Riversdale River Barging Project: Environmental Impact Assessment
SEDIMENT DYNAMICS AT THE RIVER MOUTH
Specialist Support
Cape Town
1059
PRDW were appointed by Environmental Resources Management (ERM) to assess the
impacts of the proposed Riversdale River Barging Project on: Sediment dynamics and saline
intrusion at the mouth of the Zambezi due to dredging and the impacts of coal spillage at the
mouth and offshore.
Environmental Resources Management
Chine
Zambezi River
Mozambique
2010
Proposed River Mouth Dredging Options and Critical Flow Area
Calculated Longshore Sediment Transport
A desktop assessment supported by limited
numerical modelling was used to determine the
potential impacts of the project on: saline
intrusion into the estuary, shoreline erosion
due to interruption of the longshore sediment
transport due to dredging of the bar at the
mouth of the river, impact of dredge plumes
and the fate of accidental deposition of coal
particles.
The influence of increase in the water depth of
the sand bar due to dredging of the channel
was found to be minor. The increased area of
the critical flow cross section after dredging is
seen to be small (2%) when compared against
the existing baseline critical flow cross section.
A longshore sediment transport model was
used to assess the impact of the increased
entrance depth on sediment transport. It was
shown, that with mitigation, the impact will be
minor when compared to the existing longterm
accretion. This was assessed during the baseline
studies
using
georeferenced
aerial
photographs.
Assessment of Sediment Transport at the Mouth from Aerial Photographs
Cape Town, South Africa | Santiago, Chile | Perth, Australia | Seattle, USA
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