The water surface is at the level of or above its surroundings, or it is disappears into a slit through a hidden outlet trough. Water flows over into the surrounding outlet troughs and further to the equalizing tank. Circulation via the pool edge ensures even collection of impurities from the surface. Pools with an overflow trough provide a design solution for private pools and the only choice for public pools.
You can also decide to have overflow only on certain sides of the pool. A pool raised above the surrounding level is an interesting feature. As water flows into the troughs that are situated at a lower level, you can get the feeling while swimming that your pool is endless.