Journal of Irrigation and Drainage Engineering

To reduce the negative effects of deficit irrigation on water and nitrogen (N) use, a pot experiment was conducted over two consecutive years to study the effects of zeolite (Z) on soil-water retention, water consumption, N distribution, and various soil nutrients under alternate wet–dry (AWD) irrigation. The results showed that Z significantly improved field capacity and reduced the number of ineffective tillers, thereby saving 5.8% and 12% water at the tillering and milky ripening stages, respectively. However, it could not offset its enhanced effect on evapotranspiration mainly due to a greater number of effective tillers promoted by Z addition during the jointing–booting and heading–flowering stages, and ultimately significantly increased total water consumption. AWD reduced rice grain yield, but Z significantly increased water and nutrient retention and, thus, increased water productivity by 8.9%. Although AWD increased N content in roots, it reduced total N uptake. Further, Z significantly increased N accumulation in roots and panicles and reduced N content in leaves and stems, thereby enhancing the N harvest index by 2.7%. Soil potassium, sodium, and calcium content significantly increased with Z addition, further affecting rice grain yield. In summary, zeolite increases the drought resistance of rice under AWD irrigation and increases water–nitrogen use efficiency.

The discharge characteristics of flow over and under different weir-gate structures were investigated using dimensional analysis and multivariable regression techniques. Based on the shape and geometry of weir-gates, seven weir-gate structures were classified. The interaction factor, defined as the ratio of the measured discharge over and under the weir-gate structure to the sum of the predicted weir and gate discharges from the literature, was calculated for all types of weir-gate models. Six weir-gate models were experimentally tested to study the discharge characteristics of flow over weirs of finite crest length and under gate. The interaction factors were correlated with the geometry parameters for all weir-gate models with an average coefficient of determination of 0.85. A series of regime plots was developed to assist designing the weir-gate structures as flow distributors for a sharp-crested weir-gate and a weir of finite crest length with an offset. The regime plots show the contribution of weir and gate discharges for different weir-gate geometries. A critical normalized head was introduced as the flow through the weir-gate structure is equally divided by the weir and gate. Based on the weir-gate geometry and discharge, general empirical equations were developed to estimate the critical normalized head for practical engineering applications.

The Cequia of Manresa is a 26-km open channel constructed in the fourteenth century that conveys water from the Llobregat River to the city of Manresa using an elevation difference of 10.4 m. The channel is still operational today, supplying water for domestic, industrial, and agricultural uses to an overall population of 150,000 people. A hydrometric module was constructed in 1864 to regulate the flow rate in the Cequia to under $\mathrm{1,000}\mathrm{L}/\mathrm{s}$. This module was dismantled in 1959 and is currently nonoperational. This work studied the operation of the module and determined whether it met the objectives for which it was built. The module was modeled numerically. Owing to the lack of experimental measures from the module, the model was validated with an analytical model from the literature, which demonstrated its accuracy. The model was created by applying computational fluid dynamics (CFD) using FLOW-3D software. The results showed that the numerical model reproduced the dynamic behavior of the hydrometric module (transitory), and that the old automated system operated correctly, limiting the flow to the required value. The numerical models can be used as a tool for historical research.

In this study, a hydraulically operated and diaphragm-actuated type of diaphragm valve using an elastic diaphragm was tested. With this type of valve, the opening fraction depends on the pipeline pressure; thus, it is important to determine the minimum operating pressure. The outlet pressure was determined to be the critical pressure ensuring the full opening. The valve flow coefficient was found to be a good indicator of the valve opening fraction. A test procedure was presented to determine the minimum outlet pressure. The pressure had to be continuously increased during testing to avoid hysteresis. An unsteady valve behavior was observed after a sudden intense pressure decrease.

Perforated riser principal spillways are widely used in check dams, and rectangular orifices are the preferred orifice geometry for risers constructed of brick. However, there is little research based on risers perforated with rectangular orifices. This paper discusses the discharge coefficient of such a structure, based on the experimental data and data collected from literature, during which an estimation of the discharge equations for a riser perforated with circular orifices was made. First, an existing equation for a riser with circular orifices is selected based on the coefficient of determination ($R^2$) index and the Nash–Sutcliffe efficiency (NSE) index. Then, an equation for the discharge coefficient of a riser perforated with rectangular orifices is proposed ($R^2=0.95$, $\mathrm{NSE}=0.91$) considering the factors of the diameter of the riser pipe, the width of the rectangular orifice, and the head over the centerline of the orifice. This work is expected to provide a reference for the design and investigation of a perforated riser principal spillway.

The curve number (CN) model was originally developed to estimate the total runoff resulting from a given rainfall event. However, the CN model has a limited ability to estimate realistic incremental rainfall excesses within rainfall events. This limitation is problematic because incremental rainfall excesses during a rainfall event are usually the input data required for calculating runoff hydrographs. In contrast to the CN model, the $\varphi$-index model provides more realistic estimates of incremental rainfall excesses during a rainfall event. This study investigated the relationship between the curve number and the $\varphi$-index at 10 different catchments in the United States. The results show that, for any given rainfall event, the $\varphi$-index can be directly related to the curve number, and there is a fair degree of consistency in the $\mathrm{CN}–\varphi$ relationship between catchments.

An analytically derived discharge prediction model for a conical mobile flume, referred to as a conical central baffle (CCB), is presented. The flume is suitable for use in small rectangular channels in agricultural fields or wastewater channels. The flume consists of a cone-shaped object positioned axially in a nearly horizontal prismatic open rectangular channel to produce a venturi effect. The conical obstruction has good stability against the water current owing to its lower center of gravity and can measure a wider range of flows due to its similarity to a V-notch weir. The presence of a conical obstruction alters the cross-section of a rectangular channel at different locations, which requires development of parameters related to the geometry of the cone and channel. A model was proposed to predict flow rates in the channel using the energy concept. The proposed model was tested and modified using different laboratory flumes for various flow rates. The flow rate values obtained using the proposed approach produced an error within 9% when compared with the actual flow rates. The experimental results thus validated the developed model. This flume can be used as a mobile measuring device for temporary flow measurements in small rectangular open channels with the presented approach.