Difficulties caused by sediment carried in natural streams have existed since earliest times. Although instruments and techniques for measuring stream discharge have existed for many years, only recently have attempts been made to measure sediment carried by the streams. The earliest observations of sediment discharge in the United States were made by Captain Talcott in the Mississippi River in 1838 (1). More or less continuous samples of sediment from the Rio Grande have been collected by the United States Geological Survey since 1879, and from the Colorado River Basin since 1925. Studies of sediment transport are seriously hampered by the lack of adequate measuring instruments. The most widely used method of measurement involves the collection and analysis of intermittent samples from which is computed the required information. The complexity and expense of these techniques prohibit their continual use in all but a relatively few of the world’s rivers and streams.
In an attempt to reduce the cost and improve the quality of sediment-discharge information, the Federal Interagency Committee on Water Resources, Subcommittee on Sedimentation, ahs established the immediate goal of developing an instrument for determining either directly or indirectly the sediment concentration at a point in a stream cross section (1). Their ultimate objective is the development of instruments that will automatically sense and record the quantity and character of sediment loads transported by natural streams. The record thus produced should be continuous, or intermittent at sufficient frequency to define a continuous record of the sediment discharge.
Several different ways of automatically determining the concentration of suspended sediment have been or are being studies (1). These include electronic sensors which measure resistance changes due to the presence of sediment; differential-pressure devices which measure changes in pressure between two elevations in a flowing sediment-water mixture; the use of ultrasonics for measuring suspended sediment concentration; and nuclear devices which use radioisotopes for determining concentration.
Another possibility for indirectly determining sediment concentration is to measure effects of the concentration on the dielectric properties of the transporting water. Preliminary work (2, 14) on this method consisted primarily of the design of electrical circuitry and a problem for making capacitance measurements in water – sediment samples. Electronic difficulties were encountered and the project was discontinued. More recently the problem was reviewed by electrical engineering research personnel of the Utah Water Research Laboratory, and a decision was made to conduct further feasibility tests under a cooperative agreement with the U.S. Department of Agriculture – Agricultural Research Service.
The first reported part of this study consists of the design and laboratory testing of several theoretically-workable circuit configurations of capacitance –measuring equipment. A number of these are described in detail in an appendix to this report. The second part includes results of a series of laboratory measurements of dielectric characteristics of various water-sediment and water-salt mixtures as they are influenced by temperature and concentration changes.
This report is somewhat interim in nature inasmuch as the study will continue for at least another year.
Israelsen, C. Earl and Chadwick, Duane G., "Feasibility Study of a Capacitance-Type Electronic Sediment-Sensing Device" (1967). Reports. Paper 373.