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- 5designed accordingly, rather than manipulate thecomplete vertical alignment with repeated rise andfalls to maintain a drainage gradient*On low speed roads, channel shaping will be requiredto provide minimum drainage falls to double gulliesof 6.67^* The normal kerb face should be 115nnn, butwill need to be varied between 75* and 140mm toachieve satisfactory drainage*For major roads, with 1m margins, channel shapingshould be carried out within the 1m margin. Forexample, a dual 3 lane carriageway would require doublegullies at about 16m intervals, with kerb face rangingfrom about 90mm between gullies to 140miB at the gullies*It may, however, be more suitable to adopt continuouscovered drainage channels incorporating sumped catchpits.7.3.6.8 Footway DrainageIt will normally be appropriate for footways adjacentto the carriageway to drain over the kerbs to the roadchannel, in which case the total paved area of footwayand carriageway should be used to calculate the gullyspacing according to Fig* 7*3*6.1.Where wide paved areas occur, adjacent to the carriageway,gully spacing on the carriageway will need to be veryfrequent, and it may be more appropriate to provideseparate footway drainage. This can be achieved by drainingto the back or centre of the paved area, by open or coveredchannels (with sumped gullies) connected direct to thecarrier drain. This is particularly relevant wherewide single carriageways are superelevated, to prevent theentire carriageway and footways draining to a singlechannel*