A drainage attenuating device (90) comprising: a storage container (91) having an inlet (92) and an outlet (94) and adapted to collect and store rainwater entering the storage container via the inlet; and flow restricting means adapted to restrict the flow of rainwater from the storage container towards a sewer system via the outlet in the form of a riser pipe (96). The riser pipe includes a number of apertures (98) which allow rainwater to flow into the riser pipe. The sum of all diameters of the apertures is less than the diameter of the outlet.
