Journal of Irrigation and Drainage Engineering

A highly efficient and accurate numerical model of surface water flow and solute transport is useful in the design and evaluation of a basin fertigation system. In this study, a coupled model of surface water flow and solute transport for basin fertigation was first formulated. On the basis of the implicit–explicit time scheme of governing equation of the coupled model, the advection upstream splitting method (AUSM) and central finite-volume methods with scalar dissipation characteristic were employed to discretize the spatial derivatives of physical flux, spatial derivatives of advection matrix, diffusion vector, and water-level slope vector. The forming discretized algebraic equation group of the governing equation was solved in split technique, and a one-dimensional surface-flow and solute-transport coupled numerical model for basin fertigation was proposed. The ability of the proposed model was demonstrated using two numerical tests compared with the model on the basis of the Roe finite-volume method. Three field experiments were conducted to validate the proposed model. The results showed that the model exhibits excellent performance for determining water flow and solute transport under full-time, first-half, and second-half fertilizer-application experiments. The proposed model can serve as a research and practical tool for the design and management of basin fertigation.

The authors propose a two-dimensional surface flow and solute transport model of basin irrigation with conventional fertilization. Specifically, based on the mean velocities and water depth obtained from the complete hydrodynamic model, the nonmean water flow velocities along the basin surface plane and vertical direction was constructed by use of the linear-log law in turbulence and the continuous equation of incompressible hydrodynamics. Based on these constructed velocities, the advection-diffusion equation, which can describe nonuniform solute concentration along the basin surface plane and vertical direction, was employed to describe the two-dimensional basin surface solute transport. Based on the experimental data, the proposed model was validated. The results show that the curves from the observed and simulated results are in sufficient agreement, and the proposed model can successfully simulate the basin surface water flow and solute transport for basin irrigation with conventional fertilization. The analyzed results, based on the Markov stochastic process, show that the proposed model can simulate practical effects by approximately 71.09–87.93%. The other stochastic effects, approximately 12.07–28.91%, would be simulated when the model contains other stochastic factors, such as the spatial variation of the soil physical parameters, fertilizer uniformity applied on the basin surface, and so on.

Net radiation is a key variable in hydrological studies. However, measured net radiation data are rarely available and are often subject to error because of equipment calibration or failure. Additionally, point measurements of net radiation do not represent the diversity of the regional net radiation values, which are needed for many physical and biological processes such as climate monitoring and evapotranspiration mapping. The authors present a methodology to estimate daytime net radiation using a combination of remote sensing and climatic data. This paper expands on previous original research by extending the estimation of net radiation to 24 h under all sky conditions. The procedure estimates daytime and nighttime net radiation and combines the results to calculate the 24-h net radiation values. The methodology combines information from satellite and local weather stations to estimate net radiation values. The procedure can estimate net radiation under all sky conditions using measured or estimated solar radiation. Two different methods are presented to estimate net radiation. Comparisons between measured and predicted daytime and 24-h net radiation using the two methods resulted in an average ratio ranging from 0.98–1.0 and a standard error of estimate ranging from $0.83–1.62\mathrm{MJ}{\mathrm{m}}^{-2}{\mathrm{day}}^{-1}$. Satellite data were used for the calculation of leaf area index, albedo, and ground temperature. Although satellite data are scarce, the methodology is not limited to satellite imagery. One can easily use ground level measurements of leaf area index, albedo, and temperature to estimate daytime and 24-h net radiation using the proposed methodology.

Estimates of the daily crop coefficient (Kc) for corn and irrigation scheduling were performed during 2009 and 2010 by means of two approaches: Treatment I, computation of Kc using the Food and Agriculture Organization of the United Nations (FAO) method; and Treatment II, computation of Kc from relative fraction of thermal units. Corn crop water requirements and irrigation gross depth for Treatment I were approximately 25 to 33% lower than those for Treatment II in 2009 and 2010, respectively. However, the performance of Treatment II was better in terms of grain yield, which was $9.2\mathrm{Mg}{\mathrm{ha}}^{-1}$ (in 2009) and $9.4\mathrm{Mg}{\mathrm{ha}}^{-1}$ (in 2010), approximately 37 and 29% higher, respectively, than that for Treatment I. Water productivity was approximately 10% higher for Treatment II during 2009 and practically the same percentage higher than that for Treatment I during 2010. Because of year-to-year variability, water productivity was approximately 25% (Treatment II) and 11% (Treatment I) higher for 2010 than for 2009. Finally, economic productivity for Treatment II was $\$\mathrm{2,162}{\mathrm{ha}}^{-1}$ for both seasons, much higher than that for Treatment I ($\$\mathrm{1,575}{\mathrm{ha}}^{-1}$ in 2009 and $\$1,679{\mathrm{ha}}^{-1}$ in 2010). These results confirm that using fraction of thermal units to estimate corn crop coefficient has improved the yield and water management of this crop under the conditions of this study. Because of the limitations of the study (only 2 years and one experimental plot), further evaluations under other conditions (e.g., climatic, cultivar) should be performed.

The magnitude and duration of corn transpiration reduction during center-pivot sprinkler irrigation was analyzed on a commercial plot. The irrigation event was defined as the period during which the pivot arm was passing over the transect AC and water droplets were moistening the plants (moist treatment). Corn transpiration rates were measured at three spots of that transect and simultaneously at another spot (dry treatment) located approximately 270 m east from the transect AC. Corn transpiration rates for the moist treatment location were reduced by 30–36% compared to the dry treatment location during the irrigation event. After irrigation, the transpiration reduction lasted for 1.8–2.6 h, and ranged from 22–29%. The gross wind drift and evaporation losses ranged from 10–13% of the applied water, whereas the net interception losses were 2% of the applied water. Considering the observed corn transpiration reduction during and after the irrigation, the net sprinkler evaporation losses ranged from 11–13% of the applied water, with no relevant differences along the pivot arm.

