Ecological Impact of Hydraulic Dredging from an Alpine Reservoir on the Downstream River

Silvia Quadroni (), Giuseppe Crosa, Gaetano Gentili, Alberto Doretto, Niccolò Talluto, Livia Servanzi and Paolo Espa
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Silvia Quadroni: Department of Theoretical and Applied Sciences, University of Insubria, Via JH Dunant 3, 21100 Varese, Italy
Giuseppe Crosa: Department of Theoretical and Applied Sciences, University of Insubria, Via JH Dunant 3, 21100 Varese, Italy
Gaetano Gentili: GRAIA srl, Viale Repubblica 1, 21020 Varano Borghi, Italy
Alberto Doretto: Department for the Sustainable Development and Ecological Transition, University of Eastern Piedmont, Piazza S. Eusebio 5, 13100 Vercelli, Italy
Niccolò Talluto: Department of Life Sciences and Systems Biology, University of Turin, Via Accademia Albertina 13, 10123 Torino, Italy
Livia Servanzi: Department of Science and High Technology, University of Insubria, Via GB Vico 46, 21100 Varese, Italy
Paolo Espa: Department of Science and High Technology, University of Insubria, Via GB Vico 46, 21100 Varese, Italy

Sustainability, 2023, vol. 15, issue 24, 1-15

Abstract: The evacuation of impounded sediments is one of the most critical aspects associated with reservoirs, with possible drawbacks on the water quality, biodiversity, and ecosystem integrity of downstream river reaches. In this study, the impacts of hydraulic dredging at the Ambiesta Reservoir (Eastern Italian Alps) on the physical habitat and the biological communities (i.e., benthic macroinvertebrates and fish) of the downstream river were assessed by comparing the pre-dredging conditions with data collected on three post-dredging occasions. The dredging operation lasted 68 days and removed an overall sediment volume of 30,600 m 3 . During this operation, suspended sediment concentration (SSC) was monitored by turbidimeters and, on average, it was considerably lower than the SSC limit of 1.5 g/L, which exceeded approximately 15% of the overall operation time. Additionally, the dredging operation resulted in negligible deposition of fine sediment on/into the riverbed (0.24–0.7 kg/m 2 ). Results for fish and benthic macroinvertebrate communities indicated weak differences in the density (~20% reduction) and diversity of these organisms between pre- and post-dredging sampling occasions. Moreover, the results on the biomonitoring indices based on macroinvertebrates showed a recovery during the last two sampling occasions. Compliance with the SSC limit and avoidance of high SSC peaks, along with limited fine sediment deposition, allowed to successfully mitigate the ecological impacts of this relatively long operation of sediment removal.

Keywords: reservoir desilting; hydraulic dredging; fine sediment; suspended sediment concentration; physical habitat; macroinvertebrates; fish; biomonitoring; sediment management; eco-sustainability (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2023
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