Why is there road waterlogging in rainstorm weather?

    Answer: The road waterlogging is caused mainly by the following three reasons:

    1. Natural causes:

    (1). In most parts of Shanghai, the return period design of storm drainage system is generally once a year, which is a storm intensity of 35.5 millimeters/hour. When the rain intensity exceeds this standard, waterlogging shall readily happen.

    (2) Shanghai is tidal rivers network areas, when heavy rain coincides with high tidal, the inland river can not be flowed out, the water level rise, for protect the flood protection wall facilities and prevent water overflow, the flood protection pump station off, waterlogging shall readily happen.

    2. Inadequate capacity for drainage facilities to withstand storms

    (1) Low standard of drainage system

    At present, in some areas of Shanghai, the return period design of storm drainage system is once in 6 months. When the rainfall volume exceeds 27 millimeters/hour, road waterlogging shall readily happen.

    (2) Inadequate drainage system

    Despite the fact that some systematical pumping stations and major pipelines have been established, branch pipes for water collection, for some reasons, have not yet been improved, making the actual drainage capacity lower than the system standards. Pipelines of some areas are small or the diameters downstream are smaller, leading to bottleneck which further causes waterlogging. Such situation can be seen mainly in the old city.

    (3) Some pipelines drain water to rivers naturally

    The drainage systems of some areas, especially those newly constructed areas, have not yet been fully completed. Due to the absence of pumping stations, their drainage of rain water depends mainly on such pipelines to drain water into the river naturally. When the water level of the watercourse is high, water is likely to be accumulated in some low-lying areas.

    3. Human factors

    (1) The damage of pipelines during construction shall affect drainage;

    (2) Pump-circuit damage leads to pump suspension which consequently leads to accumulation of water.

    (3) The illegal discharge of mud and oil from construction sites could block the pipelines, causing poor drainage and water accumulation.