1,720,967 research outputs found
Uncertainty of drone-derived dems and significance of detected morphodynamics in artificially scraped dunes
Full text linkThis work capitalises on the morphodynamic study of a scraped artificial dune built on the sandy beach of Porto Garibaldi (Comacchio, Italy) as a barrier to protect the touristic facilities from sea storms during the winter season and contributes to understanding of the role of elevation data uncertainty and uniform thresholds for change detection (TCDs) on the interpretation of volume change estimations. This application relies on products derived from unmanned aerial vehicle (UAV) surveys and on the evaluation of the uncertainty associated with volume change estimations to interpret the case study morphodynamics under non-extreme sea and wind conditions. The analysis was performed by comparing UAV-derived digital elevation models (DEMs)-root mean squared error (RMSE) vs. global navigation satellite system (GNSS) < 0.05 m-and orthophotos, considering the significance of the identified changes by applying a set of TCDs. In this case, a threshold of similar to 0.15 m was able to detect most of the morphological variations. The set of TCD <= 0.15 m was considered to discuss the significance of minor changes and the uncertainty of volume change calculations. During the analysed period (21 December 2016-20 January 2017), water levels and waves affected the front of the artificial dune by eroding the berm area; winds remodelled the entire dune, moving the loose sand around the dune and further inland; sediment volumes mobilised by sea and wind forcing were comparable. This work suggests that UAV-derived coastal morphological variations should be interpreted by integrating: (i) a set of uniform thresholds to detect significant changes; (ii) the uncertainty generated by the propagation of the original uncertainty of the elevation products; (iii) the characteristics of the morphodynamic drivers evaluated by adopting uncertainty-aware approaches. Thus, the contribution of subtle morphological changes-magnitudes comparable with the instrumental accuracy and/or the assessed propagated uncertainty-can be properly accounted for
Sedimentation at River Mouths bounded by Coastal Structures: A Case Study along the Emilia-Romagna Coastline, Italy
Full text linkBeach retreat in the Emilia-Romagna coast, facing the north Adriatic Sea, is well-known since decades and several factors are behind this phenomenon: a scarcity of natural sediment supply by rivers, natural and anthropogenic subsidence, and a strong urbanization of the coastal zone. Several bedload measurement campaigns in one representative river of the Ravenna province (Savio River) have been carried out since 2017. At the same time, seasonal surveys of bathymetry were undertaken at the river outlet to correlate changes in sedimentation with river input. The river mouth is constrained by artificial embankments that possibly funnel out sediment offshore during river floods. However, monitoring of bedload transport correlated with bathymetric changes between July 2017 and November 2018 still found a positive budget of almost 5000 cubic meters. Local authorities in Ravenna are planning to dredge 20000 cubic metres from the river mouth to supply small nourishments outside the studied coastal cell. According to the measurements of bathy-metric changes, the Savio mouth will need almost six years to recover, assuming the occurrence of a particularly efficient rate of sediment transport, like the one observed in the monitored period. Notably, the analysed period included a very large river flood that could overshadow the modal sediment transport operated by the river. Furthermore, with deepening of the mouth, the two villages adjacent to the outlet are likely to become more exposed to sea flooding, due to the propagation of surges inside the river mouth. The paper concludes that dredging activities should be reconsidered in view of the precarious equilibrium of the system
Transport of marked pebbles in short periods of time on a coarse clastic beach (Marina di Pisa, Italy)
No full textTransport of coarse sediments on coarse clastic beaches still presents aspects that are not fully understood. For
instance, there is a generally perceived notion that during fair-weather periods coarse grains hardly move, if not
at all. The aim of this experiment is to prove that sediments such as pebbles are subject to significant shift in very
short lapses of time and under low energy waves. An artificial coarse clastic beach at Marina di Pisa (Tuscany,
Italy) was chosen as study site: Barbarossa beach is 110 m long and is bounded by two groynes. The mean grain
size is about 40-to-50 mm. About 80 pebbles were marked by means of the RFID technology, which enables to
univocally identify the tracers. The marked pebbles were released along cross-shore transects (one pebble each on
