Pool construction in Samsun: what do climate and groundwater change?

The lowest temperature measured is -9.8 °C (February) and the highest 39.0 °C (August). With 143.4 rainy days a year, 729.7 mm of rain and an average relative humidity of 71.2 percent, there are three concrete consequences for a pool project: there is no month in which the water rises above 24 °C on its own; rain is concentrated between October and January, that is, when the pool is closed; and because humidity stays between 64 and 78 percent all year, metal surfaces do not dry out.

From a pool engineering point of view, the two decisive rows of the table are December and July. December, with 82.5 mm, is the wettest month, and in this month the pool is either empty or at winterising level; the overflow and drainage calculation is made for this scenario. July, with 38.9 mm, is the driest month and, with 277.3 hours, the sunniest; the need for evaporation make-up and topping up is highest here. From May to September, average temperatures are in the 15.9 to 24.5 °C band; an unheated outdoor pool does not reach a comfort temperature of 28 °C in any month.

Groundwater is water held in the pores of rock and soil and in rock fissures below the ground surface; the water table is the depth at which the soil pores become completely saturated with water. Surface water, on the other hand, arrives with rain and is carried away by falls and gutters; the measure against the first is taken beneath the shell, and against the second in the surround paving and overflow channel.

The Kızılırmak Delta covers 560 km² and contains more than twenty lakes; the average depth of these lakes is 1.5 m, and in spring their water surface exceeds 9,000 hectares. The delta was formed by alluvium the river carried down from the upper basin, and this alluvium, a mix of fine sand and silt, extends from the Bafra plain to the city's coastal strip. On such ground, the water table can rise to 1 to 2 m below the surface depending on the season. Sloped paving and gutters built to carry away surface water do nothing to this water beneath the shell; the two systems have to be designed separately.

The formula is Fb = ρf · g · Vdisp, where ρf is the density of the fluid, g is the acceleration due to gravity and Vdisp is the displaced volume. When the water table rises above the pool floor, the shell is pushed upwards like a boat; when full, the pool water balances this force, and when empty, only the weight of the concrete and the soil load remain.

Example: a reinforced concrete pool with an 8 x 4 m floor and 1.5 m depth displaces 8 x 4 x 1.0 = 32 m³ of water when the water table is 1.0 m above the pool floor. Taking the density of fresh water as about 1,000 kg/m³, the uplift is in the order of 32 tonnes. With a 20 cm floor and 20 cm wall thickness, the same pool has a concrete volume of roughly 6.4 + 7.2 = 13.6 m³ and, at 2,400 kg/m³, weighs around 33 tonnes; in other words, the safety margin is almost zero. If the water table rises to 1.5 m, the force reaches 48 tonnes and the pool floats. The calculation is redone on every project with the actual dimensions, toe and backfill weight.

The investigation asks for two values: the summer and winter levels of the water table, and the type of soil. The table below summarises three situations commonly met for reinforced concrete pools in Samsun and the specification clauses for them; on every project they are confirmed by the borehole results.

On corrosion, the decision is clearer. Up to a few kilometres inland from the shore, salt in the air and an average humidity of 71 percent start pitting corrosion within a few seasons on AISI 304 stainless steel ladders, lane rope fittings and skimmer lids. Chloride in the pool water amplifies this effect. The specification calls for AISI 316 or 316L for all stainless parts in contact with water and exposed to the open air, and electropolished 316L for seafront hotel pools. Anchors and fixings are chosen in the same grade; a 316 ladder fitted into a 304 fixing corrodes at the fixing because of the galvanic couple.

The heating decision is read directly from the climate table. An unheated outdoor pool in Samsun can be used for about three months, from mid-June to mid-September. With an air source heat pump, this extends from early May to late October; because Samsun's winter averages stay above 7 °C, the heat pump can run all year, though at lower efficiency than on the Mediterranean. The third option for hotel and villa pool projects is an indoor pool, with a fixed or opening roof; in this case humidity control (a dehumidification unit sized to the pool volume) becomes a larger equipment item than heating. In villa projects, a six-month season with a heat pump and solar cover is usually considered enough; in hotel pools, the target of year-round occupancy justifies an indoor pool.

Although the record low is -9.8 °C, average monthly lows are around 4 °C in January and February; prolonged freezing of the pool water surface is rare. Winterising is therefore done for groundwater and rainfall load: the water level is kept below the overflow channel, the pipework is drained and the hydrostatic valve is checked. Draining the pool completely and leaving it empty through the winter is the most expensive mistake in this region.

The delta was registered as Ramsar site number 942 on 15 April 1998 and contains 11,600 hectares of wetland. The same alluvium is the ground of the coastal plain, at 4 m altitude, on which Samsun city centre was founded; new villa areas are developing towards the slopes at the edge of this plain.

The hydrostatic relief valve and perimeter drainage in a reinforced concrete pool shell were carried over from basement and water tank engineering in areas with high water tables; Archimedes' principle comes from naval engineering. When these two pieces of knowledge are combined, the short rule for pool construction in Samsun emerges: the project starts with a ground investigation, drainage is built before the shell, the shell is never left empty below the water table, and metal in contact with water is chosen from the AISI 316 grade.