We recently conducted a service visit to the Witches Oak Reservoirs, assessing the health and performance of the Floating Ecosystems implemented in partnership with Severn Trent Water and Mott McDonald Bentley. This innovative nature-based solution utilises 5,600 m² of living bio-filter, spread across 31 islands, to pre-treat an average of 65 million m³/day of drinking water.

The service visit (August 2024) involved a comprehensive assessment of the following:

• Plant Health: A detailed survey of the plant species, including both the originally planted vegetation and any invasive species. Samples were collected for laboratory analysis to determine plant health and potential for PFA’s.
• Infrastructure Condition: Inspection of the anchors, chains, and other hardware supporting the Floating Ecosystems, assessing for damage, corrosion, or other signs of wear and tear.
• Buoyancy: Evaluation of the buoyancy of each island, identifying any issues that could impact their stability.

Original plants thrive and will continue to do so with regular maintenance. 80 samples from 11 species were collected for lab testing. The anchoring system and buoyancy’s are working effectively.

This spring, we will implement a plant control program to remove dominant/self seeded species and protect beneficial plants. Afterward, we’ll replant with hardy evergreens and Lythrum salicaria to fill gaps.

The Witches Oak Reservoir demonstrates the potential of nature-based solutions in water treatment. The overall performance of the system is positive, reinforcing the viability of this innovative approach to sustainable water management. Further monitoring and proactive maintenance will ensure long-term success.