127 research outputs found
Studio di dettaglio sulle aree della fascia costiera adriatica (settore italiano), che presentano le condizioni migliori per avviare lo studio avanzato sulla fattibilità del “sand engineering”
No full textConvenzione di ricerca tra Eni s.p.a. e il Dipartimento di Fisica e Scienze della Terra dell'Università di Ferrara (responsabile scientifico prof. Paolo Ciavola) - L’erosione costiera è un fenomeno sempre più costante lungo gran parte dei litorali dell’Europa e del mondo; in certe nazioni addirittura i processi erosivi mettono a serio rischio l’esistenza stessa dei centri abitati, od anche di vaste aree che sarebbero inondate qualora non fossero state prese adatte contromisure. L’esempio tipico è quello dei Paesi Bassi, dove da decenni ingenti risorse vengono impiegate per la protezione costiera e la ricerca su come difendersi in maniera sempre più efficace. Enormi passi avanti sono stati compiuti rispetto ai primi interventi: nel 2011, infatti, è stato realizzato per la prima volta nel mondo un ripascimento artificiale che ha coinvolto un enorme quantitativo di sabbia, circa 22 Mm3, il cosiddetto Sand Engine. Il vantaggio di questo mega-ripascimento è che dovrebbe assicurare per un periodo di 20 anni una buona alimentazione delle spiagge del litorale su cui è stato effettuato, nella fattispecie la Delfland Coast nei Paesi Bassi, senza necessità di ulteriori integrazioni come invece accade per i normali ripascimenti stagionali. Dati i risultati preliminari positivi del Sand Engine olandese, il presente studio è finalizzato alla ricerca di possibili siti sulla costa del Nord Adriatico dove poter realizzare un mega-ripascimento con criteri simili
A wireless waterproof RFID reader for marine sediment localization and tracking
No full textIn this paper an innovative RFID reader to be employed in marine sediment localization and tracking is presented. This device has been realized within the "Smart Pebble" project, where an RFID based solution is employed to measure the displacement of a swarm of pebbles during predefined periods, in order to analyze the dynamics of a beach under the effect of stormy events, and then the impact of coastal erosion on the studied stretch of coast. The reader described in this paper has been developed to facilitate the localization of the so-called Smart Pebbles, i.e. real pebbles taken from the beach under study and provided with an embedded RFID transponder, then positioned on and under the seabed. The developed device is able to detect the presence of a Smart Pebble up to a 50cm distance, and its functioning has been tested at depths up to 5 meters for prolonged spans of time (up to 4 hours). Moreover, a wireless connection based on IEEE 802.15.4 has been set up between the reader and a laptop to allow the wireless transfer of the transponder ID from the reader to a laptop positioned on the beach
Short- and medium-term response to storms on three Mediterranean coarse-grained beaches
No full textThe storm response of three Italian coarse-grained beaches was investigated to better understand the morphodynamics of coarse-clastic beaches in a microtidal context. Two of the studied sites are located on the eastern side of the country (Portonovo and Sirolo) and the third one (Marina di Pisa) is on the western side. Portonovo and Sirolo are mixed sand and gravel beaches where the storms approach from two main directions, SE and NE. Marina di Pisa is a coarse-grained, gravel-dominated beach, exposed to storms driven by SW winds. Gravel nourishments were undertaken in recent years on the three sites. Beach topography was monitored measuring the same network of cross sections at a monthly (i.e. short-term) to seasonal frequency (i.e. medium-term). Geomorphic changes were examined before and after storm occurrences by means of profile analyses and shoreline position evaluations. The beach orientation and the influence of hard structures are the main factors controlling the transport and accumulation of significant amount of sediments and the consequent high variability of beach morphology over the medium-term. For Marina di Pisa, storms tend to accumulate material towards the upper part of the beach with no shoreline rotation and no chance to recover the initial configuration. Sirolo and Portonovo showed a similar behaviour that is more typical of pocket beaches. Both beaches show shoreline rotation after storms in a clockwise or counter-clockwise direction according to the incoming wave direction. The wider and longer beach at Sirolo allows the accumulation of a thin layer of sediment during storms, rather than at Portonovo where, given its longshore and landward boundaries, the beach material tends to accumulate in greater thickness. After storms, Sirolo and especially Portonovo can quickly recover the initial beach configuration, as soon as another storm of comparable energy approaches from the opposite direction of the previous one. Large morphological variations after the storm on mixed sand and gravel beaches do not necessarily mean a slower recovery of surface topography and shoreline position. Considering that all the three beaches were recently nourished with gravel, it emerged that the differences between the nourishment and the native material, in terms of size and composition, seem to have an important influence on the dynamics of the sediment stock. Considering that recent studies have remarked the high abrasion rate of gravel, further understanding of the evolution of nourishment material with time is needed. The peculiar behaviour of gravel material artificially added to an originally sandy beach suggests the need to modify the widely used classification of Jennings and Shulmeister (2002) adding a fourth additional beach typology, which could represent human-altered beaches
