Journal of Irrigation and Drainage Engineering

Hydrologic modeling of storm water impoundments is an effective tool in evaluating different water management options for addressing regional water issues in Florida. However, modeling impoundment water dynamics could be challenging because of the difference in scale between canals and the entire impoundment. Water pumped into the impoundments is first discharged into canals inside the impoundments, which distributes the water. The canal eventually overflows and water floods all the impoundment. Two modeling approaches to simulate this process were tested on two impoundments using the integrated MIKE-SHE and MIKE 11 model. The first approach simulates the one-dimensional flow in the canal in a link-node model; and once water floods, it is modeled as two-dimensional flow. The second approach simulates the entire impoundment as a canal. In both impoundments, Modeling Approach 1 resulted in overestimation of peaks and poor results. Modeling Approach 2 showed considerable improvements in the results and a satisfactory match between observed and simulated water levels. The difference is attributed to the difficulty in representing the canal flooding process in hydrodynamic models.

The Food and Agriculture Organization of the United Nations (FAO) has proposed using the Penman–Monteith (FAO-56 PM) method as the standard method for estimating reference evapotranspiration $\left({\mathrm{ET}}_0\right)$ , and for evaluating other methods. The basic obstacle to widely using this method is the numerous required data that are not available at many weather stations. The maximum and minimum air temperatures constitute a set of minimum data necessary for the estimation of ${\mathrm{ET}}_0$ . The basic goal of the paper is to examine whether it is possible to attain the reliable estimation of ${\mathrm{ET}}_0$ only on the basis of the temperature data. This goal was reached by the evaluation of the reliability of four temperature-based approaches [radial basis function (RBF) network, Thornthwaite, Hargreaves, and reduced set Penman–Monteith methods] as compared to the FAO-56 PM method. The seven weather stations selected for this study are located in Serbia (Southeast Europe). The Thornthwaite, Hargreaves, and reduced set Penman–Monteith methods mostly underestimated or overestimated ${\mathrm{ET}}_0$ obtained by the FAO-56 PM method. In this study, methods were calibrated using the standard FAO-56 PM method. However, the RBF network better predicted FAO-56 PM ${\mathrm{ET}}_0$ than calibrated temperature-based methods at most locations. It gives reliable results in all locations and it has proven to be the most adjustable to the local climatic conditions. These results are of significant practical use because the adaptive temperature-based RBF network can be used when relative humidity, radiation, and wind speed data are not available.

Simulation models for unsteady open channel flows have been commercially available for more than 2 decades. Most of these models are now available for personal computers and can be used to study the control of irrigation canals. Studies on automatic control methods and algorithms have been performed on at least half a dozen of the available unsteady-flow simulation models. Although, many of these automation studies have been conducted by the institution that created the simulation model, these simulation models were not created with automatic gate control in mind, and thus one has to be intimately familiar with the source code in order to implement sophisticated control features. Three commercially available unsteady-flow simulation software packages that allow automatic control of gates based on algorithms written by users are: CanalCAD from the Univ. of Iowa, Hydraulics Lab; Mike 11 version 3.2 from the Danish Hydraulic Institute; and Sobek from Delft Hydraulics. In this paper, we describe the various features of these unsteady-flow simulation packages and how they interface to control engineering software/code. There are a number of tradeoffs between simplicity and functionality. All these models present difficulties and have limitations. The hope is to provide guidance on the next generation of unsteady-flow canal simulation models so that control functions can be routinely applied.

Irrigation has become commonplace for residential homeowners desiring high quality landscapes in Florida. The goal of this project was to document irrigation system uniformity in Central Florida and to quantify distribution uniformity of residential sprinkler equipment under controlled conditions. The catch-can testing procedure used was a modified version of both the American Society of Agricultural Engineers standard and Florida Mobile Irrigation Laboratory (MIL) procedures. The modified version included a larger sample size to ensure complete sample collection over the entire irrigated area. The standard MIL procedure may overestimate the uniformity for residential systems. From the tests on residential irrigation systems, the average low quarter distribution uniformity $\left({\mathrm{DU}}_{\mathrm{lq}}\right)$ value was calculated as 0.45. Rotary sprinklers resulted in significantly higher ${\mathrm{DU}}_{\mathrm{lq}}$ compared to fixed pattern spray heads with 0.49 compared to 0.41, respectively. From uniformity tests performed on rotor and spray heads under ideal conditions, rotor heads had more uniform distributions than the spray heads of 0.55 compared to 0.49, respectively. Spray heads had better uniformity when fixed quarter circle nozzles were used as opposed to adjustable nozzles. Both residential irrigation system and controlled tests resulted in $\left({\mathrm{DU}}_{\mathrm{lq}}\right)$ at the low end of industry guidelines. Residential irrigation system uniformity can be improved by minimizing the occurrence of low pressure in the irrigation system and by ensuring proper spacing is used in design and installation.

In previous analytical approaches, the direct calculation of friction loss along a lateral is usually based on empirical power-form flow resistance equations, such as the Hazen–Williams and Blasius equations. The more generalized Darcy–Weisbach resistance equation is not usually applied since its friction coefficient varies along the lateral. In this paper, initially, the Darcy–Weisbach and Hazen–Williams equations are systematically compared, leading to a correction form for the Hazen–Williams coefficient. In addition, a more accurate procedure assuming a power function form for the Darcy–Weisbach equation along irrigation laterals is also proposed. The systematic analysis of various typical flow pipe irrigation situations (e.g., sprinkler irrigation laterals of linear or radial-center pivot displacement, trickle irrigation laterals, and manifolds) indicates that the friction loss along laterals calculated using the Darcy–Weisbach equation closely follows a discharge-power form function. The two empirical parameters of the power function depend on the specific pipe characteristics as well as the specific range of discharge values along the lateral. The proposed analytical solution is extended to incorporate the local head loss, the velocity head variation, and the outflow nonuniformity along sprinkler and trickle irrigation laterals. The suggested direct computation solution is demonstrated in two application examples of sprinkler and trickle irrigation laterals and compared with accurate numerical solutions.

