Infiltration - Hood Infiltrometer

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Parameter to be measured:

Infiltration capacity, unsaturated hydraulic conductivity, bubble pressure point

Method:

Tension-infiltrometer (UGT IL-2700): Measures infiltration rate within a hood that is placed onto soil surface. Hydraulic head within hood can be adjusted between 0 (=saturated conductivity) and bubbling pressure by means of a Mariotte-bottle. Newer versions provide a pressure sensor and data interface. The "logger" device comes in two versions: Rev1 the "logger" can only monitor the water table, Rev2 the logger really logs the water level in the reservoir and stores all experiments.

Equipment:

main reservoir (with combined) Mariotte-bottle
hood (various sizes), steel rim
connecting tubes, manometer (e.g. U-style), hand pump
datasheets, stop watch, sand (for sealing hood rim with soil surface)
scissors for clipping vegetation
spade (if levelling or deeper measurements are necessary)
large water vessels for supply

Advantages:

in-situ measurement, no analysis of disturbed soil samples in lab
no contact layer with soil required (as with ceramic plates)
works with reasonably uneven surfaces and original vegetation
no need to drill neat holes (as with a constant head permeameter like the Amoozemeter) which is problematic in stony soils

Disadvantages:

heavy, comes in huge metal suitcase (17 kg) (some wire straps may help connecting the many bits and pieces to a portable pack)
large water consumption with sandy soils
many pipes and valves - requires practice and understanding to recognise errors, set-up time
lots of potentially leaky connections and many parts to loose in the field (bring silicone grease)
at some locations it is difficult to get a suction head established as air enters the hood through macropores or root channels
measurement in different depths of soil profile is complicated, though possible when digging pits
price

What to watch out for:

potential problems with

hydrophobic soils
heterogenous water content of soil before measurement
strong effects from preferential flowpaths
strong swelling/shrinking of soil
effects of impermeable layers before stationarity is achieved
inclined, uneven surfaces
inequivocal identification of stationary flow

(worksheet of H. Elsenbeer)

insolation and temperature related problems
in case of high macroporosity , use a metal ring with a larger depth to prefent the effect on the measurment than seal the hood with too much sand, because measurement area will in that case be error prone

Problems/Questions:

Links

UGT

no-frills-instruction (in German)

Projects that used the above equipment:

Other related web sites:

Punzelmeter at the University of Sydney

References

Bens, O., Wahl, N.A., Fischer, H., Hüttel, R.F. 2007. Water infiltration and hydraulic conductivity in sandy cambisols: impacts of forest transformation on soil hydrological properties. Eur J Forest Res 126,101–109, DOI 10.1007/s10342-006-0133-7.
Gardner, W.R., 1958. Some steady-state solutions of unsaturated moisture flow equations with application to evaporation from a water table. Soil Science 85, 228-232.
Schwaerzel, K., Punzel, J., 2007. Hood infiltrometer - A new type of tension infiltrometer. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL 71(5), 1438-1447, DOI: 10.2136/sssaj2006.0104.
Wooding, R.A., 1968. Steady infiltration from a shallow circular pond. Water Resources Research 4, 1259-1273.