2018-07-24_PERMIT FILE - C2010089 ‎(5)‎

• Permit No: C2010089
• IBM Index Class Name: Permit File
• Doc Date: 7/24/2018
• Doc Name: Pond NHN-002 & Ditch Designs
• Section_Exhibit Name: Appendix 2.05.3‎(4)‎-9
• Media Type: D
• Archive: No

Pond NHN-002 & Ditch Designs
Introduction
Pond NHN-002 at New Horizon North is designed to capture and contain stormwater runoff as
part of the sediment control plan. This appendix contains design specifications for Pond NHN-
002 and its collection ditches, NHN-002 North and South. Included are the stormwater runoff
values for the 10 -YR, 24 -HR and 25 -YR, 24 -HR events that the ditches and pond must control.
Stormwater Data
Pond NHN-002 is the sediment pond for drainage watersheds SWS2-A, SWS2-B and SWS2-C
as shown on Map 2.05.3(4)-9. Runoff from these areas flows either into the pond itself or into
the collection ditches. SWS2-A feeds NHN-002 South, SWS2-B feeds the pond directly and
SWS2-C feeds NHN-002 North. Table 2.05.3(4)-9-1 shows a summary of sub -watershed runoff.
Table 2.05.3(4)-9-1 Summary of Suh_WaterchM Rrnnnff Valm-c
Sub -watershed
Area
10 -YR, 24 -HR
25 -YR,
24 -HR
Acreage
Peak Discharge
(cfs)
Runoff Volume
(ac -ft)
Peak Discharge
(cfs)
Runoff Volume
(ac -ft)
SWS2-A
10.80
8.14
0.73
11.17
1.01
SWS2-B
43.20
32.47
2.89
44.46
3.95
SWS2-C
6.70
5.23
0.46
7.16
0.63
SWS2 Total
60.70
44.72
4.08
61.20
1 5.58
Sediment Pond Design
Map 2.05.3(4)-9 contains design information for Pond NHN-002 including cross-sections of the
pond and ditch designs. Discharge from Pond NHN-002 will be controlled via gated pipe system
that has been used successfully at other similar sediment ponds. An 18 -inch diameter pipe with a
pair of 6 -inch diameter valve weepholes will be used as the principal spillway (see Figure 1).
The valve is located at the end of the pipe inlet and controlled by a wheel on the pond
embankment. The pipe inlet, or weephole, is typically kept open approximately 0.5" in diameter
and can be opened further to facilitate discharge after a storm event.
Figure 1 - Example of principal spillway inlet and control valve
Appendix 2.05.3(4)-9 Page 1 June 2018 (TR -17)