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.     

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.     

Integrated Agro-Economic Approach to Deficit Irrigation on Lettuce Crops in Sicily (Italy)

The effect of four different irrigation levels on the marketable yield and economic return of summer-growth lettuce was evaluated during 2005 and 2006 in Eastern Sicily, Italy. The viability of deficit irrigation was evaluated by estimating optimum applied water levels. Actual evapotranspiration (ETa) was estimated by combining pan evaporation measures and the Penman–Monteith approach (ET0-PM). The highest marketable yield of lettuce was recorded for plots receiving 100% ET0-PM. For deficit irrigated plots, reductions in crop production were ascribed to a decrease in lettuce weight. Crop coefficients equal to 1 determined maximum crop production values. Crop water use efficiency was maximum at a 100% ET0-PM level of water applied, corresponding to yield of 0.3?t?ha?1?mm?1. Irrigation water use efficiency reached its maximum at a 40% ET0-PM level, with values of 0.54 and 0.44?t?ha?1?mm?1 during 2005 and 2006, respectively. Water applied and marketable yield of lettuce showed a significant quadratic relationship. Cost functions had a quadratic form during 2005 and a linear form during 2006. In the land-limiting condition the optimal economic levels fit the agronomic ones well. In the water-limiting condition, ranges of water deficit of 15–44% and 74–94% were as profitable as full irrigation, thus contributing to appreciable water savings.     

LEPA and Spray Irrigation for Grain Crops

Two low energy precision application (LEPA) sprinkler methods (double-ended socks and bubblers) and two spray sprinkler methods (low-elevation spray application and overhead spray) were used to irrigate corn, grain sorghum, and winter wheat in the Southern High Plains. For full or 100% irrigation, sufficient 25-mm applications were applied to maintain soil water at non-yield-limiting levels determined in earlier research with the three crops. Deficit-irrigated treatments were irrigated on the same days as the control treatment in 25 or 33% increments of the fully irrigated amount. Irrigation water was applied to or above alternate furrows with a three-span lateral move irrigation system. Corn and sorghum were grown on beds and furrows with all furrows diked, and wheat was flat-planted without basin tillage. Grain yields increased significantly with irrigation amount (p ≤ 0.05) for all crops during all years. With full irrigation, grain yields varied little among the sprinkler methods, and yields averaged 13.5, 8.9, and 4.6 Mg∕ha for corn, sorghum, and wheat, respectively. With the 25 and 50% deficit irrigation amounts, sorghum yields with LEPA irrigation were 1.1 Mg∕ha larger than with the two spray methods. For 75% irrigation of sorghum and for deficit irrigation of the other two crops, there was little yield difference between the LEPA and spray sprinkler methods. Grain yields were significantly correlated with seasonal water use with regression coefficients of 2.89, 1.84, and 0.915 kg∕m3 for corn, sorghum, and wheat, respectively.     

Irrigation Performance using Hydrological and Remote Sensing Modeling

Development of water saving measures requires a thorough understanding of the water balance. Irrigation performance and water accounting are useful tools to assess water use and related productivity. Remote sensing and a hydrological model were applied to an irrigation project in western Turkey to estimate the water balance to support water use and productivity analyses. Remote sensing techniques can produce high spatial coverage of important terms in the water balance for large areas, but at the cost of a rather sparse temporal resolution. Hydrological models can produce all the terms of the water balance at a high temporal, but low spatial resolution. Actual evapotranspiration for an irrigated area in western Turkey was calculated using the surface energy balance algorithm for land (SEBAL) remote sensing land algorithm for two Landsat images. The hydrological model soil-water-atmosphere-plant (SWAP) was setup to simulate the water balance for the same area, assuming a certain distribution in soil properties, planting dates and irrigation practices. A comparison between evapotranspiration determined from SEBAL and from SWAP was made and differences were minimized by adapting the distribution in planting date and irrigation practice. The optimized input data for SWAP were used to simulate all terms of the accumulated water balance for the entire irrigation project, and subsequently used to derive the irrigation performance indicators. The innovative methodology presented is attractive as it diminishes the need of field data and combines the strong points of remotely sensed techniques and hydrological models.     

