Pool construction in Antalya: winter downpours, 46 °C and karst ground

In July and August the average high is 34.9 °C; the highest value measured is 46.1 °C (July) and the lowest -4.6 °C (February 1950). The annual 1,050 mm of precipitation falls on only 67.4 days; December, with 262.2 mm, and January, with 210.6 mm, are the wettest months, while July has 4.0 mm. Annual sunshine is 2,864.6 hours, and sea temperature ranges from 16 °C in winter to 28.8 °C in August.

From a pool engineering point of view, the two decisive rows of the table are December and July. In December, 262.2 mm of rain falls on only 10 days; tens of millimetres in a single day are normal, and surface water from the paving around the pool strains the overflow channel and the balance tank. In July, an average high of 34.9 °C, 344.1 hours of sunshine and 4.0 mm of rain come together; the water rises above 30 °C, free chlorine is used up by the sun, and evaporation is at its highest level of the year.

Surface water and pool water are two separate systems: rain running off the surround paving into the pool carries soil, leaves and fertiliser with it; if the capacity of the overflow channel is exceeded, the balance tank fills and overflows into the garden. The pool design keeps this load away from the pool through paving that falls away from the pool, a rain gutter at the edge of the paving and garden drainage.

In an overflow pool, the balance tank holds three volumes: water displaced when bathers enter, water returning from the channel when the pump stops, and rain falling on the pool surface in a downpour. In Antalya the third item is written separately into the design; the overflow line of the balance tank is connected directly to the rainwater line. In a skimmer pool, the pool level rises above the skimmer mouth in a downpour and surface skimming stops; the design should include a level-lowering drain.

The first is water temperature: an August average of 29.0 °C and an average daytime high of 34.9 °C push outdoor pool water above 30 °C. This water does not cool swimmers, and in the Langelier calculation the temperature factor moves towards scaling; in heated hotel pools the heater is switched off from June to September, and the water is cooled with shading and night circulation. If a reversible heat pump is chosen in the pool design, it runs in cooling mode in summer.

The second is chlorine loss. Cyanuric acid exists in equilibrium with free chlorine, releases the chlorine slowly and extends the half-life of the active chlorine residual by 4 to 6 times; sunlight quickly consumes unstabilised chlorine. Under Antalya's 344 hours of July sunshine, an unstabilised outdoor pool loses by the afternoon the chlorine dosed in the morning. On the other hand, cyanuric acid does not evaporate or break down; its concentration rises as evaporated water is topped up. In the pool maintenance programme, cyanuric acid testing and the partial water replacement rate for the summer months are written into the specification.

The water of the Upper Düden Waterfall disappears into the Bıyıklı sinkhole 18 km away and then returns to the surface from a karst spring; the Lower Düden Waterfall falls directly into the Mediterranean from a height of 40 m at Lara. The same system works beneath the city: in limestone and travertine, rainwater dissolves fissures and opens voids and channels underground. For a pool shell, the problem is that bearing capacity can change from one corner of the plot to the other.

On karst ground, the shell is calculated on the assumption that part of the ground beneath it sits over a void; the raft is continuous and its reinforcement is increased. On the coastal plain, as in Samsun, an uplift calculation and a hydrostatic valve are mandatory. On the hillside plots of Kemer and Kaş, the balance tank of a sea-view overflow pool is planned together with the rock excavation beneath the shell.

A hotel pool aims for year-round occupancy: a January average of 9.8 °C and sea water falling to 16 °C call for a heated outdoor pool or an indoor pool in the winter months. Bather load is high; turnover is kept short, filter area and the balance tank grow accordingly, and automatic dosing and record keeping are mandatory. Pool construction is tied to the hotel calendar: structural work and commissioning are squeezed between rainy days from November to April.

In a rental villa pool, the season runs from May to October and a different guest uses the pool every week. The design decision is automation that keeps the pool running while the owner is away: automatic level top-up, automatic dosing, a remotely monitored pump and heat pump, and a weekly test log. An overflow pipe connected to the rainwater line ensures that the balance tank does not overflow in a December downpour while the villa is empty.

The 18 km the Düden water travels underground is a reminder that the same rock can be full of voids beneath a pool shell too; that is why the ground investigation is not skipped, even on rock. Sand and alluvium on the coast carry the uplift calculation used in Samsun and Izmir over to Antalya's deltas. The climate table, meanwhile, gives an inverted list of problems: keeping water out in winter, cooling the water and protecting the chlorine in summer.

The short rule follows from this: pool construction in Antalya starts with a ground investigation, the surround paving and balance tank are sized for the December downpour, summer operation is set up with split dosing and a cyanuric acid limit, the water is cooled when it exceeds 30 °C, and metal in contact with water on the coast is AISI 316L. Winter heating and a short turnover go into the design of a hotel pool, and automation built for operation without the owner into that of a villa pool.