Journal of Irrigation and Drainage Engineering

Modeling evapotranspiration (ET) distribution in shallow water table environments is of great importance for understanding and reproducing other hydrologic fluxes such as runoff and recharge. Unfortunately, ET distribution can be the most difficult hydrologic process to analyze. The partitioning of ET into upper zone ET, lower zone ET, and groundwater ET is complex because it depends on land cover and subsurface characteristics. One comprehensive distributed parameter model, integrated hydrologic model (IHM), builds on an improved understanding and characterization of ET partitioning between surface storages, vadose zone storage, and saturated groundwater storage. It provides a smooth transition to satisfy ET demand between the vadose zone and the deeper saturated groundwater. In this paper, the IHM was used to analyze ET contribution from different regions of the vadose zone and saturated zone. Rigorous testing was done on two distinct land covers, grass land and forest land, at a study site in West-Central Florida. Sensitivity analysis on the key parameters was investigated and influence of parameters on ET behavior was also discussed. Statistics with the root mean square error and mean bias error for forest total ET were about 1.46 and 0.04 mm/day, respectively, and 1.61 and 1.07 mm/day for grass total ET. Modeling results further proved that ET distributions from the upper and lower soil and water table, while incorporating field-scale variability of soil and land cover properties, can be predicted reasonably well using IHM model.

A practical method for developing rainfall-intensity equations for short durations (approximately one hour or less) for locations in the United States covered by NOAA Atlas 14 Volumes 1, 2, 3, and 4 is presented. For the semiarid western United States covered by Volume 1, for Puerto Rico and the U.S. Virgin Islands covered by Volume 3, and for Hawaii covered by Volume 4, single formulas apply to rainfall of all average recurrence intervals (ARIs). For the central and mid-Atlantic regions of the United States covered by Volume 2, formula coefficients are provided for several ARIs ranging from 1.58 to 1,000 years. All equations are based on a single-term exponential expression plus a constant that provides excellent fits to the available data. Mathematical expressions for the central and mid-Atlantic region coefficients as functions of the ARI are provided to simplify application of the approach. Mathematical relations representing design storm hyetographs are developed using the intensity-duration expression by distributing rainfall about the time of peak intensity proportioned by a factor $r=t_p/t_d$ , where $t_p=\text{time}$ to peak rainfall intensity, and $t_d=\text{storm}$ duration.

The USEPA’s Urban Watershed Management Branch (UWMB) has monitored storm-water drainage and best management practices (BMPs) as part of its overall research program. As part of this effort, continuous monitoring equipment was deployed to measure both storm events and periods between storms in a BMP. Of particular concern were electrodes used to measure ammonium $\left({\text{NH}}_4^{+}\right)$ concentrations. During the third deployment of the electrode there were readings of concern for ${\text{NH}}_4^{+}$ which exceeded expectations for drift or storm event response. The electrode indicated concentrations of ${\text{NH}}_4^{+}$ exceeded 2 mg/L, with a sustained maximum concentration of 8 mg/L recorded. These observations occurred between December 5, 2003 and December 10, 2003 after snow events. This period was marked by increased measures of conductivity measured which were contrary to typically low conductivity readings especially after precipitation events. Deicers (sodium chloride) spread on the roadway most likely caused increased ${\text{NH}}_4^{+}$ readings, as sodium ions are a known interference for ${\text{NH}}_4^{+}$ . To back up this claim, controlled laboratory experiments were performed on the ${\text{NH}}_4^{+}$ electrode to test the response. Two tests were performed where salt was introduced into a bucket containing a probe. A determination was also made as to whether decaying leaves may have contributed to these elevated ${\text{NH}}_4^{+}$ readings. Results of the tests indicated that at low ammonia concentrations, salt is a measurable interference. Decaying leaves did increase ${\text{NH}}_4^{+}$ concentrations as measured by the electrodes, but only to 1 mg/L which coincided with both electrode readings and sample concentrations from the field.

In this paper swarm intelligence based methodology is proposed for optimal and reliable design of irrigation channels. The input parameters involved in channel design are prone to uncertainty and the solution of deterministic model may result in flooding risk and affect the stability of the channel. To provide reliability in the design, an overtopping probability constrained design is presented in this study. The deterministic equivalent of the probabilistic constraint is derived by following the principle of first order uncertainty analysis. In order to account for the uncertainty of design parameters in the objective function, a modified cost function is proposed. A methodology is propounded to solve it in a metaheuristic environment and solved it using elitist-mutated particle swarm optimization (EMPSO) method. The EMPSO based solutions are found to be quite successful and better than the classical optimization methods. Finally, it is concluded that the proposed methodology has a good potential for reliable design of composite channels for designer specified reliability values.

In this paper, two internal model control (IMC) controllers using gain-scheduling techniques are proposed and compared for open-channel systems that allow to deal with large operating conditions. In particular, in one side, a linear parameter varying (LPV) model for an open-flow channel system based on a second-order delay Hayami model is proposed. This model will allow one to design a classic gain-scheduling strategy for the IMC controller. On the other side, the LPV model is discretized in a set of linear time invariant (LTI) models corresponding to different operating points. For each LTI model a LTI IMC controller is designed off-line. Then, a supervised gain-scheduler detects on-line which is the LTI model that represents better the open-flow channel system at the current operating point and decides which is the LTI controller that should be used. Finally, both approaches will be applied to a simulated open canal: the Lunax gallery located at Gascogne, France.

