4.2.1 Functional Characteristics
These are the physical characteristics of a protection system such as dimension, shape and
form. In particular the following attributes need to be considered:
Height of Protection Systems
The deployed height of the system above its bedding surface will determine the maximum
head of flood water which can be retained before overtopping occurs. This height also limits
the location where the system can be deployed especially where physical height restrictions
exist. The height of the system is sometimes higher than the design head of water to be
retained or the protection capability. The protection capability is deduced from structural
analyses and performance testing.
The ability to increase the height of a defence during service conditions is also very important
as it shows whether a protection system has the capability to be increased in height once
installed and the flood event is higher than predicted. This is important for sites where there is
low confidence in the ability to forecast flood levels. Where system height can be increased
during service, it is important to ensure the structural adequacy of the barrier and the bearing
capacity of the underlying soil for the total stacked loading.
Width of Protection System
The deployed width of the protection system is important in deciding whether it can be used
within the space constraints of the site. This can be a key characteristic when protection is
required on top of an embankment or wall with a set crest width or in areas where there is
limited width for closing or erecting the barrier.
Adaptability to Terrain and Bedding Conditions
The ability of the barrier to adapt to various terrain and bedding conditions need to be
considered. This is very important, as the barrier needs to act together with its bedding
surface and foundation to form the protection system. The rigidity of barriers affect their
ability to adapt to types of terrain such as undulating or sloping and soft or hard surfaces. This
adaptability would affect the seepage and stability characteristics of the system.
Adaptability to Change in Alignments
The ability of a barrier to adapt to the required vertical or horizontal change in alignment of
the location of use could be critical to its suitability especially where sharp bends or steps are
involved. Adaptability is normally achieved by the flexibility of the system due to its form or
the provision of fixings or procedures that allow some form of alignment change.
Joints and End Fixings
The form of a barrier or the accessories or fittings provided with it will affect its ability to
achieve an effective connection with its end conditions and the integrity of the joints within
separate units connected together. Good connections are very important in ensuring effective
performance of the whole of the temporary or demountable system. This is one of the aspects
that is unique to the available proprietary systems and is not normally assessable at a generic
level.