USCID 14th technical conference

Presented at Contemporary challenges for irrigation and drainage: proceedings from the USCID 14th technical conference on irrigation, drainage and flood control held on June 3-6, 1998 in Phoenix, Arizona.Includes bibliographical references.The use of drainwater for irrigation is a viable technology both for improving overall irrigation efficiency and for protecting water quality by reducing the mass output of salts and trace elements from irrigated areas. This was demonstrated in a field study at NewIands Agricultural Research Center in Fallon, NY by growing spring wheat (Triticum aestivum) under four irrigation water treatments. The four treatments were: 1) the exclusive use of canal water applied during the day; 2) the exclusive use of drainwater applied during the day; 3) the exclusive use of drainwater applied during the night; and 4) the conjunctive use of drainwater and canal water beginning with a day-time application of drainwater and finishing with canal water. The drainwater came from a shallow aquifer which had elevated levels of salinity and boron. The effects on crop yield of boron and salts applied with drainwater treatments were of primary interest. The field was divided into four blocks representing different soil conditions. Each block was divided into four plots and each plot was randomly assigned one of the four treatments. The growth response to these water qualities was evaluated by weighing plant samples harvested four times during the growing season. The hypothesis that daytime irrigation with drainwater would significantly reduce growth of spring wheat was rejected. The use of drainwater for irrigation appears technically feasible and offers opportunities for improving irrigation efficiency and for reducing the mass output of salts and trace elements from the Newlands Project

Cokriging for evaluating agricultural pollution

Agricultural irrigation is a major non-point source polluter. Evaluating the extent of this type of non-point source pollution requires sampling and analysis of drainage waters. To reduce costs, sampling efficiency is important. Cokriging can be used as a tool for interpolating between sampling times or locations. In this experiment, subsurface drainage data from irrigated lands near Twin Falls, Idaho were used. Total Dissolved Solids and NO3-N were selected as variables. The objective was to determine if 50 and 65 percent of the measured data could be removed (creating two new data sets) and accurately estimated via cokriging using a variogram model based on the remaining data. Cokriging models were developed using statistical information obtained from variograms of the remaining data. Once accurate models were developed for both the 50 and 65 percent removal cases, estimations were made for the missing data values. One-way analysis of variance and t-tests were used to test whether the means and variances of the estimated values were significantly different from those of the measured values. At the 65 percent removal level, there were significant differences in the means and variances of the estimated and measured values for NO3-N. One way analysis of variance and similarity of variance tests were used to test whether differences between the error values of the modeled and removed data were significant. By using the unedited full set of measured data for variogram modeling none of the tests produced rejections

Steady-state ditch-drainage of two-layered soil regions overlying an inverted v-shaped impermeable bed with examples of the drainage of ballast beneath railway tracks

Water-table heights due to steady surface accretion in drained two-layered soil regions overlying an inverted V -shaped impermeable bed are obtained using both the Dupuit-Forchheimer approximate analysis with flow assumed parallel to the bed and also from numerical solutions of Laplace's equation for the head distribution. For illustration, water-table profiles obtained by the two procedures are compared for surface accretion draining to ditches in a typical two-layered ballast foundation for a railway track where a very permeable ballast material overlies a less permeable sub-grade on top of an inverted V-shaped impermeable bed that slopes away both sides from a central line to drainage ditches. These results are found to be in good agreement except very near the drainage ditches where the Laplace numerical solution takes into consideration a surface of seepage that is ignored in the Dupuit-Forchheimer analysis. The Dupuit-Forchheimer analysis is also in good agreement with results of a laboratory model experiment. It is concluded that the approximate Dupuit-Forchheimer analysis can be used with confidence in these situations. It is used to investigate the effect on the water-table elevation caused by the reduction of hydraulic conductivity of the porous materials due to clogging

Opportunities for improving irrigation efficiency with quantitative models, soil water sensors and wireless technology

Increasingly serious shortages of water make it imperative to improve the efficiency of irrigation in agriculture, horticulture and in the maintenance of urban landscapes. The main aim of the current review is to identify ways of meeting this objective. After reviewing current irrigation practices, discussion is centred on the sensitivity of crops to water deficit, the finding that growth of many crops is unaffected by considerable lowering of soil water content and, on this basis, the creation of improved means of irrigation scheduling. Subsequently, attention is focused on irrigation problems associated with spatial variability in soil water and the often slow infiltration of water into soil, especially the subsoil. As monitoring of soil water is important for estimating irrigation requirements, the attributes of the two main types of soil water sensors and their most appropriate uses are described. Attention is also drawn to the contribution of wireless technology to the transmission of sensor outputs. Rapid progress is being made in transmitting sensor data, obtained from different depths down the soil profile across irrigated areas, to a PC that processes the data and on this basis automatically commands irrigation equipment to deliver amounts of water, according to need, across the field. To help interpret sensor outputs, and for many other reasons, principles of water processes in the soil–plant system are incorporated into simulation models that are calibrated and tested in field experiments. Finally, it is emphasized that the relative importance of the factors discussed in this review to any particular situation varies enormously

