Combined Flow Abstraction and Climate Change Impacts on an Aggrading Alpine River

Bakker, Maarten; Costa, Anna; A. Silva, Tiago; Stutenbecker, Laura; Girardclos, Stéphanie; Loizeau, Jean-Luc; Molnar, Peter; Schlunegger, Fritz; Lane, Stuart N.

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Title		Combined Flow Abstraction and Climate Change Impacts on an Aggrading Alpine River
Authors		Bakker, Maarten Costa, Anna A. Silva, Tiago Stutenbecker, Laura Girardclos, Stéphanie Loizeau, Jean-Luc Molnar, Peter Schlunegger, Fritz Lane, Stuart N. show all authors [1 - 9]
Published in		Water Resources Research. 2018, vol. 54, no. 1, p. 223-242
Abstract		Recent climatic warming and associated glacial retreat may have a large impact on sediment release and transfer in Alpine river basins. Concurrently, the sediment transport capacity of many European Alpine streams is affected by hydropower exploitation, notably where flow is abstracted but the sediment supply downstream is maintained. Here, we investigate the combined effects of climate change and flow abstraction on morphodynamics and sediment transfer in the Borgne River, Switzerland. From photogrammetrically derived historical Digital Elevation Models (DEMs) we find considerable net aggradation of the braided river bed (up to 5 meters) since the onset of flow abstraction in 1963. Reaches responded through bed level steepening which was strongest in the upper most reach. Widespread aggradation however did not commence until the onset of glacier retreat in the late 1980s and the dry and warm years of the early 1990s. Upstream flow intake data shows that this aggradation coincided with an increase in sediment supply, although aggradation accounts for no more than 25% of supplied material. The remainder was transferred through the studied reaches. Estimations of bed load transport capacity indicate that flow abstraction reduces transport capacity by 1-2 orders of magnitude. Whilst residual transport rates vary with morphological evolution, they are in the same order of magnitude as the sediment supply rates, which is why significant transport remains. However, the reduction in transport capacity makes the system more sensitive to short-term (annual) changes in climate-driven hydrological variability and climate-induced changes in intake management and sediment delivery rates.
Keywords		Valais — Switzerland — Wallis — Val d'Hérens — Arolla — Borgne River — Digital Elevation Models — Hydropower management — Purge — Sediment transport capacity — River bed aggradation — Climate warming — Alps — Sediment supply — Flow abstraction — Glacier retreat
Identifiers		DOI: 10.1002/2017WR021775
Full text		Article (Published version) (3.4 MB) - Free access Other version: http://doi.wiley.com/10.1002/2017WR021775
Structures		Faculté des sciences / Section des sciences de la Terre et de l'Environnement / Département F.-A. Forel des sciences de l'environnement et de l'eau Centres et instituts / Institut des sciences de l'environnement Faculté des sciences / Section des sciences de la Terre et de l'Environnement / Département des sciences de la Terre Faculté des sciences / Section des sciences de la Terre et de l'Environnement
Research groups		Limnology and Environmental Geology Limnology and Geomicrobiology
Project		FNS: Sinergia CRSII2_147689
Citation (ISO format)		BAKKER, Maarten et al. Combined Flow Abstraction and Climate Change Impacts on an Aggrading Alpine River. In: Water Resources Research, 2018, vol. 54, n° 1, p. 223-242. https://archive-ouverte.unige.ch/unige:103393