Developer Guidance

GUIDANCE FOR PROPERTY OWNERS & DEVELOPERS

Internal Drainage Boards and Development Control

The Black Sluice Internal Drainage Board (the Board) is an independent authority constituted under the 1930 Land Drainage Act, with duties “to exercise a general supervision over all matters relating to the drainage of land within its district”.

The Board acts as a non-statutory consultee to Local Planning Authorities, but importantly the Board has its own statutory powers with respect to drainage which also determines how and if a development may proceed. The Board’s current powers derive from the Land Drainage Act 1991.

The Board also acts as an agent and non-statutory sub-consultee to the Lead Local Flood Authority (Lincolnshire County Council) for matters regarding flood risk, surface water drainage and Section 23 consenting.

How the Board appraises Properties or Developments

The following factors are considered by the Board when appraising proposed properties or developments:

Rainfall Run-off and Development Contributions
Disposal of Foul or Dirty Water
Discharge Outfalls
Access to Watercourses
Filling in or Culverting Watercourses
Property Floor Levels
Site Ground Level
Environment and Biodiversity

Detailed guidance for each of these factors follows - emboldened sentences indicate the Board has statutory powers.

Application forms and other leaflets referred to may be obtained from the Board’s offices (address above), or the Board’s website www.blacksluiceidb.gov.uk.

SECTION 1 - RAINFALL RUN-OFF AND SURFACE WATER DEVELOPMENT CONTRIBUTIONS

The Board’s consent is required to increase the rate of rainfall run-off from a property or development.

The Board’s Byelaw No. 3 states that:

No person shall, without the previous consent of the Board, for any purpose, by means of any channel, siphon, pipeline or sluice or by any other means whatsoever, introduce any water into the District or, whether directly or indirectly, introduce any water into the District or, whether directly or indirectly, increase the flow or volume of water in any watercourse in the District.

Where possible, sustainable methods of disposal should be used which do not adversely affect existing surface water management, nor adversely expose people or property to an increased risk of flooding. In most instances sustainable disposal will best be achieved by dealing with rainfall run-off at or as near as possible to source using Sustainable Drainage Systems (SuDS). SuDS is now a presumption for all developments of 10 properties and above.

For example:

Rainwater recycling.
Soakaways, Infiltration areas and Swales
Filter drains and porous pavements
Attenuation or balancing ponds

NB: Soakaways and infiltration systems should be designed and proved with a percolation test in accordance with BRE Digest 365 or other approved code. No discharge fee is required by the Board.

A Surface Water Development Contribution (SWDC) shall be payable to the Board for any discharge from any property or development.

Prior written consent is required from the Board where a development will result in an increase in the rate or volume of flows into ANY watercourse. One of the conditions imposed as part of any such approval is the payment of a surface water development contribution to the Board.

The charge is made to help fund the cost of improvements to the drainage network that are required to cater for increases in the rate and/or volume of surface water flows. Surface Water Development Contributions are payable at the time and rate applicable when the consent application is validated by the Board.

The contribution is calculated by:

Determining the impermeable area of the site to be positively drained (in square metres, m2)
Establishing the charging band the impermeable area (in hectares) of the site that is to be positively drained will fall into
Establishing the charging band the proposed discharge rate (in litres/second/impermeable hectare) will fall into

The current maximum charge applicable is £129,456 per impermeable hectare (£12.95 per m²) for sites with less than 5ha of impermeable area proposing to discharge at an un-attenuated rate, with the rate decreasing proportionally for areas of 5ha and above.

Further details, including the charging bands and method of calculation, can be found on the Board’s website www.blacksluiceidb.gov.uk.

NB: The Board cannot guarantee to accept any water if it is unfeasible to increase the capacity of the existing system. Where localised off-site works are required to any watercourse, then the improvement must be approved by the Board and paid for by the property owner/developer in addition to the development contribution. The Board may be prepared to carry out the work using its powers under the Land Drainage Act 1991 on a rechargeable basis.

Where the discharge is via a third party system, such as an LCC adopted highway or SUDs system, an Anglian Water surface water sewer, or an ordinary watercourse (including those maintained by the Board), then the permission of the relevant authority or landowner is required, and an additional discharge fee may be due.

SECTION 2 - DISPOSAL OF FOUL OR DIRTY WATER

The Board’s consent is required to discharge any water into any surface water system.

Foul or dirty water, including water from vehicle wash downs, shall not be discharged directly into a surface water system. Where a separate foul water system (i.e. Anglian Water) is not provided, then the water shall be treated before disposal.

If a property owner/developer wishes to make a discharge into any watercourse within the Board’s district, then the consent of both the Board and the Environment Agency (the EA) is required as follows:

a) From the Board - to allow an increase in flow into the drainage system *

b) From the EA - who will agree the quality of the water to be discharged +

* not required for discharges of less than 1m3/day into a watercourse not maintained by the Board

+ not required for discharges less than 5m3/day

Septic tanks shall not discharge directly to a watercourse but to a soakaway system.