Long-Term Effects of Irrigation Water Conservation on Crop Production and Environment in Semiarid Areas

As water is becoming a scarcer commodity, savings in the irrigation sector could enhance water development in areas currently not being irrigated, and arrest the rapid environmental degradation due to waterlogging in arid areas. The agro-hydrological model SWAP is used to investigate possible water reductions for wheat and cotton crops under shallow water table conditions prevailing in the Fourth Drainage Project in Punjab, Pakistan. The simulations are performed for both drained and undrained conditions considering three different irrigation water qualities. The overall objective is to save good-quality irrigation water. The results indicate that when good-quality canal water is available, a reduced application to wheat (195 mm) and cotton (260 mm) will keep the soil healthier under both drained and undrained conditions. For poor-quality irrigation waters (mixed canal and tubewell or tubewell alone), this water conservation strategy will be insufficient. Therefore, more water (325 mm for wheat and 325 mm for cotton) should be applied to keep crop production and soil salinity within desirable limits. However, this will only be applicable to the areas where proper subsurface drainage systems are present. For undrained areas, this strategy will not be feasible due to rising water tables; other options like growing more salt-tolerant crops should be considered. Drainage cannot solve salinity buildup problems under all circumstances because relatively dry monsoons provide insufficient leaching water, and salts added by tubewell irrigation can only be evacuated from the soil profile if the drainage system is very intense. Reduced irrigation inputs is a proper short-term solution, although wheat production tends to decline in all areas without drainage, even when irrigated with canal water. Large-scale drainage investments associated with adjusted irrigation planning seem unavoidable in the long run.     

SDI Dripline Spacing Effect on Corn and Soybean Yield in a Piedmont Clay Soil

A subsurface drip irrigation (SDI) system was installed in the Piedmont of North Carolina in a clay soil in the fall of 2001 to test the effect of dripline spacing on corn and soybean yield. The system was zoned into three sections; each section was cropped to either corn (Zea mays L.), full-season soybean [Glycine max (L.) Merr.], or winter wheat (Triticum aestivum) double cropped to soybean representing any year of a typical crop rotation in the region. Each section had four plots; two SDI plots with dripline spacing at either 1.52 or 2.28 m, an overhead sprinkler irrigated plot, and an unirrigated plot. There was no difference in average corn grain yield for 2002–2005 between dripline spacings or between either dripline spacing and sprinkler. Irrigation water use efficiency (IWUE) was greater for sprinkler irrigated corn than for either SDI treatment and there was no difference in IWUE in soybean. Water typically moved laterally from the driplines 0.38 to 0.50 m. SDI yield and IWUE increased relative to sprinkler yields and water use efficiency in the second and third year of the study. This may suggest that initial fracturing of the heavy clay soil during SDI system installation and subsequent settling of the soil affected water distribution.     

Residential Irrigation Water Use in Central Florida

Automatic inground irrigation is a common option for residential homeowners desiring high-quality landscapes in Florida. However, rapid growth is straining water supplies in some areas of the state. The first objective of this study was to document residential irrigation water use in the Central Florida ridge region on typical residential landscapes (T1). The second objective was to determine if scheduling irrigation by setting controllers based on historical evapotranspiration (ET) (T2) and reducing the percentage of turf area combined with setting the controllers based on historical ET (T3) would lead to reductions in irrigation water use. The time frame of this study was 30?months beginning in January 2003. Irrigation accounted for 64% of the residential water use volume over all homes monitored during this project. The T1 homes had an average monthly water use of 149?mm/month. Compared to the T1 homes, T2 resulted in a 30% reduction (105?mm/month), and T3 had a 50% reduction (74?mm/month) in average monthly water use. Average monthly water use was significantly different (p<0.001) across the three irrigation treatments. Setting the irrigation controllers to apply water according to seasonal demand resulted in significantly less irrigation water applied. In addition, increasing the proportion of landscape area from 23% (T1 and T2) ornamental plants irrigated with sprinklers to 62% and irrigated with micro-irrigation (T3) resulted in the largest reduction in irrigation water applied. Compared to T2 where only the irrigation controllers were adjusted, this additional decrease in irrigation water applied was a result of low volume application on only a portion of the landscaped beds where irrigation is only applied to the root zone of plants.     

