Site: River Nene & River Great Ouse
Date: Winter 2018-19
Value: £250,000
Introduction
The Rothen Group were asked by JN Bentley and the Environment Agency to assist with the de shoaling works across numerous sites located on the River Nene & River Great Ouse. The project involved:
Understanding access & logistical restrictions
Time & ecological constraints including fish breeding season
Managing the changing river conditions
Creating gravel breeding beds for fish spawning
Installing rock armour in scour holes
Providing safety & inspection boats for the EA throughout the project
The Project
The sites came with a number of logistical challenges that needed to be considered and overcome quickly.
Due to the rural settings there was no access for land-based plant or equipment and the works had to be undertaken during the winter when locks were closed for refurbishment, further reducing access. This meant that all works had to be undertaken from waterborne plant that could be easily mobilised. There were also strict time constraints that needed to be met for ecological and environmental reasons, due to fish breeding season and bird nesting. Despite all of this, The Rothen Group and JN Bentley were able to complete the works in just under 3 months.
Ian Rothen, Founder of The Rothen Group commented: “It was obvious from the outset that this was a specialist project requiring a number of innovative solutions to work around the issues presented. Thankfully we have the equipment and experience to ensure that, even without land access, we could reach the hard to access areas, with minimal disruption.
The Rothen Group’s first step was to resolve the site access issues. To do this, The Groups’ wide-beam digger pontoon was specified for the job. The new 26ft wide beam digger pontoon is fitted with a small hydraulic power pack which operates four stability jack legs, allowing the pontoon to hold up to 8 tonnes of machinery, whilst on the water.
A marine ready excavator was then placed on the pontoon, which was used to carry out the shoal realignment. The works involved redistributing areas of gravel which had formed a shoal, downstream of lock entrances, thus significantly reducing navigation along the river. The gravels were loaded into hoppers for moving to other areas, where deeper water was present. The gravel was then spread in a tear drop shape with a special riddle bucket to sort the gravel into different sizes, to form fish spawning ground.
In addition to this, rock armour was placed in ‘scour holes’ to prevent further erosion and distribution of gravel. All the rock armour had to be loaded 3 miles away & boated to site.
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