2.3.1 Permanent Flood Protection System
A permanent flood protection system is one that requires no operational activity to provide
protection from flooding. It is technically the most reliable protection system as it is always in
place to offer flood protection up to its design standard. The most common examples of
permanent flood protection systems are flood banks (earth embankments which are the
principal form of flood defence used by Operating Authorities), and flood walls (generally
concrete or steel retaining walls). A flood wall consists of a barrier above ground level, a
foundation supporting the barrier, a cut-off barrier below ground level extending to an
impermeable layer if present and joints and end details. A flood bank has a similar structure
to the flood wall apart from the absence of the cut-off barrier in most cases. The width of a
flood bank at its base is normally enough to prevent significant seepage and uplift pressure
except in very porous soils. A soak dyke, which is often provided close to the landward toe of
an embankment helps to collect any seepage close to the surface. Figure 2.1 shows the typical
elements of a permanent flood protection system.