Journal of Irrigation and Drainage Engineering

Multi‐objective linear programming models have been formulated to evaluate the water management strategies for salinity control. The water management strategies essentially aim at minimizing irrigation return flow (IRF) through structural rehabilitation of the irrigated system. The models have been applied to a part of the area irrigated by the Bhakra Canal System (BCS) in Haryana, India. The optimal management strategies at a 70% reduction in IRF include: (1) Improving surface water application methods through precision land leveling and better design of irrigation layout (46%); (2) groundwater pumping by shallow tubewells from fresh and marginally saline aquifers (28%); (3) the lining of government controlled canals in Stage I (14%); and (4) the introduction of a combination of surface and sprinkle irrigation methods in the ratio 75:25% (12%). Appreciable increase in benefits from IRF reduction up to 70% is possible, without any increase in investment, if cost‐minimizing strategies are substituted by those maximizing benefits under the constraint of minimized cost. However, for the complete elimination of irrigation return flow, capital investments will have to be substantially enhanced. The sensitivity analysis in respect of cost $\left(c_i\right)$ and benefit $\left(B_i\right)$ coefficients indicated that the optimal plan was not very sensitive to changes in the range of $\pm 20\%\text{.}$

Practical methods for land grading design of a plane surface for rectangular and irregularly shaped fields based on a least squares analysis are presented. The least squares procedure leads to a system of three linear equations with three unknowns for determination of the best‐fit plane. The equations can be solved by determinants (Cramer's rule) using a procedure capable of solution by many programmable calculators. The detailed computational process for determining the equation of the plane and a simple method to find the centroid location of an irregular field are also given. An illustrative example and design instructions are included to demonstrate the application of the design procedure.

The feasibility of using ground‐penetrating radar (GPR) in coarsetexture soils to determine depth to the water table was demonstrated in separate studies in Massachusetts and Florida. In Massachusetts, two sites were chosen to demonstrate the application of GPR techniques for water‐table depth investigation in a topographically diverse setting. In Florida, a site was selected to demonstrate the accuracy of measurements made from GPR profile and the water‐table distribution over a study area. The difference between water‐table depths from observation well data and radar profile was within 10 cm in all samples. The coefficient of determination, $r^2\text{,}$ between the well and the radar data was 0.90.

Knowledge of the distribution of the raindrop sizes during a storm is important in many engineering applications. Since drop size information is usually expressed parametrically, it is important that the proper model to describe the distribution be used. On the basis of observed frequencies, the lognormal and upper limit distributions were tested on raindrop size data taken from different sites in the U.S. and for different rainfall rates. After estimating parameters by the method of maximum likelihood, the Kolmogorov‐Smirnov test indicates that the lognormal distribution provides a better representation than all the other models examined.

The theory of lateral flow through a two‐dimensional channel outlet is used to derive an expression for the outflow through a trapezoidal lateral weir discharging from a trapezoidal channel. The analysis is an extension of the existing hydrodynamic model for lateral flow through a rectangular weir located in the side of a rectangular channel. The weir discharge coefficient is expressed as a function of a parameter relating the geometry of the weir and the channel and a parameter denoting the ratio of the mean velocity of the channel to the resultant jet velocity of the weir flow. Experimental results are provided to validate the proposed expressions for the weir discharge coefficient.

The FAO Blaney‐Criddle (FAO‐BC) evapotranspiration equation was calibrated and tested against a Penman combination equation with local wind function and daily lysimeter measurements of alfalfa evapotranspiration. Agreement between the calibrated FAO‐BC method and lysimeters was excellent for daily, weekly and monthly estimates when measured values for solar radiation, air temperature, relative humidity and wind speed were used. An elevation correction reduced scatter in estimates among Idaho locations. Statistics describing the daily Penman and FAO‐BC estimates deviated from those calculated for measured alfalfa reference evapotranspiration. Air temperature and relative humidity data for nonagricultural weather stations were adjusted according to fetch and aridity before being used to estimate consumptive use requirements throughout Idaho. Calibration of the FAO‐BC allowed use of alfalfa‐based crop coefficients.

Various components of hydrologic cycle, e.g., rainfall, runoff, seepage, soil moisture and evapotranspiration (ET) were measured daily in a soybean plot, grown in a weighing‐type lysimeter consisting of a $120\mathrm{cm}\times 120\mathrm{cm}\times 120\mathrm{cm}$ undisturbed soil monolith and sensitivity of 0.14 mm of water. Soil was always kept at more than 75% of the total available soil moisture by rainfall or irrigation. Soybeans of 17 weeks duration, received 923 mm rainfall, 12 mm dew and 99 mm irrigation, and yielded 378 mm runoff, 190 mm deep percolation averaged for two crop seasons. There was a net gain of 71.5 mm soil profile recharge during 1981 and depletion of 29.4 mm during 1982. Average seasonal ET was 545 mm. The water use efficiency was 63 kg/ha‐cm grain with 3,419 kg/ha grain yield. The correlations of rainfall with runoff and seepage were significant. Water need after the ninth week of crop growth was jointly met from rainfall, soil moisture, and irrigation.

The empirical Lewis‐Kostiakov intake equation takes a power form in an algebraic equation that explicitly relates the cumulative infiltration depth, d, to the intake time, t, as $d={\mathrm{kt}}^n\text{,}$ in which k and n are the empirical constants. Although users of this well‐known intake (infiltration) equation are convinced that k and n have physical meanings, this equation is still regarded as empirical. This paper presents the physical derivation of the Fok power‐law infiltration equations to enable the interpretation of the physical meanings of k and n according to the infiltration time zones.

This paper describes a numerical model for irrigation of sloping and level borders. The model solves the differential form of the combined equations for the conservation of mass and momentum with the acceleration terms removed. A finite difference scheme is used with the depth gradient term expressed explicitly and averaged over the entire wetted border. The model is stable and inexpensive to run. Model results compare well with measured advance and recession times. Predicted ponding depths during infiltration and total water infiltrated over the border also agree well with observed behavior. The model gives results equivalent to those of other existing zero‐inertia and fully dynamic models but is much simpler to program and requires less computer code.