MBW3-45 ELR: No coring surveys have been found for this structure. There are no records of any previous inspections of the structure.

Transcription

1 Scour Assessment Report Location Plan: Scale 1:5,000 MBW3-45 Score: ELR: Contains Ordnance Survey data Crown copyright and database right 2010 Category: HIGH Assessment Date: 19/11/2010 Contract: Client Contact: Brian Wainwright Middlesbrough Whitby Mileage: 25miles 198yards OS NGR: NY OS 1:50,000 Sheet: 94 Watercourse Name: Watercourse Status: Agency Region: Agency Area: Existing Flood Marker: River Esk River North East Region Dales Area None present Location and Access: MBW3-45 is located approximately 1km to the north east of Grosmont, North Yorkshire. Parking is available on the farm track close to The Priory. The structure can then be accessed by following the rail track along the field north eastwards. Previous Assessments and Examinations: Assessment: No assessments have previously been carried out on this structure. Underwater Examination: Bridgeway (February 2009) - The structure was found to be in an overall fair condition. Coring Survey: Other Inspection: No coring surveys have been found for this structure. There are no records of any previous inspections of the structure. Basic Structure Information: (Photographs are appended to this report) MBW3-45 is a twin span, steel deck on masonry abutments and pier that crosses the River Esk near Grosmont, North Yorkshire. Both abutments are situated on the edge of the channel and are flat faced. They each measure 10m in length and have an effective width of 1.5m. The left abutment has some missing masonry blocks from the upstream face. Wing walls extend from all elevations on both bridge abutments. These follow the contour of the embankment. Both spans convey the watercourse and measure 9m in width and have a bed to soffit height of around 10m. The two spans are separated by a masonry pier. The pier measures 1.5m in width and runs a length of 10m through the centre of the structure. The pier has a triangular cutwater at its face. The central pier is known to be founded on steel piles. These are in the form of eight cylindrical piles which measure 1m from centre to centre. For this reason the foundation depth for the pier has been assumed as 3.0m below watercourse bed level. Also noted was a significant debris accumulation around the central pier that could affect flows around the columns. MBW3-45 Stage 1 Report.doc 1

2 Scour Assessment Report Findings of the Assessment: The scour assessment procedure categorises this structure as Priority 2 (Priority Score 16.86), using an assumed foundation depth of 1m for the abutments and 3.0m for the central pier. This rating places the structure at medium priority for scour. A structure in this category is not in immediate risk of failure from scour or other hydraulic forces likely to result in undermining of the support elements, but should be monitored regularly to ensure that it remains safe. The following actions are recommended in for structures of high priority: Detailed Hydraulic Assessment. If the High Priority is confirmed by detailed assessment, then the structure should be included in the flood warning plan or physical protection works should be undertaken. Regular underwater exams and assessments using this procedure to monitor changes which may be taking place. Regular monitoring of the structure, during or immediately following a large flood. Assumptions used in Calculation: A foundation depth of 1.0m below watercourse bed level has been assumed for the abutments and 3.0m for the piled central pier. It has also been assumed that there is no adequate existing scour protection or invert present. Sensitivity Analysis The effect of a change in foundation level is summarised below. Fdn Depth (m) Score High Category High Score is based on an assumed foundation depth of 1m High Recommendations (from NR/SP/CIV/080, NR/CS/CIV/032 & ): 1. THE STRUCTURE HAS RETURNED A HIGH PRIORITY RATING AND MUST BE REASSESSED USING (OR AN APPROPRIATE METHOD) AT YEARLY INTERVALS. 2. THE PRIORITY SCORE MUST ALSO BE REVIEWED FOLLOWING A FLOOD, ANY CHANGE TO THE CHANNEL OR STRUCTURE, AND FOLLOWING AN UNDERWATER EXAMINATION. 3. UNDERWATER EXAMINATIONS SHOULD BE CARRIED OUT AT A 3 YEAR INTERVAL OR FOLLOWING A FLOOD EVENT. Future Examinations: Underwater Examination: every 3 years Scour Review: as detailed in no.2 above Assessment: every 3 years (next due 2014) Report Sign-off Checked and Approved by Richard Buck, Director Signed: Date: 23 March 2009 MBW3-45 Stage 1 Report.doc 2

3 Scour Assessment Report A. Photographs (Photographs taken 24/11/10) Photograph 1 Upstream Elevation Photograph 2 Downstream Elevation MBW3-45 Stage 1 Report.doc 3

4 Scour Assessment Report Photograph 3 View of steel piles on central pier Photograph 4 Missing masonry slabs on left abutment (Upstream) MBW3-45 Stage 1 Report.doc 4