SIMGRO, a GIS-Supported Regional Hydrologic Model in Irrigated Areas: Case Study in Mendoza, Argentina

The SIMGRO hydrologic simulation model was extended to include irrigation practice. It could then be used to evaluate the effect of hydrologic changes in an irrigated area in the province of Mendoza, Argentina where, given an average annual rainfall of approximately 200?mm, irrigation is crucial for agriculture. A storage dam was recently constructed in the Mendoza River to control the fluctuating river flow and to guarantee that the demand for water is met throughout the year. The dam will impact on parts of the irrigation system where groundwater levels are already high and salinization occurs. To evaluate these changes and possible mitigation measures, two performance indicators that consider groundwater and surface water were used: Relative evapotranspiration and the depleted fraction. Scenario runs revealed that the irrigation water losses from the canals affect the groundwater levels in the downstream part of the irrigated area; an increase in salinity was also revealed.     

Soil Salinity Modeling over Shallow Water Tables. I:?Validation of LEACHC

Soil salinity is a very common problem in today's irrigated agriculture. High salinity levels adversely impact crop yields and reduce overall soil quality. The presence of a saline shallow water table can be a major contributor to this problem. The LEACHC version of LEACHM is one of the few numerical models that considers independent movement of individual ions along with their detailed chemistry. This model has apparently not previously been tested under saline shallow water table conditions. LEACHC was evaluated using both lysimeter and field data from the literature. The model performed reasonably well in simulating solute transport above a saline shallow water table. For both data sets used in model validation, less reactive ions (sodium and chloride) were predicted well while calcium concentrations were underpredicted. For the field data, the model predicted soil electrical conductivity (EC) profiles better than most of the individual ions. The water content profiles associated with the field data were also predicted quite well. Based on these results, LEACHC was selected as a simulation tool for evaluating the effects of management practices on salinity transport in crop root zones above a saline shallow water table.     

Regional Water Management Modeling for Decision Support in Irrigated Agriculture

Efficient water management is one of the key elements in successful operation of irrigation schemes in arid and semiarid regions. An integrated water management model was developed by combining an unsaturated flow model and a groundwater simulation model. These combined models serve as a tool for decision making in irrigation water management to maintain the water tables at a safe depth. The integrated model was applied on a regional scale in Sirsa Irrigation Circle, covering about a 0.42 million ha area in the northwestern part of Haryana, India, which is faced with serious waterlogging and salinity problems in areas underlain with saline ground irrigated by the canal network. The model was calibrated using the agrohydrologic data for the period 1977–1981 and validated for the period 1982–1990 by keeping the calibrating parameters unchanged. The model was used to study the long-term impact of two water management interventions related to the canal irrigation system—change in pricing system of irrigation water, and water supply according to demand—on the extent of waterlogging risk. Both of these strategies, if implemented, would considerably reduce aquifer recharge and consequently waterlogging risk, compared to the existing practice. The water supply according to demand strategy was slightly more effective in reducing aquifer recharge than the water pricing intervention. The implementation of the proposed water pricing policy would pose no problem in fitting into the existing irrigation system, and thus it would be easier to implement, compared to the water supply according to demand strategy, when taking technical, financial, and social considerations into account.     

Model for the Simulation of Water Flows in Irrigation Districts. II: Application

In a companion paper a model for the simulation of water flows in irrigation districts was formulated. The model combines a series of modules specialized in surface irrigation, open channel distribution networks, crop growth modeling, irrigation decision making, and hydrosaline balance. The objective of this paper is to calibrate, validate, and apply the model, using the Irrigation District Five of Bardenas (Spain) as a study area. Two years of study were used for the analysis, which could be classified as normal (2000) and dry (2001) from the point of view of crop water requirements. Model calibration was performed in one of the 11 hydrological sectors in which the district is divided. The control variable was the monthly water demand, while the calibration variables were related to irrigation operation and scheduling. The seasonal differences in observed and simulated water demand amounted to 0.9 and 1.9% for 2000 and 2001, respectively. Model validation was performed in the rest of the sectors, and the regression line of observed versus simulated monthly water demand could not be distinguished from a 1:1 line in both years. Model application explored scenarios based on management improvement (controlling the irrigation time) and structural improvement (increasing drainage water reuse for irrigation). These scenarios permitted one to sharply reduce water demand, halve the irrigation return flows, and reduce the daily irrigation period from 24?to?16?h.     

