Journal of Irrigation and Drainage Engineering

This paper assesses the potential of the “reduced-runoff” surface irrigation method for clay soils to limit tailwater runoff and evaluate its impacts on crop production and soil salinity throughout a 3-year alfalfa hay production cycle in the Imperial Valley. Despite moderately saline field conditions, tailwater runoff was reduced to <2%, thereby reducing the annual water application by approximately 28% with no loss in hay yield or quality in comparison to countywide averages. The valley average applied-water yield efficiency (yield/applied water) was increased from 8.9 to 15.2 kg/ha-mm. When corrected for yield reduction due to salinity conditions (i.e., ∼21 kg/ha-mm), this latter value is comparable to reported maximum alfalfa water-use efficiency (∼20 kg/ha-mm). Soil salinity accumulated (from 6 to 14 dS/m) at the 0.9–1.5 m depth interval of the soil profile, particularly in the lower 15% of the border checks by the end of the study. However, disking, a single leaching irrigation, and sweet corn production after termination of the alfalfa were adequate to reclaim the soil.

Alfalfa hay yield, yield-consumptive use ratio (Y/ET_c), and hay price across a range of rainfall and evapotranspiration conditions of the western states is evaluated to determine alfalfa hay water value or benefit. Included is a determination of long-term mean values and variability of yield, Y/ET_c ratios, and associated irrigation water values. These are compared with published hay water-use efficiencies, production, and water costs. Available rainfall, reference evapotranspiration ET₀, hay yields, and prices for counties in Arizona (1987–1999), California (1998–1999), and Idaho (1993–1999) were used. Alfalfa hay Y/ET_c ratios decrease with increasing ET_c, although their variability increases with increasing ET_c. The greatest Y/ET_c ratios (16–17 kg/ha-mm) and irrigation water values IW$ (IW$ = $2,800–$3,000/ha-m), with relatively moderate variability, are associated with an irrigation water IW requirement of ∼800 mm, reflecting a combination of relatively high hay values, ET_c, and beneficial rain. Although this IW$ is twice that of water delivery prices below the California delta and is comparable with average municipal water costs of $4,000/ha-m for large western cities, the average is nearly 1/3.

Lake Okeechobee, located in subtropical South Florida, is the second largest completely contained freshwater lake in the United States. The average, annual evaporation is 132 cm, reported following five years of meteorology data analysis (1993–1997). Simple models, developed from an open-water lysimeter evaporation study, are recommended to estimate daily lake evaporation from solar radiation or solar radiation and maximum air temperature. Seven evaporation estimation methods were evaluated to compare their applicability in providing daily, lake evaporation estimation for water management purposes. The analysis used five-year meteorology data, measured inside the lake. Monthly pan coefficients and annual average pan coefficients were produced for seven pan evaporation stations in the vicinity of Lake Okeechobee. Using the recommended simple models and the remote meteorology data collection, Lake Okeechobee daily evaporation can be reported at the end of each day for water management decision-making.

Many irrigated areas have shallow water tables creating waterlogging and salinization problems. This has often been controlled by installation of subsurface horizontal pipe drainage; however, these systems export large amounts of salt off farm in the drainage effluent. Improved design and management of subsurface drainage systems to reduce drainage salt loads were tested in a replicated field experiment. Deep, widely spaced drains allowed to flow without control were compared to drains with management to reduce drain flow. These were also compared with shallow, closely spaced drains that protected the root zone only and an undrained control. The deep drains flowed continuously during the two irrigation seasons with an electrical conductivity of around 11 dS/m resulting in a drainage salt load of 5,867 kg/ha. The management measures reduced drainage volume and salinity resulting in a 50% reduction in salt load. The shallow drains only flowed directly after an irrigation or rainfall event with low salinity, around 2 dS/m, resulting in a 95% reduction in salt load. This showed that by management there is great potential for reducing salt mobilization in existing drainage systems, and for new systems shallower drains will minimize salt loads.

