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After decades of being alienated from marine and estuarine wa-
ters, Shallow Channel in the lower Clarence river estuary, on the
east coast of Australia, has been reunited with tidal flows. Im-
portant seagrass beds and fish nursery areas in Shallow Channel
have been isolated from the main tidal habitats in Clarence river
estuary for over 80 years. The Clarence river estuary is one of
the largest deltas on Australia’s east coast and is noted for its
rich aquatic and migratory bird life. It is also home to numerous
threatened species including the black necked stork, mangrove
honeyeater, osprey and the black flying fox. It contains endan-
gered ecological communities such as saltmarsh and subtropical
coastal floodplain forest and is listed on the Directory of Impor-
tant Wetlands in Australia.
Restoring fish passage and tidal flows in the Clarence river
estuary, Australia.
The Shallow Channel causeway, in northern New South Wales,
was first constructed in the 1920s from logs. In the 1960s the
causeway was rebuilt as a modern road, but with no provision
to allow water to flow under the road. As a result of the blockage
of tidal flows sediments and nutrients began to build-up. This
caused algal blooms and raised temperatures in the still, shal-
low water, resulting in algal bleaching and death of the seagrass
beds. The causeway acted as a total barrier to fish passage, iso-
lating the remaining (dwindling) fish populations from the main
estuary.
Re-establishing tidal flow-through and fish passage at Shallow
Channel causeway had long been identified as a major factor to
CASE STUDY #6