This invention features a structure installed inside the manhole, on opposing sides of the stormwater drainpipe, consisting of two right-angle 'L'-shaped barriers. Under normal circumstances, these barriers hang downwards due to gravity maintaining the manhole's basic function without needing any special mechanisms.However, when the water level rapidly rises due to heavy rains or torrential downpours, the rising water pressure lifts up the L shaped barrier upwards. They then interlock.