SAB technical guidance

We are currently in the process of developing a Sustainable Drainage Design and Adoption Manual applicable to all development within the Caerphilly County Borough with the view to assist all stakeholders in understanding the processes and procedures involved in implemented complainant sustainable drainage.

This manual is intended to support the Sustainable Drainage Approval Body in the determination of approvals, and for use by developers, planners, designers and adopting authorities who are seeking advice regarding the technical standards that we require in new and redeveloped sites for the sustainable management of surface water.

The manual does not intend to replace, or rewrite statutory or best practice documents but to explain how the information within these documents can be best applied to Caerphilly County Borough Council, and sets out the additional requirements, procedures and considerations specific to SuDS in the Caerphilly county borough.

Please keep an eye on our website for further information.

Infiltration testing

The SuDS Manual (CIRIA C753) states that one of the main risks to soakaway performance is inadequate infiltration testing due to time or cost constraints at the early planning stage.

The “Statutory standards for sustainable drainage systems – designing, constructing, operating and maintaining surface water drainage systems” (referred to as the “National Standards”) does not prescribe a particular methodology for determining ground permeability and it is recognised that there are a number of different methods currently in practice. G1.14 of the National Standards does, however, make reference to the guidance available within The SuDS Manual (C753) with regards to the design of infiltration systems.

Section 25.3 of The SuDS Manual recommends that infiltration tests should be carried out in accordance with the one of the following procedures:

Similarly Building Regulations Part H3 also states that soakaways serving areas in excess of 100m² should be designed in accordance with BRE Digest 365. 

As the threshold for sites requiring SAB approval is 100m², infiltration rate testing will only be accepted if it has been carried out in accordance with the full requirements of BRE Digest 365 (2016) (preferred) or CIRIA Report 156. 

Alternative test methods, such as falling head tests in accordance with BS EN ISO 22282-2:2012 / BS5930:2015 or the small trial pit (300mm x 300mm) approaches outlined in BS 6297:2007+A1:2008 or Building Regulations Part H will only be accepted in exceptional circumstances where there are valid technical reasons why infiltration testing in accordance with BRE Digest 365 (2016) or CIRIA Report 156 is not possible. 

Where alternative methods are proposed to be used, it is recommended to discuss and agree this with the SAB at pre-application stage or prior to submitting an application.

What resources are available?

There is a wealth of information on delivering compliant SuDs freely available online. We recommend you review the following prior to contacting us or making a formal application:

More information about SAB

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