Lake Opening — Recent and Historical
Smiths Lake is what scientists classify as an intermittently closed and open lake (ICOLL) — a coastal lagoon that is predominantly closed to the ocean, but periodically opened, either naturally or mechanically, to manage water levels and maintain the health of the estuary.
How the lake works
When closed to the ocean, the main sources of water flowing into the lake are rainfall and a network of small creeks draining the surrounding catchment — including Wamwarra Creek, Bramble's Creek and Tarbuck Creek. The lake has a relatively small catchment area of 28 square kilometres, approximately three-quarters of which remains forested within Wallingat National Park, Wallingat State Forest and Myall Lakes National Park.
When open to the ocean, the lake is subject to ocean tides, swell and currents. The entrance opens naturally in response to rising water levels, and closes again as sand is redistributed by waves, tides and wind. When the entrance is mechanically opened, water can exit the lake with considerable force, creating strong currents and temporarily dangerous conditions at Sandbar Beach.
Mechanical openings
Smiths Lake has been manually opened to the ocean periodically since 1932, to prevent inundation of low-lying properties around the lake's foreshore and to improve water quality within the estuary. Initial opened by local fishermen, mechanical opening is now carried out by MidCoast Council using earthmoving equipment to cut a trench from the lake through the sandbar to the ocean.
MidCoast Council's policy is to open the lake when the water level reaches a trigger height of 2.1 metres above sea level — or earlier if a significant rainfall event is forecast. The timing of any opening is carefully planned to coincide with low tide, maximising the scouring effect and the health benefits to the estuary. Before any opening, council consults with key stakeholders, including local fishers, as the opening also plays an important role in enabling marine fish species to migrate for spawning.
During an opening, boat access to the lake is restricted and public access to Sandbar Beach is limited for safety reasons.
Monitoring and data
Lake levels are continuously monitored by Manly Hydraulics Laboratory (MHL) on behalf of the NSW Government. Current and historical water level records — including the dates and levels of past openings — are publicly available online.
Current water level data — https://mhl.nsw.gov.au/Site-209465
The Coastal Zone Management Plan for Smiths Lake Estuary, prepared under the NSW Government's estuary management framework and adopted by council in 2001, sets out the strategic management actions for the lake, including the trigger heights for opening, environmental objectives and catchment management priorities. The plan was updated in August 2018.
We are currently seeking arrangements to link the Tarbuck Bay lake level monitoring site, to the Villagefirst website, to provide live feeds updating a table of information similiar to the following.
Coastal Zone Management Plan for Smiths Lake Estuary (MidCoast Council, August 2018) — https://www.midcoast.nsw.gov.au/files/assets/public/document-resources/environment-docs/river-lake-amp-estuary-management/great-lakes/coastal_zone_management_plan_-_smiths_lake_estuary.pdf
Key facts
Catchment area — 28 square kilometres Surface area of lake — 10 square kilometres (over 3km wide in places) Islands within the lake — Big Island, Little Island and Bull Island Trigger height for opening — 2.1 metres above sea level Manual or Mechanical openings — periodically since 1932 Managed by — MidCoast Council Water level monitoring — Manly Hydraulics Laboratory (MHL) Governing plan — Coastal Zone Management Plan for Smiths Lake Estuary (2018)
Sources: NSW Environment and Heritage — Smiths Lake Estuary https://www.environment.nsw.gov.au/topics/water/estuaries/estuaries-of-nsw/smiths-lake · Wikipedia — Smiths Lake (New South Wales) https://en.wikipedia.org/wiki/Smiths_Lake_(New_South_Wales) · MHL Water Level Data https://mhl.nsw.gov.au/Site-209465 · Great Lakes Advocate https://www.greatlakesadvocate.com.au/story/7437493/midcoast-council-monitoring-smiths-lake-water-levels/ · NSW Flood Data Portal — Smiths Lake Flood Study https://flooddata.ses.nsw.gov.au/flood-projects/smiths-lake-flood-study. Content compiled for Villagefirst.