Council has dredged The Entrance channel when needed since 1993. Dredging the channel assists in:
- maintaining an exchange of water between the Tuggerah Lakes estuary and the ocean
- preserving the existing ecological values of the Tuggerah Lakes estuary
- reducing flood risks to life and property in low-lying areas around the Tuggerah Lakes estuary
- providing sand nourishment aiding in erosion and coastal protection of the North Entrance and Entrance beaches
- enhancing navigation within the channel.
How often is dredging conducted?
Dredging is only undertaken when one or more of the following triggers are reached:
- the throat of the channel (near the southern tip of the sand spit) at The Entrance reduces to an estimated width of less than 15m measured at mid tide level
- the flood tide sand shoals threaten to block the ebb tide dominant channel along the northern/eastern side of the entrance area and/or
- the flood tide shoals threaten to block the main channel east of the bridge.
This means dredging is not required every year. This measure is a result of recommended actions from the Tuggerah Lakes Estuary Management Plan to ensure that the program is run only when it is required which takes subjectivity out of the decision making process, makes the process more transparent and saves rate payers money by not undertaking unnecessary works. Not all triggers necessarily have to be met to trigger the program.
Dredging program 2020-21
The 2020 dredging program began in April 2020, with Council repairing eroded sections of the southern foreshore and closing the southern channel using earthmoving equipment.
The second phase began in September 2020, using a cutter-suction dredge to remove 30,000 cubic metres of sand from the channel, in accordance with the EPA licence and other environmental constrains. This stage will be conducted in two stages.
To dredge, Council has obtained the necessary approvals from the State Government to ensure the operations are undertaken in the most environmentally friendly manner and that measures are put in place to prevent environmental harm.
Council has been working with coastal experts Royal HaskoningDHV to develop a program that meets the NSW EPA’s licencing requirements. Earlier this year Council undertook ground level surveys of the channel and the surrounding beaches, including a hydrographic survey of the channel bed and an aerial survey of the sand spit and coastline using drone and LiDAR technology.
These surveys provide an understanding of where Council needs to focus dredging efforts, which parts of the beach require nourishment (replacement of lost sand) as well as supporting the completion of necessary regulatory and licencing requirements.
The updated licence requirements require Council to tightly monitor, manage and test water quality, in particular total suspended solids (a measure of water clarity), at the discharge locations. To manage this, the dredged sand will be pumped to an area inside the channel near Karagi reserve where it will be ‘dewatered’ - this is a process by which the water is allowed to drain from the sand and filter back into the channel, leaving the sand behind.
A floating silt curtain protects the surrounding waters within the channel by containing any silt within the dewatering area.
The dewatered sand will be loaded into dump trucks using large excavators and transported to designated beach nourishment locations.
Initial sand nourishment will focus on the North Entrance Beach and will be delivered via Karagi foreshore and a beach access track in the Karagi Reserve carpark which was also used to address recent beach erosion.
In stage two, sand will be pumped to an area along the estuary eastern beach to reinstate foreshore access and stabilise the steep erosion escarpment.
With increased numbers of heavy machinery moving around on the beaches, we remind the community to take extra care.
Our dredging plan also takes into consideration the annual arrival of the Little terns (Sternula albifrons) and we are taking measures to mitigate any impact on them while dredging is taking place. We will continue to monitor the area and will seek further advice when the terns arrive.
A site compound is in place at Karagi Reserve, as such Karagi Reserve carpark will remain closed for the duration of the dredging program.
The dredging program is jointly funded by Central Coast Council and the NSW Government through the Rescuing Our Waterways fund.
Dredging for The Entrance Channel is now complete for 2020 - https://www.centralcoast.nsw.gov.au/council/news/media-releases/dredging-entrance-wraps-year - with Council using two dredges simulataneoulsy to finish the dredging earlier than expected.
