Performance-Based Optimization of Land and Water Resources within Irrigation Schemes. I: Method

Optimum land and water allocation to different crops grown in different regions of an irrigation scheme is a complex process, especially when these irrigation schemes are characterized by different soils and environment and by a large network of canals. At the same time if the water supply in the irrigation schemes is limited, there is a need to allocate water both efficiently and equitably. This paper describes the approach to include both productivity (efficiency) and equity in the allocation process and to develop the allocation plans for optimum productivity and/or maximum equity for such irrigation schemes. The approach presented in this paper considers the different dimensions of equity such as water distribution over the season, water distribution during each irrigation, and benefits generated. It also includes distribution and conveyance losses while allocating water equitably to different allocation units. This paper explains the approach with the help of the area and water allocation model which uses the simulation–optimization technique for optimum allocation of land and water resources to different crops grown in different allocation units of the irrigation scheme.     

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.     

Productivity and Equity of Different Irrigation Schedules under Limited Water Supply

Some irrigation schemes with limited water supply in Central and Southern India follow the area proportionate water distribution based on assumed uniform characteristics of the command area (planned schedule). However in most cases, this planned schedule is overridden by the practice in which users at head draw more than their share of water (actual schedule) due to human factors and technical limitations of the planned schedule. This practice is highly inequitable as users at tail end do not get any water. This paper considers alternative schedules based on full irrigation or deficit irrigation within the framework of area proportionate water distribution in such irrigation schemes and presents the simulation–optimization technique to develop the corresponding land area and water allocation plan for different allocation units by considering the heterogeneity of the irrigation scheme. This paper further demonstrates the utility of proposed alternative schedules by comparing the productivity and equity of these schedules with planned and actual schedules for one irrigation scheme in Central India. The results show that the actual schedule reduces both productivity and equity greatly and the productivity and equity with the alternative schedules are higher than with the planned schedule. The results also show that deficit irrigation has great potential to increase both productivity and equity of irrigation schemes.     

Optimal Allocation of Irrigation Water Supplies in Real Time

This paper presents an evaluation of the potential of an optimization approach in improving real-time irrigation water management in systems with complex distribution networks. The optimization approach is based on quadratic programming. The operational objective is to maximize crop production through appropriate water allocation, while maintaining equity between different irrigation schemes and units within schemes. The approach has been evaluated through application to the irrigation system in the Lower Ayung River Basin in Bali, Indonesia. A simulation model of this irrigation system was available, and it has been possible to measure the effectiveness of the optimization approach by comparing the results of simulation runs incorporating optimization with the results of runs representing existing water allocation practice. The results indicate that the optimization approach does have potential and can significantly improve crop production at the basin scale. This paper presents a preliminary assessment of the potential of the approach and describes the development of a more sophisticated optimization approach based on real-time evaluations of crop water requirements. Considerations for practical implementation are discussed.     

Optimal Irrigation Planning under Water Scarcity

In this study optimal irrigation planning strategies are developed for the Nagarjuna Sagar Right Canal command in the semiarid region of South India. The specific objective of the study is to allocate the available land and water resources in a multicrop and multiseason environment and to obtain irrigation weeks requiring irrigation of a fixed depth of 40 mm. The problem is solved in four stages. First, weekly crop water requirements are calculated from the evapotranspiration model by the Penman-Monteith method. Second, seasonal crop water production functions are developed using the single-crop intraseasonal allocation model for each crop in all seasons. Third, allocations of area and water are made at seasonal and interseasonal levels by deterministic dynamic programming, maximizing the net annual benefit from the project. And fourth, once optimal seasonal allocations have been attained, irrigation scheduling is performed by running a single-crop intraseasonal allocation model. Optimal cropping pattern and irrigation water allocations are then made with full and deficit irrigation strategies for various levels of probability of exceedance of the expected annual water available. The results reveal that the optimization approach can significantly improve the annual net benefit with a deficit irrigation strategy under water scarcity.     

Optimal Irrigation Allocation: A Multilevel Approach

Optimal resources allocation strategies for a canal command in the semiarid region of Indian Punjab are developed in a stochastic regime, considering the competition of the crops in a season, both for irrigation water and area of cultivation. The proposed strategies are divided into two modules using a multilevel approach. The first module determines the optimal seasonal allocation of water as well as optimal cropping pattern. This module is subdivided into two stages. The first stage is a single crop intraseasonal model that employs a stochastic dynamic programming algorithm. The stochastic variables are weekly canal releases and evapotranspiration of the crop that are fitted to different probability distribution functions to determine the expected values at various risk levels. The second stage is a deterministic dynamic programming model that takes into account the multicrop situation. An exponential seasonal crop-water production function is used in this stage. The second module is a single crop stochastic dynamic programming intraseasonal model that takes the output of the first module and gives the optimal weekly irrigation allocations for each crop by considering the stress sensitivity factors of crops.     

