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<br />DRAINAGE CRITERIA MANUAL <br /> <br />MA,JOR DRAINAGE <br /> <br />Table 5-5 <br />RIPRAP REQUIREMENTS FOR CHANNEL LININGS ** <br /> <br />. <br /> <br />VSO.17/(S _1)0.66* <br />s <br /> <br />( ft 1/ sec ) <br /> <br />1.4 to 3.2 <br /> <br />3.3 to 3.9 <br /> <br />4.0 to 4.5 <br /> <br />Rock Type *** <br /> <br />5.6 to 6.4 <br /> <br />VL <br />L <br />M <br />H <br />VH <br /> <br />4.6 to 5.5 <br /> <br />* <br /> <br />Use Ss = 2.5 unless the source of rock and its densities are <br />known at the time of design. <br />Table valid only for Froude number of 0.8 or less and side <br />slopes no steeper than 2h:lv. <br />Type VL and L riprap shall be buried after placement to <br />reduce vandalism. <br />SM9 slope mattress with toe protection may be substituted <br />for Type VL or L riprap. <br />G12 gabion with toe protection may be substituted for Type M <br />and Type H riprap. <br /> <br />. <br /> <br />** <br /> <br />*** <br /> <br />5.4.3 Toe Protection <br />Where only the channel sides are to be lined, additional riprap <br />is needed to provide for long term stability of the lining. In this <br />case, the riprap blanket should extend at least 3 feet below the <br />existing channel bed and the thickness of the blanket below the <br />existing channel bed increased to at least 3 times d50 to accommodpte <br />possible channel scour during floods (see Figure 5-4a). For sandy <br />soils, consult specific criteria for channels on sandy soils. If wire <br />enclosed rock lining is used, the toe must be protected by placing <br />riprap at the toe. This is needed to protect against frequently <br />occurring abrasion, (see Figure 5-4b and 5-4c). ... <br /> <br />5-1-84 <br />