Mine Closure - Mining and the Environment: From Ore to Metal - page 813

● Adequate ini ltration and moisture retention capacities to supply plant water
needs;
● Other soil characteristics such as suitable texture, fertility and absence of growth
inhibitors. Plants adapted to arid and semi-arid areas are usually deep-rooted, while
tropical plants usually have relatively shallow root systems.
5. Accessibility and Usability - this includes both access to and access within the reha-
bilitated area and depends on the intended land use and what will be involved. For
example, will vehicular access be required for planting, cultivation, harvesting, etc?
Maintenance of accessibility commonly involves compromises in selection or design of
erosion controls.
6. Drainage Capacity - needs to be provided:
● To collect and accommodate runoff from the most intense rainfall events likely to
occur, including any run-on from surrounding areas;
● To incorporate measures such as stone-pitching, lining, and drop-structures to avoid
scouring;
● To convey runoff beyond the rehabilitated areas into the natural drainage system.
It should be recognized that, if adequate drainage is not provided, it will develop by
surface erosion, the results of which may be highly damaging.
There are usually trade-offs to be made between ini ltration and runoff. Generally,
in tropical, high rainfall areas, the priority is to 'shed' as much water as possible.
Accordingly, drains are relatively closely spaced, with moderate to steep gradients. In
arid areas, ini ltration is encouraged by broad inwardly-sloping terraces and, in some
cases by surface pitting or moon-scaping, with the result that drains may be few and far
between. Whichever approach is adopted, it should be consistent with the hydrologic
management of the overall watershed.
7. Phyto-toxicity - the most common cause of which is acid rock drainage (ARD), which
can severely restrict or prevent plant growth. ARD is discussed in detail in Chapter
Seventeen. In tailings impoundments, ARD can be prevented by means of a 'dry cover'
or capping beneath the plant growth zone, or by a 'wet cover' involving the mainte-
nance of a surface pond. In waste rock storages, ARD is managed by:
● Deep burial of potentially acid-forming material beneath the water table;
● Encapsulation within compacted clay, or
● Capping alone, with compacted clay or artii cial membranes, which may be sufi -
cient in arid areas.
All these cases involve careful design to ensure that the systems are effective at manag-
ing ARD and, at the same time, provide conditions adequate for establishment of sus-
tainable agricultural or natural vegetation communities.
8. Appearance - to achieve congruity with the surrounds, designs should:
● Avoid sharp edges and straight lines;
● Blend gradually between the interfaces of natural and artii cial landforms;
● Provide screening vegetation in areas of unavoidable scarring, and
● When planting native vegetation, straight lines, regular patterns and repetitive spac-
ing should be avoided in favour of more random arrangements.
9. Final Void Hydrology and Chemistry - hydrological and chemical studies may be
required to evaluate the extent to which the pit will i ll with water, the rate of i lling,
the likely seasonal l uctuation and whether or not water in the pit will 'turn over' as a
result of seasonal temperature differences. The water quality of the i nal pit lake is also
of environmental concern ( Case 21.3 ). This information is required to assess the need
for treatment of pit water and whether additional structures such as overl ow spillway
and drains are required.

If adequate drainage is not
provided, it will develop by
surface erosion, the results of
which may be highly damaging.

The water quality of the fi nal pit
lake is of environmental concern