MANAGING ROTATIONAL CANAL WATER SUPPLIES ON THE FARM1

ABSTRACT: A procedure to determine optimal irrigation scheduling strategies under rotational water delivery systems is presented. The methodology involves integration of water delivery amount and frequency, irrigation management strategies, evapotranspiration sequences and crop-evapotranspiration-production functions to arrive at an optimal irrigation strategy. Application of the methodology to a farm in the service area of Western Yamuna Canal (India) where a two-stage system of rotation, one among the irrigation channels and the other among the farmers, is in vogue, reveals that maximum production is obtained with water application in a rotational manner (RI) rather than with irrigation in every or alternate supply periods. Increase in mean water supply which can be effected through improvement in on-farm conveyance and application systems, has a greater effect on yield than decrease in variance of the supply. Benefit cost analyses indicates that precision land leveling is more cost effective in increasing water supply as compared to water-course lining.     

The agricultural development of sub-Saharan Africa

A study prepared by FAO on the irrigation potential of sub-Saharan Africa is compared with the results of a similar study by the World Bank. The FAO study estimates that there are approximately 33 million hectares potentially suitable for irrigation. The World Bank study indicates that the actual number may be closer to 20 million. Reasons are offered to explain the difference in the conclusions of the two studies. This paper also examines the cost of developing irrigation in the sub-Sahara as well as the food-producing potential from irrigation. Costs are found to be in line with irrigation schemes of similar size in other regions. Nevertheless, because much of the irrigation potential is located in only six countries, irrigation does not appear to be a viable means of agricultural development in the sub-Sahara.     

WATER REUSE FROM SEWAGE EFFLUENT BY IRRIGATION: A PERSPECTIVE FOR HAWAII1

ABSTRACT: Surrounded by an ocean, the Hawaiian Islands are limited in their natural fresh water resources. The major readily developable potable sources are the high quality ground water sources which serve both domestic uses and sugarcane irrigation although irrigation water does not require as high a quality as drinking water. The increasing overall fresh water requirements for the island of Oahu will outstrip the potential yield of fresh ground water sources, as developed by present technology, by the year 2000 according to Honolulu Board of Water Supply projections. There are water shortage regions on other islands. Water reuse from sewage effluent for irrigation will augment natural water resources, furnish supplemental or alternative fertilizer, and reduce ocean water pollution and the costs of engineering systems. In cooperative field testing from 1971 to 1975, it was demonstrated that effluent can be applied as supplemental water for furrow irrigation of sugarcane without detriment to ground water quality and sugar yield. Studies are in progress to test different dilutions of effluent and its use with chemical ripeners to improve crop yield. Sugarcane plantations on Oahu, Maui, and Kauai are in various stages of water reuse by effluent irrigation. Reuse is presently practiced for irrigation of golf courses and is being planned for forage crops in Hawaii.     

ALLOCATION MODEL FOR IRRIGATION WATER COST: CASE STUDY OF THE NILE VALLEY IN EGYPT1

ABSTRACT: An allocation model for irrigation water cost, based on the Use of Facilities method, is presented. The model is developed for large-scale irrigation systems which may include multipurpose reservoirs, irrigation control works, pump stations and irrigation canals of various orders. The model accounts for the water conveyance losses as well as the water gains in the irrigation canals, and their effects on irrigation cost. It is applied to the irrigation distribution system of the Nile Valley in Egypt, which contains the High Aswan Dam, 16 irrigation structures, 12 pump stations, and numerous irrigation canals. The irrigation water cost at 29 areas representing the Nile Valley is determined.     

GROUNDWATER MANAGEMENT ON THE TEXAS HIGH PLAINS1

ABSTRACT The effects of major water management practices on the pumping requirement from the Ogallala aquifer are discussed. Demand on the aquifer may be reduced as much as 15 percent by recycling irrigation runoff, 25 percent by recycling irrigation runoff and irrigating with water from playas, and 29 percent by recycling irrigation water in combination with irrigation from playas and artificial recharge of playa water to the aquifer. Other practices that can result in more efficient use of precipitation and groundwater are limited irrigation, land forming, soil profile modification, and improved irrigation systems, thereby reducing the pumping demand on the Ogallala. Additional water supplies can possibly be obtained by water harvesting, weather modification, and water importation. Conclusions reached were that the overdraft on the aquifer can be reduced by the application of sound water management practices on an area-wide basis.     

