What would you estimate the long term (1000 year) effect to be on a parcel of land that was once prime agricultural and was turned into an open cut coal mine, and subsequently 'rehabilitated' ? (I'll clarify that qu at the end)
I work in open cut coal mining in a tech/support field, we work regularly with the 'geotechs'. They care more about slump, dykes and overburden heights etc etc to answer my inane questions.
Clarification : I guess that when I see prime agricultural land have the top soil cleared, the next 30-70mt drilled, pumped full of anfo, detonated, removed and then the coal stripped out I try consider that in terms of millenia at a minimum. it took at least 6 😅 of those pesky millenia to get the earth here in the first place.
The rehabilitation appears to amount to shoving the freshly exploded rock into the old hole you have finished with - in any particular order - then find whatever top soil you can and placing approx 3mt of it on top. ensure gradient is to spec, throw down 40 trees per ha and some grass seed.
The qu :
Could you please try and explain the long term effects on this parcel of land, directly compared/referenced to how it originally/naturally was in the areas of :
-long term geo 'stabililty'
-long term effect on the ability for that land to perform as the fertile grasslands it was (Bowen Basin QLD Australia)
-long term effect on water tables
-expected long term effect on native flora and fauna returning?
(please dont infer any political or idealogical beliefs here. I am super inquisitive and I feel these questions are relative regardless of your particular swagger.... i.e. please read as neutral, sciencish questions, not meant to be edgy to anybodies sensibilties)
Thankyou in advance if you take the time. I hope the question isn't too vague to answer
Well this certainly is not the kind of answer I would have expected on a flat earth forum, and in all honesty, this (soils, flora/fauna) is not my expertise, so I'll mostly be making educated guesses.
-long term geo 'stabililty'I guess you meant this: "Does the shattering and willy-nilly (nimbly-pimpbly XD) redistribution of rock affect long term 'geo stabilty' (like foundation stability) of the area.... and does the shattering, mixing and redistribution affect the ability for the top soil to perform in that area as it historically did?"
After the gravel/crushed rock or however that is done, is placed, it probably still can compact a bit further. Don't expect this to be a hazardous event, but just something that occurs slowly, over a long time. In the end you may end up with a slight depression in the landscape (assuming it's initially filled to the brim). But yeah, this also depends on: grain size distribution, shape, if they actually try to make it compact, material used (I'm guessing it's mostly sandstones, quartz is really resistant stuff).
-long term effect on the ability for that land to perform as the fertile grasslands it was (Bowen Basin QLD Australia)onebigmonkey covered this pretty well. It really depends in the effort you put in it. If you just dump gravel or pulverized rock or whatever in a pit, it will take a very long time, but it's possible to try to restore the top soil to a certain level.
-long term effect on water tablesI'd say that this really depends on the scale that we are talking about. What kind of surface area and depth are we talking about? The local geology is also very relevant.
-expected long term effect on native flora and fauna returning?Long term, no issue. Nature is good at restoring stuff, it ususally just takes a lot of time.
In the end, it really depends on how much effort is put into reclaiming the mining site.
I figured I'd add some stuff to read:
http://cornerstonemag.net/case-studies-of-successfully-reclaimed-mining-sites/https://en.wikipedia.org/wiki/Mine_reclamation