Medium and short term riparian vegetation, island and channel evolution in response to human pressure in a regulated gravel bed river (Piave River, Italy)

Abstract

During the last decades, several Italian gravel-bed rivers suffered from different types and levels of human\ud pressures that changed their morphological and vegetation patterns. This study aims to analyze the medium-\ud and short-term evolution of vegetation cover, fluvial islands and main channel characteristics along a gravel-\ud bed reach of the Piave River (North-eastern Italy), with special emphasis on the changes in the vegetation\ud cover type and structure. The Piave River experienced different types of human disturbance such as gravel min-\ud ing, hydropower schemes, and land use changes. A sequence of aerial photographs (1960, 1970, 1982, 1991,\ud 1999, 2006, 2010 and 2012) have been analyzed to detect the medium-term (about 50 yr) evolution of riparian\ud vegetation along a reach about 30 km-long in the middle course of the Piave River. In addition, LiDAR data (2003)\ud and seven repeated topographic surveys (done between 2007 and 2011) have been used to quantify changes in\ud three cross sections on a sub-reach about 2 km-long, in order to analyze the channel evolution over a short period\ud (1–8 yr). The medium-term analysis revealed that changes in the river evolutionary trend depended on the\ud variations in human activities both in the main channel and at basin scale. In fact, during the last five decades\ud there has been a consistent and continuous increase of riparian vegetation within the river corridor, from around\ud 50% up to 68%, which corresponds to a continuous decrease from around 46% to 29% in the area of exposed gravel\ud and low flow channels. Considering the different vegetation cover types, there was a predominant increase of sta-\ud ble and tall vegetation from around 34% up to a maximum of around 67% (1999), then a slight decrease to around\ud 62% (2010 and 2012). After a slight recovery phase subsequent to the cessation of gravel mining in the late 1990s\ud and associated to flood events in the early 2000s, the Piave River appears to have been in an equilibrium phase in\ud terms of bed elevation, planform morphology and areas of vegetation, which is becoming taller and more mature,\ud as a result of the combination of flow regulation, reduced bedload input from upstream and lack of relevant flood\ud events. These results suggest that in highly regulated — in terms of flow and sediment fluxes — rivers the cessation\ud of gravel mining alone is not sufficient to revert a degradation trend and thus restore prior morphological patterns

Channel forms and vegetation adjustment to damming in a Mediterranean gravel‐bed river (Serpis River, Spain)

“…However, during the adjusted regime state, not even the three events of winter 2016-2017 caused significant alterations of the river forms. Similar observations have been made by Picco, Comiti, Mao, Tonona, and Lenzi (2017)…”

“…However, during the adjusted regime state, not even the three events of winter 2016–2017 caused significant alterations of the river forms. Similar observations have been made by Picco, Comiti, Mao, Tonona, and Lenzi () in the Piave River, but the Serpis case reports an even lower effectiveness of large magnitude floods. In the Mediterranean basins, dams have a dual use (irrigation/urban supply and flood control), and the management of floods is conditioned by urban and agricultural pressures to storage water.…”

Ongoing and Emerging Questions in Water Erosion Studies

“…For instance, the Ijuez River in the Spanish Pyrenees has been affected by a 3‐m incision since the 1960s, as a consequence of land abandonment and general reforestation (Gómez‐Villar et al, ; Sanjuán et al, ) (Figure ). This is also the case for many mountain areas worldwide (García‐Ruiz & Lana‐Renault, ), in particular in the Mediterranean and Alpine basins (Liébault & Piégay, ; Piègay et al, ; Keesstra et al, ; Sanchis‐Ibor & Segura‐Beltrán, ; Lallias‐Tacon et al, ; Picco et al, ), and also in North America (Church & Slaymaker, ; Trimble, ).…”

“…For instance, the Ijuez River in the Spanish Pyrenees has been affected by a 3-m incision since the 1960s, as a consequence of land abandonment and general reforestation (Gómez-Villar et al, 2014;Sanjuán et al, (Figure 9). This is also the case for many mountain areas worldwide , in particular in the Mediterranean and Alpine basins (Liébault & Piégay, 2002;Piègay et al, 2004;Keesstra et al, 2009;Sanchis-Ibor & Segura-Beltrán, 2014;Lallias-Tacon et al, 2016;Picco et al, 2016), and also in North America (Church & Slaymaker, 1989;Trimble, 2010). In semi-arid and sub-humid landscapes the main limiting resources for plant cover establishment and spatial organization are water and nutrients, these latter making more efficient use of water (Lasanta et al, 2000).…”

Remote sensing of river corridors: A review of current trends and future directions

“…ALS shows the greatest utility in river corridor vegetation monitoring. At reach scales, ALS has been used for riparian zone classification (Antonarakis, Richards, & Brasington, ; Gilvear, Tyler, & Davids, ; Michez et al, ), assessment of wood and debris retention (Abalharth, Hassan, Klinkenberg, Leung, & McCleary, ; Bertoldi, Gurnell, & Welber, ), upscaling from TLS models (Manners et al, ), creating rainfall interception models (Berezowski, Chormanski, Kleniewska, & Szporak‐Wasilewska, ), and for linking vegetation to morphological and anthropogenic contexts and needs (Bertoldi, Gurnell, & Drake, ; Cartisano et al, ; Picco, Comiti, Mao, Tonon, & Lenzi, ). At landform scales, ALS has been used to identify sources and volumes of woody debris (Kasprak, Magilligan, Nislow, & Snyder, ), the health of riparian ecosystems (Michez et al, ), the influence of vegetation on groundwater connectivity (Emanuel, Hazen, McGlynn, & Jencso, ), bank stability (McMahon et al, ), and water temperature through shading (Greenberg, Hestir, Riano, Scheer, & Ustin, ; Loicq, Moatar, Jullian, Dugdale, & Hannah, ; Wawrzyniak, Allemand, Bailly, Lejot, & Piegay, ).…”