Performance-Based Optimization of Land and Water Resources within Irrigation Schemes. II: Application

The area and water allocation model which uses simulation–optimization technique for optimum allocation of land and water resources to different crops cultivated in different allocation units of the irrigation scheme was modified to include both productivity and equity in the process of developing the allocation plans for optimum productivity and/or maximum equity. This paper illustrates the potential of this approach with the help of a case study on Nazare medium irrigation scheme in India. The allocation plans were developed for optimization of different performance parameters (productivity and equity) for different management strategies based on irrigation amount and irrigation interval and cropping distribution strategies of free and fixed cropping. The results indicated that the two performance objectives productivity and equity conflict with each other and in this case, equitable water distribution may be preferred over free water distribution at the cost of a small loss in productivity. Though these results relate to one case study, they show the value of the approach of incorporating productivity and equity in the allocation process with the help of the simulation-optimization model described in the companion paper.     

Multilevel Approach for Optimizing Land and Water Resources and Irrigation Deliveries for Tertiary Units in Large Irrigation Schemes. I: Method

This paper presents the area and water allocation model (AWAM), which incorporates deficit irrigation for optimizing the use of water for irrigation. This model was developed for surface irrigation schemes in semiarid regions under rotational water supply. It allocates the land area and water optimally to the different crops grown in different types of soils up to the tertiary level or allocation unit. The model has four phases. In the first phase, all the possible irrigation strategies are generated for each crop-soil-region combination. The second phase prepares the irrigation program for each strategy, taking into account the response of the crop to the water deficit. The third phase selects the optimal and efficient irrigation programs. In the fourth phase of the model, irrigation programs are modified by incorporating the conveyance and the distribution efficiencies. These irrigation programs are then used for allocating the land and water resources and preparing the water release schedule for the canal network.     

Multilevel Approach for Optimizing Land and Water Resources and Irrigation Deliveries for Tertiary Units in Large Irrigation Schemes. II: Application

The resource allocation model, area and water allocation model, incorporates the concept of deficit irrigation through a variable depth irrigation approach, VDI. It uses this to allocate land and water resources optimally to different crops in a heterogeneous irrigation scheme with limited water under rotational water supply. This model was applied to a medium irrigation scheme in India as a case study, to obtain the land and water allocation plans. These optimal allocation plans were compared to those obtained by using the model with the existing approach (full irrigation with a fixed irrigation interval of 21 days in Rabi and 14 days in the summer season). The allocation plans were obtained taking into account the different parameters that were included in the model, such as crops and cropping pattern, soils, irrigation interval, initial reservoir storage volumes, efficiencies, and the outlet and canal capacities. The total net benefits were compared for the two cases of fixed cropping distribution and free cropping distribution and a sensitivity analysis was conducted on other parameters. Summaries of the allocation plans with the VDI approach are presented for the two cases. The total net benefits obtained with the VDI approach introduced in the model were found to be 22% higher than those obtained with the existing approach. The results of this study are thus indicative of the benefits of deficit irrigation and its application within irrigation schemes that have limited water supply.     

Effect of Preharvest Deficit Irrigation on Second Crop Watermelon Grown in an Extremely Hot Climate

