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Pond 010 Design Details <br />Pond 010 is a partially incised pond designed to contain the flow from a 10 year 24 hour storm <br />below the emergency spillway. the valve on the principal spillway pipe is normally held shut. <br />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 shut <br />to provide 24 hour detention time for each pond during the large events. When a large event <br />occurs, the operator will wait a minimum of 36 hours after the storm has ceased to check the <br />water still detained by the pond. If an Imhoff cone shows that the water meets the effluent <br />standard of 0.5m1 settleable solids per liter, the valve will be opened until the water has <br />dissipated to the valve level. It will then be shut to allow detention time for subsequent storms. <br />As shown below, the 10 year inflow is 12.54 acre feet. The three year sediment volume is 0.547 <br />acre feet, therefore, the total volume required below the emergency spillway is 13.139 acre <br />feet. As shown on Map 2.05.3(3)-6-1, the emergency spillway bottom for the pond is located at <br />elevation 5618.0'. As shown on the enclosed stage storage relationship, the volume of 13.139 <br />acre feet is found at elevation 5617.85', therefore, there is more than enough volume to contain <br />the 10 year event. For this reason, no routing of the 10 year event is needed. <br />For the 25 year event, water will enter the emergency spillway. The computer program TR-20 <br />was used to flood rout the 25 year storm through the emergency spillway. The results of this <br />• routing shows that the peak flow in the emergency spillway of 6.09 cfs corresponds to an <br />elevation of 5618.41'. See page near end of printout where "Emergency Spillway Results" is <br />shown in bold type. Since the top of dam is located at elevation 5620.0', the amount of available <br />freeboard is therefore 1.59 feet. <br />n <br />LJ <br />~v~sEn row zoo6 Attachment 2.05.3(3)-6-1 <br />