4.1 – Rainwater collection and drainage systems – 9. Sizing of gutters and drainage downpipes 284 4.1. 9. SIZING OF GUTTERS AND DRAINAGE DOWNPIPES The size of the drains depends on the place of installation and therefore on the rainfall data of the area, the type of cover and the size of the pitches (for these aspects, refer to the EN 120563 standard and the extensive technical reference literature). The size of the downpipes and gutters depends on the intensity of the rainfall, the roof surface area and the discharge value (slope, surface condition). For the calculation, the net measurements of the internal sections and rainfall values reported in the local regulations and defined in liters per second per hectare: l/(s * ha) are considered. The size of the gutter is associatedwith the downpipe according to the calculation and design checks in as of Standard EN 12056-3 (rainwater discharge systems) and Standard EN 612. Calculation of the flow rate of rainwater Q = r * A * C where: Q is the water flow rate in liters per second (l/s) r is the rainfall intensity, in liters per second per hectare l/(s * ha) A is the actual roof surface area in hectares (ha) C is the sliding coefficient of the roof Generic rainfall values Rainfall rate 1 (1) 2 3 (2) r (3) 300 l/s (s*ha) 400 l/s (s*ha) 500 l/s (s*ha) (1) For areas with low rainfall. (2) For areas with heavy rainfall and snowfall. (3) The rainfall considered for the calculation is normally the regional rainfall intensity with a duration of five minutes, forecast once every five years. EXCERPT
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