Restoration of five reaches of the River Nar in and around Castle Acre in Norfolk.
The River Nar is a Site of Special Scientific Interest (SSSI) and has suffered historically from over abstraction, diffuse pollution and channel dredging as a result its conservation condition was assessed as ‘unfavourable’. FiveRivers where contracted to restore four of the reaches in late 2016 and early 2017. The sites had pre and post works biological monitoring undertaken. The reaches were restored using site won materials for bed raising using gravel sourced creating from wetland scrapes, creating low level berms. The fifth reach completed in 2019, entailed creating a 300m long new channel reconnecting the river with the flood plain.
The aim of the five river restoration projects was to reinstate natural form and flow function by using site won materials. Ecological surveys were undertaken on two of the sites a few weeks before and 12 months after work was carried out for monitoring.
The river restoration work entailed the following elements:
- Reconnecting a relic meander at Emmanuel’s Common
- Creating 500m of new channel at Castle Acre Common
- Excavate burrow pits to win gravel
- Bed raising
- Restore the natural pool, riffle glide sequence
- Install large woody material
- Berm creation
- Channel narrowing
- Lowering embankments
- Shade reduction
In October 2016 prior to the start of the restoration, biological monitoring of the fish, macroinvertebrate and macrophyte communities was undertaken across two of the sites Minns Meadow and Emmanuel’s Common and of a Control Reach.
We undertook the river restoration of the five projects using almost exclusively site won materials apart from chestnut stakes used to pin large woody material in place. Borrow pits were excavated to win gravels. The gravel was used to in channel for the creation of riffles and glides with deeper sections left as pools. Trees felled for shade reduction were used as large woody material in channels to promote flow diversity and increase natural sorting of the river bed.
The five projects together restored over 1.7km of the river that had been historically dredged.
Where the new channels have been constructed at Emmanuel’s & Castle Acre Commons the redundant channels have been left as backwater habitats and fish refuges.
The borrow pits used for the site won gravels had turves reinstated to form wetland habitat.
The berm creation, large woody material combined with the bed raising restored the river to a more sinuous channel with an increase in floodplain habitat diversity.