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Journal Articles Earth Surface Processes and Landforms Year : 2017

Monitoring gravel augmentation in a large regulated river and implications for process-based restoration

Fanny Arnaud
Hervé Piégay
D. Béal
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  • PersonId : 1012971
Pierre Collery
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  • PersonId : 949937
Lise Vaudor

Abstract

The artificial gravel augmentation of river channels is increasingly being used to mitigate the adverse effects of river regulation and sediment starvation. A systematic framework for designing and assessing such gravel augmentations is still lacking, notably on large rivers. Monitoring is required to quantify the movement of augmented gravel, measure bedform changes, assess potential habitat enhancement, and reduce the uncertainty in sediment management. Here we present the results of an experiment conducted in the Rhine River (French and German border). In 2010, 23 000 m3 of sediments (approximately the mean annual bedload transport capacity) were supplied in a by-passed reach downstream of the Kembs dam to test the feasibility of enhancing sediment transport and bedform changes. A 620-m-long and 12-m-wide gravel deposit was created 8 km downstream from the dam. Monitoring included topo-bathymetric surveys, radio-frequency particle tracking using passive integrated transponder (PIT) tags, bed grain size measurement, and airborne imagery. Six surveys performed since 2009 have been described (before and after gravel augmentation, and after Q2 and Q15 floods). The key findings are that (i) the augmented gravel was partially dispersed by the first flood event of December 2010 (Q1); (ii) PIT tags were found up to 3200 m downstream of the gravel augmentation site after four years, but the effects of gravel augmentation could not be clearly distinguished from the effects of floods and internal remobilization on more than 3500 m downstream; (iii) linear and log-linear relationships linking bedload transport, particle mobility, and grain size were established; and (iv) combined bathymetry and PIT tag surveys were useful for evaluating potential environmental risks and the first morpho-ecological responses. This confirmed the complementary nature of such techniques in the monitoring of gravel augmentation in large rivers.
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Dates and versions

hal-01563308 , version 1 (17-07-2017)

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Fanny Arnaud, Hervé Piégay, D. Béal, Pierre Collery, Lise Vaudor, et al.. Monitoring gravel augmentation in a large regulated river and implications for process-based restoration. Earth Surface Processes and Landforms, 2017, ⟨10.1002/esp.4161⟩. ⟨hal-01563308⟩
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