Cokriging for evaluating agricultural pollution

Agricultural irrigation is a major non-point source polluter. Evaluating the extent of this type of non-point source pollution requires sampling and analysis of drainage waters. To reduce costs, sampling efficiency is important. Cokriging can be used as a tool for interpolating between sampling times or locations. In this experiment, subsurface drainage data from irrigated lands near Twin Falls, Idaho were used. Total Dissolved Solids and NO3-N were selected as variables. The objective was to determine if 50 and 65 percent of the measured data could be removed (creating two new data sets) and accurately estimated via cokriging using a variogram model based on the remaining data. Cokriging models were developed using statistical information obtained from variograms of the remaining data. Once accurate models were developed for both the 50 and 65 percent removal cases, estimations were made for the missing data values. One-way analysis of variance and t-tests were used to test whether the means and variances of the estimated values were significantly different from those of the measured values. At the 65 percent removal level, there were significant differences in the means and variances of the estimated and measured values for NO3-N. One way analysis of variance and similarity of variance tests were used to test whether differences between the error values of the modeled and removed data were significant. By using the unedited full set of measured data for variogram modeling none of the tests produced rejections

Irrigation and drainage in the new millennium

Presented at the 2000 USCID international conference, Challenges facing irrigation and drainage in the new millennium on June 20-24 in Fort Collins, Colorado.Includes bibliographical references.The two-dimensional, hydrodynamic model HYDRUS-2D is used to simulate irrigation schedules for an alfalfa crop over the length of a growing season. The objective is to evaluate current practices in order to produce management alternatives that reduce irrigation drainage. HYDRUS-2D uses a finite element technique that numerically solves the Richards equation for water movement in variably saturated media. The model is calibrated by comparing its output to actual field data collected from an instrumented plot at the Newlands Agricultural Research Center in Fallon. Nevada. The simulation's scope is applied to a vertical cross-sectional study area, 21.95 m in depth by 18.50 m in width, representing half of the spacing between two parallel drains. The soil profile contains one drain and three piezometers below it. An accurate model of the site's layered soil profile is developed by selecting soil parameters that produce acceptable agreement between actual and modeled drain discharge values, as well as, root mean square error between piezometric pressure heads. The following ratio is used to determine what portion of the water leaving the soil profile is consumed by evapotranspiration, Det/(Det + Dd) where Det is the depth of water used by evapotranspiration and Dd is the depth of drainage water. Optimal results are achieved as the ratio approaches one. Using short, 24-hour intervals indicates how the ratio behaves on a daily basis during irrigation cycles and provides insight into ways to modify standard irrigation practices to create a more efficient management alternative

Irrigation and drainage in the new millennium

Presented at the 2000 USCID international conference, Challenges facing irrigation and drainage in the new millennium on June 20-24 in Fort Collins, Colorado.Includes bibliographical references.Irrigation of arid and semi-arid agricultural regions has produced salinization and waterlogging problems. Tile drainage systems will effectively lower the water table and transport salts out of the root zone. However, the salts exiting the irrigated soils via drains cause new problems, such as reducing groundwater quality and damaging wetlands habitat. This research investigates the simulation of management alternatives that control drainage and the mass flux of salts in the drainage water and demonstrates an improvement over the use of leaching fraction and leaching requirement as conceptual models. HYDRUS_2D, a two-dimensional Windows-based modeling environment, is used to simulate solute transport under the influence of alternative irrigation management practices for an alfalfa crop. HYDRUS_2D uses a finite element technique that numerically solves the Richards equation for saturated/unsaturated flow, and the Fickian-based advection/dispersion equation for solute transport in variably saturated porous media. The response to management alternatives (depth of irrigations, using water sources of varying quality in irrigating a soil with varying salinity) allows managers to evaluate the influences on the mass flux of salts in drainage water before they put a new approach into practice. The results include graphical displays of water and solute fluxes and the salt distribution in the upper soil profile