The Natural Pool
Also known as a bathing pond, the natural pool is becoming more and more popular in the garden, not just for its ecological advantages, but also for its pleasant aspect.
While we see more and more above-ground pools in gardens, an increasing number of people with an organic approach are opting for natural pools. Although fairly new in France, they are extremely popular in Sandinavian countries. These pools don't pollute, as they don't require the use of chlorine or other chemical products like algaecides.
A two-part pool
Natural pools are generally built using a waterproof tarpaulin held down with ornamental stones which serve as copings. They can also be made with polyester or concrete. In fact, the material used for a natural pool is of no importance ! What is important is how the pool is managed. It uses the same system of mechanical filtering as is used for normal pools (drainage of the bottom and surface of the pool) as well as a sand-filtering system which eliminates floating particles. It differs from normal pools in the way it treats the water. The water which comes out of the sand filter is separated in two - around 90% of it is directed towards an oxegenizing waterfall to make sure that the water is cleansed, whereas the other 10% is directed towards a natural filtering system.
Filtering plants
In this small basin, situated slightly above the big basin, special aquatic plants get rid of the mineral or organic pollution in the water. This system is a closed circuit based on gravitation. The idea is to achieve a slow flow of the water from the big basin so that it passes through the the filtering system at least twice a day.
Here is a list of some interesting plants which filter organic matter effectively and which help their sedimentation : the Mare's tail (Hippuris vulgaris), the yellow water-lily (Nuphar luthea), the lesser spearwort (Ranunculus flammula), the arrowhead (Sagittaria japonica), and the azollae ferns (Azolla).
When the natural pool is optimized, both basins should function without intervention, just like an organic eco-system.
Apart from being ecological, these pools have the advantage of melting into their surroundings. The gardener can decide to create the atmosphere he wishes, whether it be exotic or classic, all depending on his taste. This natural principal even allows one to put fish into the pool !
At Combloux, Green Concept built a natural pool using the Bioteich process. The water ( which is natural and chlorine-free) isn't replaced, it is kept in circulation. "Bioteich" and "Baignades Naturelles" are registered trade marks of OBIO GROUP SAS.
N.b. : the Bioteich process differs slightly from the system described in this article.