A model and computer program were developed to calculate water application depth and uniformity coefficient for small spray nozzles mounted on a center-pivot irrigation system. The program requires two basic inputs. First, the experimental data for the static distribution pattern of the spray nozzle, including collection time, spacing between collection cups, cup opening radius, and volume of water collected in each cup at a specific pressure and height are required. Second, irrigation system inputs including spacing between spray nozzles, radius of distal end tower and moving velocity, distance of spray nozzle from the pivot, move stop cycle time, or cycle time, and percentage of moving time from the cycle time, or percentage of moving time are needed. The outputs are water application depth and uniformity coefficient. Experiments were conducted to validate the simulation for various moving velocities, spacing between spray nozzles, cycle times, and percentages of moving time. Results showed that the uniformity coefficient of water distribution was 98.4% of the predicted coefficient and that by changing cycle time, or percentage of moving time, the uniformity coefficient was improved by as much as 14.2%.

Application efficiency is the primary criterion for furrow irrigation system design and management. In this study, the application efficiency function of a furrow irrigation system is analyzed. The application efficiency function is unimodal with respect to inlet flow rate and furrow length. Optimality conditions are derived for the cases in which application efficiency is a function of either furrow length or flow rate. Simple and sufficiently accurate equations and design and management rules are developed.

This study presents a risk-based approach for the design of infiltration basins. The design parameters include basin storage volume, drain time, and overflow risk. At a basin site, the storm-water detention storage volume is determined by design runoff capture volume, tributary watershed area, and runoff coefficient. The basin geometry is dictated by the water volume balance between the surface storage volume in the basin and the subsurface storage capacity in soil pores. The drain time at a basin site is found to be a function of initial soil water content, soil porosity, infiltration rate, and distance to the ground-water table. After knowing the basin geometry and size, the basin's performance can be evaluated by the overflow risk analysis using the local average event rainfall depth and interevent time. In practice, a sensitivity test on overflow risk can be conducted with a range of basin storage volumes. The risk-based approach presented in this study provides an algorithm to calculate the long-term runoff capture percentage for a basin size. The diminishing return on runoff capture percentage can serve as a basis to select the proper basin storage volume at the site.

Infiltration characteristics of seasonally frozen soil influence agricultural management and hydrology in many areas. In northern and northwestern China, winter and spring irrigation is conducted during periods with frozen soil when water is available. The shortage of water resources is one of the major factors restricting the further development of cropland and pasture land in this region. Therefore, heightening irrigation efficiency and determining irrigation parameters has become a high priority for agricultural management. A series of field experiments was conducted from November through March in the middle of Taiyuan Basin, Shanxi Province, China, to develop predictive equations of frozen soil infiltration for differing field treatments and varying water contents. Infiltration measurements were made on three field treatments: green bean standing stubble, winter wheat, and deep ploughing. Cumulative infiltration was greatest on the deep ploughing treatment, which had the lowest soil bulk density as compared with other treatments. A strong inverse power function (R² > 0.90) was demonstrated between water infiltration and water content during the freezing period, and the coefficients for this power function were related to frost depth. The resulting estimates of cumulative infiltration resulted in a coefficient of determination of 0.905. Double frozen layers due to surface diurnal freeze/thaw cycles during soil thawing provided an impediment to infiltration. This study provides a practical basis for determining infiltration parameters for irrigation and water resource management.

A simplified model is presented for the computation of shape and dimensions of the cross section of a self-formed straight threshold channel with noncohesive uniform sediments. The model is based on the equilibrium of the individual sediment particles lying on the channel bed under the threshold condition, due to the hydrodynamic force acting on it. The transverse momentum diffusion, caused by the Reynolds stresses, is assumed as a function of the transverse distance from the center. Channel dimensions predicted by this model are in agreement with those obtained from previous models. However, the model slightly underestimates the experimental data.