Luis Juana

Evaluation of Spain's Water-Energy Nexus

This paper explores the water-energy nexus of Spain and offers calculations for both the energy used in the water sector and the water required to run the energy sector. The article takes a prospective approach, offering evaluations of policy objectives for biofuels and expected renewable energy sources. Approximately 5.8% of total electricity demand in Spain is due to the water sector. Irrigated agriculture is one of the Spanish water sectors that show the largest growth in energy requirements. Searches for more efficient modes of farm water use, urban waste water treatment, and the use of desalinated water must henceforth include the energy component. Furthermore, biofuel production, to the levels targeted for 2020, would have an unbearable impact on the already stressed water resources in Spain. However, growing usage of renewable energy sources is not threatened by water scarcity, but legislative measures in water allocation and water markets will be required to meet the requirements of using these sources. Some of these measures, which are pushed by regional governments, are discussed in concluding sections.

Operation diagrams for irrigation management

Abstract A critical index for assessment of irrigation performance is the application efficiency Ra, defined by the ratio of net application Hn to the gross application diverted into the field Hb. A second critical index is the deficit coefficient Cd, defined as the ratio of the root zone deficit following irrigation, Hd, to the root zone requirement, Hr. Computer programs are now available which can adequately simulate the behavior of surface flow and infiltration as a function of inflow rate q0 and application time tar. They are useful to study surface irrigation techniques applied on a given field. If the characteristics of infiltration and the field geometry are known, then computer programs based on Saint Venant equations can be used to simulate irrigation performance. Results of such simulations are shown as characteristics diagrams of Cd and Ra on a field of tar and q0. The data sets were also used to plot curves of constant Ra and Hr for fixed values of Cd. The curves show the optimum combination of inflow rate and time to provide reasonable irrigation efficiencies. Means are also available to describe water application from a sprinkler system as a function of statistical parameters. A normal distribution function is assumed to simulate water applied onto the field. Results are shown as characteristics diagrams which represent Ra and Cd as a function of Christiansen uniformity coefficient Cu and the H b H r ratio.

Water Distribution in Laterals and Units of Subsurface Drip Irrigation. II: Field Evaluation

The performance of drip irrigation and subsurface drip irrigation (SDI) laterals has been compared. Two emitter models (one compensating and the other noncompensating) were assessed. Field tests were carried out with a pair of laterals working at the same inlet pressure. A procedure was developed that recorded head pressures at both lateral extremes and inlet flow during irrigation. Both models showed similar behavior and soil properties affected their discharge. On the other hand, the performance of a field SDI unit of compensating emitters was characterized by measuring pressures at different points and inlet flow. Finally, the distribution of water and soil pressure in the laterals and the unit were predicted and irrigation uniformity and soil pressure variability were also determined. Predictions agreed reasonably well with the experimental observations. Thus, the methodology proposed could be used to support the decision making for the design and management of SDI systems.

Optimal Water Allocation in Shortage Situations as Applied to an Irrigation Community

AbstractThis work studies the most beneficial way of allocating water in an irrigation community in water shortage situations. Therefore, it proposes that the irrigation surface area be divided into homogeneous zones, each with a beneficial relationship with respect to the water applied. The mathematical formula that enables one to obtain the optimal quota for the users or irrigation community as a whole has been found for individual relations of a quadratic or power type, and these have yielded different and complementary characteristics. Dimensionless variables have been used to display the results, and to compare with other alternative allocation rules such as the proportional rule, referencing the situation without water restrictions. As a result, for each water shortage situation, the water that is allocated to each user is obtained, together with the losses in individual income and the losses for the community as a whole. Furthermore, a proposal is put forth for establishing the marginal benefit fro...

Water Distribution in Laterals and Units of Subsurface Drip Irrigation. I: Simulation

A complete methodology to predict water distribution in laterals and units of subsurface drip irrigation (SDI) is proposed. Two computer programs have been developed for the hydraulic characterization of SDI; one for laterals and the other for units. Emitter discharge was considered to depend on hydraulic variability, emitter’s manufacture and wear variation, and soil pressure variation. A new procedure to solve the hydraulic calculation of SDI looped network has been established. Moreover, spatial distribution of soil variability was estimated by a geostatistical modeling software that is coupled with the computer programs. Thus the evaluation and performance of laterals and units of SDI can be addressed by changing input variables such us: length and diameters of laterals; coefficients of emitter’s discharge equation; coefficient of variation of emitter’s manufacture and wear; local losses at the emitter insertion; inlet pressure; and soil hydraulic properties and its spatial variability. Finally, the m...