OCCASION: New Planning Tool for Optimal Climate Change Adaption Strategies in Irrigation

To sustain productive irrigated agriculture with limited water resources requires a high water use efficiency. This can be achieved by the precise scheduling of deficit irrigation systems taking into account the crops’ response to water stress at different stages of plant growth. Particularly in the light of climate change with rising population numbers and increasing water scarcity, an optimal solution for this task is of paramount importance. We solve the corresponding complex multidimensional and nonlinear optimization problem, i.e., finding the ideal schedule for maximum crop yield with a given water volume by a well tailored approach which offers straightforward application facilities. A global optimization technique allows, together with physically based modeling, for the risk assessment in yield reduction considering different sources of uncertainty (e.g., climate, soil conditions, and management). A new stochastic framework for decision support is developed which aims at optimal climate change adaption strategies in irrigation. It consists of: (1) a weather generator for simulating regional impacts of climate change; (2) a tailor-made evolutionary optimization algorithm for optimal irrigation scheduling with limited water supply; and (3) mechanistic models for rigorously simulating water transport and crop growth. The result, namely, stochastic crop-water production functions, allows to assess the impact of climate variability on potential yield and thus provides a valuable tool for estimating minimum water demands for irrigation in water resources planning and management, assisting furthermore in generating maps of yield uncertainty for specific crops and specific agricultural areas. The tool is successfully applied at an experimental site in southern France. The impacts of predicted climate variability on maize are discussed.     

Managing Irrigation for Better River Ecosystems—A Case Study of the Middle Rio Grande

The technology of irrigated agriculture has often been controversial. The development agencies would praise its productivity, as only 18% of the world’s cultivated land is irrigated but produces roughly 33% of the world’s human food supply. Environmental and ecological concerns cite the degradation of natural landscapes, elimination of floodplains and wetlands, and profound impacts on wildlife habitats. Dr. Mark Fiege (University of Washington Press, Seattle, 1999) in his book entitled Irrigated Eden: The Making of an Agricultural Landscape in the American West proposes a possible reconciling view—that irrigation should be viewed as a manmade ecological system, in which land and water are modified to increase agricultural production. The reported research has used this ecological approach to study the Middle Rio Grande irrigated landscape, for the purpose of identifying options for water and ecosystem conservation. This article presents research findings related to opportunities in the agricultural sector to reduce water diversions from the river, primarily by changing the practice of continuous canal water delivery to rotational water delivery. Following the research recommendations since 2002, irrigation water users in the Middle Rio Grande Valley have reduced their diversions by more than 30%, which means more water is now available in the river for better ecology in general and for better fish and wildlife habitat in particular.     

Decision Support Systems for Efficient Irrigation in the Middle Rio Grande Valley

Water is the lifeblood of the American West and the foundation of its economy, but it remains its scarcest resource. The explosive population growth in western United States, the emerging additional need for water for environmental uses, and the national importance of the domestic food production are driving major conflicts between these competing water uses. The case of the Middle Rio Grande illustrates the problem very well. The river is the ecological backbone of the Chihuahuan Desert region in the western United States, and supports its dynamic and diverse ecology, including the fish and wildlife habitat. The Rio Grande Silvery Minnow is federally listed as an endangered species, and the irrigated agriculture in the Middle Rio Grande has come under increasing pressure to reduce its water consumption and maintain the desired level of service to its water users. This paper will present the writers ongoing research on options to make irrigation system operations more efficient in the Middle Rio Grande Conservancy District (MRGCD). Specifically, it will describe formulation and implementation of a decision support system (DSS) that can assist the MRGCD managers to more efficiently plan and implement their water delivery operations, thereby reducing river diversions. The MRGCD DSS uses linear programming to find an optimum water delivery schedule for canal service areas in the MRGCD irrigation system. The computer model is presently formulated along with the related data sets for two of the four divisions in the MRGCD. For the past 3?years, the model has been validated in the field and the evaluation indicates that the model recommendations are realistic and represent current management practices. The future plans are to complete the data files for the irrigation networks in the remaining two divisions and concurrently help the MRGCD implement the DSS to guide water delivery operation.     

