The brief
To replace a post-war concrete clapper-style bridge over a section of the River Itchen to maintain access along a popular public Right of Way. M:P commissioned a structural engineer’s report on the existing bridge which concluded that the existing deck and abutments were in poor condition with no structural value and the in-channel support piers would require repair prior to re-use. Access is poor, the river is classed by the Environment Agency as a main river and is designated a SSSI for its rare chalk stream habitat and associated species assemblages.
The solution
M:P worked with our consultant structural engineer to design a new bridge that fits the countryside setting and that could be built within the access restrictions and environmental permitting conditions of the EA and Natural England.
Construction details included new mass concrete abutments, steel screw pile and concrete support piers in-channel at third locations, galvanised steel substructure and timber superstructure. Additional elements included access ramps, grip strips, new approach path surfacing and kissing gate, along with details such as cladding to hide the steel substructure and hidden fixings.
The riverine environment necessitated careful phasing of the works, enabled by building temporary dam structures out from either bank. This allowed sections to be worked on sequentially - existing elements demolished and new sections constructed while allowing the river to continue to flow and preventing debris from entering the water.
The outcome
The design and build project balanced the requirements of the EA, Natural England, local residents, anglers, general public and client. Careful planning working with statutory bodies minimised impact on the sensitive aquatic environment and accounts for predicted increases to rainfall and river levels, reducing associated future flood risk. Within a short space of time the bridge had weathered in and continues to enable public access across this beautiful section of the river and its rare chalk stream habitats.
