Erosion - Mining and the Environment: From Ore to Metal - page 787

FIGURE 20.6
Diversion should be Used to Divert
Stormwater away from Disturbed Area

● Make sure the diversion discharges
to a stable outlet or channel.
● If practical, seed the diversion
ditches and berms.
● Avoid erosion of the diversion
(Channel grades should be rela-
tively fl at).

Stormwater

Backi lling as soon as feasible minimizes the area of disturbed land at any one time. Once
i nal grade is achieved, areas should be mulched and vegetated as soon as possible.

Controlling Water Entrance
Prior to disturbing land, sites should be carefully studied to: verify existing drainage
patterns and topography; classify runoff from adjacent areas, either as sheet or stream
l ow; and determine the effects of storm runoff. Runoff from undisturbed land should
be diverted away from or around disturbed areas, or directed through the disturbed area.
This can be engineered using berms, diversion ditches, protected channels and pipes
( Figure 20.6 ). It is important that drainage does not collect in new cuts, initiating the
development of gullies.

Runoff from undisturbed land
should be diverted away from
or around disturbed areas, or
directed through the disturbed
area.

Managing Site Drainage and Disturbed Area
Mats, mulches and blankets can be used for temporary stabilization and establishing veg-
etation on disturbed soils. Control blankets can help abate raindrop and sheet erosion
( Figure 20.7 ) . Mats and blankets are typically used on slopes or channels while mulches are
effective in helping to protect the soil surface and foster the growth of vegetation.
Terraces, check dams, tillage and other grading control measures can be utilized to
reduce erosion and to ensure slope stability. Such measures are designed to minimize both
the quantity of l ow and its velocity. Site drainage should be designed to control rill ero-
sion and to prevent the deepening or enlargement of channels, which can eventually lead
to the development of gullies.
Gradient terraces can be used to control slope lengths and slope gradient, and to address
particular erosion problem spots. Terraces are typically Earth embankments or ridge-and-
channel forms constructed along the contour of a slope at regular intervals ( Figure 20.8 ).
Terraces should be designed with adequate outlets, such as grassed waterways or vegetated
areas, to direct runoff to a point where it will not cause additional erosion. Disturbed areas
should be reclaimed to an appropriate grade to achieve long-term stability. Although the
natural topography of surrounding areas can help determine achievable slopes, construc-
tion and mining activities can modify the engineering properties and the behaviour of
Earth materials (for example, soil strength properties and permeability can change). Slope
design should be conducted by a qualii ed geotechnical engineer. All i nal grading should
be completed along contours.

Terraces should be designed
with adequate outlets to direct
runoff to a point where it will
not cause additional erosion.