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Gosford and Northern Beaches Lagoons
Water Quality and River Flow Objectives

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• Waterways affected by urban development
• The Gosford Lagoons (Wamberal, Terrigal, Avoca and Cockrone) and their catchments
• Narrabeen Lagoon and catchment
• Dee Why Lagoon and catchment
• Curl Curl and Manly lagoons and their catchments
• Manly Reservoir (within the Manly Lagoon catchment)

This section gives the Water Quality Objectives (WQOs) and the River Flow Objectives (RFOs) for the Gosford and Northern Beaches lagoons catchments, which should be used to develop plans and actions affecting water quality and river health. Only the priority RFOs are listed in this section, but the remaining objectives still need to be considered when developing flow management plans or dealing with particular local river conditions.

Waterways affected by urban development

Waterways affected by urban development that may be substantially modified and carry poor quality stormwater, and with a flow regime that is not natural. Local communities are often keen to see these waterways returned to more natural conditions.

Map: Urban development areas are coloured orange on the map.

The Gosford Lagoons (Wamberal, Terrigal, Avoca and Cockrone) and their catchments

Water Quality Objectives

Protection of:

	Aquatic ecosystems
	Visual amenity
	Secondary contact recreation
	Primary contact recreation, as a short-term objective, within 5 years
	Livestock water supply
	Irrigation water supply

River Flow Objectives

	Protect pools in dry times
	Protect natural low flows
	Maintain wetland and floodplain inundation
	Mimic natural drying in temporary waterways
	Maintain natural flow variability
	Maintain natural rates of change in water levels
	Manage groundwater for ecosystems
	Maintain or rehabilitate estuarine processes and habitats

Supporting Information

• All the lagoons and their catchments are substantially modified by urban impacts, although the Gosford Lagoons (Wamberal, Terrigal, Avoca and Cockrone) have some semi-rural areas. Most of the lagoons have remnant areas of bushland in their catchments, some of which is in national parks or nature reserves.
• Wamberal Lagoon is mostly a nature reserve.
• In some urban waterways aquatic ecosystems are considerably modified. A return to pristine aquatic ecosystems in these areas is unlikely and impractical, however, water quality conditions for existing ecosystems can be improved greatly for the benefit of local species and broader catchment health. Data from other local aquatic ecosystems of similar type, in areas that are not urbanised, may provide achievable criteria for these modified aquatic ecosystems.
• Recreational use of Wamberal and Cockrone lagoons may need to be restricted to maintain their natural values. This may mean limiting access to certain areas or for certain types of recreation.
• It is necessary to protect primary and secondary contact recreation in the lagoons but not in the catchment creeks. Water coming in from the creeks, however, will need to be of sufficient quality to maintain the recreational values of the lagoons.
• There are some limited rural uses in the catchment and protection of water levels at times of low flow may be required.
• Gosford Council has a management plan for the lagoons.

Narrabeen Lagoon and catchment

Water Quality Objectives

Protection of:

	Aquatic ecosystems
	Visual amenity
	Secondary contact recreation
	Primary contact recreation, as a medium-term objective, within 5-10 years
	Aquatic foods (cooked)

River Flow Objectives

	Maintain wetland and floodplain inundation
	Mimic natural drying in temporary waterways (and wetlands)
	Maintain natural flow variability
	Maintain natural rates of change in water levels
	Manage groundwater for ecosystems
	Maintain or rehabilitate estuarine processes and habitats

Supporting Information

• It is necessary to protect primary and secondary contact recreation in the lagoon but not in the catchment creeks. Water coming in from the creeks, however, will need to be of sufficient quality to maintain the recreational values of the lagoon.
• The catchment streams are relatively small streams, and may be highly altered, channelised and have high pollutant levels where they run through urban areas. Flows may have been modified by increased runoff due to hard surfacing of the urban areas. The affected creeks and wetlands will flood to higher levels and may be wetter than natural.

Dee Why Lagoon and catchment

Water Quality Objectives

Protection of:

	Aquatic ecosystems
	Visual amenity
	Secondary contact recreation, as a medium-term objective, within 5-10 years
	Primary contact recreation, as a longer term objective, 10 years or more
	Aquatic foods (cooked), as a longer term objective, 10 years or more

River Flow Objectives

	Maintain wetland and floodplain inundation
	Mimic natural drying in temporary waterways (and wetlands)
	Maintain natural flow variability
	Maintain natural rates of change in water levels
	Manage groundwater for ecosystems
	Maintain or rehabilitate estuarine processes and habitats

Supporting Information

• Swimming (primary contact recreation) is not a desired activity within the Dee Why Wildlife Refuge.
• The catchment streams are relatively small streams, and may be highly altered, channelised and have high pollutant levels where they run through urban areas. Flows may have been modified by increased runoff due to hard surfacing of the urban areas. The affected creeks and wetlands will flood to higher levels and may be wetter than natural.

Curl Curl and Manly lagoons and their catchments

Separate environmental objectives are set for Manly Reservoir-see below.

Water Quality Objectives

Protection of:

	Aquatic ecosystems, as a medium-term objective, within 5-10 years
	Visual amenity, as a medium-term objective, within 5-10 years
	Secondary contact recreation, as a longer term objective, 10 years or more
	Aquatic foods (cooked), as a longer term objective, 10 years or more

River Flow Objectives

	Maintain wetland and floodplain inundation
	Mimic natural drying in temporary waterways (and wetlands)
	Maintain natural flow variability
	Maintain natural rates of change in water levels
	Manage groundwater for ecosystems
	Maintain or rehabilitate estuarine processes and habitats

Supporting information

• The catchment streams are relatively small streams, and may be highly altered, channelised and have high pollutant levels where they run through urban areas. Flows may have been modified by increased runoff due to hard surfacing of the urban areas. The affected creeks and wetlands will flood to higher levels and may be wetter than natural.

Manly Reservoir (within the Manly Lagoon catchment)

Because of the better water quality of Manly Reservoir, compared with waterways further downstream in this catchment, separate environmental objectives and achievement timeframes are set.

Water Quality Objectives

Protection of:

	Aquatic ecosystems, as a medium-term objective, within 5-10 years
	Visual amenity, as a medium-term objective, within 5-10 years
	Secondary contact recreation, as a medium-term objective, within 5-10 years
	Primary contact recreation, as a medium-term objective, within 5-10 years
	Aquatic foods (cooked), as a medium-term objective, within 5-10 years

River Flow Objectives

	Mimic natural drying in temporary waterways (and wetlands)
	Maintain natural flow variability
	Maintain natural rates of change in water levels

Supporting information

• The catchment streams are relatively small streams, and may be highly altered, channelised and with high pollutant levels where they run through urban areas. Flows may have been modified by increased runoff due to hard surfacing of the urban areas. The affected creeks and wetlands will flood to higher levels and may be wetter than natural.

Supporting information for all lagoons

• All the lagoons are opened artificially at times, to prevent flooding of adjacent areas, or to allow flushing of poor quality water.
• All the lagoon beds are underlain by acid sulfate soils and there may be areas of these soils adjacent to the lagoons. Exposure of these soils through drainage or dredging will generate sulfuric acid and toxic metals, causing fish kills and ongoing water quality problems. This means that dredging or development proposals must be comprehensively assessed for their environmental impact, including the impact on fish habitat such as seagrass beds. Care needs to be taken with lagoon opening, as draining to low levels can also expose acid sulfate soils.

This page was published 1 May 2006