6.9 Entrance Modifications

The Manning River ECMP Planning Area commences 2 km up-river of AHD and is a wholeof-catchment program primarily concerned with the impact of land on water. The CMP for Old BarManning Point, which addresses coastal processes will consider the issue of entrance modifications. There will be integration and consistency between the two programs. At the river entrances, a single breakwater/training wall at the northern entrance at Harrington has created a permanent ocean entrance while Farquhar Inlet is mechanically opened to the ocean when flood trigger levels are reached.52 Entrance modification has been included in the issues analysis for both the Manning River ECMP and Old Bar-Manning Point CMP as modifications of the entrance to the Manning River may impact on both coastal and estuary processes. In March 2020, the Minister for Transport and Roads, together with the Member for Myall Lakes, announced the establishment of the Manning River Taskforce to consider options for providing a permanent entrance to the Manning River. MidCoast Council was a stakeholder to the Taskforce.

In November 2020, following its deliberation, the Taskforce released its report investigating options to improve safety and navigability of the Manning River entrance (Transport for NSW 2020). The following context is quoted from the report. “The objective of the Taskforce was to build on a previous study (Manly Hydraulics Laboratory 2018) by providing expert advice to the NSW government about the expected economic benefits that could be generated by a permanent entrance to the Manning River at Harrington, the optimal engineering solution and consideration of how such a proposal could be designed and delivered in the context of the requirements of the Coastal Management Act 2016. The Task Force was also to consider implications for potential improvements at the southern entrance of the river at Farquhar Inlet.” “The Taskforce was comprised of experts in coastal engineering, maritime infrastructure, coastal management and maritime industry, and was chaired by Transport for NSW - Maritime. The first two options considered were 1) Status Quo/ Do Nothing and 2) Routine Dredging which was described as similar to the status quo.” “The report then considered option 3) The Southern Entrance Breakwater option consisting of the construction of a southern breakwater to stabilise the entrance between that breakwater and the existing northern breakwater. That is the option which has been generally in the past supported by those seeking to improve safety and navigability of the Manning River Entrance – which is what the Taskforce was set up to investigate.” “Finally, the report considered another solution 4 the Manning Point Twin Breakwaters. This would involve the creation of a new opening at the narrowest point of the Mitchell Island sand spit. The report suggested that this would be considerably cheaper than option 3.” “The MidCoast Council has resolved to support the Expert Taskforce and its processes. As indicated in recommendation 1 set out above, before any proposal can proceed to a Final Business Case a more rigorous engineering, constructability and environmental Impact statement will be undertaken.” The Taskforce report concluded with two recommendations.

Recommendation 1 was for Transport for NSW to enter the proposed Manning River Entrance Project into the Infrastructure NSW Investor Assurance and NSW Treasury business case process. The development of a Strategic Business Case (SBC) is required to further analyse the optimal engineering outcome, the broader impacts of intervention in the area, and the relative costs and benefits of the identified options. If the benefits are found to outweigh the costs of the project, a more rigorous engineering, constructability, and environmental impact assessment should be undertaken in a Final Business Case prior to a decision to invest in a permanent solution.

52: Parsons, 2010 53: NSW Marine Estate Threat and Risk Assessment Report, BMT WBM, August 2017 54: NSW Marine Estate Management Authority, July 2018 55 (Nielsen & Gordon, 2008)

Recommendation 2 provided for an extensive

stakeholder consultation process that includes the local community and impacted industries and stakeholders as well as consideration of progress in the development of Mid-Coast Council’s two CMPs. These recommendations have been added as Management Actions in the Manning River ECMP (MA_2.05 and MA_2.06) to assist with integration between the proposed Entrance Project and the ECMP.

Modified entrances are still influenced by

tides, waves, currents, sediment movement and freshwater flooding. Entrance modifications may cause significant changes to coastal and estuarine processes and require detailed environmental impact assessment.

Estuary entrance modification was rated as

the top priority threat to the environment for the Northern region of NSW in an evidence-based Threat and Risk Assessment completed for the Marine Estate Management Authority.53 Estuarine entrance modification and associated works were listed as the highest threat to species protected under NSW legislation.54 In other locations where the entrances to estuaries have been trained, scientific evidence has demonstrated significant environmental impacts such as: • Increased tidal ranges, increased inundation of floodplains, stormwater infrastructure, coastal wetlands, reduction in estuarine habitats, species and exposure of ASS • Scouring of riverbanks and channels,55 changes

to siltation and shoaling patterns • Exacerbated down drift beach erosion • Loss of breeding grounds for migratory birds and significant alteration of aquatic flora and fauna assemblages around the entrance and within the estuary. The Manning River estuary has unique characteristics which will be considered in detail as part of any Environmental Risk Assessment associated with the proposed entrance modifications. Stakeholders include: Transport for NSW; Manning River Action Group; DPIE; MCC; Oyster farmers; recreation users; tourism industries; landowners. Related issues: coastal wetlands, floodplain drainage and ASS, biodiversity loss.

Photo: Red neck avocet, Karen Bettink