As a second crop, watermelons (Citrullus vulgaris, Crimson sweet) were grown in 2003 and 2004 in the Sanliurfa-Harran Plain in southeastern Turkey to determine the effect of preharvest water stress on fruit yield, quality (i.e., soluble solids contents and fruit size), leaf temperature, and some other physiological parameters. Preharvest drip irrigation treatments included (1) complete irrigation cutoff, dry (D); (2) full irrigation based on replenishment of soil water depleted from 0 to 90?cm soil profile (C); (3) 75% full irrigation (IR1); (4) 50% full irrigation (IR2); and (5) 25% full irrigation (IR3) with 3-day irrigation interval. Treatment plots received the same level of irrigation water until the fruit formation stage, except for Treatment D. Then, different water stress levels were imposed on treatment plots. Irrigation water applied to the five respective treatments were 636, 511, 395, 245, and 120?mm in 2003 and 648, 516, 403, 252, and 127?mm in 2004. Results indicated that fruit yield was significantly lowered by reduced water rates. The seasonal average yield response factor (ky) for both years was 1.0, but it was 0.97 for 2003 and 0.98 for 2004. The highest marketable fruit yield, obtained from treatment C, was 32.4?Mg?ha?1 in 2003 and 37.1?Mg?ha?1 in 2004. D, IR2, and IR3 treatments reduced most measured parameters, except for soluble solids contents (SSC). Both the fruit size and SSC were significantly affected by late-season irrigation management; individual fruit weights were significantly reduced, whereas SSC increased in the IR2 and IR3 treatments compared to the control values. The writers’ results clearly indicated that reduced preharvest irrigation was detrimental. Water use efficiency (WUE) was significantly affected by irrigation treatments. Even a 25% reduction in the irrigation amount caused a 15% reduction in marketable yield. This indicates that deficit irrigation in the ripening stage significantly increased water use efficiency. The study demonstrated that a moderate deficit irrigation, which is replenishment up to 50% of soil water depleted in the root zone, can be successfully used to improve WUE under semiarid climatic conditions.     

Allocation of Scarce Water Resources Using Deficit Irrigation in Rotational Systems

On irrigation schemes with rotational irrigation systems in semiarid tropics, the existing rules for water allocation are based on applying a fixed depth of water with every irrigation irrespective of the crops, their growth stages, and soils on which these crops are grown. However, when water resources are scarce, it is necessary to allocate water optimally to different crops grown in the irrigation scheme taking account of different soils in the command area. Allocating water optimally may lead to applying less water to crops than is needed to obtain the maximum yield. In this paper, a three stage approach is proposed for allocating water from a reservoir optimally based on a deficit irrigation approach, using a simulation-optimization model. The allocation results with a deficit irrigation approach are compared for a single crop (wheat) in an irrigation scheme in India, first with full irrigation (irrigation to fill the root zone to field capacity) and second with the existing rule. The full irrigation with a small irrigation interval was equivalent to adequate irrigation (no stress to the crop). It is found that practicing deficit irrigation enables the irrigated area and the total crop production in the irrigation scheme used for the case study to be increased by about 30–45% and 20–40%, respectively, over the existing rule and by 50 and 45%, respectively, over the adequate irrigation. Allocation of resources also varied with soil types.     

Model for the Simulation of Water Flows in Irrigation Districts. I: Description

Significant improvements in the profitability and sustainability of irrigated areas can be obtained by the application of new technologies. In this work, a model for the simulation of water flows in irrigation districts is presented. The model is based on the combination of a number of modules specialized on surface irrigation, open channel distribution networks, crop growth modeling, irrigation decision making, and hydrosaline balances. These modules are executed in parallel, and are connected by a series of variables. The surface irrigation module is based on a numerical hydrodynamic routine solving the Saint Venant equations, including the heterogeneity of soil physical properties. The simulation of water conveyance is performed on the basis of the capacity of the elements of the conveyance network. Crop growth is simulated using a scheme derived from the well-known model CropWat. The irrigation decision making module satisfies water orders considering water stress, yield sensitivity to stress, multiple water sources, and the network capacity. Finally, the hydrosaline module is based on a steady state approach, and provides estimations of the volume and salinity of the irrigation return flows for the whole irrigation season. The application of the model to district irrigation management and modernization studies may be limited by the volume of data required. In a companion paper, the model is calibrated, validated, and applied to a real irrigation district.     

Monthly Water Resources and Irrigation Planning: Case Study of Conjunctive Use of Surface and Groundwater Resources

The Tehran metropolitan area is one of the mega cities of the world and has an annual domestic water consumption close to one billion cubic meters. The sewer system mainly consists of traditional absorption wells. Therefore, the return flow from the domestic consumption has been one of the main sources of groundwater recharge. Some part of this sewage is drained into local rivers and drainage channels and partially contaminates the surface runoff and local flows. These polluted surface waters are used in conjunction with groundwater for irrigation purposes in the southern part of the Tehran. In this paper, a systematic approach to surface and groundwater resources modeling in the study area, with its complex system of water supply, groundwater recharge, and discharge, is discussed. A dynamic programming optimization model is developed for conjunctive use planning. The objective function of this model is developed to supply the agricultural water demands, to reduce pumping costs, and to control groundwater table fluctuations. To develop the response function of the aquifers located in the study area, a mathematical model for simulation of the Tehran aquifer water table fluctuations has been developed and calibrated with the available data. Different scenarios are defined to study the long-term impacts of the development projects on conjunctive use policies and water table fluctuations. Comparison of the results showed how significant is the effects of an integrated approach to the surface and groundwater resources allocation in Tehran metropolitan area. The proposed model is a useful tool for irrigation planning in this region.     

