Journal of Irrigation and Drainage Engineering

Approximate theoretical formulas are derived for predicting the water table position for steady rainfall or steady irrigation recharge into soil bounded by equally spaced ditch drains dug up to an impervious layer in single-, two-, and three-layered anisotropic soils. The ditch drainage problem is first solved for the single-layered case and subsequently, solutions are obtained to the twoand three-layered cases of the problem. All the solutions are based on exact mathematical procedures but utilize a physical assumption that the head loss in the arch-shaped region of the water table is negligible compared with the head loss for the remainder of the region. A correction, however, is provided to account for this head loss for all the solutions and the corrected formulas are found to be on the “safe side” for drainage design since the water table heights predicted by these formulas are higher than the actual ones. The accuracy of the proposed solution to the single-layered problem is tested by comparing it with independent solutions of Kirkham and Youngs to the same problems. A good agreement is obtained among the predicted results and the results obtained from the existing theories.

Design of a runoff-recycling-based irrigation system to provide irrigation for rice in monsoon season is a complex problem. The irrigation requirement, as well as the water availability in the form of runoff, vary both in amount and time. The design of an irrigation system based on the irrigation requirement obtained from short-period experiments may lead to faulty design. To overcome this, a simulation study of water balance of the cropped area as well as the tank has been done to determine the catchment command area ratio and size of the tank for a five year return period. It has been found that for transplanting within optimum period, the catchment command ratio should be 5.0 or more and a tank of storage capacity of 132.6 mm will be sufficient at a return period of five years for the U.P. midhills of India. It has also been found that a short-duration variety will be more suitable for such an irrigation system.

Application of the plane method to solve land-leveling (or land-forming) problems in fields, even with irregular shapes, can easily be done by using computer programs. However, the introduction of the weighted factor, associated to each node of a grid system overlapping the whole area, is necessary to give a different weight to the elevations of nodes in the proximity of the field boundaries. Therefore, the actual cut and fill depths can be computed. In this study, a procedure is presented that can be used first for an automated generation of a system of grid squares, and then for the automated computation of the weighted factor of each node of the grid system. In doing this, only a limited amount of input data is used, that is, the grid spacing and coordinates of the field corners.

Microtopography has long been regarded as a key variable affecting basin irrigation performance. This paper reports on the extension of a flat bed two-dimensional basin irrigation model to the simulation of irrigation events in basins with microtopography. The model incorporates the local surface slopes in the x and y directions to the governing set of partial differential equations. Three field experiments were used to validate the extended model. Elevation was measured over irregular grids, and geostatistical techniques were applied to estimate the nodal elevation of the computational grids. Results indicate that inclusion of microtopography improves the estimation of the advance and recession processes and produces lower, more realistic estimates of irrigation performance. To further explore this phenomenon, two numerical experiments were devised consisting of a series of simulations on a level basin with gradually growing microtopography. The times of advance and recession and the irrigation performance indexes are significantly affected by field microtopography, even if laser leveling is used.

This paper is devoted to the problem of determination of steady-state, fully saturated flow velocities and water discharge near drains, ditches, series of wells, and similar hydrogeological objects. Traditional computational methods, based on one- (1D) and two-dimensional (2D) models, give satisfying results only in simple cases, for aquifers of regular shapes and uniform properties, but fail in more complex situations. The present paper proposes a quasi-spatial model of filtration velocity. The model is composed of two elements: first, the equation of depth-averaged 2D flow (which determines the shape of the water table, in free-surface filtration, or piezometric pressure in artesian filtration), and second, the equation of vertical 2D flow in characteristic computational profiles. The capability of the model is illustrated by considering a technical example (an existing hydrogeological barrier near Janikowo in Poland).

Crop evapotranspiration ( ETc ) by crisphead lettuce varies considerably with weather conditions and irrigation management. Accurate estimates of ETc will enable irrigation applications to be matched more closely to crop requirements, which will reduce excessive applications of irrigation water. This is important in the Salinas Valley, Calif., where overpumping of ground water is associated with seawater intrusion and nitrate contamination of local aquifers. Accurate assessments of ETc are difficult in crisphead lettuce because of high soil evaporation due to frequent irrigation and slow canopy development. A model to estimate ETc for crisphead lettuce using only daily reference evapotranspiration ( ETo ) data as an input parameter was developed. The model calculates crop transpiration and soil evaporation, and also ground cover development and daily radiation interception by the canopy. The ETc model showed good agreement when compared with field measurements of ETc taken at four different locations in the Salinas Valley and using either the water balance or energy balance methods for determining ETc .