Journal of Irrigation and Drainage Engineering

A hydrological water‐balance model used for the Nanni swamps in Surinam is adjusted and applied to a similar swamp in coastal Guyana. A water balance study was performed in Guyana on two water conservancies; the Boe rasirie water conservancy and the East Demerara water conservancy. For the Boerasirie water conservancy the model is calibrated on a daily basis using the Boerasirie Conservancy Board records of 1987. The model calculates water levels using rainfall, evapotranspiration, agricultural use, and spill over different weirs. Calculated and measured water levels are compared, and parameters in the model are adjusted to minimize the difference. The conclusion is that the adjusted model gives results for the situation in Guyana over a wide range of water levels.

A complex‐variable method and series expansions are applied to optimal‐shape design problems for a channel bed. A dimensionless depth of a trapezoidal and rectangular channel is determined by minimizing the cost function constrained by specified hydraulic characteristics. The cost function includes seepage losses and the cost of lining. The hydraulic constraints are cross‐sectional area, the hydraulic radius, and the discharge. The problem of steady‐state two‐dimensional seepage involves determination of a phreatic surface with geometrical parameters as control functions. The extremes found are stable for minor perturbations of channel shape. The optimal criterion value for trapezoidal channels is close to Preissmann's for an arbitrary bed outline. The including of supplementary factors (the cost of evaporating water, of the channel land area, and so on) as criteria are discussed.

The growth of plants in an irrigated area is described as healthy or unhealthy, a two‐state process that depends on the moisture status of the soil. Probability distributions of the soil moisture deficit (SMD) and the critical soil moisture deficit (CSD) are derived by adopting a hydrological hazard function. Evapotranspiration, crop, and rainfall data from numerous locations within East Anglia, England, are used in a case study. Following water‐balance studies, crop and land‐weighted values of SMD are computed from the data, and the CSD is related to proportional yield reduction. The SMD and CSD are well represented by truncated Weibull distributions, as shown in the model development. Approximation by the exponential distribution is not statistically justifiable. Estimated parameters for different locations have low standard deviations and are not, in general, significantly different. Using regionally averaged parameters, the risks of yield reductions can be evaluated for planning purposes.

Canal adequacy, identified with discharge accuracy and the ability to convey that discharge, is investigated. Calibration techniques for canal design criteria are proposed using field data. The data are from two stable main irrigation canals in Sudan and Egypt. One is silting and the other is eroding. The techniques for discharge calibration of hydraulic structures suggested in this paper and the development of rating curves from currently available data is not new in hydraulic literature. They do, nevertheless, suggest a break from the type of rating curves presently in vogue. Attempts to modify the stream‐power design criteria of stable alluvial channels are outlined. To design a new stable canal section, nested iterations can be used to solve for the width and depth. Discharge, side slopes z, and $D_{84}$ are used as input parameters. For canal stability, the sediment transport rate used here is treated as a dependent variable. The procedure can be interpreted for canals with similar conditions.

One of the problems in high capacity pumping stations (called crossover pumping stations in Russia is controlling the pump discharge as a function of the difference in demand and actual flow. This paper presents a mathematical model that enables the design engineer to optimize the parameters early in the design process, thereby overcoming large corrections later on.

Rice soils are generally characterized by heavy textures, poor structures, low porosities and permeabilities, shallow traffic pans, and slow rates of drainage. Crop growth and yields of upland (i.e., nonrice) crops in these soils are adversely affected because of restricted root aeration and development. Under these conditions, irrigation of nonrice crops poses serious problems because of the low air porosity and the tendency of the soil to waterlog. A high‐frequency basin irrigation method for nonrice crops in rice soils is developed. It is based on a computer solution of the Lewis and Milne surface irrigation volume balance equation by numerically inverting the Laplace transform of the equation. The method provides an optimum design for the alleviation of the soil‐related adverse effects while enabling a high application efficiency and uniformity. The method is field‐tested in three different fields, in which 0.330, 0.326, and 0.374 m of water are applied in 8, 7, and 10 low‐volume irrigations, respectively. Overall application efficiencies of 90.9%, 92.3%, and 93.6% are achieved, routinely exceeding the design application efficiency.

