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Lake Cathie Management

Lake Cathie waterways

Lake Cathie is an area of high conservation value and serves a variety of users, from water birds to recreational boaters and swimmers. A 'balanced' opening strategy facilitates the decision making process with respect to opening Lake Cathie to the ocean and is vital to accommodate the conflicting environmental and social constraints on the lake. This will ensure minimal adverse impact on the ecology of the area, minimise build up of silts and sands and flooding, while providing residents and visitors opportunities for recreational activities.

Opening Lake Cathie

Council opens the Lake when conditions prescribed in the strategy are prevalent, for example, the lake height reaches 1.6m AHD or greater, there is poor water quality or when high lake levels threaten breeding cycles of critical habitat. Artificial openings have occurred on average once every 12 months. (An Artificial opening is when Council dredges the sand between the lake and the ocean with an excavator.)

 Brochure on the Lake Cathie Opening Strategy1024KB pdf(PDF, 1024KB)

Lake Cathie Water Level

The link below provides the water level data for Lake Cathie, taken from automatic recording equipment. The water level is monitored by Council.

Lake Cathie Coastal Zone Management Plan

The coastline around Lake Cathie is particularly exposed to coastal processes that threaten private and public assets. Coastal erosion has occurred south of the Lake Cathie entrance and has led to exposure of coffee rock that underlie the dune system. Coffee rock is formed by the process of induration - which is the hardening of soft sand. This coastal erosion is likely to increase over time under current predictions for climate change and the projected sea level rise. Lake Cathie has been identified as one of fifteen (15) coastal erosion “Hotspots” along the NSW coast by the Office of Environment & Heritage (OEH)

The  Coastal Zone Management Plan (CZMP) process for Lake Cathie3MB pdf(PDF, 3MB) came about after the following studies were undertaken.

  1. The Lake Cathie Coastal Hazard Study - completed in 2008 and later revised in 2010 to take into account the introduction of the NSW Government’s sea level rise planning benchmarks (NSW Sea Level Rise Policy, 2009).
  2. The Lake Cathie Coastline Management Study - Stage 1 - completed in 2009 provides a preliminary assessment of 13 potential options to address coastal hazards for this area.
  3. The Lake Cathie Coastline Management Study - Stage 2 - completed in 2012. This report identified the need for Council to address Coastal Management options and the following 4 options were assessed in more detail and included in community consultations.
    1. 400m Revetment protection for Illaroo Road
    2. Groyne
    3. Beach Nourishment
    4. Planned retreat including acquisition/voluntary purchase

Community consultation concluded with an overwhelming support for a revetment wall with beach nourishment.

The Lake Cathie CZMP incorporates a revetment and beach nourishment as the management option in particular for Illaroo Road and will guide the management of the Lake Cathie foreshore into the future to ensure the most beneficial outcome for local residents, the community and the environment.

Please note: It is noted that under Section 55G of the Coastal Protection Act 1979 the CZMP requires certification from the minister. In a letter dated March 2015 the Minister for the Environment requested a number of actions be undertaken before the CZMP would be certified. As such, Council has completed these actions and additional information has been incorporated into the Lake Cathie CZMP including the results of a social and economic assessment of coastal protection options, which supports Council’s preferred option of a revetment as the main long-term management option in the CZMP.

The revised CZMP was adopted by Council in April 2016 and was certified by the Minister for Planning on 1st November 2016.  The CZMP was published in the NSW Government Gazette on 27th January 2017.

Lake Cathie Study Area

Lake Cathie / Lake Innes Coastal Model Development and Investigation

Background Information: why Council conducted these studies

As part of the design works for the revetment wall a Geotechnical Investigation was commissioned by Council. The Geotechnical Investigation project was undertaken by an independent company, Regional Geotechnical Solutions, and included testing to confirm the geological profile and the extent of Coffee rock and other material that may impact on the rate of erosion and the size of the area that is under threat of erosion within the next 100 years.

Due to some concerns from the Lake Cathie community a review of the original Lake Cathie Coastal Hazard Study was done to determine whether the erosion hazard was accurate. The review, undertaken by Cardno Pty Ltd did not recommend any change to the existing coastal hazard planning projections.

Lake Cathie / Lake Innes Estuary Hydrodynamic Model

Over the years, the Lake Cathie/Lake Innes Estuary has been the subject of numerous environmental investigations that deal with estuarine and catchment processes such as increased sediment and nutrient loads, sediment transport and tidal flushing, increased tidal constriction and bed scour. In August 2005 Port Macquarie Hastings Council resolved to undertake a detailed modelling study to investigate potential management options and improvement works for the Estuary.

This report documents the development of a coastal hydrodynamic model for the Estuary and assesses four possible management options, including widening of Kenwood Drive Bridge, changes to the lake opening strategy, isolating Lake Innes and channel dredging upstream of Ocean Drive Bridge.

The study also discusses the possible ecological threats and impacts that may occur under changed tidal hydrodynamics, water quality and sediment transport conditions following implementation of identified management options.

The Port Macquarie-Hastings Coasts & Estuaries Management Sub-Committee met to discuss the results of the study and recommended that Council adopt the findings of the report. Accordingly, Council resolved to adopt the findings of the report which contained the following management measures:

a) Kenwood Drive bridge That Kenwood Drive bridge be widened as part of any future asset upgrade or replacement works.

b) Lake Cathie opening strategy That the current opening level of 1.6m Australian Height Datum (AHD) remain unchanged.

c) Isolation of Lake Innes from Lake Cathie That the hydrodynamic model be made available to the NSW Office of Environment & Heritage (OEH), or others, for use in any further investigation of the reversion of Lake Innes to freshwater.

d) Dredging of tidal flushing channels That no dredging works be undertaken between Ocean Drive Bridge and Kenwood Drive bridge. That dredging works be limited to removal of sediment from the entrance downstream of Ocean Drive bridge.

  Lake Cathie Lake Innes Estuary Hydrodynamic Model Development Investigation26MB pdf(PDF, 26MB)

This page was last updated on: 28 November 2017