Guide for Development


1) Introduction

Policy ME9 of the Bristol Local Plan 1997 states that:

  1. Development subject to flood risk will be required to provide the appropriate defence works at the same time as the development.
  2. Development which would increase the risk of flooding, or which is likely to cause unacceptable effects arising from surface water run off, will be required to provide for the appropriate drainage infrastructure works and retention works at the same time as the development itself.


...For all applications within flood risk areas, and in those areas where land drainage is an issue, the City Council will consult closely with relevant bodies, including the Lower Severn Drainage Board regarding the Avonmouth Area.  Appropriate works concurrent with the development will be sought through the use of conditions on the granting of planning permission...

Policy ME10 states:

Development adjacent to existing rivers and watercourses should take account of the requirement or provide access and working strips along the banks affected by the development.


The City Council will liase closely with the Environment Agency in relation to river management corridors to ensure that appropriate provisions are made for access and maintenance to agreed standards.

Chapter 12 of the 1997 Bristol Local Plan States:


12.5.3 The estuarine nature of the Avonmouth area means that drainage is of particular significance.  It is, therefore, imperative that developers hold consultation at the initial feasibility stage with the Lower Severn Drainage Board and the Environment Agency to determine the likely extent, cost and problems of the works involved.

2) Drainage Model

The Internal Drainage Board has developed a comprehensive surface water drainage model of the Avonmouth/Severnside Draft Strategy Area in order to advise the Environment Agency  who have rebuilt the sea outfalls serving the area to accommodate planned development, and secondly, to advise Planning Authorities of development issues.  This drainage model is regularly updated and capable of assessing the impact of development on the drainage network.

The drainage model has shown that a substantial investment into new provision of drainage infrastructure is required in order to accommodate the increased surface water run off from developed sites within the area and also to ensure proper protection for development against flooding.

Developers will be expected to fund the provision of improvements to the drainage network through an Area-Wide Infrastructure Charge.

3) Area – Wide Infrastructure Charge

Powers and Duties

The Avonmouth/Severnside Draft Strategy Area is an area that has specific problems relating to drainage which necessitates its inclusion within the area administered by the Lower Severn Drainage Board.

The Internal Drainage Board is empowered under the Land Drainage Act 1991, Section 66, to make Byelaws to ensure the efficient working of the drainage system of their district. Section 23 of the Land Drainage Act 1991 prevents obstructions etc. in the watercourses without the consent of the Board, which should not unreasonably be withheld.  The Board deems it reasonable to withhold a consent if its Byelaws are not adhered to, or if it is unable to ensure that its general duties in regard to the environment can be discharged.

Section 20 of the Land Drainage Act 1991 empowers the Internal Drainage Board to carry out works by agreement with any person and at that persons expense who is entitled to carry out the works.  It is understood that some occupiers/owners are entitled to carry out development works under existing planning permissions, however, new land drainage works require planning consent and a consent from the Drainage Board under its Byelaws.

Infrastructure Charge

Increases in the developed areas within the Avonmouth/Severnside catchment will lead to increases in the rate and quantity of surface water run off discharging to the existing rhine system.  The drainage network will therefore require improvement and enlargement to meet this new demand such that the risk of flooding is reduced to acceptable levels.  In this respect the Environment Agency require that all habitable floor levels be set at a minimum of 600mm above the 100 year flood level.

The responsibility for dealing with the additional surface water flows lies with the Internal Drainage Board whose policy is to levy an Infrastructure Charge on development within the Avonmouth/Severnside Area.  This charge is applied on areas of development as defined in the associated planning application (within the black line boundary) and will be calculated at the rate of £29,000/hectare as from 1st September 2014 with suitable reduction for work done “in kind” which is of general benefit to others in the catchment.  In this way the costs of infrastructure improvements will be borne equally between those who benefit.  The infrastructure charge becomes payable before a consent can be issued under the Land Drainage Act 1991.

4) Drainage Model

The Board can, by using its Drainage Model, examine the scope and scale of infrastructure improvement works that will be necessary to accommodate development without worsening the flood situation.  The Board is prepared to enter into an agreement with developers who wish to test development options in order to gain information about the need for infrastructure improvements associated with their development. Under such agreements developers will be expected to fund further study work and computer modelling undertaken by the Board.

5) Design of Infrastructure Improvements

Once the scope and scale of infrastructure improvement works have been identified and accepted by the Internal Drainage Board, the Board will issue a statement indicating its intention to award a consent for those works under the Land Drainage Act, provided that they are designed and constructed to a standard acceptable to the Board.  It should be noted that the Environment Agency and the Internal Drainage Board are not disposed to consent the culverting of open watercourses and would advise that alternatives be sought.  An advice note on culverts is available.

The Board’s charges in respect of plan checking and inspection amount to 2½% of the capital costs of the surface water and drainage works (including design and supervision costs), and are payable upon first submission of detailed design drawings.  Where these costs are estimated they should be supported by a Quantity Surveyor's account; any unpaid amounts are to be settled with the Board on final account.  It should be noted that the Board will need to fully assess proposals and not normally award its consent in the absence of detailed design information.

6) Adoption of the Works and Maintenance Agreements

The Board recognises that drainage network improvements will lead to the construction of the new ponds and rhines, which will create maintenance responsibilities for developers which may be undesirable.  The Board confirms that it requires to enter into maintenance agreements for the adoption of strategic ponds and rhines (including previously unadopted rhines) in order that the intended level of flood protection is ensured.  Such agreements will include commuted sums for maintenance, calculations for which will be prepared by the Engineer to the Board.

7) Consents Procedure

Consent to carry out works affecting the area should be made on the Boards 'Application form'.  Applicants should complete the form in duplicate and submit relevant details with their payment made payable to the Lower Severn Drainage Board.  Please note that a separate consent must be applied for each outfall or culvert etc.