<P> Catchbasins act as a first - line pretreatment for other treatment practices, such as retention basins, by capturing large sediments and street litter from urban runoff before it enters the storm drainage pipes . </P> <P> Pipes can come in many different cross-sectional shapes (rectangular, square, bread - loaf - shaped, oval, inverted pear - shaped, egg shaped, and most commonly, circular). Drainage systems may have many different features including waterfalls, stairways, balconies and pits for catching rubbish, sometimes called Gross Pollutant Traps (GPTs). Pipes made of different materials can also be used, such as brick, concrete, high - density polyethylene or galvanized steel . Fibre reinforced plastic is being used more commonly for drain pipes and fittings . </P> <P> Most drains have a single large exit at their point of discharge (often covered by a grating) into a canal, river, lake, reservoir, sea or ocean . Other than catchbasins, typically there are no treatment facilities in the piping system . Small storm drains may discharge into individual dry wells . Storm drains may be interconnected using slotted pipe, to make a larger dry well system . Storm drains may discharge into man - made excavations known as recharge basins or retention ponds . </P> <P> Storm drains are often unable to manage the quantity of rain that falls during heavy rains and / or storms . When storm drains are inundated, basement and street flooding can occur . Unlike catastrophic flooding events, this type of urban flooding occurs in built - up areas where man - made drainage systems are prevalent . Urban flooding is the primary cause of sewer backups and basement flooding which can affect properties year after year . </P>

Where does water go after it enters a storm drain
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