Irrigation Simulation Model Research Articles

Analysis of an irrigation district in northeastern Spain: II. Irrigation evaluation, simulation and scheduling

In the first paper of this series, the Loma de Quinto Irrigation District (LQD) was characterised, and water use was assessed. In this work, the analysis of the LQD is completed with field irrigation evaluations, solid-set sprinkler irrigation simulations and irrigation scheduling for optimal crop yield. The results of the irrigation evaluations indicated that the average Christiansen coefficient of uniformity (CU) for solid-sets, centre-pivots and linear-moves was 68.0, 75.5, and 80.0%, respectively. In solid-sets CU was severely reduced by wind speed. However, in centre-pivots and linear-moves CU was higher in evaluations with wind speeds between 2 and 6 m s −1 than under calm conditions. The evaluation data set was used to validate a ballistic solid-set sprinkler irrigation simulation model. The performance variables used for model validation were CU and the potential application efficiency of the low quarter (PAE lq). Both variables were adequately predicted in the range of the observed values. The model was used to extend the evaluation results to all the solid-set plots in the LQD. CU maps were produced for different wind speeds and operating pressures. These maps can be used to identify plots with low irrigation performance. The effect of irrigation scheduling on crop yield and net benefit was analysed using the CropWat simulation model. Simulations of the 1997 irrigation practices performed on a limited number of plots detected a 12% decrease in crop yield due to deficit irrigation and/or large irrigation intervals. The introduction of an optimal irrigation schedule (avoiding yield reductions) would imply increasing the alfalfa seasonal irrigation depth by 101 mm, and applying light, frequent irrigation events. Due to labour scarcity in the LQD, the implementation of the optimal schedule would require a high degree of irrigation automation, which is currently unavailable. Taking into consideration the value of the additional yield and the costs of the extra irrigation water depth and the automation devices, the resulting net benefit would be 50 ▪ ha −1. The purpose of this analysis of the LQD is to contribute to the diagnostic analysis phase of an incipient Management Improvement Program at the LQD. In order to complete this phase, an interdisciplinary committee will perform a study not just on irrigation but on a wide scope of irrigated agriculture in the LQD.

A case study for irrigation modernisation: II: Scenario analysis

Surface irrigation simulation models have seldom been used in engineering practise, and district modernisation is not an exception. Surface irrigation evaluations were performed in the Almudévar irrigation district to obtain the parameters required for surface irrigation modelling. The total district irrigated area was divided into 92 design units, for which a characteristic blocked-end border was defined. Simulation was used to establish the current irrigation performance in each design unit, and district performance contour maps were built. Irrigation performance was characterised using potential application efficiency, with an average of 54%, and irrigation time, averaging 6 h ha −1. Simulated potential application efficiency of the low quarter was similar to the seasonal irrigation performance index (an estimate of irrigation efficiency) presented in the companion paper. A set of seven modernisation scenarios was defined. Two strategies were identified to improve the potential application efficiency in the scenarios: increase the irrigation discharge into the current blocked-end borders and/or substitute the current system with a solid set sprinkler irrigation system. The performance of each scenario was estimated using irrigation models to determine efficiency, water conservation and irrigation time. The modernisation investment costs were estimated and compared to the performance of each scenario. The best results (potential application efficiency of 77%, reduced water allocation by 14.4 10 6 m 3 year −1) were obtained by a combination of blocked-end irrigation with a discharge of 200 l s −1 and sprinkler irrigation in the areas where surface irrigation efficiency could not attain 50%. The investment cost for this scenario was 3932 Euro ha −1. More expensive scenarios did not guarantee better performance.

An approach for assessing the vulnerability of the water resources of Yemen to climate change

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 12:85-89 (1999) - doi:10.3354/cr012085 An approach for assessing the vulnerability of the water resources of Yemen to climate change Ahmed Alderwish1,*, Mohamed Al-Eryani2 1Earth and Environmental Sciences Department, Sana'a University, PO Box 13743, Yemen 2Civil Engineering Department, Sana'a University, PO Box 2610, Yemen *E-mail: alderwish@hotmail.com ABSTRACT: This paper outlines the methodology followed in the study of climate change impact on water resources in Yemen and presents initial results on the vulnerability of the water resources system. The selected modeling strategy is used for the first time in climate change assessment studies and is briefly discussed. This strategy comprised 4 interacting models: a Rainfall-Runoff Model (RRM), an Irrigation Simulation Model (ISM), a Groundwater Simulation Model (GSM), and an Economic Policy Model (EPM). Adequate indication of the water system's sensitivity to climate change in arid and semi-arid regions can only be achieved when appropriate temporal and spatial scales of the assessment are used. For instance, only hourly or daily time step models can capture climate impacts on floods of ephemeral wadis. The degree of accuracy required should also be determined by the scarcity/availability of the resources. KEY WORDS: Climate change · Modeling · Climate scenarios · Management Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 12, No. 2-3. Online publication date: August 27, 1999 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 1999 Inter-Research.

Numerical Calculation of Infiltration in Furrow Irrigation Simulation Models

The computation of wetted‐perimeter‐dependent intake in a furrow irrigation simulation model using an empirical infiltration formula was examined. Different formulations were applied under increasing and decreasing depth of flow (and wetted‐perimeter) conditions. Four computational methods were compared for the former condition and only one was tested for the latter. The merit of the procedures was evaluated in relation to the performance of a finite difference unsteady surface flow model. The hydraulic model was developed using fixed spatial increments and variable time steps and solved with a shooting technique. Differences in advance trajectory resulted from application of each formulation, and numerical accuracy was also different with each computational method. Convergence of the shooting solution was obtained with all infiltration formulas during the advance phase, but there were noticeable differences in convergence rate. Only one of the formulas provided consistent results during storage and recession calculations. Numerical instability resulted as well from the application of the procedures with limited convergence.