the fair-weather berm, on the beachface and on the step crest) on the morning of September 15th, and two recovery
campaigns were carried out after 6 and 24 hours from the injection. No particular wave activity was recorded
during the time frame of the experiment. After the first recovery campaign, which was performed 6 hours later
than the injection, about 94% of the pebbles were detected. After the second recovery campaign, 24 hours later,
the recovery rate decreased to 89%. Considering that the technique provides for detection of tracers within 50
cm, the resulting loss of pebbles after so brief spans of time is remarkable. The lack of detection of few tracers
implies that the transport rate that they experienced is not negligible. The highest rate of losses was recorded on
the beachface, the zone that is subjected the most to waves even under calm conditions. Pebble movement is also
confirmed by the fact that tracers detected after the first recovery campaign were not detected once again after the
second recovery campaign, and vice versa. The results of the experiment are useful to better define the transport of
coarse sediments, verifying that pebbles have to be expected be moving even in short periods of time
Bedload transport and dune bedforms characteristics in sand-bed rivers supplying a retreating beach of the northern Adriatic Sea (Italy)
No full textStudy Region: The coast of the Emilia-Romagna Region in northern Italy consists of about 210 km of sandy beaches that have been attracting tourists for decades. Since the 1980s, erosion processes resulted in a remarkable beach retreat, notwithstanding the construction of several protections works. Study Focus: In 2005–2006 and 2017–2020, 30 floods of two small rivers feeding the beaches of Ravenna, Fiumi Uniti and Savio, were monitored and bedload was measured with a Helly-Smith sampler. Riverbed bathymetric surveys were carried out after some selected floods to investigate the occurrence and geometry of alluvial bedforms. The dune migration method was also used to calculate bedload. Results provided by this method are very encouraging. New Hydrological insights for the Region: To the authors knowledge, this field investigation on the bedload transport of small coastal rivers is the first one of this kind in the Adriatic and provides the regional land managers with a useful tool to predict the bedload yield for future scientifically based interventions, and hopefully successful, beach protection works. The bedload data indicate a higher variability of bedload for discharges lower than bankfull flow, whereas a stronger control of discharge is evident for larger floods. Though the bedload of the study rivers proved to be higher than in the largest river of the Region, it resulted rather low and witnesses sediment supply-limited conditions
Using high‐spatial resolution uav‐derived data to evaluate vegetation and geomorphological changes on a dune field involved in a restoration endeavour
No full textNowadays, the employment of high‐resolution Digital Surface Models (DSMs) and RGB orthophotos has become fundamental in coastal system studies. This work aims to explore the potentiality of low‐cost Unmanned Aerial Vehicle (UAV) surveys to monitor the geomorphic and vegetation state of coastal sand dunes by means of high‐resolution (2–4 cm) RGB orthophotos and DSMs. The area of study (Punta Marina, Ravenna, Italy), in the North Adriatic Sea, was considered very suitable for these purposes because it involves a residual coastal dune system, damaged by decades of erosion, fragmentation and human intervention. Recently, part of the dune system has been involved in a restoration project aimed at limiting its deterioration. RGB orthophotos have been used to calculate the spectral information of vegetation and bare sand and therefore, to monitor changes in their relative cover area extension over time, through the using of semi‐automatic classification algorithms in a GIS environment. Elevation data from high‐resolution DSMs were used to identify the principal morphological features: (i) Dune Foot Line (DFL); (ii) Dune Crest Line (DCL); Dune seaward Crest Line (DsCL); Stable Vegetation line (SVL). The USGS tool DSAS was used to monitor dune dynamics, considering every source of error: a stable pattern was observed for the two crest lines (DCL and DsCL), and an advancing one for the others two features (DFL and SVL). Geomorphological data, as well as RGB data, confirmed the effectiveness of planting operations, since a constant and progressive increase of the vegetated cover area and consolidation of the dune system was observed, in a period with no energetic storms. The proposed methodology is rapid, low‐cost and easily replicable by coastal managers to quantify the effectiveness of restoration projects
