Journal of Irrigation and Drainage Engineering

A number of delivery sites within an irrigation district were monitored in order to determine the amount of variability in flow rate during each water delivery. The coefficient of variation (CV) of instantaneous (1/2 hour) flow rate values averaged for each turnout ranged from 0.04–0.29. CV was related to the location of the site within the delivery system. Time of year, flow rate, and crops grown did not appear to affect CV. On‐farm water use is affected by the level of delivery flexibility and the uniformity of water deliveries. Upgrading of farm irrigation systems may require improvements in delivery flexibility and uniformity. However, increasing the delivery flexibility may result in less uniform deliveries, which may also reduce the operational conveyance efficiency of the delivery system unless the system is also upgraded. Improving the overall water use within an existing irrigation project will often require improvements in farm water management, delivery control, and canal system management.

In Doon Valley, India, when a natural forest watershed open to grazing is deforested and cultivated, volume and peak rates of runoff were higher by 15% and 72%, respectively. When the agricultural watershed is treated with soil and water conservation measures (construction of small field levees or bunds), the peak rate and volume of runoff are reduced by 86% and 62%, respectively, of the corresponding values when it was a natural forest watershed and the corresponding reduction in soil loss was 94%. When another comparable natural forest watershed is provided with brushwood check dams at appropriate locations, although no appreciable reduction in peak rate of runoff was observed, soil loss was reduced by 54%.

Selection criteria for reduced pressure center‐pivot irrigation systems are developed. An analysis of the combined effects of the application rate characteristics or center‐pivot irrigation systems and the Soil Conservation Service (SCS) soil intake family curves is used to determine the maximum depth of water which could be applied per irrigation for various types of soils and sprinkler packages. These irrigation depths are used to determine guidelines for proper selection of reduced pressure center‐pivot systems. The results can be used as a general guide to determine if a particular system may have a runoff problem under a given situation.

A computer simulation model is used to evaluate the risk of having insufficient water for supplemental irrigation. The model simulates the daily operations of a system consisting of a watershed, pond, and irrigation plot. Daily precipitation and temperature data, which drives the hydrologic functions, is readily obtained from National Weather Service archives. At least 25 years of data is used to determine the frequency of failure of the storage pond to deliver water when there is an irrigation demand. Generalized system reliability curves are generated for moisture deficits ranging from 219–582 mm (8.6–22.9 in.) at five locations in Kansas. The model is useful for designing an individual system or for establishing design guidelines for a region.

Forty contiguous plots (each $27.5m\times 3.2m$) were maintained in a cultivated fallow condition during spring and summer 1981. Twenty‐six runoff events were measured during that period. The runoff variability as expressed by differences between plots was analyzed. The coefficient of variation for individual events in which all plots exhibited runoff ranged from 0.65–0.07. Individual plots did not react consistently throughout the series of storms, but were seen to shift between producing more and less than the average volume of runoff. The implication of these results to rainfall‐runoff modeling is discussed.

High priority research objectives for irrigation and drainage in the United States are identified. These include: (1) Development of more efficient irrigation distribution and on‐farm systems and management practices to increase water use efficiency, control soil salinity, and reduce degradation of downstream water quality; (2) development of improved and new technology to conserve and manage soil and water resources to enhance soil productivity and improve production efficiency; (3) development of improved systems and practices to store and deliver water supplies to farms as needed for efficient crop production; and (4) development of more efficient drainage systems and practices to control soil water for crop production in humid regions. Current national and regional research programs are described.

The field performance of stationary giant gun irrigation systems is evaluated from the results of 70 distribution tests conducted in the interior of British Columbia, Canada. Three measures of field performance are quantitatively evaluated including maximum application rate, evaporation and spray loss and distribution uniformity. Maximum application rate is found to be a function of average wind speed in the principal wind direction. Evaporation and spray losses were dependent on climatic and operating conditions, primarily the atmospheric vapor density deficit and the average wind speed. The uniformity of application is strongly influenced by both the gun spacing and the average wind speed. The influence of operating variables such as nozzle size and pressure are accounted for in the parameters used to nondimensionalize these relationships. The equations representing these findings are derived using multiple regression and are presented algebraically. Measured values are plotted against predicted values to give a visual impression of scatter in the data. The utility of the relationships in designing and operating giant gun systems is illustrated.

Replacing the sprinklers on a center pivot irrigation system with perforated, polyflex tubes converts a sprinkler system to a trailing tube system. Such a system is similar to a traveling trickle irrigation system. The advantages of a trailing tube irrigation system are its low energy consumption and high water use efficiency. An analysis of the hydraulics of a trailing tube is presented.