irrigation scheduling for the individual farms in one of the irrigation districts in the reservoir system. Crop evapotranspiration, reservoir evaporation, and inflows are forecasted. Upon availability of the current values, the forecast is updated and the model runs to generate a more precise irrigation schedule. This feature permits the application of the model for real-time operation of the irrigation district. At the end of the season, the intraseasonal model is updated. The FDP model is applied to a real watershed with a 2-year planning horizon for the interseasonal and 6 months for the intraseasonal model.

Hydraulic Analysis and Optimum Design of Multidiameter Irrigation Laterals

Abstract: A new analytical continuous-uniform outflow approach that takes into account the effect of the number of outlets on the multidiameter lateral hydraulics is presented. The pressure head profile along the multidiameter pipeline is described by a simple analytical function providing direct calculation of the outlet pressure head along the pipeline. The method is significantly improved by introducing an adjusted spatially variable outflow equation—of power function form—for the errors caused by the assumption of equal outlet discharge. The effect of ground slope on hydraulic computation is also considered. Simple equations are derived for the direct calculation of the maximum, minimum, and inlet pressure head along the multidiameter pipeline. The optimum design problem for two-diameter laterals is also solved analytically. For specified total length of a two-diameter pipeline, a simple algebraic equation is derived to calculate directly the appropriate lengths of the reaches of different diameters in such a way that the total cost of the pipeline is minimized. Comparison tests with an accurate numerical stepwise method indicate that the proposed analytical approach is sufficiently accurate.

Drop and Energy Characteristics of a Rotating Spray-Plate Sprinkler

Abstract: A laboratory investigation was conducted to measure wetted radii and drop sizes and to estimate the energy characteristics of a rotating spray-plate sprinkler. Maximum wetted radii were positively related to increasing sprinkler elevation above an irrigated surface and increasing nozzle pressure. Nozzle diameter had a minimal effect on drop size, but nozzle pressure had a significant inverse influence. Energy parameters were calculated for sprinkler operational scenarios. Average kinetic energies over sprinkler-wetted areas were inversely related to nozzle pressure and the square of nozzle pressure. Rapidly and slowly rotating spray plate sprinklers had similar time-averaged specific power distributions. However, the rapidly rotating sprinklers had continuous rotational distribution patterns in space with relatively low peak specific power values that corresponded to natural rainfall intensities of about 20 mm/h. Slowly rotating sprinklers had discontinuous spatial distribution patterns with very high peak values that corresponded to natural rainfall intensities of about 200 mm/h.

Optimal Design of Transmission Canal

Abstract: This paper presents design equations for the least-cost canal sections considering earthwork cost which may vary with depth of excavation, cost of lining, and cost of water lost as seepage and evaporation from irrigation canals of triangular, rectangular, and trapezoidal shapes passing through a stratum underlain by a drainage layer at shallow depth. The optimal design equations are in explicit form and result into optimal dimensions of a canal in single-step computations. Using these least-cost section equations and applying the Fibonacci search method, equations for computation of the optimal subsection length and corresponding cost of a transmission canal have been presented. The optimal design equations along with the tabulated section shape coefficients provide a convenient method for the optimal design of a transmission canal. A step-by-step design procedure for rectangular and trapezoidal canal sections has been presented to demonstrate the simplicity of the method.

Performance of Historic Downstream Canal Control Algorithms on ASCE Test Canal 1

Abstract: Researchers have developed several algorithms to automatically control water levels in irrigation canals. Proportional-integral (PI) control logic has been used for downstream water-level control, ...

Numerical Modeling of Basin Irrigation with an Upwind Scheme

Abstract: In recent years, upwind techniques have been successfully applied in hydrology to simulate two-dimensional free surface flows. Basin irrigation is a surface irrigation system characterized by its potential to use water very efficiently. In basin irrigation, the field is leveled to zero slope and flooded from a point source. The quality of land leveling has been shown to influence irrigation performance drastically. Recently, two-dimensional numerical models have been developed as tools to design and manage basin irrigation systems. In this work, a finite volume-based upwind scheme is used to build a simulation model considering differences in bottom level. The discretization is made on triangular or quadrilateral unstructured grids and the source terms of the equations are given a special treatment. The model is applied to the simulation of two field experiments. Simulation results resulted in a clear improvement over previous simulation efforts and in a close agreement with experimental data. The proposed model has proved its ability to simulate overland flow in the presence of undulated bottom elevations, inflow hydrographs, and colliding fronts.

