Journal of Irrigation and Drainage Engineering

The management of water resources in irrigation is a fundamental aspect for their sustainability. For correct management, several tools and systems for decision making are necessary. Among the large number of factors that affect the optimization of water use, we must focus on irrigation uniformity and its economic implications. The following methodology, implemented in a computer model, allows us to carry out an economic analysis of the effects of different Christiansen’s uniformity coefficients (CU), which are useful for system design and calculation and also for irrigation management in order to obtain maximize gross margin. In the zone studied (Hydrogeologic System 08.29, Castilla-La Mancha, Spain) working with a solid set system and with four crops (barley, garlic, maize, and onion), there is an economic interest in designing systems with a high CU (90%) that allows us to obtain a high application efficiency $\left(E_a\right)\text{.}$ Regarding the economic optimization of the irrigation depths, the results show that the optimum gross depths are always lower than the irrigation depths for maximum crop yield. The higher the CU, the lower the depths, while the crop yield increases and the gross margin of the crop improves. These general results present significant differences among crops, according to their water requirements and their economic profitability.

Regulations for mitigating nonpoint source pollution from urban areas often include a requirement for treatment of a first-flush depth of stormwater. When the stormwater treatment technology requires specification of a design flow rate, the first-flush depth must be related to a first-flush flow rate. This paper describes a methodology to determine the relation between accumulated storm depth and corresponding flow to a treatment device for small, urban watersheds. The approach uses the rational method under the assumption that the time-of-concentration is small. Intensity–frequency relations, expressed in the form of return periods and associated intensities, were determined using a partial duration frequency analysis of regionalized precipitation data. The results of the method can be used to determine the flow rate to a treatment device that will meet a specified return period for a first-flush depth. The method is demonstrated using 13 years of 15-min data from seven Massachusetts precipitation stations.

Cotton (Gossypium hirsutum L.) is beginning to be produced on the Northern Texas High Plains as a lower water-requiring crop while producing an acceptable profit. Cotton is a warm season, perennial species produced like an annual yet it requires a delicate balance of water and water deficit controls to most effectively produce high yields in this thermally limited environment. This study measured the water use of cotton in fully irrigated, deficiently irrigated, and dryland regimes in a Northern Texas High Plains environment using precision weighing lysimeters in 2000 and 2001. A lateral-move sprinkler system was used to irrigate the fields. The water use data were used to develop crop coefficient data and compared with the FAO-56 method for estimating crop water use. Cotton yield, water use, and water use efficiency was found to be as good in this region as other more noted cotton regions. FAO-56 evapotranspiration prediction procedures performed better for the more fully irrigated treatments in this environment.

In the past, studies involving optimal design of composite channels have employed Horton’s equivalent roughness coefficient, which uses a lumped approach in assuming constant velocity across a composite channel cross section. In this paper, a new nonlinear optimization program (NLOP) is proposed based on a distributed approach that is equivalent to Lotter’s observations, which allows spatial variations in velocity across a composite channel cross section. The proposed NLOP, which consists of an objective function of minimizing total construction cost per unit length of a channel, is solved using genetic algorithm (GA). Several scenarios are evaluated, including no restrictions, restricted top width, and restricted channel side slopes, to account for certain site conditions. In addition, the proposed NLOP is modified to include constraints on maximum permissible velocities corresponding to different lining materials of the composite channel cross section, probably for the first time. The proposed methodology is applied to trapezoidal and triangular channel cross sections but can be easily extended to other shapes or compound channels. Optimal design graphs are presented to determine the channel dimensions of a composite trapezoidal channel cross section. The results obtained in this study indicate that cost savings up to 35% can be achieved for the unconstrained velocity case and up to 55% for the limiting velocity case when the proposed NLOP is solved using GA as compared with the existing NLOP solved using either the classical optimization solution technique or GA.

Numerical simulation of the two-dimensional (2D) infiltration process during furrow irrigation requires considerable computational effort, which can be reduced by analytical modeling. This paper deals with the further development of the semianalytical infiltration model FURINF (furrow infiltration). Considering the varying impact of gravity and furrow geometry, the new approach models the impact of furrow geometry on infiltration progress using a transient geometric shape factor as a function of infiltration time and furrow geometry. FURINF portrays 2D infiltration from the wetted furrow perimeter by a series of one-dimensional (1D) infiltration computations that are performed in this paper on the basis of an analytical as well as a numerical solution of the 1D Richards equation. Comparing the FURINF results provided by the analytical and numerical 1D infiltration model confirmed the adequacy and reliability of the robust and simple analytical approach, which only requires soil parameters provided by rather simple measurements. The results and performances of the analytical FURINF model (FURINF-A) are compared within the frame of a sensitivity and error analysis with the outcome of the numerical subsurface flow model HYDRUS-2D considering three different soils.

