Derbyshire County Council employed Land & Water Services to carry out dredging works on the Cromford canal to improve the ecology and habitat of the waterway. The site was registered as a SSSI which required close liaison with Environment and Regulatory bodies. The main challenge was to ensure the integrity of the SSSI site was maintained giving due regard to wildlife, Fauna and Flora and general ecology of the site and surrounding areas.

Mobilisation including access and egress to the site compound which were made difficult due to the adjacent railway tunnel and line which required careful planning and consideration. Access to the waterway was further hampered by the location of a restricted weight bridge at the entrance to the site. A 13 ton excavator was fitted with an extended turret to raise it above water level allowing the machine to track up and down the waterway to load awaiting hoppers.

The works were split into two phases to accommodate the location of an uncharted sewage pipe which was found within the working area. Arising’s were spread to land requiring exemptions and prior liaison with the local Land owner. The field utilised was sectioned and tiered to allow material to be placed, dried and spread to agreed tolerances. Our Client Derbyshire County Council were extremely pleased with the out come of the project.

The River Lambourn had become devoid of many of the natural characteristics found within chalk stream rivers. Throughout the last 100 years the river has become twice the width of what it had been leading to reduced flow conditions. The slower flow allowed silt deposits to smother the natural river bed gravels upon which the fish, invertebrates and vegetation were all dependant upon. The tree canopy to the river banks had become dense over sustained periods and many areas of the river corridor lacked natural light.

Specialist consultants and project engineers worked closely with Land & Water Services to deliver the restoration project. The works covered some 2 km of river which is a designated Site of Special Scientific Interest. Large areas of tree canopy were reduced via the selected felling of the tree limbs in order to reintroduce natural light to the corridor. All felled timber was retained upon site for reuse within the project. New revetments were installed from the bank with retained material from the tree felling being utilised to face and infill the revetments. Large tree limbs were installed at upstream angles to the bed of the river to act as flow restrictors.  These tree limbs along with the revetments narrow the river and deviate the water flows resulting in water accelerating  around the installations (conditions favoured by fish species).

Over 6,000 tons of gravel was placed into the river in order to raise the bed height, again accelerating river flows but equally providing spawning areas for fish & other aquatic species.

Works were undertaken within urban areas proving highly restrictive for access. Land & Water acted as principal contractor under full CDM regulations.

As a designated site of Special scientific interest the River Lambourn had been identified by both Natural England and the Environment Agency as not meeting the conditions required by the diverse fish species, aquatic invertebrates and stream flow normally found within a characteristic chalk stream river.

The main outlying cause of the conditions being impounded river sections by structures preventing fish movement and slow river flows. The slower river flows allow silts to deposit to the river bed smothering the natural gravels on which the fish, vegetation and invertebrates are all dependent. To address the situation Land & Water Services worked closely with Halcrow, the client’s appointed Engineer to undertake the works. 

The Land & Water contract called for a number of structures to be altered, reconfigured or completely rebuilt to high specifications. Temporary works included piled coffer dams and large scale river diversions in several areas of the site. Works to a former water wheel weir and a sluice structure were undertaken to allow the main river channel to flow 450mm below the original level. The main sluice downstream of the weir pool was extended and separated by the placement of a central wall, new stainless steel penstock valves were installed to allow full control of the water levels within the weir pool. A larinier fish pass was bolted to the new weir base in separate sections.

Provision was made for the installation of a new footbridge, the crest height to the weir pool was raised as required and a pre planted coir revetment installed. Detailed landscaping was undertaken to restore the areas affected by the works.