Journal of Irrigation and Drainage Engineering

Surface–subsurface flow during furrow irrigation is analyzed employing both a laboratory experiment and a surface–subsurface flow model. The proposed model overcomes the restrictions of traditional furrow irrigation models by rigorously describing the subsurface flow at computational nodes using the physically based two-dimensional (2D) model Hydrus-2D. Surface flow is portrayed by an analytical zero-inertia model. In order to couple both models efficiently, an iterative procedure was developed. Using a sensitivity analysis we investigated the space interval separating 2D infiltration computations. This variable showed little effect on model performance, thus permitting the selection of rather generous distances. Due to the similarity of the hydrographs at neighboring cross sections we investigated transferring the results of Hydrus-2D computations to the next downstream location. This was performed by interpolating cumulative infiltration using infiltration opportunity times. This procedure uncovered other dependencies, making the interpolation strategy unattractive. To validate the coupled surface–subsurface model, an irrigation furrow was set up in a 26.4 m long, 0.88 m wide, and 1.0 m deep tank, filled with 50 t of sandy loam soil and equipped with surface and subsurface measurement devices. Although the model results compared favorably with the observed data, the study also showed an important impact of surface cracking and preferential flow during the irrigation experiments.

Energy costs constitute the largest expenditure for nearly all water utilities worldwide and can consume up to 65% of a water utility’s annual operating budget. One of the greatest potential areas for energy cost savings is in the scheduling of pump operations. This paper presents a new management model, WAPIRRA Scheduler, for the optimal design and operation of water distribution systems. The model makes use of the latest advances in genetic algorithm (GA) optimization to automatically determine annually the least cost of pumping stations while satisfying target hydraulic performance requirements. Optimal design and operation refers to selecting pump type, capacity, and number of units as well as scheduling the operation of irrigation pumps that results in minimum design and operating cost for a given set of demand curves. The optimization process consists of three main steps: (1) generating randomly an initial set of pump combinations to start the optimization process for a given demand-duration curve; (2) minimizing the total annual cost, which consists of operation and maintenance costs and depreciation cost of the initial investment, by changing the set and discharge of pump sets based on the provided model; and (3) achieving the final criterion to stop the optimization process and reporting the optimized results of the model. Computational analysis is based upon one major objective function and solving it by means of a computer program that is developed following the GA approach to find the optimized solution of generated equations. Application of the model to a real-world project shows considerable savings in cost and energy.

Innovations are needed in both the technological and policy dimensions of water resource management to achieve the gains in productivity required to feed the world’s increasing population. Scientists and engineers will continue to discover and disseminate new information regarding the technology of water management. However, the effective demand for that information at the farm level will be limited in areas where water prices and allocations do not reflect scarcity conditions. This paper describes how public policies regarding water resources and agricultural production can motivate farmers to consider scarcity values and the off-farm impacts of irrigation and drainage activities. Farm-level and regional models of crop production are examined, and optimizing criteria derived from the models depict the role of scarcity values and policy parameters in farm-level decisions regarding water use. The rate at which improvements in water management are implemented by irrigators around the world might be enhanced substantially by replacing inappropriate policies with those that motivate farmers and others to use scarce resources efficiently.

The integrator delay zero (IDZ) model presented by Litrico and Fromion is a simple way to model a canal for control purposes that extends the classical integrator delay model. This analytical model gives a very good frequency domain approximation of the Saint-Venant transfer matrix for a pool possibly in backwater conditions. The present paper shows how this model can be used to model an irrigation canal for control design. The IDZ model is analyzed and its accuracy evaluated in the frequency and time domain on two ASCE test canals for high and low flow conditions.

A key component in the calculation of reference crop evapotranspiration $\left({\mathrm{ET}}_r\right)$ is the weather data. If the weather data have been collected from a station under nonreference conditions, the data itself may contain errors, which will in turn yield inaccurate ${\mathrm{ET}}_r$ estimates. It was proposed by Allen in 1996 that data used for evapotranspiration be scrutinized by comparing daily minimum temperature $\left(T_{\min }\right)$ and the daily average dew point temperature $\left(T_{\mathrm{dew}}\right)$. If the difference between $T_{\min }$ and $T_{\mathrm{dew}}$ is greater than $3°C$, then the site is considered to be arid (nonreference) and adjustments are recommended for temperature and dew point data. In Arizona, normal weather conditions often occur where $T_{\min }$ and $T_{\mathrm{dew}}$ do not approach each other. This study examined the appropriateness of applying the conditions set forth by Allen to temperature data collected in central Arizona. Two weather stations were set up in a $35.5\mathrm{ha}$ alfalfa field in central Arizona to measure dry bulb and wet bulb temperatures. Additionally, plant temperature data were collected to verify field conditions. Daily data were taken for 1.5 years at the University of Arizona’s Maricopa Agricultural Center. Of the 611 days of data collected, the difference between $T_{\min }$ and $T_{\mathrm{dew}}$ was greater than $3°C$ on 329 days, indicating that these data were not taken under reference conditions. Among these data, 178 days were verified as nonreference but 151 were verified as actually being under reference conditions. Making adjustments for these days (151 days) resulted in a $47\mathrm{mm}$ decrease in ${\mathrm{ET}}_r$ estimation, which mostly occurred during the summer.