The salinity status of soil can be obtained through the measurement of the pore-water electrical conductivity ${\sigma }_p$ . In the present study the WET sensor’s capability in predicting ${\sigma }_p$ through the simultaneous measurements of the soil bulk electrical conductivity $\left({\sigma }_b\right)$ and the soil dielectric constant $\left(K\right)$ is investigated. The estimation of ${\sigma }_p$ is based on a model by Hilhorst, which relates ${\sigma }_p$ to the two other quantities $K$ and ${\sigma }_b$ and an extra fitting parameter $K_0$ which is incorporated in the software of the device. The study involved experimental measurements in the laboratory using four different soils with a large range in soil texture and volumetric water content $\theta$ . In each soil type four different electrical conductivity aqueous solutions were used. The results exhibited a rather strong linear relationship between $K$ and ${\sigma }_b$ . The slope of this linear relationship appeared to depend on both the soil type and the electrical conductivity of the pore water. The value of $K_0$ seems to be soil specific and increases when the salinity level increases. The ${\sigma }_p$ prediction according to the linear model of Hilhorst deviates for almost all soils tested, except for the case of the sandy soil. Besides the linear model of Hilhorst, the Malicki and Walczak linear model was also tested for all soils under investigation and the model of Munoz-Carpena et al. was tested for sand. Malicki and Walczak model performance at predicting ${\sigma }_p$ values was approximately the same as the Hilhorst model for sand and slightly better for sandy loam. In general, one could argue that the linear models could predict ${\sigma }_p$ with some accuracy for the cases of coarse porous media.

Two methods are presented that allow converting the van Genuchten (VG) soil-water-retention (SWR) model parameters to equivalent parameters of the Campbell (C) model. The first method builds on an available solution to convert the VG model to an equivalent Brooks-Corey (BC) model, but accounts for the fact that the effective water content of the BC model and the C model are not the same, because the C model lacks the residual water content parameter, ${\theta }_r$ . The second method (II) relies on a curve-fitting exercise (minimizing the differences between the VG and C-SWR curves) to derive simultaneously the optimal capacity-matching point and SWR-matching point. Results indicate that the second method outperforms the first method and yields an improved equivalence. To bypass the time-consuming curve-fitting exercise, based on Method II two empirical regression equations are presented that allow rapid calculation of the two C-parameters, air-entry and Campbell-b, by the corresponding VG-SWR parameters.

Graphical solutions for discharge $\left(Q\right)$ , head $\left(h\right)$ , and velocity are presented for general recharge conditions on hillslopes underlain by a horizontal impermeable layer and with a constant-head boundary at the toe and a no-flow boundary upslope. Recharge $\left(R\right)$ may be defined for different sections of the hillslope having constant, but not necessarily equal, hydraulic conductivities. $Q$ diagrams are determined using conservation of mass, which requires that the change in $Q$ between two points on a hillslope be equal to the area of the $R$ diagram between them. $h$ diagrams have “exact” (with Dupuit’s assumptions) values for head. Darcy velocity, $q$ , diagrams may be made by dividing the value of the $Q$ diagram at any point by the value of the $h$ diagram at that point. Pore velocity diagrams may be made by dividing values from the $q$ diagrams by the effective porosity. Three examples illustrate the graphical solutions for various scenarios.

Discharge coefficients for water flow through a vertical, circular orifice at the bottom of a conical hopper were experimentally studied in the present paper. The conical hopper consists of a cylindrical hopper of inside diameter of 48 cm and a bottom cone of side slope of 45°. Experiments were carried out under different orifice diameters and water heads. The dependence of the discharge coefficient on the orifice diameter and water head was analyzed, and then an empirical relation was developed by using a dimensional analysis and a regression analysis. The results show that the larger orifice diameter or higher water head have a smaller discharge coefficient and the orifice diameter plays more significant influence on the discharge coefficient than the water head does. The discharge coefficient of water flow through a bottom orifice is larger than that through a sidewall orifice under the similar conditions of the water head, orifice diameter, and hopper size.

A conventional weir typically consists of an impermeable body constructed of concrete, since its primary functions are to heading up water and efficiently regulate flow. However, an impermeable body prevents the longitudinal movement of aquatic life and transportation of physical and chemical substances in water, eventually having a negative impact on the water environment. One of the advantages of gabions as a building material is that the motion of individual stones comprising the gabion is not of much concern. The wire mesh of the gabion basket serves to restrain any significant movement. Also, gabion weirs offer an alternative design that could be adopted for flash flood mitigation. In this study, a series of laboratory experiments was performed in order to investigate the flow over gabion weirs. For this purpose, two different gabion weir models were tested in two horizontal laboratory flumes of 10-m and 17-m length, 0.3-m width, and 0.3- and 0.5-m depth, respectively, for a wide range of discharge, upstream water depth, downstream water depth, weir height, weir length, and gabion filling gravel material size. The results of the gabion weir were compared with those of experiments carried out on solid weirs having the same dimension and it was found that there is a large deviation when the solid weirs equation is applied to gabion weirs (permeable weirs). So, using one of the existing solid weir flow formulas would lead to an erroneous calculated value. Multiple regression equations based on the dimensional analysis theory were developed for computing the discharge over gabion weirs for both free and submerged flow regimes. Also, equations were introduced for computing the discharge coefficient to be applied with the traditional solid weir equation.