Realizing the full potential of drip irrigation technology requires optimizing the operational parameters that are available to irrigators, such as the frequency, rate, and duration of water application and the placement of drip tubing. Numerical simulation is a fast and inexpensive approach to studying optimal management practices. Unfortunately, little work has been done to investigate the accuracy of numerical simulations, leading some to question the usefulness of simulation as a research and design tool. In this study, we compare HYDRUS-2D simulations of drip irrigation with experimental data. A Hanford sandy loam soil was irrigated using thin-walled drip tubing installed at a depth of 6 cm. Three trials (20, 40, and 60 $L\cdot m^{-1}$ applied water) were carried out. At the end of each irrigation and approximately 24 h later, the water content distribution in the soil was determined by gravimetric sampling. The HYDRUS-2D predictions of the water content distribution are found to be in very good agreement with the data. The results support the use of HYDRUS-2D as a tool for investigating and designing drip irrigation management practices.

The paper discusses a genetic algorithm (GA) developed for solution of two lateral canal scheduling problems presented recently in the literature. The GA formulations use very similar objective functions for both problems. Results obtained with the GA approach are compared with previously published results obtained through linear and integer programming. The GA approach has been demonstrated to be robust and very efficient in application to lateral canal scheduling problems. It is also easily set up and would be easily applied by practitioners.

The accurate design of drip irrigation laterals needs to consider the variation of hydraulic head due to pipe elevation changes, head losses along the lines, and also, at a given operating pressure, emitter discharge variations related to manufacturing variability, clogging, and water temperature. Hydraulic head variations are consequent to both the friction losses and local losses due to the in-line or on-line emitters along the pipe, which determine the contraction and subsequent enlargement of the flow streamlines. Moreover, in-line emitters usually have a smaller diameter than the pipe, and therefore an additional friction loss must be considered. Evaluation of energy losses and consequently the design of drip irrigation lines is usually carried out by assuming the hypothesis that local losses can be neglected, even if previous experimental researches showed that local losses can become a significant percentage of total head losses as a consequence of the high number of emitters installed along the lines. This paper reports the results of an experimental investigation to evaluate local losses in integrated laterals in which coextruded emitters are installed inside the pipe. Local losses were measured for 10 different types of commercially available integrated laterals and for different Reynolds numbers. A practical power relationship was deduced between the α coefficient, expressing the amount of local losses as a fraction of the kinetic head, and a simple geometric parameter characterizing the geometry of the emitter and the pipe. Local losses obtained for integrated laterals were then compared with those due to the on-line emitters, previously determined as a function of the pipe-emitter geometry. The proposed criterion for calculating the local losses was finally verified by using a step-by-step procedure.

The sharp-crested weir is the most commonly used device in channels for flow measurement and flow regulation due to its simplicity. Attempts have been made to study in detail the flow over different shapes of normal conventional weirs, side weirs, and oblique weirs. Most of the investigators have expressed the discharge coefficient as a function of various parameters. The concern of this paper is to study flow over an inclined inverted triangular notch weir. Based on experimental work on 0° (normal) and 15, 30, 45, and 60° weirs, the writers have established an equation for discharge in terms of the inclination angle of the weir plane with the plane normal to the flow axis. A new general algebraic optimization procedure has been developed for evolving a linear head-discharge relationship for an inclined inverted V-notch (IIVN), which is relatively superior to similar procedures developed earlier. It has been shown that the IIVN does not lose its near-linear discharging characteristics even when it is inclined to the channel bed. The discharge estimated by the linear discharge-head relationship has been found to be in good agreement with the actual discharges well within a ±5% error. Further, the advantages of the IIVN as a flow measuring and flow control device have been highlighted.

Storm overflow structures in combined sewers are used to separate sewage from storm water. For subcritical approach flow, sideweirs are currently used; however, they often behave hydraulically poor. This study was conducted to explore a combined storm overflow structure able to improve the hydraulic performance of sewer sideweirs. Such a structure consists of a low-crested sideweir and a bottom opening just downstream from the sideweir end. First, the hydraulic design procedure is described, and then, based on laboratory experiments and by using the governing flow equations, the main hydraulic features are highlighted. The results indicate that the proposed device has advantageous characteristics in terms of hydraulic efficiency, reliability, and maintenance.