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Sand Mining Restoration on the Swan Coastal Plain using Topsoil – Learning from Monitoring of Previous Rehabilitation Attempts

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Author E J B van Etten, C D McCullough and M A Lund

Description

This paper reports on the results of several years of monitoring
rehabilitation at a silica sand mine on the Swan Coastal Plain, south of Perth.
Mining here occurs below the regional watertable and leaves a post-mine
landscape of dredge pond voids (pit lakes) with surrounding battered slopes. The
restoration we recommended was to develop the pit lakes as wetlands of regional
analogue and value. Several different restoration techniques have been applied
to re-vegetate pit lake slopes over many years which have enabled an evaluation
of reasons for success/failure of different restoration approaches. Learning
acquired clearly showed the benefits of using fresh topsoil for restoration over
topsoil that has been stockpiled for several years. Most topsoil used in
restoration was from seasonal wetlands and consequently restoration was most
successful in the riparian zone from the edge of pit lakes to about 2 m
vertically above the water table. Topsoil restored areas above this level
remained poor in plant species and cover. Conversely, remedial seeding/planting
proved largely unsuccessful. Permanently and seasonally flooded pit lake margins
recolonised relatively quickly and successfully with native sedges and rushes.
Development of rehabilitated upper slope plant communities over time was evident
with loss of typical wetland species and greater growth and survivorship of
upland and dampland plant species on mid to upper rehabilitated slopes. Plant
communities of lower slopes showed a converse pattern of development, with a
shift towards a more typical wetland composition. We believe matching topsoil to
site and development of topographic profiles similar to natural wetlands of the
region are the keys to optimising restoration success of sand mines with shallow
water tables.


FORMAL CITATION:
van Etten, E J B, McCullough, C D and Lund, M A, 2011. Sand mining restoration on the swan coastal plain using topsoil –
learning from monitoring of previous rehabilitation attempts, in Proceedings
Eighth
International Heavy Minerals Conference 2011
,
pp

323-338
(The
Australasian Institute of Mining and Metallurgy: Melbourne).