Surface tension is a phenomenon that occurs on the surface of liquids in general, and water in particular, at the liquid-gas interface. Intermolecular attractive forces are responsible for this surface tension. These forces must be considered in the design and construction of swimming pools and water attractions.
In the interior of a mass of water, where each particle is surrounded by equal particles, the intermolecular forces are symmetrical and their resultant force is zero. This is not the case at the water-air interface. On the one hand, the particles are affected by the attractive forces of water, and on the other hand, the acting forces are the attractive forces of air. Therefore, the resultant of forces is not zero and therefore there is no equilibrium between them. As a consequence, a tension field develops on the surface of the water, the resultant of which balances the difference in internal forces. This tension field is called surface tension. This causes the water surface to behave like a taut membrane, and it has an imperceptible curvature.
Figure 1: Sketch of internal forces between water particles and the development of surface tension at the water-air interface.
From the point of view of the design and construction of pools and water attractions, surface tension must be taken into account in pools and water attractions intended for jumping, e.g. ponds and pools in Canyoning Parks, where canyoning activities take place. In these pools and water attractions it is advisable to break the surface tension sheet in order to soften the entry of the jumpers into the water. This can be achieved by directing water jets to the surface of the pool or water attraction in the drop zone.
Figure 2: Breaking the surface tension by means of water jets in the drop zone of a diving pool.
By Luis Llor, Senior Hydraulic Engineer in Amusement Logic’s Architecture Dept.
