FORTH REPLACEMENT CROSSING

REPORT ON THE SUSTAINED/HIGH INTENSITY RAINFALL EVENTS IN THE QUEENSFERRY AREA DURING

JUNE/JULY / AUGUST 2012 AND THE RELEVANT WORKS UNDERTAKEN BY THE FORTH REPLACEMENT CROSSING

PROJECT

INDEX

1. INTRODUCTION 2. OVERVIEW 3. CONCLUSION

ANNEX A: Scotland Rainfall (mm)Areal series Met Office Overview from hyperlink ANNEX B: Photographs

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1. INTRODUCTION This report has been compiled following an investigation into the flooding incident of 18 July 2012 after heavy rainfall in Queensferry and much of eastern central Scotland which occurred during a month when there was reportedly twice the monthly average rainfall for July(1) (see annex A)

2. OVERVIEW To summarise the chain of events leading up to flooding issues on roads within and adjacent to the site in the Queensferry area – see below:

(See attached photographs Annex B for locational references) HISTORICAL ISSUES TO OCTOBER – DECEMBER 2011 B924/A904/U221 Water flooding was evident on the B924 adjacent to Echline and also at the bottom of the U221 at the connection with the A904 in periods of prolonged and heavy rain. During tender City of Edinburgh Council (CEC) stated that they were aware of a historical water problem inthe area of the A904/U221/B924 junction in relation to flooding. Society Road During periods of heavy rain, water was previously seen discharging over and through the existing retaining wall adjacent to Inchgarvie Lodge. Again, local residents have stated that this is a historical problem. Transport Scotland as landowners of Echline Fields carried out investigation works in this area some years ago and repaired damage to the field drainage caused by other works. Echline Field adjacent to Springfield Ponding water gathered in the field area to the rear of properties at Springfield in periods of heavy rain. This also occurred in the summer of 2011 but to a lesser extent. The natural ground level forms a bowl and the existing field drainage did not cope during prolonged rain periods. This condition was recognised by the project and is catered for in the permanent works design though the installation of a new drain – an operation which was partially completed in spring 2012 and was stopped due to conflict with High Voltage utility diversion works and the effects of weather. This was completed shortly after the diversions during the working day of 18th of July 2012.

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3(1)http://www.metoffice.gov.uk/climate/uk/2012/july.html. See Annex A

RECENT ISSUES MAY – AUGUST 2012 May - June 2012 FCBC Temporary Works for earthworks operations were undertaken as follows: • A temporary lagoon at Echline Field was created (12/05/2012) to provide some attenuation adjacent to the area of the excavation • The recently installed permanent field drainage in Echline Fields adjacent to Springfield was connected temporarily (15/06/12) into an existing outfall pipe. 21 and 22 June 2012 On the 21 and 22 June 2012 after one of the wettest Junes on record(2), again, flooding was evident in each of the four locations noted above i.e. Society Road, Echline Fields, A904/ B924 Junction (Builyeon Road)and U221. Initial mitigation works undertaken were: • At the bottom north corner of Echline Fields adjacent to Inchgarvie Lodge, silt fencing and straw bales were installed to reduce the potential for siltation (22/06/2012) and to provide some retention • In the west field adjacent to the junction of the U221 with the A904, temporary drainage ditches channelling to a temporary sump were constructed (03/07/2012) to assist with retention. 4 July 2012 On the 4 July 2012 flooding was evident in each of the four locations below i.e. Society Road (Inchgarvie area), Echline Fields, A904/ B924 Junction (Builyeon Road) and U221. Further Works Undertaken were: • Drainage ditches and the temporary sump, as described above, were filled in because the large volume of water was running straight through rendering them ineffective. • Temporary containment measures were installed inthe north east corner of the west field adjacent to the junction of the U221 and A904 (06/07/12) 7 July 2012 During further rain FCBC assisted with combating flooding on the A904 with further temporary measures put into place after a site meeting with CEC. These additional measures were:

• A concealed chamber and outfall was discovered at the north east corner of the west field adjacent to the junction of the U221 and the A904. Water was channelled to this chamber through temporary straw bales.

