Hydraulic design of roof drainage gutters

In this Note the design of roof gutters is based on a solution of the gradually varied flow equation with uniform lateral inflow entering the gutter at right angles to the flow. The flow capacities of standard valley, boundary wall, northlight, box and rectangular eaves gutters were determined for a full range of lengths and for typical gradients of zero, 1 in 600 and 1 in 350. It is shown that BS 6367 is somewhat conservative in predicting capacities for short horizontal channels. For gutters laid to a fall of 1 in 600 the capacity usually increases slightly with increasing length except for gutters of small cross-section, and for gutters laid to a steeper fall the capacity increases with increasing length of gutter.