A689 Nenthall, geotechnical design works

Tender description

The site is located on the A689, adjacent to the River Nent, near Nenthall, Cumbria. An eroding riverbank close to the highway is located approximately 130m upstream of Nenthall Bridge at National Grid Reference (NGR) 375985 545695. The eastern bank of the River Nent has been shown to be eroding at a rate of about 1m per year as it encroaches the western verge of the A689, currently the highway is about 10m from the bank. As erosion progresses the height of the bank increases as the highway is elevated above the river stream level. Drainage channels/culvert discharging from highway level may contribute to the erosion. In addition to the main section of erosion there is evidence of erosion downstream on the left-hand bank, upstream of the bridge. This can be seen as undercutting of the bank towards the treeline. This does not affect the highway; however, remediation works to the main slope erosion site may have an adverse effect downstream therefore it is required that the two locations are looked at in unison. This commission requires the review of all available information which includes a PSSR, GI (provided by Coal Board, primary site only), Geomorphological Appraisal (provided by Coal Board) and Ecology Assessment and the design of the most appropriate remediation treatment for both locations if required. The design package will also include drainage requirements and be supported by the required Ecological surveys and reports.