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�► Chapter 4 - Best Management Practices for Erosion and Sediment Control ground that discharges through an opening in a storm drain inlet structure . This 4W opening can either be the inlet opening or a temporary opening made by omitting bricks or blocks in the inlet. The trap shall be between 1 ' and 2' (30 - 60 cm ) deep or measured from the low point of the inlet. A yard drain inlet or an inlet in the median strip of a dual highway would use the inlet opening for an outlet . (See Plate 4 .25e) A curb inlet would require a temporary opening . (See Plate 4 .25f) The trap should be out 1„ of the roadway to avoid interference with construction . Placing the trap on the opposite side of the opening and diverting water from the roadway to the trap is one means of accomplishing this . 5 . Other applications At times a small trap may be constructed in a drainage channel using the culvert for a road crossing . Straw bales or gravel filled bags may be used provided that there are no gaps in the installation . (See Plate 4 . 25g ) In larger traps baffles may be required to insure adequate flow length and prevent short-circuiting . (See Plate 4 .25h ) Construction Specifications .► 1 . The area under the embankment shall be cleared , grubbed , and stripped of any vegetation and root mat . To facilitate cleanout, the pool area should be cleared : o. 2 . Fill material for the embankment shall be free of roots or other woody vegetation , organic material , large stones , and other objectionable material . The embankment should be compacted in 8 inch (20 cm) layers by traversing with construction .. equipment. 3 . The earthen embankment shall be seeded with temporary or permanent vegetation �. (see Sections 6 . 65 and 6 .66) within 15 days of construction . 4 . Construction operations shalt be carried out so that erosion and water pollution are •� minimized . 5 . The structure shall be removed and the area stabilized when the upslope drainage • area has been stabilized . Maintenance 1 . Sediment shall be removed and the trap restored to its original dimensions when the sediment has accumulated to 1 /2 the design volume of the trap . Sediment removed from the basin shall be deposited in a suitable area and in such a manner that it will not erode . W 2 . The structure should be checked regularly to insure that it is structurally sound and has not been damaged by erosion or construction equipment . The height of the outlet should be checked to ensure that its center is at least one foot (30 cm ) below the top of the embankment. 4-75