Journal of Irrigation and Drainage Engineering

An analysis to determine infiltration parameters from the early stages of furrow advance is reported. The analysis uses a kinematic‐wave simulation model in conjunction with a simplex search procedure to minimize the differences between measured and predicted advance rates. The technique uses a variable and expanding data set to forecast advance times and is therefore a useful prelude to real‐time feedback control systems for the future automation of furrow irrigation systems. Results from four furrow evaluations involving a sandy loam and a silty clay loam are given to demonstrate the capability of the analysis. The analysis was first verified by using the complete advance data sets for the evaluations. The analysis yielded the same values of the three Kostiakov‐Lewis infiltration parameters found in independent field measurement. In a second investigation, the basic intake‐rate parameter in the Kostiakov‐Lewis function was fixed and the analysis was repeated with advance data from the early stages of advance to determine if and how soon the analysis would estimate reasonably accurate values of the other two infiltration parameters. The results indicate that infiltration parameters can be estimated with sufficient accuracy from early advance data to allow an accurate forecast of efficiency and uniformity at the end of the irrigation.

Rainfall data constitute an important parameter for studying water resources‐related problems. Currently, little is known about the accuracy of the estimation of rainfall in a given area, primarily because of the wide variability of rainfall distribution in space and time and the lack of information concerning the optimization of the traditional raingage network design. Remote sensing techniques could provide a more rapid and comprehensive overview of the rainfall distribution in a given area. Thus, the half‐hourly visible and thermal infrared data from the Geostationary Operational Environmental Satellite (GOES), in conjunction with the Scofield‐Oliver method and a geographic information system (GIS), were used to monitor rainfall in Florida. Eleven convective clouds that covered 26 raingage stations were analyzed. The cell size with raster format used in the GIS was $48{\mathrm{km}}^2\text{.}$ The results showed that the satellite rainfall estimations were well correlated to raingage measurements with a coefficient of determination $\left(r^2\right)$ of 0.81. The satellite data appear to be useful for monitoring the rainfall at an area where no raingage is available.

Droughts are defined using daily streamflow series and different truncation levels including 30%, 50%, 60%, 70%, 80%, and 90% of recorded daily flows. Flow ratios, which are obtained by dividing subbasin flows of different truncation levels by their corresponding outlet flows, are calculated. It is found that the flow ratios of 17 selected subbasins decrease significantly with increasing truncation levels while their mean‐flow ratios are approximately equal to their corresponding area ratios. Therefore, the estimation of irrigation water using the drainage area ratio, which has been practiced in the studied drainage basin, is impractical in case of droughts. Furthermore, assuming the time‐dependent Poissonian behavior of drought series, the drought intensity function was developed to investigate drought severity in the basin. Based on plots of drought intensity function, it is found that the drought intensity has been increasing significantly for the basin investigated.

Partial irrigation is supplying less water than a crop needs for full production. Partially irrigating crops is intended to stretch water supplies and increase total crop production and profit. Pakistan is short of water and so partial irrigation is widely practiced. Selecting crop varieties or determining proper irrigation schedules requires applying partial irrigation principles. Only a small part of the irrigation research done in Pakistan considers the effects of partially irrigating crops. All the reviewed mathematical models used to optimize irrigation avoided nonnumerical aspects of irrigation management. These simplifications tend to ignore some costs while fully accounting for all benefits, resulting in poor model performance when compared to actual system management. The most effective actions to implement partial irrigation are improving system reliability, developing and disseminating simple water management rules, and continuing current programs to improve watercourses and level fields. While a sophisticated partial irrigation scheduling program would be difficult technically, socially, and logistically, partial irrigation principles must be used to understand and direct conventional water conservation programs.

This study analyzes factors affecting deep percolation. Harmonic analysis is used to derive the effect of nonuniform irrigation on deep percolation. The Christiansen uniformity coefficient (CUC) is described by a sinusoidal function. It is shown to be proportional to the relative amplitude, the ratio between the amplitude $\left(\delta I\right)$ and mean water application $\left(Ĩ\right)$ of a sinusoidal wave. The amplitude is subject to smoothing by plant root systems of various sizes. A distinction is made between effective uniformity and observed uniformity. The theoretical study provides an analytical tool with which to evaluate the hydrological significance of irrigation uniformity. Deep percolation was shown to be affected by several factors. First is the difference between $Ī$ and the crops' water consumption. The greater the difference, the greater the amount of deep percolation. Of secondary importance is CUC. For any given amount of water, the amount that percolates below the root zone increases as CUC decreases. Smoothing of water distribution within the soil profile reduces percolation. This effect is more pronounced for a short rather than long distance between nozzles.

This study evaluates quantitatively the various components of an irrigation regime affecting deep percolation. The relationship between applied water and a point water balance is studied using a linear move sprinkler, irrigating a field of sugar beets (Beta vulgaris L. Var. HC11). Uniformity coefficients of about 0.60 and 0.80 are designed in length scales of 2.5 and 5.0 m. Measurements of soil water content with a surface neutron probe, evapotranspiration with infrared thermometer, and applied water with catch cans are carried out during the growing season and used to calculate deep percolation. The seasonal transpiration average is about $50m^3/\mathrm{ha}/\mathrm{day}(5\mathrm{mm}/\mathrm{day})\text{.}$ Water applied in excess of the daily transpiration rate is lost as deep percolation. For a given amount of water, high irrigation uniformity is associated with a small amount of deep percolation, and low uniformity with a large amount of percolation. This effect is more pronounced on a large length scale (5 m), than on a short length scale (2.5 m). Measured uniformities and their derivations are in good agreement with theoretical prediction.

