Innovation key to successful weir refurbishment project


Working on behalf of the Environment Agency and as part of Team Van Oord*, Mackley has successfully completed a project to improve flow monitoring and fish passage on the River Cray at Crayford in Kent.

Two existing weirs have been replaced with a narrower low flow channel and a Flat-V weir for the high flow section.

The scheme also saw the installation of a Larinier fish pass and separate elver pass, which were were constructed following a planned fish rescue to provide improved fish passage and monitoring.

Improved access to the river and a new hard standing and edge protection for future maintenance of the weir, were also incorporated into the scheme.

With the works taking place on and close to the river, both the timing of the scheme and methods of working had to take into account a number of environmental considerations including the presence of water voles, reptiles and nesting birds.

The success of the project, which was completed in December 2015, is attributed to a series of management decisions taken by the project team.

Andy Martin, Mackley Project Manager, said: “The first important decision was to relocate the site compound. The original compound occupied a number of parking spaces belonging to a busy industrial estate, which we quickly realised was not going to prove popular with the businesses based there.

“We got permission to use a small parcel of land to the side of the industrial estate which gave us a much better base to work from, and also minimised disruption to local businesses.”

A review of the required temporary works produced another innovation.

Andy Martin said: “Instead of fluming the river through the works using pipes on stands, team member Gary Clark came up with the smart idea of diverting the flows through the river bank using a 600mm twin wall pipe.

“This allowed us to cofferdam off the river, and with a relatively small amount of over pumping we were able to dewater the entire weir and stay pretty much ‘rain proof’ throughout the project. Burying the diversion pipe also helped maximise space on site.”

Installing an access bridge across the river enabled the project team to pile the cofferdams without the need for a crane. The bridge also provided permanent access to the far bank for plant and labour, which previously had been challenging.

If a crane had been required, it would have taken up most of the near bank compound area. Instead, this area was freed up, further minimising the impact of the works on businesses operating in the area.

The team also deployed a new design of boom from Pro-Earth which absorbs pollutants including hydrocarbons and chemicals before they can run into the water stream, and participated in a trial of Pro-Earth’s SaveSorb product for water run off.

Andy Martin concluded: “Despite some early objections from some of the businesses on the industrial estate, the site team soon brought them round and turned a potentially really difficult logistical contract into a successful one.”

River Cray: before
River Cray: during
River Cray: After
And after completion

*Team Van Oord
Team Van Oord is a joint venture partnership between Van Oord, Kier Group, Mackley and Royal HaskoningDHV.

15 February 2016

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