Page 143 - Bexley SuDS DESIGN & EVALUATION

P. 143

In addition, to the statements from the SuDS Where underground storage is preferred
Manual the following should also be after a full exploration of the available
considered:
options the designer should demonstrate

■ There are risks of structural failure due to that:
construction loading, which may exceed ■ Robust silt removal has been provided Detailed Design
design life loading that the designer may through means of filtration (bioretention,
not be aware of. permeable pavement) or other source

■ There are a wide range of attenuation control SuDS components. Catchpits will
not be accepted as a demonstrable form
products each with its own loading
characteristics. Surety must be provided of silt removal. The SuDS manual (Section
4.1) clarifies that sediments within
that a specified product is not swapped
for one of inferior quality during the catchpits can be remobilised and washed
downsteam. Equally, gullypots are
construction phase.
suggested by Table 26.15 to provide
■ Guarantees and warranties are dependent negligible to zero treatment (Ellis et al,

on the survival of product manufacturers. 2012).

■ Underground structures require structural
design consideration even if they are not
receiving vehicular loading. CIRIA report
C737 outlines the design requirements for
geocellular tanks. The SuDS Manual
(Table 21.1) provides a summary of the 138
structural design requirements using a risk
classification system (Scored between

0-3). Designers should demonstrate that
the classification system has been
followed and present the appropriate level
of design information accordingly.

Design Note:

Where the stated design life of the tank does not meet the design life of the development,
the design should demonstrate how the structure will be replaced whist maintaining the
functionality of the drainage system and the scheme. Consideration should also be given to
funding mechanism for undertaking these replacement works.

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