This paper is devoted to the improvement of the measuring range of inverted V‐notch (IVN) weir, a practical linear sharp‐crested weir, designed earlier by the writers. The range of linearity of IVN can be considerably enhanced (by more than 200%) by the addition of a retangular weir of width 0.265W (W = half crest width) at a depth of 0.735d (d = altitude of IVN), above the crest of the weir, which is equivalent to providing at this depth two vertical straight lines to the IVN, resulting in a chimney‐shaped profile; hence, the modified weir is named chimney weir. The design parameters of the weir, that is, the linearity range, base flow depth, and datum constant, which fixes the reference plane of the weir, are estimated by solving the nonlinear programming problem using a numerical optimization procedure. For flows through this weir above a depth of 0.22d, the discharges are proportional to the depth of flow measured above a reference plane situated at 0.08d above the weir crest for all heads in the range 0.22d ⩽ h ⩽ 2.43d, within a maximum percentage deviation of $\pm 1.5$ from the theoretical discharge. A significant result of the analysis is that the same linear head‐discharge relationship governing the flow through the IVN is also valid for the extended chimney weir. Experiments with three different chimney weirs show excellent agreement with the theory by giving a constant average coefficient of discharge for each weir.

Application of a remote sensing technique for estimating regional evapotranspiration requires extrapolation of instantaneous values to periods on the order of 1 day or more to be of practical use. A method for developing an extrapolation coefficient based on earth‐sun geometry is presented. The validity of the method and applicability of the concept is evaluated using year‐long regional values of measured Penman evapotranspiration. The results demonstrate that the use of an extrapolation coefficient for long‐term regional evapotranspiration estimation has a potential for future use.

The economics of deficit irrigation are examined. The concepts developed in the heuristic discussion are developed into a set of rigorous mathematical expressions for determination of optimum water use under deficit irrigation. These expressions also can be used to estimate the range of water use within which deficit irrigation would be more profitable than full irrigation. The expressions are completely general in the sense that they can be used with any crop production function and cost function that the analyst chooses. The general expressions are used to derive a set of specific expressions for a particular case study involving a quadratic production function and linear cost function.

A companion paper demonstrates that deficit irrigation can be profitable when irrigation costs are high or water supplies are limited. The present paper provides specific examples of deficit irrigation practices in the Columbia Basin with the aim of developing a better understanding of the practice and economic merits of this irrigation‐management technique. The fundamental concepts developed in the companion paper are illustrated with data from nine cooperating farms. The economic analyses account for all costs of production, including the following: (1) Variable costs of irrigation; (2) variable costs not directly associated with irrigation operations; and (3) capital and other fixed costs of production. The second and third cost categories were of greater importance to the analysis than were the direct costs of irrigation. Estimates of average 10‐year incomes were derived from farm data. Based on these estimates, farms that were practicing deficit irrigation achieved lower net incomes per hectare but higher net incomes per unit of applied water than the fully irrigated farms. This suggests that their irrigation practices were nonoptimal, but that they were benefiting financially from deficit irrigation.

Conjunctive use of surface water and ground water can usually increase yields at lower costs than more dams and reservoirs operated separately. There are three main types of conjunctive use projects: (1) Stream diversions; (2) dam and reservoir only; and (3) total system. There are many advangates of ground‐water storage compared with surface storage, and of conjunctive use compared to independent use. Physical, operational, financial, and institutional constraints may be encountered by the project proponents. Institutional issues may be the most difficult to resolve. Often, several governmental agencies may provide funds and have responsibilities for various features of conjunctive‐use projects. Implementation is more difficult in countries where surface‐water development has historically dominated water‐supply project formulation. Court decisions in California have provided guidelines for conjunctive‐use programs, especially in defining the rights of public agencies. Four areas in California that have experienced basin overdraft and increasing water demands, and where conjunctive‐use operations have been implemented, are described.

Low‐discharge, portable irrigation modules can contribute to the modernization of water management systems. Various types of irrigation modules have been developed for specific uses but are not suitable for use at the farm level. This paper, is devoted to the design, development, and testing of low‐discharge, portable Baffle‐Sluice modules with discharges in the range of 2–7 L/s for use on farms in field channels. The flow‐regulating characteristics of such modules are discussed in detail in order to assess their performance. The modules can deliver discharges within $\pm 5\%$ of design values with head variations in a range between 15 and 25 cm. The beauty of the module is that it is devoid of moving parts, and accumulation of silt within the confine of the structure is not a problem. Considering portability, the length of each module can be restricted to 50 cm. On the whole, the Baffle‐Sluice module possesses all the desirable features of a good module.

A new mathematical solution was developed for the constant-discharge boundary condition for one-dimensional horizontal flow under nonsteady conditions in a semi-infinite leaky aquifer. The solution can be used to calculate aquifer drawdowns due to discharge into a line sink as a function of the aquifer parameters transmissivity, leakance, storage coefficient, and distance from the line sink and time since the discharge began. The solution is in the form of exponential and complementary error functions, and the polynomial approximation to the solution is easier to use, computationally, than an existing integral-form solution that requires numerical integration. In the solution, the discharge into the line sink is derived from artesian storage in the aquifer and from vertical leakage through the confining bed from a source bed that is at constant hydraulic head. As an example of its use, the solution could be used to analyze the results of a canal pumping test. In this application, aquifer parameters could be determined by analyzing transient drawdowns that resulted from abruptly lowering the canal water level by means of a constant pumping rate in a canal that incised a confined leaky aquifer.