*2.1. Physiographic and Geomorphological Features*

The coastline of the Molise region (Figure 1) is approximately 36 km long and part of the Central Italian Adriatic coast. Its northern and southern boundaries are respectively the Formale del Molino channel and the Saccione Stream (Figure 1). A major part of the Molise coastline (22 km) consists in a low sedimentary coast with sandy beaches, while its central sector (ca. 14 km long) consists in a high rocky coast. The latter was formed by Plio-Pleistocene sedimentary successions composed of clayey-sandy marine and sandyconglomeratic fluvial sediments (Montesecco Clay, Serracapriola Sand, and Campomarino Conglomerate formations) [23]. The sea cliffs are cut into the Plio-Pleistocene bedrock and are mostly inactive and set back from the shoreline, with the only exception of the short

but artificially protected cliff of the Termoli promontory [21]. Consequently, the beaches are practically continuous along the entire Molise coast, leaving aside the interruptions owing to the major river mouths (Trigno and Biferno rivers and Sinarca and Saccione streams, Figure 1) and the three harbours present along the coast (Figure 1). The beaches are largely made up of fine to medium-grained sands and characterized by very variable widths ranging between a few meters and 93 m [21]. The dominant longshore transport occurs from NW to SE [10,21].

**Figure 1.** The Molise coast. Location and panoramic views of the two study areas, A and B.

The Termoli promontory divides the Molise coast into two nearly independent sectors (physiographic sub-units) [21]. These sectors, hereinafter named the northern and southern Molise coasts, are oriented in the WNW and NW-SE directions, respectively.

The Molise coast has an important ecological value thanks to the presence of 18 habitats of interest for the European Community [24,25]. In particular, there are three Sites of Community Importance (Figure 1), which include the three major river mouths (Trigno, Biferno, and Saccione) from north to south: IT7228221 (Foce Trigno-Marina di Petacciato), where test area A is located, IT7222216 (Foce Biferno-Litorale di Campomarino), which includes test area B, and IT7222217 (Foce Saccione-Bonifica Ramitelli). Habitats of community interest with a high naturalistic value cover an area of more than 340 hectares [25], highlighting the fact that the Molise coastline is one of the most important natural coastal stretches along the Italian Adriatic coast.

Concerning the reconstruction of the evolution of the Molise shoreline, in agreement with previous studies (e.g., see [21] and references therein), the subdivision in nine coastal segments (S1–S9, Figure 1) has been maintained to allow for an easy comparison of the shoreline change data calculated in the present study and those calculated previously.

Literature data (e.g., [21] and references therein) show that erosion strongly controlled the long-term evolution of the Molise coast. The coastal segments that include the Trigno and Biferno river mouths (S1 and S7) suffered important shoreline retreat (Figure 2), totalling average annual rates of −2.7 m/y and −2.9 m/y, respectively, during the period of 1954–2014 [21]. On the other hand, segments S2, S4, S5, S8, and S9 remained substantially stable (0.1 m/y–0.3 m/y), while S3 and S6 even experienced some slight advance (0.8 m/y and 1.0 m/y, respectively). Shoreline erosion was driven in particular by the decrease of fluvial sediment input to the coast, mostly resulting from in-channel mining and hydraulic interventions at the basin and from the fluvial reach scale from the 1950s onwards (e.g., [10,21] and references therein). To face the ongoing coastal erosion, numerous defence structures were built from the 1980s onwards, mostly under emergency conditions, allowing for the partial balancing out of previous erosion trends (for example, see S5 in [21]). In fact, hard defence structures (adherent breakwaters, emerged and submerged detached breakwaters, revetments, groins, and jetties) cover about 62% of the Molise coast [21]. Despite a relatively high degree of coastal protection as early as 1998, erosion continued to significantly affect the Molise coast [21]. Especially during very recent years (the period of 2011–2014), shoreline erosion not only involved segments S1 and S7 but also extended to segments S2, S3, and S9 (−4.9 m/y, −3.3 m/y, and −3.6 m/y, respectively), suggesting an ongoing process of progressive shoreline destabilization [21].

**Figure 2.** Shoreline progradation and retreat rates from 1954 to 2014 [21], location of areas with high to very high levels of erosion susceptibility [22], and location of mid-term (2004–2016) major shoreline erosion/accretion areas E1–E4 and A1–A5 [10].

Recent data provided by Buccino et al. 2020 [10] on the evolution of the Molise shoreline from 2004 to 2016 (Figure 2) highlight the presence of two major erosion areas located south of the Trigno and Biferno river mouths (E1 and E3), and of two others (E2 and E4) falling within coastal segments S4 and S8, respectively. Furthermore, the study shows the presence of several major accretion areas (A1–A5), which are characterized by a positive sediment balance.

Finally, the data reported by Aucelli et al. (2018) [22] show that most of the Molise shoreline is characterized by a high level of erosion susceptibility, while nearly the entire segment S1 and smaller portions of S4, S7, S8, and S9 are characterized by a very high susceptibility level (Figure 2).