连铸二冷参数的优化和控制研究

近些年连铸过程模拟成为研究的重点,模拟的根本目的在于优化连铸过程.为在保证连铸坯质量的前提下进一步提高连铸生产率,基于数学上的子问题接近优化技术建立了连铸过程二冷参数优化系统,可对不同钢种、不同拉速、不同冶金限制准则下的二冷各段配水进行最优化.运用优化后的这些过程参数,将使铸机以最大生产率、最小消耗运行,同时又保证了生产无缺陷铸坯.整个优化系统包括两个模块,一个是热过程模拟模块,另一个是设计优化模块,系统靠在两个模块之间反复自动循环调用而使参数得到优化.     

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.     

Irrigation Distribution Networks’ Vulnerability to Climate Change

Climate change will lead to changed demands on existing irrigation systems. This paper presents a methodology for investigating the performance of irrigation networks under climate change, and applies this to an irrigation network in Cordoba, southern Spain. The methodology uses emission scenarios (A2 and B2) developed by the Intergovernmental Panel on Climate Change. A global climate model (HadCM3) is used with downscaling to predict climate variables for 2050 and 2080 under the emission scenarios. European agricultural policy scenarios are used to predict future cropping patterns. Irrigation water requirements are then estimated for various combinations of these climate and cropping pattern scenarios, and the performance of the irrigation network is evaluated in terms of the equity and adequacy of pressure at the outlets, using EPANET. The methodology was applied to the Fuente Palmera irrigation district, which supplies water on-demand for drip irrigation. The results show that climate change would have a major impact on network performance with the existing cropping pattern, but that expected changes in cropping pattern would reduce this impact.     

Farmers’ Adaptation and Regional Land-Use Changes in Irrigation Systems under Fluctuating Water Supply, South India

In closing river basins where nearly all available water is committed to existing uses, downstream irrigation projects are expected to experience water shortages more frequently. Understanding the scope for resilience and adaptation of large surface irrigation systems is vital to the development of management strategies designed to mitigate the impact of river basin closure on food production and the livelihoods of farmers. A multilevel analysis (farm-level surveys and regional assessment through remote-sensing techniques and statistics) of the dynamics of irrigation and land use in the Nagarjuna Sagar project (South India) in times of changing water availability (2000–2006) highlights that during low-flow years, there is large-scale adoption of rainfed or supplementary irrigated crops that have lower land productivity but higher water productivity, and that a large fraction of land is fallowed. Cropping pattern changes during the drought reveal short-term coping strategies rather than long-term evolutions: after the shock, farmers reverted to their usual cropping patterns during years with adequate canal supplies. For the sequence of water supply fluctuations observed from 2000 to 2006, the Nagarjuna Sagar irrigation system shows a high level of sensitivity to short-term perturbations, but long-term resilience if flows recover. Management strategies accounting for local-level adaptability will be necessary to mitigate the impacts of low-flow years but there is scope for improvement of the performance of the system.     

Water Scarcity Effects on Equitable Water Distribution and Land Use in a Major Irrigation Project—Case Study in India

In many river basins, upstream development and interannual variations in rainfall can cause both episodic and chronic shortages in water supplies downstream. Continued rapid development of surface and groundwater throughout the Krishna Basin in southern India resulted in historically low inflows to the main canals of the Nagarjuna Sagar irrigation project (8,955?km2) during a recent drought (2002–2004). This paper presents an integrated approach to assess how cropping patterns and the spatial equity of canal flow changed with water supply shocks in the left canal command area (3,592?km2) of Nagarjuna Sagar. We combined 3?years (2000–2003) of canal release data with census statistics and high temporal resolution (8–10?days) moderate resolution imaging spectrometer (MODIS) 500-m resolution satellite imagery. The impact of water scarcity on land use pattern, delineated by MODIS images with moderate spatial resolution, was comparable with the census statistics, while the MODIS data also identified areas with changes and delays in the rice crop area, which is critical in assessing the impact of canal operations. A 60% reduction in water availability during the drought resulted in 40% land being fallowed in the left-bank canal command area. The results suggest that head reach areas receiving high supply rates during a normal year experienced the highest risks of fluctuations in water supply and cropped area during a water short year compared to downstream areas, which had chronically low water supply, and better adaptive responses by farmers. Contrary to expectations, the spatial distribution of canal flows among the three major zones of the command area was more equitable during low-flow years due to decreased flow at the head reach of the canal and relatively smaller decreases in tail-end areas. The findings suggested that equitable allocations could be achieved by improving the water distribution efficiency of the canal network during normal years and by crop diversification and introduction of alternative water sources during water shortage years. The study identified areas susceptible to decreases in water supplies by using modern techniques, which can help in decision-making processes for equitable water allocation and distribution and in developing strategies to mitigate the effects of water supply shocks on cropping patterns and rural livelihoods.     

