frog environmental silt control measures

Wednesday, November 14, 2018
frog environmnetal silt control measures take suspended soilds from >2000 mg/l down to 12 mg/l downstream of in channel work and boost oxygen levels in the water

Preventing pollution whilst working in rivers is a serious challenge for all contractors who work in and around water.

Working on the bed or banks of a river whether installing bank protection, de-shoaling or creating a river crossing can result in high levels of suspended solids being passed downstream.

Silt plumes can have a negative environmental impact and can draw the attention of the regulator.

The Afon Gwili in Carmarthenshire is a tributary of the River Loughor.

It is an important river for migratory fish including the sea trout and salmon, the catchment management plan focusses on improving water quality and protecting the river corridor habitats.

River bank stabilisation works had to be scheduled on the Afon Gwili to protect the adjacent highway and reduce high levels of erosion.

Constraints on site included the close vicinity of the road, an ancient woodland on the opposite bank, and the presence of Japanese Knotweed.

These constrictions meant that heavy plant entering the river channel was unavoidable and pollution prevention plans would be essential to minimise disturbance to the bed and banks of the river.

Works were required to control erosion and prevent damage to critical highway infrastructure.

Works were required to control erosion and prevent damage to critical highway infrastructure.

frog environmental attended site and worked closely with the contractor to assess risk of causing an incident.

Given the sensitivity of working in a river environment and the need to work without the use of any chemicals it was decided that a series of measures would be needed to improve water quality and prevent downstream silt pollution on the Afon Gwili.

The first action was to create a dry working area whilst facilitating the need to move machinery in and out the steep sided channel.

A flow diversion channel was created using an impermeable liner covered with Silt Net 150, a natural fabric to increase friction and support the entrapment of solids.

The channel became naturalised with cobbles following a flood event.

We used a range of products including: FlocMat™SiltNet 150Rock ChecksBubble Tubing®SiltMat and Silt Wattles.



Silt-Net-150-used-to-line-the-impermeable-membrane-in-the-flow-diversion-channel SiltMat-positioned-immediately-below-work-area-entrapped-muddy-water,-filtered-solids-and-slowed-the-flow-Each-SiltMat-can-capture-over-40kg-of-silt
Silt-Wattle-and-untreated-Floc-Mat Four lines of Bubble Tubing® were deployed to create a bubble curtain boosting oxygen levels downstream of works and providing a further barrier to silt movement

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