The Role of Detailed Geomorphic Variability in the Vulnerability Assessment of Potential Oil Spill Events on Mixed Sand and Gravel Beaches: The Cases of Two Adriatic Sites

The role of short to medium term geomorphic variation is analysed in two Italian mixed sand and gravel beaches to better understand how it could affect the vulnerability assessment to oil spill events. The study sites, Portonovo and Sirolo, are in one of the most congested areas for oil transportation in the Adriatic Sea (Ancona port). A "snapshot" situation populated with field data collected in April 2015 is compared to a "changing" situation built with previous field datasets (topographic surveys and surface sediment samplings) available for the two beaches. According to the ESI guidelines established by the National Oceanic and Atmospheric Administration (NOAA) in 2002, both Portonovo and Sirolo can be ranked as ESI 5 or 6A in most of the cases. Sediment size resulted the most decisive factor for the ESI assessment. As consequence of the bimodal direction of storms, the high geomorphic variability on the two sites is mainly related to storm berms which lead to rapid burial processes on both beaches. In oil spill circumstances, burial is considered the most alarming factor, especially on microtidal mixed beaches that develop storm berms so high and close to the shoreline. A quantification of the maximum potential depth reachable by the oil in the beach body is therefore needed for the most dynamic beaches: this could be achieved with repeated field measurements to be performed in the period between two consecutive ESI updates (5-7 years) and the addition of an appendix in the ESI maps dealing with the geomorphic characteristics of the beach. The significance of a changing ESI rank is that the authorities in charge of responding to the oil spill could be improperly prepared for the conditions that exist at a spill site if the geomorphology has changed from when it was first given an ESI rank

Sediment transport and morphodynamics of mixed beaches: case studies of two Mediterranean sites

Sediment transport and morphodynamics of two Mediterranean mixed beaches have been investigated. Portonovo was the study site chosen for the Adriatic coast while Marina di Pisa was the one chosen for the west side of Italy; both sites are characterised by a microtidal regime. Little is known about mixed beaches in microtidal regime since the majority of these environments is located on the ocean shores at high latitudes where the tidal regime is meso- or macrotidal. The work have mainly focused on pebble transport under low and moderate wave conditions in order to establish how size and shape of particles can affect their transport. The investigation was possible by means of radio tracer technique (RFID Radio Frequency IDentification). The remarkable asset of the method is to univocally gather displacement information for each single tracer. The technique works both on the submerged and the emerged beach and it also allowed to monitor pebble transport in the long term. Three tracer experiments were carried out with RFID technique: one at Marina di Pisa and two experiments at Portonovo. Tracer experiments had to be supported by a strong substrate of morphodynamics data which were suited on the basis of constant field data gathering: at Portonovo, beach sampling was undertaken for one year and topographic surveys were repeated for two years consecutively. The work deals also with nourishment practices since the two sites are replenished beaches. Under low energy conditions gravel and pebbles need just a small quantity of energy to be destabilized: in both experiments (Marina di Pisa and the first Portonovo experiment) swash action provided that energy, considering that the run-up levels exceeded the maximum tracer elevation for almost the entire duration of the experiments. Once that threshold is reached, marked pebbles can be displaced away from the injection point even though wave motion and swash processes are at minimum. Discs can cover greater distances than spheres but are less dynamic. Once lifted and shifted by swash flows, the discs can travel long paths, reaching a stable location characterized by feeble forces under low wave energy. On the other hand the threshold to initiate movement for spheres is lower so it is more difficult for them to find more stable position on beach profile. "Big"-sized pebbles (-5.5 to -6.5 phi) are less dynamic compared to the finer classes ("Medium", -5 to -5.5 phi; "Small", -4.5 to -5 phi). Nevertheless the “Big”-sized spheres resulted slight more dynamic than discs of the same size. Very low and steady energy conditions facilitate pebble cross-shore and offshore movement rather than longshore. A slight increase in wave height produces a predominant longshore transport characterized by non-negligible displacements. Portonovo beach seemed to be a close system regarding at least pebble transport: the central sector of the beach is a transfer zone for pebble motion while the most part of tracers was always found at beach edges. Weak storms combined to swash grazing are able to move pebbles and cobbles alongshore with great displacements (displacements 2 months after the injection: mean 190 m; max 445 m; min 15 m). Beach rotation is a common phenomenon in Portonovo; the system seems to act like a pocket beach: erosion and accretion areas change in accordance to the most frequent direction of each storm. The central area of the beach represents the pivotal point for beach rotation. Despite the high grain size heterogeneity, at Portonovo the sediment pattern is the result of the last storm direction: evident downdrift coarsening of sediments in response to storms normally occurs. Periods of fair weather (with at least very weak storms) develop a striped pattern of surface sediments. Stripes of different grain size run parallel to the shoreline: the swash zone and the lower part of the backshore increase their sediment size becoming gravelly (granules or fine pebbles) and better sorted, while scattered and non continuous stripes of sand cover the landward and the upper part of the backshore. The fill material for nourishment purposes should fit as best as possible the native sediment. At Marina di Pisa the material used for beach refill was sufficiently good: covering the natural sandy backshore with pebbles and cobbles did not prevent users from going to the beach. Deeper studies on coarse sediment abrasion rate are needed for better assessment on replenishment material and to better estimate contingent loss of volume in the refill material. At Portonovo beach, the material provided by local authorities for nourishment projects is quite compatible with the native one. In order to have an even more compatible material the use of spherical pebbles is suggested, to take advantage of their higher dynamicity relative to the discs. A size comprised between -4.5 and -5.5 phi (24 to 48 mm) should be preferred. Further investigations focusing on particle shape are needed to identify the possible primary factors that control pebble movement. Actual measurements of swash velocities for different shapes should be obtained in order to improve threshold velocity formulae, which currently do not involve any shape parameter for particles. It is believed that shape can be a discriminating factor for coarse and very coarse pebble transport (from 16 to 64 mm according to Udden-Wentworth grain size scale) at least under low energy conditions

