Journal of Irrigation and Drainage Engineering

Both old and new design and management concepts for increasing irrigation and energy‐use efficiencies and net farm profits should be integrated into current and new system designs. Computerized procedures are available for performing economic comparisons and for sizing and selecting system components during periods of price instability. New pump and motor designs coupled with pump and system efficiency testing programs and maintenance schedules can significantly reduce energy consumption at the supply end. Developments in furrow irrigation system equipment and in border system design procedures can greatly increase water application uniformities. Many sprinkler systems can be retrofitted to enable low‐pressure operation, and irrigation water requirements can be reduced by improving soil‐water management, by changing cropping patterns or by deliberate reduction in consumptive use by initiating moisture stress.

Nomographs relating discharge rate, plant uptake and soil water potential at a reference point are developed for trickle irrigation systems. The hydraulic conductivity K is assumed to be related to pressure head h by $K_0$ exp (αh) in which $K_0$ and α are empirical constants representative of the specific soil. Point or disc sources located at the soil surface as well as arrays of line sources located at the soil surface or buried at depth d are considered. For point or disc sources, the plant water uptake is from a cylindrical volume or a buried horizontal disc. For line source arrays, however, a one‐dimensional uptake is assumed. The reference point for line sources is chosen at depth $Z_M$ midway between the line emitters. For disc or cylindrical uptake, the reference point is located at the outer edge of the maximum depth of withdrawal. The nomographs are easy to use and provide answers without performing tedious computations.

Good water management in irrigated agriculture requires that irrigation water be accurately measured. Presented herein are design procedures and rating tables for modified broad‐crested weirs (which act hydraulically as long‐throated flumes) that have rectangular control sections. The ratings are presented in terms of discharge per unit width so that rectangular broad‐crested weirs of a variety of sizes can be used. This makes it easier for the designer to adapt the flume to the site rather than vice versa. These weirs or flumes can be placed in lined and unlined canals of any shape. The rating tables are presented for rectangular lined canals with given values of sill or crest height. An adjustment procedure is given to develop rating tables for other approach area and sill height combinations. The head loss across the weir required to maintain a unique head discharge relationship is also presented. Finally, a design example is given for a rectangular lined canal. With this information, a rectangular measuring flume can be designed for a wide variety of site conditions.

A weekly evaporation time series generated by the mass transfer method for Milford Lake displays a predominant annual cycle with low evaporation in spring and winter and high evaporation in summer and fall. A mathematical model for the time series is developed. The model consists of a mean weekly component represented by a Fourier approximation and a stationary random residue represented by an autoregressive model. From the synthetic evaporation series, the frequency distribution is obtained. A sensitivity analysis shows that the estimated evaporation is most sensitive to changes in water temperature.

A simulation model was developed to estimate the effect of deficit irrigation upon crop yield. The model was designed to provide relative yield estimates for numerous combinations of irrigation system, crop growth and irrigation management parameters. A daily soil moisture balance was used to predict evaporation and transpiration from which crop yields were estimated. Gross irrigation water requirements were estimated from net irrigation requirements, irrigation efficiencies, irrigation system limitations, and effective rainfall. Crop production functions that use physically defined parameters were also developed to relate crop yields to gross irrigation requirements. The production functions worked well on a limited test compared to field data. The model and production functions are general since they depend upon readily available information or physical parameters, and can be used to evaluate irrigation management alternatives.

A design procedure is presented for minimizing the capital cost of multiple‐outlet pipelines which are composed of more than one diameter. The procedure assumes uniform slope, equal outlet spacing, and equal outlet discharge over a specified range of pressure heads. The optimization technique suggested is the Lagrange Multipliers method using the Newton Raphson method to solve a system of nonlinear equations. The procedure is applicable both to laterals for sprinkler or trickle irrigation systems and to manifold lines (feeder pipes) for a group of laterals.

