Erosion - Mining and the Environment: From Ore to Metal - page 784

useful in comparing relative levels of erosion susceptibility under different conditions,
such as different cover alternatives, rather than estimating absolute sediment yields.
As mentioned above in the discussion of controlling factors, the equation assumes aver-
age rainfall conditions and predicts soil loss for sheet and rill erosion only. Greater than
average rainfall or the presence of concentrated rainfall in gullies or channels ( Figure
20.3 ) will result in more erosion than predicted by RUSLE. It should also be noted that
the equation predicts soil loss and not soil deposition. Coarser particles may only be trans-
ported to the toe of a slope and may not reach areas further downstream.
Water erosion is one of the most prominent and visible negative impacts of a mining
operation. The preceding discussion illustrates the basis of the powerful methods available
to quantify erosion potential, but their application is often beyond the scope of an environ-
mental impact assessment. Professional judgement with a sound understanding of erosion
management practices is key to predicting erosion signii cance during the EIA process.
Erosion control and sediment retardation during mine construction and operation are the
least expensive and the most effective means to reduce water-borne contamination. These
should be regarded as major priorities in preparing the environmental management plan
for a mine during the environmental impact assessment process.

Managing Water Erosion

The two key principles of water erosion management are to sustain soil cover and hence to
fence off erosion (erosion controls), and to control water quality through the reduction of
sediment loads if erosion occurs (sediment controls). The i rst principle is a priority, since
prevention is always better than cure.
Erosion management is part of mine design and mine water management.
Consideration is given to the hydrologic, geomorphologic and geological attributes of the
mining area; to mining technology and mine waste placement; and to the combined effects
of these factors on quantity and quality of runoff throughout the mine life. Finally, and
most importantly, the design of the post-mining landform commands special attention:
each piece of land is different (in terms of soil type, gradients, exposure to rainfall, run-
off from adjacent areas, etc), and the i nal landform needs to take these differences into
account.
The most effective erosion and sediment controls are those built into mine design and
into the rehabilitation sequence. Key erosion and sediment controls are then part of the
mining operation and do not require additional engineering design or construction. For
example, mining in an up-slope direction where feasible may allow use of worked-out pits
to act as runoff and sediment retention basins. Backi lling and revegetation of pits or strips
as soon as possible minimizes the extent of disturbed land at any one time, signii cantly
reducing total erosion.
Some erosion and sediment controls are only needed temporarily during construction
and during active mining phases, whereas mine rehabilitation requires the provision of
permanent solutions. It is important that erosion and sediment controls, even if only tem-
porary, are stable, robust, and designed to accommodate the signii cant peak l ows common
at the location of the mine, particularly if the mine is in the tropics. Emergency spillways
should be constructed, where appropriate in sediment ponds and other impoundments.
The choice of erosion and sediment controls, particularly the design of retention basins,
depends on the consequences of failure. It is important to understand the quality and sig-
nii cance of waters receiving eroded material, from the perspectives of safety, community
use, economic value and environmental value. Where failure will not endanger life and

The most effective erosion and
sediment controls are those built
into mine design and into the
rehabilitation sequence.

The choice of erosion and
sediment controls, particularly
the design of retention basins,
depends on the consequences
of failure.