soilprofile

Soil Water Solutions

Infiltration

Infiltrometers come in many forms. We supply three types.

Ring infiltrometers for measuring surface infiltration rate under saturated conditions. 

Suction (or disk) permeameters : used to measure hydraulic conductivity of soils under unsaturated conditions. 

Borehole (Talsma) permeameters - used to measure infiltration rates of deeper soil layers via a bore hole.

Ring infiltrometers  Rings are constructed of stainless steel 2mm thick and 20cm high These are usually sold in sets of three rings which pack inside each other for easy transport.

 (ask about our cheaper ‘disposable’ rings - good for maybe 20 uses)

A common order is for a 50cm diam ring, a 45cm ring and a 30cm ring. This allows their use as three separate single ring infiltrometers or - by using the largest and smallest inside each other configured for use as a double ring system. 

Two water height measurement systems are available

1.(For falling head method) An oblique ruler (a scale fitted with a bubble so it can be easily installed at a 1:10 slope, (ie water intersecting with the scale moves 1cm for each 1mm infiltration)

2. (for fixed water depth method)  Mariot bottles which hold the water at a preset depth and indicate the amount of water flow needed to do that.

All sets are supplied with an instruction manual & demonstration video. All prices GST incl

Price : Kit of 3 stainless steel rings (which pack inside each other) with oblique rulers $1100

Single rings 30cm $350, 40cm $400,, 50cm $450 oblique rulers $30 ea, Mariot bottles (small 3.5L) $50ea, (Large7L) $80

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Single ring system - falling head method using oblique ruler

 Closeup shows how oblique ruler indicates water depth

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 Double ring system with mariot bottle (fixed head method)

Which infiltration method to use?

The double ring method was developed to measure infiltration without the loss of water by sideways movement (sorptivity) as happens from a single ring. 

After 30 years experience in field measurement of infiltration, Soil Water Solutions has found that :-

a) It is nearly impossible to detect leaks between the inner and outer rings in a double ring system. 

b) double rings take 4x as long to set up

c) the statistical error in the final field infiltration measurement is usually proportional to the total soil area tested

d) by using larger rings, the proportion of water lost to sideways movement is dramatically reduced (eg a 2cm sideways plume accounts for as much water as the ring if the ring is 10cm diam, but the same plume on a 40cm ring is only 10% of the total

Moral of the story : use the biggest ring you can manage in single ring configuration and do as many tests as you can in the time available.  However, the down side is that you need a lot of water.  If you are concerned about sideways water flow, then compare results from tests using a small (eg 20cm dia) ring and a 50cm diam ring - the results should give an indication if the side flow is a significant problem and some guide how to correct for it.

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Suction (disk) Permeameters

These ingeneous devices allow water infiltration to be measured in unsaturated conditions.  They are used mainly by soil scientists to measure the properties of the soil body without interference from holes caused by roots or soil animals. For example, a Ring infiltrometer placed over a mouse hole will measure the flow rate through the mouse hole, but a disk permeameter will measure only the water flowing through the soil around the hole. 

Our units are usually sold as a pair of permeameters in a single steel box    price $1900 GST incl

Borehole (Talsma) Permeameters      Price $190 GST incl

These devices maintain a small (fixed) depth of water at the bottom of a borehole and measure the flow of water to do that.  They will operate in boreholes as small as 30mm diameter.  Unless otherwise requested, they are set to hold a water depth of 20mm - this allows the assumption that water only infiltrates through the bottom of the borehole. Unit is supplied as a measurement tube (which sits above ground) and an extension to go to the bottom of the borehole. Unless otherwise requested, the extension supplied will suit boreholes to 60cm depth. Longer extensions can be made easily, for a few dollars, from parts available from most plumbing suppliers.

If the depth of water in the bore is required to be greater (ie several bore diameters) then the unit can be modified by drilling a single hole in the plastic pipe - instructions are provided.

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