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Chapter 4 - Best Management Practices for Erosion and Sediment Control <br /> Embankment Cross-Section <br /> The embankment must have a minimum top width of 8 feet (2 .5 m) . The side slopes must <br /> r be 2 : 1 or flatter. The embankment may have a maximum height of 10 feet (3 m) if the side <br /> slopes are 2 : 1 . If the side slopes are 2 .5 : 1 or flatter, the embankment may have a <br /> r <br /> maximum height of 15 feet (4 .5 m) . <br /> Spillway Design <br /> The outlets for the basin may consist of a combination of principal and emergency <br /> spillways or a principal spillway alone . In either case, the outlet(s) must pass the peak <br /> runoff expected from the drainage area for a 10 year storm without damage to the <br /> embankment of the basin . Runoff computations shall be based upon the soil cover <br /> conditions which are expected to prevail during the life of the basin . Refer to Chapter 3 of <br /> this manual for calculation of the peak rate of runoff. <br /> r <br /> The spillways designed by the procedures contained in this BMP will not necessarily result <br /> in any reduction in the peak rate of runoff. If a reduction in peak runoff is needed , the <br /> r appropriate 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 /> r permanent pool of water between storm events. <br /> Principal Spillway <br /> r <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 <br />.. pipe (barrel) extending through the embankment and outletting beyond the downstream toe <br /> of the fill . If the principal spillway is used in conjunction with an emergency spillway, the <br /> principal spillway shall have a minimum capacity of 0 . 2 cfs per acre (0 .015 m3 /sec. per ha) <br /> r of drainage area when the water surface is at the crest of the emergency spillway. If no <br /> emergency spillway is used , the principal spillway must be designed to pass the entire <br /> peak flow expected from a 10-year storm . See Appendix 1 . 26A of The Florida <br /> Development Manual for design details . <br /> Design Elevations <br /> r <br /> If the principal spillway is used together with an emergency spillway , the crest of the <br /> principal spillway shall be a minimum of one foot (30 cm) below the crest of the emergency <br /> spillway. If no emergency spillway is used , the crest of the principal spillway shall be a <br /> minimum of 3 feet (90 cm) below the top of the embankment. (See Plate 4 .26b .) In either <br /> case , a minimum freeboard of one foot (30 cm) shall be provided between the design high <br /> r water and the top of the embankment. <br /> r <br /> r 4-81 <br />