Journal of Irrigation and Drainage Engineering

Design of a successful and efficient surface irrigation system involves land grading as its first step. Land grading is also an effective method for efficient surface drainage. In this research, a nonlinear optimization model based on genetic algorithms is developed for land grading design of irregular fields. The model can be used to obtain plane as well as curved surfaces. In contrast to the available models, the proposed optimization model employs an objective function in which the total volume of earth in cut is minimized. The proposed formulation eliminates the need for parallel shifting of an optimal graded surface by trial and error to adjust the cut-to-fill ratio to a desired value. This is achieved by imposing a constraint on the cut-to-fill ratio. By eliminating the need for such parallel shifting, the optimality of the graded surface is kept undisturbed. Constraints may also be imposed on the shape of the graded surface, slopes of the surface in either direction, elevation of the surface at turnout, and at any other points. The developed optimization model is applied for grading an irregular field, which appeared in several previous publications concerning land grading design. The results indicate efficiency and robustness of the developed model.

In this study, a hydrodynamic model is presented for simulating all the phases of border-strip irrigation. The explicit, second-order accurate MacCormack scheme is used for solving the governing equations of surface irrigation. In this method, the advance and recession fronts need not be considered explicitly and any infiltration equation can be coupled to the surface flow equations easily. The empirical Kostiakov equation (Model 1DKO) and the analytical Parlange equation (Model 1DPA) for infiltration are considered in this study. The implicit Parlange equation is solved using the Newton-Raphson technique. The models are validated using the experimental data available in literature. The present results are also compared with the earlier numerical results based on the characteristic method. A simple subgrid technique is introduced in order to obtain a high grid resolution near the advancing front and at the same time achieve a minimum computational cost. This is based on using two different grid sizes for computation. An equation for the optimum grid size ratio is presented and is validated using numerical experimentation.

Sound irrigation management requires information about root-water uptake patterns of different crops. In the existing literature, the extraction rate of soil moisture by the roots is assumed to be either constant or varying linearly with the root depth, during the crop period. However, both these models have limited application. With this in view, an empirical root-water uptake model in which the extraction rate varies nonlinearly with the root depth is proposed. Using experimentally obtained soil-moisture depletion values for nonlimiting soil-moisture conditions, it is found that the proposed model performs better than the constant rate models and linearly varying rate models of root-water uptake. Also, constant as well as linear extraction-rate models are found to be particular cases of the proposed model. Based on simulations for limited soil-moisture conditions, it is also found that the frequency of irrigation is sensitive to the use of root-water uptake models.

The writers analyze the hydrologic budget and quantify the ground-water recharge impact of the Great Flood of 1993 on the Great Bend Prairie aquifer of south-central Kansas. During the summer of 1993, rainfall totals exceeded normal levels by 200% in the northern portion of the study area, while air temperature and evapotranspiration were below normal levels. This extreme event provided the opportunity to revisit previously developed recharge-estimation algorithms. Average ground-water recharge for 1993 at four index sites was estimated at 178 mm using the hybrid water-fluctuation method of Sophocleous. Employing the recharge-estimation multiple-regression methodology of Sophocleous for the area, the writers estimated the 1993 recharge to be 145 mm. Both estimates are higher than the maximum annual recharge observed at the index sites during the 1985–1992 period. A January–July 1993 hydrologic balance analysis resulted in 130 mm of recharge. The recharge caused by the flood was three to more than four times the average annual recharge of the previous eight years. The regression-based recharge-estimation methodology proved to be generally reliable, even under extreme conditions.

A continuous simulation technique, based on the Soil Conservation Service (SCS) method, is used to determine annual storm runoff coefficients (ASRCs) for Orlando, Florida using 13 years of daily rainfall data. The ASRC, which is defined as the ratio of annual runoff to annual precipitation, is used to determine annual runoff volume (or depth) and annual pollutant loads in storm-water models under wet conditions. Although simulated ASRC values are very similar to values measured in other studies, they are significantly lower than the values predicted by other existing models. Estimating ASRC values by the continuous modeling approach has several advantages over existing models; relevant watershed characteristics such as soil type, cover, hydrologic condition of the soil, and antecedent moisture conditions neglected in existing models are taken into consideration, and the annual precipitation that does not produce runoff is determined precisely. Meaningful statistical comparisons can be made between the annual pollutant loads estimated using simulated ASRCs. The technique is cost-effective since continuous simulations can be done on spreadsheets, and require easily available daily rainfall data from a nearby climatological station.

Field measurements of water and solute distribution from a point source were made using the gravimetric method. The variables affecting water and solute distribution, including application rate (1.5, 2.0, and 2.5 L/h), applied volume (15, 20, and 25 L), and input concentration (100, 300, 500 mg/L) were studied and their effects are presented. There was an increased soil water content both with a higher application rate and applied volume up to about 25 cm depth and 30 cm radial distance, beyond which the difference was not significant. There was a clear relationship between application rate and shape of the wetted soil zone. An increase in rate resulted in an increase in the wetted horizontal area and decrease in the wetted soil depth for the same application volume. Solute concentration increased with higher input concentration, applied volume, and application rate up to about the same depth and radial distance as for soil water content. The wetted and chemigated soil volume was larger for higher volumes applied. This information is useful in the design, operation, and management of a chemigation system with microirrigation.

