HR: 0800h
AN: PP31A-1496    [Abstracts]
TI: High resolution measurement of water drip rates in caves using an accoustic drip counter
AU: * Collister, C
EM: chris@driptych.com
AF: PiTech Research, Red Cottage, Stowell, Sherbourne, DT9 4PD United Kingdom
AU: Mattey, D
EM: mattey@gl.rhul.ac.uk
AF: Geology Department, Royal Holloway College, Egham Hill, Egham, Surrey, TW20 0EX United Kingdom
AB: Stable isotope records in speleothem provide one of the most promising means of reconstructing precipitation and temperature variations back into the past. The interpretation of speleothem oxygen isotope records in terms of a climate signal is not straightforward and much progress has been made through cave monitoring programs, where knowledge of the response of cave seepage rates to rain input on the surface provides vital information on aquifer processes. Continuous monitoring of drip rates at sites of active speleothem growth provides imortant constraints on processes that cause chemical and isotopic change in precipitation during its passage through the aquifer and into the cave environment. A widely used method of continuously monitoring drip rates employs tipping bucket devices which provide time integrated output dependent on the volume of the bucket and drip rate. Mechanical counting devices are sometimes unreliable in cave environments owing to condensation and carbonate precipitation interfering with the mechanism and unattended long term monitoring may be problematic. Accoustic drip counting is an attractive alternative method and we have designed an simple integrated acoustic drip counter/logger which counts the number of drips falling on the lid of the device over a user-defined time interval. This device provides a high resolution record of changing drip rates that is insensitive to spurious noise, deposition of calcite films, and can collect data for periods of 1-2 years without user intervention. The drip counter and logger is entirely solid state and fully self-contained in a rugged enclosure approximately 60mm x 60mm x 40mm. The lid of the box acts as a microphone which is tuned to record falling drops and exclude spurious signals. Low power electronics are used throughout, giving a battery life of approximately two years. The sensor will record drips falling from heights as low as 25 cm and drips at the rate of 5 per second can be resolved. Very high drip rates of up to 1 per second can be logged in 5 minute intervals continuously for around 6 months; at lower drip rates the logger will record changes in drip rate over 30 minute intervals for periods of years. Work in progress is looking at the controls of stalagtite tip geometry on drop size in order to calibrate the logger in absolute flow units. We will present examples of data collected both in the laboratory and at cave sites in Gibraltar and Christmas Island where the responses of drip rate to rain events are being monitored.
UR: http://www.driptych.com
DE: 1694 Instruments and techniques
DE: 1800 HYDROLOGY
DE: 4958 Speleothems
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005