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ARS Home » Pacific West Area » Boise, Idaho » Northwest Watershed Research Center » Research » Publications at this Location » Publication #80039
Title: CALIBRATION OF TIME DOMAIN REFLECTOMETRY FOR MEASUREMENT OF LIQUID WATER INFROZEN SOILS

Author
item Seyfried, Mark
item MURDOCK, MARK - U OF IDAHO

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Some liquid water remains in the soil even when soil temperatures drop well below freezing. Measurement and prediction of this liquid water is important because it affects estimates of flooding hazard from frozen soil, which is a major problem in the Pacific Northwest. Time domain reflectometry (TDR) is the most practical instrument for field measurement of liquid water in frozen soils. Many of the measurements we have made with TDR, however, are in conflict with theoretical predictions. Some think that this conflict arises from the calibration equations used, which do not directly account for the effects of ice and low temperature on TDR measurements. We tested six different calibration equations, two which we modified specifically to account for ice and temperature effects, on three different soils over a range of water contents. We found that the two modified calibration equations produced measurements that were accurate when no ice was present and similar to each other when there was ice present, but they did not agree with theoretical predictions. Additional instrumentation must be used to resolve the question of whether the results are an artifact of the instrument or whether the theory needs to be modified. We showed that modification of TDR calibrations equation is probably not the explanation.

Technical Abstract: Some liquid water remains in the soil even when soil temperatures drop well below freezing. Measurement and prediction of this liquid water is important because it affects estimates of flooding hazard from frozen soil, which is a major problem in the Pacific Northwest. Time domain reflectometry (TDR) is the most practical instrument for field measurement of liquid water in frozen soils. Many of the measurements we have made with TDR, however, are in conflict with theoretical predictions. Some think that this conflict arises from the calibration equations used, which do not directly account for the effects of ice and low temperature on TDR measurements. We tested six different calibration equations, two which we modified specifically to account for ice and temperature effects, on three different soils over a range of water contents. We found that the two modified calibration equations produced measurements that were accurate when no ice was present and similar to each other when there was ice present, but they did not agree with theoretical predictions. Additional instrumentation must be used to resolve the question of whether the results are an artifact of the instrument or whether the theory needs to be modified. We showed that modification of TDR calibrations equation is probably not the explanation.