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<br />..,.,.....,.,_.. " <br /> <br />TABLE 1 . SLOPING RIPRAP DROP STRUCTURE DESIGN CHART <br /> <br />MAXIMUM ALLOWABLE CHUTE SLOPE - So LENGTH OF <br />UNIT DISCHARGE FOR EACH RIPRAP CLASSIFICATION DOWNSTREAM <br />q APRON LB <br />(cfs/ft M H VH (Ft) <br />15 o to 7:1 7: 1 to 4:1 N/A 15 <br />20 o to B:1 8: 1 to 5:1 5:1 to 4:1 20 <br />25 0 to 10:1 10:1 to 6: 1 6:1 to 4:1 20 <br />30 o to 12:1 12:1 to 7:1 7: 1 to 4.5:1 25 <br />35 o to 13: 1 13: 1 to 8:1 8: 1 to 6: 1 25 <br />DR* 1.75' 2.6' 3.5' ---- <br />DR* 2.0' 3.0' 4.0' ---- <br />DRW 1.5 x DR 1.25 x DR 1. 0 x DR ~ <br /> <br />* For Erosion Resistant, Cohesive Soils <br />** For Sandy or Highly Erosive Soils <br /> <br />NOTES: <br />1. q = Unit discharge = VnYn, where Vn = average <br />channel velocity and Yn = normal depth of the <br />upstream channel. <br />2. So = Longitudinal channel slope expressed in feet <br />horizontal per foot vertical. <br />3. Dr = Depth of riprap blanket in feet. <br />4. Drw = Depth of riprap blanket at the downstream face <br />of the crest wall. <br />5. Rock size, Dr and Drw shall be the same throughout <br />the drop structure. <br />6. Chute and channel side slopes shall not be steeper <br />than 4:l. <br />7. Maximum allowable drop = 4.0' <br />8. See "Urban Storm Drainage Criteria Manual" for <br />riprap gradation, classification and bedding <br />requirements. <br />9. This chart is for ordinary riprap structures only. <br />The dimensions contained herein should not be used <br />for grouted riprap or other types of drop <br />structures. Other types of drop structures require <br />their own hydraulic analysis. <br /> <br />I A. <br />