View - North East Lincolnshire Council

BOC Immingham Dissolved Acetylene Project Environmental Statement: Vol. 2 Main Text
Fluvial
9.64 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
9.65 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.
9.66 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.
Pluvial Surface Water
9.67 During construction, the operation of machinery may result in compaction of the soil which will
reduce the infiltration capacity. This may result in an increase in surface water runoff and could
lead to localised flooding. As part of the CEMP, surface water runoff will be managed such that it
will not increase the risk of flooding at the proposed development site, or to land within the
surrounding area. Any surface water flooding is considered to have, at worst, a minor adverse
impact.
Operation
Tidal
9.68 There is a potential flood risk to the staff and equipment during the operation phase of the
Dissolved Acetylene Facility from extreme events which would overtop the flood defences or from
a breach of the coastal defences.
9.69 The primary flood protection measure consists of an earth embankment with a concrete slab on
the crest, a concrete wave wall and a revetment on the front face. The average defence crest level
of these coastal defences is 6.0 m AOD.
9.70 The existing coastal defences are considered to be fair or good condition and the risk of failure of
these defences could therefore be considered minimal.
9.71 The existing flood defences beyond the proposed lifetime of the development (50 years to 2063)
are high enough to prevent overtopping such that the site is defended from coastal flooding to at
least a 1 in 200 year standard of protection. There is, however, a risk of flooding from breach of
these defences and overtopping from more extreme scenarios.
9.72 The EA has provided flood hazard outputs from a two dimensional model built to simulate the
coastal flooding and the overtopping of the existing defences at the proposed development site for
a 1 in 200 year and 1 in 1,000 year event plus an allowance for climate change to 2115. The
results of this modelling are provided in Appendix 9E.
9.73 The results of the modelling show that using the Defra report FD2320 63 the flood hazard rating is
greater than 2. The velocities and depth represent a severe flood hazard which is considered to
be dangerous for all as the breach of the defences results in deep or fast flowing water. The
impact is considered to be of major adverse significance.
5100935.404 Environmental Statement August 2011 139