Environmental Engineering Reference
In-Depth Information
20
Erosion
The Perpetual Disruptive Forces of
Water and Wind
Chapter Twenty is concerned with erosion. While neither diffi cult in concept
or involving complicated physical processes, erosion presents signifi cant
environmental management challenges, comparable to those involving acid
rock drainage and mine waste management. Erosion is the dislodgement and
transportation of soil materials through the action of water and wind, with
potentially signifi cant direct and indirect adverse impacts, both onsite and offsite.
Direct onsite impacts include the degradation and possible failure of mining infrastructure
constructed with Earth materials, such as roads, embankments and dams. Failure of a tail-
ings impoundment due to erosion is potentially catastrophic in terms of the environmental
contamination that would result. Such a failure, or, in fact, the failure of any form of slope
or embankment at a mine site, also potentially endangers property and human life in the
immediate area or further down-slope.
All slopes at mine sites which are composed of soil or highly weathered rock are poten-
tially at risk of signii cant erosion, whether they are natural or man-made. Signii cant ero-
sion can occur as a result of a discrete event, or from a slow cumulative process over time.
An example of the former is the overtopping of a dam during or after a severe rainfall
event, possibly causing severe gouging, leading to failure of the dam. More gradual ero-
sion can slowly steepen an Earth slope, leading to disrepair, decreased stability and possible
eventual collapse. In the case of natural slopes, the clearing of vegetation commonly leads
to accelerated erosion and instability.
An indirect consequence of erosion at a mine site is acid rock drainage. This occurs
when erosion exposes underlying material containing metal sulphides which, when
exposed to air and water, generate acidity as discussed in Chapter Seventeen. Another indi-
rect impact is the reduction of soil fertility in the eroded area. As mentioned in Chapter
Twenty-One, topsoil is a valuable resource. It is this topsoil that is most erodible. Erosion
of course may also destroy any achievement in site rehabilitation.
All slopes at mine sites which
are composed of soil or highly
weathered rock are potentially at
risk of signifi cant erosion.
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