**3. Methodology of Field and Laboratory Studies**

Field work was conducted following stormy weather and in the second half of September 2004. At of the end of 2004 and the start of 2005, parts of the coast section studied were subjected to beach nourishment with dredged material. Beach sampling was carried out for two days, during field classes given to students in the Construction Program of the former Technical University of Szczecin (currently the West Pomeranian Technological University in Szczecin, Poland). Gravels with a dominant grain size diameter of 2–5 cm were collected from the berm (or beach face) of dune and cliff sections of the Polish seacoast.

Owing to the low water temperature, the underwater part of the beach was not sampled. During storms and strong winds, the lower and middle parts of the beach were flooded; therefore it was assumed that gravel samples collected in the beach just after the storm cessation are representative for the assessment of morpholithodynamic processes at the land–sea interface. The weather during sampling was rainy. The sea state was 2–3 Beaufort scale, and the wind was westerly. Immediately before the sampling, the weather was windy (moderate breeze), with SW and W winds dominating (4–7 m/s), and 4–5 Beaufort scale. The atmospheric pressure was decreasing from 1020 to 998 hPa [67].

During the sampling, the beach width varied from 10 to 40 m. The beach width in the cliff sections varied 10–15 m, whereas in cliff sections with developed foredune, the width was 20–40 m.

The beach gravels were collected at a radius of about 50 m, along 250 m intervals of the coastline. Individual samples weighed from 2 to 5 kg and were collected in the area of 10 × 10 m squares. If the amount of collected rock material was above 2 kg, the sampling procedure was finished; if <2 kg, then the sampling area was expanded to 50 × 10 m rectangles. Gravel samples were collected simultaneously by two groups of eight individuals. One group started sampling in Pogorzelica (363.0 km), the other starting from the Dziwnów jetty (391.4 km). The sampling operation took two days, because—once the

windy conditions were over—the gravels were rapidly covered by sand blown in by the wind, and the beach became sandy. The gravels deposited during the storm lay beneath a thin aeolian layer [68].

Next, the gravel samples were examined for their petrographic composition. Additionally, the grain shape among individual petrographic groups was determined.

The basic petrographic groups included (i) high resistant igneous and metamorphic crystalline rocks with quartz; (ii) low resistant limestone; and (iii) low resistant sandstone, dolomite, and others (shales, flints, brick and concrete fragments). The samples consisted of 200–400 gravel grains. The grain axes were measured in each petrographic group to arrive at the maximum length, maximum width, and maximum height. Gravel morphometry was determined using the flatness index (*Ws*) of Wentworth and the gravel shape as described by Zingg [41]. The *Ws* was estimated using equation *Ws* = (*A* + *B*)/*C* [69]. Zingg's method describes the grain shape based on (i) the ratio between the intermediate (*B*) and longest (*A*) axis, and (ii) the ratio between the shortest (*C*) to intermediate (*B*) axis. The gravel grains were classified by their shape as discoid, ellipsoid, spheroid, and spindle-shaped (Figure 3).

**Figure 3.** The Zingg form index diagram [41]. Arrows indicate the tendency of shapes related to dominance of erosion and mechanical reworking of sedimentary material (after [44]).

The basic statistical parameters (arithmetic mean and standard deviation) of grain shape indices and petrographic group classification were calculated for the set of data consisting of 113 sampling stations and total number of 17,882 gravel pebbles. The mean number of gravel grains collected from single stations was 172. At nine stations gravels were not found, so only 104 stations were used in the further analysis of lithodynamics.

The petrographic composition of beach gravels may point to the source of the initial material and directions of transport in the in-shore zone. A comparison of the proportion of gravel in individual petrographic groups with the initial material allows a qualitative assessment of the intensity of the gravel-destructing processes in those groups. Also, the gravel shape may useful for interpreting the coastal dynamics. When assessing the intensity of shore erosion, lithodynamics of the coastal zone may be subject to rank-based evaluation [51,70]. Assuming the general knowledge of individual sections of the Polish coast (erosive or accumulative), and simple mechanical properties of selected group of rocks, such as hardness or presence of slaty cleavage (e.g., greater hardness of crystalline rocks, compared to sandstones, limestones, or shales), the zones of increased mechanical reworking of rocky material can be distinguished. Proportions between different types of rocks, compiled with the basic Zingg measurement statistics indicate primary depositional patterns (instantaneous deposition with no mechanical reworking traces, accumulation of initial sedimentary material) or redeposition (erosion and accumulation, reworking, or sorting traces). Presence of cusps and embayments located along the study area affects coastal dynamics, and may decrease movement of sedimentary debris (i.e., greater amount of discoidal and ellipsoidal gravels that indicate shorter mechanical reworking) [57,71].

Finally, the data obtained were subjected to lithostatistical analysis. Considering the large number of collected and measured gravel samples (*n* = 17,882), the basic statistics (means, standard deviations, and percentages) were calculated with 90% confidence intervals. Calculated parameters (amount of gravels in selected petrographic groups, shape parameters, and *Ws*) were compared with coastal dynamics data (1986–2004) and presence of groins, wavebreakers, and seawalls [56,57].

The mean values of each parameter were estimated and subsets between half the standard deviation (0.5 SD) above and below the mean were considered as unimportant for the lithodynamics interpretation. The subsets above half of the standard deviation (+0.5 SD) were treated as positive anomalies, whereas the subsets below the half the standard deviation (–0.5 SD) were negative anomalies. The positive anomalies in the group of discoidal and ellipsoidal gravels are indicators of accumulation (direct deposition without secondary reworking of sedimentary material). The positive anomalies in the group of spheroidal and spindle-shaped gravels may indicate the dominance of erosion, increased mechanical reworking, and longshore movement of sedimentary debris [70]. In this particular case study, the statistical application of 0.5 SD may be justified by robust sampling data and a flattening of distribution. Additionally, the shorter subsets expose properly obtained anomalies.

Similarly as above, the positive anomalies of the gravel flattening index (*Ws*) are indicators of accumulation, whereas negative anomalies are related to erosion and redeposition processes [44,70]. The *Ws* index positively correlates with contents of ellipsoidal and discoidal gravels.
