Acoustic gravel-transport sensor: description and field tests in Little Granite Creek, Wyoming, USA

Abstract

Abstract Acoustic systems have been developed for the measurement of bedload momentum in gravel-bed streams. The transducers are placed in the bedload either by a wading operator (GTS-I) or in a fixed installation embedded in the stream (GTS-II). The signals produced when particles impact the transducer are processed by an electronics unit to provide a continuous record of bedload momentum. A recent comparison of a GTS-II system with bedload traps in a small, mountain stream yielded promising results. Although the data are limited, they show that when the size of the bedload is known, corrections for grain velocity are made, and time-space averaging is sufficient, GTS measurements are roughly comparable to those made with bedload traps. Key words bedload; bedload transport; gravel-b ed streams; gravel-transport sensor INTRODUCTION An understanding of bedload transport in gravel-bed streams is needed for the assess-ment of the ecological and physical consequences of land-use changes in and around these systems. D & A Instrument Company is developing acoustic systems for measur-ing bedload in streams and on beaches to meet this need. The idea of using acoustic signals generated when entrained sediment particles strike a rigid object is not new. Sharp & O’Neill (1968) used a wire to detect sediment flowing in pipes and Downing (1981) used a similar technique to measure sand bedload in streams. In the early 1990s, this approach was extended to measure gravel bedload with a pipe containing an acoustic detector and recording electronics (Downing, 1993). In this paper, we describe further developments of acoustic devices for measuring gravel momentum and present the results of our tests in a small, mountain stream in Wyoming, USA.