Journal of Irrigation and Drainage Engineering

In 1989 Lenhard et al. discussed a method for converting van Genuchten's 1980 soil-water-retention model into a simpler power-law model of the form proposed by Brooks and Corey in 1964. In this paper, the effect of this conversion on the numerical modeling of infiltration in a variety of soil types is investigated. A simple modification to this conversion procedure, which matches hydraulic conductivities in the two models more closely, is also presented and tested. Both the original and the modified conversion procedure are more accurate for nonclayey soils (with a relatively narrow pore-size distribution) than for clayey soils. However, the difference in infiltration calculated using the van Genuchten and Brooks-Corey models is significantly reduced when the modified procedure is used.

Experiments to study the performance of a cavity well (nonpenetrating well) have been conducted in both the laboratory and the field. Laboratory tests were performed on a simulated sand-tank model that reproduced the flow into the well on a reduced scale. Field tests were conducted on observation wells, drilled and installed at the Shaldahari watershed in the Midnapore district of West Bengal, India. Results have been analyzed by the finite-element method, and a reasonably good agreement with computed values has been indicated. Performance of a cavity well is found to be influenced by aquifer material properties and thickness of the confining layer. Studies have been made of leaky as well as nonleaky flow under steady and nonsteady conditions.

Seepage erosion—in particular, slope failures (bank slumps, mass wasting)—is prevalent on most sandbars downstream from the Glen Canyon Dam, Ariz. The public is concerned about the loss of the extant biomass and recreational facilities on these sandbars. It is alleged that the operation of the Glen Canyon Dam is responsible for the erosion of the sandbars. In this contribution, a simple, approximate analysis is developed to determine the extent of slope failures due to seepage of bank stored water from transient dam flow. The analysis is intended to assist environmentalists, dam operators, planners, and others to predict zones in which riparian habitat and recreation use will be negatively impacted by fluctuating flows. The affected area of a sandbar was found to be dependent on the range of flows; the rate of rise of river stage; the duration of the peak discharge; and the permeability, friction angle, and cohesion of the soil. Comparison of the predictions of the analysis with field data show good agreement.

During periods of drought, an important goal of water-resource management is the establishment of realistic reservoir operating policies for water allocation, especially for a river system involved with flood-control reservoirs. This paper discusses optimization models for the flood-control reservoir operations at varied levels of drought severity. It is assumed that for a certain drought-severity level, there will be corresponding minimum demands at downstream control points and maximum inflows to reservoirs. A constant reservoir yield was estimated for each reservoir, based on the maximum duration of historic drought events on the 70% truncation level. Based on the drought evaluation, optimization models at the 70%, 80%, 90%, and 95% levels of drought severity were developed and applied to a river system involved with four flood-control reservoirs in the Scioto River Basin in central Ohio.

Irrigation scheduling, which is used to determine the frequency and dosage of irrigation applications, is required to optimize water use while at the same time maximizing crop yield and farm profit. This paper describes the broad principles and applications of a computer-assisted irrigation scheduling system, namely AISSUM (Automatic Irrigation Scheduling System of the University of Montréal). AISSUM is user-friendly and has the potential for optimizing water use and enhancing crop production. AISSUM is based on the water-balance approach to irrigation scheduling. The requisite weather and soil data are collected by a solar-powered, portable micrometeorological system (SEWBS). Crop evapotranspiration (ET) is calculated using a customized software package, EDA. Irrigation scheduling is performed by the software package AIS.IRRIG. The test results for AISSUM for an okra crop in Trinidad and a raspberry field in Québec are presented. In addition to providing real-time estimates of irrigation scheduling, AISSUM gives superior results when compared to the cycle method.

A volume balance approach to determine the parameters of the Kostiakov or modified Kostiakov infiltration equations in border and furrow irrigation is presented. The approach requires measured data from the advance phase, the postadvance (wetting) phase, or both, resulting in three different procedures to characterize infiltration. Using the entire field length the procedures provide infiltration parameters that are more representative of an actual irrigation. The volume balance computation performed by the end of the wetting phase makes it possible to determine the accuracy of each equation that can represent the infiltration process for a particular application. Inflow discharge, water front advance, average flow cross-sectional area, and outflow discharge are the required field data. Several mathematical approximations are suggested in order to simplify the field work and the amount of computation. The use of empirical factors to improve data fitting is discussed. By providing irrigation system performance information during an irrigation, this procedure can be easily adapted to guide decisions during real-time operation.

