Journal of Irrigation and Drainage Engineering

A procedure was developed to obtain better estimations of the surface volumes than in hydrological models and more rapid results than running zero inertia models. Using a zero inertia model, a database was created of the surface volume during advance in dimensionless form. Through an interpolation process it is possible to calculate the surface volume using the independent variables of the phenomenon. The empirical estimates of the surface volume and the method presented in this work were compared with the results of the zero inertia model, and it was found that the empirical estimates have a validity that is restricted to particular conditions. The proposed procedure rapidly provides precise values of this volume. The error in the estimate of the infiltrated volume that occurs in the inverse methods based on the hydrological model, due to the empirical estimates of the surface volume, was also calculated, and it was found that this error is great for short distances and low values of the dimensionless parameters.

It is commonly recommended that a straight section of pipe, 8–10 pipe diameters long, be installed immediately upstream from a flowmeter to reduce errors in flow rate measurements due to excessive turbulence. However, this recommendation frequently is not followed for irrigation pumping plants. This project investigated the error in flow rate measurements under nonoptimal conditions caused by an elbow, a check valve, and a partially opened butterfly valve. Flowmeters used for this project included two propeller meters, a Collins pitot tube meter, a Hall pitot tube meter, two types of paddle-wheel meters, and a doppler meter. Measurements were made at 2, 5, 10, and 15 pipe diameters downstream from the turbulence source. In addition, the effect of straightening vanes was also investigated. Results showed that the propeller flowmeters, the Collins meter, and the Hall tube were the least affected by excessive turbulence. Meters that make point measurements have the potential of being severely affected by excessive turbulence. All meters were strongly affected by the partially open butterfly value.

Based on the continuity of flow and sediment, an analysis on scouring in long contractions is conducted with a formula obtained from measured sediment discharge in long contractions and a formula for the flow resistance related to local scour. The analytical solution shows that the equilibrium scour depth in the contracted section depends only on the ratio of the uncontracted to the contracted channel width, and the approach flow depth. The equation is applicable to both live-bed and clear-water scouring conditions. Previous predictive equations by Straub or Gill can also arrive at the same conclusion, but only for some special cases. A comparison between the measured scour data and various analytical models confirms that the simplified equation is sufficiently accurate for most practical purposes.

The surge flow irrigation method has proven its ability to increase on-farm water use efficiency. As is well known, an intermittent flow discharge device is needed for the application of this irrigation technique. Several electronic valves that produce intermittence are currently available. As is shown in this paper, such valves represent only one option for the application of surge irrigation. Simpler and less expensive options are also feasible. In this paper, a very simple device that produces a predictable intermittent discharge is presented. The device is fluidic in nature, making the use of moving control elements or external energy sources unnecessary. The operating principles of the device are described, and general design equations are derived. Laboratory test results are presented, and on-farm application experiences are described.

In a semiinfinite flow region, prediction of the water table profile due to an abrupt rise or drop in the canal or drain water level in the cases of recharging and discharging aquifers has been done for times equal to 1.0, 2.0, 3.0, 4.0, and 5.0 days by employing a numerical solution and five analytical solutions. Comparison of the water table profile predicted by the proposed numerical solution with the existing analytical solutions (based on L2 and Tchebycheff norms) shows that the performance of Polubarinova-Kochina's 1948 solution is the best, followed by Lockington's 1997 solution, Verigin's 1949 solution, Polubarinova-Kochina's 1949 solution, and Edelman's 1947 solution for both recharging and discharging aquifers. However, for the example considered in this study, for practical purposes, any of these solutions except the Edelman solution may be adopted for predicting water table heights, because the maximum relative percentage difference in water table heights predicted by these analytical solutions and the proposed numerical solution is not more than ±1.5%.

The features of culvert flow in a basic arrangement are highlighted. Four fundamental flow types may be identified, namely critical flow, uniform flow, gated flow, and pressurized flow. A generalized design diagram is presented for the circular barrel that gives the possible transitions between various flow types. Further, the lengths of free surface flows with a central pressurized flow portion are determined as a function of the pipe Froude number. Photographs of model tests illustrate the complex flow patterns that may occur even in a simple culvert arrangement. Of particular relevance are choking conditions and features of two-phase flow in a culvert. The effects of friction coefficient, bottom slope, relative pipe length, and upstream head are detailed for free culvert outlet conditions.

Evapotranspiration is an essential component of the hydrologic cycle, and its accurate estimation is necessary for many hydrologic studies. Via the pan coefficient (Kp), pan evaporation data are widely used to estimate grass reference crop evapotranspiration (ETo). An equation for predicting Kp that includes both categorical (wind run and relative humidity) and quantitative (fetch length) data was developed using the indicator regression approach. The developed equation predicted Kp values better than the existing equations.