CASE STUDY #6
Restoring fish passage and tidal flows in the Clarence river estuary, Australia.
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.
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
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