A Wireless Sensor Network Framework for Real-Time Monitoring of Height and Volume Variations on Sandy Beaches and Dunes
No full textIn this paper, the authors describe the realization and testing of a Wireless Sensor Network (WSN) framework aiming at measuring, remotely and in real time, the level variations of the sand layer of sandy beaches or dunes. The proposed framework is based on an innovative low cost sensing structure, able to measure the level variations with a 5-cm degree of precision and to locally transfer the acquired data through the ZigBee protocol. The described sensor is integrated in a wider ZigBee wireless sensor network architecture composed of an array of sensors that, arranged according to a grid layout, can acquire the same data at different points, allowing the definition of a dynamic map of the area under study. The WSN is connected to a local Global System for Mobile Communications (GSM) gateway that is in charge of data processing and transmission to a cloud infrastructure through a General Packet Radio Service (GPRS) connection. Data are then stored in a MySQL database and made available any time and anywhere through the Internet. The proposed architecture has been tested in a laboratory, to analyze data acquisition, processing timing and power consumption and then in situ to prove the effectiveness of the system. The described infrastructure is expected to be integrated in a wider IoT architecture including different typologies of sensors, in order to create a multi-purpose tool for the study of coastal erosive processes
Influence of particle shape on pebble transport in a mixed sand and gravel beach during low energy conditions: Implications for nourishment projects
No full textBeach nourishments using coarse-gravel sediments are becoming a frequent practice to buffer coastal erosion, but usually little attention is spent on fill material characteristics. A better understanding of the influence of sediment characteristics on transport is crucial to establish the best compatibility of fill material with native beach sediments. Pebble transport is here investigated by means of the RFID tracing technique. The main purpose of the experiment was to verify whether the prevalent shapes populating the beach (disks and spheres) show a different transport under low energy conditions. Tracers were injected in a small and straight portion of a mixed sand and gravel beach, deploying couples of marked particles of the same size (one sphere and one disk-shaped pebble on the main geomorphic elements of the beach face), in order to avoid size influence on transport. Tracer recovery was undertaken 6 and 24 h after the injection and wave characteristics were measured during the whole experiment duration by means of a S4 directional wave gauge. After 6 h the marked pebbles underwent significant displacement with a prevalent longshore component, which became evident after 24 h. The swash zone proved to be the most dynamic area of the beach. Spheres covered longer distances and resulted more dynamic than disks, thanks to their capability to roll-over in the swash zone. Lately, many experiments have been carried out with marked pebbles, but this is the first time that an experiment is conceived to prove how shape influences pebble transport. Disks are more subject to burial and due to their higher dynamicity spheres are preferred to disks for nourishment fill material. A fill material comprised of spheres is regularly responding to hydrodynamic forces and can positively speed up the beach recovery after storms especially in highly dynamic systems like pocket beaches, typically subjected to beach rotation processes. The results show an implication for coastal managers having to choose fill sources for replenishments
The impact of coarse sediment tracing experiments for an in-depth characterization (management; planning) of artificial pebble beaches
No full textArtificial coarse-clastic beaches are often used in a twofold way to support coastal management: a large replenishment can be either perceived as a form of protection from storm surge and erosion or as a mere reconstruction of a beach to promote summer resort activities and, in turn, revenues. As a matter of fact, the economy of most of the Italian littoral communities is tightly connected to tourism; on the other hand, most of the Italian coastal areas are also subjected to severe erosive processes and are in dire need of efficient defense schemes. Based on the higher level of stability during storms, coarse-clastic beaches have been progressively built in many sites to replace sandy beaches that were completely wiped out by erosion processes. Marina di Pisa, a small village 11 km west of the city of Pisa, is an example of this practice: during the last 10 years, five artificial coarse-clastic beaches have been realized (three in the 2006-2008 timespan; two in 2015). They were basically intended to protect the littoral promenade from dangerous storm surge events, but they ended up being frequently used by tourists in a recreational way. On the wake of this newfound utilization, the knowledge about coarse-clastic beaches, which once was poor compared to that of sandy beaches, is now richer; still, there are several aspects that are far from being completely understood.
