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Channel changes during and after extreme floods in two catchments of the Northern Apennines (Italy)
Full text linkThe Nure and Trebbia catchments were affected by an extreme flood event on 13-14th September 2015. This study investigates the morphological responses to the flood of the Nure and Trebbia rivers and 18 tributaries with the aims to: i) quantify channel changes in width and pattern; (ii) identify the morphological and hydrological factors which might have driven channel response; (iii) quantify channel changes which have occurred after the flood event. Channel changes were characterized by field surveys and geomorphological analysis of multi-temporal orthophotos acquired before (2011), immediately after the flood (2015) and in 2020. In the tributaries, reach-scale channel widths after the flood reached up to 15 times their pre-flood values, whereas in the main channels the post/pre-flood width ratio attained a maximum value of 4. Augmented channel width in the main rivers was mostly associated with banks and islands erosion, whereas in the tributaries it was also due to deposition of coarse sediments onto the former floodplains. Islands were swept away in the main channels while both island erosion and formation occurred in the tributaries. In terms of channel pattern, preflood single-thread reaches displayed mainly multi-thread morphologies after the flood, mostly in response to a sudden input of coarse sediment supply. In the 5 yr following the flood, channels slightly narrowed but still remained wider than in 2011. The narrower reaches before the flood resulted to be the most sensitive to changes even some years after the flood. Statistical analyses between the channel width changes and a series of variables showed significant positive correlations with confinement index, channel slope, and the local storm rainfall depth. This study confirms how channel widening during large floods - usually neglected in flood hazard mapping and river basin management - is a very important process which must be considered in flood hazard assessment in mountain rivers
Geomorphological map of the Biferno river valley floor system (Molise, Southern Italy)
No full textA 1:20,000-scale geomorphologic map of the valley floor system of the Biferno River (Molise
Region, Italy) is presented in this paper. Map analysis and aerial photography interpretation, in
addition to field surveys, have allowed digital mapping of fluvial landforms and associated coastal, slope and anthropogenic forms which have characterised the valley floor in different periods. Comparative multi-temporal analysis performed in a GIS for the time-period 1869–
2010 allowed the reconstruction of spatial-temporal relationships between most of the mapped
landforms and acquisition of quantitative data on channel adjustments. The geomorphologic
map provides an overall large-scale view of major channel adjustments over the past 150
years as well as the current morphological setting and dynamics of the Biferno valley floor. It
provides a basic map for land planning policy with the observed distribution of active
geomorphic processes to be used for landslide and erosion susceptibility assessment and the
data obtained on channel adjustments essential in investigating land cover change over the
same period. As the Biferno valley floor system is characteristic of major river systems in
Central-Southern Italy, the reconstructed framework of valley floor transformations turns out
to be useful when assessing a representative channel evolution model and potential scenarios
concerning near future dynamics of similar river systems
Channel adjustments in a Mediterranean river over the last 150 years in the context of anthropic and natural controls
No full textvolutionary trajectories and related control factors of the Fortore River (southern Italy) are analyzed over a 150-
year period as to assess channel modifications. A multitemporal GIS analysis of topographic maps and aerial photographs
together with topographic and geomorphological field surveys were performed. Attention was focused
on the impact caused by human disturbance, above all the presence of the Occhito damat only 40 kmupstreamof
the Fortore mouth (central Adriatic coast).
Results show that channel adjustments occurred in three distinct phases and were primarily driven by human
disturbance that diversely affected reaches located upstream and downstream of the dam. Fromthe last decades
of the nineteenth century to the 1950s (phase 1), channel widening prevailed along upstream reaches whilst
narrowing along downstream reaches. Major channel adjustments occurred from the 1950s until the end of
the 1990s (phase 2), especially channel narrowing of up to 81% in upstream reaches and 98% in downstream
reaches. Narrowingwas accompanied by channel-bed lowering of 1 to 5mand by pattern changes in prevalence
from multithread to largely prevailing single-thread channel configurations. In-channel mining, channel works,
and hydraulic interventions are considered key driving factors of observed channel adjustments. The closure of
the Occhito dam in 1966 had significant and permanent effects on downstream reaches through overall discharge
regulation and permanent sediment trapping as also proved by the progressive retreat of the Fortore
river mouth area. From 2000 to 2015 (phase 3), a substantial trend inversion was observed with overall channel
widening and partial aggradation of upstream reaches and total stabilization of downstream reaches. As
highlighted by an integrated multitemporal analysis of recent channel changes and flood events, the latter
have played an important role in channel recovery of upstream reaches.