THE DEVELOPMENT OF A MODEL TO EVALUATE HYDROLOGIC RISK IN WATER RESOURCE SYSTEM DESIGN1

In this paper, a procedure for analyzing a water resource system with special emphasis on evaluation of acceptable economic risk due to occasional failures to deliver water is proposed. The basic methodology includes the development of a simple mathematical model which describes the physical hydrologic and economic characteristics of a single reservoir irrigation and city water supply system and an evaluation of economic benefits of the system with full and partial deliveries of water. The system is simulated for various combinations of decision variables (system magnitudes) and an optimum design is obtained by response surface technology. Emphasis is placed on the basic model and methodology although, in order to introduce some realism, the procedure is applied to data based on the existing reservoir system on the South Concho River in West Central Texas.     

THE EFFECTS OF CLIMATE CHANGE AND IRRIGATION ON CRITERION LOW STREAMFLOWS USED FOR DETERMINING TOTAL MAXIMUM DAILY LOADS1

ABSTRACT: This paper addresses the possible impacts of global climate change on low streamflows in the Midwest, both directly, through lower precipitation, and indirectly, by rendering irrigation profitable in areas where it has found little application in the past. In the analysis presented here, streamflow data are altered to represent the effect of climate change and stream-supplied irrigation, and then used to estimate new values for two low-flow criteria, the one- and seven-day-ten-year low flows (₇Q₁₀ and ₁Q₁₀) under 20 climate change and irrigation scenarios. Additionally, the frequencies of violation of these two criteria, and multiple violations in a three-year period, are determined. Results show that the potential impact of the assumed climate change scenarios on low flow standards is substantial. A 25 percent decrease in mean precipitation results in a 63 percent reduction in design flow, even in the absence of irrigation. With irrigation, the reduction can be as much as 100 percent. The frequency of single violations of low flow criteria is found to increase several fold with irrigation. The frequency of multiple violations of low flow criteria in a three-year period is sensitive to climate change, increasing from around 20 percent to nearly 100 percent as the climate change becomes more severe.     

Irrigation Water Allocation Using an Inexact Two‐Stage Quadratic Programming with Fuzzy Input under Climate Change

Agricultural irrigation accounts for nearly 70% of the total water use around the world. Uncertainties and climate change together exacerbate the complexity of optimal allocation of water resources for irrigation. An interval‐fuzzy two‐stage stochastic quadratic programming model is developed for determining the plans for water allocation for irrigation with maximum benefits. The model is shown to be applicable when inputs are expressed as discrete, fuzzy or random. In order to reflect the effect of marginal utility on benefit and cost, the model can also deal with nonlinearities in the objective function. Results from applying the model to a case study in the middle reaches of the Heihe River basin, China, show schemes for water allocation for irrigation of different crops in every month of the crop growth period under various flow levels are effective for achieving high economic benefits. Different climate change scenarios are used to analyze the impact of changing water requirement and water availability on irrigation water allocation. The proposed model can aid the decision maker in formulating desired irrigation water management policies in the wake of uncertainties and changing environment.     

FARM-LEVEL MANAGEMENT OF DEEP PERCOLATION EMISSIONS IN IRRIGATED AGRICULTURE1

ABSTRACT: Source control costs for deep percolation emissions from irrigated agriculture are analyzed using a farm-level model. Crop area, irrigation system and applied water are chosen to maximize the net benefits of agricultural production while accounting for the environmental damages and disposal costs of those emissions. Deep percolation is progressively reduced as environmental and disposal costs are increased. This occurs primarily through the adoption of more efficient irrigation technology and reductions in applied water for a given technology Higher surface water prices, such as through irrigation reform and constrained surface supplies, are additionally considered in light of the drainage problem, as are the effects, both short- and long-term, on ground water use.     

A STOCHASTIC MODEL TO EVALUATE RIPARIAN IRRIGATION EXPANSION IN THE EASTERN UNITED STATES1

ABSTRACT: Irrigation has expanded in parts of the eastern United States. In some areas, the adjoining surface (riparian) water is the most economical source of irrigation water. Expanded demand for riparian water may lead to conflict among irrigators and other streamflow users. Accurate information on the potential for and impacts of riparian irrigation expansion is needed to decide if control of such expansion is necessary. In this study, a stochastic economic model to evaluate the impacts of potential irrigation expansion is presented. The model considers the soil, location, and land use characteristics of individual sites, as well as weather and streamflow patterns. The application of the model to an eastern Virginia watershed indicates that, with maximum potential expansion, water availability becomes limited and yields will be reduced in some years. As a result, the expected net returns from irrigation and the probability of breaking even on the investment are reduced substantially. The results suggest the need to consider regulation of surface water allocation for irrigation development in riparian watersheds.     

