2013-10-30_REVISION - M1977310 ‎(3)‎

• Permit No: M1977310
• IBM Index Class Name: REVISION
• Doc Date: 10/30/2013
• Doc Name: DRAINAGE DESIGN PLAN FOR THE JD6 MINE
• From: COTTER
• To: DRMS
• Type & Sequence: AM1
• Email Name: TC1
• Email Name: SJM
• Media Type: D
• Archive: No

JD -6 Mine — Drainage Design Plan 2
2. DESIGN CRITERIA & METHODOLOGY
2.1 Design Storms
The magnitudes of design storms for the site are shown in Table 2. The rainfall intensities for 24 -hour
storms with 2 -year to 100 -year recurrence intervals were interpolated from the NOAA Atlas 2, Vol. III
(USDC, 1973), for the purpose of runoff calculations and engineering design. Per DRMS
recommendations, control structures for the JD -6 Mine presented in this design report are engineered to
contain the 10 -year 24 -hour storm event and safely pass a 100 -year 24 -hour storm event.
Table 2. Design Storm Parameters
Recurrence
Interval
Duration
(Hours)
Storm Magnitude
NOAA Atlas
inches
100-year
24
3.0
50-year
24
2.7
25-year
24
2.4
10-year
24
2.0
5-year
24
1.6
2-year
24
1.2
2.2 Runoff Estimates
2.2.1 Volume
Catchment runoff was estimated using Technical Release 55 (TR -55) developed by the U. S. Department of
Agriculture Natural Resources Conservation Service (NRCS, 1986). TR -55 presents simplified procedures
to calculate storm runoff volume, peak rate of discharge, hydrographs, and storage volumes required for
floodwater reservoirs in small watersheds.
Runoff depth (qd) is calculated in TR -55 by the Curve Number (CN) method, using the following equation:
(P — 0.26)2
Rd _ (P +0.8S)
where: qd = Runoff depth, inches (qd = 0, if P < 0.2S),
P = Rainfall depth, inches
S = Potential maximum rainfall retention after runoff begins, inches
This method assumes initial abstraction (losses before runoff begins due to retention in surface depressions,
interception by vegetation, evaporation, infiltration etc.) is equal to 0.2S.
The parameter S is related to curve number (CN) by:
S = 1000 _ 10
CN
Site soils consist predominantly of Bodot and Ustic Torriorthents, which are listed as hydrologic soil group
C in the NRCS Web Soil Survey (NRCS, 2012a, 2012b). Site - specific curve numbers are discussed in
Section 3.
4148A.131028 Whetstone Associates