A multi-temporal and multi-scale analysis based on historical data collection and review, maps and aerial photograph interpretation, field observations, topographic surveys, and GIS investigations was performed to (i) examine the morphological evolution of lower Orba River since the mid-nineteenth century, (ii) identify its controlling factors, and (iii) correctly interpret ongoing hydrogeomorphic conditions under a river management perspective. The riverbed experienced overall slight and non-homogeneous morphological adjustments, along with some horizontal displacements, up to the early twentieth century (Phase 0). Subsequently, two phases of channel degradation were identified. The first, from the 1920s to the 1950s (Phase 1), is characterized by slight narrowing (12.3%), the beginning of incision, and rare and little lateral migration. The second, between the 1950s and the years around 2010 (Phase 2), displays significant channel incision (mostly from the 1950s to the 1970s, from 0–1 m to 4–5 m), weak narrowing (21.0%), and only minor horizontal displacements. Over the last decade (Phase 3), widespread slight channel widening (3.4%, up to 25.7% at the reach scale) associated with the absence of a generalized bed-level variation trend was observed. The study reach has exhibited a single-thread or transitional channel since the mid-nineteenth century. Channel incision was mainly caused by extensive in-channel sediment extractions primarily carried out between the 1950s and the early 1980s at the reach and catchment scales. The long-term presence of widespread channelization works was recognized as the main reason why overall little riverbed planform adjustments occurred during the whole period investigated. The most recent dynamics were triggered by floods and were interpreted as the river response to human-induced alterations. The riverbed changes that occurred during the twentieth century match the channel adjustments commonly experienced by Italian single-thread and transitional channels as a response to various types of human disturbances. However, the detected morpho-evolutionary phases of the Orba River are only partially in agreement with those reported in the literature for other Italian rivers affected by similar anthropogenic pressures, as some differences exist in timing and magnitude of prevalent channel adjustments. An overall slight potential for channel recovery, priorities for rehabilitation, and the main objectives for the next-decades management were identified. This research provides insights into the medium- and short-term morphological evolution of Italian rivers, and its outcomes represent an essential piece to drive river management towards sustainable and effective river restoration and risk mitigation measures framed within a larger, multidisciplinary, and objective-based context. A wide spectrum of both consolidated and newly developed GIS-based planform metrics was considered to assess the channel morphological evolution in detail, providing an operative reference framework for future investigations.

Morphological adjustments of the lower Orba River (NW Italy) since the mid-nineteenth century

Mandarino A.
2022

Abstract

A multi-temporal and multi-scale analysis based on historical data collection and review, maps and aerial photograph interpretation, field observations, topographic surveys, and GIS investigations was performed to (i) examine the morphological evolution of lower Orba River since the mid-nineteenth century, (ii) identify its controlling factors, and (iii) correctly interpret ongoing hydrogeomorphic conditions under a river management perspective. The riverbed experienced overall slight and non-homogeneous morphological adjustments, along with some horizontal displacements, up to the early twentieth century (Phase 0). Subsequently, two phases of channel degradation were identified. The first, from the 1920s to the 1950s (Phase 1), is characterized by slight narrowing (12.3%), the beginning of incision, and rare and little lateral migration. The second, between the 1950s and the years around 2010 (Phase 2), displays significant channel incision (mostly from the 1950s to the 1970s, from 0–1 m to 4–5 m), weak narrowing (21.0%), and only minor horizontal displacements. Over the last decade (Phase 3), widespread slight channel widening (3.4%, up to 25.7% at the reach scale) associated with the absence of a generalized bed-level variation trend was observed. The study reach has exhibited a single-thread or transitional channel since the mid-nineteenth century. Channel incision was mainly caused by extensive in-channel sediment extractions primarily carried out between the 1950s and the early 1980s at the reach and catchment scales. The long-term presence of widespread channelization works was recognized as the main reason why overall little riverbed planform adjustments occurred during the whole period investigated. The most recent dynamics were triggered by floods and were interpreted as the river response to human-induced alterations. The riverbed changes that occurred during the twentieth century match the channel adjustments commonly experienced by Italian single-thread and transitional channels as a response to various types of human disturbances. However, the detected morpho-evolutionary phases of the Orba River are only partially in agreement with those reported in the literature for other Italian rivers affected by similar anthropogenic pressures, as some differences exist in timing and magnitude of prevalent channel adjustments. An overall slight potential for channel recovery, priorities for rehabilitation, and the main objectives for the next-decades management were identified. This research provides insights into the medium- and short-term morphological evolution of Italian rivers, and its outcomes represent an essential piece to drive river management towards sustainable and effective river restoration and risk mitigation measures framed within a larger, multidisciplinary, and objective-based context. A wide spectrum of both consolidated and newly developed GIS-based planform metrics was considered to assess the channel morphological evolution in detail, providing an operative reference framework for future investigations.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11567/1090682
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