Building Construction Handbook, Eighth Edition

Road Drainage ~ this consists of laying the paved area or road to
a suitable crossfall or gradient to direct the run-off of surface
water towards the drainage channel or gutter. This is usually
bounded by a kerb which helps to convey the water to the road
gullies which are connected to a surface water sewer. For drains or
sewers under 900 mm internal diameter inspection chambers will be
required as set out in the Building Regulations. The actual spacing
of road gullies is usually determined by the local highway authority
based upon the carriageway gradient and the area to be drained
into one road gully. Alternatively the following formula could be
used:-

D=^280

pffiffiffiffiffiS

W where D = gully spacing

S = carriageway gradient (per cent)

W = width of carriageway in metres

\If S = 1 : 60 = 1„66% and W = 4„500

D=^280

pffiffiffiffiffiffiffiffiffiffiffiffiffi1„66

4„500 = say 80„000

Road Drainage