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The Total Required Volume is the Runoff Volume in addition to the Sediment Storage Volume <br />(10.92 + 0.77 = 11.69 ac -ft) <br />• The Dewater Invert Elevation is set to the Sediment Storage Elevation + 0.6 ft (5676.0 +0.6). <br />• Similar reports are used to define these parameters for NHN -002 and NHN -003. <br />2) Model the pond with only the emergency spillway. This treats the gated principal spillway as if it is <br />closed. This simulation will determine the peak elevation of water surface for the 10 -year 24 -hour <br />precipitation event. It should be noted that in the case that the pond is sized such that it contains the 10- <br />year 24 -hour storm, the SEDCAD program will give a warning that no sediment calculation is conducted <br />due to no outflow. <br />The second SEDCAD report in Appendix 2.05.3(4) -2 titled as 10 -Year 24 -hour Storm Event for Pond <br />NHN- 001 (gated)" is run with initial pool elevation as 5676.6 ft, which is the Dewater Invert Elevation. This <br />SECAD report is used to determine the following parameters in Table 3: <br />• 10 -year 24 -hour Peak Water Surface Elevation is the peak stage as 5682.32 ft in Elevation - <br />Capacity- Discharge Table on page 6. <br />• The Proposed Emergency Spillway elevation of 5683.5 ft and its Design Capacity Volume of <br />15.40 ac -ft are from the table on page 7. <br />• The Percent Excess Volume is calculated as follows: <br />(Design Capacity Volume — Total Required Volume) / Total Required Volume *100 <br />• The Principal Spillway Riser Elevation of 5683.5 ft is set 0.2 ft higher than the 10 -year 24 -hour <br />peak water surface elevation of 5683.3. <br />• Similar reports are used to define these parameters for NHN -002 and NHN -003. <br />3) Repeat the Step 2 but for 25 -year 24 -hour precipitation event to size the pond emergency spillway. The <br />bottom elevation of the emergency spillway is set such that there is a minimum one foot difference in <br />elevation between the 25 year -24 hour precipitation event water level flowing through the emergency <br />spillway and the top of the embankment. <br />The third SEDCAD report in Appendix 2.05.3(4) -2 titled as "25 -Year 24 -hour Storm Event for Pond NHN - <br />001(gated)" is used to size the emergency spillway and to ensure a one foot freeboard. This SECAD <br />report is used to determine the following parameters in Table 3: <br />The 25 -year 24 -hour peak water surface elevation is 5683.68 ft from the elevation- capacity- <br />discharge table on page 7. <br />• The Pond Top Elevation of 5685 ft is at least 1 foot higher than that.25 -year 24 -hour peak water <br />surface elevation. <br />• Similar reports are used to define these parameters for NHN -002 and NHN -003. <br />Note that the runoff volume is calculated using the 10 -year, 24 -hour design storm for each pond. The design <br />capacity volume is measured from the lowest discharge elevation (the Dewater Invert Elevation) of the principal <br />4 <br />