Wim and
Clint has done some nice work on the comparisons and
makes the point that Watermarks have little
sensitivity in the 0 to -10kPa range (and/or would
require special calibration for this range).
For hillslope work, accurate measurements in this
range are essential. The unsaturated hydraulic
conductivity (K) of soil decreases by orders of
magnitude between 0 (saturation) and -10kPa. The
tensiometer transducers should be well calibrated
because the conductivity (and hence soil water
responses) could be very different between 0 and even
-.5 kPa. The installation depths should be accurately
measured from a reference datum so the exact depth of
saturation (or +ve head) can be measured.
Watermarks are probably better suited to irrigation
studies - they are cheaper, more robust (a point
already made) and tensiometers do need a lot of care
to ensure good readings.
Martin
VU Amsterdam
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