Managing Irrigation Water Shortage: a Comparison Between Five Allocation Rules Based on Crop Benefit Functions

In this work the efficiency of five allocation rules of irrigation water is analyzed and compared. We define the most efficient rule as the one that minimizes the economic losses arising from a reduction in water availability. The first allocation rule is an equal quota granted to all irrigators. The second one is based on proportional reductions. By means of the third rule all losses of income per hectare are matched, while the fourth makes that all relative losses to the reference incomes are matched. Lastly the fifth rule seeks to maximize private benefit and economic efficiency. We prove that this one would likely be preferred by farmers growing more than one crop. The fundamentals of these rules are included, showing the analytical deduction of the crop-specific reallocations from any prescribed water reduction rule within an irrigation district, as well as the losses of income ensuing from reduced water deliveries. The methodology used herein to compare the efficiency of all these rules is dependent on the relations between allocations and yields. To estimate them, a simple and practical procedure is presented. The five allocation rules are applied to an irrigation community and compared to each other in terms of economic efficiency. Differences in economic losses arising from one rule or another will be sharper the more heterogeneous communities are. Different losses across rules will also be related to the level of water shortage.

Estimation of Cavitation Limits From Local Head Loss Coefficient

Cavitation effects in valves and other sudden transitions in water distribution systems are studied as their better understanding and quantification is needed for design and analysis purposes and for predicting and controlling their operation. Two dimensionless coefficients are used to characterize and verify local effects under cavitating flow conditions: the coefficient of local head losses and the minimum value of the cavitation number. In principle, both coefficients must be determined experimentally, but a semianalytical relationship between them is here proposed so that if one of them is known, its value can be used to estimate the corresponding value of the other one. This relationship is experimentally contrasted by measuring head losses and flow rates. It is also shown that cavitation number values, called cavitation limits, such as the critical cavitation limit, can be related in a simple but practical way with the mentioned minimum cavitation number and with a given pressure fluctuation level. Head losses under conditions of cavitation in sharp-edged orifices and valves are predicted for changes in upstream and downstream boundary conditions. An experimental determination of the coefficient of local head losses and the minimum value of the cavitation number is not dependent on the boundary conditions even if vapor cavity extends far enough to reach a downstream pressure tap. Also, the effects of cavitation and displacement of moving parts of valves on head losses can be split. A relatively simple formulation for local head losses including cavitation influence is presented. It can be incorporated to water distribution analysis models to improve their results when cavitation occurs. Likewise, it can also be used to elaborate information about validity limits of head losses in valves and other sudden transitions and to interpret the results of head loss tests.

Modernization of irrigation systems in Spain: review and analysis for decision making

Abstract This article presents a method for analyzing the economic feasibility of modernizing irrigation systems. By using substitution relationships between two variables, one can determine irrigation performance and farm profit above which modernization would be justified from an economic point of view; and also the investments and energy consumption up to which modernization could be considered cost-effective. By means of representative average values, this method is applied to the now widespread conversion from surface irrigation to drip irrigation in Spain. Two conclusions are drawn. First, modernization may, in some instances, be justified only if more productive crop patterns are implemented. Second, saving water is a cheaper option than using an alternative resource only under certain conditions.

The Water Markets as Effective Tools of Managing Water Shortages in an Irrigation District

In this work, the efficiency of water markets in an irrigation district is put under consideration. This efficiency is referred to the private economic losses arising from a reduction in the availability of water, so the most efficient or optimal allocation will be the one that minimizes these losses or the one that provides the maximum private benefit. On this view, the optimal allocation has been studied in an irrigation community, and it has been compared with the rule of fixing a same quota and the proportional reduction. Besides, from the water allocation made by these last two rules, a water market has been simulated. Formulation for all of them is provided. Results show that water markets will improve the suboptimal allocation made by the rule of fixing a same quota and the proportional rule, even when transaction costs are high. They also show that, mostly, the greater the water restrictions, the greater are the gains from trade. It can be inferred too that, as long as all determinants have been taken into account and transaction costs are low enough, the aggregate losses of income ensuing from any prescribed water reduction will be the lowest both by means of the optimal allocation as with a market. Anyhow, results and conclusions clearly dependent on the relations made between allocations and crop yields.

Matrix Methodology to Study the Probability of Pressure Deficit in On-Demand Branched Irrigation Networks

AbstractThis paper presents a matrix algebraic expression based on the probability of pressure deficit. A set of expressions to calculate the average and the variance of the aggregated head losses ...