Comparing Field, Probabilistic, and 2D Numerical Approaches to Assess Gravel Mobility in a Gravel‐Bed River

Abstract

Sediment transport is a key process that affects the morphology and ecological habitat diversity of rivers. As part of a gravel augmentation program to mitigate sediment deficit below a dam, gravel mobility in the Ain River in Eastern France was investigated by tracking of a large amount (n = 1063) of PIT‐tagged gravels in the field, conducting a probabilistic approach based on published tracer studies, and performing two‐dimensional (2D) numerical modeling of flow and bedload transport. This comparative study highlights the strengths, weaknesses, and complementary aspects of the three approaches to the understanding of river gravel mobility. Thanks to recent technological improvements, PIT‐tagged gravels provide an increasingly reliable and accurate representation of bedload movement in the field, although it remains limited in spatio‐temporal resolution. Based on an exponential distribution, the probabilistic approach correctly reproduces the average trend in travel distances by the different classes of particles over hydrological periods, including one or several significant floods. Furthermore, the 2D numerical modeling accounts for the variability of local hydrodynamic conditions and can simulate realistic displacement distributions for the different classes of particles with high spatio‐temporal resolution. Numerical modeling is a very encouraging approach, which makes our study original because it is the first time that the estimation of mean travel distances, the application of an exponential distribution, and the comparison with a hydrodynamic model are combined. A more effective modeling strategy involves incorporating a probabilistic transport model in the 2D numerical model to reproduce the observed scatter of the individual particle trajectories.This article is protected by copyright. All rights reserved.

Coastal Retreat on the Spanish Mediterranean Coast in a Climate Change Context: Effects of the Regulation of the Segura River at Its Mouth and the Coastal Sand Dune in Guardamar del Segura (Alicante, Spain)

“…This would reveal the quantity and size of the sediment that is stored in the reservoirs and the amount that continues to circulate [60,61]. Trackers could also be installed in elements such as gravel to determine their displacement in different future hydrological events [62][63][64][65]. Therefore, the study could be expanded with another series of data if sufficient means were available.…”

Characterizing the effects of morphological microstructures and hydropeaks on fish stranding in rivers

“…In the Lower Ain River, down-ramping rates are relatively low (about 4-6 m 3 s À1 h À1 , i.e. 5.3-9,9 cm h À1 on average, calculated with a 2D-model developed between Pont d'Ain and the confluence with the Rhône River (used in Arnaud et al, 2023 andJudes et al, 2023), Table 1), whereas in the literature, fish stranding is associated with a down-ramping rates higher than 6 cm h À1 for post-emerged trout and higher than 12 and 24 cm h À1 for grayling larvae and juvenile, respectively (Moreira et al, 2019). Schmutz et al (2015) observed a threshold of 15 cm h À1 below which the probability of observing a good fish ecological status is achieved, converging with Halleraker et al (2003) recommendations to reduce down-ramping rates to less than 10-15 cm h À1 .…”