Application of TDR to water level measurement

A specialised time domain reflectometry (TDR) probe for measuring water lev el in tanks collecting surface runoff was developed, calibrated and field-t ested. The water level probe - in the form of a slightly modified soil mois ture probe - was developed as part of a TDR measuring system designed for c ontinuous monitoring of soil water content and surface runoff in plot studi es of water erosion and sediment transport. A computer algorithm for the an alysis of TDR traces from the new probe was developed and incorporated into existing software for automated acquisition and analysis of TDR data. Labo ratory calibration showed that water level could be measured with sufficien t accuracy (standard deviation <2 mm) for a range of applications in hydrol ogy. Soil erosion is typically a short duration process closely linked to s oil moisture content and rainfall intensity. A major benefit of integrating time critical measurements of surface runoff and soil moisture into a sing le system is the synchronisation of measurements. Measurements were made on a regular schedule except during rainfall events when the measuring rate d epended on rainfall intensity. In a parallel calibration study it was shown that the performance of the TD R probe was comparable to a commercial ultrasonic liquid level sensor used for measuring runoff at an erosion site not instrumented for automated TDR measurements. (C) 2000 Elsevier Science B.V. All rights reserved.