Specialists from Natural Resources Wales (NRW) are taking a new, innovative approach to flood maintenance work on the River Rhymney which is benefiting both people and wildlife.
Approximately 900 tonnes of shoal had built up in the river near the flood banks at Ystrad Mynach, causing the river to flow into a deep, narrow channel. This was damaging the flood banks, making them unstable.
The shoal needed to be removed to make sure the flood defences could continue to protect people from flooding, but traditional excavation methods could have threatened wildlife in the river.
To combat this, a different approach was taken and water was diverted around the shoal so the excavator could work in a dry environment – reducing the movement of silt which can harm fish and insects.
Special silt wattles and silt mats were used to slow down the flow of the river and to capture sediment dislodged by the work. Working with company Frog Environmental, an innovative ‘bubble curtain’ was also trialled for the first time in a river in the UK.
This curtain of air bubbles stretches across the river and helps to manage silt, as well as providing an acoustic barrier to absorb sound and increasing oxygen levels in the river - protecting fish and other river life during the disturbance.
David Penny, Operations Engineer at NRW said:
“Shoal, predominately river gravel, building up in rivers is a common problem. In some cases it reduces the amount of water a river can hold – causing water to flood out over the banks, and in other cases like this, it actually damages the banks we’ve put there to reduce flooding.
“Sometimes the only option is to go in and remove it, but it’s always a concern that our work to protect people, will impact on wildlife. By doing things in different way we’ve successfully avoided this.”
In other improvements to the surrounding area, large riverside trees were felled and the wood used to bolster the flood banks and reduce future erosion.
It is hoped that by creating open space around the river and increasing the amount of natural light, new grasses and native wildflowers will flourish, soaking up more rainfall and reducing erosion.
“What we’ve done here is tackled a specific problem which could impact on the local community, but rather than looking at it in isolation, we’ve focused on the whole picture and the needs of the wider environment.
“We’ve protected the flood banks for the future and at the same time improved the habitat for plants and wildlife to thrive.
“By tackling old problems like this in new, innovative ways we are helping to make our environment more sustainable and resilient for the future.”
A survey is now planned to identify the best position to create a wooden barrier in the river to deflect water and stabilise river flows through the bridge piers. This should also help to prevent shoal from building up again in the future, reducing the cost of maintenance and the quality of the environment in the long term.