This paper introduces a model for the design and management of conjunctive irrigation and drainage systems. The mathematical model is based on the numerical implementation of a quasi-three-dimensional finite-difference model, which solves the Richards equation and the advective-dispersive transport equation for one-dimensional vertical flow and salt transport in the variably saturated zone above the water table; and it also solves the depth-averaged Boussinesq equation and two-dimensional advective-dispersive transport equation for areal flow and salt transport in the fully saturated zone below the water table. The model is fully interactive and is provided with a graphic user interface (GUI). It can be used to estimate the growth response of a crop to its soil-water-air-solute subsurface environment as influenced by drainage design and management practices such as irrigation scheduling, leaching, and cropping patterns. An illustrative example is included to demonstrate the capabilities of the model as a design and management tool in irrigation and drainage systems.

The Colorado State University Irrigation and Drainage (CSUID) model is a simulation model, which can be used in the design and management of conjunctive irrigation and drainage systems. It is based on the numerical implementation of a quasi-three-dimensional finite-difference model, which solves the Richards equation and the advective-dispersive transport equation for one-dimensional vertical flow and salt transport in the variably saturated zone above the water table; and it also solves the depth-averaged Boussinesq equation and two-dimensional advective-dispersive transport equation for areal flow and transport in the fully saturated zone below the water table. In this paper, the model is validated and applied. Its performance is compared to known analytical solutions of simplified problems, the performance of other numerical models, and results of reported laboratory and field experiments. Its capabilities as a design and management tool are demonstrated by considering a hypothetical field problem. It is shown that the model can be used to evaluate design and management strategies to achieve the improved performance of conjunctive irrigation and drainage systems.

A simple and efficient method was developed to determine soil macroporosity and hydraulic conductivity for dual-porosity models from measurements of unconfined infiltration rates. The utility of this method was demonstrated by analyzing unconfined infiltration tests conducted with a tension infiltrometer at ponded conditions and at negative 3, 6, and 15 cm of water-supply pressure. The conductivity of soil macropores (pores > 1 mm in diameter) was 3.6 times the conductivity of the soil matrix. This contrast in the magnitudes of the hydraulic conductivity may justify the use of dual-porosity models of water flow and solute transport. Positive but small correlation between soil macroporosity and hydraulic conductivity of the soil matrix was identified. Soil macroporosity remained constant near the surface but it decreased with soil depth. The narrow range of 0 to −15 cm of water pressure may govern water flow and contaminant transport under field conditions because of the rapid decrease of conductivity with water pressure, which was reflected by a short macroscopic-length scale. The method described in this paper relied on measurements of unconfined infiltration rates to minimize soil disturbance. This method provided several advantages over measuring the macroporosity with double-ring infiltrometer, which requires driving a ring into the soil to establish one-dimensional flow.

The effects of cloud seeding projects on streamflow volumes are small with respect to the standard deviations of these volumes. Previous assessments were carried out using probabilistic methods, either directly or after a separation of carried-over flow. The present work examines, through a case study, the practicability of the extension of these methods to situations of weakly dependent data. The selected case is an operational seeding over the Kaweah Watershed in California. Annual volumes of streamflow, for 11 seeded years, are compared to volumes for 25 unseeded years at that river and to concurrent volumes at the Merced River, which serves as a control. The effect of seeding is assessed through a multiple regression of flow volumes at the Kaweah River, against concurrent and preceding volumes at the Merced River. The model is formulated for the unseeded period and applied to the seeded period. A large increase in flow volumes, from the unseeded to the seeded period, is observed for both rivers. With respect to the change in Merced River, the rate of augmentation at the Kaweah River is estimated as being between 9% and 18%, significant at a two-tailed level of 0.54–0.05. The coefficient of variation for the unseeded period attains a value of 0.50, and the range of results seems narrow enough to conclude the effect is positive and valuable.

A one-dimensional sharp interface finite-element model is used for parametric studies on the transient behavior of seawater intrusion due to the linear variation of the surface source level. The validity of the numerical solution is established by comparing it with the results of the Hele-Shaw analog model. A general relationship between saltwater toe movement, and different rates of linear rise in the surface source level, located at various distances from the coast, was established. The movement of the interface is also monitored after the rise in the surface source level is stopped. The results obtained from the studies are applicable to a wide range of practical cases and are useful in management schemes on the control of seawater intrusion in coastal areas.