The River Wensum
The River Wensum Restoration & Floodplain Enhancement Project
The Project began in 2012 and was facilitated by the Catchment Restoration Fund and was completed in early 2016 with the restoration of the entire stretch of the Wensum running through Pensthorpe. A previous successful restoration of the Meander Loop was completed in 2010 by the Environment Agency with great success.
The River Wensum is considered one of the most important lowland chalk rivers and has both EU Special Area of Conservation (SAC) status and Site of Special Scientific Interest (SSSI) status yet it is in unfavourable ecological condition. This is as a result of pollution from both agricultural and urban run-off and reduced functionality due to extensive dredging and straightening.
The extensive design and planning stage allowed the Project team including Dr Rob Dryden and Adam Thurtle both from the Environment Agency, project designer Robin Chase from Atkins and Tim Nevard from Pensthorpe Conservation Trust to ensure that the needs of the river laid out in the River Wensum Restoration Strategy would be achieved.
Rivers are not uniform in depth, speed or width, therefore one of the key areas of river restoration is returning the river to a more natural sinuosity and with variable depths. Different features naturally found in rivers will be used to restore the river and create suitable habitat for several key species.
Gravel Glides are raised areas of washed gravel due to a faster flow, they create ideal habitat for key species such as water crowfoot and spawning sites for fish such as bullhead and brown trout.
Deflectors occur when a large tree falls into the river, this feature creates a build up of silt on the deflector side and a faster river speed on the opposite side, it provides species such as brook lamprey vital habitat at different life stages.
Composite Berms mimic a build up of silt at areas of bank-side vegetation they are at a level that allows water to flow over them during flooding.
Brushwood Berms work in a similar way to composite berms, they are created using staked brushwood, the slower flow rate through the brushwood creates the perfect cover for young fish and invertebrate.
For many the white-clawed crayfish (Ustropotamobius pallipes) may not be the first species they associate with rivers but this globally endangered freshwater crustacean is the main reason that the River Wensum has the Special Area of Conservation E.U. status.
White-clawed crayfish require high levels of calcium, so are found mainly in chalk rivers such as the River Wensum, however they are not very tolerant of pollution or changes in water quality or river morphology. The main issue facing the white-clawed crafish is the introduced and invasive signal crayfish (Pacifastacus lenisculus), these were introduced in the 1970’s from North America, escaping from farms. The bigger and more aggressive signal crayfish out-competes the white-clawed and also carries a fungus which can cause high mortality rates for our only native freshwater crayfish.
Water crowfoot and starwort create floating mats which are very important habitat for invertebrates and young fish. These plants are very sensitive to changes in flow and water levels as well as pollution.
The River Wensum is recognised as an important location for ranunculus and the River Wensum Restoration & Floodplain Enhancement Project aims to restore conditions so that this key habitat can flourish.
A splash in the water as you walk along a river bank may be the only evidence of water voles (Arvicola terrestris), occasionally you will have a glimpses as they head back to their burrow. Water vole numbers are in decline due mainly to loss of habitat and predation by mink.
Water vole surveys carried out at Pensthorpe have shown that there is a healthy populations particularly near the restored Meander Loop section of the River Wensum. Future work on the river aims to restore the required habitats so that we hear those splashes more often.