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

Using High-Spatial Resolution UAV-Derived Data to Evaluate Vegetation and Geomorphological Changes on a Dune Field Involved in a Restoration Endeavour

Nowadays, 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

Beach morphodynamics and types of foredune erosion generated by storms along the Emilia-Romagna coastline, Italy

The objectives of this study are to examine the response of a dune and beach system on the Adriatic coastline in northern Italy to the arrival of storms, compare it with seasonal (months) and medium-term (3-year) morphodynamic change, and evaluate results predicted by the numerical model XBeach. The studied coastline stretches 4 km from the Bevano River mouth to the north of the site to the township of Lido di Classe to the south, where the beach is protected by coastal structures. Fieldwork consisted of topographic profile surveys using RTK-DGPS technology (7 times over an approx. 3-year period). 103 samples of surface sediment were collected along 20 of the cross-shore profiles at 6 distinct cross-shore positions, selected on the basis of morphological beach characteristics. Data analyses of dune and beach slopes enabled the study area to be divided into 6 separate morphological zones using the spatial (longshore and cross-shore) variation of morphologies located on the backshore and intertidal beach observed in a preliminary survey of the area. Other criteria were a spatial consistency in beach slopes and/or presence/absence of intertidal morphologies identified in the aerial photographs and Lidar data. The swash zone slope did not show any significant variability for the entire area. A weak seasonal trend in the variability of the mean foredune slope was observed, with steeper slopes typically during winter and flatter slopes during summer. Analysis of grain size revealed that the beach sediment is well-sorted fine sand tending to medium, with a decreasing trend in size from the Bevano River mouth southwards towards Lido di Classe. According to the Masselink and Short (1993) classification, the natural part of the study site has an Intermediate Barred Beach (IBB) and following the Short (1999) classification, results in a modally LBT (longshore bar-trough) or LTT (low tide terrace) with a small section being TBR (transverse bar and rip). Storms are considered the main factor controlling changes in the beach and dune slope. The most significant storm was recorded in March 2010 with a peak significant wave height of 3.91 m. Contrary to the seasonal dune trend, several foredune slopes were observed to flatten following this event, which can be attributed to the action of dune slumping from the already weakened dune state. Modelling of foredune erosion, using a process-based model (XBeach), reproduced the erosion of the upper beach and dune toe reasonably well, but is currently limited by the acceptable slope value for dune stability, which does not account for biotic factors (e.g. plant roots). The comparison between the storm impact categories of Sallenger (2000) and the DSF (Dune Stability Factor) of Armaroli et al. (2012) shows a very good correspondence between the effects of the winter 2008–2009 storms and the vulnerability of the dune system predicted using both classifications

Local-scale post-event assessments with GPS and UAV-based quick-response surveys:A pilot case from the Emilia-Romagna (Italy) coast

Coastal communities and assets are exposed to flooding and erosion hazards due to extreme storm events, which may increase in intensity due to climatological factors in the incoming future. Coastal managers are tasked with developing risk-management plans mitigating risk during all phases of the disaster cycle. This necessitates rapid, time-efficient post-event beach surveys that collect physical data in the immediate aftermath of an event. Additionally, the inclusion of local stakeholders in the assessment process via personal interviews captures the social dimension of the impact of the event. In this study, a local protocol for post-event assessment, the quick-response protocol, was tested on a pilot site on the Emilia-Romagna (Italy) coast in the aftermath of an extreme meteorological event that occurred in February 2015. Physical data were collected using both real-time kinematic Geographical Positions Systems and unmanned aerial vehicle platforms. Local stakeholders were interviewed by collecting qualitative information on their experiences before, during, and after the event. Data comparisons between local and regional surveys of this event highlighted higher data resolution and accuracy at the local level, enabling improved risk assessment for future events of this magnitude. The local survey methodology, although improvable from different technical aspects, can be readily integrated into regional surveys for improved data resolution and accuracy of storm impact assessments on the regional scale to better inform coastal risk managers during mitigation planning