OPTIMUM DESIGN OF BORDER IRRIGATION SYSTEM1

ABSTRACT: Border irrigation systems like most of the other surface irrigation systems, do not need too much energy and special equipment. Thus, many farmers have used this system for a long time. On the other hand, design of surface irrigation systems including border irrigation requires many input parameters, and need intensive engineering calculations. The burden of these requirements probably led the users to experimental design of the systems with low efficiencies. However, accurate design and high quality optimization of the border irrigation system that can result in a highly efficient system is possible. In this study, an optimization model for border irrigation system is presented. The Hook Jeev's pattern search optimization method in conjunction with a general mathematical model of border irrigation is used to maximize the irrigation application efficiency. The border irrigation storage and distribution efficiencies, border slope and length, inflow rate, cutoff time, and the Manning's roughness coefficient are selected as constraints. The model is applied to field-measured data. The results show that it is possible to select a suitable combination of the border system's parameters (border's length, inflow rate, and cutoff time) to obtain a maximum application efficiency.     

POTENTIAL IMPACT OF IRRIGATION ON WATER RESOURCES IN THE LITTLE WABASH BASIN OF ILLINOIS1

The level of water demand for supplemental irrigation and the impact of such demand on water supplies were estimated, as a function of the price of corn (Zea Mays L.). The method of estimation was based on an economic analysis of irrigation practice which assumed constant irrigation costs, profit maximizing behavior on the part of irrigators, and which was deliberately structured to underestimate the level of irrigation water use. The analysis was applied to and used data from the Little Wabash basin in Illinois. No irrigation was predicted at a corn price below $3.50 per bushel. Between $3.50 and about $6.50 per bushel, irrigation was estimated to be profitable for a small region of the basin where acceptable groundwater was available. Above about $6.50 to $7.50, irrigation was found to be profitable in the remainder of the basin, where impoundment storage was required. The potential impact on the water resources of the basin is significant. For a corn price between $3.50 and about $6.50, the probability of a shortfall, defined as the event where the potential demand exceeds the supply, was estimated to be between 2 percent and 20 percent during the growing season. Above about $7.50, this probability was found to be about one-third. The development of policies to control withdrawals for irrigation and other uses is endorsed.     

ECONOMIC ANALYSIS OF WATER-SAVING TECHNIQUES IN IRAN1

ABSTRACT: The possibility of increasing the water supply for irrigation through adoption of more efficient water-application techniques as an alternative to new irrigation projects was studied in an irrigated region of Iran. Excessive water application at the farm level ranks high among the causes of water shortages in the selected region. An empirical analysis of the effect of water-saving technology on the farm operator's net return was made choosing two farms in the region as a case study. The problems facing these farms are common to most farms throughout the country. The results of the budgeting analysis of the selected farms indicated that an improvement in irrigation technique can result in the expansion of water supply and higher marginal value product for water. Comparing the costs of irrigation systems with the net returns resulting from the higher efficiency showed that such an investment is economically feasible.     

VALUING IRRIGATION WATER: A SIMULATION/MATHEMATICAL PROGRAMMING APPROACH1

ABSTRACT: A two-stage simulation/mathematical programming model was developed to derive irrigation water values that reflect efficient response to reduced water supplies. The failure of many previous water valuation studies to represent the dynamic dimension of irrigation was shown to result in overestimation of derived water values. Water values are also shown to be dramatically influenced by both application system characteristics, as well as the relative costs of irrigation inputs. Finally, the marginal value of irrigation water was shown to vary considerably over the irrigation season, reaching its maximum when atmospheric demand is highest and crops are most susceptible to water stress. Results presented should be of interest to policymakers investigating the viability of alternative water reallocation mechanisms.     

Agronomic Water Mass Balance vs. Well Measurement for Assessing Ogallala Aquifer Depletion in the Texas Panhandle

The Ogallala Aquifer is depleting faster than it is being replenished. Interpretation of well data suggests that the water table in some counties is not declining, or not as much as might be expected in view of the amount of land being irrigated. As the Ogallala Aquifer in the Texas Panhandle receives almost no recharge, a possible explanation is that the current method of using well data for estimating the quantity of water remaining in the aquifer is underestimating water in storage. This study used an agronomic water mass balance approach to estimate how much water has been used for irrigation compared to amounts estimated by well data. The major finding was in counties where irrigation well capacities have declined significantly but irrigation is continuing, there is likely more water in storage than presently estimated, but the amounts of water being used for irrigation in those counties are greater than estimated changes of water in storage. The proposed hypothesis for this difference is there are mounds of water between wells that are not being accounted for and data are presented and discussed to support this conjecture.     

