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Investigation of River Discharge Fluctuations in a Shallow Gravel-Bed River

Author(s): Kazuhiko Ishikawa; Kiyosi Kawanisib; Mahdi Razaz; Yano Junki

Linked Author(s): Kiyoshi Kawanishi

Keywords: Continuous measurements of river discharge; River discharge time series; Acoustic tomog-raphy; Power spectr

Abstract: Continuous measurements of flow rate in a shallow gravel-bed river were carried out using a new acoustic method. It is very difficult to measure continuous flow rates in extremely shallow and wide rivers by traditional methods. In the present study, Fluvial Acoustic Tomography System (FATS) was developed and utilized to measure flow rate. Reciprocal sound transmissions were performed between the two acoustic stations located diagonally on both sides of the river. FATS enabled the measurement of the depth-and range–averaged sound speed and flow velocity along the ray path. In contrast to traditional point/transect measurements of discharge, in a fraction of a second, FATS covers the entire cross-section of river in a single measurement. The flow rates measured by FATS were compared to those estimated by moving-boat Acoustic Doppler Current Profiler (ADCP) and rating curve methods. FATS estimates were in good agreement with ADCP estimates over a range of 20 to 65 m 3 /s. On the other hand the flow rate by RC method fairly agreed with FATS estimates for greater discharges than around 40 m 3 /s. Spectra of discharge fluctuations were estimated in wide frequency range (10 -6 to 10 -1 min -1). As expected from the spectrum model of Dolgonosov et al. (2008), the spectra of discharge fluctuations had two different power-law trends, separated by crossover frequency (f c ≈3×10 -4 min □1), with spectral exponent 1 at low frequencies and 2.8 at high frequencies. The crossover frequency is substantially high in comparison to those of Russian rivers.


Year: 2012

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