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Data Quality Assurance in Pressure Transducer-Based Automatic Water Level Monitoring

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  21st Century Watershed Technology: Improving Water Quality and Environment Conference Proceedings, 21-24 February 2010, Universidad EARTH, Costa Rica  701P0210cd.(doi:10.13031/2013.29414)
Authors:   D M Endale, D S Fisher, M B Jenkins, H H Schomberg
Keywords:   Pressure transducer, Water level, Flume, Flow rate, Water quality, Water quantity

Submersible pressure transducers integrated with data loggers have become relatively common measuring devices in flow or well water elevation measurements. However, drift, linearity, hysteresis and other problems can lead to erroneous data. Researchers at the USDA-ARS in Watkinsville, GA, carried out over a two-year period continuous monitoring of flow from a spring using a flume fitted with a pressure transducer and data logger. Over the same period, periodic manual checking of flow rate was performed. Initially, over a 162-day period in 2003 with 77 comparisons, the automated system under measured the flow rate by approximately 17% (mean, 0.383 versus 0.459 L s-1; significant based on a Wilcoxon Rank Sum Test). Over a 349-day period in 2004 in 66 days of comparison, flow rate was 0.294 L s-1 for the manual and 0.299 L s-1 for the automated system (a 1.7% difference; non-significant). Over 235 days during the latter part of the monitoring period, the automated system over measured the flow rate by approximately 29% (mean 0.599 versus 0.463 L s-1; significant). In a similar set up at a pond outflow, an offset of 32 mm in flow depth caused a negative outflow error of 27.4% (13,141 m3) over a 30-day period. Flow rate is an important hydrologic variable in water quantity and quality investigations. Proper data quality assurance is needed in flow rate estimation utilizing pressure transducers to avoid the propagation of errors from flow estimation to that of pollutant load. The same principle should apply in other similar sensors.

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