Laserfiche WebLink
Chapter 4 - Best Management Practices for Erosion and Sediment Control . . <br /> .r <br /> Design Criteria <br /> • Trap Capacity <br /> The sediment trap must have an initial storage volume of 134 cubic yards, or 3600 cubic <br /> feet per acre ( 252 m. /ha) of drainage area, measured from the low point of the ground to <br /> the crest of the gravel outlet. Sediment should be removed from the basin when the <br /> volume is reduced by one-half. <br /> • <br /> For a natural basin , the volume may be approximated . as follows: <br /> • V = 0.4xAxD <br /> where : V = the storage volume in ft.3 <br /> • A = the surface area of the flood area at the crest of the outlet, in ft.Z <br /> D = the maximum depth , measured from low point in trap to crest of outlet, <br /> in ft. <br /> • <br /> Excavation <br /> • If excavation is necessary to attain the required storage volume , side slopes should be no <br /> steeper than 2 :1 . <br /> • Embankment Cross-Section <br /> The maximum height of the sediment trap embankment shall be 5 feet (1 .5 m) as <br /> • measured from the low point. Minimum top widths (W) and outlet heights (Ho) for various <br /> embankment heights (H ) are shown in Table 4.25a . Side slopes of the embankment shall <br /> be 2:1 or flatter. <br /> • <br /> Table 4. 25a7 <br /> MINIMUM TOP WIDTH (W) AND OUTLET HEIGHT (Ho) REQUIRED FOR <br /> SEDIMENT TRAP EMBANKMENT ACCORDING TO HEIGHT OF EMBANKMENT (feet) <br /> • H: Ho W <br /> 2. 0 1 . 0 2.0 <br /> .. 2.5 1 . 5 2. 5 <br /> 3 . 0 2 . 0 2.5 <br /> 3. 5 2 . 5 3.0 <br /> 4. 0 3 . 0 3 . 0 <br /> 4.5. 3 . 5 4 . 0' <br /> • <br /> 5 . 0 4 . 0 4 .5 <br /> • <br /> 4-69 <br /> • <br />