The problem of the effect of recharge duration on water-table response in areas with tile drains is studied using Green's function approach to the linearized Boussinesq's equation for one-dimensional, saturated flow with appropriate boundary conditions. Pulse and decaying sinusoidal type recharge excitations with given periods of drainage are fitted by Fourier series and used as forcing functions. The resulting response equation explicitly predicts water-table buildup over time and the oscillations at dynamic equilibrium, providing a method for analyzing the effect of recharge duration on water-table rise and flow toward the drains. The approach presented herein with this feature, is seen as an improvement on the drainage spacing approach of Maasland and McWhorter for annually repeated recharge events. However, it is seen that the duration of recharge, for constant recharge depth has negligible effect on the maximum water-table rise and flow toward drains at dynamic equilibrium in cases similar to those studied by McWhorter. Peak values of water-table height predicted by both the methods were close as parameters of the flow were changed but with different patterns. The method proposed in this paper results in drainage flow pattern different from the result of McWhorter and will be a useful tool for those cases where more realistic water-table heights and flow toward drains are important.

A seasonal furrow irrigation model consisting of submodels to predict irrigation schedule (water balance), irrigation design (surface irrigation hydraulics), and crop yield (yield function) under spatially and temporally variable conditions was developed and verified with the field data. The model was used to predict irrigation performance for each irrigation event during the season, soil moisture before each irrigation, seasonal evapotranspiration (ET), and bean yield along the furrow at 10-m intervals. In addition, measured inputs along the furrow, including heterogeneous infiltration, soil moisture, and yield were used in conjunction with the model to estimate mean (17.3%) and variation in available water-holding capacity (AWC) (15.4%–19.8%). Variation in crop yield represents an integrated effect of variability in infiltration, soil water characteristics, root depth, soil fertility, microclimate, fertilizer and pesticide applications, plants, and disease. Using the calibrated model, nearly 88% of the variance in ET estimated with the yield function was explained by simulated variation in infiltration characteristics, soil water-holding capacity, and root depth. By assuming homogeneous infiltration characteristics, soil water properties, and root depth, the average absolute error in seasonal ET increased by only 0.6 cm but the variance explained decreased to 30%. Although in absolute terms the impact of heterogeneity seems negligible, Raghuwanshi (1994) showed that heterogeneity strongly affected the optimal flow rate and irrigation time as well as net returns to water.

The main design parameter for a square nozzle is its inside contraction angle, and key design parameters for a triangular nozzle include the inside contraction angle and the length-to-width ratio of the triangular orifice. The variation of discharge coefficient, pattern radii, and uniformity of water application as a function of the parameters previously mentioned were studied. For a square nozzle, both the discharge coefficient and the pattern radius decreased with increasing inside contraction angle when the angle exceeded 50°. The suitable inside contraction angle is around 30°. For a triangular nozzle, the influence of the inside contraction angle on its discharge coefficient and water application was insignificant for an angle range of 10°–45°, but the water application profiles from a single sprinkler were sensitive to the orifice height-to-width ratio. A 1.00 height-to-width ratio nozzle discharges more water near the sprinkler and yields a higher uniformity coefficient than other ratio nozzles for a given sprinkler pressure and spacing.

Weirs are important hydraulic structures constructed across rivers for diverting water for irrigation and power generation. Optimal design of these structures has not been attempted earlier as it involved diverse fields like hydrology, free surface flow, seepage, economics, optimization, and so on. Furthermore, occurrence of a large number of state variables in the constraints is another hindrance in the optimization process. Presented herein is a methodology of optimal designs of pileless, and single-pile sloping floor weirs that are structurally safe. The methodology presented is useful to the design engineer.

Based on the kinematic-wave equations, a time of concentration formula for overland flow over a series of planes is derived. The formula is applicable to a cascade of planes, to planes of different roughnesses, to planes of different flow regimes, to planes of different soil types and infiltration rates resulting in different net intensities, to planes subject to different rainfall intensities, and to planes with a combination of all these variables. For practical applications, the formula is developed in terms of the Manning resistance coefficient that is applicable to turbulent or near turbulent flow only. For the series of planes subject to uniform rainfall excess, under the full-area contribution, the corresponding peak discharge formula in terms of the Manning resistance coefficient is derived. This formula can also be used to estimate the peak discharge under the partial-area contribution. The derived formulas are all consistent with the published formulas for a single plane.

A statewide survey was conducted during 1992 to determine which methods growers used to irrigate their crops in 1991. A questionnaire was distributed to 10,000 of the estimated 80,000 growers in California. Respondents represent nearly 6 of the total 1991 irrigated crop land in California. A comparison with studies done during 1972 and 1980 showed that the amount of land irrigated by surface methods has declined, while the amount of land irrigated by sprinkler and drip methods has increased. The area planted to field crops has declined, while that planted to permanent crops such as fruit and nut trees and grapevines has increased. A rapid increase in the use of drip irrigation in vineyards is the most significant change.