If septic tanks are not approved by the EA, then a package treatment unit will be required; the Board recommends that, unless there is a 600mm freeboard from the unit outlet invert to normal water level, the unit should have a pumped discharge.

Septic tanks shall not discharge directly to a watercourse but to a soakaway system designed and proved to BRE Digest 365. Where soakaways are not suitable due to ground conditions, then owner will be responsible for emptying the tank as required.

SECTION 3 - DISCHARGE OUTFALLS

The Board’s prior written consent is required before any structure is placed in any watercourse.

All outfalls shall have a suitable headwall to protect the banks from erosion. No part of the headwall unit or pipe end shall protrude beyond the profile of the bank in order that flails and weed cutting machinery is not obstructed. Suitable scour protection shall be placed below and/or in front of the headwall if necessary. Details of a suitable headwall can be obtained from the Board. A suitable non-return valve or spring-loaded flap is also recommended over the pipe end to prevent surcharging during periods of high water levels.

Outfall connections into piped systems shall preferably be to a manhole, although the use of a proprietary saddle connector may be permitted.

SECTION 4 - ACCESS TO WATERCOURSES AND BYELAWS

No obstructions shall be placed in, over, under or within 9 metres of the edge of a Board-maintained watercourse without the prior written consent of the Board.

The Board’s Byelaw states:

“No person, without the previous consent of the Board, shall erect any building or structure, whether temporary or permanent, or plant any tree, shrub, willow or similar growth within 9 metres of the landward toe of the bank where there is an embankment or wall, or within 9 metres of the top of the batter where there is no embankment or wall, or where the watercourse is enclosed within 9 metres of the enclosing structure”

The Board has a separate policy leaflet regarding this byelaw.

Access to and maintenance of all other watercourses or piped systems (not vested with any authority) is the responsibility of the riparian owners (i.e. the land or property owners on either bank).

Developers should take into account the future maintenance of riparian or private watercourses and piped systems when designing the site layout; access may be required for weed cutting excavators or for jetting equipment for piped systems.

DEVELOPERS SHALL INFORM PURCHASERS OF THE PRESENCE OF ANY WATERCOURSES AND THEIR OWNERSHIP AND MAINTENANCE RESPONSIBILITIES WITHIN COMMON LAW.

SECTION 5 - FILLING IN OR CULVERTING WATERCOURSES

The Board’s prior written consent is required before ANY watercourse is culverted, filled in, or otherwise obstructed.

Section 23 of the Land Drainage Act 1991 states that no person shall:

erect any mill dam, weir or other like obstruction to the flow of any ordinary watercourse or raise or otherwise alter any such obstruction; or
erect a culvert in an ordinary watercourse, or
alter a culvert in a manner that would be likely to affect the flow of an ordinary watercourse,

without the consent in writing of the drainage board concerned.

[Ordinary watercourses include every river, steam, ditch, drain, cut, dike/dyke, sluice, sewer (other than a public sewer) through which water flows and which does not form part of a Main River].

The Board considers that it is beneficial for watercourses to remain open wherever possible for both drainage and environmental purposes. Culverting or filling destroys wildlife habitats, damages a natural amenity and interrupts the continuity of the linear habitat of a watercourse. It can also remove functional flood plain storage and therefore increase the risk of flooding.

The Board has a policy leaflet regarding the culverting of Board-maintained Watercourses.

SECTION 6 - PROPERTY FLOOR LEVELS

The Board may make recommendations to the Planning Authority in respect of good practice in relation to flood risk and land drainage.

National Planning Policy Framework (NPPF): Technical Guidancestates that: site layout and surface water drainage systems should cope with events that exceed the design capacity of the system so that water can be safely stored or conveyed from the site without adverse impact.

Sewers for Adoption specifies that: site rainfall runoff systems should be designed not to flood any part of the site in a 1:30 year (3.3%) event.

The Board recommends that no property should flood in a 1:100 year (1%) site specific event, therefore flood storage above a 1:30 year event may need to be provided in areas such as roads, parking, open space etc. In addition, the Board may recommend a minimum floor level based on recorded flooding or catchment modelling. Other authorities or insurance companies may require a higher standard of protection or floor level.

SECTION 7 - SITE GROUND LEVELS

The Board recommends that the ground level of the site should not be raised above the level of neighbouring land unless it can be shown that it will not:

Obstruct overland surface water flow from neighbouring land
Cause surface water to flow overland off the site onto neighbouring land
Raise the sub-surface water table causing water logging of neighbouring land

In general, if ground levels are raised above surrounding land then interceptor infiltration drains (French Drains) will need to be installed around the site boundary. The future responsibility (including maintenance) of such drains shall lie with the relevant land or property owner.

SECTION 8 - ENVIRONMENT AND BIODIVERSITY

It is the Board’s statutory duty, when considering whether to issue consent, to take into account any likely adverse effect on the environment.

The Board is a signatory to the Lincolnshire Biodiversity Action Plan (BAP) and welcomes opportunities to work in partnership with developers to carry out environmental improvements on Board-maintained Watercourses.

JULY 2019