August 2012

4(2)http://www.metoffice.gov.uk/climate/uk/2012/june/averages.html http://www.metoffice.gov.uk/climate/uk/datasets/Rainfall/ranked/Scotland.txt. See Annex A

Following the meeting with CEC a number of further measures were agreed to be implemented at the earliest practicable opportunity:

• An additional temporary drainage crossing under the A904. Installation -11/07/2012 – 12/07/2012

• Installation of the section of permanent outfall under Society Road on 11/07/2012 – 12/07/2012

• Improvements to the bunding in the north east corner of the west field adjacent to the junction of the U221 and the A904 on 17/07/2012

• Completion of field drain (permanent works) at the east side of Echline Fields adjacent to the properties at Springfield on 18/07/12

The following measures were also implemented:

• Debris was cleared from Society Road and the existing outlets in the vicinity of Linn Mill Burn Bridge were unblocked.

18 July 2012 Heavy rain throughout the day, the intensity of which increased in the afternoon, resulted in flooding at all of the locations noted above, including a long section of the A904 between the A90 and the B924 and throughout the wider area in Fife and West Lothian. The accumulated water in the low area of the B924 threatened some houses in Springfield and entered small number of others. Road brush and bowser units were deployed to draw water from the junction of the U221 and A904. Gullies were also cleaned at the corner of the U221/A904. FCBC utilised the plant they had available on site and this was deployed until the increasing volume of water rendered them ineffective. The soil covering was removed during the working day from the top of the recently installed permanent drain in the field adjacent to Springfield to expose the stone filter media and thus accelerate the removal of the exceptional volume of surface water which had built up in that area. It was noted in the late morning that the gullies on the B924 were ‘bubbling’ up and not coping with the volume of water. At the junction of the U221 and A904 the temporary bund was successfully guiding surface water into the previously concealed chamber and associated outfall. As the rainfall intensity increased in the afternoon, parts of Queensferry and the locality became overwhelmed by the volume of water and existing drainage systems failed to cope. As a consequence of these exceptional conditions no further water could discharge into the previously concealed chamber and the volume of water was such that water began to flow over the bund. It is important to clarify that the bund did not burst but it did leak and over-top due to the volume of water.

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In the early evening, CEC and the emergency services attended to a low lying section of the B924 where flood waters had accumulated, the B924 being closed at its junction with Springfield Crescent. At approximately 18:45 FCBC were asked by the police to attend the site to assist in clearing the ‘muddy’ water on the A904. At about 21:40, the rain had stopped and all the gullies were coping with the surface water flows, and the council were in the process of removing their water pump and hoses from the low lying section of the B924. 6 August 2012 On the 6 August 2012 further intense rainfall occurred in the morning and early evening which caused water flows onto the A904. This provided a good test to the drainage mitigation developed and now installed. However, following the above event, the mitigation is being reviewed and further measures to improve resilience are being implemented. Although the water flows above were minor, further larger pumps are being provided for future control. Further investigation of the existing road drainage system has been undertaken and a better understanding of the drainage flows in the area has been gained.

3. CONCLUSION It is believed that the recent problems of flooding in the Queensferry area have resulted from the following key factors:

• Lengthy periods of rain throughout June and July resulting in saturated ground conditions causing any rainfall to discharge as run-off sooner than would normally occur.

• Exceptionally intense(42.8 mm)follow-on rainfall experienced on the afternoon of 18 July 2012.

• Existing road drainage system failing to cope with the exceptional water flow.

Notwithstanding the above and in the interests of helping to minimise the effects of any future similar rainfall event the project has put in place additional mitigation measures which are the subject of a separate action plan (Action Plan to Mitigate Against Flood Risk for Sustained/High Intensity Rainfall Events in the Queensferry Area.)

ANNEX A

Scotland Rainfall (mm).Areal series, starting from 1910. Values are ranked and displayed to 1 dp. Where values are equal, rankings are based in order of year descending. Data are provisional from January 2012 & Winter 2011/12. Last updated 01/08/2012. It can be seen that for June the 2012 rainfall is ranked 7th in 131 years. Average is 84mm. For July the ranking is 20th in 131 years with an average of 101mm

