An autonomous and low-power instrument platform for monitoring water and solid discharges in mesoscale rivers

Abstract

Abstract. We present the development of the RIPLE platform designed for the monitoring at high temporal frequency (~ 10 min) of water discharge, solid fluxes (bedload and suspended load) and properties of fine particles (settling velocity) in mesoscale rivers. This platform responds to a request to continuously measure these variables in rivers using a single, centralized device, and in the most direct way possible. The platform integrates the following instruments: (i) for water discharge: water level and surface velocity radars, digital cameras, echo-sounder; (ii) for fine sediment load: turbidimeters, automatic samplers including the SCAF (sediment settling velocity characterization device), (iii) for bedload: a hydrophone, (iv) for water quality: a conductivity probe and water sampling. As far as water discharge monitoring is concerned, priority has been given to non-intrusive instruments to improve the robustness of the system. All the instruments are driven by a data logger (Campbell® CR6), which stores locally the data and then upload them to a remote server every hour during the day using a 3G modem. SMS (Short Message Service) alerts can be sent depending on scheduled conditions (e.g. low battery voltage, water level threshold, all samples of the automatic sampler collected). The platform has been designed to be as autonomous as possible: it is powered by a battery supplied by a solar panel. Limiting the power consumption of the platform was one of the main technical challenges, because of the quantity of instruments integrated. A simple 100 W solar panel is sufficient to power up the entire platform, even during winter or low insulation conditions. The RIPLE platform has been designed to facilitate its use and maintenance. A user-friendly interface has been developed enabling to visualize the data collected by the platform from an internet connection. It is also possible to remotely configure the platform within this interface, for example to modify water sampling thresholds or alert thresholds. Finally, the platform is relatively easy to move from one site to another site because its installation requires little civil engineering. To date, RIPLE has been tested on two rivers of the Alps in France: the Romanche river in Bourg d'Oisans (45.1158° N, 6.0134° E, 710 m elevation) from September, 2016 to July, 2018 and the Galabre river in La Robine sur Galabre (44.1586° N, 6.2360° E, 680 m elevation) since October, 2018, demonstrating the proper functioning of the platform.