4.2 Road drainage construction
The specification for the construction of road drainage is detailed in the Manual of Contract Documents for Highway Works Volume 1: Specification for Highway Works. Where discharging into an existing watercourse or public sewer, road drainage should additionally meet the requirements of Scottish Water (as the drainage authority) and Scottish Environment Protection Agency (SEPA).
The connection of road drainage systems to the public network should be undertaken only on the authority and to the requirements of Scottish Water.
The developer is required to incorporate Sustainable Drainage Systems (SuDS) into their proposals. These must deal with excess water from a site, and return it to the water system in a controlled manner to alleviate flood risk and reduce discharge of diffuse pollutants. Refer to SuDS Supplementary Planning Guidance, noting in particular that while the use of permeable paving on carriageways is not supported, it may be acceptable in parking areas.
Road drainage design should be in accordance with the current Specification subject to the qualification that the minimum pipe diameter permitted will be 150mm. Land drainage or other appropriate measures must be taken to prevent water flowing onto the road from adjacent properties.
4.2.3 Sub-grade drainage
It is important to provide efficient permanent drainage of the sub-grade and any other permeable layer of the road. Ideally, the water table should be prevented from rising to within 0.6 metres of the formation level. This requirement is additional to those of the surface water drainage detailed below.
4.2.4 Camber, crossfall and gradients
Carriageways should be cambered with a fall of 2.5% from the centreline to the channel except on curves where, to eliminate adverse camber, a crossfall of 2.5% between upper channel and centre line should be formed with increased crossfall between centre line and lower channel to allow for a 25mm centre line increase when boned channel to channel. For roads surfaced with block paving, 2.5% crossfall should be provided throughout. At a junction, the carriageway of the minor road should be graded into the channel of the major road. Footways and footpaths should be constructed with a crossfall towards the road channel. Channel gradients should not be flatter than 0.8%.
4.2.5 Gullies, connections and chambers
Gullies should be trapped and constructed in accordance with Clause 508 of the Specification and as detailed here. Gully gratings and frames must be positioned with grating bars running at right angles to the kerb and be of the captive variety.
Connections should be constructed in accordance with Clause 508 of the Specification. They must be formed with junction pipes unless the Roads Authority has specifically approved the use of saddles.
Chambers should be constructed in accordance with Clause 507 of the Specification and as detailed in HCD drawings F3 to F12 as appropriate to that type.
Section 3.4.9 of the SCOTS National Roads Development Guide details the acceptable channel distance between gullies for a road comprising carriageway and two 2m-wide footways. The spacing may require to be altered according to the road layout (e.g. at junctions) and special measures will be required where the grade is necessarily flatter than 0.8 per cent (sags, crests, etc.). Irrespective of design spacings, a gully should be positioned:
- Just upstream of the tangent point at road junctions;
- short of the point where adverse camber is removed when applying super elevation; and
- at any local low point.
Note: These webpages are for reference by developers of housing and employment sites in East Lothian. They provide guidance on transport infrastructure against which Planning Applications will be assessed and evaluated, and set out East Lothian Council's procedures regarding the construction and adoption of new roads in accordance with current legislation. These pages supersede all previous versions of our Standards for Development Roads document. Revisions 01/07/2023 Document release