The morphodynamics of three artificial pebble beaches at Marina di Pisa (Italy): coarse sediment transport and beach profile evolution

This three-year long research involved an insight investigation of the morphodynamics of three artificial coarse-grained beaches at Marina di Pisa, Italy, to best define the processes, such as sediment transport, beach profile evolution, and volume displacement, acting on an environment that is somewhat neglected in the literature. Marina di Pisa is a small, seaside village, located just west of the city of Pisa along the southernmost sector of the Ligurian Sea coast, whose shoreline experienced severe erosion processes during the last 150 years. The previously existing sandy beach was thoroughly wiped out, which prompted the local authorities to set up a long series of protection structures, and eventually gravel and pebble replenishments. The beaches where the fieldworks took place are just the sites of three huge beach fills carried out in 2006. The ensuing artificial coarse-grained beaches (named Cella 6, Cella 7, and Barbarossa) are composed of 30-to-90 mm marble pebbles, and are characterized by a similar project configuration. The twin beaches Cella 6 and Cella 7 differ from Barbarossa in length (240 m as opposed to 110 m) and in the presence of a submerged breakwater 50 m off the coastline, whereas Barbarossa is devoid of any offshore structure. The fieldworks involved primarily the investigation of transport tendencies and pathways of the coarse sediment along these beaches by means of a rapidly developing tracing technology, the Radio Frequency Identification. The RFID technique enables to detect pebbles previously coupled to small, passive transponders. The limit of the technology was constituted by the inefficacy of the underwater detection of the tracers, but this shortcoming has been here overcome by the employment of low frequency radio signals, which allow a fine transmission of the signal even underwater. Along with the sediment transport patterns, the evolution of the beach profile was assessed in a two-year long span of time. The subaerial topographic surveys were performed by means of an accurate RTK-GPS instrument, while the sea floor morphology was investigated by the employment of an echo-sounder Single Beam device. The data collected during these surveys were further processed to obtain reckoning of the sediment volumes that play a major role in the evolution of the beaches relative to the changing sea weather conditions. The results of the research might be spent to expand the comprehension of coarse-grained beaches to begin with. In addition, providing an in-depth definition of the morphodynamic processes governing this kind of beach, they might be useful to improve and optimize coarse replenishments, which are progressively more common as a form of protection from coastal erosion, and to back up studies on ancient gravelly shorelines

Short- and medium-term response to storms on three Mediterranean coarse-grained beaches

The 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

Litho-sedimentological and morphodynamic characterization of the Pisa Province coastal area (northern Tuscany, Italy)

In this paper litho-sedimentological and morphodynamic maps of the coastal sector belonging to the Pisa Province are presented as an example of how increasing the accessibility to data on lithology, sedimentology, and morphodynamics may lead to a better approach to coastal management. The database used to build the maps includes an original rendering of remote sensing data (aerial imagery) and new field data (geologic survey), as well as data retrieved from the scientific literature (grain-size and past coastline positions). The maps show that the geometry of beach ridges is an indication of the evolution of the Arno River delta in the last 3000 years, highlighting the relationships between geological aspects and morphodynamic features. The maps represent the synthesis of different data available in the database, and they may be a useful support to coastal management as they are more easily understandable and straightforward than the database from which are created

A wireless sensor network framework for real-time monitoring of height and volume variations on sandy beaches and dunes

In 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

Impressive abrasion rates of marked pebbles on a coarse-clastic beach within a 13-month timespan

In this paper the abrasion rate on a coarse-clastic beach was evaluated by calculating the volume loss recorded on indigenous pebbles within a 13-month timespan. The experiment was carried out at Marina di Pisa (Italy) on an artificial beach that was built to counteract the erosion processes affecting this sector of the coast. A total of 240 marble pebbles (120 rounded and 120 angular) were marked using the RFID technology and injected on the beach. The volume loss measured after consecutive recovery campaigns was progressively increasing, reaching the maximum value after 13 months (61% overall). The average volume loss is consistent between rounded and angular pebbles at any time (59.3% and 64.2% after 13 months respectively), meaning that the roundness is not a primary control factor on abrasion rate. The pebbles that did not reach such abrasion rates after 8 and 10 months (volume loss less than 20%) were found at heights equal or greater than 2 m above mean sea level, on the crest of the storm berm that formed during the strongest storms. This implies that the highest wearing is achieved in the lower portion of the backshore, which is also the area that underwent major topographic modifications. Here, sea water action might also exert chemical influence on the pebbles, adding to the mechanical abrasion. The main result of this research, indicating an impressive volume loss on beach pebbles in a short timespan, could be of key importance for coastal managers. The optimization of coarse sediment beach nourishments is also relevant, taking into right consideration that the volume loss due to sediment abrasion might exceed 50% of the original fill volume just after 1 year in the most dynamic portion of the beach