Recovery of a coastal dune system at Punta Marina (Italy) following dune preservation schemes and reintroduction of vegetation
No full textBedload transport processes in a coastal sand-bed river: the study case of Fiumi Uniti river in the northern Adriatic
No full textOver the last decades, most of the Emilia-Romagna (Italy) beaches have been affected by marked erosion that is still progressing, which is primarily due to the reduction of sediment supply by the local rivers. In addition to larger fluvial systems, the role of small rivers has been recognized as important in contributing to both beach stability and changes. Bedload measurements were carried out by previous authors in 2005–2006 but, in order to widen the data set of river sediment supply for the whole region, a new bedload measurement campaign was performed in 2017 on the Fiumi Uniti River, a typical example of a small river system whose sediment supply variations substantially influence the stability of the beaches adjoining its mouth. Marked changes were observed in the bedload transport rates and bed material grain size between the two sampling campaigns of 2005/2006 and 2017. The threshold conditions for bed particle entrainment are analysed by means of the Shields classical criterion and other approaches. The results indicate that all these criteria are unable to predict the actual value, except for Carling and Bagnold criteria. This result has large implications in the assessment of bedload yield in sand-bed rivers
Storm recovery on two Italian coarse-grained beaches: a comparison between a mixed sand and gravel and a pebble beach
Full text linkHigh energy events emphasize beach erosion processes, sometimes leading to huge volume deficits not balanced by recovery under fair-weather conditions. In this scenario, artificial replenishments are frequently used as a form of coastal protection with large volumes of sediments re-injected in the system without strongly altering the environment as it happens with hard structures. Since climate change is expected to accentuate in the near future erosion effects, the need to artificially feed beaches is likely to increase. Gravel and pebbles are more and more often used as beach fill, on some occasions replacing sandy sediments. That was the case for two beaches located at either sides of the Italian Peninsula (Portonovo, Adriatic Sea; Marina di Pisa, Ligurian Sea), which constitute the study area of the present research. Portonovo is a 500 m-long mixed sand and gravel beach with a significant pebble-sized content (about 40%), unloaded on the beach during multiple replenishments. Marina di Pisa is an artificial, 180 m-long beach, mainly composed of 40-to-90 mm pebbles; it was built in 2008 as a part of a larger protection scheme. Groins or headlands that prevent any sediment exchange with adjacent areas bound both beaches. Periodic topographic surveys were carried out to evaluate the response of these human-altered beaches to high-energy events. The topographic surveys, undertaken with a DGPS-RTK instrument along cross-shore transects (from the landward end of the backshore to about 1.5 m depth seaward), were done following intense storm events occurred during the time period of the research. Transects were done out every 10 m along the entire length of the beaches. Prior to the first topographic survey, a sediment tracing experiment was set up as a form of control of the results provided by the geomorphologic analysis. Pebbles directly sampled from the beaches were marked by means of the RFID technology and injected back all along the beachface. As expected, considerable beach profile changes after the storms were identified, in particular at Portonovo (mixed beach), where huge sediment volumes were displaced longshore according to the incident wave direction as opposed to Marina di Pisa (gravel dominated), where the main beach changes developed along the cross-shore direction. In terms of resilience, results showed a better response of the Portonovo beach rather than the Marina di Pisa beach. The different response might be ascribed to the grain-size that constitutes the beaches: no physical process can rework the pebbles at Marina di Pisa once they are moved during the storms towards the back-end of the backshore or seaward of the step, thus preventing any beach recovery process to take place. Since the awareness on storm impacts is more critical than in the past, the understanding of beach recovery to extreme events needs new insights to combine the preservation of natural beach evolution as well as maintenance for end-users. That is particularly pressing on coarse-grained beaches, where the need to predict storm impact and recovery is much more vital considering that finding suitable sediment to refill the beach is never an easy task
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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