PERMFILE41947

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 4/8/2005
• Section_Exhibit Name: 2.05 Operation and Reclamation Part 2
• Media Type: D
• Archive: Yes

' West Elk Mine
• There aze several distinct stream channels within the pemut area. Each of these streams has been
identified with an index number which provides the basis for identifying stream channel
characteristics before and after mining, as presented in Exhibit 55. WWE defined the existing
stream channel chazacteristics for various pazameters, including channel slopes, peak flow rates for
a variety of frequencies of occurrence, flow velocities for each of the frequencies, sediment
transport regime, stage-discharge relationships, channel profiles and channel and overbank stability.
The existing channel shapes were related to the "dominant discharge," which has atwo-yeaz
frequency of occurrence. Sediment transport has been defined for each stream using the annual
sediment load and sediment loads associated with large floods.
All of these streams (with the exception of Raven Creek, and Deep Creek which has a potentially
affected segment of 3,000 feet in Section 26) within the current, !Box Canyon and West Flatiron
mining azeas are ephemeral, based on U.S. Geological Survey topographic maps and extrapolation
of gaged streamflow data. Flows occur only in response to snowmelt and significant rainfalls.
Raven Creek, a perennial stream, as stipulated in the COC-67011 Federal Lease and Environmental
Assessment is protected by a riparian protection zone of 660 feet (1/8 mile) either side of the
riparian zone from surface disturbances (surface occupancy) and a undermining prohibition.
As discussed in Exhibit 55, WWE and Mr. Pemberton used a variety of statistically-based methods
to determine a representative average annual yield value that would apply to these drainages.
• Exhibit 55 concludes that for the purpose of computing pre and post-mining average annual
sediment yields, an appropriate mean annual runoff for the subject basins of 475 acre-feet per
squaze mile per year should be adopted, even though site-specifii data for the basins indicate a
mean annual runoff of considerably less than this amount. ,
From the standpoint of water rights, analyses of water yield byLWWE for the Division No. 4
Colorado Water Court for the 1986 West Elk Mine water augmentation plan indicated that the
typical annual water yield for tributaries to the Dry Fork of Minnesota Creek were approximately
200 acre-feet per square mile per yeaz. This is consistent with theaverage annual yield of the Dry
Fork basin, which is also about 200 acre-feet per square mile per year based on the available data.
In short, the appropriate average annual streamflow for the channel's ranges from 200 and 475 acre-
feet per squaze mile per yeaz, with 200 acre-feet per square mile per yeaz being used for water rights
purposes and 475 acre-feet per square mile being used for sediment~yield purposes.
In addition to computing average annual yields, WWE and Mr. Pemberton calculated floodflows
for multiple return frequency events. These aze presented in Exhibit 55. This is important because
it is necessary to evaluate how the stream channels will respond to large flood flows after
subsidence has occurred, especially with respect to sediment transport.
The projected subsidence for the stream channels was determined using output from the CISPM,
Version 2.0, calibrated using site-specific subsidence data. The stream channels were analyzed to
determine the magnitude of change resulting from the change inchannel slope. The changes to
• stream channel characteristics were analyzed using standard procedures of the sedimentation and
2.05-150 November 1004 PRII
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