Pond Water Source for Irrigation on Steep Slopes

Existing technologies have been tailored to deliver cost-effective irrigation on a railway embankment and excavated steep slopes (referred to as batters) within a semiarid environment. Irrigation is to aid the establishment of 100% grass cover within a few weeks to mitigate soil erosion problems. It is based on water sourced from a temporary excavated pond plus the use of a solar powered pump and a drip irrigation system. Railway batter erosion remediation is timed for the wet summer season when irrigation can be used to supplement natural rainfall. For a given irrigation demand and catchment area, critical (minimum) pond volume is estimated from regional charts developed for ungauged catchments. About 20% of the critical volume is added to account for evaporation losses and dead storage. Also, seepage losses need to be considered if the soil is medium to coarse textured and if the pond is not lined with an impermeable material. Initial results are very encouraging with a cost estimate of AU$2.74/m2 of batter area treated (irrigated). Irrigation unit cost is expected to decrease with a larger scale irrigated batter area and the refinement of technologies and installation procedures. Although irrigation methodologies were developed for railway embankments and excavated slopes, they can also be used for erosion control on steep slopes such as road embankments or excavated slopes and earth dam side slopes.     

Knowledge-Based Model for Supplementary Irrigation Assessment in Agricultural Watersheds

In this paper a knowledge-based model for supplementary irrigation assessment in rainfed agricultural watersheds is presented. The supplementary irrigation assessment problem is divided into different components and is modeled separately. Geographic Information System (GIS) is used to aggregate spatially varying attributes required for the modeling. A graphical user interface is developed in a GIS platform by using the ERDAS macro language tools. The model was applied to two case study areas in India: a subwatershed of Gandheshwari area (West Bengal), and Harsul watershed (Maharashtra). In the Gandheshwari subwatershed, the water availability was found to be inadequate to meet the irrigation requirement and hence the model identified the areas that can be irrigated with different outsource water supply. On the other hand, surface runoff generated in the Harsul watershed was found to be sufficient to meet the supplementary irrigation requirement, thereby showing the feasibility for supplementary irrigation in the area. Using the model, the effect of any rainfall condition can be simulated and hence appropriate measures can be taken in advance to reduce the risk of crop failure.     

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.     

Analytical Solution for Normal Irrigation Distribution Parameters

The model most widely used to represent sprinkler irrigation distribution parameters is based on numerical solutions to the normal cumulative probability density function. For most practical irrigation design and management applications, numerical solutions are too laborious. One other study reported analytical approximations for several irrigation distribution parameters derived from the normal model. The estimation error resulting from those approximations were variable over the operational range of irrigation uniformity and irrigation adequacy and were quite high in some ranges. In this note, more accurate analytical approximations are presented for the distribution coefficient, the application efficiency, the water requirement efficiency, the deficiently irrigated volume, and the average deficit over the deficiently irrigated area. On average, over the entire operational range of irrigation uniformity and irrigation adequacy, the new approximations are about an order of magnitude more accurate than the previous approximations and introduce negligible error for most practical applications.     

Coupled Crop and Solid Set Sprinkler Simulation Model. II: Model Application

In this work, applications of the coupled solid set sprinkler irrigation and crop model AdorSim introduced in the companion paper are presented. The sprinkler irrigation model is based on ballistic theory, while the crop model is based on CropWat. AdorSim was used to evaluate the effect of sprinkler spacing on seasonal irrigation water use (WU) and crop yield. The most relevant results were related to the characterization of advanced irrigation scheduling strategies. The differences in crop yield and WU derived from irrigating at different times of the day were estimated for two locations strongly differing in wind speed. Irrigation guidelines were established in these locations to relate gross water use and water stress induced yield reductions. Simulations were also applied to estimate adequate wind speed thresholds for irrigation operation. In the experimental conditions, thresholds of 2.0–2.5?m?s?1 proved effective to control yield reductions and to minimize WU.