Journal of Irrigation and Drainage Engineering

Previous research in the estimation of surface irrigation parameters from advance time or surface profile observations has focused on the development of solutions for parallel surface flow conditions. This study was conducted to assess the usefulness of a polar model simulating radial flow in the estimation of infiltration and roughness parameters of a point-inflow level-basin irrigation event. The two-step explicit McCormack scheme was applied to the solution of the governing equations. The method of characteristics was used at boundary nodes. Point-wise semiimplicit discretization of the friction and geometric source terms was used. Results of this model compared well with those obtained with a two-dimensional Cartesian model simulating radial flow. Gradient and nongradient minimization techniques were applied to determine pairs of infiltration and roughness parameters. The estimation of the parameters is as feasible for radial flow as it is for parallel flow.

The time-rated infiltration families proposed by Merriam and Clemmens were further developed and evaluated using infiltration data for noncracking soils. Infiltration experiments were monitored, using a double-ring infiltrometer, at 10 field sites in New South Wales (NSW), Australia. Published infiltration data for soils in Botswana were also included to extend the range of soil types and field conditions in the study. A methodology was developed for identifying the infiltration family of soil at a given field. The time-rated infiltration family concept along with the methodology developed was evaluated under a range of field conditions. For 80% of field situations, the error introduced in infiltration characteristics due to the use of the family concept is <35% with an average value of the error about 20%. The infiltration characteristics of soil at a given site in this study exhibited a high variability although the measurements were made only a few meters apart. This observation reinforces potential benefits of using infiltration family concepts in the design and management of irrigation systems.

The bottom opening is a standard structure in storm sewers, provided the approach flow is supercritical. Based on extended experimentation and by using the governing flow equations, the hydraulic characteristics of bottom openings were derived. These include the approach reach, the end depth ratio, the average discharge coefficient, the tailwater depth, and the hydraulic loss across the outlet. Further, velocity distributions in the outlet zone are discussed. The results of this study reveal that the approach Froude number has a significant effect on the flow mechanism. General expressions are derived for the lower and upper nappes of the flow across the bottom opening, and a hydraulic design procedure is described. A generalized streamwise coordinate is also introduced that allows description of supercritical sewer flow. It is demonstrated that the excess discharge to the treatment station under design discharge is within the requirements of European standards.

The mathematical expression of the modified Penman equation requires values for the adjustment factor C, the saturation vapor pressure and its slope with respect to air temperature, the extraterrestrial radiation, and the maximum sunshine duration, among others. The values of these parameters are measured, taken from tables, or estimated from analytical expressions. Using tables is cumbersome and introduces uncertainties in estimating the parameters. Various research works found in the literature refer to the analytical evaluation of these parameters, but the need to more accurately calculate them is essential since errors introduced in evapotranspiration estimates are sometimes quite significant. In this paper, mathematical expressions that describe the parameters used for the calculation of the Penman reference crop evapotranspiration are derived through a nonlinear regression procedure. Comparisons of these expressions to those found in the literature show that they undoubtedly give more reliable results.

An analytical solution is obtained for estimation of seepage from a canal to symmetrically placed drainages founded on infinite pervious soil medium with uniform infiltration from the free surface zone. Integral equations are obtained by using Zhukovsky's function, a special function, and the Schwarz-Christoffel transformation. These equations are then solved numerically to obtain the value of seepage loss and profile of the free surface. Results are obtained for different values of parameters such as canal width, the distance between the canal and drainages, depth of drainages below canal level, infiltration rate, etc.; and the same are presented in the form of graphs, showing the effect of these parameters on the seepage discharge and the free surface profile. Nomographs are also prepared for easy evaluation of canal seepage discharge.

Infiltration parameter estimation (IPE) is a simulation model of furrow irrigation that allows us to estimate infiltration parameters in real time. The model calculates infiltration parameters from measured advance times in the field using a kinematic wave model that includes spatial and temporal variability of infiltration due to variations of the wetted perimeter. The model then calculates cutback inflow rates to reduce runoff and the irrigation application time as a function of the required water depth. Thus, real-time irrigation control and management by the IPE model leads to better irrigation application efficiencies.

An investigation of the automated, downstream control of sloping-top canals using an idealized controller is presented here. The case for an idealized formulation of canal control is given and a simplified, idealized control scenario is derived for use in this research. The investigation mainly includes (1) examination of canal control dynamics to determine a given pool's underlying, inherent controllability, and how one might then manipulate pool-end gates to meet canal control objectives; (2) derivation of an idealized-control methodology; and (3) examination of a canal's control opportunities given its inherent-controllability indices and implementation of the idealized controller. Comparisons are made with other downstream control methodologies. The transition to a field-worthy controller is considered. Application of the inherent-controllability indices and the idealized controller to a given canal offers an expedient, cost-effective means of obtaining insight into site-specific control options prior to further research, or to the design and deployment of a field-worthy controller.