Morpho-sedimentological and vegetational characterization of Grande beach at São Francisco do Sul Island (Santa Catarina, Brazil)

A multidisciplinary study based on several digital (geology, lithology, shoreline evolution, photo-interpretation of aerial and ortho-photographs) and field (topographic and vegetational surveys, grain-size analysis) datasets prompted new insights to a better definition of the processes in action at the Grande beach at Sao Francisco do Sul Island (Santa Catarina, Brazil). The resulting data enabled us to produce a multi-thematic map at 1:50,000 scale that might be useful in assisting decision-makers to manage the coastal system, taking into account involved factors at once and not separately. In addition, the map may be implemented and integrated with new information, since the database is provided in geographical information system. The results confirmed the importance of addressing coastal systems with a multi-faceted approach that can be applied everywhere, not only in settings similar to Sao Francisco do Sul Island

Sand supply from shoreface to foredunes: aeolian transport measurements and morphological evolution of a Tuscany beach stretch (Italy)

The coastal dunes are a highly dynamic sedimentary environment characterized by a continuous time-space readjustment in terms of morphology, shape and dimension. This is mainly due to the periodic fluctuation of the volume of sand available and by the force of the deflation processes, which are in turn driven by the interplay among pattern of vegetation cover, surface roughness and local-regional wind regime. The aim of our research is to quantify the deflation, transport and deposition of sands in a natural coastal field dune system located in the northern coast of Tuscany, Italy. The northern part of the investigated area is characterized by stable coastline condition while southwards strong erosive processes took place since 1800 year. Sedimentological data come from a series of sand collectors spaced along transects orthogonal to the coastline from the backshore to the semi stable dune field. The collectors were constructed of PVC pipe 100 x height 10 cm, with two openings 7 cm wide and 50 cm tall arranged on opposite sides of the tube. Opening willing to windward served for sand collection, and to leeward, covered with a metal wire 60μm opening. Collectors were buried along, until the base of the free window coincide with the surface of the ground about 1,5 m. The sand trapped within each collector was sampled every two hours for three consecutive times. In laboratory sand samples were weighed and subject to grain size analysis by means of mechanical sieves. The local winds parameters and their fluctuation with the time were acquired through a Meteorological mobile station. The station is equipped with three ammeters located to three different heights from ground surface: 40, 120 and 180 cm. A wireless sensor allows the constant output of data (each 5 sec) to a device. Temperature, and relative humidity value are furnished every 30 minutes. Analysis of data has evidenced the time-space fluctuation of sand volume in the two study area (stable area and under erosion). Basing on this methodological approach the time-space fluctuation of sand volume experienced by the two study areas (stable area and under erosion) has been estimated

Anthropogenic Impact on Beach Heterogeneity within a Littoral Cell (Northern Tuscany, Italy)

In this paper the evolution of the Northern Tuscany littoral cell is documented through a detailed analysis of the increasing anthropogenic pressure since the beginning of the 20th century. This sector of the Tuscany coast has been experiencing strong erosion effects that resulted in the loss of large volumes of sandy beaches. The anthropogenic impact on natural processes have been intensified by the construction of two ports in the early decades of the 20th century. Competent authorities reacted by building hard protection structures that tried to fix the position of the shoreline but offset the erosion drive downdrift. Therefore, in the last 20 years a regional Plan was undertaken to gradually replace the hard defense schemes with a softer approach, which involved a massive use of sediment redistribution activities. Many nourishments have been done ever since, using both sand and gravel. All these hard and soft protection operations have been archived in a geodatabase, and visualized in maps that clearly show the progressive change from hard to soft defense. This database may improve the approach to any future analysis of the littoral cell both in terms of research and management, while providing a practical example that may be easily replicated elsewhere

A wireless waterproof RFID reader for marine sediment localization and tracking

In 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