Journal of Irrigation and Drainage Engineering

Drainage design for water quality management in irrigated areas requires use of hydrodynamic models that delineate flow paths of subsurface water moving to drains. Use of only traditional drainage design equations for protection against water logging and salinization are inadequate for water quality management; these equations should be coupled with mechanistic models that account for transport and chemical changes in the vadose and saturated zones that replace those associated with a leaching fraction, or requirement concepts. Drainage designs should now make use of hydrodynamic and chemical models that simulate flow and transport of water and chemical constituents from infiltration to drainage discharge. Management should be able to manipulate the models prior to implementing steps aimed at controlling the quantity and quality of drainage discharge.

In the past, irrigation and drainage systems were designed and managed as separate entities. As water supplies become scarce and environmental restrictions increase, there will be a demand for the integrated design and management of irrigation and drainage systems. This type of system will make optimum use of existing water supplies and should reduce the impact of return flow on the environment. Modifications in current drainage design practice are presented that will facilitate integrated management. Recommended modifications include changing the design minimum water table depth from 1.2 to 0.9 m and the depth of drains from 2.4 to 1.5 m. These changes, coupled with either improved irrigation management or the incorporation of crop water use from shallow ground water, will result in approximately the same drain spacings as calculated using the USBR transient design procedure. Adopting the new drain depth criterion should result in less drain water and lower salt loads being discharged. These concepts were demonstrated with simulations using a drainage system designed for a cotton crop growing in the presence of shallow ground water.

This study was conducted on the water-district scale and provides insight into the effects of percolating irrigation water, local ground water, and regional ground water on the quantity and quality of drainwater from on-farm drains in the western San Joaquin Valley, Calif. Ground-water flow is downward in the upslope areas of the water district, but is upward from depths greater than 25 m below land surface in some downslope areas. Transitional areas exist where ground water flows laterally for distances as great as 3.6 km prior to interception by the on-farm drainage systems. Model results indicate that about 89% of the annual drainflow during 1987–91 originated as recharge directly above the drainage systems, and 11% of the annual drainflow was lateraland upward-moving ground water that originated as recharge in areas upslope of the drainage systems. There is general correlation between drainage systems that discharge high concentrations of selenium and areas that intercept upward-moving ground water.

Due to increasingly stringent regulations on the discharge of wastewaters as well as the decreasing availability of freshwater resources, there is a need to consider the expanded use and reuse of marginal quality waters for irrigation and other purposes. This paper addresses broad issues related to the potential reuse of (1) Treated municipal wastewaters; (2) food processing wastewaters; (3) confined animal lagoon waters; and (4) saline waters, including irrigation drainage waters, on croplands and pastures, landscapes, and agroforestry systems. The long-term efficacy of irrigation with marginal quality waters is dependent on several factors, such as unique limiting water quality characteristics and site-specific crop, soil and climatic conditions. Opportunities exist to use marginal quality waters beneficially. However, their use requires more intensive management and monitoring than use of higher quality waters. Site-specific management options are used to partially overcome many of the potentially adverse impacts, but some impacts are unavoidable. In many instances, the upper bounds of wastewater usage are not fully known and potential long-term cumulative impacts on the environment require further research.

Flow measurement (both temporary and continuous) in rectangular irrigation channels, sewers or drains, can easily be carried out quickly using measuring flumes. This study presents a particular kind of measuring flume, whose throat section is obtained with a mobile pier-shaped prism in the center of a rectangular channel. This kind of construction allows moving this measuring device from one measuring station to another, if necessary, so that it is absolutely mobile. The experimental study of five similar prisms placed in two different laboratory channels is reported. Particular attention is given to the study of submerged flow conditions because of flow measurements with minimum energy dissipation. Nondimensional analysis is used to find a generalized solution, and the results described are valid for any geometrically similar measuring device. Under submerged flow conditions, the error in discharge measurement—from ±3% to ±6%—is often acceptable in practical applications.

In this paper the writer reports the results of an investigation carried out to test the applicability of the self-similarity hypothesis for determining the flow-resistance law in small-diameter plastic pipes. The incomplete self-similarity (ISS) hypothesis is applied for establishing both the flow-resistance law and the velocity distribution. The analysis shows that the head loss per unit length can be accurately estimated using a theoretical approach based on the ISS hypothesis for the velocity profile in a circular smooth pipe. A new relationship between the Γ coefficient of the power-velocity profile and the flow Reynolds number, based on previous measurements carried out in plastic polyethylene (PE) pipes with nominal diameter equal to 16, 20, and 25 mm and for flow Reynolds numbers ranging from 3,037 to 36,112, is also established.

This paper presents a water-level control system for the Meuse river, the implementation of which is planned to start in 1997. A simplified model is used for the tuning of and design of the controllers. To obtain a highly reliable control system, a decentralized control structure is used. The control system has been tested extensively in computer simulations, the test results of which are shown.

A new modified linked approach is introduced to solve the governing partial differential equations for subsurface flow and salt transport by finite difference. It combines the attractive features of the standard linked and continuous (composite) modeling approaches. The standard linked approach can be adopted to model irrigation-drainage systems that are traditionally based on a purely agricultural objective of maintaining crop productivity despite the presence of a saline shallow ground-water table. With current concerns on the water quality of agricultural drainage, a more rigorous modeling approach (i.e., continuous approach) is required, however, at the expense of a large increase in the computational requirement. By using one- (1D), two- (2D), and three-dimensional (3D) flow and salt transport problems, it is shown that the modified linked approach efficiently satisfies current modeling requirements of both crop productivity and water quality protection. Results of applying the model to estimate the effectiveness of the drains to intercept soil water from shallow layers (<2 m deep) as affected by drain spacing, drain depth, surface recharge, and depth to impermeable layer are presented.

