Environmental Engineering Reference
In-Depth Information
(a)
(b)
Figure 4.4
(a) A scalded landscape in
semi-arid New South Wales, Australia
(photograph courtesy of Anthony
Ringrose-Voase), and (b) after
implementing water - ponding technology
(photograph courtesy of Ray Thompson.)
Box 4.3 Fixing landscape processes: mulching an eroded slope
A landscape-scale restoration technology commonly
applied around the world is to cover reformed slopes,
such as on rehabilitated mine sites, with coarse, rocky
materials to protect these slopes from erosion, at least
until vegetation establishes to provide cover. In many
cases, these rocky materials fail to adequately protect
slopes, which develop erosion rills (Figure 4.5).
In one such case in semi-arid New South Wales,
Australia, early monitoring revealed that erosion rills
were developing on a rehabilitated tailings dam wall.
A project was undertaken by a student at the Austral-
ian National University to intervene and fi x this problem
before rills eroded into gullies (Summerfi eld 2006). A
series of soil-slaking and dispersion tests was carried
out on slope materials to determine the potential for
further erosion. The soil was found to readily slake,
which means that natural soil aggregates broke down
into micro-aggregates when rapidly immersed in rain-
water. However, dispersion (clay particles in aggre-
gates being released into the water as a cloud) was
minimal. This implied that a protective cover on the
slope would counter the erosive effects of raindrops
and intercept overland fl ows to capture sediments.
A denser cover of rocks might suffi ce, but a self-
replacing organic mulch or plant cover would be far
less expensive, and sustainable. Meadow hay, which
was locally abundant in round bales, was rolled out
across the slope in long lines, and subsequent moni-
toring found that sediment was being effectively
trapped by the hay. Erosion was immediately halted
and germination of seeds in the hay grew into a pro-
tective covering. Prompt monitoring of the initial land-
form confi rmed a simple and inexpensive fi x to the
restoration problem.
