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378-7 Pond <br />protection should be added later <br />if monitoring indicates the need. <br />Practice standard 430-FF provides <br />criteria for cathodic protection <br />of welded steel pipe. <br />preferably using a drain backfill <br />envelope continuously along the <br />conduit to where it exits the <br />embankment. Protecting the drain <br />fill outlet from surface erosion <br />will be necessary. <br />Seepage control .along a pipe <br />conduit spillway shall be provided <br />if any of the following conditions <br />exist: <br />1. The effective height of dam is <br />greater than 15 ft. <br />2. The conduit is of smooth pipe <br />larger than 8 in, in diameter. <br />3.. The conduit is of corrugated <br />metal pipe larger than 12 in. in <br />diameter. <br />Seepage along pipes extending <br />through the embankment shall be <br />controlled by use of a filter and <br />• drainage diaphragm, unless it is <br />determined that antiseep collars <br />will adequately serve the purpose <br />The drain fill and drainage <br />diaphragm is to consist of sand, <br />meeting fine concrete aggregate <br />requirements (at least 15% passing <br />the No. 40 sieve but no more than <br />10% passing the No. 100 sieve). <br />If unusual soil conditions exists, <br />a special design analysis shall be <br />made. , <br />The diaphragm shall be a minimum <br />of 2 ft. thick and extend a clear <br />distance vertically upward and <br />horizontally at least three times <br />the pipe diameter, and vertically <br />downward at least 18 in. beneath <br />the principal spillway conouit <br />invert. The drain diaphraom shall <br />be located immediately downstream <br />of the cutoff trench, <br />approximately parallel to the <br />centerline of the dam. <br />The drain diaphragm shall outlet <br />at the embankment downstream toe, <br />When antiseep collars are used, <br />they shall have a watertight <br />connection to the pipe. Maximum <br />spacing shall be approximately 14 <br />times the minimum projection of <br />the collar measured perpendicular <br />to the pipe. Collar material <br />shall be compatible with pipe <br />materials. The antiseep collar(s) <br />shall increase by 15% the seepage <br />path along the .pipe. <br />Closed conduit spillways designed <br />for pressure flow must have <br />adequate antivortex devices. <br />To prevent clogging of the <br />conduit, an appropriate trash <br />guard shall be installed at the <br />inlet or riser. <br />A pipe with a suitable valve shall <br />be provided to drain the pool area <br />if needed for proper pond <br />management. <br />Supply pipes through the dam to <br />watering troughs and other <br />appurtenances shall have an inside <br />diameter of not less than 1-1/4 <br />in. <br />Where headgates or valves are <br />used, they shall be located on the <br />pond end of the outlet conduit. <br />Galvanized steel supply pipes may <br />have downstream valves, provided <br />the pipe and valve are protected <br />against freezing. <br />SCS, Colorado, January 1989 <br />