Our first project to restore Blackburn’s rivers is now complete. Bypass channels, or fish passes, have been constructed alongside two large weirs near Hoghton Bottoms and Lower Darwen, these channels will allow fish such as trout, salmon, and eels to migrate further upstream into river habitat that has been inaccessible for decades.
The weirs were originally built in order to harness the water for the local mills, which, at one time, were abundant in this area. However, the mills at these sites have long since been demolished some time ago. Despite this the weirs have remained and continued to affect the ecology and habitat quality of the river, as well as providing a barrier to the upstream migration of spawning fish.
Now that the bypass channels are working it is expected that there will be an increase in the fish populations here, and with more fish other wildlife will also return to the river such as otters and kingfishers. This is also good news for the people of Blackburn and Darwen, with these improvements in the rivers and associated habitats providing more diverse green spaces for people to visit and enjoy.
Following the success of these fish passages further work will be carried out on a section of the River Roddlesworth near Feniscowles in 2019. The section of river that is being improved is currently flowing through an underground culvert on the site of the former Star Paper Mill and is completely devoid of wildlife with no natural features. The area is now being redeveloped into housing which is providing us with the opportunity to return this section of river to a more natural state, allowing it to see daylight for the first time since the mill was built in 1875.
The River Roddlesworth flows down from the moors above Darwen, passing through woodlands and reservoirs before finally joining the River Darwen at Feniscowles. Just before this confluence the river is diverted into an underground culvert beneath the site of an old paper mill. It is here that our latest project is taking place.
The site of the old paper mill is now being developed into housing. Initially the plans for the development included the removal of the old culvert and the creation of a new concrete lined channel across the site. However, after discussing the project with the Ribble Rivers Trust the developer’s plans were changed and a project was set up to construct a ‘close to nature’ river channel around the site instead.
An example of a ‘closer to nature’ river channel
With support from the European Regional Development Fund and with our project partners Edenvale Young the new channel will be designed with features that will mimic those of a natural river. Following the course prefabricated by the developers, the new channel will have features such as pools and riffle sequences which will create a variance in flow that will provide the best habitat possible for several species of fish and invertebrates. It is hoped that in time these invertebrates and fish will attract different species of birds to the area and perhaps even mammals such as otters. The quality of the river habitat above and below the site is already good and so by renaturalising this section we hope to connect the habitats and create a wildlife corridor.
In addition to the renaturalisation of the River Roddlesworth there are three fish passage projects taking place above and below the mill site which will reconnect the fragmented habitat and open a further 19 hectares of river habitat for migrating fish and other wildlife.
Houghton Bottoms weir
The lowermost of these is Hoghton Bottoms Weir which was originally constructed to power a mill and cotton factory but is now surplus to requirements. It is proposed that a rock ramp be constructed on the left side of the weir, providing a channel that ﬁsh can use to bypass the structure.
The uppermost weir to be targeted is Lower Darwen Weir. A map from 1845 shows a mill race running from this weir to Ewood Cotton Mill with another, later map showing a second connection to a paper mill. Lower Darwen Weir is close to a swimming pool, nursery and industrial estate meaning that removal of the weir is not an option. Instead a rock ramp bypass channel will be built to the left of the weir which will encourage fish passage and help to stabilise the areas of erosion on the riverbank.
Thirdly the weir located just upstream of the ‘close to nature’ channel will enable fish to move along the length of the River Roddlesworth as far as the Roddlesworth reservoirs.
A map showing the current route of the River Roddlesworth in blue and the new route in red
Why is this work necessary?
The North West of England has a rich industrial heritage but this industry has resulted in environmental damage and neglect. Blackburn and Darwin’s rivers have historically been used for the disposal of sewage, waste and chemicals and dyes from the mills. In addition to this the towns expansion and the resulting mills, factories and houses meant that the rivers were subjected to greater controls with many being forced through stone and concrete lined channels which created a fragmented river habitat capable of supporting very little life.
A decline in industry and the introduction of environmental regulations has meant that water quality has already improved dramatically as has the diversity and abundance of wildlife. However, weirs and culverts are still proving problematic for wildlife and people; weirs and culverts can be barriers to fish migration, reducing their breeding potential and limiting the amount of number of species that can rely on them for food. Culverts also provide limited space for water and during periods of heavy flow they are often overwhelmed which causes flooding.
How will we determine the project’s success?
One of the ways we can measure the success of fish passage projects is by using Passive Integrated Transponders or PITs (which are similar to microchips in cats and dogs) to track the movements of brown trout. This tracking data will show us how easy the fish find it to ascend the rock ramps and continue their migration upstream.
Water level loggers will also be installed upstream and downstream of the site to collect baseline data then, once the ‘close to nature’ channel is constructed the loggers will again be used to measure the flow. It is predicted that the project will have a positive impact on the size, duration and timings of peak flows.
It is also hoped that following the project Blackburn with Darwen will see an increase in the abundance and diversity of wildlife across the district, helping to encourage a greater understanding, appreciation and enjoyment of the outdoors.