All gullies should be trapped and the maximum length of gulley connection should not be more than 15m. It will not be acceptable to connect one gulley connection directly into another. Gully spacing should be calculated in accordance with Table 41 and the accompanying notes.
Carriageway gradient | 1/100 | 1/80 | 1/60 | 1/40 or steeper |
---|---|---|---|---|
Area drained (including footways and so on) (m2) (a) | 170(b)(c) | 180(b) (c) | 200(b) (c) | 240(b) (c) |
(a) When calculating the areas drained, allowances must be made for all footways, footpaths, paved areas and verges (classed at 30% impermeable) that fall towards the carriageway.
(b) Gullies must not be spaced more than 40m apart, irrespective of the areas drained, except at summits where the first gully should not be more than 40m from the high point.
(c) Double gullies must always be provided at sag points and low points and each must have its individual connection to the main sewer, highway drain or outfall.
In footpaths, footways and cycleways separated from carriageways, gullies or channels connected to the highway drainage system must be provided where surface water would otherwise discharge onto adjacent property or cause flooding of footpaths, footways or carriageways.
Gullies upstream of the tangent point at road junctions must be sited so that surface water in the channel does not flow across the junction. Care should be taken to avoid ponding near the mid-point of radius kerbs. Where the road is super-elevated, a gully should be sited just before the point where the adverse camber is removed to prevent water in the upstream channel flowing across the carriageway. A gully should be sited directly upstream of any pedestrian/dropped crossing point to prevent water in the channel causing a hazard to users of the crossing.
Care should be taken to avoid ponding in the transition length, when the longitudinal gradient is flat or where there are traffic islands, central reserves or traffic-calming measures.
Gullies must not be sited:
- within pedestrian crossing points. Where possible, locate them directly upstream of the crossing point.
- where traffic would be prevented from passing while they are being emptied, for example within a carriageway width restriction.
Double gullies should be provided at low spots or vertical sag curves along the channel and should not be connected with “y” connection.
A contour plan must be provided to show that gullies are located in the correct position as part of the design submission for works under Section 38 or Section 278 agreements and any other situation requested.
Plans should show the catchment areas for each gully, in accordance with Table 41 above. The area of surface water drained must be shown on the drawing for each gully along with the longfall at the gully location.