Slowing the flow and increasing habitat for floodplain plants and animals
The proposed works to restore in-stream habitat features and remove some sections of bank protection will reconnect the river with the floodplain, allowing water to flow into the existing paleo-channels (remnants of the original, pre-straightening, river channel) and flow through the site as a second river. This not only increases the amount of habitat available for both freshwater and floodplain plants and animals, but also slows the flow of water in high flows, improves floodplain storage and ground infiltration and removes sediment from the system.
More water stored on the floodplain
Although it should be very clearly noted that these interventions will not prevent flooding in Patterdale, they will help to reduce the flood risk. For example, more sediment will be stored in the floodplain through the improved connectivity between the river and its floodplain instead of being transported down to Grisedale Bridge and blocking the arch there, which has been known to contribute to localised flooding in the past. The project will also store around 5000m3 of water during flood events which, whilst only a relatively small amount, is still less water being transported down the beck at any one time.
Environmentally, a more naturalised river channel and floodplain means improved habitat diversity and therefore biodiversity too. In stream, habitat will be created for a whole range of creatures, ranging from invertebrates such as mayflies and stoneflies, to brown trout (which we know are present at the site) and eels (which have been recorded there in the past). This will in turn help other wildlife such as otters, who rely on these species for food.
Changes to the floodplain will also benefit wildlife. Plant diversity will be improved due to the changed hydrological regime and will increase the number of invertebrates – from worms to moths and butterflies. These invertebrates play an important part in the ecosystem. As well as improving soil quality and helping pollination, they are the food source of a huge range of wildlife, particularly bats and a number of bird species.
The final result of this project then, will be a site that provides environmental and flood benefits, is still a working farm and that complements the beauty of the Grisedale valley which is enjoyed by huge numbers of people every year.
By Lev Dahl, River Restoration Manager, Eden Rivers Trust