This paper presents a model to estimate the soil salinity for different on-farm management strategies under irrigated conditions. It is based on research in the Maniçoba irrigation scheme in northeast Brazil, where upward flow from the shallow water table is the main cause of soil salinization. The model calculates soil water and salt balances for the topsoil. It is calibrated for the topsoil of abandoned plots and for the root zone $\left(0.9\mathrm{m}\right)$ of mango trees. Simulating the effect of different management scenarios on soil salinity may help to organize the switch from intensive surface irrigation to more efficient irrigation practices.

Cumulative infiltration was computed as a function of time-varying ponded water depths using a Green and Ampt analysis. The input water depths were field-measured values from two irrigation events on Superstition sand, one from a basin and one from a border. For both types of irrigation, the computed cumulative infiltration at a given measuring station was nearly the same whether using a variable head input or a constant (average) head during the time of opportunity. As an example, at the first measurement station for the basin event, the ponded depth went from a 0 to 9 cm depth over the 2–12 min. from the time water was introduced into the basin; this was followed by a decrease to a depth of 4 cm at 60 min. The computed infiltration using the depth hydrograph was 14.3 cm compared to 14.1 cm when using an average depth. A smaller value of 13.7 cm is found using the appropriate time of opportunity with a field averaged depth and a considerably smaller value of 12.4 cm was found when a zero-depth boundary is considered. Basin and border uniformities were also computed based on variable and different constant depths and the results were found to be reasonably robust whether infiltration is computed using a variable or an appropriate constant ponded depth.

The Jordan Valley is one of the primary regions for growing winter crops of fruit and vegetables in Israel and Jordan. Control of water management in these fields is obtained by solid-set irrigation systems and subsurface drainage. Detailed field observations were conducted at a location near the Jordan River, south of Lake Kinneret. Water table heights were measured by approximately $100\text{piezometers}$ . An exiting wide spacing $\left(160\mathrm{m}\right)$ subsurface drainage system was monitored and the total drainage discharge from this regional drainage system to Lake Kinneret was measured. Rainfall, irrigation, and evapotranspiration rates were measured and overall hydrological balance was conducted. The old irrigation method in the region was border irrigation with very high leaching fraction and poor irrigation efficiency. During the 1970s the irrigation method was changed to computer operated drip irrigation. The leaching fraction was reduced and irrigation efficiency increased. Reduction of the total drainage discharge to Lake Kinneret by a factor of about 10 was observed. Water table rise under hand moving sprinkler and soil-set drip irrigation methods were measured and compared for assessment of salinization of the root zone by upward movement of groundwater. The result indicates the strong effect of irrigation time interval on the extent of these rises. The effect of irrigation mode on the extent of water table rises was measured at the field by comparing that under hand moving sprinkler irrigation to that under water solid set drip method. This effect depends, among other variables, on the irrigation time interval, a fact which complicates prediction of water table rise under different irrigation practices. These field results support previous theoretical analysis by the writers and highlighted the interrelationship between irrigation practice and drainage design. The effect of water table drawdown towards the Jordan River was monitored and found to be about 4.6%. The strong influence of the Jordan River on water table height at the drained field is magnified by the existence of sandy layers in the soil profile. This observed gradient may be used for the estimation of lateral seepage flow from the irrigated agricultural field towards the adjacent Jordan River. This study provides a useful source of data for future studies in similar situations.

The application of theory developed for direct integration of gradually varied flow equations to uniform and critical flow computation greatly reduces the computational effort. A small generalized subroutine is able to compute accurately the various parameters involved in the computation for all types of natural and constructed cross sections. Although the equations are implicit, in a majority of cases the number of iterations needed to achieve the required accuracy is less than 3. The method is even useful for computation by hand held calculators.

A comparative analysis of the distribution uniformities of infiltrated water depth in blocked end furrows between three irrigations with increased-discharge (IDI) and three irrigations with constant flow rate (CFI) is presented. The goal is to evaluate IDI irrigation contrasted to CFI irrigation, which is the most commonly used in underdeveloped countries. The average distribution uniformities of IDI irrigation is 9% higher than that of CFI irrigation. Therefore, IDI irrigation is a viable alternative of efficient irrigation in blocked end furrows. Field assays were performed in $290\mathrm{m}\text{long}\times 0.75\mathrm{m}\text{wide}$ , 0.6% slope furrows in clay loam.

Despite the importance of overland time of concentration on the design discharge, engineers are often bewildered by the array of formulas available in the literature without knowing the accuracy of each formula. This assessment covers nine formulas published between 1946 and 1993, which are intended for overland flow only that is subjected to uniform rain. The assessment compares the estimates from the formulas with experimental values that are derived under the same conditions for two surfaces: concrete and grass. The assessment shows that formulas that do not account for the rainfall intensity are only valid for a limited range of rainfall intensities. The formulas that account for the rainfall intensity generally show better agreement with the experimental data. Finally, the assessment gives two rankings of the formulas for the two surfaces in accordance to their accuracy as compared to the experimental data. The formula that has the best accuracy for both surfaces is the Chen and Wong formula.