Biodegradable* geosynthetic clay liner for flood protection project in Brixen

There are various reasons for rising water levels within the Eisack’s cross-section. These include increasing urbanisation, higher flood discharges due to glacial melt, increasing rainfall intensity, diminishing retention areas and a depletion in water-absorbing substrates (e.g. snow or fine-grained soil).

High water levels in Brixen pose a dual flooding risk: if the Eisack overflows its banks, the town centre will be flooded directly. But the town is also threatened by potential rising ground water level.

Three measures created capacity for a 1-in-100-year flood event: the concrete floodwall was raised, the river cross-section was widened, and the riverbed was deepened. As a result, the low permeability sediment was reduced to a level that could not guarantee a separation of water level of Eisack and surrounding groundwater. To ensure sealing of the deepened riverbed, Bentofix^® Green biodegradable* bentonite mats were installed. These mats use bentonite powder as the sealing medium, while the carrier and cover geotextiles are made from biodegradable* raw materials.

This provides the encapsulation of the bentonite to create a geosynthetic clay liner (GCL), enabling straightforward installation. The use of degradable raw materials avoids the release of non-degradable polymers into the river ecosystem (e.g., through bedload transport or hydraulic abrasion). While the fibres can degrade in the Eisack’s environment, the bentonite remains in the riverbed, maintaining its sealing function even after the geotextiles have degraded*.