Geoscience Reference
In-Depth Information
purpose: where the land was formerly in agricultural use, for example, planning re-
quirements have usually specified its restoration to agriculture as part of the overall
scheme. With the likelihood that much existing agricultural land will come out of pro-
duction in the future, this goal is less needful. It may be more appropriate to restore
areas for public recreation or even to create particular communities for wildlife con-
servation. Both mineral extraction and agriculture have destroyed many rich wildlife
habitats so this last option is attracting increasing attention. This section describes a
few examples of these different approaches.
Perhaps the classic example of land restoration, and certainly the most extensive,
is that from open-cast coal workings. By 1988, more than 52,000 hectares (27 square
miles) had been restored in Britain since the Open-cast Coal Executive was set up in
1942. From the outset it was determined that topsoil should be replaced when the min-
ing was completed. (Open-cast strip mining for ironstone in Northamptonshire had no
such requirement.) However, it was quickly discovered that simply levelling the spoil
with its mixture of clay, shale and boulders, and covering it with a skim of topsoil,
was not enough. Farmers soon complained that they could not grow crops satisfact-
orily on the restored lands. A new code of practice was therefore introduced which
provided for the separate stripping, storing and replacement of subsoil and topsoil to
cover the overburden to a depth of 0.9 metres. It also allowed for a five year period of
management by the Ministry of Agriculture, involving the installation of permanent
under-drainage, before returning the land to the farmer.
Once the topsoil and subsoil are removed from the working area and stored, the
excavation proceeds, in the simplest case, rather like a gardener double digging. A
dragline opens a cut in the overburden and the exposed coal is removed. Further par-
allel cuts are then made, the overburden from each new cut being cast into the void
of the last one, and the final void backfilled with the overburden from the first cut.
Before the subsoil is replaced, the overburden is usually ripped with a special 3-tined,
heavy-duty, winged ripper working to a depth of about 0.5 m in two directions at right
angles to break up surface pans. Any large stones brought to the surface are also re-
moved. The stored subsoil is then spread in two layers about 0.3 m deep, each lay-
er again being 'rooted' to remove anything that would impede a plough. Finally the
topsoil is spread and cultivated. The whole emphasis during this restoration phase is
on creating the best physical conditions for life processes to start up again. It is pos-
sible actually to improve on the original conditions during this process by inverting
strata to bring a lighter material nearer the surface. The main dangers to be avoided
are compaction, which would lead to poor drainage, and the loss or deterioration of
topsoil.
