Save Steve Irwins Place

[VrWagz1]

Im not really for this, even though i am in the mining game myself. It seems to nice a place to be digging the joint up, especially as it only seems the mine is going to have a 10 year life. So its not going to give people jobs for 30 years or so, it sounds like a quick rape and pillage job. Even though a good job is usually done on regeneration after they replace the overburden and it all looks good again, the problem is you cant replace the eco system that was there.
By the sounds of it they are no going very deep, but the still run the risk of damaging small water tables their explorations will not have found, which can be vital to other parts of the reserve kilometers down the track.
All mining always does some sort of permanent damage that cannot be repaired and all its affects cannot be predicted, often things happen at the time and the mine can only do its best to patch things up then, but by that stage permanent damage is done. Masterofreality your from around here, how many times has parts of the Nepean been dried up now, due to the underground mines causing major cracking in its bed. The mines never meant to do that and all they can do is remediate the damage. Helensburg had to pur the river bed only a year or 2 ago now. Dendrobium has caused massive cracks in the forests above it, they are a foot wide and a meter or two deep and thats what you can see on the surface and its right next to a dam, which is slightly concerning.

 

[MasterOfReality]

Masterofreality your from around here, how many times has parts of the Nepean been dried up now, due to the underground mines causing major cracking in its bed. The mines never meant to do that and all they can do is remediate the damage. Helensburg had to pur the river bed only a year or 2 ago now. Dendrobium has caused massive cracks in the forests above it, they are a foot wide and a meter or two deep and thats what you can see on the surface and its right next to a dam, which is slightly concerning.

I have actually completed a PhD on this very issue - longwall mining under waterbodies.

The Greens are calling for a 1km buffer around all waterbodies. Thats crap. They will not explain the rationale behind this 1km figure. I know where they got it from (a government surveyor noticed horizontal movements 1km away from a longwall) and per usual, they have taken it out of context. They will not even consider the possibility of optimising the buffer distances, but what can you expect from them.

It has been demonstrated many times that longwall mining can approach waterbodies, and even mine under waterbodies without damage. That was illustrated in the Reynolds Enquiry in 1974, and I think another enquiry is underway or has just finished.

I have been given access to the data from Marhynes Hole in Appin and have seen the excellent rehab results, and I monitored the progress of the Waratah Rivulet above Metropolitan Colliery. Its true, I saw the rockbars crack and water drain. A big misconception is that the water drains into the mines, and that is simply not true. The water takes another subterranean path and rejoins the river/creek further down. Another big misconception is that the damage is permanent. Its not. When the longwall passes and the area comes down on the other side of the subsidence trough, cracks close back up, waterflow resumes and the eco system is restored. They will close up anyway over the course of time.

The conclusions from my 5 years of research was that longwall mining can take place under waterbodies and not cause any considerable damage - the key is limiting the tilts and strains on the surface, which in turn dictates longwall width.

If the government chooses to place a buffer zone, that distance can be optimised for maximum coal extraction and minimum ground disturbance.

The cracks at Dendrobium are likely to be superficial in the scheme of things. Geotechnical issues aside, longwall mining has been happening under or around dams in the Illawarra for around 40 years now without incident.

Edit - I forgot to mention that the places above are in areas of high topographical relief (eg river valleys) which exacerbate the effects of mining. However a relationship exists between the geometry of the valleys and the longwall width to depth of cover ratio. We are in the process of producing design charts for this, as its inevitable that the government will legislate a stand-off distance which will force BHPB to rethink its longwall design procedures.

Do I think a stand-off distance or buffer zone is a good idea? It depends on the case in question. BHPB have been a bit pig-headed when it comes to this, but now they are being forced to consider the alternatives as the state government isn't that mining friendly and has a more open ear to green groups . I remember they didn't want a piece of my research, yet a year ago they were asking very politely if they could take a peek. If they cannot demonstrate their case then they have to wear the consequences and accept a standardised buffer distance.

I believe in the Illawarra the longwalls are deep enough to undermine waterbodies without lasting effects. I think they need to stay around 350-400m deep for this to occur, and the massive width of some of these longwalls are simply not feasible. If the longwalls are shallower than this, or wider longwalls are proposed then I think a buffer system should be enforced.

See, I'm not a mining at all costs type of person I just like to consider all the facts first before making an educated decision.

 

[VrWagz1]

The 1km thing they were banging on about is rubbish, i havnt heard much of it lately, so hopefully it has evaporated out of their heads. Though you say, im still not convinced a water table can be restored once it is cracked, though it may come back to a point i cant see how it could ever be 100% again. And no the water does not drain into the mine, thats a new one to me, do people think i swim to the face, what a stupid thing to think.

 

[MasterOfReality]

The 1km thing they were banging on about is rubbish, i havnt heard much of it lately, so hopefully it has evaporated out of their heads. Though you say, im still not convinced a water table can be restored once it is cracked, though it may come back to a point i cant see how it could ever be 100% again. And no the water does not drain into the mine, thats a new one to me, do people think i swim to the face, what a stupid thing to think.

Hehe, I went to a mine subsidence seminar once and to their credit, a community rep turned up. However, the rubbish that came out of her mouth was unbelievable in light of the answers we were providing her, backed up with field studies.

In the Illawarra, the water table is mostly protected by the Bulgo Sandstone. I think (but I have to check this) the aquifers are above this unit. This unit is massive (and strong) and its the unit that halts the caving process on making its way to the surface (also caving angles come into it but that another whole chapter ). There will be drawdown of the water table but its affect on rivers is neglible. People often confuse the natural water table with surface river flows.

There is a threshold value (3.5 ML per day) which has been fairly consistent that indicates if the water flow in a river is above a certain level, then mining directly underneath will not affect flow.

There was one spot in Helensburgh I was monitoring - one place drained a little and then flow was restored after the longwall passed. However another place 500 m down stream busted up in a big way and drained substantially. It looked visually horrible, but after a decent rainfall flows were temporarily restored which lead us to believe that any damage is temporary and once grouting occurs, then the site will largely be rehabbed.

Its an area of mining science which is developing, and therefore is open to argument and counter-argument.

Makes life interesting

 

[thestig]

50,000 Megatonne Cobalt Salted Doomsday Device

Normally I'd side with Minux and Greenfoam. But the Irwins are involved.. So I say fck it.. I'll make an exception.

Mine the fck out that joint.. And when your done nuke it just for good measure.

Sorry guys.

L8r