Quantifying sediment transport from periodic transect measurements in rivers and estuaries

Abstract

Sediment transport in rivers and estuaries is typically monitored infrequently and discontinuously, which is a key reason why sediment budget estimations are often poor. On the contrary, water discharge is often monitored with high accuracy, and continuously, which requires periodic ship measurements for recalibration of rating curves. Even in tidal rivers, continuous flow measurements can be obtained by upscaling transect flow measurements to cover the entire cross-section, which rarely occurs for sediment transport (Kästner et al., 2018). This contribution discusses how existing discharge measurement schemes can be extended to yield continuous measurements of sediment transport, separating between suspended load and bedload sediment fluxes. A new approach is outlined, which relies on repeated cross-river transect measurements, using multiple acoustical and optical instruments. Innovative suspended load measurements make use of acoustic profilers with multiple sound frequencies and a spectrometer, which can measure suspended sediment mean particle size and carbon content from light absorbance (Sehgal et al., 2022). Inference of bedload transport from bedform tracking improves when taking secondary bedforms into account, which can migrate fast and persist in the lee of primary dunes, contributing significantly to the total bedload transport (Zomer et al., 2021). For sand-bed rivers in particular, a generic approach to upgrade existing discharge monitoring programmes to include continuous sediment transport may be feasible with limited additional ship survey time.Kästner, K., Hoitink, A. J. F., Torfs, P. J. J. F., Vermeulen, B., Ningsih, N. S., & Pramulya, M. (2018). Prerequisites for accurate monitoring of river discharge based on fixed‐location velocity measurements. Water resources research, 54(2), 1058-1076.Sehgal, D., Martínez‐Carreras, N., Hissler, C., Bense, V. F., & Hoitink, A. J. F. (2022). Inferring suspended sediment carbon content and particle size at high frequency from the optical response of a submerged spectrometer. Water Resources Research, 58(5), e2021WR030624.Zomer, J. Y., Naqshband, S., Vermeulen, B., & Hoitink, A. J. F. (2021). Rapidly migrating secondary bedforms can persist on the lee of slowly migrating primary river dunes. Journal of Geophysical Research: Earth Surface, 126(3), e2020JF005918.