Measuring Irrigation Well Discharges

Abstract

Irrigation wells frequently discharge directly into canals. Upstream elbows, the pump head, or other pipe fittings may produce a distorted flow profile that is detrimental to the proper installation and operation of commonly available pipe meters. Before attempts to condition the flow with longer discharge piping or straightening vanes, it is desirable to know how distorted the flow profile really is. If this information can be provided, the meter technician can determine whether a correction in the meter coefficient will suffice, or if flow conditioning equipment is needed, or whether flow conditioning equipment, if already installed, is working effectively. An economical method of field evaluating the result of an installed meter in this compromised situation is described. The method uses a conveniently fashioned pitot-tube system that can be clamped to the pump discharge pipe. It is used to quickly detect the velocity at several points across the pipe diameter. Distorted profiles can be detected and measured. Pitot-tube systems have long been used in pipe flows. Most require that special taps be drilled in the outflow pipe of the well. Some use special double-tube constructions that are difficult to build using simple machine-shop procedures. This pitot impact tube, with its static pressure companion tube, can be constructed using common shop techniques and standard small pipe fittings.