Seoul city will establish new design standards for the structure of storm drain inlets and the method of consolidating them to sewer pipes to reduce road flooding during heavy downpours. With experiments showing that areas near Gangnam Station could be submerged up to 1 meter when 100 millimeters of rain falls per hour, the city aims to improve drainage performance from the very first step of sending road rainwater into sewer pipes.
On the 27th, according to Seoul city, the city began drawing up detailed design standards for storm drain inlets to be applied across Seoul. It plans to set standards within the year by reviewing not only the structure and shape of storm drain inlets but also the slope of the consolidation pipe connecting the inlet to the main sewer, water flow speed, and connection method.
A storm drain inlet is the first gateway through which rain that falls on roads enters underground sewers. If its ability to receive rainwater is weak or it is blocked by leaves and trash, water can pool on roads even if the sewer has capacity. Drainage is also delayed if the slope of the consolidation pipe is gentle or if it is not properly consolidated to the sewer.
Seoul city will compare the structures and forms of storm drain inlets used domestically and abroad and verify drainage performance through experiments. It will examine not only how well they receive rainwater but also how prone they are to blockage by leaves and trash and how easy they are to clean. It will also analyze the proper slope of consolidation pipes, water flow speed, and methods of connecting to the main sewer.
In April, Seoul city released installation guidelines that classify storm drain inlets by regional characteristics into flood-prevention type, odor-reduction type, landscape-harmony type, and pedestrian-safety type. This time, it will establish detailed design standards that include structure, drainage performance, and the construction method for consolidation pipes.
A Seoul city official said, "Current sewer design standards lack unified detailed criteria for storm drain inlet structures and methods of consolidating pipes," adding, "Installing storm drain inlets with good drainage performance and standardizing the construction method for consolidation pipes will help reduce road flooding."
As extreme downpours become more frequent, the limits of existing urban drainage facilities are also becoming evident. In an urban flood simulation conducted last month for areas near Gangnam Station by the Korea Institute of Civil Engineering and Building Technology (KICT), it was analyzed that when 100 millimeters of rain falls per hour, flooding depths in some areas could reach up to 1 meter, exceeding existing drainage capacity.
The research team reflected in the simulation the topography of the Banpocheon basin, the storm sewer network, road slopes, and storm drain inlets. Experiments that replicated actual roads and drainage facilities produced similar results. The Gangnam Station area is lower in elevation than its surroundings, making it a place where flood damage recurs during heavy downpours. In Aug. 2022, during a record-breaking rainstorm, the Gangnam Station intersection, Daechi Station, and roads across Seocho District were submerged.
The new standards will apply first to sections where storm drain inlets are newly installed or where aging facilities are replaced. They will also apply to areas where roads and sewer facilities are upgraded through redevelopment and reconstruction, with plans to expand them citywide in Seoul by 2040.
Seoul city will also revise installation standards for sewer pipes, power lines, communication lines, and gas pipes beneath roads. It plans to build 3D data on the locations of key downtown underground utilities and, by analyzing pipe sizes and soil conditions, set appropriate burial depths and minimum distances between facilities.