Hydrologic Data Acquisition Am) the Instrlmentation Gap

Any scheme for developing our water resources must eventually focus on the hydrologic theme for answers to pressing questions about anticipated availability of water. These answers will only be as realistic as the data is reliable, inferring accuracy as well as sufficiency. To that effect, more hydrologic and meteorologic data collection stations must be added to the existing network throughout the country, and the basic instrumentation presently in use should be made more versatile, but without an accompanying near-astronomical increase in cost and in complexity. The ubiquitous so-called current meters are a case in point. Current meters have almost certainly received more man-hours of use in the field of Water Resources than any other instrument ever devised to measure stream velocity. In spite of more esoteric equipment appearing on the specialized market each year, the time-honored method of stream gaging by the velocity-area method is still widely practiced, and the basic instrument remains the current meter. The same persistent use is essentially true for the anemometer, or “wind current meter.” Over the past 30 years, a great many studies have been made to define operational parameters, particularly with respect to the statistics of data reliability. Today's needs are different from those acceptable a few years back, yet in many instances yesterday's instrument can be metamorphosed to satisfy present practice. Besides a discussion of some of the fundamental problems of data collection which must be accounted for in all areas of water resources where water and air currents must be known in space and in time, the authors present a brief critique of several new hybrid types of current meters. Two of these meters were designed especially to fill the gap between sophisticated and specialized equipment of high cost, and relatively inexpensive simpler devices lacking however the advantages of automation and self-recording features. Since the mechanical performance of current meters has been the subject of many past studies fully reported in various professional journals, it appeared advantageous to develop electronic refinements on such a type of widely used instrument. A period of research, first at Washington State University and presently at Clarkson College of Technology, produced two electronic packages applicable to current meters. The rationale of these studies was to increase the usefulness of current meters by providing velocity readout, either instantaneous or time-averaged; to include data recording on tape if and when such would be desired, together with the necessary playback facility; and to keep the electronic system independent of the current meter size. The paper describes in some detail the photo-electronic tachometer which seems to offer more reliability and flexibility of operation than induction-type transducers. One of the features most worthy of consideration is the adaptability of such device to any size of current meter frame and vanes. The rotation of an impeller one-half inch in diameter is recorded by the instrument as faithfully as that of one six inches in diameter. Where velocity transients are to be observed, the advantages of a greatly reduced inertia are evident. The inherent ruggedness of low current drain transistors and integrated circuits should make this light-actuated meter readout device well-suited for remote applications.