Affect of compaction over monitoring site

[owner-sowacs@aqua.ccwr.ac.za]

>Hi all,
>
>> We did not do any systematic analysis or experiments but in one study we 
<SNIP>
>> impenetrable profile.  They also liked to grow along interfaces.
>> 
>> As my Agrometeorology used to say: "the closer you get to what you want to
>> measure, the more you disturb whats you want to measure" ... (or words to
>> that effect - apologies).
>
>My experience is limited, but I would like to make some comment based 
>on that limited experience.
>1. Horizontally buried sensors (I presently use a 2 meter lngth of 
>sensor to prevent water distribution errors) appear to be 
>less overgrown by roots than vertically buried sensors. Is this due 
>to water infilration down the sides of the vertical tube?

I was referring to horizontally INSERTED point probes, rather than the long
length probes I think you are referring to. (How's the work coming on them,
by the way Johan?)

>> 
>> The importance of site disturbance is often over-looked, or else it is
>> impractical to take measures sufficient to prevent it completely.
>>
>2. While it appears to be a physical law that nothing can be measured 
>without disturbing it, it only takes two irrigation cycles for 
>everything to appear normal. Having said that, there is a slow small 
>movement of the base line over months, probably  due to further 
>compaction.

As long as a sensor is required only as a relative measure, this will be of
no consequence. If this drift is real, then fine and well - and it indicates
that the sensor takes account of the bulk density - and changes due to
settling/compaction.  But if the drift is an artefact of the sensor, then it
cannot be used for absolute measures. How would one differentiate? Perhaps
use a sand test bed that will not settle or compact?

>
>Regards
> 
>Johan Smit
>smit.js@pixie.co.za
>P.O.Box 9551 George 6530 RSA
>Tel +2744,8745533
>
>

--
Bruce Metelerkamp

   _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/  _/ _/ _/ _/ _/ _/ _/
  _/ _/brooz@nodamnedspam.pobox.com   http://pobox.com/~brooz  _/ _/ 
 _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/  _/ _/ _/ _/ _/ _/ _/ _/ _/ 

... remove the "nodamned.." bit .... :>