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14. Implement catchment management actions for urbanised tributaries as outlined in the Stormwater Management Plan to control turbidity and sediment wash-off

Some of the actions recommended in the Pittwater Stormwater Management Plan (PSMP) (PBP, 1999) address erosion and turbidity generation in the estuary, particularly due to areas of unvegetated, exposed ground surface and unsealed roads (especially on Scotland Island). This option involves ensuring such recommended actions, plus the Scotland Island Erosion and Sediment Control Plan (Witheridge 2004) are adequately incorporated into the Pittwater Integrated Water Cycle Management Plan and implemented as priority actions. Work by Council and the community to address erosion and sediment problems on Scotland Island has commenced.

Responsibility: Council is responsible for incorporating the PSMP into the Pittwater Integrated Water Cycle Management Plan.

15. Carry out major rehabilitation in areas of degraded creeklines and tributaries, or at least riparian plantings to shade the creek / drain and prevent super-heating of inflowing water

Many of the natural tributaries draining to Pittwater have been replaced with formalised ‘hydraulically efficient’ channels, culverts and pipes. This has tended to increases velocities within waterways, as evident by erosion at the downstream end of drains and channels. Formalised drains also provide little habitat value and can super-heat the water, particularly during summer.

This option proposes “deformalising” some tributaries by replacing existing concrete lined drains with more natural meandering vegetated channels. Where the ability to do works is limited by space and land ownership issues, or potential flood impacts channels should be revegetated for shade and to prevent water heating as a minimum. Priority locations for creek rehabilitation or enhancement would include:

• Careel Creek (particularly upstream from Barrenjoey Road)
• Mona Vale Main Drain (open drain through light industrial area at Mona Vale)
• Cahill Creek (upstream of Bayview Golf Course)
• Bayview Golf Course channels and watercourses (restoration of environmental flows and habitat enhancement).
• Bayview Golf Course floodgates (investigation of the operation and impacts of Pittwater Road floodgates on flooding, water quality and fish movement).

Responsibility: This option would be implemented by Council (in co-operation with private property owners as necessary) although assistance / approvals should be sought from HNCMA and DECC.

16. Review and ensure compliance with Council regulations regarding sediment and erosion control on building sites in the catchment

This option involves reviewing current sediment and erosion control requirements for new urban developments. If the requirements do not reflect current best practice, the requirements shall be amended to ensure that all possible action is taken to reduce sediment loads to the estuary. Second, this option involves auditing to ensure sediment and erosion control requirements and all related conditions of consent for developments are adhered to by builders and developers.

Responsibility: Council compliance officers and approvals staff will perform assessment and policing/enforcement of this option.

17. As necessary, remediate areas that experience erosion, ensuring that the process will not continue to cause problems in the future

The 26 areas of foreshore erosion identified in the Pittwater EPS should be remediated. Preference should be given to soft-engineering for remediation works, such as shoreline re-grading and revegetation and modifying the erosion mechanism, rather than construction of additional rock walls around the foreshore. Detailed investigation of bank erosion mechanisms and remediation options (as at Rowland Reserve) for each site would need to be conducted prior to implementing works.

Responsibility: Investigations and remediation works would be carried out by Council, ith the assistance of DECC, plus property owners if on private land.