A numerical investigation of artificial recharge in multilayered, anisotropic, unconfined porous media is performed for radial flow configuration. The numerical studies, carried out with a saturated‐unsaturated flow model, include the simulation of experimental observations previously documented. The numerical analysis considers the effects of the initial depth of saturation, source geometry, anisotropy as well as material property, and the ratio of equivalent hydraulic conductivity between layers. Once the geometry of the flow region is fixed, the shape of the flow domain and the quantity of flow are determined for any multilayered isotropic‐anisotropic system. For the control series of two cases studied, free‐surface locations closely match the experimental observations. The recharge zone configurations are evaluated by determining the source aspect ratio. In multilayered anisotropic systems, a higher degree of anisotropy results in a greater inflow and a higher position for the free surfaces, when the degree of anisotropy is greater than one. When the recharge is to be accomplished by an infiltrometer, steady‐state flow occurs after a substantial amount of time. This study indicates that the ratio of percent increase in flow rates and percent increase in infiltrometer radii approaches unity.

Estimation of evapotranspiration is a key requirement of hydrologic balance studies and climate analysis. The study reported involved collection of precise weighing lysimeter and meteorological data from three sites representing distinct climates. The combined data set for daily amounts of evapotranspiration and meteorological variables covers a total of 19 years on either an annual or growing season basis. The pan evaporation, Priestley‐Taylor, original Penman, and Penman‐Monteith evapotranspiration estimating methods are compared with lysimeter measurements using a moving average of 1–30 days. The results indicate the applicability of the various methods as a function of climate regime and the reduction in standard error of the estimate and increase in the coefficient of determination as a function of length of the moving average period. The results can be used both to determine which methods are most applicable for different climates and the expected magnitude of the error as a function of the estimating interval. This study indicates that a 5–10‐day moving average can reduce the standard error of the estimate and increase the coefficient of determination significantly between estimated and measured reference evapotranspiration for several estimating methods for various climates.

Conservation tillage systems help to maintain residue materials from the previous crop on the soil surface. The potential for serious erosion may exist if crop residues are removed by overland flow. This study is conducted to identify the hydraulic conditions required to initiate residue movement by overland flow. Corn, cotton, peanut, pine needles, sorghum, sunflower, and wheat residue are placed in a flume on smooth and sand surfaces, and flow is then introduced in progressive increments. The discharge rate and flow velocity required to initiate residue movement are identified. Hydraulic measurements are used to calculate the ratio of critical flow depth to residue diameter, critical Reynolds number, critical shear stress, dimensionless shear stress, and boundary Reynolds number. Regression equations are developed to relate dimensionless shear stress to boundary Reynolds number. Close agreement is found between predicted and actual dimensionless shear stress. If residue diameter is known, the regression equations can be used to estimate the beginning of motion for other residue materials. Information obtained in this study can be used to help identify proper residue management practices for conservation tillage systems.

Most of the available methods for roughness prediction assume that the flow is steady and uniform, and many of them are laboratory-oriented and lack verification with field data. Three existing roughness prediction formulas are tested against measured field data. The data used are for three main alluvial irrigation canals with discharges ranging from 35 to 318 m³/s and a reach of the Nile River located 80 km downstream from the High Aswan Dam, Egypt. Roughness equations include the Engelund-Hansen roughness predictor and the Manning-Strickler and Colebrook-White equations with the equivalent roughness determined by the van Rijn method. The computed values of roughness, however, deviate significantly from the measured values except for very few cases. The test results clearly demonstrate how difficult the prediction task is, and show that prior to the use of any formula, calibration against local data is essential.

Long-throated flumes and broad-crested weirs are becoming widely used for open-channel flow measurement, primarily because of their simplicity and numerical predictability. These flumes and weirs are constructed such that flow in the throat or crest is nearly parallel, i.e., no streamline curvature. Under these conditions, standard critical depth relationships apply (i.e., hydrostatic pressures). Design is based on determining the amount of contraction from the approach section to the throat that is needed to produce critical flow. The existing design procedure is to determine an acceptable contraction amount by trial and error. In this paper, mathematical relationships are developed for precisely determining the amount of contraction needed. These relationships are solved with a convergent-iterative procedure. Several new relationships for critical flow are also developed.

One-dimensional horizontal flow in a semi-infinite confined aquifer can be described in terms of mathematical solutions that relate the drawdown to aquifer parameters and the aquifer flow rate. A new analytical solution, that considers the effects of storage in a finite-width sink into which flow occurs from the aquifer, was developed for the nonleaky aquifer case. The solution is written in the form of exponential and complementary error functions, and a drain function is defined based on the solution. A type curve for the drain function is plotted, and aquifer parameters can be determined by matching drawdown data from observation wells to the type curve. Applications of this drain function and type-curve matching procedure would include analyzing aquifer drawdowns resulting from a canal pumping test, in which a significant part of the discharge from the canal was derived from water stored in the canal as well as from discharge from a nonleaky aquifer into the canal.