Operational Cost Benefits Study of Flexible On-Farm Irrigation Supply Systems

Efficient on-farm use of water and labor for all methods requires a water supply flexible in frequency, rate, and duration and under the control of the irrigator at the point of application. For surface irrigation, the use of large capacity systems for supply and distribution are essential and economical, especially when considering the reduced labor needs, increased irrigation efficiency, and reduced potential high water table problems resulting from having a large, flexible supply associated with a flexible arranged-demand schedule. Automation and stability of flow at the farm turnout, comparable to a domestic system with variable flow delivery conditions, are typically accomplished by use of large capacity semiclosed pipeline systems. A cost comparison of capital investment for various sized, flexible supply systems with resulting farm water and labor costs is presented which shows the great value from the upgraded management made possible.     

Irrigation Scheduling. I: Integer Programming Approach

This paper shows how a sequential irrigation schedule for a tertiary unit can be interpreted as a single machine scheduling problem with earliness, tardiness, and a common deadline. An integer program solution is presented for this irrigation scheduling problem. Two different models are presented to reflect different management options at the tertiary level. The first model allows jobs to be scheduled noncontiguously. In the second model only contiguous jobs are allowed. The second model has three submodels reflecting the various ways in which contiguous jobs can be scheduled over a fixed interval. Earlier work in determining unit costs of earliness/tardiness is reviewed and an alternative improved method is suggested. The models presented in this paper are applied to a tertiary unit with 16 users, both as a single interval and multi-interval irrigation scheduling problem. An alternative integer program is also presented which although computationally more efficient can only be used for single period scheduling problems. The models developed in this paper can be used to solve small scheduling problems and also to calibrate the heuristics as presented in the companion paper.     

Irrigation Scheduling. II: Heuristics Approach

A sequential irrigation schedule that honors user demands of duration and minimizes earliness and tardiness is interpreted as a single-machine schedule with earliness and tardiness costs and a common deadline (or fixed interval). A heuristic solution is presented for this irrigation scheduling problem. Four models are presented to reflect the different methods in which an irrigation system at the tertiary unit level may be operated, the first model permits jobs to be noncontiguous, i.e., idle time between jobs is permitted, whereas the others permit contiguous jobs only. The heuristic is tested extensively and the solution quality is compared with either an optimum solution from an integer program or the best available solution obtained from an integer program within allocated computation time. The heuristic is computationally efficient for all models presented, however for schedules with noncontiguous jobs, or where idle time is inserted before and after a contiguous set of jobs, solution quality deteriorates. The work brings the science of single scheduling from operations research into irrigation scheduling and suggests areas for further development.     

Measuring On-Farm Irrigation Efficiency with Chloride Tracing under Deficit Irrigation

Water is a limited resource in agricultural production in arid climates. Under such conditions, high irrigation efficiency can be obtained either through implementation of efficient irrigation systems such as drip or sprinkler systems or through the age-old practice of deficit irrigation with gravity systems. The method used to increase irrigation efficiency is often dictated by economic and/or social factors. In either case, the effectiveness of water management at the farm level needs to be evaluated by measuring irrigation efficiency. The objective of this study was to evaluate the irrigation efficiencies for three crops in Southern New Mexico using the chloride technique. The chloride technique is a simple method in which the natural chloride in the irrigation water is used as a tracer to estimate the leaching fraction and the irrigation efficiency at the farm level. Soil samples were collected from various fields in 15 cm increments to a depth of 180 cm at the end of the irrigation season. The samples were analyzed for moisture and chloride content. In addition to the chloride technique, on-farm irrigation efficiencies were measured using applied water, yield, and water production functions. Water production functions and yields were used to estimate total evapotranspiration while flow measurements were used to calculate the amount of applied water. The results showed that high irrigation efficiency can be accomplished using deficit irrigation. Irrigation efficiency values ranged from 83 to 98%. Irrigation efficiencies using the chloride technique were compared with efficiencies estimated from direct flow measurements. The differences between the two methods ranged from 2 to 11.4%. The results showed that even though the chloride technique is subject to sampling errors and simplified theoretical assumptions, it can be used to estimate on-farm irrigation efficiency with considerable accuracy.     

