Infiltration - Hood Infiltrometer

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

Links

UGT

no-frills-instruction (in German)

Projects that used the above equipment:

• SESAM
• COMTESS
• Natural Slope
• CAOS

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.