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r <br /> Chapter 4 - Best .Mana ement Practices. for. Erosion and Sediment Control <br /> Anti-seep collars <br /> Anti-seep collars shall be used. on the barrel of the principal spillway within the normal <br /> . saturation zone of the embankment to Increase the seepage length by at least 10% , if <br /> either of the following two conditions is met: <br /> 1 . The settled. height of the embankment exceeds 10 feet (3 m) . <br /> 2 . The embankment has a low silt-clay content (Unified Soil Classes SM or GM) and <br /> the barrel is greater than 10 inches (25 cm) in diameter. <br /> The anti-seep collars shall be installed within the saturated zone . The maximum spacing <br /> between collars shall be 14 times the projection of the collar above the barrel . Coilars shall <br /> not be closer than 2 feet 4 o cm) to a pipe joint. Collars should be placed sufficiently far <br /> apart to allow space for hauling and compacting equipment. Connections between the . <br /> collars and the barrel shall be watertight. See Plate 4.26e and Appendix 1 .26A for design <br /> procedure and details . <br /> r <br /> Emergency Spillway <br /> The emergency spillway shall consist of an open channel constructed next to the <br /> embankment over undisturbed material or properly compacted fill. The spillway shall have <br /> a control section at least 20 feet (6 m) in length . The control section is a level portion of <br /> the spillway channel at the highest elevation in the channel . (See Appendix 1 . 26A and <br /> Plate 4.26f) . The primary spillway and the emergency spillway shall both discharge to <br /> stabilized outlets. (See Plate 4. 26g). . <br /> Ca acif <br /> The emergencyspillway shall be designed to carry the peak rate of runoff expected from a <br /> 10-year storm , less any reduction due to the flow through the principal spillway . See <br /> Appendix 1 . 26A for. design details . <br /> r <br /> Design elevations <br /> The design high water through the emergency spillway shall be at least one foot (30 cm) <br /> below the top of the embankment. The crest of the emergency spillway channel shall be at <br /> least one foot (30 cm) above the crest of the principal spillway. <br /> r <br /> Location <br /> The emergency spillway channel shall be located to avoid fill material. It consucted on fill, . <br /> the fiilwill be properly compacted in lifts . The channel shall be located so as to avoid sharp <br /> turns or bends . The channel shall return the flow of water to a defined channel <br /> ' downstream from the embankment. <br /> 4-87 <br />