Christiansen, C. 1995. 
Applications of TDR in Wetting Front Measurements.
Paper in the Proceedings of the Symposium: Time-Domain Reflectometry Applications in Soil Science, (Foulum, Denmark, Sept 16, 1994) SP Report No. 11, June, Vol. 3, pp. 125-130.
(posted July 9, 1996)

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TDR equipment was used in order to determine wettingfront propagation in a vertical profile. Seven waveguides were inserted horizontally in a profile to a depth of 1.4 meter and they were connected to a multiplexer and a TDR cable tester. Two series of measurements were carried out using two different sources of water supply. The first series was made during a infiltration measurement with a dobblering infiltrometer and lasted for about 6 hours. The measurements clearly showed the time at which the infiltration water reached each level in the soil profile. With these time registrations it was possible to calculate internal flowrates at the bottom of the wettingfront. The second series was made with a sprinkling system, used as a rainfall simulator, and lasted for 17 days. During that period there were four significant events of natural rainfall. These events were easy to recognize due to a sudden increase in water content in the uppermost levels. These two experiments showed that TDR equipment are suitable for time series measurements, However these point measurements could give rise to problems if the infiltrating water does not propagate down through the soil with a well-defined wetting front, but tends to ‘finger' due to instability in the wetting zone. This, together with the possibility of macropore flow or preferential flow paths, and the possibility of great spatial variability in the soil hydraulic properties, makes it difficult to draw any conclusions with just one set of data from a single test plot.