Evaluation of the Water Delivery Performance of the Menemen Left Bank Irrigation System Using Variables Measured On-Site

This study determines the water delivery performance at secondary and tertiary canal level of the Menemen Left Bank Irrigation system, an open canal irrigation system located in Turkey, for the irrigation seasons of the years 2005–2007. At secondary canal level, water supply ratio was used, and at tertiary level, the indicators of adequacy, efficiency, dependability, and equity were used. In calculating these indicators in this study, the amounts of water diverted to the canals, efficiency of water conveyance, and of water application were measured. Of these indicators, the water supply ratio was determined for the secondary canal, and the other indicators were determined for a total of six selected tertiary canals at the head, middle, and lower end of the secondary. At secondary level, the water supply ratios obtained to total irrigation water requirements for the months of July and August, when requirement for irrigation water is at a maximum, was determined to be less than one, while the water supply ratios obtained to net irrigation water requirement was found to be more than one. With regard to water delivery performance at tertiary level, adequacy, efficiency, dependability, and equity were found to be poor for each of the three years of the study, with efficiency rising to “fair” level only in 2005. In order to raise the water delivery performance of the system, it is necessary to reduce water conveyance losses to increase the water application efficiency, to prepare water distribution plans which take in tertiary canals, and to measure and monitor the water diverted to the canals.     

Reservoir Release Policy for Large Irrigation System

This paper describes the formulation of a model for optimized crop and water planning decisions in an irrigation system in Thailand. It facilitates consultation in which representatives of stakeholders, officials, farmers, and researchers can contribute to the decision making. Linear programming and the analytical hierarchy process are the principal modeling tools to optimize the collective system objectives: productivity, equity, and security. The results of the model are compared with observed events of one dry season. The optimized policy generated by the model suggested a diversified cropping pattern, which would decrease the water requirement by 16.4% and enhance net benefit per cubic meter of water used by 39.9%. The erratic water availability from the reservoir and the operational procedures inside the system are reviewed, analyzing historical data in terms of reliability, resiliency, and vulnerability. These include lack of proper assessment of available water, effective farmer organization, and prompt data processing and communication. Furthermore, for the effective implementation of an optimized irrigation policy, a water release pattern of the storage reservoir has been suggested.     

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.     

Optimal Reservoir Operations for Irrigation Using a Three Spatial Scales Approach

A three-step computational model for the optimal weekly interseasonal operation of a multipurpose (irrigation, environmental, domestic/industrial) reservoir is developed. Environmental and domestic/industrial uses are evaluated and considered as priority uses that induce deficit irrigation conditions. The spatiotemporal variability of the irrigation water demand at the basin level is accounted for. The objective is the maximization of the interseasonal agricultural profitability at the basin level. The optimal allocation process solves the competition for water on different temporal scales (weekly, seasonal, and interseasonal) and on different spatial scales (in basins among irrigation areas and in irrigation areas among crops). The three steps are simulation model operating at the soil-crop unit level, optimization model operating at the multicrop area level, and optimization model operating at the basin level. This consists of parametric dynamic programming for which an analytical objective function was defined and an analytical solution was determined. This solution replaces the iterative procedure, so that it is possible to account for all the variables without running into the “curse of dimensionality” problem. The environmental use allocation is expressed as a function of a parameter, the variations of which give different environmental protection levels. The validation case study emphasizes the importance of considering the spatiotemporal variability of the demand. This is consistent with the “computationally tractable” model algorithm.     