Comparison between the Fortore River and other rivers in southern Italy has allowed us to ascertain that the reconstructed
evolutionary trajectories are quite similar and that control factors are essentially the same. In particular,
it confirms the role of major hydraulic structures as to the amount of channel adjustments of downstream reaches and the ensuing scarce to nil potential to channel recovery of regulated reaches
Morphological changes in Alpine rivers following the end of the Little Ice Age
No full textThis work investigates the channel changes of Alpine rivers from the end of the Little Ice Age (1850s) to the 1950s, with the aim to determine the possible role of climatic variations occurred in this period before the onset of anthropic pressures (i.e., dams, check-dams, bank protections, and gravel mining). The research was conducted on 17 river catchments of South Tyrol (northern Italy), glaciated and unglaciated. A multitemporal GIS analysis approach was adopted to assess the morphological changes (in terms of channel width and pattern) from three different sources: (i) Austrian cadastral map (1858), (ii) maps from the Italian Institute of Military Geography (1917–1925), and (iii) two aerial photo sets taken in 1945 and 1954. The analysed river network (a total of 480 km) was subdivided into 162 morphologically homogeneous reaches (76 confined, 81 partly confined, and 5 unconfined), with lengths ranging from 630 to 5500 m, slope from 0.3 to 24%, and drained area from 20 to ~ 4000 km2. The statistical relationships among morphological changes and reach- and basin-scale factors were analysed by univariate and multivariate methods, and the relationships between width changes and 36 controlling factors were explored using Principal Component Analysis. The variability in width and morphological pattern changes were very pronounced between and within single rivers, highlighting the value of such a large data set. Overall, the analysed rivers varied their morphological pattern, mostly exhibiting a shift from multithread/transitional to single-thread patterns, but unchanged planform types were also common. Variations in channel width varied substantially among the analysed rivers, which featured narrowing (slightly prevailing) and widening (the least common) as well as many cases of very limited changes. Channel width variations appear statistically, although weakly, related to some morphometric variables; and significant differences emerge comparing glaciated vs. unglaciated basins. Climate-related variations (glacier dynamics and channel disturbance frequency) are argued to be the dominant factors that affected channel variations
Palaeo-landscape reconstruction and assessment of long-term erosion rates through DEM analysis: preliminary results from the Molise Apennine (Central-Southern Italy)
No full textAreas simultaneously susceptible and (dis-)connected to debris flows in the Dolomites (Italy): regional-scale application of a novel data-driven approach
Full text linkIn mountain regions, the impact of areas on the sediment conveyance can not only be described by their susceptibility to debris flow release, but also by their structural connectivity to the rivers. This generates the need to combine susceptibility and connectivity for accurate analyses of sediment transport. Our study exploits an approach developed by [Steger, er al. 2022; https://doi.org/10.1002/esp.5421] and upscales it to the South Tyrolean Dolomites region. The approach comprised the modeling of debris flow release susceptibility using an interpretable machine learning algorithm, the training of a logistic regression model, and the combination of the resultant classified maps to create a joint susceptibility-connectivity map. The results show the quantitative thresholds for the susceptibility probability and the Index of Connectivity (IC) that allow to discriminate between susceptible and not susceptible, as well as connected and disconnected areas, which are represented via a variety of maps
Suspended transport of gravel in rivers: Empirical evidence from the 2022 flood in the Misa River (Eastern Apennines, Italy)
Full text linkIn September 2022, an exceptional flood in the Misa River basin (Eastern Apennines, Italy) resulted in the unusual deposition of gravelly lobes on terraces up to 6 m higher than the riverbed. These deposits suggest that coarse bed sediments were transported in suspension rather than as bedload, as typically occurs under competent flow conditions. To verify this hypothesis, we combined field evidence-obtained from geomorphological and sedimentological surveys-with theoretical insights based on sediment transport theory. Our findings indicate that medium-sized gravels, which are part of the riverbed material, were transported in suspension within the water column. This phenomenon required specific conditions to generate the necessary shear stress and energy, including (i) a high-magnitude flood enriched with fine sediments, which increased the fluid density and viscosity, and (ii) an entrenched channel with stable banks that limited channel widening during the flood event. When these processes coincided with alluvial plain inundation by overbank flows, gravel transported in suspension was able to reach and settle on elevated surfaces, such as terraces far above the active channel. These observations highlight the potential for gravel-bed rivers to support the transport of coarse sediment in suspension under extreme flood conditions and specific geomorphological constraints on the active river channels. By demonstrating the role of sediment concentration, channel morphology and flood dynamics, our research provides new insights into sediment transport mechanisms and contributes to a broader understanding of the morphodynamic processes governing gravel-bed rivers under such exceptional conditions, with broad implications for refining flood hazard models and improving sediment transport predictions in fluvial systems
Hydromorphology meets mammal ecology: morphological quality index, recent channel adjustments and otter resilience
No full textThe need for a multidisciplinary approach for characterizing water bodies in terms of morphological, chemical and ecological quality has
hastened the growth of hydromorphology as a cross-disciplinary topic at the interface of hydrology, geomorphology and ecology. Many
authors have analysed how hydroecology may affect freshwater biodiversity, although little is known about how this biodiversity might
be affected by river morphological quality. We examined how well the presence of the semi-aquatic Eurasian otter can be predicted by
the rivers’ morphological quality and its adjustments over the last decades. We tested the morphological quality index (MQI) methodology
in 38 reaches of five rivers in southern Italy, 23 of which were positive to otter presence. In each reach, we examined 28 indicators contributing
to the MQI and its 11 sub-indices. The results showed a significant relationship between the probability of the presence of otters, MQI,
and some sub-indices. The best performing sub-indices were related to channel adjustments and the continuity of river processes. A more
detailed analysis of channel adjustments showed a detrimental effect of channel incision (>3m) and a positive effect of narrowing, particularly
where it occurred simultaneously with the development of forest in the new floodplain. The continuity of river processes has driven the
migration of river banks and the development of ponds and secondary channels, likely increasing the availability of dens and resting sites and
the hunting capabilities of otters. Our results stressed the importance of fluvial dynamics and sustainable adaptive river management for the
habitat quality of semi-aquatic species
Reservoir rehabilitation: The new methodological approach of Economic Environmental Defence
No full textThis paper proposes a new methodological approach to silted reservoir management and defence, which combines the reservoir rehabilitation process and the utilization of the recovered water volumes and sediments. This approach, strategic from both the economical and environmental points of view, is here defined as Economic Environmental Defence (EED) of a reservoir. The EED approach is applied to the case study of Guardialfiera reservoir, where the available experimental data allowed the estimation of siltation up to date, the analysis of the distribution of sediment particle size along the reservoir bottom and the possibility to propose a feasible utilization of water and sediments resulting from the reservoir rehabilitation
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