Bridge Repairs – Environmentally Sensitive Pre-filled Rock Solutions for Scour Prevention

Recently installed Rock Bag XL at scour holes under bridge

Recently installed Rock Bag XL at scour holes under bridge

Salix pre-filled Rock Mattresses & 2T Rock Bags XL replace traditional concrete scour protection, providing a far more environmentally sensitive and cost effective solution

Essential bridge infrastructure works in Cumbria to prevent riverbed scour have previously used concrete saddles that require the area to be sheet piled, then coffer dams placed in order to create a “dry” area in which to pump the concrete. The bedload material is then placed back over the concrete.

During high flow events this bed material load washes off the concrete slab leaving an exposed area of concrete. Then in times of drought and low flows there is no hydro-morphological connectivity upstream and downstream.

Installing the ground anchorsClose-up of ground anchors and pre-filled rock mattresses with Geogrid anti abrasionCan you spot the 2T Rock bags XL?2T Rock bags XL hardly visible after a few months
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Close-up of ground anchors and pre-filled rock mattresses with Geogrid anti abrasion

Lotic (flowing water) habitats are a rich source of biodiversity, especially in a river’s hyporheic zone which consists of water in the interstices found in river gravels below the riverbed. This zone is extremely biologically active, and can function as a refuge for organisms during flood events.

Placing concrete in any form or thickness within this active zone creates a barrier that completely destroys this unique habitat. Many of the Cumbrian rivers are important salmonid fisheries and SSSI & SAC sites.

Local engineers and clients are now recognising the use of Salix pre-filled rock mattresses and Rock Bags XL as a viable cost effective, environmentally sensitive alternative to concrete.

We have proven independent research from Swansea University of high benthic invertebrate populations and species diversity that salmonid species feed off, living within the stone interstices of our Rock Rolls and mattresses.

In order to prevent movement in times of high flow, suitable fixings may be required apart from lacing the rock rolls and mattresses together. Salix have teamed up with Gripple, a specialist in ground anchors to provide the correct specification of ground anchors.

A major benefit in terms of cost and time, is the speed of installation of the pre-filled rock solutions.

Salix’s rock products are simply lifted into place with in-built strops or rings directly in or out of flowing water. There is also no wastage of stone and the pre-filled nature of the products guarantees consistent high quality.

Salix manufacture and supply Rock Rolls, Rock Mattresses and Rock Bag XL that are far more environmentally beneficial than traditional hard engineering with their ability to accrete sediment, vegetate and support invertebrates.

The Water Framework Directive (WFD) is an important legislation that encourages better practice rather than destroying habitat. Asset protection and civil engineering solutions should not ignore this vitally important environmental impact. Balancing a robust long term solution that works with nature rather than against it must be the way forward.