Resource Management of Bridge Deck Rehabilitation: Jacques Cartier Bridge Case Study

The condition and performance of bridges vary widely across North America. The large amount of expenditures on bridges needs significant efforts to optimize budget and resource allocation and to select the best rehabilitation or replacement method, which reduces project cost and duration. Simulation has been widely used in the construction area to optimize productivity and resource allocation. Current research optimizes resource combination for bridge deck rehabilitation projects using discrete event simulation. The Jacques Cartier Bridge redecking project is selected as a case study. Data related to productivity and duration of different activities were collected from the project. Probability distributions are fitted, which show the robustness of normal distribution to fit most variables. A simulation model is developed for this project in order to experiment with and perform sensitivity analysis. Based on the simulation results, an optimum resource combination of deck rehabilitation is obtained, which is [five teams, two saws, three old section trucks, and five new panel trucks] TSON 5235 with the unit (panel) cost of $747/h (direct cost only). The model developed is tested against real productivity where it shows reasonable results. The present research is relevant to both researchers and practitioners. It provides bridge redecking researchers with a real case study, a simulation model, and an approach to analyze projects. It also provides practitioners with an approach to optimize the usage of their resources considering direct project cost.     

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.     

Predicting Soil Salinity under Various Strategies in Irrigation Systems

This paper presents a model to estimate the soil salinity for different on-farm management strategies under irrigated conditions. It is based on research in the Mani?oba irrigation scheme in northeast Brazil, where upward flow from the shallow water table is the main cause of soil salinization. The model calculates soil water and salt balances for the topsoil. It is calibrated for the topsoil of abandoned plots and for the root zone (0.9?m) of mango trees. Simulating the effect of different management scenarios on soil salinity may help to organize the switch from intensive surface irrigation to more efficient irrigation practices.     

A Paradigm Shift in Irrigation Management

In coming decades, irrigated agriculture will be called upon to produce up to two thirds of the increased food supply needed by an expanding world population. But the increasing dependence on irrigation will coincide with accelerating competition for water and rising concern about the environmental effects of irrigation. These converging pressures will force irrigators to reconsider what is perhaps the most fundamental precept of conventional irrigation practice; that crop water demands should be satisfied in order to achieve maximum crop yields per unit of land. Ultimately, irrigated agriculture will need to adopt a new management paradigm based on an economic objective—the maximization of net benefits—rather than the biological objective of maximizing yields. Irrigation to meet crop water demand is a relatively simple and clearly defined problem with a singular objective. Irrigation to maximize benefits is a substantially more complex and challenging problem. Identifying optimum irrigation strategies will require more detailed models of the relationships between applied water, crop production, and irrigation efficiency. Economic factors, particularly the opportunity costs of water, will need to be explicitly incorporated into the analysis. In some cases the analysis may involve multi-objective optimization. The increased complexity of the analysis will necessitate the use of more sophisticated analytical tools. This paper examines the underlying logic of this alternative approach to irrigation management, explores the factors that will compel its adoption, and examines its economic and environmental implications. Two important concerns, sustainability and risk, are discussed in some depth. Operational practices for implementing the new approach are contrasted with current, conventional irrigation practices. Some of the analytical tools that might be employed in the search for optimum irrigation strategies are reviewed. Finally, the limited and largely intuitive efforts that have already been made to implement this new paradigm are discussed.     

Long-Term Operation of Irrigation Dams Considering Variable Demands: Case Study of Zayandeh-rud Reservoir, Iran

Dependency of water demands on the climate variation occurs especially in regions where agricultural demand has a significant share of the total water demands. The variability between demands that are based on annual climate conditions may be larger than the uncertainty associated with other explanatory variables in long-term operation of an irrigation dam. This paper illustrates certain benefits of using variable demands for long-term reservoir operation to help manage water resources system in Zayandeh-rud river basin in Iran. A regional optimal allocation of water among different crops and irrigation units is developed. The optimal allocation model is coupled with a reservoir operating model, which is developed based on the certain hedgings that deals with the available water and the water demands mutually. This coupled model is able to activate restrictions on allocating water to agricultural demands considering variation of inflow to the reservoir, variation of demands, and the economic value of allocating water among different crops and irrigation units. Using this model, long-term operation of Zayandeh-rud dam is evaluated considering different scenarios of inflow to the reservoir as well as agricultural demands. The results indicate that the use of operating rules which consider variable demands could significantly improve the efficiency of a water resources system in long-term operation, as it improves the benefit of Zayandeh-rud reservoir operation in comparison with conventional water supply approaches.