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BOC Immingham Dissolved Acetylene Project Environmental Statement: Vol. 2 Main Text
9.74 The modelling of the overtopping of the coastal defences for a 0.1% AEP climate change scenario
to 2115 indicates that there is considerable risk to the proposed development site. However, up to
2063 the climate change 0.1% AEP water level is below the crest level of the flood defences. The
impact of overtopping is therefore considered to be minor adverse significance.
9.75 The Electrical Switch Room will be protected from flooding by flood doors. The design and
operation of the doors has not been finalised; however, they will either remain closed (unless
access is needed), or will be automatically closed in the event of a flood warning being received.
9.76 Two refuge areas providing a Safe Haven for staff during an extreme tidal event with breach or
overtopping of the coastal defences will be provided within the Generator Building. The layout of
the refuge areas are provided in Appendix 9F and shows the elevations of the areas to be
6.61 mAOD on the first floor and 8.88 mAOD on the second floor Both of these refuge areas are
well above the 1 in 1,000 year (0.1% AEP) extreme sea level plus climate change to 2115 of
6.45 m AOD.
9.77 All other areas will be allowed to flood and in doing so should not pose a risk to site personnel or
to the continuing operation of the site.
9.78 The site is designed to hold two weeks supply of product. When the flood waters have receded,
and it’s safe to return to the site, a portable generator will be used to provide the site’s power
requirements and enable manufacturing to recommence.
9.79 As discussed for the assessment of construction impacts, a flood warning system and flood
evacuation procedures will be implemented for the site.
9.80 With the application of measures outlined above, the significance of the operation impact of tidal
flooding will be reduced to negligible.
Fluvial
9.81 There is a potential flood risk to the staff and equipment from extreme events in Middle Drain
coinciding with tide-locking due to a failure of the pumping station. The pumping station operates
with duty and standby pumps with sufficient pump capacity to provide a standard of protection of
0.1% AEP for Middle Drain. The pumping infrastructure is in good condition and the risk of failure
of the duty and standby pumps could therefore be considered minimal. The impact of failure is
considered to be minor adverse significance.
Groundwater
9.82 As the groundwater is likely to be in hydraulic continuity with the Humber Estuary the main
influence on groundwater levels within the development site will be the tidal levels. Thus the
measures described above for tidal flooding would also protect against this form of groundwater
flooding.
9.83 Consideration will be given to controlling groundwater by land drains to prevent the Deluge
Lagoon from being filled by a high groundwater table in the winter months. Groundwater control
might involve a small pumping station which would discharge into the surface water drainage
network.
9.84 With the control measures described for tidal flood risk (discussed above) and surface water
runoff (discussed below), the construction impact for groundwater could be considered to be
negligible.
5100935.404 Environmental Statement August 2011 140