Exploring the Relationship between River Discharge and Coastal Erosion: An Integrated Approach Applied to the Pisa Coastal Plain (Italy)

Abstract

Coastal erosion coupled with human-induced pressure has severely affected the coastal areas of the Mediterranean region in the past and continues to do so with increasing intensity today. In this context, the Pisa coastal plain shows a long history of erosion, which started at the beginning of the nineteenth century. In this work, shoreline positions derived from historical maps as well as airborne and DGPS (Differential Global Positioning System) surveys were analyzed in a GIS (Geographic Information System) environment to identify the main changes that have occurred in the last 142 years. These analyses were compared with 100 years of discharge data measured at the S. Giovanni alla Vena gauge to identify a possible correlation between the two sets of information. Finally, Sentinel-2 and Landsat images were studied to identify the dispersion of sediments transported by the Arno River. In particular, we found a minimum of fluvial discharge in the years 1954, 1978, and 2012 corresponding to a peak of erosion, while the reduced erosion rate and the fluvial discharge increased in the years 1928–1944, 1954–1975, and after 2012. The qualitative anticorrelation between discharge and erosion is particularly true if we take into account flood events with a value of discharge greater than 700 m3/s, which are those able to transport suspended sand. The remote sensing analyses of Sentinel-2 images acquired during the floods of 6 February 2019 and 3 December 2019, under the most typical wind and sea state conditions for this area (wind coming from SW and storms coming from W/SW and SW) show that during these events a consistent amount of sediment was transported by the river. However, the majority of these sediments are not deposited along the coastline but are dispersed offshore. Grain-size analyses on the transported sediment show that plumes are formed by coarse-to-medium sand, suitable for coastal nourishment, but the reconstructed sediment dispersion lines show that some sectors of the coastline are constantly in the shade. These areas are the most affected by erosion.

Multi-Decadal Deltaic Land-Surface Changes: Gauging the Vulnerability of a Selection of Mediterranean and Black Sea River Deltas

“…The impact of shoreline engineering structures is clearly displayed by differential shoreline erosion and accretion. The high L→W levels of the Arno (89%) and the Ombrone (71%) also indicate significant rates of shoreline erosion on a coast beleaguered by problems of a fluctuating river sediment supply [30] and a fragmented longshore drift system characterized by several cells created by engineering structures to stave off erosion [31,32]. This is a pattern of disrupted sediment connectivity, involving both the river-to-coast continuum and increasingly engineered shorelines, that repeats itself throughout the Mediterranean [33].…”

Integrating Different Databases to Offer a Geological Perspective of Coastal Management: A Review Case from the Northern Tuscany Littoral Cell (Italy)

“…In order to reconstruct the coastline evolution, the available data were acquired from different geo-databases [42,70,71]. The historical evolution of the coastline position was based on the integration of the available geomorphological data related to the outcropping beach ridges [72][73][74][75] with archeological data [36,72,73].…”

“…The peak coastline retreat was reached in the area north of the Arno River mouth in the 1938-1954 period (about 20 m per year). Research by [71] presented an assessment of coastal area spatial variation in the same sector during the last 140 years. They reported that more than 2.5 km 2 of the area experienced constant erosion, whereas just 0.5 km 2 showed constant accretion.…”

Study on the Positioning Accuracy of GNSS/INS Systems Supported by DGPS and RTK Receivers for Hydrographic Surveys

“…Users can achieve accuracies in the order of 1-3 m, depending on the correction transmission method applied under the DGPS system [46,47]. The DPGS system enables position determination with accuracies considerably exceeding the autonomous GPS positioning, which makes it suitable for use, e.g., in hydrography for hydroacoustic system positioning [48][49][50], cartography [51], locating mobile devices [52,53], air navigation, including the use of UAVs [54,55], marine navigation, primarily in coastal shipping and during the Dynamic Positioning (DP) [56][57][58], bathymetric surveys of harbours and inland, as well as marine waters [59], geodetic surveys of the coastal zone [60,61], the autonomous vehicle positioning process [62][63][64], precision agriculture for reliable yield mapping or crop soil variability [65] or even for studying glacier changes [66] and displacements of, e.g., dams [67].…”