Effect of water table depth and rainfall timing on bromide and nitrate transport was investigated using large undisturbed columns (30 cm in diameter and 90 cm long) obtained from Rossburg silt loam and Clermont silt loam soils. Three water table treatments and two time delays (the time interval between chemical and water applications) were used to simulate a range of saturated conditions in the soil profile and rainfall timing. Water was applied for 60 d at a rate of 970 mL/d, equivalent to a daily rainfall of 13.3 mm, using an automated irrigation system. Discharge from the water table control pipe at each column was sampled for bromide and nitrate concentration. Findings from this study include: (1) water table depth significantly affected bromide and nitrate breakthrough patterns and nitrate recovery; (2) water table depth and time delay interactively affected nitrate transport; (3) soil type was not a significant factor in this case; and (4) bromide and nitrate had similar breakthrough characteristics, yet the relative concentration of nitrate was consistently lower than that of bromide.

This paper describes the development of an artificial neural network (ANN) model to simulate fluctuations in midspan water-table depths and drain outflows, as influenced by daily rainfall and potential evapotranspiration rates. Unlike conventional models, ANN models do not require explicit relationships between inputs and outputs. Instead, ANNs map the implicit relationship between inputs and outputs through training by field observations. Compared with conventional models, the ANN model requires fewer input parameters since the inputs that remain constant are not considered by ANNs. Therefore ANNs can be executed quickly on a microcomputer. These benefits can be exploited in the real-time control of water-table management systems. The model was developed using field observations of water-table depths from 1991 to 1993 and drain outflows from 1991 to 1994 made at an agricultural field in Ottawa, Canada. The root mean squared errors and standard deviation of errors of simulated results were found to range from 46.5 to 161.1 mm and 46.6 to 139.2 mm, respectively, thus showing potential applications of ANNs in land drainage engineering.

This paper presents our research on the issue of water rights to return flow from irrigation of urban landscapes. Municipalities in Colorado's Front Range, with rights to transmountain water and other “use to extinction” water rights, have begun to examine lawn irrigation as a possible source to augment their supplies. They claim that a significant percentage of water applied to lawns is not used by the turf grass, and eventually returns to the streams and ground-water systems. In accordance with their water rights, this deep percolation water can be reused by the municipalities. This paper reviews the methodologies used by various cities to estimate deep percolation and return flow as a function of applied water. It then analyzes how these findings were evaluated by the Water Courts in their decisions concerning credits for return flow. To provide an independent analysis of the irrigation–return flow relationships, research was recently conducted at the Colorado State University (CSU) (1992–96). The CSU research results indicate that the small lysimeters used by various cities are of acceptable accuracy compared to a large lysimeter and standard evapotranspiration equations for estimating consumptive use. For estimating deep percolation, results of this research support the findings of the previous studies conducted for the city of Colorado Springs and for the Cottonwood Water and Sanitation District in Denver.

The volume balance (VB) algebraic equations based on the power advance assumption (i.e., the time invariance of the subsurface shape factor) may deviate significantly from accurate VB numerical solutions. By systematic analysis of the accurate VB numerical solutions obtained using the Kostiakov infiltration formula, the behavior of the subsurface shape factor as a function of time is examined. A new equation describing the time variation of the subsurface factor is derived. Using dimensionless analysis the new VB algebraic equation is demonstrated over the practical range of variation of surface irrigation parameters. The validation of the new VB equation is extended to infiltration formulas of any mathematical form. Comparison tests indicate that the suggested VB equation is more accurate than previous equations that assume time invariance of the subsurface factor.

In application of the volume balance (VB) models, it is generally assumed that the average depth of surface water is constant. This basic assumption may cause significant errors in computing advance. In this paper an accurate algebraic VB equation is developed to predict the advance phase in surface irrigation. In the suggested analysis the average surface water depth is considered to be variable in time. By systematic analysis of accurate kinematic-wave (KW) numerical solutions, the behavior of the surface profile shape factor used in the VB equation is examined. A new equation describing the time dependence of the surface shape factor is derived. Comparison tests indicated that the suggested variable surface shape factor VB equation produces essentially the same results as the KW numerical method. The suggested equation is improved for the case of level or low sloping borders.

Overtopping of embankments during floods leads to a spatially varied flow (SVF). In order to estimate the water surface profiles and the amount of water spilling over the embankment for a given steady-state flow condition, a mathematical model for SVF over a broad-crested weir is formulated. The mathematical model is tested for accuracy using laboratory experiments. The computed water surface profiles and the discharge estimates are within 3 and 10%, respectively, of the experimentally observed values.