Journal of Irrigation and Drainage Engineering

Ballistic simulation has been successfully applied to impact sprinklers. However, ballistic simulation of center pivot sprinkler irrigation has been limited by the difficulty in estimating the initial drop velocity vector in fixed and rotating spray plate sprinklers. Initial velocity is severely affected by the impact of the jet on the sprinkler deflecting plate (or plates). In this work, experimental techniques based on drop photography have been used to obtain the droplet velocity and angle in the vicinity of a fixed spray plate sprinkler by using three different nozzle diameters. Furthermore, simulation techniques based on the inverse solution of drop trajectory were combined to determine the initial velocity vector and energy loss at the spray. Our analysis suggests that the ballistic model can be used to simulate drop inverse trajectory in these sprinklers, although the ballistic model can benefit from 5 to 10% effective drag-force screening. The ratio of initial drop velocity to jet velocity was between 0.67 and 0.82, whereas the kinetic energy losses in the spray sprinklers amounted to 33–55%.

Many control strategies can be found in the literature for controlling river systems. One of these methods is model predictive control (MPC), and it has already shown its efficiency for set-point control of reaches and irrigation channels. This paper shows that MPC can also be used for flood control of river systems. The proposed controllers use the buffer capacity of water reservoirs in an optimal way when there is a risk of flooding, and they recover the used buffer capacity as fast as possible. The performance of the controllers is tested on a river system consisting of multiple channels, gates, and a water reservoir. One controller is used in combination with a Kalman filter, which estimates all the states of the river system on the basis of a very limited number of measured water levels. It was observed that the influence of this estimator on the control performance was minimal.

A series of laboratory experiments was performed to present the overbank flow in asymmetric rectangular compound channels. For this purpose, two different sets of asymmetric models with rectangular compound cross sections were tested for a wide range of discharges. The first set consisted of nine compound cross-section models formed by a combination of three step heights and three main channel widths. The second set consisted of six compound cross section-models formed using a combination of two step heights and three main channel widths. The mean flow measurements were then related to a dimensionless parameter called the relative depth defined as the ratio of the depth above the floodplain bed to the depth above the main channel bed. The variations and interactions of the three outlined mean flows were investigated with respect to relative depth. A set of single-variable regression models has been developed for estimating the three mean flow types using relative depth as the only independent variable. Another set of multiple-variable regression models was derived using two additional dimensionless parameters, which take into account the width dimensions of the constructed asymmetric compound channel. The application of several key statistics and validation procedures indicated the high significance and reliability of the developed models in predicting the three mean flow types.

Weirs used for water discharge measurement in open-channel systems normally operate under free-flow conditions, for which the specific energy reaches a minimum at the weir crest. This type of transitional open-channel flow can be simulated using the ideal fluid flow theory. The traditional application of that theory requires the computation of the flow net over the weir. In this work, a potential flow model using a semi-inverse mapping is proposed in order to simulate potential flow over weirs. The model reduces the computation of the entire flow net to the determination of the streamline flow pattern only. The computations are conducted numerically using a simple finite-difference technique, in which conservation of energy, momentum, and the critical flow condition with curvilinear streamlines is considered. The model is used to display parameters of engineering interest at the point of minimum specific energy.

This paper depicts some limitations of a canal scheduling model that gives water delivery schedules for a rotational distribution system using the concept of weights based on the irrigation performance indicators. The indicators used are equity, adequacy, timeliness, and location (based on the convenience of gate operator). Possible improvements in the model are suggested to remove the drawbacks of untimely water supplies to some of the distributaries, poor supply to demand ratios, and the inconveniences faced by the gate operator in opening some of the distributaries. This proposed model is designated as the improved planning model for canal scheduling. Based on this, a canal operational schedule is recommended for the whole irrigation distribution system for the kharif season, which is more effective in fulfilling the multiple objectives of irrigation.

Optimization models are widely used in agricultural water resources management programs. However, optimization models in most applications use data that is subject to uncertainty. Recently, robust optimization has been used as an optimization model that incorporates uncertainty. This paper proposes a linear programming model with the objective of maximizing the total gross margin for the delivery of water to agricultural areas that cover an irrigation network over a planning horizon. The writers apply uncertain data in this system in the form of a robust optimization approach. The writers also consider analysis of the sensitivity of the total gross margin in accordance with the variations of the degree of conservatism (reliability), irrigation efficiency, and price of irrigation water. The results of changes to these parameters in a wide range of variations caused large changes in the optimal total gross margin of the planning horizon. Application of the proposed model to the case study of the Nekooabad irrigation network in the province of Isfahan, Iran, over a 3-year planning horizon (2012–2014) demonstrates the reliability and flexibility of the model.

Weirs and notches are efficient devices for measuring flow rates. Banks of slit weirs forming multislit weirs allow both precise discharge measurements in a very large range of flow rates and permit a good flow regulation. V-shaped weirs are traditionally used as precise laboratory flow measuring devices, especially in the low discharge ranges. In the current investigation, the method of images was used to form the V-shaped multislit weir system to allow measurement and regulation of flows in a large range of flows that includes very low flow rates. Experimental studies were conducted to determine the discharge coefficients of V-shaped multislit weirs over a wide range of weir Reynolds numbers. The study provided a single relation between the weir discharge coefficient and the weir Reynolds number for both the rectangular and V-shaped multislit weir systems.

A Parshall flume is a common device for measuring open-channel flows. Some Parshall flumes, however, have been modified or constructed without a downstream diverging section. A Parshall flume that does not have its divergent section is known as a Montana flume. Both physical modeling and computational fluid dynamics (CFD), or numerical modeling, have been utilized to assess the accuracy of and calibrate Montana flumes. Montana flumes under free-flow conditions operate similarly to Parshall flumes and, therefore, share the same rating curves. However, Montana flumes that operate under submerged conditions can deviate by as much as 15% from equations used to correct the submerged Parshall flume flow rate. The research summarized in this paper illustrates comparable results between numerical and physical modeling tests performed on a 6-in. (15.2-cm) submerged Montana flume. In addition, with the numerical model calibrated to the physical model, the same numerical procedure is used to expand testing to other sized Montana flumes under submergence. Accordingly, nine sizes of Montana flumes are numerically simulated between 6 in. (15.2 cm) and 8 ft (2.44 m). Subsequently, correction factors are created in each case for each Montana flume under submerged conditions and the application of the factors is demonstrated.