The joy of ocean pools
Originally published on www.engineering.unsw.edu.au by Mary O'Connell.
The School of Civil and Environmental Engineering's legendary Water Research Laboratory has recently been involved in research and design of that equally legendary Sydney and NSW icon – the beloved ocean pool.
Almost half of all known coastal pools in the world (150) are located in NSW, with 70 cherished pools lying mostly between Newcastle and Wollongong, including over 30 located on the Sydney urban coastline.
Advantages of ocean pools
Ocean pools are a highly valued local asset. They offer several advantages over swimming in the ocean, such as a safety from rips; partial protection from large waves and stinging jellyfish; a well-defined space for training and practising; for community gathering, and the potential for safer night swimming, while still providing a close psychological connection with the ocean – and sky.
Ocean pools also offer several advantages over conventional swimming pools. For swimmers, ocean saltwater is more buoyant; and minimal chemicals are used for cleaning; while management advantages involve no heating costs; lower pumping and/or filtration costs; potentially reduced costs for staffing, cleaning and maintenance.
The WRL team found that the social, physical and economic benefits of establishing brand new ocean pools soon outweigh any design, construction and maintenance costs.
Brief history of pools
Most NSW ocean pools were initially built from the late 1800s to early 1930s, and most have either been substantially renewed by the relevant local council, or have degraded into a “ghost” pool. The original pools had little formal engineering design, but often involved local residents and/or surf life savers excavating favourable portions of rock shelves, and later enhancing these with concrete, usually through numerous construction iterations. The last new construction was at Cronulla in the 1960s, which was rebuilt in the early 1990s.
The good news is that new ocean pools are being considered in several places around the country including Adelaide, Ballina, and Port Macquarie, for a variety of reasons – more protection from sea dangers, increasing community safety, health and well-being, and all the ineffable but still often measurable benefits of a closer physical and psychological relationship with the ocean.
Due to the ageing nature of many existing ocean pools, and community aspirations for new and improved ocean pools, WRL were asked to apply contemporary coastal engineering techniques to the design of ocean pools.
Firstly the WRL team – James Carley, Ian Coghlan and Chris Drummond, with independent design colleague Nicole Larkin - undertook detailed investigations into four ocean pools on Sydney’s northern beaches: Dee Why, North Curl Curl, South Curl Curl and Freshwater.
WRL completed drone and RTK GPS surveys of these pools and their surrounding rock platforms. These were combined with existing published seabed surveys and seabed composition maps to develop an approach path for ocean waves into the pools.
In addition to observations and measurements by WRL engineers, interviews were undertaken with present and retired Council staff involved with the management and renovation of these pools, together with regular users.
WRL then applied contemporary coastal engineering techniques to the design of ocean pools. This would cover construction of a 50 m x 20 m main pool; a 250 to 450 m2 wading pool; and 250 to 450 m2 of constructed public space. This is an important aspect of every pool – the gathering place for the locals who soon become official or unofficial partners with councils in cherishing, maintaining and guarding the pools.
Factors considered by WRL included: capital costs; maintenance costs; safety from waves; potential for natural flushing; potential for sand and seagrass infill; impact on beach processes; engineering certainty; ease of construction; ease of disabled access; potential for boulder/debris impacts; and preservation/maintenance of water quality, including separation from external contamination.
Ocean pool patronage
While the Royal Life Saving Society (RLS) has collated usage statistics for various aquatic facilities around Australia, (in 2017 there were 1,027 Australian public aquatic facilities, and average visits per pool per year were 99,000), there are few direct measurements of ocean pool patronage, as most are free and ungated. Beach usage data, however, is collected by many councils through paid lifeguards. WRL used this data to estimate ocean pool patronage for the 2017-2018 season for six ocean pools on Sydney’s Northern Beaches.
The proportion of beach users estimated to use the various pools ranged from 10% at more remote pools such as North Curl Curl (estimated 50,000 pool visits pa), to 50% at South Curl Curl (estimated 220,000 pool visits pa) where the pool has excellent access and the beach is one of Sydney’s most dangerous.
Capital costs for new pools
WRL estimated initial capital costs for a new ocean pool would be from $3-$8M, noting that it is difficult to put a definite one-size-fits-all pool construction costing, as firstly, each pool's infrastructure will depend on its unique local physical conditions, and secondly, operating in the marine environment presents risks and challenges not encountered during conventional construction.
Maintenance staff, material and pump electricity costs were calculated at $90-$110k pa with ongoing refurbishment costs of upgrading - at intervals of about 10 to 20 years - $800k to $1.5M future costs.
Economic value of beach or pool visit
Using the work of beach economist of Dr Dave Anning and the RLS 2017 economic modelling of aquatic facilities, WRL developed similar estimates for the economic and social -including health benefits per ocean pool visit. The RLS values were: economic benefit of pool visit: $13.83 plus health economic benefit: $26.39, to derive a total benefit of pool visit: $40.22. WRL assessed the ocean pools to have an equivalent socio-economic-health benefit of $40 per person visit per annum.
Therefore a typical pool use of 150,000 year, such as Freshwater or Queenscliff, provides an economic and health benefit to the community of $6 million per year; while a high use pool such as Dee Why (260,000 per year) provides benefit value of over $10 million per year.
That is, a typical new pool would have paid for itself in two years. And the fortunate locals and visitors to that area will have a new place of bliss.