5 Calculation Results Analysis Specification NR/SP/CIV/080 Region: LNE ELR: MBW3 Number: 45 Date:17-Mar-11 Result:16.86 Element Name General Scour (m) Local Scour (m) Total Scour (m) Foundation depth (m) Preliminary Priority Rating Load Bearing Material Adequate Invert Present Scour Protection Present Element Priority Rating LH Abutment Unknown Unknown Unknown RH Abutment Unknown Unknown Unknown Pier Unknown Unknown Unknown Worst Case Element - RH Abutment Rating Element Priority 20 This page is intentionslly left blank Priority 1 High 19 Priority 1 High 18 Priority 1 High 17 Priority 2 High Priority 3 Medium Priority 4 Medium 14 Priority 5 Low 13 Priority 6 Low Priority 6 Low Priority Rating Priority 6 Element Result Low Total scour depth: m Foundation Depth (m) 1.0 Total Scour Depth (m) 8.17 Final Priority Rating High Priority Printed by: JBA Page Number: 1 of 4 Printed from: NRScour.Analysis.doc Date of printing: 17/03/2011 License No.: NRScour Version No.: 2.0

6 Calculation Results Analysis Specification NR/SP/CIV/080 Region: LNE ELR: MBW3 Number: 45 Date:17-Mar-11 Result:16.86 This page is intentionally left blank Printed by: JBA Page Number: 2 of 4 Printed from: NRScour.Analysis.doc Date of printing: 17/03/2011 License No.: NRScour Version No.: 2.0

7 Calculation Results Analysis Specification NR/SP/CIV/080 Region: LNE ELR: MBW3 Number: 45 Worst Case Element - RH Abutment Date:17-Mar-11 Result:16.86 DETAILS SYMBOL VALUE UNIT SCORE Type of Stream Score St # 6 Bank Stability Score Bs # 3 Non Tidal data Distance from River source to Bridge L km 85% Distance upstream x 8.76 km O.S. contour line a m 10% Distance upstream y 1.03 km O.S. contour line b m River Slope (a-b)/(x-y) m/km Non Tidal Score # 6 Tidal data Spring tide range H 0.00 m Upstream tidal area Au 0.00 m 2 Upstream tidal volume V 0.00 m 3 Bridge area at Mean Sea Level A m 2 Tidal period T 1.00 s Tidal velocity u 0.00 m/s Tidal Score # 1 Flashiness Score (highest of Non Tidal and Tidal Score) Fs # 6 River Type Tr # Main dimensions of watercourse Channel width Wu m Channel depth Yu 2.50 m Channel width under bridge Wb m Channel depth under bridge Yb 2.50 m Floodplain width Wo m Floodplain depth Yo 0.75 m Size ratios Channel width/underbridge width Wu/Wb 1.00 Floodplain depth/channel depth Yo/Yu 0.30 Floodplain width/channel width Wo/Wu 2.50 Relative general scour dg 1 /Yu 0.20 Additional general scour Scour at bends Sb # 4 Bed material size D mm Bed material grading Bm # 5 General scour coefficient dg/yu 0.45 General Scour depth dg 1.12 m Printed by: JBA Page Number: 3 of 4 Printed from: NRScour.Analysis.doc Date of printing: 17/03/2011 License No.: NRScour Version No.: 2.0

8 Calculation Results Analysis Specification NR/SP/CIV/080 Region: LNE ELR: MBW3 Number: 45 Date:17-Mar-11 Result:16.86 Worst Case Element - RH Abutment DETAILS SYMBOL VALUE UNIT SCORE Pier or abutment width Wp 3.00 m Pier or abutment length Lp m Pier or abutment thinness Lp/Wp 3.33 Angle of attack α deg Angle of Attack/Thinness Score Aa # 1.3 Pier group Column to Column distance parallel to flow C m Parallel group Score Gc # 1.0 Column to Column distance normal to flow C m Normal group Score Gc # 1.0 Pier group Score (highest of Parallel and Normal Score) Gc # 1.0 Shape and blockage Element nose shape Score Ns # 7 Debris blockage Score Bd # 5 Relative flow depth General scoured depth Yu+dg 3.62 m Relative flow depth Ym/Wp 1.21 Relative flow depth Score Rf # 5 Local scour coefficient FL 1.57 # Local Scour depth dl 7.05 m Total scour depth dt=dg + dl 8.17 m Foundation depth df 1.00 m Adjustment depth Factor AF 0.00 m Adjusted total scour dt - AF 8.17 m Preliminary rating PPR # Load bearing material Unknown Rating amendments Amendment for River type PPR+Tr # Amendment for Load bearing material # Amendment for Adequate invert or riprap # Priority category # 2 Printed by: JBA Page Number: 4 of 4 Printed from: NRScour.Analysis.doc Date of printing: 17/03/2011 License No.: NRScour Version No.: 2.0