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

Flood Risk Assessment Tesco Supermarket, Swaffham
6.0 SUSTAINABLE DRAINAGE SYSTEMS (SUDS)
6.1 Existing Conditions
The site is currently brownfield site, partially developed on its southern
half. The site is located within a Flood Zone 1 – Low Risk.
6.2 Existing Drainage
The undeveloped area of the site currently drains via overland runoff
and natural soakage into the ground. The remainder of the site is
positively drained or drains to local soakaways.
During extreme rainfall events, the ground may not be able to absorb
all water falling on the site, in which case surface water runoff will be
displaced and flow as sheet runoff to the north of the site, to be drain
into the existing informal ditch on the northern boundary.
6.3 Sustainable Drainage Systems (SUDS)
The objectives of sustainable drainage systems are to –
recharge the groundwater resource as near to the source of
surface water runoff as practicable;
protect downstream watercourses and catchments from
flooding; and to
preserve or protect groundwater and surface water quality.
Accordingly, it is intended to employ SUDS techniques where
practicable to dispose of surface water on site.
The proposed SUDS aim at reducing the amount and rate of water flow
downstream by a combination of –
infiltration into the ground;
holding water in storage areas; and,
slowing down the movement of water.
Considerations which will influence the choice of SUDS are –
potential ecological, environmental and amenity benefits or
impacts;
permeability of the ground;
degree of hydraulic continuity with river water and reactivity to
changes in river levels;
degree and nature of any ground contamination found;
health and safety consequences.
Page 15
Jubb Consulting Engineers Limited February 2012
P9632-G300C-Rep-120209-MH