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Florida Erosion and Sediment Control Inspector's Manual �• <br /> Plate 4. 26a Sediment Basin Storage Volumes <br /> Source: Virginia DSWC <br /> Embankment Cross-Section <br /> The embankment must have a minimum top width of 8 feet (2 . 5 m) . The side slopes must be <br /> 2 : 1 orflatter. The embankment may have a maximum height of 10 feet (3 m) if the side slopes <br /> are 2 : 1 . If the side slopes are 2 .5 : 1 or flatter, the embankment may have a maximum height <br /> of 15 feet (4 . 5 m ) . ,r <br /> Spillway Design <br /> The outlets for the basin may consist of a combination of principal and emergency spillways <br /> or a principal spillway alone . In either case, the outlet(s) must pass the peak runoff expected <br /> from the drainage area for a 10 year storm without damage to the embankment of the basin . <br /> Runoff computations shall be based upon the soil cover conditions which are expected to <br /> prevail during the life of the basin . Refer to Chapter 3 of this manual for calculation of the peak <br /> rate of runoff. <br /> The spillways designed by the procedures contained in this BMP will not necessarily result in <br /> any reduction in the peak rate of runoff. If a reduction in peak runoff is needed , the appropriate , <br /> hydrographs should be generated to choose the basin and outlet sizes . <br /> To increase the efficiency of the basin , the spillway(s) must be designed to maintain a <br /> permanent pool of water between storm events . <br /> Principal Spillway <br /> The principal spillway shall consist of a solid (non-perforated ) , vertical pipe or box of <br /> corrugated metal or reinforced concrete joined by a watertight connection to a horizontal pipe .� <br /> (barrel ) extending through the embankment and outletting beyond the downstream toe of the <br /> fill . If the principal spillway is used in conjunction with an emergency spillway, the principal <br /> spillway shall have a minimum capacity of 0 .2 cfs per acre (0 .015 M3 /sec, per ha) of drainage •� <br /> area when the water surface is at the crest of the emergency spillway . If no emergency <br /> spillway is used , the principal spillway must be designed to pass the entire peak flow <br /> expected from a 10-year storm . See Appendix 1 . 26A of The Florida Development Manual <br /> for design details . <br /> Design Elevations <br /> If the principal spillway is used together with an emergency spillway, the crest of the principal <br /> spillway shall be a minimum of one foot (30 cm) below the crest of the emergency spillway. <br /> If no emergency spillway is used , the crest of the principal spillway shall be a minimum of 3 <br /> feet (90 cm ) below the top of the embankment. (See Plate 4 .26b .) In either case, a minimum <br /> freeboard of one foot (30 cm ) shall be provided between the design high water and the top <br /> of the embankment. <br /> ■ <br /> 4-82 <br /> ■ <br />