Recently, Council conducted a hydrographic survey at The Entrance Channel to estimate the change of seabed due to the major flood event in March 2021. The survey results shown that a total amount of approximately 124,000 cubic metres of sand has been removed from the channel. The volume change are calculated against data surveyed in November 2020 after a dredging campaign. From 18 March to 23 March 2021, Central Coast experienced a widespread flooding as a result of heavy rain continuously for 6 days across the region.
Water quality monitoring
A condition of the licence is also to monitor water quality during dredging activities to ensure there is no negative impact on the environment. To do this Council monitors pH and Total Suspended Solids (TSS) during dredging activities.
The pH scale is used to measure the acidity of a solution on a scale of 0-14. Dredging can affect pH when Acid Sulfate Soils (ASS) are disturbed and exposed to air. ASS is the common name given to soils and sediments containing iron sulfides. When exposed to air, these soils can produce sulfuric acid which can be harmful to plants and animals. Water samples collected during dredging activities should generally have a pH level of between 6.5 and 8.5. The pH levels in Tuggerah Lakes vary daily and seasonally.
TSS consists of organic and inorganic solid materials that are carried in suspension within the water column. These particles can include silt, sand, microalgae and industrial waste. A high concentration of TSS can reduce water quality. Dredging consists of transporting and depositing silt and sand sediments. TSS is therefore an expected component of undertaking these activities. Water samples collected during dredging activities should generally have a TSS level of below 50mg/L.
Other factors that may alter pH and TSS levels include:
- time of day
- water temperature
- amount of algal or plant growth in the water
- discharges of industrial wastes
- atmospheric deposition (acid rain, dry particle deposition)
- burning of fossil fuels by cars, factories and smelters.
Water Quality Tolerance Table: Environmental Protection Licence 3200.
|Total Suspended Solids (TSS)||Grab||50mg/L|
Conditions of EPL3200:
- sampling at any point 50 metres from the dredge in operation
- sampling is to be undertaken between one hour and 6 hours of the dredge commencing operations
The impacts of building a breakwall or twin breakwalls at The Entrance has been investigated by numerous coastal engineers over the past decades. The most recent study commissioned by the NSW State Government’s Office of Environment and Heritage found that all breakwall options considered within their study did not self-scour (except under extreme flood conditions) meaning that maintenance dredging, such as the current program, would still be required to maintain an open channel with the ocean.
Construction of any breakwall/training wall at The Entrance Channel will therefore not replace the need to dredge, the dredging program would still need to be undertaken to maintain an exchange of water between the estuary and the ocean. The studies additionally found that the construction of a breakwall would provide no added benefit to the lake in terms of flushing or improving water quality in the lake.
Council dredges The Entrance channel to the Tuggerah Lakes estuary to maintain exchange between the estuary and the ocean. This may offer some benefit:
- to preserve the existing ecological values of the estuary
- to reduce flood risks to life and property in low-lying areas around the estuary
- to enhance navigation within The Entrance Channel
Central Coast Council holds an Environmental Protection Licence (EPL) No. 3200 with the EPA for dredging of the Entrance Channel.
A Prevention Notice (Number 1598442) was issued by the EPA to Council in November 2018 for causing ‘water pollution’ by disposing of dredge spoil directly into the surf zone of North Entrance Beach. This was standard practice for surplus dredge spoil when North Entrance was fully nourished to capacity.
On 7 August 2020, the EPA revoked the Prevention Notice after variations to EPL3200 were approved.
Dredging is only undertaken when a set of indicators are reached, which is why dredging is not required every year. This measure saves rate payers money by not undertaking unnecessary works and ensures an exchange of water is maintained between the estuary and the ocean.
The indicators include:
- The throat of the channel (near the southern tip of the sand spit) at The Entrance reduces to an estimated width of less than 15m measured at mid tide level. Estimating this measurement has been assisted by the CoastalComms camera installed to monitor The Entrance.
- The flood tide sand shoals threaten to block the ebb tide dominant channel along the northern/eastern side of The Entrance area.
