The river diversion works had to meet two basic requirements.

First, some of the new river channel was to be below groundwater level and the mixing of groundwater and river water had to be avoided, as did any rise in groundwater level. Second, there must be a zone above the waterline capable of supporting trees and vegetation so that the new river bank would eventually look natural.

Normally, a tree planted above a synthetic liner will fall over at some time in the future as the roots cannot get an adequate hold on top of the liner. Roots cannot grow through synthetic liners.

However, Huesker's Austrian subsidiary was able to supply a product which satisfied both of the challenging requirements. A geosynthetic clay liner (GCL), often referred to as a bentonite mat, was available. The GCL Nabento RL-N with 4,500 g/m 2of pure sodium bentonite sealing medium and rough, sand coated textured surfaces, fulfils two functions at once. It provides the required seal between river and groundwater, and it is self healing if penetrated. Below the waterline it provides a reliable seal while above this level, the roots of trees and shrubs can penetrate.

The Huesker product uses the bentonite powder as a sealing material. It has excellent swelling properties, when roots grow through the liner the swelling clay surrounds the root and thus retains most of its sealing properties.

This special ability of the GCL is so effective that timber piles can be driven through it and can be assumed to be sealed.

This helped to make the new section of the River Glan look natural. Piles slow the flow along the new section of river, allowing eddy zones to be established providing quiet water for waterfowl as well as spawning and breeding grounds for fish.

Overlaps in the liner were made sheer and tension resistant by NaBento special adhesive, which seals the joints and prevents slippage at overlapped areas such as when fill is deposited by heavy equipment, especially at the longitudinal overlaps in the river banks.

MJInformation No: 21806