Journal of Irrigation and Drainage Engineering

Irrigation system planning and management of a semiarid region in Indian Punjab is imperative for sustainable agriculture. For the management of soil and water resources of these regions, three nonstructural management models have been developed and linked together to aid in planning the optimum allocation of land and water resources to achieve the objective of maximizing return in the command area of a canal distributary. A ground-water simulation model uses the mass-balance approach to simulate water-table depths. The seasonal crop water response models are developed to compute crop yields. Interseasonal irrigation system planning models maximize net annual return through conjunctive use of surface water and gypsum-treated sodic ground water to achieve an optimal cropping pattern using a linear programming algorithm. The linear programming models are operated at five water mixing indexes (mixing of surface water and poor quality ground water in different proportions) and seven probability of exceedence levels where rainfall, crop water requirements, and canal water supply are assumed as random variables. These random variables are fitted well to the gamma probability density function.

The subject of investigation in this paper is large channels of an urban sewerage network. The analysis of dynamical properties of a sewer, as a component of the controlled system is performed in terms of automatic control theory. The analytic relationship of channel “3 dB frequency” as a function of its morphometric and operating mode parameters is obtained. An analysis of frequency characteristics, assuming that the water flow in large sewers is quasistatic, was carried out. The theoretical results were verified by means of flow depth variation curves surveyed in real situations of Moscow's sewerage network. Estimation of the maximal value of the rate of sewage depth change in sewers was performed by using graph-analytic techniques of applied spectral analysis. Results indicate that the amplitudes of the harmonic components of the sewage flow depth variations, greater than third, are no more than 10% of the value of the constant component. It was concluded that the hypothesis concerning the quasistatic operating conditions in large channels is reasonable for any practical length of time. This substantially simplifies the mathematical model of a channel and leads to sewerage network controlling algorithms that are more convenient for realization.

Steady-state solutions for the motion of the freshwater-seawater interface due to series of injection wells were obtained using a sharp interface finite element model. The performance of the numerical model was tested with the existing analytical solution. The model was then used to perform the parametric studies on the effects of the location of the series of injection wells, spacing of the wells, and the freshwater injection rate on the seawater intrusion into coastal confined aquifers. The performances of the injection wells in single and double series along the coast were studied and compared. The key variables were grouped into nondimensional parameters, and the relationship between them was presented as a set of characteristic curves. Results indicate that the reduction of seawater intrusion (up to 60–90%) can be achieved through proper selection of the injection rate and spacing between the wells.

A sensitivity analysis of potential evapotranspiration (PET) rates under both CO ₂ and air temperature changes was conducted. PET was modeled with the Penman-Monteith equation so that the effects of atmospheric CO ₂ concentrations on plant stomatal resistance, and the effects of temperature on land-surface–atmosphere water vapor exchanges were explicitly taken into account. A root-zone soil-water balance was performed using a physically based soil-crop-climate model to analyze the sensitivity of soil moisture to changes in atmospheric temperature and CO ₂ concentrations, and the effects of CO ₂ fertilization on plant photosynthesis and crop yield. A wide spectrum of directional climate change scenarios were analyzed, including both a 3°C increase and a 3°C decrease in air temperature, and both a 50 and a 100% increase in atmospheric CO ₂ concentrations. An additive crop yield model and an optimal irrigation scheduling model were used to maximize agricultural benefits by maximizing crop yield and minimizing irrigation costs. The model was applied to an irrigated potato crop in the San Luis Valley of Colorado.

The sensitivity of irrigated agriculture to water-table fluctuations and agroeconomic parameters was analyzed in the context of long-term climatic variability. Capillary rise was modeled as a function of soil moisture content and depth to the water table. The capillary rise model was used to define the sensitivity of soil moisture depletion, actual evapotranspiration, and agricultural benefits to changes in water-table depth. Water-table fluctuations had a pronounced effect on root-zone soil moisture, irrigation water use requirements, and agricultural benefits. An economic analysis was performed to determine the sensitivity of site-specific irrigated potato production in the San Luis Valley given the potential changes in available irrigation water supply and agroeconomic parameters. Agricultural benefits were found to be highly sensitive to production costs variations, to deviations of crop market prices from their mean values, and to available irrigation water supply.

The materials presented in this paper are the result of a North Atlantic Treaty Organization (NATO) Advanced Research Workshop on “Sustainability of Irrigated Agriculture (Sustainability of Water Resources Utilization in Agriculture),” which was held in Vimeiro, Portugal between 21 and 26 March 1994. The workshop was cosponsored by the Science and Technology for Development (STD) program of the European Union, Centre International de Hautes Études Agronomiques Mediterranéennes (CIHEAM) Centre Technique de Coopération Agricole et Rurale (CTA), Institut Francais de Recherche pour L'ingenierie de L'agriculture et de L'environnement (CEMAGREF) and Junta Nacional de Investigacao Cienifica e Tecnologica (JNICT). The purpose of that workshop was to provide in-depth discussion on irrigated agriculture among researchers and professionals of different disciplines coming from both developed and developing countries. The workshop objective was to integrate existing science and technology into improved irrigation system performance and agricultural water management, and to provide recommendations for future research directed toward sustainability of water use in agriculture. A total of 43 papers were presented and discussed under the following topics: sustainability of world irrigation systems; water management and water policies; sustainability of indigenous water and soil conservation systems; irrigation water management and scheduling; on-farm irrigation systems; irrigation scheme management; sustainability and environment concerns; and technological transfer. The research priorities presented in this paper evolved from group discussions and are based on a common understanding of the challenges that our generation faces to ensure sustainable agricultural development, both in developed and developing countries. The priorities were established by voting of the workshop participants.

The constant revolutions per minute (RPM) of electric motors prevents adjusting the pump performance to match variable operating conditions, and thus the pump output is usually reduced or throttled with a valve in the discharge pipe. Variable frequency drives for electric motors have the potential to adjust the pump performance to match operating conditions by reducing motor and pump RPM. Field tests at five sites showed that the pump performance at the reduced RPM could reasonably match the throttled conditions at a reduced horsepower demand. However, pumping plants using a variable frequency drive should be operated at least 500–1,000 h per year to recoup costs.