The size and great dynamism of coastal systems require faster and more automated mapping methods like the use of a remotely piloted aircraft system (RPAS) or unmanned aerial vehicle (UAV). This method allows for shorter intervals between surveys. The main problem for surveying using low-altitude digital photogrammetry in beach areas is their visual homogeneity. Obviously, the fewer the homologous points defined by the program, the lower the accuracy. Moreover, some factors influence the error performed in photogrammetric techniques, such as flight height, flight time, percentage of frame overlap (side and forward), and the number of ground control points (GCPs). A total of 72 different cases were conducted varying these factors, and the results were analyzed. Among the conclusions, it should be highlighted that the error for noon flights is almost double that for the early morning flights. Secondly, there is no appreciable difference regarding the side overlap. But, on the other side, RMSE increased to three times (from 0.05 to 0.15 m) when forward overlap decreased from 85% to 70%. Moreover, relative accuracy is 0.05% of the flying height which means a significant increase in error (66%) between flights performed at 60 and 100 m height). Furthermore, the median of the error for noon flights (0.12 m) is almost double that for the early morning flights (0.07 m) because of the higher percentage of grids with data for early flights. Therefore, beach levelings must never be performed at noon when carried out by RPAS. Eventually, a new parameter has been considered: the relationship between the number of GCPs and the surface to be monitored. A minimum value of 7 GCP/Ha should be taken into account when designing a beach leveling campaign using RPAS.

Sieving is one of the most used operational methods to determine sand size parameters which are essential to analyze coastal dynamics. However, the influence of hand versus mechanical shaking methods has not yet been studied. Herein, samples were taken from inside the hopper of a trailing suction dredger and sieved by hand with sieves of 10 and 20 cm diameters on board the dredger. Afterwards, these same samples were sieved with a mechanical shaker in the laboratory on land. The results showed differences for the main size parameters D₅₀, standard deviation, skewness, and kurtosis. Amongst the main results, it should be noted that the highest values for D₅₀ and kurtosis were given by the small sieves method. On the other hand, the lowest values were given by the mechanical shaker method in the laboratory. Furthermore, standard deviation and skewness did not seem to be affected by the sieving method which means that all the grainsize distribution was shifted but the shape remained unchanged. The few samples that do not follow these patterns have a higher percentage of shells. Finally and definitely, the small sieves should be rejected as a sieving method aboard.

A methodology for monitoring the behaviour and size of sand after a beach nourishment process is presented herein. Four sampling campaigns (before and just after the nourishment, after six months and one year later) were performed on four beaches of the Gulf of Cadiz (Spain). D₅₀ and sorting size parameters were analysed. Among the results, it should be noted that differences of up to 20% between native and nourished sand values disappear only one year after the nourishment.

New design parameters for biparabolic beach profiles (SW Cadiz, Spain)

The North Atlantic coast of Morocco is characterised by a flat rocky outcrop in the south (Asilah Beach) and a sandy beach free of rocky outcrops in the north (Charf el-Akab). These natural beaches were monitored for a period of two years (April 2005–January 2007) and two different profiles (one for each beach) were analysed based on differences in the substrate. Topographic data were analysed using statistics and empirical orthogonal functions (EOFs) to determine beach slope and volumetric changes over time. Several morphologic phenomena were identified (accretion/erosion and seasonal tilting of beach profiles around different hinge points), attesting to their importance in explaining variability in the data. Periods of accretion were similar in both profiles, but the volumetric rate of change was faster in the sand-rich (SR) profile than in the reef flat (RF) profile. Moreover, the erosion rate for the SR profile was greater than the RF profile (135.18 m³/year vs. 55.39 m³/year). Therefore, the RF acted as a geological control on the evolution of its profile because of wave energy attenuation. Thus, special attention should be given to the RF profile, which has larger slopes, less amounts of mobilised sand, and slower erosion/accretion rates than the SR profile.

The current use of photogrammetric systems with RPAS (remotely piloted aircraft systems) for the acquisition of topographic data in every type of coastal area has the benefit of a low risk for the personnel involved, good precision, increased productivity, and lower costs. However, their accuracy has not yet been researched in areas with steep terrain. In this paper, we study dune areas with slopes between 20 and 30%. The objective of this work is to examine the influence of the inclination of both the flight and the camera and to compare the results with those obtained using constant-height flights. With the data collected during three field campaigns, a total of 18 cases were studied. Among the results obtained, in the case of the horizontal flights, a vertical error of 0.048 m was detected for a 0° inclination of the camera versus an error of 0.086 m for a 10° inclination, thus an increase in the camera inclination decreased the accuracy by 44%. Moreover, the flight inclination did not lead to a significant reduction in the error. Therefore, as a main conclusion, the planning of horizontal flights as well as the non-tilt of the camera are recommended.