Road debris, de-icing scoria rock, glass, branches and oil collect within the sediment trap.  Four-feet wide and four-inches below grade, material drops down, allowing cleaner water to enter into the rain garden.  Simple ones, such as this one, are filled with 4-inch to 12-inch rough edge rock.  This one captured 50 gallons of material when it was cleaned in 2019.  Other methods, including suspending a grate in an open-trap system, would allow for even more debris offset from roads and the river.  back to top