  JUN  Year  JUL  Year    JUN  Year  JUL  Year 

Max Value   155  1938  185.6  1940      72.8  1989  88.3  1991 

  137.9  2002  181.4  1988      71.5  1993  88  1992 

  137.8  1948  170.1  1939      71.2  1976  85.4  1926 

  137.7  1931  165.8  2010      70.8  2009  85  1995 

  135  1966  162.9  1956      70.6  1967  84.8  1981 

  131.7  2004  159.9  1985      70.4  1955  84.4  1997 

  130.4  1980  158  1953      67.3  1971  83.8  1986 

  129.4  2012  154.6  2009      67.3  1970  83.4  1999 

  126.6  1928  150.9  1957      67  1968  83.3  1952 

  125.1  1912  150.5  1946      66.2  1933  83.1  1969 

  123.5  1927  149.9  1936      66  1974  81.7  1978 

  122.8  1990  145  1938      64.9  1977  80.8  2003 

  116.7  1944  144.7  1998      64.3  1996  80.6  1973 

  115.1  1991  144  1924      64  1939  80.5  1912 

  114.4  1919  143.3  1959      64  1923  77.6  1971 

  114  1965  143.2  1970      63.8  1953  77.2  1963 

  113.5  1945  141.9  1918      63.3  1984  76.3  2004 

  112.8  1972  139.7  1950      63.2  1975  76.3  1996 

  111.9  1999  134.5  2007      62.7  1951  75.2  1944 

  111.3  1935  133.5  1931      62.2  1978  74.6  1925 

  110.1  1946  127.7  2012      62  1918  74.3  1962 

  109.4  2007  127.2  1915      61.4  1934  71.4  1990 

  109.2  1947  126.8  2002      58.9  1986  71  2006 

  108.5  1998  125.6  1932      58.3  1942  70.9  1935 

  107.4  1994  121.5  1937      57  1910  67.7  1966 

  107.2  1954  121.1  1923      53.5  1982  67  1949 

  106.9  2008  120.9  1958      52.8  1936  64.6  1994 

  104.9  2005  118  1910      49.8  1920  63.7  1976 

  102.2  1913  117.2  1951      47.6  1914  59.8  1977 

  101.1  1943  115.4  1922      44.5  1949  55.4  1972 

  100.1  2011  114.3  1916      41.6  1915  54.7  1917 

  95.5  1952  113.9  1980      41  1995  51.7  1984 

  94.6  1981  113.8  1934      39.8  2010  51.5  2000 

  94.5  1997  113.5  1961      39.1  1992  49.4  1982 

  93.5  1959  112.9  1942      38.8  1940  49.2  2005 

  92.8  1987  110.4  1933      36.9  1932  47.8  1989 

  91.1  1973  110.1  1993      33.2  1921  45.8  1983 

  91  1950  109.1  1948      32.8  1925  39.7  1919 

  89.8  1917  109  1920      30.9  1941  33.7  1955 

  89.4  1956  108.1  1929    Min. Value  30.1  1988  32.7  1913 

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  89.2  1963  107.2  2008    Avg  83.47    101.39   

  88.1  2001  106.3  1954               87.9  1929  105.6  1987               87.8  1916  105.3  1947               86.9  1924  104.5  1965               86.6  1926  104.4  1941               85.5  1930  104.4  1921             

Avg. YEAR  82.5  1911  102  1974               82.3  1962  101.7  1975               81.3  1964  101.5  1927               80.5  1937  100.9  1979               79.2  1985  100.2  2001               79.2  1969  99.9  2011               78.7  1958  99.2  1960               76.2  1961  99  1928               76  2003  98.9  1968               75.7  2006  98.4  1967               75.5  1960  95  1964               75.4  1957  94.8  1945               75.3  1983  93.7  1914               74.3  1922  92.2  1911               74.1  1979  90.3  1930               74  2000  90  1943             

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ANNEX B AERIAL PHOTOGRAPHS

INDICATION OF GROUND WATER FLOW AROUND A904/U221

New U221 New A904

A904

Previously concealed chamber& outfall

U221

Temporary Drain

Crossing

B924

Route of New Connecting Road

Topographical Low Area

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Excavation south launch

area Temp Sump

ExcavationSP8/ 9

Water removed by completion of permanent

works drain

South site compound

Temp Drain Crossing

AERIAL VIEW ECHLINE FIELD MAP SITUATION

 

U/G CO/H C

Detention Basins

 

AERIAL VIEW ECHLINE FIELD SHOWING APPROXIMATE RELATIVE POSITIONS OF ORIGINAL OVERHEAD CABLES

(O/H C), REPLACEMENT UNDERGROUND CABLES; (U/G C) AND PROPOSED DETENTION BASINS