The artificial beaches at Marina di Pisa have been the test site of several scientific studies aimed to increase the understanding of this peculiar setting, which is not yet included in any existing classification scheme. These analyses concerned grain-size and morphometry of the pebbles, beach profile evolution, and sediment tracing experiments. The latter have been particularly crucial to improve the sedimentologic characterization of the beaches, both in terms of transport processes and of textural parameters. The experiments were conceived to enable the unambiguous identification of individual pebbles, to avoid the statistical approach often used to perform such experiments in the past. The technique that provided the best cost/efficiency ratio was the radio frequency identification technology (RFID), which consists of an antenna that transmits low frequency radio signals and of small transponders (2 mm thick discs of about 30 mm diameter) inserted into the pebbles. Each transponder is identified by a code, which is coupled to each marked pebble. Three separated experiments were carried out to address different aspects: i) tracer transport in the short term (6 and 24 hours); ii) tracer transport in the medium term (two months); iii) mass loss of the tracers in the long term (13 months). The first experiment involved the injection of 78 tracers to address the transport rate in short timespans (6 and 24 hours) and in complete absence of wave motion (fair-weather conditions). The results showed that pebbles of 10 cm diameter experienced significant displacement even though wave activity was at a low, which is a finding that had never been pointed out before. The second experiment was carried out injecting about 100 tracers and performing a recovery campaign after two months. The positions of the detected pebbles allowed to point out peculiar but univocal trajectories determined by the topographic features of the sea floor. The third experiment was intended to assess the abrasion rate of the tracers, because after frequent observations the volume of the beach was clearly reducing even though sediment loss out of the beach system was never detected. In fact, a progressively increasing mass loss was measured on marked pebbles at different times during a 13 months timespan. The final measurement showed a mass loss of more than 60% on all the pebbles recovered after the last recovery campaign, raising major doubts on the long term durability of such defense schemes. These results confirm that coarse-clastic beaches are highly dynamic also when wave motion is barely detectable, which means that in the foreshore pebble grazing is always active, not only during storms as it was previously thought. Therefore, the high abrasion rate measured on individual pebbles at Marina di Pisa is an aspect that must be carefully taken into account while setting up future artificial coarse-clastic beach construction, because the efficiency and durability of the intervention may be reduced if mass loss due to wearing would not be fully factored in
On the displacement of marked pebbles on two coarse-grained beaches during short fair-weather periods (Marina di Pisa and Portonovo, Italy)
No full textThe transport of particles along a shore is a paramount process when it comes to the
evolution of a coastal environment. Factors affecting sediment displacement lead the
morphodynamics of a given beach towards a state of erosion, equilibrium or expansion. A
proper management of a littoral area cannot set aside an insight awareness of the influence
that the processes acting on the nearshore exert on the sediments the beaches are composed
of. For this reason particle transport is a topic that has been widely addressed in the scientific
literature especially for sandy beaches (White, 1998; Ciavola, 2004). Only recently sediment
movement on coarse-grained beaches has been matter of several research studies (Allan et al.,
2006; Curtiss et al., 2009; Bertoni et al., 2012): scientific productivity on this environment
increased mostly because of new technical solutions that solved many of the logistic
problems encountered previously (Buscombe and Masselink, 2006; Bertoni et al., 2010). For
instance, the chance to track individual pebbles by means of the RFID (Radio Frequency
Identification) technique provided a major boost towards the definition of coarse sediments
displacement on coarse-grained beaches (Allan et al., 2006; Bertoni et al., 2010). In addition,
the use of gravel and pebble beaches as a form of coastal protection has progressively
increased lately, because they are more resistant to wave action rather than sandy beaches.
