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Big Swamp

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Introduction

Introduction

Coralville, New South Wales, Australia

Creating a new standard for large-scale intertidal restorations. Big Swamp is the local name for a series of drained agricultural floodplains located on the Manning River estuary on the mid-north coast of New South Wales, Australia. Historically a large, brackish backswamp known for its abundant bird populations, the Big Swamp floodplain has undergone major hydrologic changes over the past 120 years due to the construction of drainage networks, canals, levees, and floodgates. Unfortunately, the combination of extensive drainage and sulfidic subsoils has acidified the soil and adjacent waters. Following rainfall events, large plumes of acidic water spread through the lower estuary, lowering the pH and creating anoxic conditions toxic to aquatic life. To overcome these issues, the project team, led by MidCoast Council, undertook a detailed study followed by an extensive earthworks program to remediate the site. They filled in over 13 kilometers of canals in the drainage network, established a new tidal wetland ecosystem, enhanced the natural tidal flushing dynamics, and restored over 820 hectares of low-lying land. This nature-based approach has significantly improved water quality and has received multiple awards, including the prestigious Green Globe Award.

Article Cover: Big Swamp wetland has been created using Engineering With Nature principles and highlights the value of large scale projects. (Photo by MidCoast Council)

Producing Efficiencies

Before the project began, the team conducted a major scientific study to prioritize hot spots and inform proposed solutions. This included a novel study that traced the off-site impacts and determined how acidic discharges from the Big Swamp floodplain impacted other ecosystems, such as oyster reefs. The resulting data showed the team how to best optimize inundation on the floodplain. The final works included drain infilling, levee decommissioning, and the design of a new river channel to encourage tidal inundation and flushing, providing freshwater retention and flood mitigation.

Using Natural Processes

The Big Swamp Restoration Project restored the natural cycle of tidal flushing by constructing a new tidal river channel to encourage inundation of over 250 hectares. This innovative technique ensures that buffering agents inherent in seawater naturally spread across the acidic floodplain with every tide, neutralizing the acid and soil contaminants through regular chemical processes. This approach encourages the development of an organic soil horizon, fostering the growth of a salt marsh ecosystem—an endangered ecosystem type in Australia—and quickly improving the water quality.

Below (top to bottom): The project has mapped the recovery of the site from a bare landscape lacking vegetation to an increasingly lush tidal wetland with high rates of blue carbon accumulation. (Photo by MidCoast Council)

Broadening Benefits

The Big Swamp restoration fits into a larger area of restored wetlands, serving as an educational case study in using natural processes to improve water quality and to mitigate floods. The project was also the first in Australia to include a detailed cost-benefit analysis of the social, environmental, and economic benefits of the current land uses versus alternatives, including wetland creation. This assessment provided a distributional analysis of the wetland restoration’s benefits, ensuring an equitable sharing of the positive outcomes, and proving that large-scale intertidal restorations need not rely on a trial-anderror approach.

Before image of major on-ground engineering works to create tidal infrastructure that uses natural inundation patterns to improve water quality.
(Photo by MidCoast Council)
After image of major on-ground engineering works to create tidal infrastructure that uses natural inundation patterns to improve water quality. 
(Photo by MidCoast Council)

Promoting Collaboration

This restoration provides an excellent example of multidisciplinary collaboration. The project was led by local government (MidCoast Council) with funding support from state (New South Wales Fisheries) and federal agencies. Researchers at the University of New South Wales’ Water Research Laboratory drove the technical components; and nonprofit groups, including Wetland International, supported community engagement. The project was ultimately successful due to the local stakeholders, landowners, and the oyster industry who invested resources into the project’s implementation. Importantly, the local council, who has assumed ownership of the property, now serves as its steward and continues to adaptively manage the site.

Intertidal mangroves and salt marsh are thriving on-site post wetland creation.
(Photo by MidCoast Council)
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