flood risk assessment in connection with a planning - Breckland ...

Flood Risk Assessment Tesco Supermarket, Swaffham
than a 0.1% annual probability of occurrence or 1000 return period).
The primary source of flooding to the site is from overland flow and
surface water runoff.
8.5 Flood Risk from the Development
The main source of potential flooding from the new development is
currently from overland flow and surface water drainage.
The proposed development site will not increase offsite discharges
from the proposed increase in impermeable surfacing. Rainwater falling
onto the site will be managed by a combination of sustainable drainage
techniques including soakaways and permeable paving. Overflows for
these will be linked to an infiltration basin which will have capacity for
extreme events (up to 1-in-100 years) to facilitate soakage to ground.
8.6 Flood Mitigation Measures
Infiltration systems have been assessed for their possible use at the
site. The soakaway testing during the site investigation works has
identified that the permeability of the ground in good.
It is proposed to service the subject site with a new positive drainage
system employing SUDS techniques including a combination of an
infiltration drainage, soakaways and permeable paving. Diagram SK03
_A illustrates the drainage strategy as evolved with discussion to date
with the Environment Agency.
The exact attenuation volumes will be verified at the detailed design
stage. The final drainage strategy will need to be agreed with the EA.
8.7 SUDS
Excess surface water produced by the site will be managed by
infiltration. This is consistent with the sustainability objectives set out in
the planning policy. The subject site‟s discharge will not increase runoff
from the site.
8.8 Conclusion
The scheme proposed adequately meets the standard criteria for
acceptable flood risk. The proposed development is located within a
Flood Zone 1 (Low Risk), all uses proposed uses in the flood zone are
therefore acceptable. No further sequential test assessment is
required.
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Jubb Consulting Engineers Limited February 2012
P9632-G300C-Rep-120209-MH