A low-cost technique to quantify river suspended sediment transport towards the assessment of coastal sediment budget

Direct measurements of river sediment transport are required for several different activities, which span from the mere scientific curiosity to the application of the collected data for management aspects. While the former drives the effort of the scientific community to expand the knowledge about river dynamics, the benefits resulting from a successful quantification of river sediment load would be mostly felt in terms of improving and optimizing the management of both river and coastal systems. Many techniques involving various disciplines and different levels of technological solutions have been developed ultimately, sometimes using cumbersome equipments that do not allow extended data collection or rather expensive devices anyone cannot afford to employ. A low-cost instrument able to collect and transmit in real time the measurements of river suspended sediment load is here presented. The proposed device is essentially a densimeter based on the Archimedes’ Principle (Figure 1). The mechanical structure is composed by two separate structures linked together: a device composed by four floats, whose immersion level varies according to the density of water, and a floating structure storing the microprocessor and transmission unit, together with the sensor in charge of measuring the immersion level of the other device. The immersion level is measured through an ultrasound sensor that is able to calculate its exact distance from the upper surface of the four floats device. The microprocessor unit is composed by an Arduino Mini board in charge of acquiring and processing the collected data, translating an immersion level information into a water density data, while the transmission unit is composed by an XBee Series 2 radio module, in charge of transmitting the density information to a data collection gateway provided with GSM connection positioned ashore. This gateway will transmit the locally collected data to a remote data collection centre that will store them in a database making them available through the Internet. The future applications of the technique underlined by the development of the above mentioned device involve the investigation of the bedload transport, which is crucial for the complete definition of river contribution for sediment budget evaluation purposes. Based on the source-to-sink concept, river sediment transport as a whole is among the primary factors controlling the natural feeding of beaches: the lack of reliable measurements hinders the chance to adequately assess the sediment budget of specific sectors of coast, which in turn prevents the coastal managers to take conscious, and possibly right, decisions when the future of a coastal system (intended as catchment – beach – offshore) is on the line.