2016-08-05_PERMIT FILE - C2010089

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