Laserfiche WebLink
• c) The principal spillway design is an 18-24" diameter CMP or other pipe which will have a valve <br />on the entrance. This pipe will be stopped down in the inlet side to a 6" valve which will be <br />controlled by a wheel on the pond embankment. During normal conditions, the valve will be cracked <br />slightly open to provide the equivalent cross-sectional area of a 2" diameter orifice opening. This <br />opening has been evaluated and is known to provide 24 hour detention time for each pond during <br />the large events while allowing dewatering of the pond within a reasonable amount of time. If <br />clogging occurs, the valve will simply be opened (at least 24 hours after a large storm) and <br />maintained from the spillway inlet side. The valve will then be screwed back to a set position to <br />provide the above mentioned cross-sectional area. <br />d) Appropriate combinations of principal and emergency spillways to safely contain or discharge <br />the runoff from a 25-year, 24-hour precipitation or larger event, as required by the CDMG's <br />regulations, will be installed. If a pond is designed to contain the runoff from a 25 year 24 event, an <br />emergency spillway cut into the dam will still be installed. <br />e) Pond freeboard will be a minimum of 1.0 feet from the highest level of water allowed in the <br />pond (or emergency spillway) to the top of dam. <br />f) All pond dams will be designed to have a height of less than 10.0 feet measured from the <br />original ground in the middle of the dam to the top of the dam. The top of dam width will be at least <br />10.0 feet in all areas. <br />g) All ponds will have a keyway cut along the entire width of the dam as shown on Map Atf <br />2.05.3(3)6-1. This keyway will be filled with competent material and compacted to the same <br />standards as the dam foundation. <br />h) All principal spillways will have 2 seep collars installed within the dam which will be at least 2x <br />the pipe diameter. All dam fill will be compacted around the seep collars and principal spillway pipe <br />to 90% of the maximum dry density of the fill material. <br />i) The emergency spillways will be a rip-rap lined trapezoidal channel of 10 feet bottom width and <br />2:1 sideslopes. <br />• (Revised ~/zooat 2.05.3(3) - 14 <br />