Method for delaying run-off of flash-storm water or ordinary rainwater from roofs and other surfaces with water-retention capability

摘要

To retain water on roofs of buildings with a water-retention basin, a vortex-type throttle valve is fitted on the roof and is connected to a drain pipe leading to a drain. The throttle valve makes it possible to control rainwater run-off at a given rate determined by the size of the throttle valve. If rain falls at a high rate, the excess is retained. Overflow protection is provided by fitting on top of the throttle, a length of pipe which permits the unrestricted flow of water through the throttle valve. Alternatively, the drain pipe can be extended upwards to the maximum permitted water-retention level, thus allowing the water which exceeds this level to pass directly into the drain pipe.