Channel Adjustments and Island Dynamics in the Brenta River (Italy) Over the Last 30 years

Abstract

Many gravel bed rivers in the European Alpine area suffered different ranges and types of human pressure that modified their morphology and altered their processes. This work presents the case of the middle portion of the Brenta River, historically impacted by human activities such as floodplain occupations, bank protection, gravel mining, hydropower schemes and water diversion. Dam operation and gravel mining have produced considerable modifications in the natural sediment regime generating important morphological channel responses (narrowing and incision). Large areas of the former active channel have been colonized by riparian vegetation, both as islands and as marginal woodlands. Overall, the river changed its morphological pattern from braided to wandering. The present study analyses the timing and extent of the planform morphological changes that occurred over the last 30 years along the middle portion of the river (20 km long) through the examination of aerial photos, repeated topographic measurements and hydrological data. A series of recent aerial photos (1981, 1990, 1994, 1999, 2003, 2006, 2008, 2010 and 2011) have been used to assess the medium and short‐term morphological changes of the floodplains and the active channel area. As to the medium‐term modification, the recent changes in in‐channel gravel mining have determined a new trend of active channel widening through erosion of vegetated areas. The analysis has also allowed to assess the morphological effect of single flood events. Only floods with recurrence interval higher than 8–10 years appear to be able to determine substantial erosion of floodplain and island margins. Copyright © 2013 John Wiley & Sons, Ltd.

Bank erosion and large wood recruitment along a gravel bed river

“…Similar results were observed by Piégay et al (1999) along a wandering French river (Drôme River), with an input of LW from the floodplains of about 82% and 62% in two different periods. Contrary to what has been reported by many authors (Bertoldi et al, 2009;Comiti et al, 2011;Mikus et al, 2013;Moretto et al, 2014), during the not extraordinary November 2014 flood, a considerable volume of LW was recruited from the short study reach considered here. This is in agreement with a recent publication in which the authors found that riparian vegetation can also be considerably eroded during low magnitude floods (RI≤2-3 years) (Surian et al, 2015).…”

Characteristics of fluvial islands along three gravel bed-rivers of North-Eastern Italy

“…In this sense the Fontaniva reach is strongly influenced by longitudinal embankments and bridges (Moretto et al, 2013). …”

Relationships between woody vegetation and geomorphological patterns in three gravel-bed rivers with different intensities of anthropogenic disturbance

“…Although the effect of hydrological regulation on fluvial geomorphological configuration and its interaction with riparian vegetation has already been demonstrated [37], to our knowledge quantitative data are still missing on these interactions in rivers subject to different levels of disturbance, but comparable in terms of climate, geology, and biogeography.…”

“…The construction of 8 dams (storage capacity of about 64,500,000 m 3 ) is considered as the second most important human alteration of river morphology, decreasing both flow and sediment discharges, disconnecting around 40% (Tab. 1) of the basin area from the lower river channel in terms of bedload transport [37]. Finally, along about 90% of the main course river training works (i.e.…”

“…2a) [27,28,35,36,38,61]. Thanks to the imposition of regulatory constraints on commercial gravel extraction in the late 1990s, there has been a partial width recovery [37], which is anyhow quite limited because sediment supply to the river is greatly reduced by the presence of dams and torrent control works in the basin, and by bank protection limiting sediment input from lateral mobility. Following Surian and Rinaldi [60] conceptual models, this river adjusted to the human disturbances of the second half the 20 th century mainly through channel narrowing, from braided to wandering morphology, combined with a significant incision (case H, Fig.…”