Hydro Excavation| Vacuum trenching| water vac

Eric Frei

I'm going way out there to say that I believe the vac-u-digga style of water blasting and a vacuum sucking up the sludge around tree roots is invasive and damaging.

Tree roots like branches have bark on them. Just like ringbarking a tree if the bark is stripped off the roots that root will likely die and decay.

The bark on roots is not as tough as the bark on tree trunks and branches. It is often moist too and once lifted it peels easily like an orange peel.

When the trees in New Farm Park were falling some water vacuuming was done:-



You can see that the roots were skinned of their bark.

If the nozzles are changed and even pressure reduced then the soil cannot be cut/penetrated. It's reasonable to say that any pressure sufficient to cut through soil will skin the roots.

In and switch to air excavation. They admit that pressures as low as 500 psi skin the roots.

The trouble with skinned roots vs cut roots is that cut roots will sprout and grow more roots. Skinned roots will likely die and rot. Some-one may falsely believe that the skinned root still offers anchorage but in a few years decay would have ended that theory.

Open for discussion ......

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spb

Damage can certainly be done with the hydro, but lower pressure and technique are the answer. I shoot the high pressure water underneath the roots creating a hole underneath, then the soil collapses through from around the roots, rather than applying water to the actual roots.

Forest Keeper

We like to use the Air Spade for this kind of work. It great for root collar excavations, aerating etc. It doesn't seem to do much damage to the roots and the trees we've worked on seem to really respond favorably when loosening compacted soils

Garry Brockley

I would agree with the theory that cut roots are better than skinned roots, one significant area being with cut roots the surface area is sigificantly less than skinned roots and therefore a lesser area for the tree to protect from invading pathogens and easier to compartmentalise.

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Eric Frei

In addition cut roots, like stub cuts in the canopy, can generate new growth, and new roots can continue the supply where as ring barked roots will lose their vascular capacity and decay with no regeneration.

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derwoodii

Agree, I canna understand the practice of excavating a trees root system to see that der,, duh,, there are roots there... Kinda obvious to prove what. In the end you destroy a great % of feeder roots and leave bare structural roots in disturbed and now likely bio mass unbalanced soil medium.

Often used trying to gain a few meters for a development plan, please just leave it or sox it, don't friggin torture it to a slow death.

I done some cruel stuff to tree roots but not seen a need yet to use these vac or air knife things when a spade a broom or hand blower gets it done if ever a small explore needed.

derwoodii

Ops sos Forest just read your post, looks like your an advocate for these things so hopin not to offend your practice. I'd just get anxious strippin bare my flesh and small vascluar veins with 150 scfm / 90 psig supersonic jet in the hope it would do me better.
Your work says it does, so well done. I'd just rather not or perhaps do sections over a time. Have you had trees respond poorly.

Forest Keeper

One use that we have seen very effective is rescuing trees from serious soil compaction after a construction project where the contractor didn't take the necessary precautions to protect the trees. After having heavy equipment drive all over the root zone of certain trees, they go into rapid decline and need the soil aerated. I can't imagine using radial trenching being a valid option anymore. We have done many of these jobs and have never seen root damage like in Eric's picture, result from air tools. I'm sure careless use of an air tool could be harmful but then again the improper use of a chainsaw could be pretty harmful as well.
We've also helped utility companies run lines under the root zone of trees with the air spade where the roots would have had to be drastically cut otherwise.
We have found that if we add a nice compost to the back fill, the bio mass will actually be increased. This is especially true since we are dealing with urban trees which typically have terrible soil profiles to begin with .

derwoodii

Agree touché, diligent use in the right hands for valid tasks may be a benefit. It just seems very invasive, perhaps a choice of two evils soil compaction vs soil disturbance. Your experience proves works are worth while.
I was very interested when these knifes 1st appear but after demo of one,, Argh the noise the mess and cost/effort to set up i.e hire big compressor just outweighed in my mind the job benefits vs simple gentle hand work.

I got an interesting job underway with a newly planted crane sized macro fig that needs root and soil medium massage due to poor install specs. I may ask others here ? how too, your help will be valued.

Eric Frei

I urge you all to read through this thread and much of the documentation within it.

Soil Aeration Experiments| Grade Changes| Compaction| Decompaction

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derwoodii

OK ta Eric, gonna need a big pot of (compost) tea and (organic bio mass) cake to read though all that.