WetlandCare Australia -Projects Archive
Passage to the sea - Fish flow restored at Clarence River's Shallow Channel
After 80 years of being alienated from marine and estuarine waters, Shallow Channel in the lower Clarence River Estuary, NSW, has been reunited with tidal flows.
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. Endangered ecological communities are also present, such as saltmarsh and subtropical coastal floodplain forest.
In the 1920s, in order to provide better access to Yamba in northern NSW, local residents built Shallow Channel Causeway from logs and earth (called a "corduroy" for obvious reasons). In the '60s a modern road was constructed over the current causeway but no provisions were made for water flows.
Shallow Channel is one of several channels which provide connections from the Clarence River to Lake Wooloweyah, a 24 square kilometre tidal lagoon which is a significant nursery for fish, crab and prawn species. Shallow Channel is about 1.5km long and links Oyster Channel to Romiaka Channel. With flows from Oyster Channel blocked by the causeway for decades, Shallow Channel has suffered from reduced tidal exchange. It has received only limited 'blind end' back flows from the small and distant Romiaka Channel.
Shallow Channel has suffered from significantly reduced tidal exchange for 80 years. This has led to sediment and nutrient build-up, algal blooms and raised water temperatures, which impact negatively on aquatic habitat. The causeway also acted as a total barrier to fish passage, isolating the significant fish nurseries and sea grass beds in the channel from the main estuary.
Restoring tidal flow-through in Shallow Channel has long been identified as vital to improving ecological processes in the lower Clarence estuary. Recreational fishers in particular had expressed their concern about the poor water quality and fish habitat, and rarely fished the area despite its accessible location.
In 2008, a $420,000 double-celled box culvert was constructed at Shallow Channel Causeway. It was initially facilitated by WetlandCare Australia, with funds contributed by: the Recreational Fishing Community Grants Program; Clarence Valley Council, NSW Department of Primary Industries' 'Bringing Back the Fish' program; and Northern Rivers Catchment Management Authority. Installation of the culvert was managed by Clarence Valley Council.
Photo: The new culvert in Shallow Channel causeway.
The completed culvert has dramatically improved connectivity between Shallow Channel and Oyster Channel for tidal flows and fish passage. The once permanently-submerged sandbars and mudflats in Shallow Channel are now exposed at low tide and wading birds have returned. Over time, sediment will be mobilised and the channel structure reinstated. Nutrient and dissolved oxygen levels should soon return to normal, and temperature extremes over most of the area will be a thing of the past. This will relieve the previous stresses on sea grass beds and other important aquatic habitats, and vastly improve the overall ecological health of Shallow Channel.
Fish passage has also greatly improved, with recreational fishers now regularly joining the active pelicans in Shallow Channel. Numerous fish species including whiting, flathead, yellow-finned bream, eel and mullet will benefit from the improved fish passage and habitat at Shallow Channel. The value of the area as a food resource for resident and migratory shore birds such as pelicans, oystercatchers, terns, egrets, sandpipers and spoonbills has also increased.
WetlandCare Australia collected baseline habitat health data from sites near Shallow Channel Causeway using the recently developed Wetland Assessment Technique (estuarine modules). Generally these sites were relatively intact but had room for improvement in habitat quality. The assessment will be repeated and the data used to help assess changes in wetland habitat.
The success of this project is due to the excellent co-operation between stakeholders and the pooling of available resources. Over several years, WetlandCare Australia, NSW Department of Primary Industry, and Clarence Valley Landcare have also negotiated and completed additional habitat restoration works with adjoining landowners to further enhance estuarine habitat. Restoration works have included stock control fencing, mangrove regeneration, weed control, erosion control, riparian revegetation and acid sulphate soil remediation.
Photo: Pelicans feeding in Shallow Channel after tidal flows had been restored.