Resources - Soughs
Just what is a sough and what does it do?
Having identified a business opportunity of supplying the need for some limestone in an area that has an abundance of it and subsequently bought the land with rights to dig it up and sell it, you set about taking off the topsoil to expose the limestone.
With that out of the way, you can dig out all of the rock you want. Up to a point. Sooner or later, you manage to get down to the water table the deeper you dig, the more groundwater you attract until you realise that instead of a quarry, you are now digging a large well.
In the case of Hilts quarry, Crich and the surrounding area lies on rock that sits within a dome of impervious material although on one side, there is a different material although this is also impervious to water. Water has a tendency to fill up these domes and other than any natural breaks in the barrier, the water will just sit there unless there is a route underneath the impervious layer that comes out somewhere else.
The only way that you can mine any more is to drain the water away. There are two ways of doing this: pump the water out faster than the aquifer can supply it; or, lower the water table.
If you go to a nearby stream that is lower than the level of water you want to drain the aquifer down to and then start digging a tunnel, at a slight incline, into the hillside, water will naturally drain out of the hillside, through the walls of the tunnel and out, into the stream.
This tunnel is called a sough pronounced suff and it does not require any energy to make it work as it is fed entirely by gravity.
If you carry on digging, through the impervious layer of the cone, into the rock inside, you will lower the water table in there as well, thus taking it below the level of the bottom of your quarry, thus draining it so that you can carry on quarrying.
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