Journal of Irrigation and Drainage Engineering

Linear quadratic optimal control theory is applied to the automatic control of two different eight-pool irrigation canals. The model used to design the controller is derived from the Saint-Venant equations discretized through the Preissmann implicit scheme. The linear quadratic closed-loop optimal controller is obtained from steady-state solution of the matrix Riccati equation. A Kalman filter reconstructs the state variables and the unknown perturbations from a reduced number of measured variables. Both perturbation rejection and tracking aspects are incorporated in the controller. Known offtake withdrawals and future targets are anticipated through an open-loop scheme utilizing time varying solutions of the linear quadratic optimization problem. The controller and Kalman filter are tested on a full nonlinear model and prove to be stable, robust, and precise.

Two considerations motivated this study of the operation, maintenance, and rehabilitation (OM&R) costs of Egypt's Nile River irrigation system. The first is the deteriorating operating condition of the numerous structures that compose the system. The second derives from the major changes in financial policies being instituted by the government of the Arab Republic of Egypt (GOARE), particularly those related to the agricultural sector. New policies will allow farmers to sell more freely on the open market and will permit most farm commodity prices to move toward international free market levels. Because of these new pricing policies, the GOARE must seek new revenue sources to replace the old ones. The overall objective of this study was to determine the net OM&R costs of the main irrigation and water supply system in Egypt, as it is currently supported, and what those costs might be under an enhanced or acceptable budget allocation. The analysis is limited to OM&R costs of the main system, defined as the Nile River structures and the main and secondary canals. It excludes the on-farm portions of the system (mesqas and below). The study considers four policy scenarios. The first reflects recent budget allocations for OM&R in Egypt. The second reflects the cost of the system if it is improved to an “adequate” degree. The third scenario incorporates planned reclamation of not yet developed new land into the first scenario; the fourth scenario incorporates such reclamation into the second scenario. The study findings suggest that the nationwide average annual OM&R costs of the main distribution system allocated to irrigation are about 75 Egyptian pounds (LE) per feddan per year in 1991 prices. It is estimated that the cost would increase to about LE109 per feddan per year with the proposed system improvements (scenario 2). The equivalent costs per 1,000 m³ of water are about LE11 and LE16, respectively. By international standards these costs are reasonable and economically viable. The application of a cost allocation model to the Nile River system is more of a continuing process than a definite conclusion. As insights are gained from use of the model for sensitivity and “what if” studies, it will be possible to evaluate data and system improvement priorities in terms of continually changing policies and social needs.

A nonhydrostatic model for overland flow is developed for the purpose of providing the framework for predicting the fate and transport of chemicals under surface irrigation. The technique is based on the turbulent Navier-Stokes equations for the surface wave and the Richards equation for the movement of moisture in the underlying porous medium. The model consists of a novel two-dimensional combination of the marker-and-cell and finite-element methods and utilizes a deforming computational grid that automatically adapts to moving wave fronts in the solution. Convergence and conservation tests are performed to demonstrate the robustness of the model. Results are presented for laminar and turbulent flow cases and compared to similar computations based on traditional depth-averaged models.

A system for measuring water droplet impact energy is described, which consists of piezoelectric film connected to a high-speed data acquisition board in a personal computer. The system converts the impact forces of individual water droplets falling onto the piezoelectric film into an output voltage, which is measured and analyzed. Eight DT3-type piezoelectric films were calibrated under laboratory conditions for kinetic energy values ranging from 0.01 × 10⁻³ to 1.2 × 10⁻³ J by releasing water droplets of various sizes from specific heights. The DT3-type piezoelectric film is effective for water droplets smaller than 4.6 mm in diameter. Results were used to produce a general model for the response of this film type. The ease of use and robustness of the system was demonstrated by measuring droplet impact forces under a lateral-move irrigation machine.

Selecting areas for a subsurface drainage system and the proper design of such a system require sufficient and reliable soil data, which are inherently variable in both space and time. This study shows how geostatistical techniques can be applied for both feasibility and design stages of a drainage project to provide decision makers and designers with reliable estimates, a way of selecting areas for a subsurface drainage system and determining its implementation priority, and a way of accurate design of that system. The study is applied to a practical area of 1,533 ha in the Nile Delta of Egypt. Results showed that measured values of water table depth and soil salinity yielded ≈40% underestimation of drainage necessity and 59% overestimation of soil salinity levels, respectively, compared with their kriged values. The effect of using the kriged hydraulic conductivity on the determined lateral drain spacing and the required lateral drain pipe length was demonstrated. Five percent wider drain spacing was obtained with kriged hydraulic conductivity compared with its measured value with most steady- and unsteady-state drainage formulas. This value was approximately doubled using some other unsteady formulas. The minimum sample size for estimating a mean value at a given precision level could be reduced by three to seven times using kriging technique.

The normalized water content calculated with the simple algebraic equation Θ_fc= (q_fc/K_s)^1/n, where q_fc= 0.05 mm/day and K_s= hydraulic conductivity, can be used to estimate field capacity. The water content calculated with this relationship is close to the water content at 1/3 bar matric potential for all soils. It is suggested that the concept of “field capacity” be refined by relating it to the mobility of soil moisture (drainage flux). Field capacity should not be characterized solely by a particular drainage time, because the time to reach field capacity depends on soil properties, but also on the initial water content and water depth in the soil.

Numerical solutions in Newton-Raphson form are presented for the standard step method of calculating the free surface profile in a gradually varied flow. The solutions are based on three different resistance equations: Chezy, Manning, and Colebrook-White.