Sustainable Drainage System (SuDS)

From 07 January 2019, all new and significant developments will have to implement some kind of sustainable drainage system (SuDS) as part of its design and build.

These SuDS must be designed and built in accordance with standards published by Welsh Government and approved by the local authority acting in its role as a SuDS approval body (SAB). The SAB will then have the duty to adopt any compliant systems; serving multiple properties.

If you would like more information about this process, please contact the SAB team:

• sab@valeofglamorgan.gov.uk

SAB Pre-Application Service

To ensure drainage proposals are in line with Welsh Government’s Statutory Standards it is encouraged that pre-application discussions are held in advance of a full application being submitted. This discretionary service is offered to discuss the drainage requirements of your development, whilst also specifying details that will need to be submitted to support a full application.

To gain benefit from this pre-application service it is advised to provide as much technical information as possible to enable a considered response and to facilitate further discussion.

Supporting key information that would be beneficial to a productive pre-application includes:

-       Assessment of flood risk from all sources

-       Details of natural overland flow routes

-       Details of ground conditions / site investigations

-       Details of site topography

-       Details of existing watercourses and site boundaries

-       Drainage catchment plan for both existing and proposed development.

-       Details of sensitive environments and their ability to be affected by the development

-       National Standards principles and compliance assessment

Associated fees relating to this discretionary service can be found in the attached document.  

We will provide these discretionary services within 60 days of submission of the relevant documentation and appropriate fee. Full fees are to be paid upfront and are non-refundable. VAT will be charged on discretionary services.

• Commuted Sums
   

  Securing a sustainable funding mechanism for the lifetime of development is a key objective of the SuDS Approving Body (SAB). The SAB has a responsibility for the management and maintenance of SuDS assets after they have been adopted. Commuted sums ensure that the SAB has the resources to cover the upkeep and (where appropriate) the replacement of the assets they have adopted. The effectiveness of SuDS and the associated multiple benefits will rely on appropriate maintenance.

   

  In order to ensure consistency throughout Wales, the methodology identified in “Commuted Sums for Maintaining Infrastructure Assets” prepared by the CSS (County Surveyors Society), will be used to calculate commuted sums for all drainage assets being adopted by the SAB, whether through a S38 agreement or a bespoke legal agreement for the life of the development.

   

  The calculation of a commuted sum includes consideration of:

   

  • The estimated periodic maintenance cost of the asset to be adopted e.g. silt clearance. The SuDs manual provides useful information on this element and sums will be in accordance with agreed maintenance schedules.
  • The future cost of renewal or replacement (e.g. permeable paving has design life of 20 years, over the lifetime of the development this could lead to 3 or more replacements).
  • The duration over which the sum is required. Commuted sums for SuDS features serving residential developments will be calculated over a 100yr period.  Non-residential developments will be calculated using the proposed lifetime of the development, usually 75 years or less if agreed with the SAB on a case-by-case basis.  The Association of Directors of Planning and Transport recommends commuted sums for highway structures should be calculated to cover a 120 year period.  Commuted sums for SuDS features, other than those classified as structures, solely serving the adopted highway will be calculated over a 60 year period.
  • The effective annual interest rate that will provide a return on the sum invested prior to its expenditure after the effects of inflation have been taken into account. The discount rate is usually recalculated on an annual basis, based on the long-term neutral base rate and retail price index excluding mortgages, and applied from 1^st April each year. Based on a LTNBR of 4.5% and RPIX inflation of 7.7% the discount rate for 2021/22 is -3.0%. We appreciate the current rate of inflation will significantly increase the commuted sums required for new applications. as such we will undertake an interim review quarterly to consider whether an increase in the discount rate - thereby reducing commuted sums - is appropriate