2014-02-07_REVISION - M1979094HR ‎(5)‎

• Permit No: M1979094HR
• IBM Index Class Name: REVISION
• Doc Date: 2/7/2014
• Doc Name: Revised DDP
• From: Whetstone Associates
• To: DRMS
• Type & Sequence: AM1
• Email Name: TC1
• Email Name: DMC
• Media Type: D
• Archive: No

JD -7 Mine — Drainage Design Plan 12
Table 5. Generalized Least Squares Regression Equations for Estimating Regional Flood -
Frequency Relations for Western Colorado
(from Thomas, et al., USGS, 1997)
Recurrence
Average standard
Equivalent years of
interval, in years
Equation
error of prediction,
record
in percent
2
Q---0.0204AREA1601(ELEV /1,000) -3.s
68
0.14
5
Q= 0.181AREA' "'(ELEV /1,000) -2.9
55
0.77
10
Q---1.18AREA0-488(ELEV /1,000) -22
52
1.70
25
Q= 18.2AREA0465(ELEV /1,000) "' -'
53
2.81
50
Q= 248AREAo.449
57
3.36
100
g--292AREAo.444
59
3.94
2.2.3.4 HydroCAD
Peak discharge from sub - basins having complex pond routing and exfiltration was computed using the
HydroCAD -10 software, distributed by HydroCAD Software Solutions, LLC. HydroCAD® uses the
procedures described in TR -55 and TR -20 with added features for multiple pond routing, variable pond
geometry, pond pumping, exfiltration, baseflow and inflow losses (that is, inflow to and exfiltration from
reaches), and an increased number of "nodes" (reaches, sub - basin, and ponds) over the limited number
available in WinTR -55.
2.3 Structure Design
The primary function of drainage structures is to control runoff water by intercepting it and transferring it
safely into the local drainage network. Such structures are designed to carry the expected runoff discharge
for an event with a chosen average recurrence interval. Erosion in the structures themselves is controlled
either by reducing the water velocity or by protecting the surface. Structures evaluated at the JD -7 Mine
include channels, culverts, retention ponds, and spillways.
2.3.1 Channel Capacity
Channel capacity was evaluated with a single section analysis using Manning's Equation. In the WinTR -55
and HydroCAD® models, channels were assigned a trapezoidal geometry with side slope ratios
corresponding to site conditions.
The value of the roughness coefficient ( Manning's n) selected for each channel affects channel velocity,
conveyance capacity, and peak flows. The most important factors that affect the selection of channel n
values are:
1. Type and size of the materials that compose the bed and banks of the channel; and
2. Shape of the channel.
Cowan (1956) developed a procedure for estimating the effects of these factors to determine the value of n
for a channel. The value of n may be computed by:
n = (nb +nl +n2 +n3 +n4)•m
4149A.140207 Whetstone Associates