Nondimensional runoff curves useful in the design of reuse systems are presented for free outflow irrigation borders. Pertinent open channel variables affecting runoff in border irrigation, including inflow rate, surface resistance, border slope, soil infiltration characteristics, application time, and length of border, were studied and their effects presented. Maximum advance distance, which is of interest in designing border irrigation systems, is also given by the zero runoff curves. A zero‐inertia mathematical model was used to develop the nondimensional predictive graphical solution in terms of four reduced variables.

A method to determine optimal water use in alkali soils under reclamation is developed. The procedure involves a deterministic linear programming model for allocation of surface and ground water for irrigation of crops within the project area and for water export; development of a technique to estimate the system parameters which are of a transient nature; and generation of system response at different stages of soil reclamation. The dynamic nature of the agricultural system and the nonlinearity of the crop water production function are incorporated by using separate input data for each time increment in the model and by introducing multiple activities for each crop, respectively. The model is applied to a representative alkali area in the Indo‐Gangetic plains in India. Optimal cropping patterns over a period of 20 yr at five discrete stages of reclamation are determined. Parametric analysis is used to determine optimal water resources management policies with regard to canal water diversion, ground water mining, and export water.

Two‐dimensional (2‐D) infiltration equations for furrow irrigation expressed in explicit algebraic forms are developed and based on four consecutive time intervals which were derived in a previous study (1). From another study an extension is made for 2‐D infiltration (4). Since the geometric cross section of a furrow can have different forms, a simple rectangular cross section is used for illustration. Two‐dimensional infiltration in a furrow is assumed to be a composite of 1‐D and 2‐D infiltration components. These components of infiltration are computed using developed 1‐D and 2‐D infiltration equations obtained from previous studies. Because the resulting equations are presented in explicit algebraic power forms, the physical parameters of the soil media (hydraulic conductivity, capillary potential, pressure head, soil porosity, and moisture content) can be examined as dependent design parameters of furrow infiltration. The validity of the developed equations has been examined in laboratory experiments at dry and wet soil conditions. The results of computed and measured infiltration show good agreement.

The problem of increasing ground water salinity in areas irrigated by ground water has been studied; however, few if any measures have been implemented to control the salinity build‐up. One reason for this inaction may be that decision makers and the public do not have a clear idea of the potential benefit from controlling ground water degradation. Consequently, this study sought to calculate the economic benefits. Mathematical programming was used to determine the economic incentives for controlling the salinity problem using several regions in the San Joaquin Valley in California. The results showed that using benefit‐cost procedures, there was little or no economic incentive to control ground water degradation.

Corrugated plastic drainage tubing has been available in North America for only 15 years. It now represents 75% of the drainage pipe used in agriculture for subsurface drainage. Hydraulic tests are available for diameters from 35 mm–300 mm, however, this type of tubing is now available to 750 mm. Data from hydraulic tests found in the literature is used to develop an estimating equation for the flow rate of corrugated plastic drainage tubing when the tubing geometry is known. This method may be used for flow rate estimation until actual tests are available.

Advantages and disadvantages of the parabolic canals are described. Procedures are given for determining all design parameters for parabolic cross-sections. The changes in velocity, area and wetted perimeter depand on changes in the sideslope at the water surface. Numerical solution tables for different parameters are presented. An example of design calculations is given.

Voluminous data on monthly averages of Class A pan evaporation can be described concisely by mapping the parameters of Fourier series describing the seasonal variations. Average monthly Class A pan evaporation data were obtained for the 146 U.S. stations east of the Rocky Mountains. The average monthly pan evaporation, converted to daily rates, was assumed to occur at mid-month. A Fourier series with a single harmonic explained more than 95 percent of the variance of monthly mean evaporation for most of the stations. Maps of the means and amplitudes and phase angles of the first harmonic are presented. The magnitudes of the errors introduced by the Fourier series fit, and interpolation of parameters from the maps, are demonstrated for selected stations. These parameter maps provide a quick and easy method of estimating input for simple water balance models.