Journal of Irrigation and Drainage Engineering

This paper develops a general introduction into the concepts of a flexible irrigation water supply in rate, frequency, and duration together with the benefits to the farmer for doing so. A flexible water supply allows the farmer the opportunity to choose an on-farm irrigation practice that best meets the needs of the desired crop, the cost and availability of labor, and other local economic or social situations. As water quality issues are more closely tied to the issues of water quantity, water use efficiency must improve. A flexible irrigation water supply can lead to improved efficiencies. Non-point-source pollution and in-stream flows also become factors in other social issues such as the care of threatened and endangered species. Flexible supplies can again help. This paper also shows, through a case study, the application of a limited rate arranged system to an irrigation district in Washington State where significant flexibility has led to efficient water use and economic and environmental benefits.

Data were obtained from 61 agricultural districts within the Mid-Pacific Region of the U.S. Bureau of Reclamation, regarding the level of water delivery service provided to users, water pricing, associated characteristics, and plans for modernization. A flexibility index was developed and used by the writers to characterize the degree of water delivery flexibility provided by each district. The flexibility index provides a rating of 3–15 (15 being the highest value) based upon the frequency, rate, and duration of irrigation water delivery service to farmers. The data show that 42% of the districts received a flexibility score of 12 or greater, with two of the districts receiving almost perfect scores. Based on these results, a program for technical assistance to irrigation districts was developed and implemented. A high priority item was supervisory control and data acquisition systems.

Furrow irrigation performance is affected by spatial variability of infiltration; thus, its characterization is essential for accurate performance evaluation. A time-series modeling approach was used to characterize the spatial and temporal correlation structure of field-measured infiltration data. The time-series analysis indicated minimal spatial correlation of infiltration characteristics along the furrow for the space intervals used (5 m). The time-series analysis led to a strategy by which relationships between infiltration characteristics at short- and long-intake opportunity times for a limited number of infiltration tests could be used to “extend” infiltration information gathered by doing shorter duration tests at other furrow locations.

Irrigation districts are made up of multiple units that are hydrologically connected. If the irrigation units are arranged in parallel, an improvement of the on-field irrigation consumptive use coefficient (ICUC) has more impact on the district ICUC than if the irrigation units are arranged in series. But water quality degrades with the number of reuses. Knowing the topological relations of the irrigation units, the water use in an irrigation district may be analyzed at high and low spatial resolution. A site-specific analysis was conducted on a complex irrigation district (Tulelake Irrigation District) located in a valuable ecosystem in Northern California. Simulated applied water and drainage were greater for areas having high water-consuming crops. The estimated concentration of salts was higher in the center and southern areas. Concentration was higher for soils high in organic matter and for areas where water was reused several times. For comparison purposes, even a complex irrigation district may be reduced to an equivalent number of command areas arranged perfectly in series.

This paper is the fourth in a series on friction factors for sprinkler laterals. The widely used friction correction factor F was developed by Christiansen for the hydraulic analysis of sprinkler laterals. A significant modification to this factor was the adjusted friction correction factor F_a. The adjusted friction correction factor can be used when the first sprinkler is a fraction of a full spacing from the lateral inlet. To design laterals with outlets and outflow at the downstream end, friction correction factor G was developed with the corresponding adjusted friction correction factor G_a. To calculate the average pressure head along a lateral, the average correction factors F_AVG and G_AVG were developed. These average correction factors can be used where friction correction factors F and G are used to analyze a lateral. This paper introduces two final adjusted average correction factors F_aAVG and G_aAVG, which can be used to determine the average pressure head in laterals analyzed using F_a or G_a. Use of these factors is demonstrated in an example.

The performance and progressive development of irrigation distribution and rotation methods were studied in two government-sponsored systems of Niger, West Africa. Systemwide water distribution was monitored intensively throughout several growing seasons and farmer surveys were conducted at both sites. Characteristics of farmer-managed rotation among tertiary canals and among parcels were examined in relation to farmer response to physical and organizational system constraints. A method for indexing the orderliness of irrigation rotation was developed. Where water deliveries were limited, organizational efforts on behalf of the farmers resulted in functional, orderly rotation and distribution among parcels. Farmers exhibit less incentive to organize efficient and orderly rotation among parcels where access to water is less limited. Several organizational and design factors influence the degree to which farmers are both willing and able to organize functional water distribution among themselves. Also, farmers may circumvent design intentions or management strategies imposed on them by irrigation authorities in order to establish their own more effective water management methods, which tend to better accommodate local labor and production constraints. Technical and organizational considerations related to water distribution and management derived from the study results may serve to facilitate the design and operation of small-holder systems in the Sahel.

This paper presents the results of an exploratory study on the hydraulics of a fish bypass-pool that is built to facilitate successful fish passage through an irrigation diversion channel. The hydraulic performance of the bypass-pool was investigated by performing two major experimental runs to evaluate the flow recirculation patterns within the pool when two different outlet configurations were used. This was to determine which outlet design prevents or minimizes the presence of “stagnant” regions within the pool, where fish could rest until ensnared by a predator. These experiments show that the flow from the forebay area of the irrigation diversion structure, entering the pool as a jet, diffuses because of the circulation and turbulence within the bypass pool. The diffusing jet impinges upon the back-wall of the pool and dives into the pool creating several recirculation patterns within the pool. The results collected in this study provide useful information about the jet velocity decay through the pool, the eddy length scale within the pool, the velocity contours, and the level of energy dissipation within the pool. A rational basis was developed for evaluation of the hydraulic performance of a bypass-pool by considering the recirculation pattern and turbulent flow microstructures formed within the pool.

Design of a minimum cost canal section involves minimization of the sum of costs per unit length of the canal, subject to uniform flow condition in the canal. Essentially it is a problem of minimization of a nonlinear objective function subject to a nonlinear equality constraint. In this investigation, the objective function has been expressed as the cost per unit length of the canal for lining, the depth-dependent unit volume earthwork cost, and the cost of water lost as seepage and evaporation losses. A general resistance equation has been used as an equality constraint. Using a nonlinear optimization technique on an augmented function, generalized empirical equations and section shape coefficients have been obtained for the design of minimum cost irrigation canals of triangular, rectangular, and trapezoidal shapes. The optimal dimensions for any shape can be obtained from the proposed equations along with tabulated section shape coefficients. The equation for optimal cost along with the corresponding section shape coefficients is useful during the planning of a canal project. A design example with sensitivity analysis has been included to demonstrate the simplicity of the present method.

Discharge characteristics for a skew sluice gate, ranging between the two extreme cases of a side sluice gate and a normal sluice gate, have been explored. The concept of an elementary discharge coefficient was utilized for obtaining the discharge through a skew sluice gate. Based on experimental investigation, equations for elementary discharge coefficients for skew sluice gates in free- and submerged-flow conditions were obtained. These equations describe the behavior of the elementary discharge coefficients for large ranges of the upstream water depth to gate opening ratio, tailwater depth to gate opening ratio, and skew angle. Using these equations, it is possible to obtain the discharge passing through a bifold skew sluice gate and it is expected that these equations will be useful to obtain the discharge through sluice gates having any plan shape.

The two analytical solutions researched by Theis, and also Glover and Balmer, for the rate of stream depletion are shown to be the same in the mathematical sense by solving the integral appearing in the Theis solution. Expressions for the volume of stream depletion expressed as a fraction of total volume pumped relative to the rate of depletion are obtained for pumping and recovery. The optimum location of a well near the stream and the time to reach equilibrium are suggested.