Reliable information on irrigation methods is important for determining agricultural water demand trends. The authors have therefore conducted a study over the course of 2011 to collect information on the irrigation methods that were used by growers to irrigate their crops in 2010. The results were compared with earlier surveys to assess trends in cropping and irrigation methods. A one-page questionnaire was developed to collect information on irrigated land by crop and irrigation method. The questionnaire was mailed to 10,000 growers in California who were randomly selected from a list of 58,000 growers by the USDA National Agricultural Statistics Service, excluding rice, dry land, and livestock producers. From 1972–2010, the planted area has increased from 15 to 30% for orchards and from 6 to 15% for vineyards. The area planted with vegetables has remained relatively static, whereas that planted to field crops has declined from 67 to 41% of the irrigated area. The land irrigated with low-volume (drip and micro-sprinkler) irrigation has increased by approximately 38%, whereas the amount of land irrigated by surface methods has decreased by approximately 37%.

Integrated watershed management plays an important role in the environment and ecosystem. This paper analyzes multiobjective optimizations of agricultural land-use management problems with uncertainty involved. For each trial land-use scenario, multiple objective functions are constructed based on coupled simulation of the AnnAGNPS watershed model and the CCHE1D channel network model. To account for parameter uncertainties and uncertainties in numerical model results, the combined objective function is calculated using a fuzzy logic system based on interval computations to obtain a membership function, which yields not only a crisp value but also a range of variations. The proposed approach is tested with a land-use management study for the Goodwin Creek Experimental Watershed in northern Mississippi. The results show that it is a convenient way to introduce uncertainty-related considerations into an optimization framework, and it can incorporate various model parameters that are difficult or impossible for other uncertainty analysis techniques to consider. More importantly, this approach allows for the development of a complex system of estimating the responses between management goals and miscellaneous environmental factors under uncertainty.

A piano key (PK) weir is a type of nonlinear (labyrinth-type) control structure with a relatively small spillway footprint. No standard PK weir design procedure is available, and the amount of published information on PK weirs is limited. PK weirs have a large number of geometric parameters that can affect head-discharge performance. A PK weir geometric design has, however, been recommended in the literature, along with a head-discharge relationship specific to that PK weir geometry. To develop a better understanding of the effects of PK weir geometry on discharge efficiency, nine laboratory-scale four-cycle PK weir configurations were tested (including the recommended design). The effects of the following PK weir geometry or modifications on weir performance were partially isolated: varying the inlet-to-outlet key ratio, raising the crest via a parapet wall, rounding the upstream apex walls, and varying the crest type. The appropriateness of the recommended head-discharge equation specific to the recommended design was evaluated, and the relative head-discharge efficiency of trapezoidal labyrinth and PK weirs with respect to footprint restrictions and crest length were compared.

A well-designed level basin irrigation system is easy to manage and has significant potential for achieving high application efficiency and improved salinity control, particularly when the field is laser-leveled. Over the years, three different criteria have arisen to design level basin irrigation systems. These are the volume-balance design criterion proposed by the Soil Conservation Service of the USDA, the limiting length design criterion, and the completion-of-advance design criterion. For achieving a performance that is close to the design performance, in addition to proper design, a well-defined irrigation schedule must be followed such that the soil moisture deficit at the time of irrigation is close to the design depth. The actual overall performance of a level basin irrigation system will otherwise be lower than the design performance. Using a mathematical simulation model, the performance of a level basin designed using the completion-of-advance design approach was found to be robust relative to one designed using the limiting length approach.

The Sediment, Erosion, Discharge by Computer Aided Design (SEDCAD) program is extensively used in the mining industry for engineering site layout plans with best management practices (BMPs) for erosion control. Although SEDCAD is the primary BMP design tool used in this industry, very limited published information is available on its performance estimating site runoff and sediment yields. This study compared sediment yields from three surface coal mining sites in east Tennessee with SEDCAD modeled outputs. Study sites included active mining operations on steep slopes ($>20°$) where after mining, approximate natural hillslope contours were reconstructed by using loose spoil materials on top of slope, at shallow depths of 1–2 m, following the Forest Reclamation Approach. The SEDCAD model inputs included the site-derived hydrologic curve number (CN) of 59 and average erodibility $K$ factors ranging from $0.001–0.034\mathrm{Mg}·\mathrm{ha}·\mathrm{h}·{\mathrm{ha}}^{-1}·{\mathrm{MJ}}^{-1}·{\mathrm{mm}}^{-1}$ varying on the basis of pre- and postrill development periods and mining site. The SEDCAD overestimated sediment yields as a function of erosivity ($R$) up to 1.6 times greater than the minimally measured yields in two of the three study sites. A sensitivity analysis of input parameters found CN selection can greatly affect modeled outputs for sediment yield. For example, a 40% deviation in selecting a CN would double the computed sediment yield. Results from this study provide design engineers using SEDCAD a better understanding of the uncertainty with model outputs to improve selection and design of erosion BMPs on surface coal mining sites.

The study deals with the discharge coefficient for siphon spillways based on the results of experimental methods and numerical simulations. Siphon spillways are used as the outlet in reservoirs to control the incoming flood flows. A scaled plexiglass model of a siphon was fabricated and tested in the laboratory flume to determine the siphon discharge coefficient over a range of Reynolds numbers. The RNG $k\text{-}\epsilon$ model was used to obtain the discharge coefficient of the siphon. The existing experimental results and the present test data were used to validate the model predictions. The agreement of the model with test data was reasonable. A properly validated model permits the evaluation of the siphon discharge coefficient for different flow configurations encountered in the field, without recourse to expensive experimental procedures.