Pool construction in Izmir: evaporation, alluvial ground and the seismic joint

The highest temperature measured is 43.2 °C (July) and the lowest -8.2 °C (January). The annual 730.5 mm of precipitation is spread over 87.2 days, and most of it is concentrated between November and February; only 3.0 mm falls in July. For a pool project, three concrete conclusions follow: unheated outdoor pool water rises above 28 °C in July and August, there is no topping up from rain throughout the summer, and evaporation is at its highest in the longest and sunniest months of the year.

From a pool engineering point of view, the decisive row of the table is July: 381.6 hours of sunshine, 48.7 percent humidity and 3.0 mm of rain come together in the same month. This combination quickly uses up both the water and the free chlorine. December, with 131.3 mm, is the wettest month; the overflow channel and perimeter drainage are sized for this month, when the pool is at winterising level.

In Izmir, the imbat, the breeze that blows from the gulf onto land on summer afternoons, constantly sweeps away the saturated layer of air above the pool surface; replaced by air at 48 percent humidity, this layer keeps evaporation going. The result is that a pool of the same size needs much more fresh water than on the Black Sea coast. The pool design supplies this water in one of two ways: in an overflow system, automatic filling linked to the level sensor in the balance tank; in a skimmer system, a float-operated top-up line.

Evaporated water means more than a loss of volume. The water goes, but dissolved solids (TDS), calcium hardness and cyanuric acid stay in the pool and their concentrations rise. Each top-up adds the calcium and bicarbonate that come with mains water. That is why in Izmir the pool maintenance programme doubles the frequency of TDS and cyanuric acid monitoring in the test log during the summer months; cyanuric acid extends the half-life of free chlorine by 4 to 6 times, and without this stabiliser sunlight quickly uses up the chlorine.

Most of Bayraklı, Karşıyaka, Bornova and Çiğli sit on this loose sediment; the altitude in the city centre is 2 m. In the villa areas of Çeşme, Urla, Alaçatı and Seferihisar, the ground is mostly rock and dense gravel, but plots near the shore have saline groundwater in contact with seawater.

On rock, the cost of excavation rises but the shell calculation becomes simpler. On alluvium, the pool shell is reinforced to work as a continuous raft against differential settlement of the ground beneath it; the points where the skimmer line and main drain pipes leave the shell are detailed with flexible penetrations. The same reinforced concrete pool drawing cannot be used on these two kinds of ground.

Ground motion in Bayraklı and Karşıyaka was amplified by ground conditions made up of loose sediments; in the Izmir basin, ground motion was amplified 2.5 to 3 times. The same earthquake produced a tsunami with a wave height reaching 6 m at Akarca in Seferihisar and a run-up of 5.0 to 5.6 m at Sığacık.

For the pool shell, this translates into two design decisions. First, in an earthquake a water-filled pool sways with both its own mass and the load of sloshing water; if the shell is rigidly connected to the building, the two structures sway at different periods and crack at the connection. That is why a seismic joint with elastic filler is left between the pool and the building, terrace or retaining wall, and the surround paving sits so that it can move independently of the shell. Second, on alluvium ground amplification enters the calculation: in loose sand and silt, the pool shell is designed with a continuous raft and increased reinforcement against possible liquefaction or differential settlement of the ground beneath it.

The January average is 9.0 °C, and although the record low is -8.2 °C, prolonged freezing is rare. The pool is not drained, the level is taken below the overflow channel, and the pump and filter lines are protected. Paving falls and gutters are checked for December and January rainfall (127.5 mm and 131.3 mm) so that the surround paving does not carry surface water into the pool.

An air source heat pump extends the season from mid-April to early November; because Izmir's winter averages stay above 9 °C, the heat pump can run at low load all year. In Izmir, an indoor pool comes up mostly in hotel and residential complex projects with a year-round occupancy target.

In the summer months there is the opposite problem: water above 28 °C does not cool swimmers and is unfavourable for the chemistry. In the Langelier calculation, the temperature factor moves towards scaling as the water warms; in heated hotel pools the heater is switched off in July, and water temperature is lowered with shading and night circulation. In some pool projects a reversible heat pump is chosen and run in cooling mode in summer. This decision enters the plant room and electrical capacity calculation at the pool construction stage; it is difficult to add later.