Acoustic Mapping Velocimetry

Marian Muste, Sandor Baranya, Ryota Tsubaki, Dongsu Kim, Hao-Che Ho, Heng-Wei Tsai, Danielle Law

Monday 29 june 2015

14:05 - 14:20h at Oceania (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) River morphodynamics

Parallel session: 2B. Sediment - River

Knowledge of sediment dynamics in rivers is of great importance for various practical purposes. Despite its high relevance in riverine environment processes, the monitoring of sediment rates remains a major and challenging task for both suspended and bedload estimation. While the measurement of suspended load is currently an active area of testing with non-intrusive technologies (optical and acoustic), bedload measurement does not mark a similar progress. This paper describes an innovative combination of measurements techniques and analysis protocols that establishes the proof-of-concept for a promising technique, labeled herein Acoustic Mapping Velocimetry (AMV). The technique estimates bedload using non-intrusive measurements acquired in rivers developing bedforms. The raw information for AMV is collected with acoustic multi-beam technology that in turn provides maps of the river bathymetry over swaths of the river cross-section (acoustic mapping). As long as the acoustic maps can be acquired relatively quickly and the repetition rate for the mapping is commensurate with the movement of the bedforms, the acoustic maps can capture continuously the progression of the bedform movement. Conversion of the bed elevation maps in homologous gray-level “images” followed by application of particle image velocimetry concepts to the obtained maps allow quantification of the bedform dynamics as two-dimensional velocity maps superposed on the streambed plane. Furthermore, use of the velocity fields in conjunction with conventional analytical methods for estimation of the bed movement (e.g., Exner equation) enable estimation of bedload rates over the whole imaged area in any direction. The technique represents a promising approach for in-situ measurement of the bedform dynamics either as a distribution of bedload rates over the stream cross section or as a bulk bedload rate in the streamwise direction, as typically requested in most of the practical applications.