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Chapter 4 - Best Management 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. Collars shall <br /> not be closer than 2 feet (60 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 /> 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 />.. <br /> Capacity <br /> The emergency spillway 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 />�. 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 /> Location <br /> The emergency spillway channel shall be located to avoid fill material . If constructed on fill , <br /> the fill will 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 />