River Ogwen Site Visit

This week the RRC and Natural Resources Wales held a site visit to the Ynni Ogwen hydropower scheme in Braichmelyn, near Bethesda; and the Afon Ogwen valley in Nant Ffrancon in North Wales.

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14 delegates met at the Zip World Penrhyn Quarry in Braichmelyn, just as the rain started in the morning! A short walk through the slate filled landscape took the group down to the Ynni Ogwen hydropower scheme on the River Ogwen. Griff Morris and Gareth Cemlyn Jones, directors of the scheme, talked through how the project works and who was involved. This project has been running since May 15th 2017, and is community and volunteer led. The hydropower which is generated is planned to be utilised by local households using Smart meters.

The scheme involved constructing an intake weir across half of the channel, for water to supply the hydropower generator, before being pumped back out of the power house into the channel downstream. The other half of the channel provides a natural, fast flowing, boulder-ridden stream for migratory fish. This stream is important for Atlantic salmon, therefore maintaining good environmental flows for ecology was crucial. Gideon Carpenter from NRW talked the group through the importance of licensing and abstraction licences. The scheme had to maintain a low flow channel, which was monitored using a water level recorder instream. Gareth showed the group the powerhouse where the generator is monitored, and the amount of produced energy is recorded.

Following discussions in the rain about catchment involvement in river restoration, funding, and hydropower schemes, the group made their way to the shelter of the Zip World café to dry off before heading to the next site.

The second visit started at Ogwen Cottage (Cwm Idwal visitor centre), just as the rain started to ease off. The River Ogwen in the Snowdonia Mountains was modified in the 1960s for land drainage and farmland, leaving poor ecological habitat and reduced fish numbers. Restoration was completed in 1998, including creating pools and riffles and installing natural cascades. Gravels, cobbles and boulders which had previously been dredged out of the river to improve velocity and reduce local flooding, were reinstated, raising the river bed across the whole stretch of almost 1km. The group walked down into the valley and across the farmland to see the features instream.

The channel was at low flow during the visit, so there was clear visibility of the instream features. Old Ordnance Survey maps also show an island was once present at this site, before the river was dredged in the 1960s. The restoration in 1998 restored, reinstated and enhanced the island feature through excavating the left side of the channel to create a side channel. The low flow during the visit meant the channel was dry, although it showed where the river would cut across the landscape to create the feature during higher flows. Furthermore, boulders were used to create cascades, diversifying flow patterns and raising the water level, helping to inundate the excavated side channel and highlight the river island.

The group discussed the impact of the restoration on geomorphological processes, and how the scheme could be altered and designed differently to further enhance habitat and natural flow paths. One point that was raised was the importance of lateral connectivity and floodplain connection, and how a totally natural river would not have a prominent step between the channel and the surrounding land, but be free to flood onto the adjacent floodplain. In this valley the land use is mainly pasture, as the National Trust owned land is used for organic farmland. This highlights the importance of catchment stakeholder involvement and engagement.

You can view Manual of Techniques Case Studies on the River Ogwen here –

Restoring and stabilising over-deepened river bed levels

Restoring a ford as a stock and vehicular crossing point

Thank you to Sue Hearn from Natural Resources Wales for helping to organise and deliver this site visit. Thankfully the sun came out in the afternoon, and the group enjoyed learning more about restoration at both sites.

 

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