Designed & Built By
The Afon Ogwen flows through the Nant Ffrancon valley in the Snowdonia National Park and is part of the Glydeiriau Site of Special Scientific Interest. In its upper reaches the Afon Ogwen is a high-energy mountain river. The river is the main outflow from Llyn Ogwen (Lake Ogwen), from which it flows northwards over Rhaeadr Ogwen (Ogwen Falls) down into the large u-shaped glacial valley of Nant Ffrancon.
During the 1960s the Ogwen was deepened by dredging over a 4km length downstream of the waterfall. This was to reduce the frequency of flooding over the valley floor to improve livestock grazing. The river was dredged using two draglines and boulder riffles, cascades, fords and stepping stone obstacles were removed and used to create levees.
Over the succeeding 30 years the river responded to the channel deepening by flushing through virtually all of the finer river bed gravels and scouring both river bed and bank soils in many places. The reach became severely denuded of any stable habitat for flora and fauna and a once thriving salmon fishery declined. Flooding was still troublesome to farmers.
An appraisal of the problem concluded that far too much floodwater was being conveyed in the enlarged channel and that it would be necessary to restore pre-works river bed profiles to correct this imbalance. Re-routing of more frequent floods over the floodplain fields would result from this, helping to sustain other desirable habitats.
Rehabilitation involved recreating boulder cascades, gravel features, stepping stones, islands and a ford in the river according to historical records of former crossing points. Bed levels were raised by an average of 1m. The boulder cascades have transformed the visual appearance of the river from a deeply incised, canalised waterway to a shallower, wider regime that displays many more dynamic features as water tumbles over and between boulders into long pools and runs. Severe flooding during the succeeding two winters has not caused any significant structural damage to the restoration works and flood patterns overland are as predicted.