Theory; Preliminary Note - UMS HYPROP Operation Manual

Theory

Preliminary note

HYPROP (HYdraulic PROPerty analyser) is a device to measure hydraulic
key functions of soil samples in a comfortable and reliable way by using an
evaporation experiment.
Wind (1966) developed the evaporation method in the mid-sixties. For this 5
tensiometers were put in a soil sample. The sample was set on a balance and
over the evaporation process the tensions and the mass change of the samp-
le were measured in time intervals. Based on these data the water retention
function and the unsaturated hydraulic conductivity in the range between
saturation and maximum 500 hPa (50 kPa) were calculated by means of an
iteration process. Schindler (1980) simplified this method. He used only 2 ten-
siometers and simplified the evaluation procedure. HYPROP is working based
on this method. The method was tested several times and its fitness for use was
proven by scientific analysis (Wendroth et al., 1993, Peters and Durner, 2008;
Peters et al., 2015). New research results yielded a further simplified measuring
procedure (Schindler and Mueller, 2006) and an extended measuring range
(Schindler et al., 2010a and Schindler et al., 2010b). Using the HYPROP one can
today measure simultaneously the water retention curve and the unsaturated
hydraulic conductivity function in the range between water saturation and
close to the permanent wilting point. The measuring time amounts – depen-
ding on the soil – from 2 days (clay samples) to maximum 10 days (peat and
sand samples). Additionally the dry bulk density of the sample is determined.
The measurement and evaluation can be run in two modes. In the multi ba-
lance mode (one balance per sample) the lab employees' work effort is limi-
ted to set up and take away the samples. In the single balance mode (one
balance for more samples) up to 20 samples can be measured in parallel. In
this mode it is necessary to put the probes manually on the balance twice a
day. This takes about 15 s per sample and weighing. The measurement of the
tension runs automatically. The software HYPROP-VIEW enables a comforta-
ble data logging and storage. The software HYPROP-FIT provides the same
comfort for data evaluation, fitting and export of the hydraulic key functions.
The hysteresis of the saturation and dewatering characteristics of the hydrau-
lic key functions is described in Schindler et al. (2015).
76 | Theory