Interserve, one of the Environment Agency's partners in the National Contractor Framework No 2, is undertaking the flood defence works around the city of Ripon in North Yorkshire. Ripon has a long history of flooding, as it is situated at the confluence of the rivers Laver, Skell and Ure.
The works include:
A flood storage reservoir on the river Laver
- New flood defence walls and embankments in residential areas
- Improvements to existing bridges in the city
- Replacement of an existing weir and the construction of a new river gauging system further upstream.
Work commenced in October 2009 on the flood storage reservoir located on the river Laver upstream of Ripon. These initial activities consisted of enabling works to improve access to the remote rural location, securing of the extensive site boundaries and establishing the site facilities.
The protection of the local environmental and existing habitats such as otters, bats, nesting birds and aquatic river life, have been key considerations during construction.
The ongoing permanent site works started in February 2010 and 160 linear metres of 13-tonne concrete box culverts have been successfully installed on site. These culverts will divert the river Laver through the new 100,000 m3 earth retaining dam wall.
The cast in-situ inlet and outlet structures have been completed and new inlet and outlet channels and revetments are being constructed to allow the river to be diverted onto the new alignment in June 2011. The earthworks will then follow with all materials being sourced from the site. Advance testing is being carried out to assess the suitability of clay and gravels available from borrow pits in nearby fields.
The dam is designed to retain excess river flows from up to a 1 in 100 year storm event. Should this be exceeded, the structure will be allowed to overflow via spillways fitted with erosion protection measures and a reinforced concrete tail bay to prevent scour at the toe of the dam wall.
The detailed designs for the city works were carried out concurrently with the construction of the dam, which commenced in summer 2010, thus optimising the programme duration. The works include new flood defences in fifteen residential properties along Borrage Lane, which runs alongside the River Skell downstream of the point where the rivers Skell and Laver merge. Residents have been extensively consulted throughout the design and construction. Other works in this area include clearing a blocked arch at Borrage Bridge.
In the Fishergreen area of the city, gabion baskets are being installed along the right bank of the river Skell in order to prevent the riverbank eroding any further therefore protecting the main sewer, road and residential properties, which run alongside this part of the river. Two new earth embankments are being constructed on the left bank and sheet piling is also being installed in this area.
In the North Bridge area of the city some roads are being raised, sheet piling is being installed and another earth embankment will be constructed.
To inform residents of the forthcoming works, Interserve visited local residents in Alma Weir, Fishergreen and the North Bridge and also held open information evenings promoting the benefits of the project to the community.
We also organised educational visits to local schools and educational centres targeting 4 to 11 year-olds, in order to increase awareness on the dangers of playing on construction sites.
Video presentations and a poster competition were launched for the schools and centres. The pupils created posters showing the dangers of playing on a construction site and the winning three pieces were displayed around the construction sites. Judged by the site team, they were presented with prizes for their hard work. Pupils from Sharrow Church of England Primary School were thrilled with the protective hard hats, vests they were provided and they were shown clay that the construction team were working with on the dam. Ripon Cathedral Primary School pupils visited Alma weir (pictured). This was followed by sharing the important safety messages during an assembly to parents and the rest of the school.