Impact of Irrigation Management Transfer on Land and Water Productivity and Water Supply in the Gediz Basin, Turkey

In the 1990s, Turkey started a fast transfer program in which a large proportion of government-managed irrigation systems were put into the hands of Water Users’ Associations (WUAs) in a very short space of time. One of the first systems to be handed over was the Gediz Basin. This study aims to set out the effects of the transfer of irrigation management in this basin on water and land productivity and water supply. For this purpose, the indicators of productivity and water supply proposed by the International Water Management Institute have been used to show changes between the pretransfer, transfer, and post-transfer periods. WUA averages for the post-transfer period calculated from the results ranged $2,076–$2,898?ha?1 for output per command area, $2,747–$4,585?ha?1 for output per irrigated area, $0.26–$0.68?m?3 for output per irrigation supply, $0.30–$0.63?m?3 for output per unit water consumed, 0.88–1.49 for relative water supply, and 0.99–1.99 for relative irrigation supply. During the period evaluated by the study, there was a decline in water supply indicators, as against a steady increase in the productivity of water and land use. The basic reason for this decrease in supply is the long-lasting and ongoing drought in the region.     

Demand Forecasting for Irrigation Water Distribution Systems

One of the main problems in the management of large water supply and distribution systems is the forecasting of daily demand in order to schedule pumping effort and minimize costs. This paper examines methodologies for consumer demand modeling and prediction in a real-time environment for an on-demand irrigation water distribution system. Approaches based on linear multiple regression, univariate time series models (exponential smoothing and ARIMA models), and computational neural networks (CNNs) are developed to predict the total daily volume demand. A set of templates is then applied to the daily demand to produce the diurnal demand profile. The models are established using actual data from an irrigation water distribution system in southern Spain. The input variables used in various CNN and multiple regression models are (1) water demands from previous days; (2) climatic data from previous days (maximum temperature, minimum temperature, average temperature, precipitation, relative humidity, wind speed, and sunshine duration); (3) crop data (surfaces and crop coefficients); and (4) water demands and climatic and crop data. In CNN models, the training method used is a standard back-propagation variation known as extended-delta-bar-delta. Different neural architectures are compared whose learning is carried out by controlling several threshold determination coefficients. The nonlinear CNN model approach is shown to provide a better prediction of daily water demand than linear multiple regression and univariate time series analysis. The best results were obtained when water demand and maximum temperature variables from the two previous days were used as input data.     

Uniformity Distribution and its Economic Effect on Irrigation Management in Semiarid Zones

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 (Ea). 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.     

Water Quality Aspects of Irrigation and Drainage: Past History and Future Challenges for Civil Engineers

This paper presents a brief history of irrigation and drainage related to ASCE activities on its Jubilee. This paper discusses legislation and policies that affect irrigation and drainage practices, water quality constituents of increasing concern in irrigation and drainage practices, and presents a prognosis on the future of declining freshwater resources available for irrigated agriculture and growing water quality problems in irrigation and drainage. Civil engineers in ASCE’s Irrigation and Drainage Division have compiled an 80-year history of highly meritorious service and accomplishments. In the next millennium, civil engineers will face a formidable challenge in managing and protecting the precious freshwater resources in the U.S.     

