Monitoring aeolian sand transport on coastal dunes by means of low-­cost solutions.

Sand dune development is predominantly carried out by wind, which exerts its effect on sand grains. This process occurs through complex rules involving friction factors, wind speed and direction, grain size, airflow, presence or absence of obstacles and different types of transport. The understanding of the interaction between these factors is crucial to increase the understanding of coastal dune dynamics characterization of coastal dune dynamics. The aim of this study is to measure aeolian wind transport and to evaluate the morphological changes that occur on the frontal dunes. The study boasts a multidisciplinary approach, low running costs and easy applicability on other sites. The tests were performed at the Migliarino - San Rossore - Massaciuccoli Regional Park (Tuscany, Italy) on a dune system character by strong morpho dynamics. The equipment consists of (Figure 2): four PVC sand traps with a 7 cm opening for the entrance of the sand; 3 wireless sensors built in 3 plastic planks each one containing 24 photoresistors (LDR), 5 cm spaced; a anemometric station composed of 6 sensors, arranged at different heights (0.40 m, 1.20 m and 2.00 m). Each instrument is planned to acquire data in continuum and to send them to a remote station that stores all the information (Figure 3). In the field, the traps were buried up to the limit of the opening and arranged perpendicular to the coastline. The SAND TRAPS were placed on the frontal dune and on the backdune area. Each trap bears internal digital balance that measures the amount of sand collected every 20 minutes: these measurements are automatically sent to the data collection. Moreover, this system has a rotation mechanism that autonomously repositions the instrument in accordance with the changing wind direction, making the system reliable and efficient.The WIRELESS SENSORS were buried vertically on the surface of the dune. They calculate dune height variation through the detection of presence or absence of sunlight. This information is transformed into an electrical signal, whose value points out whether each LDR is sunk in sand dune or not. These values help to understand if the dune is moving and how it actually moves. The proposed sensing structure (composed by 24 sensors positioned at a 5cm distance) can cover 120 cm of length with a resolution of 5cm. Preliminary results acquired by the anemometer station in August 2016: wind direction and speed have been measured at three different heights (0.4, 1.2 and 2 m) (Table 1). Predominant wind from SW have been recorded at 0.4 and 1.2 m heights, while southern wind prevailed at 2 m height. The average wind speed was 10.1 m/s, 13.5 m/s and 14.6 m/s respectively: as expected, these values confirm that higher wind speed are reached at higher elevations. Wireless sensors and sediment trap proved their efficiency: data acquisition and real-time transmission to the remote station worked properly, but the working period was too short to gain significant results (Table 2 and 3).