The Tehran metropolitan area is one of the mega cities of the world and has an annual domestic water consumption close to one billion cubic meters. The sewer system mainly consists of traditional absorption wells. Therefore, the return flow from the domestic consumption has been one of the main sources of groundwater recharge. Some part of this sewage is drained into local rivers and drainage channels and partially contaminates the surface runoff and local flows. These polluted surface waters are used in conjunction with groundwater for irrigation purposes in the southern part of the Tehran. In this paper, a systematic approach to surface and groundwater resources modeling in the study area, with its complex system of water supply, groundwater recharge, and discharge, is discussed. A dynamic programming optimization model is developed for conjunctive use planning. The objective function of this model is developed to supply the agricultural water demands, to reduce pumping costs, and to control groundwater table fluctuations. To develop the response function of the aquifers located in the study area, a mathematical model for simulation of the Tehran aquifer water table fluctuations has been developed and calibrated with the available data. Different scenarios are defined to study the long-term impacts of the development projects on conjunctive use policies and water table fluctuations. Comparison of the results showed how significant is the effects of an integrated approach to the surface and groundwater resources allocation in Tehran metropolitan area. The proposed model is a useful tool for irrigation planning in this region.

Steady, 2D Darcian seepage from a zero-depth reservoir into a homogeneous porous bank is studied analytically. Using the Green-Ampt assumption for hydraulic conductivity as a function of pressure and the Vedernikov model for the tension-saturated zone, a free boundary problem with the capillary fringe spread along the bank surface is solved. Accurate direct calculations are made for the extent of the capillary rise along a vertical and horizontal bank. Unsaturated flow from a vertical phreatic surface into a bank with either an impermeable or isobaric vertical soil slope is analyzed in terms of the Philip model. Explicit expressions for the Darcian velocity components, stream function, and/or Kirchhoff potential are presented. The flow topology and characteristics are shown to depend strongly on the boundary condition at the soil surface.

This study aims to obtain sharp crested triangular side-weirs discharge coefficients both in the straight channel and along the bend by using a total of 1,735 experiments. It was found that triangular side-weirs discharging coefficients along the bend depend on the upstream Froude number in the main channel $\left(F\right)$, the apex angle of side-weir $\left(\theta \right)$, and the bend angle $\left(\alpha \right)$. Because there is much greater intensity of secondary flow created by lateral flow with an increase of the overflow length, sharp crested triangular side-weirs discharge coefficients of the apex angle $\theta =120°$ were achieved more frequently than the others even at the straight channel in subcritical flow conditions. In a curved channel, the path of maximum velocity and the secondary current created by the bend both cause a much greater deviation angle towards the side-weir which is involved within $F$ and $L/b$. Therefore, triangular side-weirs discharging coefficients along the bend are greater than the values obtained in the straight channel.

A novel and computationally efficient algorithm is presented to compute the water surface profiles in steady, gradually varied flows of open channel networks. This algorithm allows calculation of flow depths and discharges at all sections of a cyclic looped open channel network. The algorithm is based on the principles of (1) classifying the computations in an individual channel as an initial value problem or a boundary value problem; (2) determining the path for linking the solutions from individual channels; and (3) an iterative Newton–Raphson technique for obtaining the network solution, starting from initial assumptions for discharges in as few channels as possible. The proposed algorithm is computationally more efficient than the presently available direct method by orders of magnitude because it does not involve costly inversions of large matrices in its formulation. The application of this algorithm is illustrated through an example network.

For steady flow near the free overfall (end section) of a horizontal trapezoidal channel, the velocity distribution is nonuniform and the streamlines are curved. An accurate relation between discharge rate and end depth was formulated including these effects. To determine these effects, the streamline pattern in the vertical plane of channel symmetry was determined using measured velocity components and the water surface profile. At the end section, the streamline pattern yielded the streamline curvature, which in turn provided the curvature correction required to predict the true static pressure head profile. The measured static pressure head distribution agreed well with the predicted static pressure head distribution for the end section. The pressure force at the end section was obtained on the basis of the measured static pressure distribution at the end section, and this information yielded a reliable relation between the end depth and the channel discharge rate. Analysis of present and past experimental data indicated that, the pressure head coefficient was the dominant parameter that influences the relationship between discharge rate and end depth in trapezoidal channels. Near the end depth, in the region above the maximum velocity point, the total energy determined from the measured velocity and pressure fields was essentially constant.

This paper presents a direct solution technique derived by using a power law for the friction factor for three cases of pipe design. The parameters used in the form of the power law presented herein are allowed to vary with pipe size and Reynolds number as well as pipe type, thus providing wide coverage with good accuracy for the computation of friction factors of commercial pipes.

The problem of steady-state seepage from a lined canal toward asymmetrical drainages has been solved using the finite-element method, analyzing the effect of canal lining on canal seepage discharge. Studies show that the effectiveness of canal lining in reducing seepage is less when drainage distance is large. With a decrease in the permeability of the canal lining, the canal seepage also decreases; however, the decrease in canal seepage is relatively more when the ratio of lining permeability and subsoil permeability ranges in the region from $2$. The decrease in canal seepage is very steep with initial increase in the lining thickness. However, with further increase in the lining thickness, the decrease in canal seepage is not very significant. Therefore, an effective lining permeability must range between $1$ and $1$ of the subsoil permeability and its thickness must be kept less than $0.2$, where $h_1$ is the difference between right drainage water level and canal water level.