Background
Pendle Water is a highly modified tributary of the River Calder which starts on its namesake hill Pendle hill and flows through what is now Lomeshaye Industrial Estate. The river channel has been modified for various industrial uses throughout the last 100 years starting with sewage works installed along the river in the early 1900’s which saw much of the channel straightened and lined with concrete. As of the 80’s an industrial estate was created along both banks of the river which saw further modification and straightening of the river further reducing already poor habitat quality.
Straightening the river and lining it has created a vast multitude of erosion and scour issues directly downstream. Which is why this works package was a joint venture between the Ribble Rivers Trust and Pendle Borough Council allowing this project not only to focus on the river being restored but also remediating the increased erosion occurring along the banks, caused because of the modified channel.
To allow the land adjacent to the river to be developed for industrial purposes the banks along the river required stabilising works to occur in conjunction with the remediation of the river channel, to reduce water velocity. Both projects running simultaneously was the best way to gain maximum efficiency from the benefits of each project.
Objectives
Concrete Removal & Check Weir Installation
There were multiple organisations invested in the concrete removal works. Ribble Rivers Trust obtained the funding for the restoration of Pendle Water through a Water Environment Grant under the “Ribble Life for Water” scheme. A programme funded by the European Agricultural Fund for Rural Development (EAFRD) through the Environment Agency and Natural England.
The scope of these works was to re-naturalise the riverbed without meander creation within the channel, due to developments and businesses along either bank. This goal was achieved by removing all concrete lining within and adjacent to the watercourse while also adding check weirs as the concrete was extracted. These check weirs slow the flow of the water within the straightened channel, a task normally undertaken by meanders. Rock armour installation along both banks was the third and final process within the in-channel section of the works. The purpose of the rock armour was protecting the banks and reducing any lateral erosion that may occur, while providing bank support previously supplied by the concrete.
Bank Stabilisation Works
Pendle Borough Council were running a separate scheme with different funding sources; however, it ran simultaneously, this allowed for the best outcome possible from both projects due to their complimentary nature. The aim for the works was to protect the right bank (looking downstream) being subjected to scour, at the end of the modified channel, allowing the land beyond to be developed by Pendle Borough Council for the extension of the industrial estate. The funding for this process in Sanctus’ works was procured from European Regional Development Fund as well as the Lancashire Enterprise Partnership and Lancashire County Council.
Scope of Works
Fish Translocation
Prior to any works within the channel, Ribble Rivers Trust procured an FR2 permit and undertook the electrofishing works on behalf of Sanctus within sections of the watercourse. These discrete sections were enclosed with suitably sized stop nets up and down stream of the working footprint to prevent the translocated fish re-entering the working area. This process was repeated multiple times throughout the works with the nets being moved to adjust to the working areas at the time.
Haul Road & Access Creation
Due to the large quantity of stone to be transported to the watercourse, a haul road was installed to ensure there were no issues with plant bearing loads gaining access into and out of the river up a steep batter. Access was also created downstream for the bank stabilising works where two haul roads were installed for the scour hole infill and the rock armour at the toe of our bank protection.
Concrete Bed Removal
Sanctus are committed to sensitive working within the natural environment and doing so in a safe manner. Works were designed to produce minimal sediment release. The final product produced a much more naturalised river channel, allowing the watercourse to support a wider variety of aquatic species than the homogenous concrete environment allowed previously. All 240 metres of concrete were removed in conjunction with check weir and rock armour installation to the river.
Check Weir and Rock Armour Installation
Without being able to alter the lateral profile of the river, steps were taken to ensure that these works produced a river channel that was as natural as possible, a challenge Sanctus was more than prepared for. Check weirs were installed on top of a strengthened bed, wrapped in a geo-membrane, to give them added cohesion with the riverbed, withstanding vastly increased river levels and therefore water velocities which would subject these structures to scouring.
Rock armour placement along the bank edges of the improved watercourse provides security for the banks either side of the river by reducing channel migration, bank undermining and scour. Also providing habitats previously unavailable due to the urbanisation of the river, improving the environmental value of these works.
Bank Stabilisation
To reduce the effects of the erosion on the bank downstream of the concrete channel, multiple steps were taken to protect the land beyond the right-hand bank for future development by Pendle Borough Council. Our primary task as part of this procedure was the removal of a large tree on the edge of the bank, which was kept on site and cut into a bench for future walkers, adding to the social value of the works that Sanctus ensures is a part of all projects.
The stabilising works themselves consisted of the existing bank being cut to a design allowing for the best blend of land protection and ensuring these protection measures didn’t encroach too far into the potential development space. A membrane was anchored to the cut batter to allow for the collection of sediment during high flow conditions and encourage plant growth along the bank which ultimately was seeded to expedite this process. The toe of the batter, including the membrane, was protected by rock armour along its length.
Challenges
Works Delivery in a High Velocity Flow
Sanctus are committed to ensuring the highest standard of environmental protection measures and with the high velocity of water this created a plethora of challenges. Increased water levels after a period of rainfall provided unsafe working conditions within the channel but also would put immense strain on any silt/fish mitigation measures within the watercourse, often dislodging them from their fixings. This in turn required extra electrofishing sessions which needed to be completed prior to any works continuing.
Sanctus controlled sediment within the fast-flowing river with multiple silt curtains and sediment mats to prevent water quality reductions downstream.
Public Interference
In planning the delivery of works at Pendle Water, Sanctus recognised the requirement to prepare for the public attempting to access site. Despite informative signage and physical barriers, access was still made from the opposite bank of the river which saw relatively large quantities of litter ending up between our downstream and upstream nets, including multiple occurrences of sharps upon net clearances. Sanctus have rigorous sharp object management procedures by use of sharps boxes and grabbing equipment to prevent such items being manually handled. All litter, where possible, was removed and disposed of to prevent water quality being reduced further.
Site Unknowns
Upon gaining access to site there were multiple unknown elements. Sanctus had been informed the scour hole in the riverbed, directly adjacent to the concrete lining, was 4 metres deep but until we began works and undertook a bathymetric survey, we did not know the extent of this scour hole. Spanning a much larger area than previously believed it changed our approach to how we undertook the bank stabilising works. A challenge Sanctus took head on and made a system of work that was safe and allowed for the job to be completed to the Sanctus high standards.
The concrete layer lining the bed was originally 150mm however this was not consistent throughout the whole of the riverbed lining, with it reaching well over half a metre for some sections that were removed. This resulted in an alteration of method requiring different equipment to be brought in to complete the works, increased sediment therefore needed controlling on top of this. This further added to the challenge presented by working in a high energy watercourse, but Sanctus were more than prepared to ensure these arising issues didn’t waver our endeavour to complete the projects at hand to the highest possible standard.
Conclusion
There has never been a more crucial time for British Rivers to have an improvement in their quality in urban environments where impacts such as industrial, road and urban runoff create abundant water quality issues. Restoring the river back to what it used to be is simply the right thing to do for residents, occupants of the industrial estate and the wildlife that inhabit the newly improved blue space in Pendle Water.
Sanctus have taken great pleasure in improving urban wilding opportunities such as this one. We have learnt a lot from undertaking these works and are confident that our works in Pendle Water have been the enabling works to kickstart a great economic opportunity for the local area and add to the ecological and environmental value of the area on top of this.
