Authorities count the cost of bridge work

12 November 2009

Engineers can no longer bank on low water levels in summer rivers when estimating the costs of bridge strengthening or reconstruction works, one council has claimed.

The warning has come from Denbighshire Council, which has suffered cost increases on two bridge projects. One was affected by flooding twice this summer, despite it being drier than the previous two summers. In future, temporary bridge supports will need to be stronger, yet also interfere less with water flow.

A capital bid for £190,000 was made in October 2008 for strengthening Grade 2-listed Pont Telpyn, near Ruthin. Bob Humphreys, Denbighshire’s section manager for bridges and structures, told councillors this week the cost was now estimated at £439,000.

Officers had responded to ‘considerable external pressure’ from the public and councillors by scheduling the project for the earliest opportunity, awarding a ‘cost plus’ contract before design works were completed. The project included river diversion and temporary scaffolding to support the fragile bridge.

Works were delayed by flooding in July but were almost finished when another flood occurred, on 6 September. Debris, including a large tree with branches intact, caught on the scaffolding, partially restricting river flow. ‘The bridge suffered scour damage to one abutment which resulted in significant settlement to that abutment,’ said Mr Humphreys. The bridge was consequently closed, with a two-mile diversion for vehicles and pedestrians.

He explained: ‘Traditionally, any work over watercourses is timed for the summer, where access requirements and temporary works were less demanding, and consequently less costly, due to low river levels. However, recent experiences with this scheme and Victoria Bridge, Corwen, show we can no longer rely on low river levels in the summer.’

He said more robust and less intrusive temporary works will therefore need to be adopted in future, which will inevitably increase costs.

‘There may be projects where the costs of such robust temporary works are prohibitive and we have to accept the risk of a summer flooding event,’ he added.

The Victoria Bridge project involved temporary propping and access from the river. A Denbighshire spokesman said that ‘unusually high river levels’ in summer 2008 delayed progress and washed away temporary works. Some elements were postponed to 2009.

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