Thus, improving the knowledge about this environment is of great significance also to
optimize future projects involving the construction of artificial coarse-grained beaches
Coarse-grained beach response after storms in three Italian sites
No full textThe storm response of three Italian mixed beaches is investigated. Two sites are located on the eastern side of the country (Portonovo and Sirolo) and one on the western side (Marina di Pisa). Portonovo and Sirolo are two mixed sand and gravel beaches (MSG) where the storms approach from two main directions (SE and NE). Marina di Pisa is a composite mixed beach subject to storms driven by SW. Gravel nourishments were undertaken in recent years on the three sites. Beach evolution was monitored measuring the same network of topographic profiles at a monthly to seasonal frequency. Beach orientation and the presence of protecting structures are the main reasons for the displacement and the accumulation of significant amount of sediments. In Marina di Pisa storm wave tend to pile material towards the upper part of the beach with no rotation of the shoreline. Sirolo and Portonovo act like pocket beaches with shoreline
rotation that occurs after each storm in a clockwise or counter-clockwise direction. The wider and longer beach in Sirolo allows sediment to accumulate moderately during storms rather in Portonovo, given its longshore boundaries, the material tend to pile up in greater thickness. Periods of fair weather tend to decrease beach slope in Marina di Pisa and to increase beach width in Sirolo. After a big storm, in Sirolo and even more in Portonovo, the original beach configuration can be reached only after another storm of similar energy approaches by the opposite direction of the previous one
The role of particle shape on pebble transport in a mixed sand and gravel beach (Portonovo, Italy)
No full textA better knowledge of the relationship between sediment characteristics and sediment transport is crucial to establish the suitability of fill material for gravel nourishments. In this paper pebble transport is investigated by means of RFID passive tracing technology. Tracers were injected in a small portion of a mixed sand and gravel beach separating sphere from disc shaped pebbles. Tracer recovery was undertaken 6 and 24 h after the injection and wave characteristics were measured during the whole experiment duration. After 6 h the marked pebbles already covered significant displacements with a prevalent longshore component which became evident after 24 h. According to statistical analyses (T-tests and box plots) no significant difference among the displacement of different shapes resulted. The swash zone proved to be the most dynamic area of the beach where all the pebble displacements took place. Because of their higher dynamic, spheres are preferred to discs for nourishment purposes
Fast retreat of a barrier system due to reduced sediment supply (Bellocchio, Northern Adriatic Sea, Italy)
No full textThe erosion issue is a constant threat along most of the littoral areas around the Mediterranean Sea. The Northern Adriatic Sea makes no exception, in particular the Emilia-Romagna region is subject to erosion processes that jeopardize human activities and natural ecosystems along large stretches of the coast. Th
e factors responsible for the erosion processes are multiple and often depend on the characteristics of the site: the Bellocchio area can be considered as a case study for the landward retreat of a barrier system, caused by the decrease of sediment supply from the River Reno. A series of aerial ortho-photographs was analyzed to define the evolution of the sector of coast comprised between the village of Porto Garibaldi to the north and the River Reno’s mouth to the south. The photographs, spanning from 1942 to 2010, showed a severe landward migration of the whole system, in particular the area north of the river’s mouth, where a large spit was progressively eroded and eventually disappeared. The recent evolution of the Bellocchio site is a further confirmation that a successful
management of the littoral areas does not involve only coastal processes, but also the evolution of the sediment source feeding the beaches
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