Development of a vertical TDR probe to evaluate the vertical moisture profile in peat columns to assess biological clogging

Time domain reflectometry (TDR) is used to monitor the moisture content in soils including peat. The objective of this study was to develop a TDR-based method to measure the vertical moisture profile in a peat biofilter operating in the field, where access to the filter is limited to the top surface. The moisture profile with depth can then be used to infer or assess the operating status of a filter in terms of clogging. The successful application of water content measurement using horizontal TDR probes has been demonstrated by many researchers. In this study, a single TDR probe was sequentially advanced into a peat column to estimate the vertical moisture profile and the results were compared to horizontal TDR and gravimetric measurements. The experiment was carried out in six peat columns during a drainage process and two columns during a clogging process. Water contents by the vertical and horizontal probes agreed very well, although the data was slightly more scattered in the columns subject to clogging due to signal attenuation. Total signal attenuation was observed with longer probes in clogged peat soils. However, there was a consistent discrepancy between the TDR measured water contents and those determined gravimetrically, which is believed to be caused by a systematic error, possibly error with the calibration curve.