Long-term pavement performance in wet climates is directly related to the amount, extent, and duration of internal moisture. Retention of moisture in base/subbase layers can lead to damage and premature failure of the pavement structure. A positive subdrainage system can mitigate moisture retention. Two types of subdrainage collector systems are commonly used for removing subsurface moisture from pavement systems. These are the conventional perforated pipe edge drains and the prefabricated edge drains (PFEDs) or geotextile fin drains. Significant research was conducted in Indiana on in-place asphalt, concrete, and overlaid pavement sections incorporating these two types of subdrainage systems. Data collected from instrumented sites show varying response rates and time of outflow with respect to precipitation for pavement and collector types. Pavement-shoulder joints were found to be the major source of surface infiltration. Statistical analysis has shown significant influence of base permeability in addition to pavement and drain types on outflow volumes.

In recent years, beneficial effects of plants on the remediation of large volumes of slightly contaminated soils have been addressed by various researchers. Water is the main agent moving soluble contaminants in the soil profile, and an important one in transferring contaminants to root surfaces and subsequently to the shoot. Although there are a number of models for water flow in cropped soil, the parameters of the models, which often include rooting density, root permeability, and root water potential, are chosen by trial and error such that an overall model fits the data. Such methods can be tiresome and impractical. Therefore, the purpose of this research is to study the root water interaction of crops by developing a simple predictive technique that is usable in a wide range of applications, such as in-situ plant remediation, for contaminated soil near the surface zone. The simulation model is developed by incorporating a time-specific root distribution model into a vertical unsaturated soil water flow equation. The model validation for the time-specific root distribution is carried out using field data for cotton. A good agreement is observed between the simulation and field data. Based on constant daily water flux to individual roots under well-watered soil conditions, the cumulative amount of water consumed over time and the water uptake rate at each growth stage for cotton are investigated for the preliminary study of proper irrigation schedules. These results are included in upper boundary conditions in computer simulations of the water flow model. Soil hydraulic properties, which are important parameters in water flow model, vary as soil water content changes. Variations in the parameters of the model results in a nonlinear partial differential equation. The water flow model is solved by the Crank-Nicholson numerical scheme. The simulation results show the mechanism of plant root influence on soil water conditions across time and soil depth, which is in close agreement with results obtained in other studies. Usage of the present model is restricted to annual crop growth in soils frequently irrigated under favorable conditions. However, this simple predictive technique, coupled with a root growth and distribution model will allow for practical use in a large variety of agricultural studies. Additionally, since the model describes the variation of water flow and moisture content throughout the soil profile, it will provide necessary input for calculating the transport of solutes in the soil profile.

The soil moisture characteristic (SMC) forms an important input to mathematical models of water and solute transport in the unsaturated-soil zone. Owing to their simplicity and ease of use, texture-based regression models are commonly used to estimate the SMC from basic soil properties. In this study, the performances of six such regression models were evaluated on three soils. Moisture characteristics generated by the regression models were statistically compared with the characteristics developed independently from laboratory and in-situ retention data of the soil profiles. Results of the statistical performance evaluation, while providing useful information on the errors involved in estimating the SMC, also highlighted the importance of the nature of the data set underlying the regression models. Among the models evaluated, the one possessing an underlying data set of in-situ measurements was found to be the best estimator of the in-situ SMC for all the soils. Considerable errors arose when a textural model based on laboratory data was used to estimate the field retention characteristics of unsaturated soils.

Artificial recharge of the ground-water table from rectangular basins has been the subject of extensive study in the last 30 years. Although, for finite aquifers, the ground-water mound profile can be accurately predicted, the generalization of finite-aquifer solutions does not hold for infinite aquifers. For an infinite aquifer, the ground-water mound profile has been obtained in the form involving a definite integral (Hantush's mound function). The definite integral has been tabulated for a certain range of arguments. However, to use this table, double interpolation is necessary, which increases the error. Furthermore, a tabular solution cannot be used for analytical purposes. Thus, there is a distinct lack of more useful and computationally preferred algebraic approximations of the definite integral. The present study offers an algebraic approximation of Hantush's mound function.

As a protection measure against scour and undermining, sheet piles are provided at the upstream and the downstream ends of a weir. One or two rows of intermediate sheet piles are also provided to reduce the uplift pressures on the downstream floor. Due to the complexities of analysis, it is not known whether the provision of intermediate sheet piles is economical. This paper investigates the effectivity of multiple sheet piles as a means of reducing the floor thickness and, eventually, the cost.

Several canal gate automation methods and devices were selected for comparison and analysis. Algorithms that simulate gate operation were developed for the P+PR, BIVAL, Littleman, Colvin, Zimbelman, CARDD, and UMA methods. The algorithm for each method was evaluated in newly developed software, which was integrated into an unsteady hydraulic simulation model. Three small and three large canal systems were used to determine appropriate parameter values for each of the different automation methods. Each of the systems included both threeand five-pool versions, allowing comparisons with previously reported results by the developers of some of the methods. An analysis and comparison of the applicability of the respective methods is presented, along with recommendations for determining calibration constants, as determined from experience gained in performing more than 1,000 simulation runs.