PERMFILE126504

• Permit No: C1980005
• IBM Index Class Name: Permit File
• Doc Date: 9/12/2006
• Doc Name: Permanent Impoundment PECOCO
• Section_Exhibit Name: Tab 07 Appendix 7-6g
• Media Type: D
• Archive: No

• SPILLWAYS
PECOCO will have separate principal and emergency spillways (see Exhibit 7-18 for location
and configuration of spillways). The principal spillway will consist of a 24" diameter
CMP with a trash rack at the inlet. This pipe will maintain the water level to the
6774,9' elevation. Peak stage at the principal spillway during the passage of the
10-year, 24-hour event will be elevation 6775.10. This results in 1.9 feet of freeboard
to the inlet or the emergency spillway.
The emergency spillway will consist of a trapezoidal channel. Assuming the principal
spillway was plugged, the trapezoidal channel could safely pass the 100-year, 24-hour
I
storm runoff volume. Peak stage elevation during the passage of the 100-year storm is
6777.4, leaving 3.6 feet of freeboard to the top of embankment. 15'i th a velocity of 2,90
i fps, the grass lined emergency spillway channel and outsl ope will be stable. Please refer
to Addendum 2 for capacities of both spillways during passage of the 10 year, and 100-year
storm events. the design de taiis for the emergency spillway are as follows.
•
Type
Bottom Width
Length
Side Slopes
Outf all Slope
Inlet Elevation
100-year, 24-hour Peak Stage
Trapezoidal Channel
10 feet
40 feet
3H:1V
2va
6777.0
b777,4
•
SUMMARY
Impountlment capacity below the principal spillway is completely incised. During passage
of [he 10-year, 24-hour, storm the emergency spillway does not di scharne >ediment
downstream nor is there any flow through the emergency spillway. The pond will safely
pass [he flow from the 100-year, 24 -hour precipitation event.
7-6g-17