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Chapter 4 we Best Management Practices for Erosion and Sediment Control <br /> the design criteria , they must be designed as permanent ponds by a qualified professional <br /> engineer. Permanent ponds are beyond the scope of this BMP . <br /> .r Design Criteria <br /> Maximum Drainage Area <br /> Unless the structure is designed as a permanent pond by a qualified professional engineer, <br /> the maximum allowable drainage area into the basin shall be 150 acres (61 ha) . <br /> Basin Capacity <br /> .� The design capacity of the basin must be at least 134 cubic yards or 3600 cubic feet per acre <br /> (252 m3/ha) of drainage area measured from the bottom of the basin to the crest of the <br /> principal spillway (riser pipe) . Sediment should be removed from the basin when the volume <br /> r.. of the basin has been reduced to 55 cubic yards per acre ( 104 m3/ha) of drainage area . The <br /> elevation of the sediment clean out level should be calculated and clearly marked on the riser. <br /> In no case shall the sediment clean out level be higher than one foot (30 cm) below the top of <br /> .. the riser. (See Plate 4 . 26a) , <br /> Basin Shape <br /> To improve sediment trapping efficiency of the basin , the effective flow length must be twice <br /> the effective flow width . This basin shape may be attained by properly selecting the site of the <br /> r. basin , by excavation , or by the use of baffles . See Appendix 1 . 26A for design details . <br /> 67 C.Y . / AC ." CRY " STORAGE <br /> : . ' . . . . . . . : . :. . '. DEWATERING <br /> DEMCE <br /> 67 C .Y. / 4C. <br /> V0 ET " STORAGE �~�` . 'P�.o. :. :r: <br /> . . . . . . . . . . . . . . <br /> 8.08 <br /> 's — „ <br /> - - - e�H1 :imi3 a_r <br /> Awk <br /> SEDIMENT CLEANOUT POINT <br /> ( " <br /> WET " STORAGE REDUCED <br /> TO 34 C.Y./ ACRE) <br /> Mir <br /> 4-81 <br /> M <br />