New Policies are Needed to Encourage Improvements in Irrigation Management

Innovations are needed in both the technological and policy dimensions of water resource management to achieve the gains in productivity required to feed the world’s increasing population. Scientists and engineers will continue to discover and disseminate new information regarding the technology of water management. However, the effective demand for that information at the farm level will be limited in areas where water prices and allocations do not reflect scarcity conditions. This paper describes how public policies regarding water resources and agricultural production can motivate farmers to consider scarcity values and the off-farm impacts of irrigation and drainage activities. Farm-level and regional models of crop production are examined, and optimizing criteria derived from the models depict the role of scarcity values and policy parameters in farm-level decisions regarding water use. The rate at which improvements in water management are implemented by irrigators around the world might be enhanced substantially by replacing inappropriate policies with those that motivate farmers and others to use scarce resources efficiently.     

Optimal Reservoir Operation for Irrigation of Multiple Crops Using Genetic Algorithms

This paper presents a genetic algorithm (GA) model for obtaining an optimal operating policy and optimal crop water allocations from an irrigation reservoir. The objective is to maximize the sum of the relative yields from all crops in the irrigated area. The model takes into account reservoir inflow, rainfall on the irrigated area, intraseasonal competition for water among multiple crops, the soil moisture dynamics in each cropped area, the heterogeneous nature of soils, and crop response to the level of irrigation applied. The model is applied to the Malaprabha single-purpose irrigation reservoir in Karnataka State, India. The optimal operating policy obtained using the GA is similar to that obtained by linear programming. This model can be used for optimal utilization of the available water resources of any reservoir system to obtain maximum benefits.     

Development and Evaluation of Soil Moisture-Based Seepage Irrigation Management for Water Use and Quality

A 2-year study was conducted at a seepage-irrigated vegetable farm in south Florida to develop and evaluate an improved, soil moisture-based irrigation management practice that could potentially reduce irrigation water use, prevent water quality impairment, and maintain or improve crop yield. The improved practice reduced irrigation water use by 36% compared to the conventional irrigation management. Moreover, the improved practice also increased rainfall retention and decreased runoff events by lowering the water table 13?cm compared to the conventional practice. Total dissolved phosphorus (P) concentrations in groundwater were higher (p<0.01) for the improved practice compared with the conventional practice in two of the three fields where ground water quality was monitored. Higher P concentrations for the improved practice were likely due to the dilution effect. Statistically, no differences (p>0.05) were observed in groundwater nitrogen (N) (NOx–N, NH4–N, and total dissolved N) concentrations between the improved and the conventional practices. Similarly, no statistical difference was observed in crop yield between the improved and the conventional practices, although the average total yield was higher for the improved practice. The improved practice also reduced the incidence of plant disease compared to the conventional practice which resulted in crop failure in some fields. Thus, use of the improved practice reduced irrigation water use without impacting crop yield.     

Quantifying Management of Irrigation and Drainage Systems

To evaluate the performance of irrigation systems, different indicators have been used by researchers. In this study some of the water management problems of three different irrigation systems in Iran are presented. In addition, the water delivery performance of the Doroodzan Irrigation and Drainage Network in southern Iran is evaluated in detail. The analyses included wet and dry seasons and were based on the indicators of overall project water delivery efficiency (ep) and the monthly water requirement of crops. The distribution and conveyance of water in the Doroodzan Irrigation Network was unreliable in both seasons. With an overall project efficiency of around 46%, about 20% of the total delivered water was distributed unreliably. Water distribution equity along tertiaries was also found to be poor. A contributing factor could be the poor operation and maintenance of gates.     

Irrigation Scheduling with Travel Times

In preparing water allocation schedules for fields in a lateral unit, the time required for water to travel from one point on a lateral to another can be significant and is dependent on the sequence in which users abstract water. This paper illustrates the problem of ignoring travel time and/or considering travel time to be sequence independent. For two users, each requesting water for a duration of 4 h, by assuming travel time to be sequence independent, one user receives water for 5 h, a 25% increase, and the other receives water for only 3 h, a 25% decrease. This paper presents a formulation of the irrigation scheduling problem for sequential users with sequent dependent travel time. The formulation is implemented as an integer program and applied to part of a lateral unit on the Juan Distributary, Haryana, India. Two models are presented, the first of which allows for noncontiguous jobs, i.e., idle time is permitted between jobs. The second model does not permit noncontiguous jobs.