It is estimated that over 90% of our rivers in the UK have been modified by humans through practices such as straightening, over-widening, dredging, draining of floodplains and the addition of in-river barriers. These modifications all impact on natural processes and therefore are detrimental to river health and biodiversity.
River restoration refers to several different activities that restore the natural state and function of a river. West Wales Rivers Trust routinely look for opportunities to restore the natural routes of rivers by barrier removal (see below) or by ‘re-meandering’ and/or reconnecting floodplains where land is not developed or of low agricultural value. Where constraints do not allow this, we seek to improve habitat diversity within existing channels through the introduction of ‘large woody material’ or through the removal of hard engineered banksides in favour of natural revetments.
We have also delivered several kilometres fencing to exclude livestock and prevent the poaching of banksides, and riverside tree planting to keep rivers cool and filter run-off.
Barrier removals
In-river barriers such as weirs have a number of impacts on river habitat and biodiversity, including:
- Habitat fragmentation: river sections which were once continuous become divided into separate fragments, restricting the movements of organisms such as fish and separating them from habitats / resources / the completion of their life-cycle and escape from pollution events.
- Degradation of habitat: upstream of weirs, rivers become lake-like, drowning out natural features like riffles, causing important spawning and nursery habitats for river fishes to be lost and reducing oxygen content.
- Sediment transport is halted by weirs, reducing the supply of gravel to the downstream reach, leading to incised channels and reduced spawning and nursery habitats.
West Wales Rivers Trust have mapped the majority of barriers in our catchment and have had considerable success in removing or mitigating many of them to open up many hundreds of kilometres of river to migratory fish, as well as, importantly, to re-naturalise flows and restore habitat. However, there are still hundreds to go, so our efforts continue!
See further examples of our weir removals and fish easements here: Happy World Fish Migration Day! | West Wales Rivers Trust
Invasive Non-Native Species
Invasive non-native species are animals or plants which have not colonised naturally but have been introduced (accidently or deliberately) by people and now have the ability to pose a threat to the environment, economy or people. Currently, there are over 2000 non-native plants established in the UK but not all of these are invasive. Around 15% of these plants pose a threat to the way we live and once established, their damage is irreversible, through damage to infrastructure such as roads and houses, biodiversity loss through competing with native species, and damaging river habitat. Invasive species in West Wales include Himalayan balsam, American skunk cabbage, Japanese knotweed, Giant Hogweed and American signal crayfish.
West Wales Rivers Trusts works to map and identify funding and partnership opportunities to remove and control invasive non-native species (INNS) to promote biodiversity, reduce flood risk and protect our rivers.