Development of Comprehensive Soil Salinity Index

Abstract: Crop yield is a function of many agroclimatic factors. However, excessive wetness, dryness, or soluble salts in the root zone are three important stresses that inhibit crop growth and reduce yield. Stress due to wetness can be expressed by an index such as SEW\D30\N (sum of excess water over 30 cm); however, a similar index is not available for stress due to soil salinity. An index, the sum of excess salinity over threshold (SES\i\dT), is proposed here. This index represents the cumulative salinity status of the root zone with respect to a specific crop in excess of the crop’s threshold level. Specifically, it incorporates the sum of daily salinity excesses over the threshold salinity level of the crop at different points in the root zone and over a specific crop-growth stage (or over an entire cropping period). The proposed salinity index, however, needs to be evaluated with field data before it can be used to characterize salt buildup in soil under different irrigation regimes.

Monitoring and Evaluation Scheme using the Multiple-Criteria-Decision-Making Technique: Application to Irrigation Projects

Abstract: The application of monitoring and evaluation (M&E) systems to assess agricultural projects has received some attention in recent years. These systems provide valuable information for managers and decision makers by analyzing the implementation process, the progress of trends, and the long-term and short-term effectiveness of these projects. An algorithm is developed to monitor and evaluate drip and pressure irrigation projects in Iran. Different indicators are identified and the framework of an integrated evaluation system is demonstrated using an analytical hierarchy process for multiple-criteria-decision making. There is much subjective information that is quantified and normalized in order to remove any bias in evaluators’ assessment of qualitative measures or sensitivity to linguistic expressions. The application of this system to rank projects in different regions (zones) in Iran is also presented in this paper. The results have shown the significant value of such systems in providing information and...

2. Numerical Simulations of Water Flow and Solute Transport Applied to Acid Sulfate Soils

Abstract: Field investigations of Rassam et al. in 2001 have highlighted the effects of infiltration, drainage, and evapotranspiration on the dynamics of water flow and solute transport in acid sulfate ~AS! soils. In this work, HYDRUS-2Dis adopted as the modeling tool to elucidate the trends observed in that field experiment. Hypothetical simulations have shown that the relative contribution of drains to lowering the water table is significant only when closely spaced drains are installed in coarse textured soils, evapotranspiration being the main driving force in all other cases. AS soils reaction products that are close to a drain are readily transportable during infiltration and early drainage, but those produced farther away from it near the midpoint between drains are only slowly transported during a prolonged drainage process. Simulating the field trial of Rassam et al. has shown that drain depth and evapotranspiration significantly affect solute fluxes exported to the ecosystem. Managing AS soils should target minimal drain depth and density. Partial or full lining of the drains should be considered as a management option for ameliorating the environmental hazards of AS soils.

Analytical Solution for Transient Water Table Heights and Outflows from Inclined Ditch-Drained Terrains

Abstract: This paper presents two analytical solutions of the linearized Boussinesq equation for an inclined aquifer, drained by ditches, subjected to a constant recharge rate. These solutions are based on different initial conditions. First, the transient solution is obtained for an initially fully saturated aquifer. Then, an analytical expression is derived for the steady state solution by allowing time to approach infinity. As this solution represents the groundwater table shape more realistically, this water table profile is used as an initial condition in the derivation of the second analytical solution for the groundwater table height, and the in- and outflow into the ditches. The solutions allow the calculation of the transient behavior of the groundwater table, and its ouflow, due to changing percolation rates or water level heights in both ditches.

Applications of Drag-Reducing Polymers in Sprinkler Irrigation Systems: Sprinkler Head Performance

Abstract: The study investigates the effects of polymer additives on sprinkler performance. Experiments were carried out on a medium-pressure sprinkler to determine the effect of polymer additives. Two kinds of polymer additives with several concentrations were used: a low molecular weight polymer, sodium carboxymethylcellulose, and a high molecular weight polymer, polyacrylamide. The results show that with polymer additives the radius of throw and the sprinkler flow rate increase. The jet is slightly affected. Generally, polyacrylamide shows better results than sodium carboxymethylcellulose.

Microirrigation Lateral Design using Lateral Discharge Equation

Abstract: A simple and accurate method is developed for designing single, paired, and tapered microirrigation laterals. The hydraulics of the lateral is evaluated using a lateral discharge equation approach. A simple power equation is used to express the relationship between the inlet flow rate and inlet pressure head of the lateral. Keeping the flow variation within the specified limit, a procedure for designing the length of the tapered section is developed. The lateral is designed using a step-by-step method. The length of the tapered section is determined by the golden section search method.