A flexible solution for a botanic garden water feature

Nick Benge at landscaping, water feature construction and pond maintenance specialist, Water Gems (Alba), discusses the recent refurbishment of the ornamental pools at the Royal Botanical Gardens Edinburgh using Firestone Building Products’ PondGard EPDM liner in the latest issue of ABC+D magazine.

The Royal Botanical Gardens Edinburgh (RGBE) dates back to 1670 and currently encompasses more than 70 acres of landscaped grounds, providing a haven of tranquillity just a mile outside the city of Edinburgh, along with a centre of horticultural excellence.

Named after an 18th century Regius Keeper and famous botanist, the Gardens’ John Hope Gateway provides a biodiversity and information centre, with a ground floor exhibition space and first floor restaurant overlooking a trio of terraced ornamental pools, designed to cascade down into each other.

Problems with the pipework for the pools had prevented the cascade design from operating properly and the failure of the original lining material was also a factor in the decision to commission a refurbishment project. The scheme involved draining the pools and replacing the existing lining and making changes to the pipework and pumping system before refilling the ponds.

The original layout of the pools abutting the John Hope Gateway building had also made it difficult to clean the floor- to-ceiling windows on the ground floor as there was no standing room between the façade and the water. As a result, construction of a new walkway between the building and the water feature was included in the scheme to aid future window cleaning and maintenance.

“EPDM lining is an extremely robust and flexible material that can be folded into corners and awkward angles” Nick Benge, Water Gems

Excavation

With the water drained from the pool, the first step was to remove the gravel that was weighting and concealing the existing pond lining and removing the liner itself. The original PVC-P lining system specified had lacked the flexibility required for the complex geometry of the pool’s shape, causing some of the joints and fixings to fail.

With the lining removed, it was possible to excavate the pipework that had been laid below the surface of the pond cavity, clean it and reconfigure it to provide a more effective solution for controlling the water flow, in line with the cascade design of the ornamental pools.

It was possible to re-use much of the existing pipework components within the new configuration and a new overflow pipe was connected to the existing drains. A new filtration system, comprising a submersible pump and hose was also fitted with a timer to ensure energy-efficient operation.

Re-lining

Following a small amount of backfilling onto the refurbished pipework, a geotextile membrane was laid into the pond cavity, prior to installation of the new liner. Firestone’s PondGard EPDM lining system was chosen for the scheme because it is an extremely robust and flexible material that is just 1mm thick and can be folded into corners and awkward angles without any risk of tearing or cracking.

Chemically inert, U/V stable and temperature stable, EPDM offers excellent resistance to algae growth and micro- organisms. PondGard EPDM lining has also been tested by the UK Water Research Centre to prove it is non-hazardous to aquatic life, enabling fish to be introduced to the finished pool if RGBE should choose to do so at a future date.

The lightweight EPDM lining was laid onto the pool surface with a pre-calculated configuration for optimising use of the membranes, which are supplied on rolls with widths in 3m increments up to 15.25 x 30.5m long. The lining was cut and laid into the cavity with a 150mm lap on all joins, which were sealed using Firestone’s QuickSeam 3” Splice Tape, a self- adhesive tape which provides a permanent watertight seal between each section of liner.

The liner was adhered to the concrete walls around the lower section of the pool using Firestone Bonding Adhesive. For the granite walls at the top of the pool, the liner was fixed with stainless steel straps connected to the wall and folded back onto itself to provide a robust mechanical fixing solution.

In the areas where the liner follows the cascade into the next pool, QuickSeam FormFlash was used to form the detailing. The pool was then filled with water, with no settling requirement for the new liner.

Long term performance

The ornamental pools at the John Hope Gateway have now been fully refurbished and are functioning according to the original design vision, providing a cascading water feature that offers a relaxing vista for visitors to the exhibition centre and the restaurant above.

With a service life of at least 40 years, the EPDM liner will retain its flexibility and waterproofing performance over time for RGBE visitors to enjoy for generations.