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2016-01-28 - Colloque/Présentation - poster - Anglais - 1 page(s)

Kaufmann Olivier , Bastin Christophe , Barcella Claudio , Watlet Arnaud , Van Ruymbeke M., "Design and Calibration of a System for Monitoring Highly Variable Dripwater Flows in Caves" in 5th International Geologica Belgica Meeting, Mons, Belgique, 2016

  • Codes CREF : Géologie (DI1411)
  • Unités de recherche UMONS : Géologie fondamentale et appliquée (F401)

Abstract(s) :

(Anglais) Monitoring dripwater flows in caves is of great importance when studying infiltration processes in the vadose zone. Many systems exist, such as rain gauges of various types, that measure dripping water flows. However such systems, especially those with moving parts, tend to fail quickly due to calcite deposition. Here, we present an original system designed to monitor highly variable dripwater flows in caves ranging from less than one litre per hour to several tens of litres per hour. In this system, the dripping water collected in an inverted cone flows in a container feeding a small upper tank which in turn feeds a larger lower tank. The emptying of the tanks is done by auto siphoning. A capacitive sensor plunging in each tank returns a high frequency FM signal dependent on the water level in the tank. Signals from these sensors are integrated over time and monitored with a datalogger at rates ranging from 1 Hz to 0.2 Hz in order to be able to report rapid changes in flow rates. The design step of the tanks and sensors included the development of a specific code to simulate the functioning of the system and predict the responses of the sensors. A special attention was given to the characteristics of the admission and siphoning tubes as well as the shapes of the tanks and sensors. Several designs were tested before selecting the final one. In the selected design, the system is about 1.2 m high, the upper tank has a capacity of about 0.25 l and the lower one is about ten times larger. At very low flows, the limited capacity of the upper tank leads to maintain an acceptable resolution on the measurement while at very high flows, the upper tank is overloaded and an overflow channels excess water directly in the lower tank. Calibration and control of the system, is done with a peristaltic pump circulating water at several flow rates in a closed circuit. Water is pumped from a container to the top of the monitoring system, flows inside the monitoring system and the outflow returns in the container. In this way, it is possible to maintain a constant flow in the system for long periods as well as to explore a large range of flow rates.