Salix Rock Mattresses, Coir Rolls and Coir Pallets are being used on the Exeter FAS Scheme to enhance the wildlife habitats whilst at the same time providing cost effective long term erosion control.

We’ve been involved in this £32 million Exeter Flood Alleviation Scheme (FAS) by providing design advice to the Environment Agency’s consultants CH2M on establishing wetlands and waterline marginal planting. In 2014/15 we supplied large quantities of native wetland plants to Phase 1 of the project.

The plants were grown at our in-house nursery into Coir Rolls and Coir Pallets, to create pre-established mature vegetation that ensures instant habitat the day of installation plus effective erosion control, rather than just planting plug plants that take longer to establish and can also be washed out in flood.

Later this year we will be supplying more pre-established plants in our Coir Rolls and Coir Pallets in the autumn.

Already this year we have worked with BAM Nuttall, the main contractor to replace the expensive traditional hard engineered banks with our ecologically sensitive rock.

Rapid vegetation takes place in the Rock Mattresses – stopping erosion and providing a low carbon, nature based solution

Savings were achieved as the ready filled Rock Mattresses reduced the resources required on site.

The speed of installation for the 200m was crucial as the tidal influence meant that they could only work one week per month. The flexible nature of the ready-filled Rock Mattress resulted in a robust but natural slope profile, which is important as this is a significant stretch of river for fishing. Rock Mattresses are also a low carbon alternative to many hard engineering options, creating environmental resilience to climate change as we face more extreme weather events.

Salix commissioned research work that measured the invertebrate life in the mattress stone voids.

One month after installation the Environment Agency’s Fisheries Officer was delighted to see mullet feeding in the water where the ready-filled Rock Mattresses extend below the waterline, demonstrating how effective our Rock Mattresses are at providing habitats. You can watch a video on the research into the environmental benefits of our Rock Mattresses by Dr Ruth Callaway of Swansea University.

Key Points

  1. Rock Mattresses replaced the original blockstone design bank edge protection which detailed stone that was not easily sourced and also would’ve required extensive excavation below water to install. Therefore, Rock Mattresses were a value engineering option.
  2. Only minor bank trimming required for installation of our Rock Mattresses which resulted in reduced risk of sediment into the river and a natural slope was retained = cost and time savings
  3. Fast installation of Rock Mattresses as they arrive on site with lifting strops and pre-filled = works programme kept on track.
  4. Top dressing the Rock Mattresses above average water level with seeded soil and below the water is an invertebrate habitat in the stone spaces of the Rock Mattresses = original bank habitat value restored