Journal of Irrigation and Drainage Engineering

Several authors have reported that the spatial variability of infiltration and soil surface elevation can have a pronounced effect on surface irrigation performance. This study was conducted to assess the improvement of the predictive capability of a level-basin irrigation model when both sources of spatial variability are considered. A 2D simulation model was used to simulate irrigation events with or without spatial variability of infiltration and/or elevation. Four irrigations that were applied to a corn crop planted on an experimental, laser-leveled basin were simulated. Introducing soil surface elevation variability improved the quality of the simulation of advance, recession, and crop yield, whereas introduction of infiltration variability did not. If infiltration is randomly distributed in the basin, it does not seem justified to introduce its variability in the model. As for soil surface elevation variability, its introduction would be justified even if laser leveling was used. Finally, the introduction of both sources of variability led to an accurate estimation of distribution uniformity.

This paper presents the results from a detailed field experiment of water movement on a border-irrigated bay in northern Victoria, Australia, an area characterized by shallow ground-water tables and salinization problems. The objective of the study was to quantify the impact of changes in irrigation management on salt and water movement within and from the bay and on recharge to the region's shallow ground-water table. Results showed that the evapotranspiration volume almost wholly explained the soil moisture changes between irrigation events and that deep drainage was negligible. Infiltration was mainly confined to the advanced stages of irrigation, with the soil rapidly becoming saturated across the bay, due to the presence of soil cracks. Such findings suggest that more efficient management of border irrigation supply to the bay will not lead to the lowering of the shallow ground-water table—conclusions that have important implications for irrigation management.

This paper presents results from an experiment to measure the salt transport processes within a border-irrigated bay in northern Victoria, Australia, an area with shallow saline ground water and cracking soils. The overland flow and drainage salinity measurements showed that lateral surface washoff of salt from the soil surface was the main process of salt transport into surface water. Soil salinity measurements showed that, although salt was removed from the near-surface soil, there was negligible leaching downward through the profile. This was due to the near saturation of the soil, the presence of cracks that minimize the vertical leaching, as well as the lack of deep drainage of ground water. These findings highlight the importance of lateral washoff in the transfer of salt from irrigation bays, suggesting that reduction in irrigation event volumes is likely to reduce salt export and thus affect the sustainability of irrigation in this area.

The wetted perimeter is an open-channel parameter that influences surface drag and also influences infiltration in furrows and unlined canals. Various approximations to the wetted perimeter are examined for channel cross sections in which the top width is a power law of depth. Exact solutions are available only for select values of the exponent. Interpolation between exact values, partial sums of series approximations, and numerical integration are compared. A simple nonlinear interpolation scheme or a three-term summation yields results accurate to within 1% of the range of typical channel geometries. Common numerical approximations are shown to yield errors in excess of a range of from 3 to 10%.

This work deals with the recharging-dewatering problem for an unconfined aquifer. In particular, the evolution of the aquifer free surface consequent to changes in the water level in a trench near the aquifer itself has been investigated. The problem has been analyzed using a numerical approach so as not to eliminate the nonlinearities of the boundary conditions: the Laplace equation has been solved using the finite-element method coupled to an interpolation-collocation method for the solution of the free surface kinematic condition. Many configurations, which are most likely to cover cases of practical interest, have been studied, and the results have been summarized in a simple formula that permits the evaluation of the aquifer portion that is affected by recharging-dewatering actions.

The end-gun discharge of center pivots is expressed as a ratio of the inflow at the pivot. Using this ratio, equations are developed for the friction correction factor and pressure distribution factor. If end-gun discharge is reduced to zero, then these equations reduce to the well-established equations for the friction correction factor and pressure distribution factor. For an end-gun ratio of unity, the friction correction factor also becomes unity, reflecting that the lateral is in fact a pipeline without outlets. The pressure distribution factor becomes linear, reflecting that head loss varies linearly with length. For a lateral of constant diameter and typical end-gun discharge there is a significant increase in head loss due to friction. However, there is insignificant difference in the estimate using either this technique or the effective radius technique. The pressure distribution factor is slightly higher, indicating that in laterals with end guns the pressure head toward the center of the lateral is higher. The equations presented can be used to design center-pivot laterals with end guns or the first segment of a tapered center-pivot lateral.

The street hydraulic capacity to convey storm water is dictated by the street gutter geometry and hydraulic characteristics. With the consideration of traffic safety, the street hydraulic conveyance capacity (SHCC) is also subject to a reduction defined by the water velocity and flow depth in the street gutter. In this study, the street hydraulic equation is rearranged to demonstrate that the water velocity and depth product in a gutter flow can serve as a safety criterion for determining the allowable SHCC. The velocity and water depth product and discharge reduction methods were examined and revised to establish the consistency in predictions. The revised design procedures developed in this study replace the current iterative process with a direct estimation of the allowable SHCC when a safety criterion is specified.

River recharge is one of the important factors affecting the yield of nearby wells. The mathematical complexities of the existing methods in computation of rate and volume of stream depletion can be very much simplified through numerical methods without loss of much accuracy. In the present study, simple equations for stream depletion rate and total volume of stream flow depleted are presented. The example illustrates the relative simplicity of the proposed equations.

There are various types of water measurement devices available. The type of flume used in a particular application depends on site-specific factors or limitations and the need for precision and cost. In measuring water in open drains, it is often desirable to prefabricate the flume to avoid the need for dewatering prior to installation. Traditionally, cutthroat flumes have been used in open drain systems or ditches due to ease of fabrication and installation. However, due to the extended transitional length and width associated with the cutthroat flume, transportation of the flume requires special facilitation or permits. A simple Venturi flume was proposed and tested that has several advantages over the traditional cutthroat flume. These advantages include lower construction cost, simplicity in fabrication, ease of transportation, and less width requirements where large flows are to be measured.