Natural Pools

Create the ultimate in immersive, back to nature experiences while increasing your sustainability credentials.

Natural PoolsNatural pools are designed to be hygienically operated without the need for continuous chemical disinfection, and with minimum energy and water requirements. Inspired by natural lake systems, natural pools are often constructed to look like a pond or a lake and incorporate a natural filtration system in the form of a regeneration zone. In this zone specially selected plants and an aggregate substrate filter nutrients, algae and micro-organisms out of the water.

Natural swimming pools – which can be as small as 15m2 – come in two main forms:
• the traditional natural pool (or pond);
• and the living pool, which visually looks more like a traditional filtered pool.
In the case of natural pools, a dividing wall reaching to approximately 100mm below the water surface separates the regeneration zone from the swimming zone to prevent contamination of swimming water with soil and aggregate material. Water may also be passed through a mesh screen and phosphate sink, and additional aquatic plants added to the swimming area, to provide further water purification if required.

Living pools, on the other hand, can be designed to look conventional, with clear separation of the main swimming area from the planted regeneration area. They may even be heated and located indoors, as demonstrated on the Artehof Aparthotel and Campsite in Germany.

Typically, glampers spend their holidays closer to nature and are receptive to the concept of natural pools. These pools avoid the use of chlorine and other disinfection agents or treatment systems such as ozonation, thereby almost eliminating the resource depletion and ecotoxicity impacts of swimming pools, and significantly reducing energy consumption.

Natural pools require more space than conventional pools of the same swimming area. However, they can be integrated into the surrounding landscape, and can support local biodiversity by providing a habitat for aquatic species. So, in addition to reduced ecotoxicity effects, natural pools are likely to result in a significant positive effect on biodiversity compared with conventional pools.

Construction design
As with conventional pools, it is important that the pool and filter system (regeneration area) are sized to cope with expected peak demand. Natural pools are not able to hygienically cope with high peak usage rates.

The edge of the pool should be raised, and/or a drainage ditch constructed completely around the pool to ensure that no run-off water enters the pool. Construction of the main body of the pool is as per conventional pools. A rubber membrane or similar flexible impermeable barrier may be used depending on the desired finish.

The main distinguishing feature of a natural pool is the regeneration zone separated from the main body of the pool by a submerged diving wall. There are a few options to consider:

Concrete or cinderblock walls
• Precise geometric shapes
• Vertical walls from top to bottom in the swimming area
• Higher input in materials and costs
• Self-construction is possible.

Corner element construction
• Pre-fabricated components
• Quick and easy construction
• Attractive design
• Swimming area can be shaped as desired
• Wooden slats provide seating.

Earthwall construction
• Gently sloping shape of the swimming area
• Economically priced
• Larger surface area needed due to greater width of earth wall.

Regeneration zones
Regeneration zones are comprised of an inert coarse substrate such as gravel or loamy sand. Topsoil is avoided, as the idea is to provide a substrate for plant roots to absorb nutrients from the percolating water, and not to introduce additional nutrient sources. Additional components of the regeneration zone may include lime and elements to bind nutrients and fine particles.

A range of aquatic plants can be used, both in the regeneration zone and the main pool body. These can include submerged oxygenators, floating plants, shallow marginals, deep marginals, bog/marsh and waterside species. Wherever possible, indigenous plants should be used as they should be adapted to the local environment and will maximise the biodiversity benefits arising from a natural pool.

In order to provide effective water treatment, the mix must contain marsh plants that are able to decompose compounds to their constituent elements within the root zone.

Natural PoolsAdditional filtration systems
Following filtration in the regeneration zone, water may be pumped through a self-cleaning mesh screen of 0.3mm to remove any remaining algae and micro-particles. Although usually not necessary when the regeneration zone is operating correctly, a phosphorus filter may be installed to prevent algae growth (phosphorus is a limiting nutrient in freshwater). Closed pressure filters are available that can be installed separately within the pool and cycle water through a filter substrate containing elements that bind phosphate.

Maintenance
Aquatic plants grow quickly and may require periodic thinning and pruning. Removing the plant mass each autumn acts as a sink for impurities and nutrients from the system. A surface leaf skimmer should be used to remove floating debris from the water, while silt (a combination of decaying vegetation, dust and other detritus) can be removed by either a vacuum or bottom purge system. Where present, phosphorus filter systems need to be periodically rinsed, and the filter substrate changed every few years.

Economics
The cost of construction for a natural pool is in the region of £300-£600 per m2 and decreases as the pool area increases. However, maintenance costs are significantly lower, as chemical purchasing is avoided and electricity consumption is typically lower than for conventional pools as the shallow water in the regeneration zone heats up quickly.

 


Advantages
Natural pools offer considerable advantages over conventional swimming pools. These include:
• No harmful chemicals
• An attractive and natural-looking feature
• Water warms up more quickly in the sun owing to shallow depth in the regeneration zone
• Less maintenance
• Biodiversity gain
• The creation of a unique back to nature experience for guests.

About Open Air Business 1329 Articles
The voice of outdoor hospitality - in print and online. If you liked this article, subscribe to the printed magazine here. We produce industry e-news between issues - please sign up here