- 1st September 2017
- Posted by: Sabina Gubbin
- Category: Projects
Brougham bridge is a three-span masonry arch bridge crossing the River Eamont adjacent to Brougham Castle near Penrith. The structure was built in around 1813 and is a good example of an early 19th century turnpike bridge.
The structure suffered significant damage as a result of Storm Desmond in 2015 and has been closed and subject to repair since then. Before the structure is re-opened, the owners wanted to understand the residual scour risk at the structure so that the appropriate management procedures could be adopted in the future.
We visited the site and reviewed the existing available information to undertake a Level 2 Scour Assessment. This was in accordance with Volume 3 Section 4 Part 21 BD 97/12 of the Design Manual for Roads and Bridges – The Assessment of Scour and Other Hydraulic Actions at Highway Structures, May 2012.
The bridge and catchments characteristics were established from the site visit as well as the nature of the repair works. This included sheet piling and rock armour to the river bed which provided some of the bridge elements with adequate scour protection.
We were provided with an existing hydraulic model of the river and structure and this was used to determine the water depth and velocity for the assessment process. In addition, we produced a 2D HEC-RAS model using the freely available LiDAR DTM data. The model was run with the 200yr + 35% climate change hydrograph. The velocity results are shown below.
The output showed the influence of the adjacent A66 highway structure which is located approximately 120m downstream of Brougham Bridge.
There was limited foundation depth information and so we assumed a foundation depth of 1m, but carried out a sensitivity analysis by assessing the elements with varying foundation depths.
With over 20 years’ of experience in carrying out scour risk assessments, we were able to identify the significant issues at the structure and to use appropriate variables in the BD97/12 assessment process. We reviewed the impact of the repair works currently being completed and detailed additional investigations and remedial works required to control and manage the scour risk in the future.
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