- The flood tide sand shoals threaten to block the main channel east of the bridge.
The channel would go through a cycle of closing and opening. This is a completely normal process. It may cause the ecology of the estuary to experience some change. It is understood in the event of a major flood event the channel would overtop/ self-scour and open anyway to let the flood waters out naturally.
Dredging is undertaken during the autumn and winter months for a number of environmental and social reasons:
- The threatened birds species the Little Tern (Sterna albifrons) is known to breed on The Entrance sand spit and feed within the entrance channel during the spring-summer months
- Commercial fishers have indicated their preference for the dredging to not be undertaken during the prawning season which generally ends by March
- For aesthetic and safety reasons’ dredging is not undertaken during the peak tourist season in the area which coincides with the December (summer) school holidays.
If feasible, the dredged sand is used to beneficially renourish areas that have been determined via conducting land, hydrographic, drone/aerial and visual surveys. The use of dredged sand for renourishment has three main aims:
- to provide maximum environmental benefit to the dune system by protecting the dunes and the ecosystems reliant on them
- to protect assets and the recreational amenity of the beach for the community
- to keep the sand circulating within the complex entrance system to prevent a loss of sand over time. This is necessary to maintain the sand spit, The Entrance sand bar and flood tide shoals that are the natural control on lake levels and provide protection of the estuary from ocean storms.
Therefore, the sand is pumped onto the northern shore of The Entrance Channel with the aim of nourishment of the beach, dunes and offshore shoals for coastal erosion protection measures. The exact location of sand placement is determined year to year based on the current environmental conditions and competing demands.
Sand may also be pumped to The Entrance beach to cover exposed rock shelves that exist in the wash zone which pose a safety risk to the public and have resulted in previous beach closure. Some sand may be placed in front of Dunleith Tourist Park and Karagi car park to replenish the shoreline at this location.
Dredging is not permitted for other purposes such as commercial gain from sale of the extracted sand.
To undertake dredging Council must gain the necessary approvals from the NSW Government to ensure the operations are undertaken in the most environmentally friendly manner and that measures are put in place to prevent environmental harm. These approvals include a licence under the Protection of the Environment Operations Act 1997 (POEO Act). One of the conditions of the licence is to monitor water quality during dredging activities to ensure there is no negative impact on the environment.
Council has also prepared a range of documentation to support the dredging campaign including the Review of Environmental Factors (REF), Pollution Incident Response Management Plan (PIRP) and Construction Environmental Management Plan (CEMP), as well as obtained a Crown Licence (#3683371) and Fisheries Permit (PN19/110).
Central Coast Council dredges The Entrance Channel, on behalf of the NSW Government on average every two to three years.
The most recent programs were in 2018 and 2015.
The 2020 dredging campaign will take around two and a half months to complete, commencing in mid-September and concluding end of November 2020, and will depend on factors including weather conditions and the arrival of the Little Tern.
Yes, before our most recent Review of Environmental Factors (REF) was renewed in 2009 dredging was undertaken on average every 12 months.
The conditions set out in the REF have resulted in a change in the way dredging is conducted and thus a longer time between dredging programs. The change in frequency is balanced by an increase in the time spent dredging on each occasion.
Dredging is permitted on the western side within the approved footprint area detailed in the Review of Environmental Factors (REF). Primarily dredging is conducted on the east side of the bridge as it aims at extracting or trapping shifting sand shoals prior to them entering the estuary west of the bridge.
Council dredges for reasons outlined in its REF and in compliance with its dredging licences.
The Crown Land Licence does not permit dredging to be conducted within 10m of any wharf/jetty or pile or within 15m of any bridge or submarine crossing.
Council does not dredge for navigation; this is the responsibility of the NSW Roads and Maritime Services.
Dredged sand may be placed on the beach on occasions, in such a way to try and avoid large piles of sand from accumulating. Council aims to ensure the beach resembles a natural slope at the end of each program. If required, bulldozers or other heavy machinery are be used to reshape the beach.