ON‐FARM WATER CONSERVATION PRACTICES IN SOUTHERN ALBERTA1

ABSTRACT: In southern Alberta, as elsewhere, pressures on limited water supplies are increasing. Not surprisingly, a great deal of attention has been focused on irrigated agriculture, which accounts for the largest share of water consumed in the region. In order to meet broadly accepted water conservation goals, some commentators have suggested that irrigation water use should be metered and that irrigators should be charged based on the amount of water used. An alternative proposal would have water management authorities rely upon the perceived adaptability of irrigators. This paper offers a perspective on the willingness of irrigators to conserve water. Based on a survey of 183 irrigation farmers conducted over the summer and early fall of 1998, we found that irrigators are generally aware of the need to conserve water and soil moisture, and that a variety of water conserving strategies were being employed. Water saving technologies specific to irrigation agriculture were less widely adopted. The findings suggest that there is considerable potential to reduce the amount of water consumed by the irrigation sector through increased efficiency, but that change will be limited if current economic circumstances and institutional arrangements persist.     

The Use of Irrigation Water in Bulgaria’s Plovdiv Region During Transition

The amount of water Bulgaria uses for irrigation sharply declined during the transition. Large sections of the existing irrigation systems were abandoned, and those still in use are hardly maintained. Crops such as wheat and barley have replaced more water-intensive crops, such as vegetables, rice, and maize. This problem has an impact on the future development of agriculture and the allocation of the countrys water resources. The central argument is that land fragmentation in the wake of decollectivization and restitution contributes to the irrigation systems abandonment. This article focuses on the institutional factors involved, but also considers additional factors that might have influenced the process. Further, it examines the causes driving these changes and analyzes their effect on irrigation. It is based on a review of the relevant legislation as well as fieldwork in 17 villages located in the Plovdiv region of Bulgaria. The article concludes that institutional settings, in addition to changes in large-scale market forces and the state enforcement mechanism, have contributed to the irrigation decline in Bulgaria.Published online Note: This version was published online in June 2005 with the cover date of August 2004.     

Nitrate leaching beneath a containerized nursery crop receiving trickle or overhead irrigation

Container production of nursery crops is intensive and a potential source of nitrogen release to the environment. This study was conducted to determine if trickle irrigation could be used by container nursery producers as an alternative to standard overhead irrigation to reduce nitrogen release into the environment. The effect of overhead irrigation and trickle irrigation on leachate nitrate N concentration, flow-weighted nitrate N concentration, leachate volume, and plant growth was investigated using containerized rhododendron (Rhododendron catawbiense Michx. 'Album') supplied with a controlled-release fertilizer and grown outdoors on top of soil-monolith lysimeters. Leachate was collected over two growing seasons and overwinter periods, and natural precipitation was allowed as a component of the system. Precipitation accounted for 69% of the water entering the overhead-irrigated system and 80% of the water entering the trickle-irrigated system. Leachate from fertilized plants exceeded the USEPA limit of 10 mg L(-1) at several times and reached a maximum of 26 mg L(-1) with trickle irrigation. Average annual loss of nitrate N in leachate for fertilized treatments was 51.8 and 60.5 kg ha(-1) for the overhead and trickle treatments, respectively. Average annual flow-weighted concentration of nitrate N in leachate of fertilized plants was 7.2 mg L(-1) for overhead irrigation and 12.7 mg L(-1) for trickle irrigation. Trickle irrigation did not reduce the amount of nitrate N leached from nursery containers when compared with overhead irrigation because precipitation nullified the potential benefits of reduced leaching fractions and irrigation inputs provided under trickle irrigation.     

ADOPTION OF WATER-SAVING PRACTICES BY IRRIGATORS IN THE HIGH PLAINS1

ABSTRACT: The High Plains has been viewed as an immense garden because of its highly productive agricultural system based on irrigation. But there is concern that the aquifers are being depleted and that the region may be returning to its natural state of a vast shortgrass prairie. Efforts to avoid this scenario and to ensure continued survival of the integrated agribusiness economy focus on conserving water in irrigation. This paper examines the adoption of 39 water-saving practices for ten counties in Kansas, Nebraska, Oklahoma, and Texas. The frequency of adoption was estimated from a survey of 709 irrigators, and the variance was found primarily to be a function of location and secondarily to be influenced by number of wells, type of irrigation system, depth to water, age, and education. Locational differences remained strong even when the influence of secondary factors were controlled.     

Energy pricing and groundwater use

The current policy of many state governments in India to supply cheap and subsidized power to farmers for irrigation pumping is being increasingly questioned by many environmentalists and agriculturalists. States where power tariffs for irrigation are subsidized and cheap have seen a fall in their groundwater tables which could threaten the long-term sustainability of irrigated agriculture in these areas. This paper presents the results of a survey, undertaken to understand the effect of energy pricing on groundwater tables. The paper argues that current energy pricing policies are at cross purposes to groundwater conservation. Equity effects of energy pricing for irrigation pumping is also discussed .