Abstract
Abstract. Most Alpine rivers have undergone significant alterations in flow and sediment regimes. These alterations have notable effects on river morphology and ecology. One option to mitigate such effects is flow regime management, specifically through the reintroduction of channel-forming discharges. The aim of this work is to assess the morphological changes induced in the Piave River (Italy) by two distinct controlled-flood strategies, the first characterized by a single artificial flood per year and the second by higher-magnitude but less frequent floods. This work involved applying a two-dimensional reduced-complexity morphodynamic model (CAESAR-LISFLOOD) to a 7 km long reach, characterized by a braided pattern and highly regulated discharges. Numerical modelling allowed the assessment of morphological changes for four long-term scenarios (2009–2034). The scenarios were defined considering the current flow regime and the natural regime, which was estimated by a stochastic physically based hydrologic model. Changes in channel morphology were assessed by measuring active-channel width and braiding intensity. A comparison of controlled-flood scenarios to a baseline scenario (i.e. no controlled floods) showed that artificial floods had little effect on channel morphology. More channel widening (13.5 %) resulted from the high-magnitude flood strategy than from the application of the other strategy (8.6 %). Negligible change was observed in terms of braiding intensity. The results indicate that controlled floods do not represent an effective solution for morphological recovery in braided rivers with strongly impacted flow and sediment regimes.
Highlights
This paper addresses two main issues: (i) the effectiveness of controlled floods for the geomorphic recovery of a strongly regulated braided river and (ii) the suitability and reliability of the reduced-complexity CAESAR-LISFLOOD morphodynamic model to reproduce the morphological evolution of large gravel-bed rivers at given mesoscales
Results suggest that the controlled flood (CF) scenarios (SC2, SC3 and Scenario 4 (SC4)) and the baseline scenario (SC1) provide similar longterm morphological trajectories characterized by alternate phases of widening and narrowing and notable changes in active-channel width
The simulated future scenarios show that (i) none of the CF strategies provide significant long-term morphological benefits or reverse ongoing channel width trends and (ii) a small number of high-magnitude floods (i.e. SC4) provide slightly better morphological recovery than do yearly low-magnitude floods (i.e. scenarios 2 (SC2) and SC3), as well as have a significantly lower operational cost
Summary
Human activities in riverine areas (i.e. river damming and engineering, gravel mining and land use change in the drainage basin) have historically led to notable changes in flow regimes (Gore and Petts, 1989; Poff et al, 1997, 2007; Magilligan and Nislow, 2005; Zolezzi et al, 2011; Magilligan et al, 2013; Ferrazzi and Botter, 2019) and in the ecological (Collier, 2002; Céréghino et al, 2004; Paetzold et al, 2008; McDonald et al, 2010; Overeem et al, 2013; Espa et al, 2015) and geomorphic functioning of river systems (Hicks et al, 2003; Petts and Gurnell, 2005; Melis, 2011; Ziliani and Surian, 2012; Magilligan et al, 2013; Mueller et al, 2014; Lobera et al, 2016). Several studies have documented the hydrologic impacts of extensive dam systems, in partic-
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